1 \input texinfo @c -*-texinfo-*-
2 @comment %**start of header
5 @settitle GNU tar @value{VERSION}
14 @c 1. Pay attention to @FIXME{}s and @UNREVISED{}s
15 @c 2. Before creating final variant:
16 @c 2.1. Run `make check-options' to make sure all options are properly
18 @c 2.2. Run `make master-menu' (see comment before the master menu).
20 @include rendition.texi
26 @c Put everything in one index (arbitrarily chosen to be the concept index).
35 This manual is for @acronym{GNU} @command{tar} (version
36 @value{VERSION}, @value{UPDATED}), which creates and extracts files
39 Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
40 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
43 Permission is granted to copy, distribute and/or modify this document
44 under the terms of the GNU Free Documentation License, Version 1.1 or
45 any later version published by the Free Software Foundation; with no
46 Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
47 and with the Back-Cover Texts as in (a) below. A copy of the license
48 is included in the section entitled "GNU Free Documentation License".
50 (a) The FSF's Back-Cover Text is: ``You have the freedom to
51 copy and modify this GNU manual. Buying copies from the FSF
52 supports it in developing GNU and promoting software freedom.''
56 @dircategory Archiving
58 * Tar: (tar). Making tape (or disk) archives.
61 @dircategory Individual utilities
63 * tar: (tar)tar invocation. Invoking @GNUTAR{}.
66 @shorttitlepage @acronym{GNU} @command{tar}
69 @title @acronym{GNU} tar: an archiver tool
70 @subtitle @value{RENDITION} @value{VERSION}, @value{UPDATED}
71 @author John Gilmore, Jay Fenlason et al.
74 @vskip 0pt plus 1filll
80 @top @acronym{GNU} tar: an archiver tool
85 @cindex archiving files
87 The first part of this master menu lists the major nodes in this Info
88 document. The rest of the menu lists all the lower level nodes.
91 @c The master menu goes here.
93 @c NOTE: To update it from within Emacs, make sure mastermenu.el is
94 @c loaded and run texinfo-master-menu.
95 @c To update it from the command line, run
106 * Date input formats::
113 * Configuring Help Summary::
114 * Fixing Snapshot Files::
117 * Free Software Needs Free Documentation::
118 * Copying This Manual::
119 * Index of Command Line Options::
123 --- The Detailed Node Listing ---
127 * Book Contents:: What this Book Contains
128 * Definitions:: Some Definitions
129 * What tar Does:: What @command{tar} Does
130 * Naming tar Archives:: How @command{tar} Archives are Named
131 * Authors:: @GNUTAR{} Authors
132 * Reports:: Reporting bugs or suggestions
134 Tutorial Introduction to @command{tar}
137 * stylistic conventions::
138 * basic tar options:: Basic @command{tar} Operations and Options
139 * frequent operations::
140 * Two Frequent Options::
141 * create:: How to Create Archives
142 * list:: How to List Archives
143 * extract:: How to Extract Members from an Archive
146 Two Frequently Used Options
152 How to Create Archives
154 * prepare for examples::
155 * Creating the archive::
164 How to Extract Members from an Archive
166 * extracting archives::
169 * extracting untrusted archives::
175 * using tar options::
185 The Three Option Styles
187 * Long Options:: Long Option Style
188 * Short Options:: Short Option Style
189 * Old Options:: Old Option Style
190 * Mixing:: Mixing Option Styles
192 All @command{tar} Options
194 * Operation Summary::
196 * Short Option Summary::
208 Advanced @GNUTAR{} Operations
217 How to Add Files to Existing Archives: @option{--append}
219 * appending files:: Appending Files to an Archive
226 Options Used by @option{--create}
228 * override:: Overriding File Metadata.
229 * Ignore Failed Read::
231 Options Used by @option{--extract}
233 * Reading:: Options to Help Read Archives
234 * Writing:: Changing How @command{tar} Writes Files
235 * Scarce:: Coping with Scarce Resources
237 Options to Help Read Archives
239 * read full records::
242 Changing How @command{tar} Writes Files
244 * Dealing with Old Files::
245 * Overwrite Old Files::
250 * Data Modification Times::
251 * Setting Access Permissions::
252 * Directory Modification Times and Permissions::
253 * Writing to Standard Output::
254 * Writing to an External Program::
257 Coping with Scarce Resources
262 Performing Backups and Restoring Files
264 * Full Dumps:: Using @command{tar} to Perform Full Dumps
265 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
266 * Backup Levels:: Levels of Backups
267 * Backup Parameters:: Setting Parameters for Backups and Restoration
268 * Scripted Backups:: Using the Backup Scripts
269 * Scripted Restoration:: Using the Restore Script
271 Setting Parameters for Backups and Restoration
273 * General-Purpose Variables::
274 * Magnetic Tape Control::
276 * backup-specs example:: An Example Text of @file{Backup-specs}
278 Choosing Files and Names for @command{tar}
280 * file:: Choosing the Archive's Name
281 * Selecting Archive Members::
282 * files:: Reading Names from a File
283 * exclude:: Excluding Some Files
284 * wildcards:: Wildcards Patterns and Matching
285 * quoting styles:: Ways of Quoting Special Characters in Names
286 * transform:: Modifying File and Member Names
287 * after:: Operating Only on New Files
288 * recurse:: Descending into Directories
289 * one:: Crossing File System Boundaries
291 Reading Names from a File
297 * problems with exclude::
299 Wildcards Patterns and Matching
301 * controlling pattern-matching::
303 Crossing File System Boundaries
305 * directory:: Changing Directory
306 * absolute:: Absolute File Names
310 * General date syntax:: Common rules.
311 * Calendar date items:: 19 Dec 1994.
312 * Time of day items:: 9:20pm.
313 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
314 * Day of week items:: Monday and others.
315 * Relative items in date strings:: next tuesday, 2 years ago.
316 * Pure numbers in date strings:: 19931219, 1440.
317 * Seconds since the Epoch:: @@1078100502.
318 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
319 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
321 Controlling the Archive Format
323 * Compression:: Using Less Space through Compression
324 * Attributes:: Handling File Attributes
325 * Portability:: Making @command{tar} Archives More Portable
326 * cpio:: Comparison of @command{tar} and @command{cpio}
328 Using Less Space through Compression
330 * gzip:: Creating and Reading Compressed Archives
331 * sparse:: Archiving Sparse Files
333 Making @command{tar} Archives More Portable
335 * Portable Names:: Portable Names
336 * dereference:: Symbolic Links
337 * hard links:: Hard Links
338 * old:: Old V7 Archives
339 * ustar:: Ustar Archives
340 * gnu:: GNU and old GNU format archives.
341 * posix:: @acronym{POSIX} archives
342 * Checksumming:: Checksumming Problems
343 * Large or Negative Values:: Large files, negative time stamps, etc.
344 * Other Tars:: How to Extract GNU-Specific Data Using
345 Other @command{tar} Implementations
347 @GNUTAR{} and @acronym{POSIX} @command{tar}
349 * PAX keywords:: Controlling Extended Header Keywords.
351 How to Extract GNU-Specific Data Using Other @command{tar} Implementations
353 * Split Recovery:: Members Split Between Volumes
354 * Sparse Recovery:: Sparse Members
356 Tapes and Other Archive Media
358 * Device:: Device selection and switching
359 * Remote Tape Server::
360 * Common Problems and Solutions::
361 * Blocking:: Blocking
362 * Many:: Many archives on one tape
363 * Using Multiple Tapes:: Using Multiple Tapes
364 * label:: Including a Label in the Archive
370 * Format Variations:: Format Variations
371 * Blocking Factor:: The Blocking Factor of an Archive
373 Many Archives on One Tape
375 * Tape Positioning:: Tape Positions and Tape Marks
376 * mt:: The @command{mt} Utility
380 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
381 * Tape Files:: Tape Files
382 * Tarcat:: Concatenate Volumes into a Single Archive
387 * Standard:: Basic Tar Format
388 * Extensions:: @acronym{GNU} Extensions to the Archive Format
389 * Sparse Formats:: Storing Sparse Files
396 * PAX 0:: PAX Format, Versions 0.0 and 0.1
397 * PAX 1:: PAX Format, Version 1.0
401 * Generate Mode:: File Generation Mode.
402 * Status Mode:: File Status Mode.
403 * Exec Mode:: Synchronous Execution mode.
407 * GNU Free Documentation License:: License for copying this manual
413 @chapter Introduction
416 and manipulates @dfn{archives} which are actually collections of
417 many other files; the program provides users with an organized and
418 systematic method for controlling a large amount of data.
419 The name ``tar'' originally came from the phrase ``Tape ARchive'', but
420 archives need not (and these days, typically do not) reside on tapes.
423 * Book Contents:: What this Book Contains
424 * Definitions:: Some Definitions
425 * What tar Does:: What @command{tar} Does
426 * Naming tar Archives:: How @command{tar} Archives are Named
427 * Authors:: @GNUTAR{} Authors
428 * Reports:: Reporting bugs or suggestions
432 @section What this Book Contains
434 The first part of this chapter introduces you to various terms that will
435 recur throughout the book. It also tells you who has worked on @GNUTAR{}
436 and its documentation, and where you should send bug reports
439 The second chapter is a tutorial (@pxref{Tutorial}) which provides a
440 gentle introduction for people who are new to using @command{tar}. It is
441 meant to be self-contained, not requiring any reading from subsequent
442 chapters to make sense. It moves from topic to topic in a logical,
443 progressive order, building on information already explained.
445 Although the tutorial is paced and structured to allow beginners to
446 learn how to use @command{tar}, it is not intended solely for beginners.
447 The tutorial explains how to use the three most frequently used
448 operations (@samp{create}, @samp{list}, and @samp{extract}) as well as
449 two frequently used options (@samp{file} and @samp{verbose}). The other
450 chapters do not refer to the tutorial frequently; however, if a section
451 discusses something which is a complex variant of a basic concept, there
452 may be a cross-reference to that basic concept. (The entire book,
453 including the tutorial, assumes that the reader understands some basic
454 concepts of using a Unix-type operating system; @pxref{Tutorial}.)
456 The third chapter presents the remaining five operations, and
457 information about using @command{tar} options and option syntax.
459 The other chapters are meant to be used as a reference. Each chapter
460 presents everything that needs to be said about a specific topic.
462 One of the chapters (@pxref{Date input formats}) exists in its
463 entirety in other @acronym{GNU} manuals, and is mostly self-contained.
464 In addition, one section of this manual (@pxref{Standard}) contains a
465 big quote which is taken directly from @command{tar} sources.
467 In general, we give both long and short (abbreviated) option names
468 at least once in each section where the relevant option is covered, so
469 that novice readers will become familiar with both styles. (A few
470 options have no short versions, and the relevant sections will
474 @section Some Definitions
478 The @command{tar} program is used to create and manipulate @command{tar}
479 archives. An @dfn{archive} is a single file which contains the contents
480 of many files, while still identifying the names of the files, their
481 owner(s), and so forth. (In addition, archives record access
482 permissions, user and group, size in bytes, and data modification time.
483 Some archives also record the file names in each archived directory, as
484 well as other file and directory information.) You can use @command{tar}
485 to @dfn{create} a new archive in a specified directory.
488 @cindex archive member
491 The files inside an archive are called @dfn{members}. Within this
492 manual, we use the term @dfn{file} to refer only to files accessible in
493 the normal ways (by @command{ls}, @command{cat}, and so forth), and the term
494 @dfn{member} to refer only to the members of an archive. Similarly, a
495 @dfn{file name} is the name of a file, as it resides in the file system,
496 and a @dfn{member name} is the name of an archive member within the
501 The term @dfn{extraction} refers to the process of copying an archive
502 member (or multiple members) into a file in the file system. Extracting
503 all the members of an archive is often called @dfn{extracting the
504 archive}. The term @dfn{unpack} can also be used to refer to the
505 extraction of many or all the members of an archive. Extracting an
506 archive does not destroy the archive's structure, just as creating an
507 archive does not destroy the copies of the files that exist outside of
508 the archive. You may also @dfn{list} the members in a given archive
509 (this is often thought of as ``printing'' them to the standard output,
510 or the command line), or @dfn{append} members to a pre-existing archive.
511 All of these operations can be performed using @command{tar}.
514 @section What @command{tar} Does
517 The @command{tar} program provides the ability to create @command{tar}
518 archives, as well as various other kinds of manipulation. For example,
519 you can use @command{tar} on previously created archives to extract files,
520 to store additional files, or to update or list files which were already
523 Initially, @command{tar} archives were used to store files conveniently on
524 magnetic tape. The name @command{tar} comes from this use; it stands for
525 @code{t}ape @code{ar}chiver. Despite the utility's name, @command{tar} can
526 direct its output to available devices, files, or other programs (using
527 pipes). @command{tar} may even access remote devices or files (as archives).
529 You can use @command{tar} archives in many ways. We want to stress a few
530 of them: storage, backup, and transportation.
532 @FIXME{the following table entries need a bit of work.}
535 Often, @command{tar} archives are used to store related files for
536 convenient file transfer over a network. For example, the
537 @acronym{GNU} Project distributes its software bundled into
538 @command{tar} archives, so that all the files relating to a particular
539 program (or set of related programs) can be transferred as a single
542 A magnetic tape can store several files in sequence. However, the tape
543 has no names for these files; it only knows their relative position on
544 the tape. One way to store several files on one tape and retain their
545 names is by creating a @command{tar} archive. Even when the basic transfer
546 mechanism can keep track of names, as FTP can, the nuisance of handling
547 multiple files, directories, and multiple links makes @command{tar}
550 Archive files are also used for long-term storage. You can think of
551 this as transportation from the present into the future. (It is a
552 science-fiction idiom that you can move through time as well as in
553 space; the idea here is that @command{tar} can be used to move archives in
554 all dimensions, even time!)
557 Because the archive created by @command{tar} is capable of preserving
558 file information and directory structure, @command{tar} is commonly
559 used for performing full and incremental backups of disks. A backup
560 puts a collection of files (possibly pertaining to many users and
561 projects) together on a disk or a tape. This guards against
562 accidental destruction of the information in those files.
563 @GNUTAR{} has special features that allow it to be
564 used to make incremental and full dumps of all the files in a
568 You can create an archive on one system, transfer it to another system,
569 and extract the contents there. This allows you to transport a group of
570 files from one system to another.
573 @node Naming tar Archives
574 @section How @command{tar} Archives are Named
576 Conventionally, @command{tar} archives are given names ending with
577 @samp{.tar}. This is not necessary for @command{tar} to operate properly,
578 but this manual follows that convention in order to accustom readers to
579 it and to make examples more clear.
584 Often, people refer to @command{tar} archives as ``@command{tar} files,'' and
585 archive members as ``files'' or ``entries''. For people familiar with
586 the operation of @command{tar}, this causes no difficulty. However, in
587 this manual, we consistently refer to ``archives'' and ``archive
588 members'' to make learning to use @command{tar} easier for novice users.
591 @section @GNUTAR{} Authors
593 @GNUTAR{} was originally written by John Gilmore,
594 and modified by many people. The @acronym{GNU} enhancements were
595 written by Jay Fenlason, then Joy Kendall, and the whole package has
596 been further maintained by Thomas Bushnell, n/BSG, Fran@,{c}ois
597 Pinard, Paul Eggert, and finally Sergey Poznyakoff with the help of
598 numerous and kind users.
600 We wish to stress that @command{tar} is a collective work, and owes much to
601 all those people who reported problems, offered solutions and other
602 insights, or shared their thoughts and suggestions. An impressive, yet
603 partial list of those contributors can be found in the @file{THANKS}
604 file from the @GNUTAR{} distribution.
606 @FIXME{i want all of these names mentioned, Absolutely. BUT, i'm not
607 sure i want to spell out the history in this detail, at least not for
608 the printed book. i'm just not sure it needs to be said this way.
609 i'll think about it.}
611 @FIXME{History is more important, and surely more interesting, than
612 actual names. Quoting names without history would be meaningless. FP}
614 Jay Fenlason put together a draft of a @GNUTAR{}
615 manual, borrowing notes from the original man page from John Gilmore.
616 This was withdrawn in version 1.11. Thomas Bushnell, n/BSG and Amy
617 Gorin worked on a tutorial and manual for @GNUTAR{}.
618 Fran@,{c}ois Pinard put version 1.11.8 of the manual together by
619 taking information from all these sources and merging them. Melissa
620 Weisshaus finally edited and redesigned the book to create version
621 1.12. The book for versions from 1.14 up to @value{VERSION} were edited
622 by the current maintainer, Sergey Poznyakoff.
624 For version 1.12, Daniel Hagerty contributed a great deal of technical
625 consulting. In particular, he is the primary author of @ref{Backups}.
627 In July, 2003 @GNUTAR{} was put on CVS at savannah.gnu.org
628 (see @url{http://savannah.gnu.org/projects/tar}), and
629 active development and maintenance work has started
630 again. Currently @GNUTAR{} is being maintained by Paul Eggert, Sergey
631 Poznyakoff and Jeff Bailey.
633 Support for @acronym{POSIX} archives was added by Sergey Poznyakoff.
636 @section Reporting bugs or suggestions
639 @cindex reporting bugs
640 If you find problems or have suggestions about this program or manual,
641 please report them to @file{bug-tar@@gnu.org}.
643 When reporting a bug, please be sure to include as much detail as
644 possible, in order to reproduce it. @FIXME{Be more specific, I'd
645 like to make this node as detailed as 'Bug reporting' node in Emacs
649 @chapter Tutorial Introduction to @command{tar}
651 This chapter guides you through some basic examples of three @command{tar}
652 operations: @option{--create}, @option{--list}, and @option{--extract}. If
653 you already know how to use some other version of @command{tar}, then you
654 may not need to read this chapter. This chapter omits most complicated
655 details about how @command{tar} works.
659 * stylistic conventions::
660 * basic tar options:: Basic @command{tar} Operations and Options
661 * frequent operations::
662 * Two Frequent Options::
663 * create:: How to Create Archives
664 * list:: How to List Archives
665 * extract:: How to Extract Members from an Archive
670 @section Assumptions this Tutorial Makes
672 This chapter is paced to allow beginners to learn about @command{tar}
673 slowly. At the same time, we will try to cover all the basic aspects of
674 these three operations. In order to accomplish both of these tasks, we
675 have made certain assumptions about your knowledge before reading this
676 manual, and the hardware you will be using:
680 Before you start to work through this tutorial, you should understand
681 what the terms ``archive'' and ``archive member'' mean
682 (@pxref{Definitions}). In addition, you should understand something
683 about how Unix-type operating systems work, and you should know how to
684 use some basic utilities. For example, you should know how to create,
685 list, copy, rename, edit, and delete files and directories; how to
686 change between directories; and how to figure out where you are in the
687 file system. You should have some basic understanding of directory
688 structure and how files are named according to which directory they are
689 in. You should understand concepts such as standard output and standard
690 input, what various definitions of the term @samp{argument} mean, and the
691 differences between relative and absolute file names. @FIXME{and what
695 This manual assumes that you are working from your own home directory
696 (unless we state otherwise). In this tutorial, you will create a
697 directory to practice @command{tar} commands in. When we show file names,
698 we will assume that those names are relative to your home directory.
699 For example, my home directory is @file{/home/fsf/melissa}. All of
700 my examples are in a subdirectory of the directory named by that file
701 name; the subdirectory is called @file{practice}.
704 In general, we show examples of archives which exist on (or can be
705 written to, or worked with from) a directory on a hard disk. In most
706 cases, you could write those archives to, or work with them on any other
707 device, such as a tape drive. However, some of the later examples in
708 the tutorial and next chapter will not work on tape drives.
709 Additionally, working with tapes is much more complicated than working
710 with hard disks. For these reasons, the tutorial does not cover working
711 with tape drives. @xref{Media}, for complete information on using
712 @command{tar} archives with tape drives.
714 @FIXME{this is a cop out. need to add some simple tape drive info.}
717 @node stylistic conventions
718 @section Stylistic Conventions
720 In the examples, @samp{$} represents a typical shell prompt. It
721 precedes lines you should type; to make this more clear, those lines are
722 shown in @kbd{this font}, as opposed to lines which represent the
723 computer's response; those lines are shown in @code{this font}, or
724 sometimes @samp{like this}.
726 @c When we have lines which are too long to be
727 @c displayed in any other way, we will show them like this:
729 @node basic tar options
730 @section Basic @command{tar} Operations and Options
732 @command{tar} can take a wide variety of arguments which specify and define
733 the actions it will have on the particular set of files or the archive.
734 The main types of arguments to @command{tar} fall into one of two classes:
735 operations, and options.
737 Some arguments fall into a class called @dfn{operations}; exactly one of
738 these is both allowed and required for any instance of using @command{tar};
739 you may @emph{not} specify more than one. People sometimes speak of
740 @dfn{operating modes}. You are in a particular operating mode when you
741 have specified the operation which specifies it; there are eight
742 operations in total, and thus there are eight operating modes.
744 The other arguments fall into the class known as @dfn{options}. You are
745 not required to specify any options, and you are allowed to specify more
746 than one at a time (depending on the way you are using @command{tar} at
747 that time). Some options are used so frequently, and are so useful for
748 helping you type commands more carefully that they are effectively
749 ``required''. We will discuss them in this chapter.
751 You can write most of the @command{tar} operations and options in any
752 of three forms: long (mnemonic) form, short form, and old style. Some
753 of the operations and options have no short or ``old'' forms; however,
754 the operations and options which we will cover in this tutorial have
755 corresponding abbreviations. We will indicate those abbreviations
756 appropriately to get you used to seeing them. Note, that the ``old
757 style'' option forms exist in @GNUTAR{} for compatibility with Unix
758 @command{tar}. In this book we present a full discussion of this way
759 of writing options and operations (@pxref{Old Options}), and we discuss
760 the other two styles of writing options (@xref{Long Options}, and
761 @pxref{Short Options}).
763 In the examples and in the text of this tutorial, we usually use the
764 long forms of operations and options; but the ``short'' forms produce
765 the same result and can make typing long @command{tar} commands easier.
766 For example, instead of typing
769 @kbd{tar --create --verbose --file=afiles.tar apple angst aspic}
775 @kbd{tar -c -v -f afiles.tar apple angst aspic}
781 @kbd{tar -cvf afiles.tar apple angst aspic}
785 For more information on option syntax, see @ref{Advanced tar}. In
786 discussions in the text, when we name an option by its long form, we
787 also give the corresponding short option in parentheses.
789 The term, ``option'', can be confusing at times, since ``operations''
790 are often lumped in with the actual, @emph{optional} ``options'' in certain
791 general class statements. For example, we just talked about ``short and
792 long forms of options and operations''. However, experienced @command{tar}
793 users often refer to these by shorthand terms such as, ``short and long
794 options''. This term assumes that the ``operations'' are included, also.
795 Context will help you determine which definition of ``options'' to use.
797 Similarly, the term ``command'' can be confusing, as it is often used in
798 two different ways. People sometimes refer to @command{tar} ``commands''.
799 A @command{tar} @dfn{command} is the entire command line of user input
800 which tells @command{tar} what to do --- including the operation, options,
801 and any arguments (file names, pipes, other commands, etc.). However,
802 you will also sometimes hear the term ``the @command{tar} command''. When
803 the word ``command'' is used specifically like this, a person is usually
804 referring to the @command{tar} @emph{operation}, not the whole line.
805 Again, use context to figure out which of the meanings the speaker
808 @node frequent operations
809 @section The Three Most Frequently Used Operations
811 Here are the three most frequently used operations (both short and long
812 forms), as well as a brief description of their meanings. The rest of
813 this chapter will cover how to use these operations in detail. We will
814 present the rest of the operations in the next chapter.
819 Create a new @command{tar} archive.
822 List the contents of an archive.
825 Extract one or more members from an archive.
828 @node Two Frequent Options
829 @section Two Frequently Used Options
831 To understand how to run @command{tar} in the three operating modes listed
832 previously, you also need to understand how to use two of the options to
833 @command{tar}: @option{--file} (which takes an archive file as an argument)
834 and @option{--verbose}. (You are usually not @emph{required} to specify
835 either of these options when you run @command{tar}, but they can be very
836 useful in making things more clear and helping you avoid errors.)
845 @unnumberedsubsec The @option{--file} Option
848 @xopindex{file, tutorial}
849 @item --file=@var{archive-name}
850 @itemx -f @var{archive-name}
851 Specify the name of an archive file.
854 You can specify an argument for the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option whenever you
855 use @command{tar}; this option determines the name of the archive file
856 that @command{tar} will work on.
859 If you don't specify this argument, then @command{tar} will examine
860 the environment variable @env{TAPE}. If it is set, its value will be
861 used as the archive name. Otherwise, @command{tar} will use the
862 default archive, determined at compile time. Usually it is
863 standard output or some physical tape drive attached to your machine
864 (you can verify what the default is by running @kbd{tar
865 --show-defaults}, @pxref{defaults}). If there is no tape drive
866 attached, or the default is not meaningful, then @command{tar} will
867 print an error message. The error message might look roughly like one
871 tar: can't open /dev/rmt8 : No such device or address
872 tar: can't open /dev/rsmt0 : I/O error
876 To avoid confusion, we recommend that you always specify an archive file
877 name by using @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) when writing your @command{tar} commands.
878 For more information on using the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option, see
881 @node verbose tutorial
882 @unnumberedsubsec The @option{--verbose} Option
885 @xopindex{verbose, introduced}
888 Show the files being worked on as @command{tar} is running.
891 @option{--verbose} (@option{-v}) shows details about the results of running
892 @command{tar}. This can be especially useful when the results might not be
893 obvious. For example, if you want to see the progress of @command{tar} as
894 it writes files into the archive, you can use the @option{--verbose}
895 option. In the beginning, you may find it useful to use
896 @option{--verbose} at all times; when you are more accustomed to
897 @command{tar}, you will likely want to use it at certain times but not at
898 others. We will use @option{--verbose} at times to help make something
899 clear, and we will give many examples both using and not using
900 @option{--verbose} to show the differences.
902 Each instance of @option{--verbose} on the command line increases the
903 verbosity level by one, so if you need more details on the output,
906 When reading archives (@option{--list}, @option{--extract},
907 @option{--diff}), @command{tar} by default prints only the names of
908 the members being extracted. Using @option{--verbose} will show a full,
909 @command{ls} style member listing.
911 In contrast, when writing archives (@option{--create}, @option{--append},
912 @option{--update}), @command{tar} does not print file names by
913 default. So, a single @option{--verbose} option shows the file names
914 being added to the archive, while two @option{--verbose} options
915 enable the full listing.
917 For example, to create an archive in verbose mode:
920 $ @kbd{tar -cvf afiles.tar apple angst aspic}
927 Creating the same archive with the verbosity level 2 could give:
930 $ @kbd{tar -cvvf afiles.tar apple angst aspic}
931 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
932 -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst
933 -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
937 This works equally well using short or long forms of options. Using
938 long forms, you would simply write out the mnemonic form of the option
942 $ @kbd{tar --create --verbose --verbose @dots{}}
946 Note that you must double the hyphens properly each time.
948 Later in the tutorial, we will give examples using @w{@option{--verbose
951 @anchor{verbose member listing}
952 The full output consists of six fields:
955 @item File type and permissions in symbolic form.
956 These are displayed in the same format as the first column of
957 @command{ls -l} output (@pxref{What information is listed,
958 format=verbose, Verbose listing, fileutils, GNU file utilities}).
960 @item Owner name and group separated by a slash character.
961 If these data are not available (for example, when listing a @samp{v7} format
962 archive), numeric @acronym{ID} values are printed instead.
964 @item Size of the file, in bytes.
966 @item File modification date in ISO 8601 format.
968 @item File modification time.
971 If the name contains any special characters (white space, newlines,
972 etc.) these are displayed in an unambiguous form using so called
973 @dfn{quoting style}. For the detailed discussion of available styles
974 and on how to use them, see @ref{quoting styles}.
976 Depending on the file type, the name can be followed by some
977 additional information, described in the following table:
980 @item -> @var{link-name}
981 The file or archive member is a @dfn{symbolic link} and
982 @var{link-name} is the name of file it links to.
984 @item link to @var{link-name}
985 The file or archive member is a @dfn{hard link} and @var{link-name} is
986 the name of file it links to.
989 The archive member is an old GNU format long link. You will normally
993 The archive member is an old GNU format long name. You will normally
996 @item --Volume Header--
997 The archive member is a GNU @dfn{volume header} (@pxref{Tape Files}).
999 @item --Continued at byte @var{n}--
1000 Encountered only at the beginning of a multi-volume archive
1001 (@pxref{Using Multiple Tapes}). This archive member is a continuation
1002 from the previous volume. The number @var{n} gives the offset where
1003 the original file was split.
1005 @item unknown file type @var{c}
1006 An archive member of unknown type. @var{c} is the type character from
1007 the archive header. If you encounter such a message, it means that
1008 either your archive contains proprietary member types @GNUTAR{} is not
1009 able to handle, or the archive is corrupted.
1014 For example, here is an archive listing containing most of the special
1015 suffixes explained above:
1019 V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header--
1020 -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at
1022 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
1023 lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple
1024 -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues
1025 hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
1033 @unnumberedsubsec Getting Help: Using the @option{--help} Option
1039 The @option{--help} option to @command{tar} prints out a very brief list of
1040 all operations and option available for the current version of
1041 @command{tar} available on your system.
1045 @section How to Create Archives
1048 @cindex Creation of the archive
1049 @cindex Archive, creation of
1050 One of the basic operations of @command{tar} is @option{--create} (@option{-c}), which
1051 you use to create a @command{tar} archive. We will explain
1052 @option{--create} first because, in order to learn about the other
1053 operations, you will find it useful to have an archive available to
1056 To make this easier, in this section you will first create a directory
1057 containing three files. Then, we will show you how to create an
1058 @emph{archive} (inside the new directory). Both the directory, and
1059 the archive are specifically for you to practice on. The rest of this
1060 chapter and the next chapter will show many examples using this
1061 directory and the files you will create: some of those files may be
1062 other directories and other archives.
1064 The three files you will archive in this example are called
1065 @file{blues}, @file{folk}, and @file{jazz}. The archive is called
1066 @file{collection.tar}.
1068 This section will proceed slowly, detailing how to use @option{--create}
1069 in @code{verbose} mode, and showing examples using both short and long
1070 forms. In the rest of the tutorial, and in the examples in the next
1071 chapter, we will proceed at a slightly quicker pace. This section
1072 moves more slowly to allow beginning users to understand how
1073 @command{tar} works.
1076 * prepare for examples::
1077 * Creating the archive::
1083 @node prepare for examples
1084 @subsection Preparing a Practice Directory for Examples
1086 To follow along with this and future examples, create a new directory
1087 called @file{practice} containing files called @file{blues}, @file{folk}
1088 and @file{jazz}. The files can contain any information you like:
1089 ideally, they should contain information which relates to their names,
1090 and be of different lengths. Our examples assume that @file{practice}
1091 is a subdirectory of your home directory.
1093 Now @command{cd} to the directory named @file{practice}; @file{practice}
1094 is now your @dfn{working directory}. (@emph{Please note}: Although
1095 the full file name of this directory is
1096 @file{/@var{homedir}/practice}, in our examples we will refer to
1097 this directory as @file{practice}; the @var{homedir} is presumed.)
1099 In general, you should check that the files to be archived exist where
1100 you think they do (in the working directory) by running @command{ls}.
1101 Because you just created the directory and the files and have changed to
1102 that directory, you probably don't need to do that this time.
1104 It is very important to make sure there isn't already a file in the
1105 working directory with the archive name you intend to use (in this case,
1106 @samp{collection.tar}), or that you don't care about its contents.
1107 Whenever you use @samp{create}, @command{tar} will erase the current
1108 contents of the file named by @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) if it exists. @command{tar}
1109 will not tell you if you are about to overwrite an archive unless you
1110 specify an option which does this (@pxref{backup}, for the
1111 information on how to do so). To add files to an existing archive,
1112 you need to use a different option, such as @option{--append} (@option{-r}); see
1113 @ref{append} for information on how to do this.
1115 @node Creating the archive
1116 @subsection Creating the Archive
1118 @xopindex{create, introduced}
1119 To place the files @file{blues}, @file{folk}, and @file{jazz} into an
1120 archive named @file{collection.tar}, use the following command:
1123 $ @kbd{tar --create --file=collection.tar blues folk jazz}
1126 The order of the arguments is not very important, @emph{when using long
1127 option forms}. You could also say:
1130 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1134 However, you can see that this order is harder to understand; this is
1135 why we will list the arguments in the order that makes the commands
1136 easiest to understand (and we encourage you to do the same when you use
1137 @command{tar}, to avoid errors).
1139 Note that the sequence
1140 @option{--file=@-collection.tar} is considered to be @emph{one} argument.
1141 If you substituted any other string of characters for
1142 @kbd{collection.tar}, then that string would become the name of the
1143 archive file you create.
1145 The order of the options becomes more important when you begin to use
1146 short forms. With short forms, if you type commands in the wrong order
1147 (even if you type them correctly in all other ways), you may end up with
1148 results you don't expect. For this reason, it is a good idea to get
1149 into the habit of typing options in the order that makes inherent sense.
1150 @xref{short create}, for more information on this.
1152 In this example, you type the command as shown above: @option{--create}
1153 is the operation which creates the new archive
1154 (@file{collection.tar}), and @option{--file} is the option which lets
1155 you give it the name you chose. The files, @file{blues}, @file{folk},
1156 and @file{jazz}, are now members of the archive, @file{collection.tar}
1157 (they are @dfn{file name arguments} to the @option{--create} operation.
1158 @xref{Choosing}, for the detailed discussion on these.) Now that they are
1159 in the archive, they are called @emph{archive members}, not files.
1160 (@pxref{Definitions,members}).
1162 When you create an archive, you @emph{must} specify which files you
1163 want placed in the archive. If you do not specify any archive
1164 members, @GNUTAR{} will complain.
1166 If you now list the contents of the working directory (@command{ls}), you will
1167 find the archive file listed as well as the files you saw previously:
1170 blues folk jazz collection.tar
1174 Creating the archive @samp{collection.tar} did not destroy the copies of
1175 the files in the directory.
1177 Keep in mind that if you don't indicate an operation, @command{tar} will not
1178 run and will prompt you for one. If you don't name any files, @command{tar}
1179 will complain. You must have write access to the working directory,
1180 or else you will not be able to create an archive in that directory.
1182 @emph{Caution}: Do not attempt to use @option{--create} (@option{-c}) to add files to
1183 an existing archive; it will delete the archive and write a new one.
1184 Use @option{--append} (@option{-r}) instead. @xref{append}.
1186 @node create verbose
1187 @subsection Running @option{--create} with @option{--verbose}
1189 @xopindex{create, using with @option{--verbose}}
1190 @xopindex{verbose, using with @option{--create}}
1191 If you include the @option{--verbose} (@option{-v}) option on the command line,
1192 @command{tar} will list the files it is acting on as it is working. In
1193 verbose mode, the @code{create} example above would appear as:
1196 $ @kbd{tar --create --verbose --file=collection.tar blues folk jazz}
1202 This example is just like the example we showed which did not use
1203 @option{--verbose}, except that @command{tar} generated the remaining
1205 lines (note the different font styles).
1211 In the rest of the examples in this chapter, we will frequently use
1212 @code{verbose} mode so we can show actions or @command{tar} responses that
1213 you would otherwise not see, and which are important for you to
1217 @subsection Short Forms with @samp{create}
1219 As we said before, the @option{--create} (@option{-c}) operation is one of the most
1220 basic uses of @command{tar}, and you will use it countless times.
1221 Eventually, you will probably want to use abbreviated (or ``short'')
1222 forms of options. A full discussion of the three different forms that
1223 options can take appears in @ref{Styles}; for now, here is what the
1224 previous example (including the @option{--verbose} (@option{-v}) option) looks like
1225 using short option forms:
1228 $ @kbd{tar -cvf collection.tar blues folk jazz}
1235 As you can see, the system responds the same no matter whether you use
1236 long or short option forms.
1238 @FIXME{i don't like how this is worded:} One difference between using
1239 short and long option forms is that, although the exact placement of
1240 arguments following options is no more specific when using short forms,
1241 it is easier to become confused and make a mistake when using short
1242 forms. For example, suppose you attempted the above example in the
1246 $ @kbd{tar -cfv collection.tar blues folk jazz}
1250 In this case, @command{tar} will make an archive file called @file{v},
1251 containing the files @file{blues}, @file{folk}, and @file{jazz}, because
1252 the @samp{v} is the closest ``file name'' to the @option{-f} option, and
1253 is thus taken to be the chosen archive file name. @command{tar} will try
1254 to add a file called @file{collection.tar} to the @file{v} archive file;
1255 if the file @file{collection.tar} did not already exist, @command{tar} will
1256 report an error indicating that this file does not exist. If the file
1257 @file{collection.tar} does already exist (e.g., from a previous command
1258 you may have run), then @command{tar} will add this file to the archive.
1259 Because the @option{-v} option did not get registered, @command{tar} will not
1260 run under @samp{verbose} mode, and will not report its progress.
1262 The end result is that you may be quite confused about what happened,
1263 and possibly overwrite a file. To illustrate this further, we will show
1264 you how an example we showed previously would look using short forms.
1269 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1273 is confusing as it is. When shown using short forms, however, it
1274 becomes much more so:
1277 $ @kbd{tar blues -c folk -f collection.tar jazz}
1281 It would be very easy to put the wrong string of characters
1282 immediately following the @option{-f}, but doing that could sacrifice
1285 For this reason, we recommend that you pay very careful attention to
1286 the order of options and placement of file and archive names,
1287 especially when using short option forms. Not having the option name
1288 written out mnemonically can affect how well you remember which option
1289 does what, and therefore where different names have to be placed.
1292 @subsection Archiving Directories
1294 @cindex Archiving Directories
1295 @cindex Directories, Archiving
1296 You can archive a directory by specifying its directory name as a
1297 file name argument to @command{tar}. The files in the directory will be
1298 archived relative to the working directory, and the directory will be
1299 re-created along with its contents when the archive is extracted.
1301 To archive a directory, first move to its superior directory. If you
1302 have followed the previous instructions in this tutorial, you should
1311 This will put you into the directory which contains @file{practice},
1312 i.e., your home directory. Once in the superior directory, you can
1313 specify the subdirectory, @file{practice}, as a file name argument. To
1314 store @file{practice} in the new archive file @file{music.tar}, type:
1317 $ @kbd{tar --create --verbose --file=music.tar practice}
1321 @command{tar} should output:
1328 practice/collection.tar
1331 Note that the archive thus created is not in the subdirectory
1332 @file{practice}, but rather in the current working directory---the
1333 directory from which @command{tar} was invoked. Before trying to archive a
1334 directory from its superior directory, you should make sure you have
1335 write access to the superior directory itself, not only the directory
1336 you are trying archive with @command{tar}. For example, you will probably
1337 not be able to store your home directory in an archive by invoking
1338 @command{tar} from the root directory; @xref{absolute}. (Note
1339 also that @file{collection.tar}, the original archive file, has itself
1340 been archived. @command{tar} will accept any file as a file to be
1341 archived, regardless of its content. When @file{music.tar} is
1342 extracted, the archive file @file{collection.tar} will be re-written
1343 into the file system).
1345 If you give @command{tar} a command such as
1348 $ @kbd{tar --create --file=foo.tar .}
1352 @command{tar} will report @samp{tar: ./foo.tar is the archive; not
1353 dumped}. This happens because @command{tar} creates the archive
1354 @file{foo.tar} in the current directory before putting any files into
1355 it. Then, when @command{tar} attempts to add all the files in the
1356 directory @file{.} to the archive, it notices that the file
1357 @file{./foo.tar} is the same as the archive @file{foo.tar}, and skips
1358 it. (It makes no sense to put an archive into itself.) @GNUTAR{}
1359 will continue in this case, and create the archive
1360 normally, except for the exclusion of that one file. (@emph{Please
1361 note:} Other implementations of @command{tar} may not be so clever;
1362 they will enter an infinite loop when this happens, so you should not
1363 depend on this behavior unless you are certain you are running
1364 @GNUTAR{}. In general, it is wise to always place the archive outside
1365 of the directory being dumped.)
1368 @section How to List Archives
1371 Frequently, you will find yourself wanting to determine exactly what a
1372 particular archive contains. You can use the @option{--list}
1373 (@option{-t}) operation to get the member names as they currently
1374 appear in the archive, as well as various attributes of the files at
1375 the time they were archived. For example, you can examine the archive
1376 @file{collection.tar} that you created in the last section with the
1380 $ @kbd{tar --list --file=collection.tar}
1384 The output of @command{tar} would then be:
1393 The archive @file{bfiles.tar} would list as follows:
1402 Be sure to use a @option{--file=@var{archive-name}} (@option{-f
1403 @var{archive-name}}) option just as with @option{--create}
1404 (@option{-c}) to specify the name of the archive.
1406 @xopindex{list, using with @option{--verbose}}
1407 @xopindex{verbose, using with @option{--list}}
1408 If you use the @option{--verbose} (@option{-v}) option with
1409 @option{--list}, then @command{tar} will print out a listing
1410 reminiscent of @w{@samp{ls -l}}, showing owner, file size, and so
1411 forth. This output is described in detail in @ref{verbose member listing}.
1413 If you had used @option{--verbose} (@option{-v}) mode, the example
1414 above would look like:
1417 $ @kbd{tar --list --verbose --file=collection.tar folk}
1418 -rw-r--r-- myself user 62 1990-05-23 10:55 folk
1421 @cindex listing member and file names
1422 @anchor{listing member and file names}
1423 It is important to notice that the output of @kbd{tar --list
1424 --verbose} does not necessarily match that produced by @kbd{tar
1425 --create --verbose} while creating the archive. It is because
1426 @GNUTAR{}, unless told explicitly not to do so, removes some directory
1427 prefixes from file names before storing them in the archive
1428 (@xref{absolute}, for more information). In other
1429 words, in verbose mode @GNUTAR{} shows @dfn{file names} when creating
1430 an archive and @dfn{member names} when listing it. Consider this
1435 $ @kbd{tar --create --verbose --file archive /etc/mail}
1436 tar: Removing leading `/' from member names
1438 /etc/mail/sendmail.cf
1440 $ @kbd{tar --test --file archive}
1442 etc/mail/sendmail.cf
1447 @opindex show-stored-names
1448 This default behavior can sometimes be inconvenient. You can force
1449 @GNUTAR{} show member names when creating archive by supplying
1450 @option{--show-stored-names} option.
1453 @item --show-stored-names
1454 Print member (as opposed to @emph{file}) names when creating the archive.
1457 @cindex File name arguments, using @option{--list} with
1458 @xopindex{list, using with file name arguments}
1459 You can specify one or more individual member names as arguments when
1460 using @samp{list}. In this case, @command{tar} will only list the
1461 names of members you identify. For example, @w{@kbd{tar --list
1462 --file=afiles.tar apple}} would only print @file{apple}.
1464 Because @command{tar} preserves file names, these must be specified as
1465 they appear in the archive (i.e., relative to the directory from which
1466 the archive was created). Therefore, it is essential when specifying
1467 member names to @command{tar} that you give the exact member names.
1468 For example, @w{@kbd{tar --list --file=bfiles.tar birds}} would produce an
1469 error message something like @samp{tar: birds: Not found in archive},
1470 because there is no member named @file{birds}, only one named
1471 @file{./birds}. While the names @file{birds} and @file{./birds} name
1472 the same file, @emph{member} names by default are compared verbatim.
1474 However, @w{@kbd{tar --list --file=bfiles.tar baboon}} would respond
1475 with @file{baboon}, because this exact member name is in the archive file
1476 @file{bfiles.tar}. If you are not sure of the exact file name,
1477 use @dfn{globbing patterns}, for example:
1480 $ @kbd{tar --list --file=bfiles.tar --wildcards '*b*'}
1484 will list all members whose name contains @samp{b}. @xref{wildcards},
1485 for a detailed discussion of globbing patterns and related
1486 @command{tar} command line options.
1493 @unnumberedsubsec Listing the Contents of a Stored Directory
1495 To get information about the contents of an archived directory,
1496 use the directory name as a file name argument in conjunction with
1497 @option{--list} (@option{-t}). To find out file attributes, include the
1498 @option{--verbose} (@option{-v}) option.
1500 For example, to find out about files in the directory @file{practice}, in
1501 the archive file @file{music.tar}, type:
1504 $ @kbd{tar --list --verbose --file=music.tar practice}
1507 @command{tar} responds:
1510 drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
1511 -rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues
1512 -rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk
1513 -rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz
1514 -rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar
1517 When you use a directory name as a file name argument, @command{tar} acts on
1518 all the files (including sub-directories) in that directory.
1521 @section How to Extract Members from an Archive
1523 @cindex Retrieving files from an archive
1524 @cindex Resurrecting files from an archive
1527 Creating an archive is only half the job---there is no point in storing
1528 files in an archive if you can't retrieve them. The act of retrieving
1529 members from an archive so they can be used and manipulated as
1530 unarchived files again is called @dfn{extraction}. To extract files
1531 from an archive, use the @option{--extract} (@option{--get} or
1532 @option{-x}) operation. As with @option{--create}, specify the name
1533 of the archive with @option{--file} (@option{-f}) option. Extracting
1534 an archive does not modify the archive in any way; you can extract it
1535 multiple times if you want or need to.
1537 Using @option{--extract}, you can extract an entire archive, or specific
1538 files. The files can be directories containing other files, or not. As
1539 with @option{--create} (@option{-c}) and @option{--list} (@option{-t}), you may use the short or the
1540 long form of the operation without affecting the performance.
1543 * extracting archives::
1544 * extracting files::
1546 * extracting untrusted archives::
1547 * failing commands::
1550 @node extracting archives
1551 @subsection Extracting an Entire Archive
1553 To extract an entire archive, specify the archive file name only, with
1554 no individual file names as arguments. For example,
1557 $ @kbd{tar -xvf collection.tar}
1564 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
1565 -rw-r--r-- me user 21 1996-09-23 16:44 blues
1566 -rw-r--r-- me user 20 1996-09-23 16:44 folk
1569 @node extracting files
1570 @subsection Extracting Specific Files
1572 To extract specific archive members, give their exact member names as
1573 arguments, as printed by @option{--list} (@option{-t}). If you had
1574 mistakenly deleted one of the files you had placed in the archive
1575 @file{collection.tar} earlier (say, @file{blues}), you can extract it
1576 from the archive without changing the archive's structure. Its
1577 contents will be identical to the original file @file{blues} that you
1580 First, make sure you are in the @file{practice} directory, and list the
1581 files in the directory. Now, delete the file, @samp{blues}, and list
1582 the files in the directory again.
1584 You can now extract the member @file{blues} from the archive file
1585 @file{collection.tar} like this:
1588 $ @kbd{tar --extract --file=collection.tar blues}
1592 If you list the files in the directory again, you will see that the file
1593 @file{blues} has been restored, with its original permissions, data
1594 modification times, and owner.@footnote{This is only accidentally
1595 true, but not in general. Whereas modification times are always
1596 restored, in most cases, one has to be root for restoring the owner,
1597 and use a special option for restoring permissions. Here, it just
1598 happens that the restoring user is also the owner of the archived
1599 members, and that the current @code{umask} is compatible with original
1600 permissions.} (These parameters will be identical to those which
1601 the file had when you originally placed it in the archive; any changes
1602 you may have made before deleting the file from the file system,
1603 however, will @emph{not} have been made to the archive member.) The
1604 archive file, @samp{collection.tar}, is the same as it was before you
1605 extracted @samp{blues}. You can confirm this by running @command{tar} with
1606 @option{--list} (@option{-t}).
1608 Remember that as with other operations, specifying the exact member
1609 name is important. @w{@kbd{tar --extract --file=bfiles.tar birds}}
1610 will fail, because there is no member named @file{birds}. To extract
1611 the member named @file{./birds}, you must specify @w{@kbd{tar
1612 --extract --file=bfiles.tar ./birds}}. If you don't remember the
1613 exact member names, use @option{--list} (@option{-t}) option
1614 (@pxref{list}). You can also extract those members that match a
1615 specific @dfn{globbing pattern}. For example, to extract from
1616 @file{bfiles.tar} all files that begin with @samp{b}, no matter their
1617 directory prefix, you could type:
1620 $ @kbd{tar -x -f bfiles.tar --wildcards --no-anchored 'b*'}
1624 Here, @option{--wildcards} instructs @command{tar} to treat
1625 command line arguments as globbing patterns and @option{--no-anchored}
1626 informs it that the patterns apply to member names after any @samp{/}
1627 delimiter. The use of globbing patterns is discussed in detail in
1630 You can extract a file to standard output by combining the above options
1631 with the @option{--to-stdout} (@option{-O}) option (@pxref{Writing to Standard
1634 If you give the @option{--verbose} option, then @option{--extract}
1635 will print the names of the archive members as it extracts them.
1638 @subsection Extracting Files that are Directories
1640 Extracting directories which are members of an archive is similar to
1641 extracting other files. The main difference to be aware of is that if
1642 the extracted directory has the same name as any directory already in
1643 the working directory, then files in the extracted directory will be
1644 placed into the directory of the same name. Likewise, if there are
1645 files in the pre-existing directory with the same names as the members
1646 which you extract, the files from the extracted archive will replace
1647 the files already in the working directory (and possible
1648 subdirectories). This will happen regardless of whether or not the
1649 files in the working directory were more recent than those extracted
1650 (there exist, however, special options that alter this behavior
1653 However, if a file was stored with a directory name as part of its file
1654 name, and that directory does not exist under the working directory when
1655 the file is extracted, @command{tar} will create the directory.
1657 We can demonstrate how to use @option{--extract} to extract a directory
1658 file with an example. Change to the @file{practice} directory if you
1659 weren't there, and remove the files @file{folk} and @file{jazz}. Then,
1660 go back to the parent directory and extract the archive
1661 @file{music.tar}. You may either extract the entire archive, or you may
1662 extract only the files you just deleted. To extract the entire archive,
1663 don't give any file names as arguments after the archive name
1664 @file{music.tar}. To extract only the files you deleted, use the
1668 $ @kbd{tar -xvf music.tar practice/folk practice/jazz}
1674 If you were to specify two @option{--verbose} (@option{-v}) options, @command{tar}
1675 would have displayed more detail about the extracted files, as shown
1676 in the example below:
1679 $ @kbd{tar -xvvf music.tar practice/folk practice/jazz}
1680 -rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz
1681 -rw-r--r-- me user 20 1996-09-23 16:44 practice/folk
1685 Because you created the directory with @file{practice} as part of the
1686 file names of each of the files by archiving the @file{practice}
1687 directory as @file{practice}, you must give @file{practice} as part
1688 of the file names when you extract those files from the archive.
1690 @node extracting untrusted archives
1691 @subsection Extracting Archives from Untrusted Sources
1693 Extracting files from archives can overwrite files that already exist.
1694 If you receive an archive from an untrusted source, you should make a
1695 new directory and extract into that directory, so that you don't have
1696 to worry about the extraction overwriting one of your existing files.
1697 For example, if @file{untrusted.tar} came from somewhere else on the
1698 Internet, and you don't necessarily trust its contents, you can
1699 extract it as follows:
1702 $ @kbd{mkdir newdir}
1704 $ @kbd{tar -xvf ../untrusted.tar}
1707 It is also a good practice to examine contents of the archive
1708 before extracting it, using @option{--list} (@option{-t}) option, possibly combined
1709 with @option{--verbose} (@option{-v}).
1711 @node failing commands
1712 @subsection Commands That Will Fail
1714 Here are some sample commands you might try which will not work, and why
1717 If you try to use this command,
1720 $ @kbd{tar -xvf music.tar folk jazz}
1724 you will get the following response:
1727 tar: folk: Not found in archive
1728 tar: jazz: Not found in archive
1732 This is because these files were not originally @emph{in} the parent
1733 directory @file{..}, where the archive is located; they were in the
1734 @file{practice} directory, and their file names reflect this:
1737 $ @kbd{tar -tvf music.tar}
1743 @FIXME{make sure the above works when going through the examples in
1747 Likewise, if you try to use this command,
1750 $ @kbd{tar -tvf music.tar folk jazz}
1754 you would get a similar response. Members with those names are not in the
1755 archive. You must use the correct member names, or wildcards, in order
1756 to extract the files from the archive.
1758 If you have forgotten the correct names of the files in the archive,
1759 use @w{@kbd{tar --list --verbose}} to list them correctly.
1761 @FIXME{more examples, here? hag thinks it's a good idea.}
1764 @section Going Further Ahead in this Manual
1767 @FIXME{need to write up a node here about the things that are going to
1768 be in the rest of the manual.}
1770 @node tar invocation
1771 @chapter Invoking @GNUTAR{}
1773 This chapter is about how one invokes the @GNUTAR{}
1774 command, from the command synopsis (@pxref{Synopsis}). There are
1775 numerous options, and many styles for writing them. One mandatory
1776 option specifies the operation @command{tar} should perform
1777 (@pxref{Operation Summary}), other options are meant to detail how
1778 this operation should be performed (@pxref{Option Summary}).
1779 Non-option arguments are not always interpreted the same way,
1780 depending on what the operation is.
1782 You will find in this chapter everything about option styles and rules for
1783 writing them (@pxref{Styles}). On the other hand, operations and options
1784 are fully described elsewhere, in other chapters. Here, you will find
1785 only synthetic descriptions for operations and options, together with
1786 pointers to other parts of the @command{tar} manual.
1788 Some options are so special they are fully described right in this
1789 chapter. They have the effect of inhibiting the normal operation of
1790 @command{tar} or else, they globally alter the amount of feedback the user
1791 receives about what is going on. These are the @option{--help} and
1792 @option{--version} (@pxref{help}), @option{--verbose} (@pxref{verbose})
1793 and @option{--interactive} options (@pxref{interactive}).
1797 * using tar options::
1809 @section General Synopsis of @command{tar}
1811 The @GNUTAR{} program is invoked as either one of:
1814 @kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
1815 @kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
1818 The second form is for when old options are being used.
1820 You can use @command{tar} to store files in an archive, to extract them from
1821 an archive, and to do other types of archive manipulation. The primary
1822 argument to @command{tar}, which is called the @dfn{operation}, specifies
1823 which action to take. The other arguments to @command{tar} are either
1824 @dfn{options}, which change the way @command{tar} performs an operation,
1825 or file names or archive members, which specify the files or members
1826 @command{tar} is to act on.
1828 You can actually type in arguments in any order, even if in this manual
1829 the options always precede the other arguments, to make examples easier
1830 to understand. Further, the option stating the main operation mode
1831 (the @command{tar} main command) is usually given first.
1833 Each @var{name} in the synopsis above is interpreted as an archive member
1834 name when the main command is one of @option{--compare}
1835 (@option{--diff}, @option{-d}), @option{--delete}, @option{--extract}
1836 (@option{--get}, @option{-x}), @option{--list} (@option{-t}) or
1837 @option{--update} (@option{-u}). When naming archive members, you
1838 must give the exact name of the member in the archive, as it is
1839 printed by @option{--list}. For @option{--append} (@option{-r}) and
1840 @option{--create} (@option{-c}), these @var{name} arguments specify
1841 the names of either files or directory hierarchies to place in the archive.
1842 These files or hierarchies should already exist in the file system,
1843 prior to the execution of the @command{tar} command.
1845 @command{tar} interprets relative file names as being relative to the
1846 working directory. @command{tar} will make all file names relative
1847 (by removing leading slashes when archiving or restoring files),
1848 unless you specify otherwise (using the @option{--absolute-names}
1849 option). @xref{absolute}, for more information about
1850 @option{--absolute-names}.
1852 If you give the name of a directory as either a file name or a member
1853 name, then @command{tar} acts recursively on all the files and directories
1854 beneath that directory. For example, the name @file{/} identifies all
1855 the files in the file system to @command{tar}.
1857 The distinction between file names and archive member names is especially
1858 important when shell globbing is used, and sometimes a source of confusion
1859 for newcomers. @xref{wildcards}, for more information about globbing.
1860 The problem is that shells may only glob using existing files in the
1861 file system. Only @command{tar} itself may glob on archive members, so when
1862 needed, you must ensure that wildcard characters reach @command{tar} without
1863 being interpreted by the shell first. Using a backslash before @samp{*}
1864 or @samp{?}, or putting the whole argument between quotes, is usually
1865 sufficient for this.
1867 Even if @var{name}s are often specified on the command line, they
1868 can also be read from a text file in the file system, using the
1869 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option.
1871 If you don't use any file name arguments, @option{--append} (@option{-r}),
1872 @option{--delete} and @option{--concatenate} (@option{--catenate},
1873 @option{-A}) will do nothing, while @option{--create} (@option{-c})
1874 will usually yield a diagnostic and inhibit @command{tar} execution.
1875 The other operations of @command{tar} (@option{--list},
1876 @option{--extract}, @option{--compare}, and @option{--update})
1877 will act on the entire contents of the archive.
1880 @cindex return status
1881 Besides successful exits, @GNUTAR{} may fail for
1882 many reasons. Some reasons correspond to bad usage, that is, when the
1883 @command{tar} command line is improperly written. Errors may be
1884 encountered later, while processing the archive or the files. Some
1885 errors are recoverable, in which case the failure is delayed until
1886 @command{tar} has completed all its work. Some errors are such that
1887 it would be not meaningful, or at least risky, to continue processing:
1888 @command{tar} then aborts processing immediately. All abnormal exits,
1889 whether immediate or delayed, should always be clearly diagnosed on
1890 @code{stderr}, after a line stating the nature of the error.
1892 Possible exit codes of @GNUTAR{} are summarized in the following
1897 @samp{Successful termination}.
1900 @samp{Some files differ}. If tar was invoked with @option{--compare}
1901 (@option{--diff}, @option{-d}) command line option, this means that
1902 some files in the archive differ from their disk counterparts
1903 (@pxref{compare}). If tar was given @option{--create},
1904 @option{--append} or @option{--update} option, this exit code means
1905 that some files were changed while being archived and so the resulting
1906 archive does not contain the exact copy of the file set.
1909 @samp{Fatal error}. This means that some fatal, unrecoverable error
1913 If @command{tar} has invoked a subprocess and that subprocess exited with a
1914 nonzero exit code, @command{tar} exits with that code as well.
1915 This can happen, for example, if @command{tar} was given some
1916 compression option (@pxref{gzip}) and the external compressor program
1917 failed. Another example is @command{rmt} failure during backup to the
1918 remote device (@pxref{Remote Tape Server}).
1920 @node using tar options
1921 @section Using @command{tar} Options
1923 @GNUTAR{} has a total of eight operating modes which
1924 allow you to perform a variety of tasks. You are required to choose
1925 one operating mode each time you employ the @command{tar} program by
1926 specifying one, and only one operation as an argument to the
1927 @command{tar} command (the corresponding options may be found
1928 at @ref{frequent operations} and @ref{Operations}). Depending on
1929 circumstances, you may also wish to customize how the chosen operating
1930 mode behaves. For example, you may wish to change the way the output
1931 looks, or the format of the files that you wish to archive may require
1932 you to do something special in order to make the archive look right.
1934 You can customize and control @command{tar}'s performance by running
1935 @command{tar} with one or more options (such as @option{--verbose}
1936 (@option{-v}), which we used in the tutorial). As we said in the
1937 tutorial, @dfn{options} are arguments to @command{tar} which are (as
1938 their name suggests) optional. Depending on the operating mode, you
1939 may specify one or more options. Different options will have different
1940 effects, but in general they all change details of the operation, such
1941 as archive format, archive name, or level of user interaction. Some
1942 options make sense with all operating modes, while others are
1943 meaningful only with particular modes. You will likely use some
1944 options frequently, while you will only use others infrequently, or
1945 not at all. (A full list of options is available in @pxref{All Options}.)
1947 @vrindex TAR_OPTIONS, environment variable
1948 @anchor{TAR_OPTIONS}
1949 The @env{TAR_OPTIONS} environment variable specifies default options to
1950 be placed in front of any explicit options. For example, if
1951 @code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as
1952 if the two options @option{-v} and @option{--unlink-first} had been
1953 specified before any explicit options. Option specifications are
1954 separated by whitespace. A backslash escapes the next character, so it
1955 can be used to specify an option containing whitespace or a backslash.
1957 Note that @command{tar} options are case sensitive. For example, the
1958 options @option{-T} and @option{-t} are different; the first requires an
1959 argument for stating the name of a file providing a list of @var{name}s,
1960 while the second does not require an argument and is another way to
1961 write @option{--list} (@option{-t}).
1963 In addition to the eight operations, there are many options to
1964 @command{tar}, and three different styles for writing both: long (mnemonic)
1965 form, short form, and old style. These styles are discussed below.
1966 Both the options and the operations can be written in any of these three
1969 @FIXME{menu at end of this node. need to think of an actual outline
1970 for this chapter; probably do that after stuff from chapter 4 is
1974 @section The Three Option Styles
1976 There are three styles for writing operations and options to the command
1977 line invoking @command{tar}. The different styles were developed at
1978 different times during the history of @command{tar}. These styles will be
1979 presented below, from the most recent to the oldest.
1981 Some options must take an argument@footnote{For example, @option{--file}
1982 (@option{-f}) takes the name of an archive file as an argument. If
1983 you do not supply an archive file name, @command{tar} will use a
1984 default, but this can be confusing; thus, we recommend that you always
1985 supply a specific archive file name.}. Where you @emph{place} the
1986 arguments generally depends on which style of options you choose. We
1987 will detail specific information relevant to each option style in the
1988 sections on the different option styles, below. The differences are
1989 subtle, yet can often be very important; incorrect option placement
1990 can cause you to overwrite a number of important files. We urge you
1991 to note these differences, and only use the option style(s) which
1992 makes the most sense to you until you feel comfortable with the others.
1994 Some options @emph{may} take an argument. Such options may have at
1995 most long and short forms, they do not have old style equivalent. The
1996 rules for specifying an argument for such options are stricter than
1997 those for specifying mandatory arguments. Please, pay special
2001 * Long Options:: Long Option Style
2002 * Short Options:: Short Option Style
2003 * Old Options:: Old Option Style
2004 * Mixing:: Mixing Option Styles
2008 @subsection Long Option Style
2010 @cindex long options
2011 @cindex options, long style
2012 @cindex options, GNU style
2013 @cindex options, mnemonic names
2014 Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
2015 dashes in a row, e.g., @option{--list}. The long names are more clear than
2016 their corresponding short or old names. It sometimes happens that a
2017 single long option has many different names which are
2018 synonymous, such as @option{--compare} and @option{--diff}. In addition,
2019 long option names can be given unique abbreviations. For example,
2020 @option{--cre} can be used in place of @option{--create} because there is no
2021 other long option which begins with @samp{cre}. (One way to find
2022 this out is by trying it and seeing what happens; if a particular
2023 abbreviation could represent more than one option, @command{tar} will tell
2024 you that that abbreviation is ambiguous and you'll know that that
2025 abbreviation won't work. You may also choose to run @samp{tar --help}
2026 to see a list of options. Be aware that if you run @command{tar} with a
2027 unique abbreviation for the long name of an option you didn't want to
2028 use, you are stuck; @command{tar} will perform the command as ordered.)
2030 Long options are meant to be obvious and easy to remember, and their
2031 meanings are generally easier to discern than those of their
2032 corresponding short options (see below). For example:
2035 $ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
2039 gives a fairly good set of hints about what the command does, even
2040 for those not fully acquainted with @command{tar}.
2042 @cindex arguments to long options
2043 @cindex long options with mandatory arguments
2044 Long options which require arguments take those arguments
2045 immediately following the option name. There are two ways of
2046 specifying a mandatory argument. It can be separated from the
2047 option name either by an equal sign, or by any amount of
2048 white space characters. For example, the @option{--file} option (which
2049 tells the name of the @command{tar} archive) is given a file such as
2050 @file{archive.tar} as argument by using any of the following notations:
2051 @option{--file=archive.tar} or @option{--file archive.tar}.
2053 @cindex optional arguments to long options
2054 @cindex long options with optional arguments
2055 In contrast, optional arguments must always be introduced using
2056 an equal sign. For example, the @option{--backup} option takes
2057 an optional argument specifying backup type. It must be used
2058 as @option{--backup=@var{backup-type}}.
2061 @subsection Short Option Style
2063 @cindex short options
2064 @cindex options, short style
2065 @cindex options, traditional
2066 Most options also have a @dfn{short option} name. Short options start with
2067 a single dash, and are followed by a single character, e.g., @option{-t}
2068 (which is equivalent to @option{--list}). The forms are absolutely
2069 identical in function; they are interchangeable.
2071 The short option names are faster to type than long option names.
2073 @cindex arguments to short options
2074 @cindex short options with mandatory arguments
2075 Short options which require arguments take their arguments immediately
2076 following the option, usually separated by white space. It is also
2077 possible to stick the argument right after the short option name, using
2078 no intervening space. For example, you might write @w{@option{-f
2079 archive.tar}} or @option{-farchive.tar} instead of using
2080 @option{--file=archive.tar}. Both @option{--file=@var{archive-name}} and
2081 @w{@option{-f @var{archive-name}}} denote the option which indicates a
2082 specific archive, here named @file{archive.tar}.
2084 @cindex optional arguments to short options
2085 @cindex short options with optional arguments
2086 Short options which take optional arguments take their arguments
2087 immediately following the option letter, @emph{without any intervening
2088 white space characters}.
2090 Short options' letters may be clumped together, but you are not
2091 required to do this (as compared to old options; see below). When
2092 short options are clumped as a set, use one (single) dash for them
2093 all, e.g., @w{@samp{@command{tar} -cvf}}. Only the last option in
2094 such a set is allowed to have an argument@footnote{Clustering many
2095 options, the last of which has an argument, is a rather opaque way to
2096 write options. Some wonder if @acronym{GNU} @code{getopt} should not
2097 even be made helpful enough for considering such usages as invalid.}.
2099 When the options are separated, the argument for each option which requires
2100 an argument directly follows that option, as is usual for Unix programs.
2104 $ @kbd{tar -c -v -b 20 -f /dev/rmt0}
2107 If you reorder short options' locations, be sure to move any arguments
2108 that belong to them. If you do not move the arguments properly, you may
2109 end up overwriting files.
2112 @subsection Old Option Style
2113 @cindex options, old style
2114 @cindex old option style
2116 Like short options, @dfn{old options} are single letters. However, old options
2117 must be written together as a single clumped set, without spaces separating
2118 them or dashes preceding them@footnote{Beware that if you precede options
2119 with a dash, you are announcing the short option style instead of the
2120 old option style; short options are decoded differently.}. This set
2121 of letters must be the first to appear on the command line, after the
2122 @command{tar} program name and some white space; old options cannot appear
2123 anywhere else. The letter of an old option is exactly the same letter as
2124 the corresponding short option. For example, the old option @samp{t} is
2125 the same as the short option @option{-t}, and consequently, the same as the
2126 long option @option{--list}. So for example, the command @w{@samp{tar
2127 cv}} specifies the option @option{-v} in addition to the operation @option{-c}.
2129 @cindex arguments to old options
2130 @cindex old options with mandatory arguments
2131 When options that need arguments are given together with the command,
2132 all the associated arguments follow, in the same order as the options.
2133 Thus, the example given previously could also be written in the old
2137 $ @kbd{tar cvbf 20 /dev/rmt0}
2141 Here, @samp{20} is the argument of @option{-b} and @samp{/dev/rmt0} is
2142 the argument of @option{-f}.
2144 On the other hand, this old style syntax makes it difficult to match
2145 option letters with their corresponding arguments, and is often
2146 confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example,
2147 @samp{20} is the argument for @option{-b}, @samp{/dev/rmt0} is the
2148 argument for @option{-f}, and @option{-v} does not have a corresponding
2149 argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f
2150 /dev/rmt0}} is clearer, putting all arguments next to the option they
2153 If you want to reorder the letters in the old option argument, be
2154 sure to reorder any corresponding argument appropriately.
2156 This old way of writing @command{tar} options can surprise even experienced
2157 users. For example, the two commands:
2160 @kbd{tar cfz archive.tar.gz file}
2161 @kbd{tar -cfz archive.tar.gz file}
2165 are quite different. The first example uses @file{archive.tar.gz} as
2166 the value for option @samp{f} and recognizes the option @samp{z}. The
2167 second example, however, uses @file{z} as the value for option
2168 @samp{f} --- probably not what was intended.
2170 Old options are kept for compatibility with old versions of @command{tar}.
2172 This second example could be corrected in many ways, among which the
2173 following are equivalent:
2176 @kbd{tar -czf archive.tar.gz file}
2177 @kbd{tar -cf archive.tar.gz -z file}
2178 @kbd{tar cf archive.tar.gz -z file}
2181 @cindex option syntax, traditional
2182 As far as we know, all @command{tar} programs, @acronym{GNU} and
2183 non-@acronym{GNU}, support old options. @GNUTAR{}
2184 supports them not only for historical reasons, but also because many
2185 people are used to them. For compatibility with Unix @command{tar},
2186 the first argument is always treated as containing command and option
2187 letters even if it doesn't start with @samp{-}. Thus, @samp{tar c} is
2188 equivalent to @w{@samp{tar -c}:} both of them specify the
2189 @option{--create} (@option{-c}) command to create an archive.
2192 @subsection Mixing Option Styles
2194 @cindex options, mixing different styles
2195 All three styles may be intermixed in a single @command{tar} command,
2196 so long as the rules for each style are fully
2197 respected@footnote{Before @GNUTAR{} version 1.11.6,
2198 a bug prevented intermixing old style options with long options in
2199 some cases.}. Old style options and either of the modern styles of
2200 options may be mixed within a single @command{tar} command. However,
2201 old style options must be introduced as the first arguments only,
2202 following the rule for old options (old options must appear directly
2203 after the @command{tar} command and some white space). Modern options
2204 may be given only after all arguments to the old options have been
2205 collected. If this rule is not respected, a modern option might be
2206 falsely interpreted as the value of the argument to one of the old
2209 For example, all the following commands are wholly equivalent, and
2210 illustrate the many combinations and orderings of option styles.
2213 @kbd{tar --create --file=archive.tar}
2214 @kbd{tar --create -f archive.tar}
2215 @kbd{tar --create -farchive.tar}
2216 @kbd{tar --file=archive.tar --create}
2217 @kbd{tar --file=archive.tar -c}
2218 @kbd{tar -c --file=archive.tar}
2219 @kbd{tar -c -f archive.tar}
2220 @kbd{tar -c -farchive.tar}
2221 @kbd{tar -cf archive.tar}
2222 @kbd{tar -cfarchive.tar}
2223 @kbd{tar -f archive.tar --create}
2224 @kbd{tar -f archive.tar -c}
2225 @kbd{tar -farchive.tar --create}
2226 @kbd{tar -farchive.tar -c}
2227 @kbd{tar c --file=archive.tar}
2228 @kbd{tar c -f archive.tar}
2229 @kbd{tar c -farchive.tar}
2230 @kbd{tar cf archive.tar}
2231 @kbd{tar f archive.tar --create}
2232 @kbd{tar f archive.tar -c}
2233 @kbd{tar fc archive.tar}
2236 On the other hand, the following commands are @emph{not} equivalent to
2240 @kbd{tar -f -c archive.tar}
2241 @kbd{tar -fc archive.tar}
2242 @kbd{tar -fcarchive.tar}
2243 @kbd{tar -farchive.tarc}
2244 @kbd{tar cfarchive.tar}
2248 These last examples mean something completely different from what the
2249 user intended (judging based on the example in the previous set which
2250 uses long options, whose intent is therefore very clear). The first
2251 four specify that the @command{tar} archive would be a file named
2252 @option{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc},
2253 respectively. The first two examples also specify a single non-option,
2254 @var{name} argument having the value @samp{archive.tar}. The last
2255 example contains only old style option letters (repeating option
2256 @samp{c} twice), not all of which are meaningful (eg., @samp{.},
2257 @samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked
2258 the first sentence of this paragraph..}
2261 @section All @command{tar} Options
2263 The coming manual sections contain an alphabetical listing of all
2264 @command{tar} operations and options, with brief descriptions and
2265 cross-references to more in-depth explanations in the body of the manual.
2266 They also contain an alphabetically arranged table of the short option
2267 forms with their corresponding long option. You can use this table as
2268 a reference for deciphering @command{tar} commands in scripts.
2271 * Operation Summary::
2273 * Short Option Summary::
2276 @node Operation Summary
2277 @subsection Operations
2285 Appends files to the end of the archive. @xref{append}.
2287 @opsummary{catenate}
2291 Same as @option{--concatenate}. @xref{concatenate}.
2297 Compares archive members with their counterparts in the file
2298 system, and reports differences in file size, mode, owner,
2299 modification date and contents. @xref{compare}.
2301 @opsummary{concatenate}
2305 Appends other @command{tar} archives to the end of the archive.
2312 Creates a new @command{tar} archive. @xref{create}.
2317 Deletes members from the archive. Don't try this on an archive on a
2318 tape! @xref{delete}.
2324 Same @option{--compare}. @xref{compare}.
2330 Extracts members from the archive into the file system. @xref{extract}.
2336 Same as @option{--extract}. @xref{extract}.
2342 Lists the members in an archive. @xref{list}.
2348 Adds files to the end of the archive, but only if they are newer than
2349 their counterparts already in the archive, or if they do not already
2350 exist in the archive. @xref{update}.
2354 @node Option Summary
2355 @subsection @command{tar} Options
2359 @opsummary{absolute-names}
2360 @item --absolute-names
2363 Normally when creating an archive, @command{tar} strips an initial
2364 @samp{/} from member names. This option disables that behavior.
2367 @opsummary{after-date}
2370 (See @option{--newer}, @pxref{after})
2372 @opsummary{anchored}
2374 A pattern must match an initial subsequence of the name's components.
2375 @xref{controlling pattern-matching}.
2377 @opsummary{atime-preserve}
2378 @item --atime-preserve
2379 @itemx --atime-preserve=replace
2380 @itemx --atime-preserve=system
2382 Attempt to preserve the access time of files when reading them. This
2383 option currently is effective only on files that you own, unless you
2384 have superuser privileges.
2386 @option{--atime-preserve=replace} remembers the access time of a file
2387 before reading it, and then restores the access time afterwards. This
2388 may cause problems if other programs are reading the file at the same
2389 time, as the times of their accesses will be lost. On most platforms
2390 restoring the access time also requires @command{tar} to restore the
2391 data modification time too, so this option may also cause problems if
2392 other programs are writing the file at the same time (@command{tar} attempts
2393 to detect this situation, but cannot do so reliably due to race
2394 conditions). Worse, on most platforms restoring the access time also
2395 updates the status change time, which means that this option is
2396 incompatible with incremental backups.
2398 @option{--atime-preserve=system} avoids changing time stamps on files,
2399 without interfering with time stamp updates
2400 caused by other programs, so it works better with incremental backups.
2401 However, it requires a special @code{O_NOATIME} option from the
2402 underlying operating and file system implementation, and it also requires
2403 that searching directories does not update their access times. As of
2404 this writing (November 2005) this works only with Linux, and only with
2405 Linux kernels 2.6.8 and later. Worse, there is currently no reliable
2406 way to know whether this feature actually works. Sometimes
2407 @command{tar} knows that it does not work, and if you use
2408 @option{--atime-preserve=system} then @command{tar} complains and
2409 exits right away. But other times @command{tar} might think that the
2410 option works when it actually does not.
2412 Currently @option{--atime-preserve} with no operand defaults to
2413 @option{--atime-preserve=replace}, but this may change in the future
2414 as support for @option{--atime-preserve=system} improves.
2416 If your operating or file system does not support
2417 @option{--atime-preserve=@-system}, you might be able to preserve access
2418 times reliably by using the @command{mount} command. For example,
2419 you can mount the file system read-only, or access the file system via
2420 a read-only loopback mount, or use the @samp{noatime} mount option
2421 available on some systems. However, mounting typically requires
2422 superuser privileges and can be a pain to manage.
2424 @opsummary{auto-compress}
2425 @item --auto-compress
2428 During a @option{--create} operation, enables automatic compressed
2429 format recognition based on the archive suffix. The effect of this
2430 option is cancelled by @option{--no-auto-compress}. @xref{gzip}.
2433 @item --backup=@var{backup-type}
2435 Rather than deleting files from the file system, @command{tar} will
2436 back them up using simple or numbered backups, depending upon
2437 @var{backup-type}. @xref{backup}.
2439 @opsummary{block-number}
2440 @item --block-number
2443 With this option present, @command{tar} prints error messages for read errors
2444 with the block number in the archive file. @xref{block-number}.
2446 @opsummary{blocking-factor}
2447 @item --blocking-factor=@var{blocking}
2448 @itemx -b @var{blocking}
2450 Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
2451 record. @xref{Blocking Factor}.
2457 This option tells @command{tar} to read or write archives through
2458 @code{bzip2}. @xref{gzip}.
2460 @opsummary{check-device}
2461 @item --check-device
2462 Check device numbers when creating a list of modified files for
2463 incremental archiving. This is the default. @xref{device numbers},
2464 for a detailed description.
2466 @opsummary{checkpoint}
2467 @item --checkpoint[=@var{number}]
2469 This option directs @command{tar} to print periodic checkpoint
2470 messages as it reads through the archive. It is intended for when you
2471 want a visual indication that @command{tar} is still running, but
2472 don't want to see @option{--verbose} output. You can also instruct
2473 @command{tar} to execute a list of actions on each checkpoint, see
2474 @option{--checkpoint-action} below. For a detailed description, see
2477 @opsummary{checkpoint-action}
2478 @item --checkpoint-action=@var{action}
2479 Instruct @command{tar} to execute an action upon hitting a
2480 breakpoint. Here we give only a brief outline. @xref{checkpoints},
2481 for a complete description.
2483 The @var{action} argument can be one of the following:
2487 Produce an audible bell on the console.
2491 Print a single dot on the standard listing stream.
2494 Display a textual message on the standard error, with the status and
2495 number of the checkpoint. This is the default.
2497 @item echo=@var{string}
2498 Display @var{string} on the standard error. Before output, the string
2499 is subject to meta-character expansion.
2501 @item exec=@var{command}
2502 Execute the given @var{command}.
2504 @item sleep=@var{time}
2505 Wait for @var{time} seconds.
2507 @item ttyout=@var{string}
2508 Output @var{string} on the current console (@file{/dev/tty}).
2511 Several @option{--checkpoint-action} options can be specified. The
2512 supplied actions will be executed in order of their appearance in the
2515 Using @option{--checkpoint-action} without @option{--checkpoint}
2516 assumes default checkpoint frequency of one checkpoint per 10 records.
2518 @opsummary{check-links}
2521 If this option was given, @command{tar} will check the number of links
2522 dumped for each processed file. If this number does not match the
2523 total number of hard links for the file, a warning message will be
2524 output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2525 synonym for @option{--one-file-system}. The current semantics, which
2526 complies to UNIX98, was introduced with version
2527 1.15.91. @xref{Changes}, for more information.}.
2531 @opsummary{compress}
2532 @opsummary{uncompress}
2537 @command{tar} will use the @command{compress} program when reading or
2538 writing the archive. This allows you to directly act on archives
2539 while saving space. @xref{gzip}.
2541 @opsummary{confirmation}
2542 @item --confirmation
2544 (See @option{--interactive}.) @xref{interactive}.
2546 @opsummary{delay-directory-restore}
2547 @item --delay-directory-restore
2549 Delay setting modification times and permissions of extracted
2550 directories until the end of extraction. @xref{Directory Modification Times and Permissions}.
2552 @opsummary{dereference}
2556 When creating a @command{tar} archive, @command{tar} will archive the
2557 file that a symbolic link points to, rather than archiving the
2558 symlink. @xref{dereference}.
2560 @opsummary{directory}
2561 @item --directory=@var{dir}
2564 When this option is specified, @command{tar} will change its current directory
2565 to @var{dir} before performing any operations. When this option is used
2566 during archive creation, it is order sensitive. @xref{directory}.
2569 @item --exclude=@var{pattern}
2571 When performing operations, @command{tar} will skip files that match
2572 @var{pattern}. @xref{exclude}.
2574 @opsummary{exclude-backups}
2575 @item --exclude-backups
2576 Exclude backup and lock files. @xref{exclude,, exclude-backups}.
2578 @opsummary{exclude-from}
2579 @item --exclude-from=@var{file}
2580 @itemx -X @var{file}
2582 Similar to @option{--exclude}, except @command{tar} will use the list of
2583 patterns in the file @var{file}. @xref{exclude}.
2585 @opsummary{exclude-caches}
2586 @item --exclude-caches
2588 Exclude from dump any directory containing a valid cache directory
2589 tag file, but still dump the directory node and the tag file itself.
2591 @xref{exclude,, exclude-caches}.
2593 @opsummary{exclude-caches-under}
2594 @item --exclude-caches-under
2596 Exclude from dump any directory containing a valid cache directory
2597 tag file, but still dump the directory node itself.
2601 @opsummary{exclude-caches-all}
2602 @item --exclude-caches-all
2604 Exclude from dump any directory containing a valid cache directory
2605 tag file. @xref{exclude}.
2607 @opsummary{exclude-tag}
2608 @item --exclude-tag=@var{file}
2610 Exclude from dump any directory containing file named @var{file}, but
2611 dump the directory node and @var{file} itself. @xref{exclude,, exclude-tag}.
2613 @opsummary{exclude-tag-under}
2614 @item --exclude-tag-under=@var{file}
2616 Exclude from dump the contents of any directory containing file
2617 named @var{file}, but dump the directory node itself. @xref{exclude,,
2620 @opsummary{exclude-tag-all}
2621 @item --exclude-tag-all=@var{file}
2623 Exclude from dump any directory containing file named @var{file}.
2624 @xref{exclude,,exclude-tag-all}.
2626 @opsummary{exclude-vcs}
2629 Exclude from dump directories and files, that are internal for some
2630 widely used version control systems.
2632 @xref{exclude,,exclude-vcs}.
2635 @item --file=@var{archive}
2636 @itemx -f @var{archive}
2638 @command{tar} will use the file @var{archive} as the @command{tar} archive it
2639 performs operations on, rather than @command{tar}'s compilation dependent
2640 default. @xref{file tutorial}.
2642 @opsummary{files-from}
2643 @item --files-from=@var{file}
2644 @itemx -T @var{file}
2646 @command{tar} will use the contents of @var{file} as a list of archive members
2647 or files to operate on, in addition to those specified on the
2648 command-line. @xref{files}.
2650 @opsummary{force-local}
2653 Forces @command{tar} to interpret the file name given to @option{--file}
2654 as a local file, even if it looks like a remote tape drive name.
2655 @xref{local and remote archives}.
2658 @item --format=@var{format}
2659 @itemx -H @var{format}
2661 Selects output archive format. @var{Format} may be one of the
2666 Creates an archive that is compatible with Unix V7 @command{tar}.
2669 Creates an archive that is compatible with GNU @command{tar} version
2673 Creates archive in GNU tar 1.13 format. Basically it is the same as
2674 @samp{oldgnu} with the only difference in the way it handles long
2678 Creates a @acronym{POSIX.1-1988} compatible archive.
2681 Creates a @acronym{POSIX.1-2001 archive}.
2685 @xref{Formats}, for a detailed discussion of these formats.
2688 @item --group=@var{group}
2690 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
2691 rather than the group from the source file. @var{group} is first decoded
2692 as a group symbolic name, but if this interpretation fails, it has to be
2693 a decimal numeric group @acronym{ID}. @xref{override}.
2695 Also see the comments for the @option{--owner=@var{user}} option.
2705 This option tells @command{tar} to read or write archives through
2706 @command{gzip}, allowing @command{tar} to directly operate on several
2707 kinds of compressed archives transparently. @xref{gzip}.
2709 @opsummary{hard-dereference}
2710 @item --hard-dereference
2711 When creating an archive, dereference hard links and store the files
2712 they refer to, instead of creating usual hard link members.
2720 @command{tar} will print out a short message summarizing the operations and
2721 options to @command{tar} and exit. @xref{help}.
2723 @opsummary{ignore-case}
2725 Ignore case when matching member or file names with
2726 patterns. @xref{controlling pattern-matching}.
2728 @opsummary{ignore-command-error}
2729 @item --ignore-command-error
2730 Ignore exit codes of subprocesses. @xref{Writing to an External Program}.
2732 @opsummary{ignore-failed-read}
2733 @item --ignore-failed-read
2735 Do not exit unsuccessfully merely because an unreadable file was encountered.
2738 @opsummary{ignore-zeros}
2739 @item --ignore-zeros
2742 With this option, @command{tar} will ignore zeroed blocks in the
2743 archive, which normally signals EOF. @xref{Reading}.
2745 @opsummary{incremental}
2749 Informs @command{tar} that it is working with an old
2750 @acronym{GNU}-format incremental backup archive. It is intended
2751 primarily for backwards compatibility only. @xref{Incremental Dumps},
2752 for a detailed discussion of incremental archives.
2754 @opsummary{index-file}
2755 @item --index-file=@var{file}
2757 Send verbose output to @var{file} instead of to standard output.
2759 @opsummary{info-script}
2760 @opsummary{new-volume-script}
2761 @item --info-script=@var{script-file}
2762 @itemx --new-volume-script=@var{script-file}
2763 @itemx -F @var{script-file}
2765 When @command{tar} is performing multi-tape backups, @var{script-file} is run
2766 at the end of each tape. If @var{script-file} exits with nonzero status,
2767 @command{tar} fails immediately. @xref{info-script}, for a detailed
2768 discussion of @var{script-file}.
2770 @opsummary{interactive}
2772 @itemx --confirmation
2775 Specifies that @command{tar} should ask the user for confirmation before
2776 performing potentially destructive options, such as overwriting files.
2779 @opsummary{keep-newer-files}
2780 @item --keep-newer-files
2782 Do not replace existing files that are newer than their archive copies
2783 when extracting files from an archive.
2785 @opsummary{keep-old-files}
2786 @item --keep-old-files
2789 Do not overwrite existing files when extracting files from an archive.
2790 @xref{Keep Old Files}.
2793 @item --label=@var{name}
2794 @itemx -V @var{name}
2796 When creating an archive, instructs @command{tar} to write @var{name}
2797 as a name record in the archive. When extracting or listing archives,
2798 @command{tar} will only operate on archives that have a label matching
2799 the pattern specified in @var{name}. @xref{Tape Files}.
2802 @item --level=@var{n}
2803 Force incremental backup of level @var{n}. As of @GNUTAR version
2804 @value{VERSION}, the option @option{--level=0} truncates the snapshot
2805 file, thereby forcing the level 0 dump. Other values of @var{n} are
2806 effectively ignored. @xref{--level=0}, for details and examples.
2808 The use of this option is valid only in conjunction with the
2809 @option{--listed-incremental} option. @xref{Incremental Dumps},
2810 for a detailed description.
2812 @opsummary{listed-incremental}
2813 @item --listed-incremental=@var{snapshot-file}
2814 @itemx -g @var{snapshot-file}
2816 During a @option{--create} operation, specifies that the archive that
2817 @command{tar} creates is a new @acronym{GNU}-format incremental
2818 backup, using @var{snapshot-file} to determine which files to backup.
2819 With other operations, informs @command{tar} that the archive is in
2820 incremental format. @xref{Incremental Dumps}.
2825 This option tells @command{tar} to read or write archives through
2826 @command{lzip}. @xref{gzip}.
2831 This option tells @command{tar} to read or write archives through
2832 @command{lzma}. @xref{gzip}.
2836 This option tells @command{tar} to read or write archives through
2837 @command{lzop}. @xref{gzip}.
2840 @item --mode=@var{permissions}
2842 When adding files to an archive, @command{tar} will use
2843 @var{permissions} for the archive members, rather than the permissions
2844 from the files. @var{permissions} can be specified either as an octal
2845 number or as symbolic permissions, like with
2846 @command{chmod}. @xref{override}.
2849 @item --mtime=@var{date}
2851 When adding files to an archive, @command{tar} will use @var{date} as
2852 the modification time of members when creating archives, instead of
2853 their actual modification times. The value of @var{date} can be
2854 either a textual date representation (@pxref{Date input formats}) or a
2855 name of the existing file, starting with @samp{/} or @samp{.}. In the
2856 latter case, the modification time of that file is used. @xref{override}.
2858 @opsummary{multi-volume}
2859 @item --multi-volume
2862 Informs @command{tar} that it should create or otherwise operate on a
2863 multi-volume @command{tar} archive. @xref{Using Multiple Tapes}.
2865 @opsummary{new-volume-script}
2866 @item --new-volume-script
2868 (see @option{--info-script})
2871 @item --newer=@var{date}
2872 @itemx --after-date=@var{date}
2875 When creating an archive, @command{tar} will only add files that have changed
2876 since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it
2877 is taken to be the name of a file whose data modification time specifies
2878 the date. @xref{after}.
2880 @opsummary{newer-mtime}
2881 @item --newer-mtime=@var{date}
2883 Like @option{--newer}, but add only files whose
2884 contents have changed (as opposed to just @option{--newer}, which will
2885 also back up files for which any status information has
2886 changed). @xref{after}.
2888 @opsummary{no-anchored}
2890 An exclude pattern can match any subsequence of the name's components.
2891 @xref{controlling pattern-matching}.
2893 @opsummary{no-auto-compress}
2894 @item --no-auto-compress
2896 Disables automatic compressed format recognition based on the archive
2897 suffix. @xref{--auto-compress}. @xref{gzip}.
2899 @opsummary{no-check-device}
2900 @item --no-check-device
2901 Do not check device numbers when creating a list of modified files
2902 for incremental archiving. @xref{device numbers}, for
2903 a detailed description.
2905 @opsummary{no-delay-directory-restore}
2906 @item --no-delay-directory-restore
2908 Modification times and permissions of extracted
2909 directories are set when all files from this directory have been
2910 extracted. This is the default.
2911 @xref{Directory Modification Times and Permissions}.
2913 @opsummary{no-ignore-case}
2914 @item --no-ignore-case
2915 Use case-sensitive matching.
2916 @xref{controlling pattern-matching}.
2918 @opsummary{no-ignore-command-error}
2919 @item --no-ignore-command-error
2920 Print warnings about subprocesses that terminated with a nonzero exit
2921 code. @xref{Writing to an External Program}.
2926 If the @option{--null} option was given previously, this option
2927 cancels its effect, so that any following @option{--files-from}
2928 options will expect their file lists to be newline-terminated.
2930 @opsummary{no-overwrite-dir}
2931 @item --no-overwrite-dir
2933 Preserve metadata of existing directories when extracting files
2934 from an archive. @xref{Overwrite Old Files}.
2936 @opsummary{no-quote-chars}
2937 @item --no-quote-chars=@var{string}
2938 Remove characters listed in @var{string} from the list of quoted
2939 characters set by the previous @option{--quote-chars} option
2940 (@pxref{quoting styles}).
2942 @opsummary{no-recursion}
2943 @item --no-recursion
2945 With this option, @command{tar} will not recurse into directories.
2948 @opsummary{no-same-owner}
2949 @item --no-same-owner
2952 When extracting an archive, do not attempt to preserve the owner
2953 specified in the @command{tar} archive. This the default behavior
2956 @opsummary{no-same-permissions}
2957 @item --no-same-permissions
2959 When extracting an archive, subtract the user's umask from files from
2960 the permissions specified in the archive. This is the default behavior
2966 The archive media does not support seeks to arbitrary
2967 locations. Usually @command{tar} determines automatically whether
2968 the archive can be seeked or not. Use this option to disable this
2971 @opsummary{no-unquote}
2973 Treat all input file or member names literally, do not interpret
2974 escape sequences. @xref{input name quoting}.
2976 @opsummary{no-wildcards}
2977 @item --no-wildcards
2978 Do not use wildcards.
2979 @xref{controlling pattern-matching}.
2981 @opsummary{no-wildcards-match-slash}
2982 @item --no-wildcards-match-slash
2983 Wildcards do not match @samp{/}.
2984 @xref{controlling pattern-matching}.
2989 When @command{tar} is using the @option{--files-from} option, this option
2990 instructs @command{tar} to expect file names terminated with @acronym{NUL}, so
2991 @command{tar} can correctly work with file names that contain newlines.
2994 @opsummary{numeric-owner}
2995 @item --numeric-owner
2997 This option will notify @command{tar} that it should use numeric user
2998 and group IDs when creating a @command{tar} file, rather than names.
3002 The function of this option depends on the action @command{tar} is
3003 performing. When extracting files, @option{-o} is a synonym for
3004 @option{--no-same-owner}, i.e., it prevents @command{tar} from
3005 restoring ownership of files being extracted.
3007 When creating an archive, it is a synonym for
3008 @option{--old-archive}. This behavior is for compatibility
3009 with previous versions of @GNUTAR{}, and will be
3010 removed in future releases.
3012 @xref{Changes}, for more information.
3014 @opsummary{occurrence}
3015 @item --occurrence[=@var{number}]
3017 This option can be used in conjunction with one of the subcommands
3018 @option{--delete}, @option{--diff}, @option{--extract} or
3019 @option{--list} when a list of files is given either on the command
3020 line or via @option{-T} option.
3022 This option instructs @command{tar} to process only the @var{number}th
3023 occurrence of each named file. @var{Number} defaults to 1, so
3026 tar -x -f archive.tar --occurrence filename
3030 will extract the first occurrence of the member @file{filename} from @file{archive.tar}
3031 and will terminate without scanning to the end of the archive.
3033 @opsummary{old-archive}
3035 Synonym for @option{--format=v7}.
3037 @opsummary{one-file-system}
3038 @item --one-file-system
3039 Used when creating an archive. Prevents @command{tar} from recursing into
3040 directories that are on different file systems from the current
3043 @opsummary{overwrite}
3046 Overwrite existing files and directory metadata when extracting files
3047 from an archive. @xref{Overwrite Old Files}.
3049 @opsummary{overwrite-dir}
3050 @item --overwrite-dir
3052 Overwrite the metadata of existing directories when extracting files
3053 from an archive. @xref{Overwrite Old Files}.
3056 @item --owner=@var{user}
3058 Specifies that @command{tar} should use @var{user} as the owner of members
3059 when creating archives, instead of the user associated with the source
3060 file. @var{user} is first decoded as a user symbolic name, but if
3061 this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
3064 This option does not affect extraction from archives.
3066 @opsummary{pax-option}
3067 @item --pax-option=@var{keyword-list}
3068 This option enables creation of the archive in @acronym{POSIX.1-2001}
3069 format (@pxref{posix}) and modifies the way @command{tar} handles the
3070 extended header keywords. @var{Keyword-list} is a comma-separated
3071 list of keyword options. @xref{PAX keywords}, for a detailed
3074 @opsummary{portability}
3076 @itemx --old-archive
3077 Synonym for @option{--format=v7}.
3081 Same as @option{--format=posix}.
3083 @opsummary{preserve}
3086 Synonymous with specifying both @option{--preserve-permissions} and
3087 @option{--same-order}. @xref{Setting Access Permissions}.
3089 @opsummary{preserve-order}
3090 @item --preserve-order
3092 (See @option{--same-order}; @pxref{Reading}.)
3094 @opsummary{preserve-permissions}
3095 @opsummary{same-permissions}
3096 @item --preserve-permissions
3097 @itemx --same-permissions
3100 When @command{tar} is extracting an archive, it normally subtracts the
3101 users' umask from the permissions specified in the archive and uses
3102 that number as the permissions to create the destination file.
3103 Specifying this option instructs @command{tar} that it should use the
3104 permissions directly from the archive. @xref{Setting Access Permissions}.
3106 @opsummary{quote-chars}
3107 @item --quote-chars=@var{string}
3108 Always quote characters from @var{string}, even if the selected
3109 quoting style would not quote them (@pxref{quoting styles}).
3111 @opsummary{quoting-style}
3112 @item --quoting-style=@var{style}
3113 Set quoting style to use when printing member and file names
3114 (@pxref{quoting styles}). Valid @var{style} values are:
3115 @code{literal}, @code{shell}, @code{shell-always}, @code{c},
3116 @code{escape}, @code{locale}, and @code{clocale}. Default quoting
3117 style is @code{escape}, unless overridden while configuring the
3120 @opsummary{read-full-records}
3121 @item --read-full-records
3124 Specifies that @command{tar} should reblock its input, for reading
3125 from pipes on systems with buggy implementations. @xref{Reading}.
3127 @opsummary{record-size}
3128 @item --record-size=@var{size}
3130 Instructs @command{tar} to use @var{size} bytes per record when accessing the
3131 archive. @xref{Blocking Factor}.
3133 @opsummary{recursion}
3136 With this option, @command{tar} recurses into directories (default).
3139 @opsummary{recursive-unlink}
3140 @item --recursive-unlink
3143 directory hierarchies before extracting directories of the same name
3144 from the archive. @xref{Recursive Unlink}.
3146 @opsummary{remove-files}
3147 @item --remove-files
3149 Directs @command{tar} to remove the source file from the file system after
3150 appending it to an archive. @xref{remove files}.
3152 @opsummary{restrict}
3155 Disable use of some potentially harmful @command{tar} options.
3156 Currently this option disables shell invocation from multi-volume menu
3157 (@pxref{Using Multiple Tapes}).
3159 @opsummary{rmt-command}
3160 @item --rmt-command=@var{cmd}
3162 Notifies @command{tar} that it should use @var{cmd} instead of
3163 the default @file{/usr/libexec/rmt} (@pxref{Remote Tape Server}).
3165 @opsummary{rsh-command}
3166 @item --rsh-command=@var{cmd}
3168 Notifies @command{tar} that is should use @var{cmd} to communicate with remote
3169 devices. @xref{Device}.
3171 @opsummary{same-order}
3173 @itemx --preserve-order
3176 This option is an optimization for @command{tar} when running on machines with
3177 small amounts of memory. It informs @command{tar} that the list of file
3178 arguments has already been sorted to match the order of files in the
3179 archive. @xref{Reading}.
3181 @opsummary{same-owner}
3184 When extracting an archive, @command{tar} will attempt to preserve the owner
3185 specified in the @command{tar} archive with this option present.
3186 This is the default behavior for the superuser; this option has an
3187 effect only for ordinary users. @xref{Attributes}.
3189 @opsummary{same-permissions}
3190 @item --same-permissions
3192 (See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
3198 Assume that the archive media supports seeks to arbitrary
3199 locations. Usually @command{tar} determines automatically whether
3200 the archive can be seeked or not. This option is intended for use
3201 in cases when such recognition fails. It takes effect only if the
3202 archive is open for reading (e.g. with @option{--list} or
3203 @option{--extract} options).
3205 @opsummary{show-defaults}
3206 @item --show-defaults
3208 Displays the default options used by @command{tar} and exits
3209 successfully. This option is intended for use in shell scripts.
3210 Here is an example of what you can see using this option:
3213 $ @kbd{tar --show-defaults}
3214 --format=gnu -f- -b20 --quoting-style=escape
3215 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
3219 Notice, that this option outputs only one line. The example output
3220 above has been split to fit page boundaries.
3222 @opsummary{show-omitted-dirs}
3223 @item --show-omitted-dirs
3225 Instructs @command{tar} to mention the directories it is skipping when
3226 operating on a @command{tar} archive. @xref{show-omitted-dirs}.
3228 @opsummary{show-transformed-names}
3229 @opsummary{show-stored-names}
3230 @item --show-transformed-names
3231 @itemx --show-stored-names
3233 Display file or member names after applying any transformations
3234 (@pxref{transform}). In particular, when used in conjunction with one of
3235 the archive creation operations it instructs @command{tar} to list the
3236 member names stored in the archive, as opposed to the actual file
3237 names. @xref{listing member and file names}.
3243 Invokes a @acronym{GNU} extension when adding files to an archive that handles
3244 sparse files efficiently. @xref{sparse}.
3246 @opsummary{sparse-version}
3247 @item --sparse-version=@var{version}
3249 Specifies the @dfn{format version} to use when archiving sparse
3250 files. Implies @option{--sparse}. @xref{sparse}. For the description
3251 of the supported sparse formats, @xref{Sparse Formats}.
3253 @opsummary{starting-file}
3254 @item --starting-file=@var{name}
3255 @itemx -K @var{name}
3257 This option affects extraction only; @command{tar} will skip extracting
3258 files in the archive until it finds one that matches @var{name}.
3261 @opsummary{strip-components}
3262 @item --strip-components=@var{number}
3263 Strip given @var{number} of leading components from file names before
3264 extraction. For example, if archive @file{archive.tar} contained
3265 @file{/some/file/name}, then running
3268 tar --extract --file archive.tar --strip-components=2
3272 would extract this file to file @file{name}.
3275 @item --suffix=@var{suffix}
3277 Alters the suffix @command{tar} uses when backing up files from the default
3278 @samp{~}. @xref{backup}.
3280 @opsummary{tape-length}
3281 @item --tape-length=@var{num}
3284 Specifies the length of tapes that @command{tar} is writing as being
3285 @w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
3287 @opsummary{test-label}
3290 Reads the volume label. If an argument is specified, test whether it
3291 matches the volume label. @xref{--test-label option}.
3293 @opsummary{to-command}
3294 @item --to-command=@var{command}
3296 During extraction @command{tar} will pipe extracted files to the
3297 standard input of @var{command}. @xref{Writing to an External Program}.
3299 @opsummary{to-stdout}
3303 During extraction, @command{tar} will extract files to stdout rather
3304 than to the file system. @xref{Writing to Standard Output}.
3307 @item --totals[=@var{signo}]
3309 Displays the total number of bytes transferred when processing an
3310 archive. If an argument is given, these data are displayed on
3311 request, when signal @var{signo} is delivered to @command{tar}.
3318 Sets the data modification time of extracted files to the extraction time,
3319 rather than the data modification time stored in the archive.
3320 @xref{Data Modification Times}.
3322 @opsummary{transform}
3324 @item --transform=@var{sed-expr}
3325 @itemx --xform=@var{sed-expr}
3326 Transform file or member names using @command{sed} replacement expression
3327 @var{sed-expr}. For example,
3330 $ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
3334 will add to @file{archive} files from the current working directory,
3335 replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
3336 discussion, @xref{transform}.
3338 To see transformed member names in verbose listings, use
3339 @option{--show-transformed-names} option
3340 (@pxref{show-transformed-names}).
3342 @opsummary{uncompress}
3345 (See @option{--compress}, @pxref{gzip})
3350 (See @option{--gzip}, @pxref{gzip})
3352 @opsummary{unlink-first}
3353 @item --unlink-first
3356 Directs @command{tar} to remove the corresponding file from the file
3357 system before extracting it from the archive. @xref{Unlink First}.
3361 Enable unquoting input file or member names (default). @xref{input
3364 @opsummary{use-compress-program}
3365 @item --use-compress-program=@var{prog}
3366 @itemx -I=@var{prog}
3368 Instructs @command{tar} to access the archive through @var{prog}, which is
3369 presumed to be a compression program of some sort. @xref{gzip}.
3374 Display file modification dates in @acronym{UTC}. This option implies
3381 Specifies that @command{tar} should be more verbose about the
3382 operations it is performing. This option can be specified multiple
3383 times for some operations to increase the amount of information displayed.
3390 Verifies that the archive was correctly written when creating an
3391 archive. @xref{verify}.
3396 Print information about the program's name, version, origin and legal
3397 status, all on standard output, and then exit successfully.
3400 @opsummary{volno-file}
3401 @item --volno-file=@var{file}
3403 Used in conjunction with @option{--multi-volume}. @command{tar} will
3404 keep track of which volume of a multi-volume archive it is working in
3405 @var{file}. @xref{volno-file}.
3408 @item --warning=@var{keyword}
3410 Enable or disable warning messages identified by @var{keyword}. The
3411 messages are suppressed if @var{keyword} is prefixed with @samp{no-}.
3414 @opsummary{wildcards}
3416 Use wildcards when matching member names with patterns.
3417 @xref{controlling pattern-matching}.
3419 @opsummary{wildcards-match-slash}
3420 @item --wildcards-match-slash
3421 Wildcards match @samp{/}.
3422 @xref{controlling pattern-matching}.
3427 Use @command{xz} for compressing or decompressing the archives. @xref{gzip}.
3431 @node Short Option Summary
3432 @subsection Short Options Cross Reference
3434 Here is an alphabetized list of all of the short option forms, matching
3435 them with the equivalent long option.
3437 @multitable @columnfractions 0.20 0.80
3438 @headitem Short Option @tab Reference
3440 @item -A @tab @ref{--concatenate}.
3442 @item -B @tab @ref{--read-full-records}.
3444 @item -C @tab @ref{--directory}.
3446 @item -F @tab @ref{--info-script}.
3448 @item -G @tab @ref{--incremental}.
3450 @item -J @tab @ref{--xz}.
3452 @item -K @tab @ref{--starting-file}.
3454 @item -L @tab @ref{--tape-length}.
3456 @item -M @tab @ref{--multi-volume}.
3458 @item -N @tab @ref{--newer}.
3460 @item -O @tab @ref{--to-stdout}.
3462 @item -P @tab @ref{--absolute-names}.
3464 @item -R @tab @ref{--block-number}.
3466 @item -S @tab @ref{--sparse}.
3468 @item -T @tab @ref{--files-from}.
3470 @item -U @tab @ref{--unlink-first}.
3472 @item -V @tab @ref{--label}.
3474 @item -W @tab @ref{--verify}.
3476 @item -X @tab @ref{--exclude-from}.
3478 @item -Z @tab @ref{--compress}.
3480 @item -b @tab @ref{--blocking-factor}.
3482 @item -c @tab @ref{--create}.
3484 @item -d @tab @ref{--compare}.
3486 @item -f @tab @ref{--file}.
3488 @item -g @tab @ref{--listed-incremental}.
3490 @item -h @tab @ref{--dereference}.
3492 @item -i @tab @ref{--ignore-zeros}.
3494 @item -j @tab @ref{--bzip2}.
3496 @item -k @tab @ref{--keep-old-files}.
3498 @item -l @tab @ref{--check-links}.
3500 @item -m @tab @ref{--touch}.
3502 @item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
3503 @ref{--portability}.
3505 The latter usage is deprecated. It is retained for compatibility with
3506 the earlier versions of @GNUTAR{}. In future releases
3507 @option{-o} will be equivalent to @option{--no-same-owner} only.
3509 @item -p @tab @ref{--preserve-permissions}.
3511 @item -r @tab @ref{--append}.
3513 @item -s @tab @ref{--same-order}.
3515 @item -t @tab @ref{--list}.
3517 @item -u @tab @ref{--update}.
3519 @item -v @tab @ref{--verbose}.
3521 @item -w @tab @ref{--interactive}.
3523 @item -x @tab @ref{--extract}.
3525 @item -z @tab @ref{--gzip}.
3530 @section @GNUTAR{} documentation
3532 @cindex Getting program version number
3534 @cindex Version of the @command{tar} program
3535 Being careful, the first thing is really checking that you are using
3536 @GNUTAR{}, indeed. The @option{--version} option
3537 causes @command{tar} to print information about its name, version,
3538 origin and legal status, all on standard output, and then exit
3539 successfully. For example, @w{@samp{tar --version}} might print:
3542 tar (GNU tar) @value{VERSION}
3543 Copyright (C) 2010 Free Software Foundation, Inc.
3544 Copyright (C) 2010 Free Software Foundation, Inc.
3545 License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
3546 This is free software: you are free to change and redistribute it.
3547 There is NO WARRANTY, to the extent permitted by law.
3549 Written by John Gilmore and Jay Fenlason.
3553 The first occurrence of @samp{tar} in the result above is the program
3554 name in the package (for example, @command{rmt} is another program),
3555 while the second occurrence of @samp{tar} is the name of the package
3556 itself, containing possibly many programs. The package is currently
3557 named @samp{tar}, after the name of the main program it
3558 contains@footnote{There are plans to merge the @command{cpio} and
3559 @command{tar} packages into a single one which would be called
3560 @code{paxutils}. So, who knows if, one of this days, the
3561 @option{--version} would not output @w{@samp{tar (@acronym{GNU}
3564 @cindex Obtaining help
3565 @cindex Listing all @command{tar} options
3566 @xopindex{help, introduction}
3567 Another thing you might want to do is checking the spelling or meaning
3568 of some particular @command{tar} option, without resorting to this
3569 manual, for once you have carefully read it. @GNUTAR{}
3570 has a short help feature, triggerable through the
3571 @option{--help} option. By using this option, @command{tar} will
3572 print a usage message listing all available options on standard
3573 output, then exit successfully, without doing anything else and
3574 ignoring all other options. Even if this is only a brief summary, it
3575 may be several screens long. So, if you are not using some kind of
3576 scrollable window, you might prefer to use something like:
3579 $ @kbd{tar --help | less}
3583 presuming, here, that you like using @command{less} for a pager. Other
3584 popular pagers are @command{more} and @command{pg}. If you know about some
3585 @var{keyword} which interests you and do not want to read all the
3586 @option{--help} output, another common idiom is doing:
3589 tar --help | grep @var{keyword}
3593 for getting only the pertinent lines. Notice, however, that some
3594 @command{tar} options have long description lines and the above
3595 command will list only the first of them.
3597 The exact look of the option summary displayed by @kbd{tar --help} is
3598 configurable. @xref{Configuring Help Summary}, for a detailed description.
3601 If you only wish to check the spelling of an option, running @kbd{tar
3602 --usage} may be a better choice. This will display a terse list of
3603 @command{tar} options without accompanying explanations.
3605 The short help output is quite succinct, and you might have to get
3606 back to the full documentation for precise points. If you are reading
3607 this paragraph, you already have the @command{tar} manual in some
3608 form. This manual is available in a variety of forms from
3609 @url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{}
3610 distribution, provided you have @TeX{} already installed somewhere,
3611 and a laser printer around. Just configure the distribution, execute
3612 the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the
3613 usual way (contact your local guru to know how). If @GNUTAR{}
3614 has been conveniently installed at your place, this
3615 manual is also available in interactive, hypertextual form as an Info
3616 file. Just call @w{@samp{info tar}} or, if you do not have the
3617 @command{info} program handy, use the Info reader provided within
3618 @acronym{GNU} Emacs, calling @samp{tar} from the main Info menu.
3620 There is currently no @code{man} page for @GNUTAR{}.
3621 If you observe such a @code{man} page on the system you are running,
3622 either it does not belong to @GNUTAR{}, or it has not
3623 been produced by @acronym{GNU}. Some package maintainers convert
3624 @kbd{tar --help} output to a man page, using @command{help2man}. In
3625 any case, please bear in mind that the authoritative source of
3626 information about @GNUTAR{} is this Texinfo documentation.
3629 @section Obtaining @GNUTAR{} default values
3631 @opindex show-defaults
3632 @GNUTAR{} has some predefined defaults that are used when you do not
3633 explicitly specify another values. To obtain a list of such
3634 defaults, use @option{--show-defaults} option. This will output the
3635 values in the form of @command{tar} command line options:
3639 $ @kbd{tar --show-defaults}
3640 --format=gnu -f- -b20 --quoting-style=escape
3641 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3646 Notice, that this option outputs only one line. The example output above
3647 has been split to fit page boundaries.
3650 The above output shows that this version of @GNUTAR{} defaults to
3651 using @samp{gnu} archive format (@pxref{Formats}), it uses standard
3652 output as the archive, if no @option{--file} option has been given
3653 (@pxref{file tutorial}), the default blocking factor is 20
3654 (@pxref{Blocking Factor}). It also shows the default locations where
3655 @command{tar} will look for @command{rmt} and @command{rsh} binaries.
3658 @section Checking @command{tar} progress
3660 Typically, @command{tar} performs most operations without reporting any
3661 information to the user except error messages. When using @command{tar}
3662 with many options, particularly ones with complicated or
3663 difficult-to-predict behavior, it is possible to make serious mistakes.
3664 @command{tar} provides several options that make observing @command{tar}
3665 easier. These options cause @command{tar} to print information as it
3666 progresses in its job, and you might want to use them just for being
3667 more careful about what is going on, or merely for entertaining
3668 yourself. If you have encountered a problem when operating on an
3669 archive, however, you may need more information than just an error
3670 message in order to solve the problem. The following options can be
3671 helpful diagnostic tools.
3673 @cindex Verbose operation
3675 Normally, the @option{--list} (@option{-t}) command to list an archive
3676 prints just the file names (one per line) and the other commands are
3677 silent. When used with most operations, the @option{--verbose}
3678 (@option{-v}) option causes @command{tar} to print the name of each
3679 file or archive member as it is processed. This and the other options
3680 which make @command{tar} print status information can be useful in
3681 monitoring @command{tar}.
3683 With @option{--create} or @option{--extract}, @option{--verbose} used
3684 once just prints the names of the files or members as they are processed.
3685 Using it twice causes @command{tar} to print a longer listing
3686 (@xref{verbose member listing}, for the description) for each member.
3687 Since @option{--list} already prints the names of the members,
3688 @option{--verbose} used once with @option{--list} causes @command{tar}
3689 to print an @samp{ls -l} type listing of the files in the archive.
3690 The following examples both extract members with long list output:
3693 $ @kbd{tar --extract --file=archive.tar --verbose --verbose}
3694 $ @kbd{tar xvvf archive.tar}
3697 Verbose output appears on the standard output except when an archive is
3698 being written to the standard output, as with @samp{tar --create
3699 --file=- --verbose} (@samp{tar cfv -}, or even @samp{tar cv}---if the
3700 installer let standard output be the default archive). In that case
3701 @command{tar} writes verbose output to the standard error stream.
3703 If @option{--index-file=@var{file}} is specified, @command{tar} sends
3704 verbose output to @var{file} rather than to standard output or standard
3708 @cindex Obtaining total status information
3710 The @option{--totals} option causes @command{tar} to print on the
3711 standard error the total amount of bytes transferred when processing
3712 an archive. When creating or appending to an archive, this option
3713 prints the number of bytes written to the archive and the average
3714 speed at which they have been written, e.g.:
3718 $ @kbd{tar -c -f archive.tar --totals /home}
3719 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3723 When reading an archive, this option displays the number of bytes
3728 $ @kbd{tar -x -f archive.tar --totals}
3729 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3733 Finally, when deleting from an archive, the @option{--totals} option
3734 displays both numbers plus number of bytes removed from the archive:
3738 $ @kbd{tar --delete -f foo.tar --totals --wildcards '*~'}
3739 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3740 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3741 Total bytes deleted: 1474048
3745 You can also obtain this information on request. When
3746 @option{--totals} is used with an argument, this argument is
3747 interpreted as a symbolic name of a signal, upon delivery of which the
3748 statistics is to be printed:
3751 @item --totals=@var{signo}
3752 Print statistics upon delivery of signal @var{signo}. Valid arguments
3753 are: @code{SIGHUP}, @code{SIGQUIT}, @code{SIGINT}, @code{SIGUSR1} and
3754 @code{SIGUSR2}. Shortened names without @samp{SIG} prefix are also
3758 Both forms of @option{--totals} option can be used simultaneously.
3759 Thus, @kbd{tar -x --totals --totals=USR1} instructs @command{tar} to
3760 extract all members from its default archive and print statistics
3761 after finishing the extraction, as well as when receiving signal
3764 @anchor{Progress information}
3765 @cindex Progress information
3766 The @option{--checkpoint} option prints an occasional message
3767 as @command{tar} reads or writes the archive. It is designed for
3768 those who don't need the more detailed (and voluminous) output of
3769 @option{--block-number} (@option{-R}), but do want visual confirmation
3770 that @command{tar} is actually making forward progress. By default it
3771 prints a message each 10 records read or written. This can be changed
3772 by giving it a numeric argument after an equal sign:
3775 $ @kbd{tar -c --checkpoint=1000} /var
3776 tar: Write checkpoint 1000
3777 tar: Write checkpoint 2000
3778 tar: Write checkpoint 3000
3781 This example shows the default checkpoint message used by
3782 @command{tar}. If you place a dot immediately after the equal
3783 sign, it will print a @samp{.} at each checkpoint@footnote{This is
3784 actually a shortcut for @option{--checkpoint=@var{n}
3785 --checkpoint-action=dot}. @xref{checkpoints, dot}.}. For example:
3788 $ @kbd{tar -c --checkpoint=.1000} /var
3792 The @option{--checkpoint} option provides a flexible mechanism for
3793 executing arbitrary actions upon hitting checkpoints, see the next
3794 section (@pxref{checkpoints}), for more information on it.
3796 @opindex show-omitted-dirs
3797 @anchor{show-omitted-dirs}
3798 The @option{--show-omitted-dirs} option, when reading an archive---with
3799 @option{--list} or @option{--extract}, for example---causes a message
3800 to be printed for each directory in the archive which is skipped.
3801 This happens regardless of the reason for skipping: the directory might
3802 not have been named on the command line (implicitly or explicitly),
3803 it might be excluded by the use of the
3804 @option{--exclude=@var{pattern}} option, or some other reason.
3806 @opindex block-number
3807 @cindex Block number where error occurred
3808 @anchor{block-number}
3809 If @option{--block-number} (@option{-R}) is used, @command{tar} prints, along with
3810 every message it would normally produce, the block number within the
3811 archive where the message was triggered. Also, supplementary messages
3812 are triggered when reading blocks full of NULs, or when hitting end of
3813 file on the archive. As of now, if the archive is properly terminated
3814 with a NUL block, the reading of the file may stop before end of file
3815 is met, so the position of end of file will not usually show when
3816 @option{--block-number} (@option{-R}) is used. Note that @GNUTAR{}
3817 drains the archive before exiting when reading the
3818 archive from a pipe.
3820 @cindex Error message, block number of
3821 This option is especially useful when reading damaged archives, since
3822 it helps pinpoint the damaged sections. It can also be used with
3823 @option{--list} (@option{-t}) when listing a file-system backup tape, allowing you to
3824 choose among several backup tapes when retrieving a file later, in
3825 favor of the tape where the file appears earliest (closest to the
3826 front of the tape). @xref{backup}.
3829 @section Checkpoints
3830 @cindex checkpoints, defined
3832 @opindex checkpoint-action
3834 A @dfn{checkpoint} is a moment of time before writing @var{n}th record to
3835 the archive (a @dfn{write checkpoint}), or before reading @var{n}th record
3836 from the archive (a @dfn{read checkpoint}). Checkpoints allow to
3837 periodically execute arbitrary actions.
3839 The checkpoint facility is enabled using the following option:
3842 @xopindex{checkpoint, defined}
3843 @item --checkpoint[=@var{n}]
3844 Schedule checkpoints before writing or reading each @var{n}th record.
3845 The default value for @var{n} is 10.
3848 A list of arbitrary @dfn{actions} can be executed at each checkpoint.
3849 These actions include: pausing, displaying textual messages, and
3850 executing arbitrary external programs. Actions are defined using
3851 the @option{--checkpoint-action} option.
3854 @xopindex{checkpoint-action, defined}
3855 @item --checkpoint-action=@var{action}
3856 Execute an @var{action} at each checkpoint.
3859 @cindex @code{echo}, checkpoint action
3860 The simplest value of @var{action} is @samp{echo}. It instructs
3861 @command{tar} to display the default message on the standard error
3862 stream upon arriving at each checkpoint. The default message is (in
3863 @acronym{POSIX} locale) @samp{Write checkpoint @var{n}}, for write
3864 checkpoints, and @samp{Read checkpoint @var{n}}, for read checkpoints.
3865 Here, @var{n} represents ordinal number of the checkpoint.
3867 In another locales, translated versions of this message are used.
3869 This is the default action, so running:
3872 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=echo} /var
3879 $ @kbd{tar -c --checkpoint=1000} /var
3882 The @samp{echo} action also allows to supply a customized message.
3883 You do so by placing an equals sign and the message right after it,
3887 --checkpoint-action="echo=Hit %s checkpoint #%u"
3890 The @samp{%s} and @samp{%u} in the above example are
3891 @dfn{meta-characters}. The @samp{%s} meta-character is replaced with
3892 the @dfn{type} of the checkpoint: @samp{write} or
3893 @samp{read} (or a corresponding translated version in locales other
3894 than @acronym{POSIX}). The @samp{%u} meta-character is replaced with
3895 the ordinal number of the checkpoint. Thus, the above example could
3896 produce the following output when used with the @option{--create}
3900 tar: Hit write checkpoint #10
3901 tar: Hit write checkpoint #20
3902 tar: Hit write checkpoint #30
3905 Aside from meta-character expansion, the message string is subject to
3906 @dfn{unquoting}, during which the backslash @dfn{escape sequences} are
3907 replaced with their corresponding @acronym{ASCII} characters
3908 (@pxref{escape sequences}). E.g. the following action will produce an
3909 audible bell and the message described above at each checkpoint:
3912 --checkpoint-action='echo=\aHit %s checkpoint #%u'
3915 @cindex @code{bell}, checkpoint action
3916 There is also a special action which produces an audible signal:
3917 @samp{bell}. It is not equivalent to @samp{echo='\a'}, because
3918 @samp{bell} sends the bell directly to the console (@file{/dev/tty}),
3919 whereas @samp{echo='\a'} sends it to the standard error.
3921 @cindex @code{ttyout}, checkpoint action
3922 The @samp{ttyout=@var{string}} action outputs @var{string} to
3923 @file{/dev/tty}, so it can be used even if the standard output is
3924 redirected elsewhere. The @var{string} is subject to the same
3925 modifications as with @samp{echo} action. In contrast to the latter,
3926 @samp{ttyout} does not prepend @command{tar} executable name to the
3927 string, nor does it output a newline after it. For example, the
3928 following action will print the checkpoint message at the same screen
3929 line, overwriting any previous message:
3932 --checkpoint-action="ttyout=\rHit %s checkpoint #%u"
3935 @cindex @code{dot}, checkpoint action
3936 Another available checkpoint action is @samp{dot} (or @samp{.}). It
3937 instructs @command{tar} to print a single dot on the standard listing
3941 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=dot} /var
3945 For compatibility with previous @GNUTAR{} versions, this action can
3946 be abbreviated by placing a dot in front of the checkpoint frequency,
3947 as shown in the previous section.
3949 @cindex @code{sleep}, checkpoint action
3950 Yet another action, @samp{sleep}, pauses @command{tar} for a specified
3951 amount of seconds. The following example will stop for 30 seconds at each
3955 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=sleep=30}
3958 @cindex @code{exec}, checkpoint action
3959 Finally, the @code{exec} action executes a given external program.
3963 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint}
3966 This program is executed using @command{/bin/sh -c}, with no
3967 additional arguments. Its exit code is ignored. It gets a copy of
3968 @command{tar}'s environment plus the following variables:
3971 @vrindex TAR_VERSION, checkpoint script environment
3973 @GNUTAR{} version number.
3975 @vrindex TAR_ARCHIVE, checkpoint script environment
3977 The name of the archive @command{tar} is processing.
3979 @vrindex TAR_BLOCKING_FACTOR, checkpoint script environment
3980 @item TAR_BLOCKING_FACTOR
3981 Current blocking factor (@pxref{Blocking}).
3983 @vrindex TAR_CHECKPOINT, checkpoint script environment
3984 @item TAR_CHECKPOINT
3985 Number of the checkpoint.
3987 @vrindex TAR_SUBCOMMAND, checkpoint script environment
3988 @item TAR_SUBCOMMAND
3989 A short option describing the operation @command{tar} is executing.
3990 @xref{Operations}, for a complete list of subcommand options.
3992 @vrindex TAR_FORMAT, checkpoint script environment
3994 Format of the archive being processed. @xref{Formats}, for a complete
3995 list of archive format names.
3998 Any number of actions can be defined, by supplying several
3999 @option{--checkpoint-action} options in the command line. For
4000 example, the command below displays two messages, pauses
4001 execution for 30 seconds and executes the @file{/sbin/cpoint} script:
4005 $ @kbd{tar -c -f arc.tar \
4006 --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
4007 --checkpoint-action='echo=Sleeping for 30 seconds' \
4008 --checkpoint-action='sleep=30' \
4009 --checkpoint-action='exec=/sbin/cpoint'}
4013 This example also illustrates the fact that
4014 @option{--checkpoint-action} can be used without
4015 @option{--checkpoint}. In this case, the default checkpoint frequency
4016 (at each 10th record) is assumed.
4019 @section Controlling Warning Messages
4021 Sometimes, while performing the requested task, @GNUTAR{} notices
4022 some conditions that are not exactly errors, but which the user
4023 should be aware of. When this happens, @command{tar} issues a
4024 @dfn{warning message} describing the condition. Warning messages
4025 are output to the standard error and they do not affect the exit
4026 code of @command{tar} command.
4028 @xopindex{warning, explained}
4029 @GNUTAR{} allows the user to suppress some or all of its warning
4033 @item --warning=@var{keyword}
4034 Control display of the warning messages identified by @var{keyword}.
4035 If @var{keyword} starts with the prefix @samp{no-}, such messages are
4036 suppressed. Otherwise, they are enabled.
4038 Multiple @option{--warning} messages accumulate.
4040 The tables below list allowed values for @var{keyword} along with the
4041 warning messages they control.
4044 @subheading Keywords controlling @command{tar} operation
4048 Enable all warning messages. This is the default.
4051 Disable all warning messages.
4052 @kwindex filename-with-nuls
4053 @cindex @samp{file name read contains nul character}, warning message
4054 @item filename-with-nuls
4055 @samp{%s: file name read contains nul character}
4056 @kwindex alone-zero-block
4057 @cindex @samp{A lone zero block at}, warning message
4058 @item alone-zero-block
4059 @samp{A lone zero block at %s}
4062 @subheading Keywords applicable for @command{tar --create}
4065 @cindex @samp{contains a cache directory tag}, warning message
4067 @samp{%s: contains a cache directory tag %s; %s}
4068 @kwindex file-shrank
4069 @cindex @samp{File shrank by %s bytes}, warning message
4071 @samp{%s: File shrank by %s bytes; padding with zeros}
4073 @cindex @samp{file is on a different filesystem}, warning message
4075 @samp{%s: file is on a different filesystem; not dumped}
4076 @kwindex file-ignored
4077 @cindex @samp{Unknown file type; file ignored}, warning message
4078 @cindex @samp{socket ignored}, warning message
4079 @cindex @samp{door ignored}, warning message
4081 @samp{%s: Unknown file type; file ignored}
4082 @*@samp{%s: socket ignored}
4083 @*@samp{%s: door ignored}
4084 @kwindex file-unchanged
4085 @cindex @samp{file is unchanged; not dumped}, warning message
4086 @item file-unchanged
4087 @samp{%s: file is unchanged; not dumped}
4088 @kwindex ignore-archive
4089 @cindex @samp{file is the archive; not dumped}, warning message
4090 @kwindex ignore-archive
4091 @cindex @samp{file is the archive; not dumped}, warning message
4092 @item ignore-archive
4093 @samp{%s: file is the archive; not dumped}
4094 @kwindex file-removed
4095 @cindex @samp{File removed before we read it}, warning message
4097 @samp{%s: File removed before we read it}
4098 @kwindex file-changed
4099 @cindex @samp{file changed as we read it}, warning message
4101 @samp{%s: file changed as we read it}
4104 @subheading Keywords applicable for @command{tar --extract}
4107 @cindex @samp{implausibly old time stamp %s}, warning message
4108 @cindex @samp{time stamp %s is %s s in the future}, warning message
4110 @samp{%s: implausibly old time stamp %s}
4111 @*@samp{%s: time stamp %s is %s s in the future}
4112 @kwindex contiguous-cast
4113 @cindex @samp{Extracting contiguous files as regular files}, warning message
4114 @item contiguous-cast
4115 @samp{Extracting contiguous files as regular files}
4116 @kwindex symlink-cast
4117 @cindex @samp{Attempting extraction of symbolic links as hard links}, warning message
4119 @samp{Attempting extraction of symbolic links as hard links}
4120 @kwindex unknown-cast
4121 @cindex @samp{Unknown file type `%c', extracted as normal file}, warning message
4123 @samp{%s: Unknown file type `%c', extracted as normal file}
4124 @kwindex ignore-newer
4125 @cindex @samp{Current %s is newer or same age}, warning message
4127 @samp{Current %s is newer or same age}
4128 @kwindex unknown-keyword
4129 @cindex @samp{Ignoring unknown extended header keyword `%s'}, warning message
4130 @item unknown-keyword
4131 @samp{Ignoring unknown extended header keyword `%s'}
4134 @subheading Keywords controlling incremental extraction:
4136 @kwindex rename-directory
4137 @cindex @samp{%s: Directory has been renamed from %s}, warning message
4138 @cindex @samp{%s: Directory has been renamed}, warning message
4139 @item rename-directory
4140 @samp{%s: Directory has been renamed from %s}
4141 @*@samp{%s: Directory has been renamed}
4142 @kwindex new-directory
4143 @cindex @samp{%s: Directory is new}, warning message
4145 @samp{%s: Directory is new}
4147 @cindex @samp{%s: directory is on a different device: not purging}, warning message
4149 @samp{%s: directory is on a different device: not purging}
4150 @kwindex bad-dumpdir
4151 @cindex @samp{Malformed dumpdir: 'X' never used}, warning message
4153 @samp{Malformed dumpdir: 'X' never used}
4157 @section Asking for Confirmation During Operations
4158 @cindex Interactive operation
4160 Typically, @command{tar} carries out a command without stopping for
4161 further instructions. In some situations however, you may want to
4162 exclude some files and archive members from the operation (for instance
4163 if disk or storage space is tight). You can do this by excluding
4164 certain files automatically (@pxref{Choosing}), or by performing
4165 an operation interactively, using the @option{--interactive} (@option{-w}) option.
4166 @command{tar} also accepts @option{--confirmation} for this option.
4168 @opindex interactive
4169 When the @option{--interactive} (@option{-w}) option is specified, before
4170 reading, writing, or deleting files, @command{tar} first prints a message
4171 for each such file, telling what operation it intends to take, then asks
4172 for confirmation on the terminal. The actions which require
4173 confirmation include adding a file to the archive, extracting a file
4174 from the archive, deleting a file from the archive, and deleting a file
4175 from disk. To confirm the action, you must type a line of input
4176 beginning with @samp{y}. If your input line begins with anything other
4177 than @samp{y}, @command{tar} skips that file.
4179 If @command{tar} is reading the archive from the standard input,
4180 @command{tar} opens the file @file{/dev/tty} to support the interactive
4183 Verbose output is normally sent to standard output, separate from
4184 other error messages. However, if the archive is produced directly
4185 on standard output, then verbose output is mixed with errors on
4186 @code{stderr}. Producing the archive on standard output may be used
4187 as a way to avoid using disk space, when the archive is soon to be
4188 consumed by another process reading it, say. Some people felt the need
4189 of producing an archive on stdout, still willing to segregate between
4190 verbose output and error output. A possible approach would be using a
4191 named pipe to receive the archive, and having the consumer process to
4192 read from that named pipe. This has the advantage of letting standard
4193 output free to receive verbose output, all separate from errors.
4196 @chapter @GNUTAR{} Operations
4209 @section Basic @GNUTAR{} Operations
4211 The basic @command{tar} operations, @option{--create} (@option{-c}),
4212 @option{--list} (@option{-t}) and @option{--extract} (@option{--get},
4213 @option{-x}), are currently presented and described in the tutorial
4214 chapter of this manual. This section provides some complementary notes
4215 for these operations.
4218 @xopindex{create, complementary notes}
4222 Creating an empty archive would have some kind of elegance. One can
4223 initialize an empty archive and later use @option{--append}
4224 (@option{-r}) for adding all members. Some applications would not
4225 welcome making an exception in the way of adding the first archive
4226 member. On the other hand, many people reported that it is
4227 dangerously too easy for @command{tar} to destroy a magnetic tape with
4228 an empty archive@footnote{This is well described in @cite{Unix-haters
4229 Handbook}, by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG
4230 Books, ISBN 1-56884-203-1.}. The two most common errors are:
4234 Mistakingly using @code{create} instead of @code{extract}, when the
4235 intent was to extract the full contents of an archive. This error
4236 is likely: keys @kbd{c} and @kbd{x} are right next to each other on
4237 the QWERTY keyboard. Instead of being unpacked, the archive then
4238 gets wholly destroyed. When users speak about @dfn{exploding} an
4239 archive, they usually mean something else :-).
4242 Forgetting the argument to @code{file}, when the intent was to create
4243 an archive with a single file in it. This error is likely because a
4244 tired user can easily add the @kbd{f} key to the cluster of option
4245 letters, by the mere force of habit, without realizing the full
4246 consequence of doing so. The usual consequence is that the single
4247 file, which was meant to be saved, is rather destroyed.
4250 So, recognizing the likelihood and the catastrophic nature of these
4251 errors, @GNUTAR{} now takes some distance from elegance, and
4252 cowardly refuses to create an archive when @option{--create} option is
4253 given, there are no arguments besides options, and
4254 @option{--files-from} (@option{-T}) option is @emph{not} used. To get
4255 around the cautiousness of @GNUTAR{} and nevertheless create an
4256 archive with nothing in it, one may still use, as the value for the
4257 @option{--files-from} option, a file with no names in it, as shown in
4258 the following commands:
4261 @kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
4262 @kbd{tar cfT empty-archive.tar /dev/null}
4265 @xopindex{extract, complementary notes}
4270 A socket is stored, within a @GNUTAR{} archive, as a pipe.
4272 @item @option{--list} (@option{-t})
4274 @GNUTAR{} now shows dates as @samp{1996-08-30},
4275 while it used to show them as @samp{Aug 30 1996}. Preferably,
4276 people should get used to ISO 8601 dates. Local American dates should
4277 be made available again with full date localization support, once
4278 ready. In the meantime, programs not being localizable for dates
4279 should prefer international dates, that's really the way to go.
4281 Look up @url{http://www.cl.cam.ac.uk/@/~mgk25/@/iso-time.html} if you
4282 are curious, it contains a detailed explanation of the ISO 8601 standard.
4287 @section Advanced @GNUTAR{} Operations
4289 Now that you have learned the basics of using @GNUTAR{}, you may want
4290 to learn about further ways in which @command{tar} can help you.
4292 This chapter presents five, more advanced operations which you probably
4293 won't use on a daily basis, but which serve more specialized functions.
4294 We also explain the different styles of options and why you might want
4295 to use one or another, or a combination of them in your @command{tar}
4296 commands. Additionally, this chapter includes options which allow you to
4297 define the output from @command{tar} more carefully, and provide help and
4298 error correction in special circumstances.
4300 @FIXME{check this after the chapter is actually revised to make sure
4301 it still introduces the info in the chapter correctly : ).}
4313 @subsection The Five Advanced @command{tar} Operations
4315 @cindex basic operations
4316 In the last chapter, you learned about the first three operations to
4317 @command{tar}. This chapter presents the remaining five operations to
4318 @command{tar}: @option{--append}, @option{--update}, @option{--concatenate},
4319 @option{--delete}, and @option{--compare}.
4321 You are not likely to use these operations as frequently as those
4322 covered in the last chapter; however, since they perform specialized
4323 functions, they are quite useful when you do need to use them. We
4324 will give examples using the same directory and files that you created
4325 in the last chapter. As you may recall, the directory is called
4326 @file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk},
4327 and the two archive files you created are
4328 @samp{collection.tar} and @samp{music.tar}.
4330 We will also use the archive files @samp{afiles.tar} and
4331 @samp{bfiles.tar}. The archive @samp{afiles.tar} contains the members @samp{apple},
4332 @samp{angst}, and @samp{aspic}; @samp{bfiles.tar} contains the members
4333 @samp{./birds}, @samp{baboon}, and @samp{./box}.
4335 Unless we state otherwise, all practicing you do and examples you follow
4336 in this chapter will take place in the @file{practice} directory that
4337 you created in the previous chapter; see @ref{prepare for examples}.
4338 (Below in this section, we will remind you of the state of the examples
4339 where the last chapter left them.)
4341 The five operations that we will cover in this chapter are:
4346 Add new entries to an archive that already exists.
4349 Add more recent copies of archive members to the end of an archive, if
4354 Add one or more pre-existing archives to the end of another archive.
4356 Delete items from an archive (does not work on tapes).
4360 Compare archive members to their counterparts in the file system.
4364 @subsection How to Add Files to Existing Archives: @option{--append}
4366 @cindex appending files to existing archive
4368 If you want to add files to an existing archive, you don't need to
4369 create a new archive; you can use @option{--append} (@option{-r}).
4370 The archive must already exist in order to use @option{--append}. (A
4371 related operation is the @option{--update} operation; you can use this
4372 to add newer versions of archive members to an existing archive. To learn how to
4373 do this with @option{--update}, @pxref{update}.)
4375 If you use @option{--append} to add a file that has the same name as an
4376 archive member to an archive containing that archive member, then the
4377 old member is not deleted. What does happen, however, is somewhat
4378 complex. @command{tar} @emph{allows} you to have infinite number of files
4379 with the same name. Some operations treat these same-named members no
4380 differently than any other set of archive members: for example, if you
4381 view an archive with @option{--list} (@option{-t}), you will see all
4382 of those members listed, with their data modification times, owners, etc.
4384 Other operations don't deal with these members as perfectly as you might
4385 prefer; if you were to use @option{--extract} to extract the archive,
4386 only the most recently added copy of a member with the same name as
4387 other members would end up in the working directory. This is because
4388 @option{--extract} extracts an archive in the order the members appeared
4389 in the archive; the most recently archived members will be extracted
4390 last. Additionally, an extracted member will @emph{replace} a file of
4391 the same name which existed in the directory already, and @command{tar}
4392 will not prompt you about this@footnote{Unless you give it
4393 @option{--keep-old-files} option, or the disk copy is newer than
4394 the one in the archive and you invoke @command{tar} with
4395 @option{--keep-newer-files} option.}. Thus, only the most recently archived
4396 member will end up being extracted, as it will replace the one
4397 extracted before it, and so on.
4399 @cindex extracting @var{n}th copy of the file
4400 @xopindex{occurrence, described}
4401 There exists a special option that allows you to get around this
4402 behavior and extract (or list) only a particular copy of the file.
4403 This is @option{--occurrence} option. If you run @command{tar} with
4404 this option, it will extract only the first copy of the file. You
4405 may also give this option an argument specifying the number of
4406 copy to be extracted. Thus, for example if the archive
4407 @file{archive.tar} contained three copies of file @file{myfile}, then
4411 tar --extract --file archive.tar --occurrence=2 myfile
4415 would extract only the second copy. @xref{Option
4416 Summary,---occurrence}, for the description of @option{--occurrence}
4419 @FIXME{ hag -- you might want to incorporate some of the above into the
4420 MMwtSN node; not sure. i didn't know how to make it simpler...
4422 There are a few ways to get around this. Xref to Multiple Members
4423 with the Same Name, maybe.}
4425 @cindex Members, replacing with other members
4426 @cindex Replacing members with other members
4427 @xopindex{delete, using before --append}
4428 If you want to replace an archive member, use @option{--delete} to
4429 delete the member you want to remove from the archive, and then use
4430 @option{--append} to add the member you want to be in the archive. Note
4431 that you can not change the order of the archive; the most recently
4432 added member will still appear last. In this sense, you cannot truly
4433 ``replace'' one member with another. (Replacing one member with another
4434 will not work on certain types of media, such as tapes; see @ref{delete}
4435 and @ref{Media}, for more information.)
4438 * appending files:: Appending Files to an Archive
4442 @node appending files
4443 @subsubsection Appending Files to an Archive
4444 @cindex Adding files to an Archive
4445 @cindex Appending files to an Archive
4446 @cindex Archives, Appending files to
4449 The simplest way to add a file to an already existing archive is the
4450 @option{--append} (@option{-r}) operation, which writes specified
4451 files into the archive whether or not they are already among the
4454 When you use @option{--append}, you @emph{must} specify file name
4455 arguments, as there is no default. If you specify a file that already
4456 exists in the archive, another copy of the file will be added to the
4457 end of the archive. As with other operations, the member names of the
4458 newly added files will be exactly the same as their names given on the
4459 command line. The @option{--verbose} (@option{-v}) option will print
4460 out the names of the files as they are written into the archive.
4462 @option{--append} cannot be performed on some tape drives, unfortunately,
4463 due to deficiencies in the formats those tape drives use. The archive
4464 must be a valid @command{tar} archive, or else the results of using this
4465 operation will be unpredictable. @xref{Media}.
4467 To demonstrate using @option{--append} to add a file to an archive,
4468 create a file called @file{rock} in the @file{practice} directory.
4469 Make sure you are in the @file{practice} directory. Then, run the
4470 following @command{tar} command to add @file{rock} to
4471 @file{collection.tar}:
4474 $ @kbd{tar --append --file=collection.tar rock}
4478 If you now use the @option{--list} (@option{-t}) operation, you will see that
4479 @file{rock} has been added to the archive:
4482 $ @kbd{tar --list --file=collection.tar}
4483 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4484 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4485 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4486 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4490 @subsubsection Multiple Members with the Same Name
4491 @cindex members, multiple
4492 @cindex multiple members
4494 You can use @option{--append} (@option{-r}) to add copies of files
4495 which have been updated since the archive was created. (However, we
4496 do not recommend doing this since there is another @command{tar}
4497 option called @option{--update}; @xref{update}, for more information.
4498 We describe this use of @option{--append} here for the sake of
4499 completeness.) When you extract the archive, the older version will
4500 be effectively lost. This works because files are extracted from an
4501 archive in the order in which they were archived. Thus, when the
4502 archive is extracted, a file archived later in time will replace a
4503 file of the same name which was archived earlier, even though the
4504 older version of the file will remain in the archive unless you delete
4505 all versions of the file.
4507 Supposing you change the file @file{blues} and then append the changed
4508 version to @file{collection.tar}. As you saw above, the original
4509 @file{blues} is in the archive @file{collection.tar}. If you change the
4510 file and append the new version of the file to the archive, there will
4511 be two copies in the archive. When you extract the archive, the older
4512 version of the file will be extracted first, and then replaced by the
4513 newer version when it is extracted.
4515 You can append the new, changed copy of the file @file{blues} to the
4516 archive in this way:
4519 $ @kbd{tar --append --verbose --file=collection.tar blues}
4524 Because you specified the @option{--verbose} option, @command{tar} has
4525 printed the name of the file being appended as it was acted on. Now
4526 list the contents of the archive:
4529 $ @kbd{tar --list --verbose --file=collection.tar}
4530 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4531 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4532 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4533 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4534 -rw-r--r-- me user 58 1996-10-24 18:30 blues
4538 The newest version of @file{blues} is now at the end of the archive
4539 (note the different creation dates and file sizes). If you extract
4540 the archive, the older version of the file @file{blues} will be
4541 replaced by the newer version. You can confirm this by extracting
4542 the archive and running @samp{ls} on the directory.
4544 If you wish to extract the first occurrence of the file @file{blues}
4545 from the archive, use @option{--occurrence} option, as shown in
4546 the following example:
4549 $ @kbd{tar --extract -vv --occurrence --file=collection.tar blues}
4550 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4553 @xref{Writing}, for more information on @option{--extract} and
4554 see @ref{Option Summary, --occurrence}, for a description of
4555 @option{--occurrence} option.
4558 @subsection Updating an Archive
4559 @cindex Updating an archive
4562 In the previous section, you learned how to use @option{--append} to
4563 add a file to an existing archive. A related operation is
4564 @option{--update} (@option{-u}). The @option{--update} operation
4565 updates a @command{tar} archive by comparing the date of the specified
4566 archive members against the date of the file with the same name. If
4567 the file has been modified more recently than the archive member, then
4568 the newer version of the file is added to the archive (as with
4571 Unfortunately, you cannot use @option{--update} with magnetic tape drives.
4572 The operation will fail.
4574 @FIXME{other examples of media on which --update will fail? need to ask
4575 charles and/or mib/thomas/dave shevett..}
4577 Both @option{--update} and @option{--append} work by adding to the end
4578 of the archive. When you extract a file from the archive, only the
4579 version stored last will wind up in the file system, unless you use
4580 the @option{--backup} option. @xref{multiple}, for a detailed discussion.
4587 @subsubsection How to Update an Archive Using @option{--update}
4590 You must use file name arguments with the @option{--update}
4591 (@option{-u}) operation. If you don't specify any files,
4592 @command{tar} won't act on any files and won't tell you that it didn't
4593 do anything (which may end up confusing you).
4595 @c note: the above parenthetical added because in fact, this
4596 @c behavior just confused the author. :-)
4598 To see the @option{--update} option at work, create a new file,
4599 @file{classical}, in your practice directory, and some extra text to the
4600 file @file{blues}, using any text editor. Then invoke @command{tar} with
4601 the @samp{update} operation and the @option{--verbose} (@option{-v})
4602 option specified, using the names of all the files in the @file{practice}
4603 directory as file name arguments:
4606 $ @kbd{tar --update -v -f collection.tar blues folk rock classical}
4613 Because we have specified verbose mode, @command{tar} prints out the names
4614 of the files it is working on, which in this case are the names of the
4615 files that needed to be updated. If you run @samp{tar --list} and look
4616 at the archive, you will see @file{blues} and @file{classical} at its
4617 end. There will be a total of two versions of the member @samp{blues};
4618 the one at the end will be newer and larger, since you added text before
4621 The reason @command{tar} does not overwrite the older file when updating
4622 it is because writing to the middle of a section of tape is a difficult
4623 process. Tapes are not designed to go backward. @xref{Media}, for more
4624 information about tapes.
4626 @option{--update} (@option{-u}) is not suitable for performing backups for two
4627 reasons: it does not change directory content entries, and it
4628 lengthens the archive every time it is used. The @GNUTAR{}
4629 options intended specifically for backups are more
4630 efficient. If you need to run backups, please consult @ref{Backups}.
4633 @subsection Combining Archives with @option{--concatenate}
4635 @cindex Adding archives to an archive
4636 @cindex Concatenating Archives
4637 @opindex concatenate
4639 @c @cindex @option{-A} described
4640 Sometimes it may be convenient to add a second archive onto the end of
4641 an archive rather than adding individual files to the archive. To add
4642 one or more archives to the end of another archive, you should use the
4643 @option{--concatenate} (@option{--catenate}, @option{-A}) operation.
4645 To use @option{--concatenate}, give the first archive with
4646 @option{--file} option and name the rest of archives to be
4647 concatenated on the command line. The members, and their member
4648 names, will be copied verbatim from those archives to the first
4649 one@footnote{This can cause multiple members to have the same name. For
4650 information on how this affects reading the archive, see @ref{multiple}.}.
4651 The new, concatenated archive will be called by the same name as the
4652 one given with the @option{--file} option. As usual, if you omit
4653 @option{--file}, @command{tar} will use the value of the environment
4654 variable @env{TAPE}, or, if this has not been set, the default archive name.
4656 @FIXME{There is no way to specify a new name...}
4658 To demonstrate how @option{--concatenate} works, create two small archives
4659 called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
4660 files from @file{practice}:
4663 $ @kbd{tar -cvf bluesrock.tar blues rock}
4666 $ @kbd{tar -cvf folkjazz.tar folk jazz}
4672 If you like, You can run @samp{tar --list} to make sure the archives
4673 contain what they are supposed to:
4676 $ @kbd{tar -tvf bluesrock.tar}
4677 -rw-r--r-- melissa user 105 1997-01-21 19:42 blues
4678 -rw-r--r-- melissa user 33 1997-01-20 15:34 rock
4679 $ @kbd{tar -tvf jazzfolk.tar}
4680 -rw-r--r-- melissa user 20 1996-09-23 16:44 folk
4681 -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
4684 We can concatenate these two archives with @command{tar}:
4688 $ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
4691 If you now list the contents of the @file{bluesrock.tar}, you will see
4692 that now it also contains the archive members of @file{jazzfolk.tar}:
4695 $ @kbd{tar --list --file=bluesrock.tar}
4702 When you use @option{--concatenate}, the source and target archives must
4703 already exist and must have been created using compatible format
4704 parameters. Notice, that @command{tar} does not check whether the
4705 archives it concatenates have compatible formats, it does not
4706 even check if the files are really tar archives.
4708 Like @option{--append} (@option{-r}), this operation cannot be performed on some
4709 tape drives, due to deficiencies in the formats those tape drives use.
4711 @cindex @code{concatenate} vs @command{cat}
4712 @cindex @command{cat} vs @code{concatenate}
4713 It may seem more intuitive to you to want or try to use @command{cat} to
4714 concatenate two archives instead of using the @option{--concatenate}
4715 operation; after all, @command{cat} is the utility for combining files.
4717 However, @command{tar} archives incorporate an end-of-file marker which
4718 must be removed if the concatenated archives are to be read properly as
4719 one archive. @option{--concatenate} removes the end-of-archive marker
4720 from the target archive before each new archive is appended. If you use
4721 @command{cat} to combine the archives, the result will not be a valid
4722 @command{tar} format archive. If you need to retrieve files from an
4723 archive that was added to using the @command{cat} utility, use the
4724 @option{--ignore-zeros} (@option{-i}) option. @xref{Ignore Zeros}, for further
4725 information on dealing with archives improperly combined using the
4726 @command{cat} shell utility.
4729 @subsection Removing Archive Members Using @option{--delete}
4730 @cindex Deleting files from an archive
4731 @cindex Removing files from an archive
4734 You can remove members from an archive by using the @option{--delete}
4735 option. Specify the name of the archive with @option{--file}
4736 (@option{-f}) and then specify the names of the members to be deleted;
4737 if you list no member names, nothing will be deleted. The
4738 @option{--verbose} option will cause @command{tar} to print the names
4739 of the members as they are deleted. As with @option{--extract}, you
4740 must give the exact member names when using @samp{tar --delete}.
4741 @option{--delete} will remove all versions of the named file from the
4742 archive. The @option{--delete} operation can run very slowly.
4744 Unlike other operations, @option{--delete} has no short form.
4746 @cindex Tapes, using @option{--delete} and
4747 @cindex Deleting from tape archives
4748 This operation will rewrite the archive. You can only use
4749 @option{--delete} on an archive if the archive device allows you to
4750 write to any point on the media, such as a disk; because of this, it
4751 does not work on magnetic tapes. Do not try to delete an archive member
4752 from a magnetic tape; the action will not succeed, and you will be
4753 likely to scramble the archive and damage your tape. There is no safe
4754 way (except by completely re-writing the archive) to delete files from
4755 most kinds of magnetic tape. @xref{Media}.
4757 To delete all versions of the file @file{blues} from the archive
4758 @file{collection.tar} in the @file{practice} directory, make sure you
4759 are in that directory, and then,
4762 $ @kbd{tar --list --file=collection.tar}
4767 $ @kbd{tar --delete --file=collection.tar blues}
4768 $ @kbd{tar --list --file=collection.tar}
4774 @FIXME{Check if the above listing is actually produced after running
4775 all the examples on collection.tar.}
4777 The @option{--delete} option has been reported to work properly when
4778 @command{tar} acts as a filter from @code{stdin} to @code{stdout}.
4781 @subsection Comparing Archive Members with the File System
4782 @cindex Verifying the currency of an archive
4785 The @option{--compare} (@option{-d}), or @option{--diff} operation compares
4786 specified archive members against files with the same names, and then
4787 reports differences in file size, mode, owner, modification date and
4788 contents. You should @emph{only} specify archive member names, not file
4789 names. If you do not name any members, then @command{tar} will compare the
4790 entire archive. If a file is represented in the archive but does not
4791 exist in the file system, @command{tar} reports a difference.
4793 You have to specify the record size of the archive when modifying an
4794 archive with a non-default record size.
4796 @command{tar} ignores files in the file system that do not have
4797 corresponding members in the archive.
4799 The following example compares the archive members @file{rock},
4800 @file{blues} and @file{funk} in the archive @file{bluesrock.tar} with
4801 files of the same name in the file system. (Note that there is no file,
4802 @file{funk}; @command{tar} will report an error message.)
4805 $ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
4808 tar: funk not found in archive
4811 The spirit behind the @option{--compare} (@option{--diff},
4812 @option{-d}) option is to check whether the archive represents the
4813 current state of files on disk, more than validating the integrity of
4814 the archive media. For this latter goal, see @ref{verify}.
4816 @node create options
4817 @section Options Used by @option{--create}
4819 @xopindex{create, additional options}
4820 The previous chapter described the basics of how to use
4821 @option{--create} (@option{-c}) to create an archive from a set of files.
4822 @xref{create}. This section described advanced options to be used with
4826 * override:: Overriding File Metadata.
4827 * Ignore Failed Read::
4831 @subsection Overriding File Metadata
4833 As described above, a @command{tar} archive keeps, for each member it contains,
4834 its @dfn{metadata}, such as modification time, mode and ownership of
4835 the file. @GNUTAR{} allows to replace these data with other values
4836 when adding files to the archive. The options described in this
4837 section affect creation of archives of any type. For POSIX archives,
4838 see also @ref{PAX keywords}, for additional ways of controlling
4839 metadata, stored in the archive.
4843 @item --mode=@var{permissions}
4845 When adding files to an archive, @command{tar} will use
4846 @var{permissions} for the archive members, rather than the permissions
4847 from the files. @var{permissions} can be specified either as an octal
4848 number or as symbolic permissions, like with
4849 @command{chmod} (@xref{File permissions, Permissions, File
4850 permissions, fileutils, @acronym{GNU} file utilities}. This reference
4851 also has useful information for those not being overly familiar with
4852 the UNIX permission system). Using latter syntax allows for
4853 more flexibility. For example, the value @samp{a+rw} adds read and write
4854 permissions for everybody, while retaining executable bits on directories
4855 or on any other file already marked as executable:
4858 $ @kbd{tar -c -f archive.tar --mode='a+rw' .}
4861 @item --mtime=@var{date}
4864 When adding files to an archive, @command{tar} will use @var{date} as
4865 the modification time of members when creating archives, instead of
4866 their actual modification times. The argument @var{date} can be
4867 either a textual date representation in almost arbitrary format
4868 (@pxref{Date input formats}) or a name of an existing file, starting
4869 with @samp{/} or @samp{.}. In the latter case, the modification time
4870 of that file will be used.
4872 The following example will set the modification date to 00:00:00,
4876 $ @kbd{tar -c -f archive.tar --mtime='1970-01-01' .}
4880 When used with @option{--verbose} (@pxref{verbose tutorial}) @GNUTAR{}
4881 will try to convert the specified date back to its textual
4882 representation and compare it with the one given with
4883 @option{--mtime} options. If the two dates differ, @command{tar} will
4884 print a warning saying what date it will use. This is to help user
4885 ensure he is using the right date.
4890 $ @kbd{tar -c -f archive.tar -v --mtime=yesterday .}
4891 tar: Option --mtime: Treating date `yesterday' as 2006-06-20
4896 @item --owner=@var{user}
4899 Specifies that @command{tar} should use @var{user} as the owner of members
4900 when creating archives, instead of the user associated with the source
4901 file. The argument @var{user} can be either an existing user symbolic
4902 name, or a decimal numeric user @acronym{ID}.
4904 There is no value indicating a missing number, and @samp{0} usually means
4905 @code{root}. Some people like to force @samp{0} as the value to offer in
4906 their distributions for the owner of files, because the @code{root} user is
4907 anonymous anyway, so that might as well be the owner of anonymous
4908 archives. For example:
4911 $ @kbd{tar -c -f archive.tar --owner=0 .}
4918 $ @kbd{tar -c -f archive.tar --owner=root .}
4921 @item --group=@var{group}
4924 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
4925 rather than the group from the source file. The argument @var{group}
4926 can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
4929 @node Ignore Failed Read
4930 @subsection Ignore Fail Read
4933 @item --ignore-failed-read
4934 @opindex ignore-failed-read
4935 Do not exit with nonzero on unreadable files or directories.
4938 @node extract options
4939 @section Options Used by @option{--extract}
4940 @cindex options for use with @option{--extract}
4942 @xopindex{extract, additional options}
4943 The previous chapter showed how to use @option{--extract} to extract
4944 an archive into the file system. Various options cause @command{tar} to
4945 extract more information than just file contents, such as the owner,
4946 the permissions, the modification date, and so forth. This section
4947 presents options to be used with @option{--extract} when certain special
4948 considerations arise. You may review the information presented in
4949 @ref{extract} for more basic information about the
4950 @option{--extract} operation.
4953 * Reading:: Options to Help Read Archives
4954 * Writing:: Changing How @command{tar} Writes Files
4955 * Scarce:: Coping with Scarce Resources
4959 @subsection Options to Help Read Archives
4960 @cindex Options when reading archives
4962 @cindex Reading incomplete records
4963 @cindex Records, incomplete
4964 @opindex read-full-records
4965 Normally, @command{tar} will request data in full record increments from
4966 an archive storage device. If the device cannot return a full record,
4967 @command{tar} will report an error. However, some devices do not always
4968 return full records, or do not require the last record of an archive to
4969 be padded out to the next record boundary. To keep reading until you
4970 obtain a full record, or to accept an incomplete record if it contains
4971 an end-of-archive marker, specify the @option{--read-full-records} (@option{-B}) option
4972 in conjunction with the @option{--extract} or @option{--list} operations.
4975 The @option{--read-full-records} (@option{-B}) option is turned on by default when
4976 @command{tar} reads an archive from standard input, or from a remote
4977 machine. This is because on @acronym{BSD} Unix systems, attempting to read a
4978 pipe returns however much happens to be in the pipe, even if it is
4979 less than was requested. If this option were not enabled, @command{tar}
4980 would fail as soon as it read an incomplete record from the pipe.
4982 If you're not sure of the blocking factor of an archive, you can
4983 read the archive by specifying @option{--read-full-records} (@option{-B}) and
4984 @option{--blocking-factor=@var{512-size}} (@option{-b
4985 @var{512-size}}), using a blocking factor larger than what the archive
4986 uses. This lets you avoid having to determine the blocking factor
4987 of an archive. @xref{Blocking Factor}.
4990 * read full records::
4994 @node read full records
4995 @unnumberedsubsubsec Reading Full Records
4997 @FIXME{need sentence or so of intro here}
5000 @opindex read-full-records
5001 @item --read-full-records
5003 Use in conjunction with @option{--extract} (@option{--get},
5004 @option{-x}) to read an archive which contains incomplete records, or
5005 one which has a blocking factor less than the one specified.
5009 @unnumberedsubsubsec Ignoring Blocks of Zeros
5011 @cindex End-of-archive blocks, ignoring
5012 @cindex Ignoring end-of-archive blocks
5013 @opindex ignore-zeros
5014 Normally, @command{tar} stops reading when it encounters a block of zeros
5015 between file entries (which usually indicates the end of the archive).
5016 @option{--ignore-zeros} (@option{-i}) allows @command{tar} to
5017 completely read an archive which contains a block of zeros before the
5018 end (i.e., a damaged archive, or one that was created by concatenating
5019 several archives together).
5021 The @option{--ignore-zeros} (@option{-i}) option is turned off by default because many
5022 versions of @command{tar} write garbage after the end-of-archive entry,
5023 since that part of the media is never supposed to be read. @GNUTAR{}
5024 does not write after the end of an archive, but seeks to
5025 maintain compatibility among archiving utilities.
5028 @item --ignore-zeros
5030 To ignore blocks of zeros (i.e., end-of-archive entries) which may be
5031 encountered while reading an archive. Use in conjunction with
5032 @option{--extract} or @option{--list}.
5036 @subsection Changing How @command{tar} Writes Files
5039 @FIXME{Introductory paragraph}
5042 * Dealing with Old Files::
5043 * Overwrite Old Files::
5045 * Keep Newer Files::
5047 * Recursive Unlink::
5048 * Data Modification Times::
5049 * Setting Access Permissions::
5050 * Directory Modification Times and Permissions::
5051 * Writing to Standard Output::
5052 * Writing to an External Program::
5056 @node Dealing with Old Files
5057 @unnumberedsubsubsec Options Controlling the Overwriting of Existing Files
5059 @xopindex{overwrite-dir, introduced}
5060 When extracting files, if @command{tar} discovers that the extracted
5061 file already exists, it normally replaces the file by removing it before
5062 extracting it, to prevent confusion in the presence of hard or symbolic
5063 links. (If the existing file is a symbolic link, it is removed, not
5064 followed.) However, if a directory cannot be removed because it is
5065 nonempty, @command{tar} normally overwrites its metadata (ownership,
5066 permission, etc.). The @option{--overwrite-dir} option enables this
5067 default behavior. To be more cautious and preserve the metadata of
5068 such a directory, use the @option{--no-overwrite-dir} option.
5070 @cindex Overwriting old files, prevention
5071 @xopindex{keep-old-files, introduced}
5072 To be even more cautious and prevent existing files from being replaced, use
5073 the @option{--keep-old-files} (@option{-k}) option. It causes @command{tar} to refuse
5074 to replace or update a file that already exists, i.e., a file with the
5075 same name as an archive member prevents extraction of that archive
5076 member. Instead, it reports an error.
5078 @xopindex{overwrite, introduced}
5079 To be more aggressive about altering existing files, use the
5080 @option{--overwrite} option. It causes @command{tar} to overwrite
5081 existing files and to follow existing symbolic links when extracting.
5083 @cindex Protecting old files
5084 Some people argue that @GNUTAR{} should not hesitate
5085 to overwrite files with other files when extracting. When extracting
5086 a @command{tar} archive, they expect to see a faithful copy of the
5087 state of the file system when the archive was created. It is debatable
5088 that this would always be a proper behavior. For example, suppose one
5089 has an archive in which @file{usr/local} is a link to
5090 @file{usr/local2}. Since then, maybe the site removed the link and
5091 renamed the whole hierarchy from @file{/usr/local2} to
5092 @file{/usr/local}. Such things happen all the time. I guess it would
5093 not be welcome at all that @GNUTAR{} removes the
5094 whole hierarchy just to make room for the link to be reinstated
5095 (unless it @emph{also} simultaneously restores the full
5096 @file{/usr/local2}, of course!) @GNUTAR{} is indeed
5097 able to remove a whole hierarchy to reestablish a symbolic link, for
5098 example, but @emph{only if} @option{--recursive-unlink} is specified
5099 to allow this behavior. In any case, single files are silently
5102 @xopindex{unlink-first, introduced}
5103 Finally, the @option{--unlink-first} (@option{-U}) option can improve performance in
5104 some cases by causing @command{tar} to remove files unconditionally
5105 before extracting them.
5107 @node Overwrite Old Files
5108 @unnumberedsubsubsec Overwrite Old Files
5113 Overwrite existing files and directory metadata when extracting files
5116 This causes @command{tar} to write extracted files into the file system without
5117 regard to the files already on the system; i.e., files with the same
5118 names as archive members are overwritten when the archive is extracted.
5119 It also causes @command{tar} to extract the ownership, permissions,
5120 and time stamps onto any preexisting files or directories.
5121 If the name of a corresponding file name is a symbolic link, the file
5122 pointed to by the symbolic link will be overwritten instead of the
5123 symbolic link itself (if this is possible). Moreover, special devices,
5124 empty directories and even symbolic links are automatically removed if
5125 they are in the way of extraction.
5127 Be careful when using the @option{--overwrite} option, particularly when
5128 combined with the @option{--absolute-names} (@option{-P}) option, as this combination
5129 can change the contents, ownership or permissions of any file on your
5130 system. Also, many systems do not take kindly to overwriting files that
5131 are currently being executed.
5133 @opindex overwrite-dir
5134 @item --overwrite-dir
5135 Overwrite the metadata of directories when extracting files from an
5136 archive, but remove other files before extracting.
5139 @node Keep Old Files
5140 @unnumberedsubsubsec Keep Old Files
5143 @opindex keep-old-files
5144 @item --keep-old-files
5146 Do not replace existing files from archive. The
5147 @option{--keep-old-files} (@option{-k}) option prevents @command{tar}
5148 from replacing existing files with files with the same name from the
5149 archive. The @option{--keep-old-files} option is meaningless with
5150 @option{--list} (@option{-t}). Prevents @command{tar} from replacing
5151 files in the file system during extraction.
5154 @node Keep Newer Files
5155 @unnumberedsubsubsec Keep Newer Files
5158 @opindex keep-newer-files
5159 @item --keep-newer-files
5160 Do not replace existing files that are newer than their archive
5161 copies. This option is meaningless with @option{--list} (@option{-t}).
5165 @unnumberedsubsubsec Unlink First
5168 @opindex unlink-first
5169 @item --unlink-first
5171 Remove files before extracting over them.
5172 This can make @command{tar} run a bit faster if you know in advance
5173 that the extracted files all need to be removed. Normally this option
5174 slows @command{tar} down slightly, so it is disabled by default.
5177 @node Recursive Unlink
5178 @unnumberedsubsubsec Recursive Unlink
5181 @opindex recursive-unlink
5182 @item --recursive-unlink
5183 When this option is specified, try removing files and directory hierarchies
5184 before extracting over them. @emph{This is a dangerous option!}
5187 If you specify the @option{--recursive-unlink} option,
5188 @command{tar} removes @emph{anything} that keeps you from extracting a file
5189 as far as current permissions will allow it. This could include removal
5190 of the contents of a full directory hierarchy.
5192 @node Data Modification Times
5193 @unnumberedsubsubsec Setting Data Modification Times
5195 @cindex Data modification times of extracted files
5196 @cindex Modification times of extracted files
5197 Normally, @command{tar} sets the data modification times of extracted
5198 files to the corresponding times recorded for the files in the archive, but
5199 limits the permissions of extracted files by the current @code{umask}
5202 To set the data modification times of extracted files to the time when
5203 the files were extracted, use the @option{--touch} (@option{-m}) option in
5204 conjunction with @option{--extract} (@option{--get}, @option{-x}).
5210 Sets the data modification time of extracted archive members to the time
5211 they were extracted, not the time recorded for them in the archive.
5212 Use in conjunction with @option{--extract} (@option{--get}, @option{-x}).
5215 @node Setting Access Permissions
5216 @unnumberedsubsubsec Setting Access Permissions
5218 @cindex Permissions of extracted files
5219 @cindex Modes of extracted files
5220 To set the modes (access permissions) of extracted files to those
5221 recorded for those files in the archive, use @option{--same-permissions}
5222 in conjunction with the @option{--extract} (@option{--get},
5223 @option{-x}) operation.
5226 @opindex preserve-permissions
5227 @opindex same-permissions
5228 @item --preserve-permissions
5229 @itemx --same-permissions
5230 @c @itemx --ignore-umask
5232 Set modes of extracted archive members to those recorded in the
5233 archive, instead of current umask settings. Use in conjunction with
5234 @option{--extract} (@option{--get}, @option{-x}).
5237 @node Directory Modification Times and Permissions
5238 @unnumberedsubsubsec Directory Modification Times and Permissions
5240 After successfully extracting a file member, @GNUTAR{} normally
5241 restores its permissions and modification times, as described in the
5242 previous sections. This cannot be done for directories, because
5243 after extracting a directory @command{tar} will almost certainly
5244 extract files into that directory and this will cause the directory
5245 modification time to be updated. Moreover, restoring that directory
5246 permissions may not permit file creation within it. Thus, restoring
5247 directory permissions and modification times must be delayed at least
5248 until all files have been extracted into that directory. @GNUTAR{}
5249 restores directories using the following approach.
5251 The extracted directories are created with the mode specified in the
5252 archive, as modified by the umask of the user, which gives sufficient
5253 permissions to allow file creation. The meta-information about the
5254 directory is recorded in the temporary list of directories. When
5255 preparing to extract next archive member, @GNUTAR{} checks if the
5256 directory prefix of this file contains the remembered directory. If
5257 it does not, the program assumes that all files have been extracted
5258 into that directory, restores its modification time and permissions
5259 and removes its entry from the internal list. This approach allows
5260 to correctly restore directory meta-information in the majority of
5261 cases, while keeping memory requirements sufficiently small. It is
5262 based on the fact, that most @command{tar} archives use the predefined
5263 order of members: first the directory, then all the files and
5264 subdirectories in that directory.
5266 However, this is not always true. The most important exception are
5267 incremental archives (@pxref{Incremental Dumps}). The member order in
5268 an incremental archive is reversed: first all directory members are
5269 stored, followed by other (non-directory) members. So, when extracting
5270 from incremental archives, @GNUTAR{} alters the above procedure. It
5271 remembers all restored directories, and restores their meta-data
5272 only after the entire archive has been processed. Notice, that you do
5273 not need to specify any special options for that, as @GNUTAR{}
5274 automatically detects archives in incremental format.
5276 There may be cases, when such processing is required for normal archives
5277 too. Consider the following example:
5281 $ @kbd{tar --no-recursion -cvf archive \
5282 foo foo/file1 bar bar/file foo/file2}
5291 During the normal operation, after encountering @file{bar}
5292 @GNUTAR{} will assume that all files from the directory @file{foo}
5293 were already extracted and will therefore restore its timestamp and
5294 permission bits. However, after extracting @file{foo/file2} the
5295 directory timestamp will be offset again.
5297 To correctly restore directory meta-information in such cases, use
5298 the @option{--delay-directory-restore} command line option:
5301 @opindex delay-directory-restore
5302 @item --delay-directory-restore
5303 Delays restoring of the modification times and permissions of extracted
5304 directories until the end of extraction. This way, correct
5305 meta-information is restored even if the archive has unusual member
5308 @opindex no-delay-directory-restore
5309 @item --no-delay-directory-restore
5310 Cancel the effect of the previous @option{--delay-directory-restore}.
5311 Use this option if you have used @option{--delay-directory-restore} in
5312 @env{TAR_OPTIONS} variable (@pxref{TAR_OPTIONS}) and wish to
5313 temporarily disable it.
5316 @node Writing to Standard Output
5317 @unnumberedsubsubsec Writing to Standard Output
5319 @cindex Writing extracted files to standard output
5320 @cindex Standard output, writing extracted files to
5321 To write the extracted files to the standard output, instead of
5322 creating the files on the file system, use @option{--to-stdout} (@option{-O}) in
5323 conjunction with @option{--extract} (@option{--get}, @option{-x}). This option is useful if you are
5324 extracting files to send them through a pipe, and do not need to
5325 preserve them in the file system. If you extract multiple members,
5326 they appear on standard output concatenated, in the order they are
5327 found in the archive.
5333 Writes files to the standard output. Use only in conjunction with
5334 @option{--extract} (@option{--get}, @option{-x}). When this option is
5335 used, instead of creating the files specified, @command{tar} writes
5336 the contents of the files extracted to its standard output. This may
5337 be useful if you are only extracting the files in order to send them
5338 through a pipe. This option is meaningless with @option{--list}
5342 This can be useful, for example, if you have a tar archive containing
5343 a big file and don't want to store the file on disk before processing
5344 it. You can use a command like this:
5347 tar -xOzf foo.tgz bigfile | process
5350 or even like this if you want to process the concatenation of the files:
5353 tar -xOzf foo.tgz bigfile1 bigfile2 | process
5356 However, @option{--to-command} may be more convenient for use with
5357 multiple files. See the next section.
5359 @node Writing to an External Program
5360 @unnumberedsubsubsec Writing to an External Program
5362 You can instruct @command{tar} to send the contents of each extracted
5363 file to the standard input of an external program:
5367 @item --to-command=@var{command}
5368 Extract files and pipe their contents to the standard input of
5369 @var{command}. When this option is used, instead of creating the
5370 files specified, @command{tar} invokes @var{command} and pipes the
5371 contents of the files to its standard output. The @var{command} may
5372 contain command line arguments. The program is executed via
5373 @code{sh -c}. Notice, that @var{command} is executed once for each regular file
5374 extracted. Non-regular files (directories, etc.) are ignored when this
5378 The command can obtain the information about the file it processes
5379 from the following environment variables:
5382 @vrindex TAR_FILETYPE, to-command environment
5384 Type of the file. It is a single letter with the following meaning:
5386 @multitable @columnfractions 0.10 0.90
5387 @item f @tab Regular file
5388 @item d @tab Directory
5389 @item l @tab Symbolic link
5390 @item h @tab Hard link
5391 @item b @tab Block device
5392 @item c @tab Character device
5395 Currently only regular files are supported.
5397 @vrindex TAR_MODE, to-command environment
5399 File mode, an octal number.
5401 @vrindex TAR_FILENAME, to-command environment
5403 The name of the file.
5405 @vrindex TAR_REALNAME, to-command environment
5407 Name of the file as stored in the archive.
5409 @vrindex TAR_UNAME, to-command environment
5411 Name of the file owner.
5413 @vrindex TAR_GNAME, to-command environment
5415 Name of the file owner group.
5417 @vrindex TAR_ATIME, to-command environment
5419 Time of last access. It is a decimal number, representing seconds
5420 since the Epoch. If the archive provides times with nanosecond
5421 precision, the nanoseconds are appended to the timestamp after a
5424 @vrindex TAR_MTIME, to-command environment
5426 Time of last modification.
5428 @vrindex TAR_CTIME, to-command environment
5430 Time of last status change.
5432 @vrindex TAR_SIZE, to-command environment
5436 @vrindex TAR_UID, to-command environment
5438 UID of the file owner.
5440 @vrindex TAR_GID, to-command environment
5442 GID of the file owner.
5445 Additionally, the following variables contain information about
5446 tar mode and the archive being processed:
5449 @vrindex TAR_VERSION, to-command environment
5451 @GNUTAR{} version number.
5453 @vrindex TAR_ARCHIVE, to-command environment
5455 The name of the archive @command{tar} is processing.
5457 @vrindex TAR_BLOCKING_FACTOR, to-command environment
5458 @item TAR_BLOCKING_FACTOR
5459 Current blocking factor (@pxref{Blocking}).
5461 @vrindex TAR_VOLUME, to-command environment
5463 Ordinal number of the volume @command{tar} is processing.
5465 @vrindex TAR_FORMAT, to-command environment
5467 Format of the archive being processed. @xref{Formats}, for a complete
5468 list of archive format names.
5471 If @var{command} exits with a non-0 status, @command{tar} will print
5472 an error message similar to the following:
5475 tar: 2345: Child returned status 1
5478 Here, @samp{2345} is the PID of the finished process.
5480 If this behavior is not wanted, use @option{--ignore-command-error}:
5483 @opindex ignore-command-error
5484 @item --ignore-command-error
5485 Ignore exit codes of subprocesses. Notice that if the program
5486 exits on signal or otherwise terminates abnormally, the error message
5487 will be printed even if this option is used.
5489 @opindex no-ignore-command-error
5490 @item --no-ignore-command-error
5491 Cancel the effect of any previous @option{--ignore-command-error}
5492 option. This option is useful if you have set
5493 @option{--ignore-command-error} in @env{TAR_OPTIONS}
5494 (@pxref{TAR_OPTIONS}) and wish to temporarily cancel it.
5498 @unnumberedsubsubsec Removing Files
5500 @FIXME{The section is too terse. Something more to add? An example,
5504 @opindex remove-files
5505 @item --remove-files
5506 Remove files after adding them to the archive.
5510 @subsection Coping with Scarce Resources
5513 @cindex Small memory
5514 @cindex Running out of space
5522 @unnumberedsubsubsec Starting File
5525 @opindex starting-file
5526 @item --starting-file=@var{name}
5527 @itemx -K @var{name}
5528 Starts an operation in the middle of an archive. Use in conjunction
5529 with @option{--extract} (@option{--get}, @option{-x}) or @option{--list} (@option{-t}).
5532 @cindex Middle of the archive, starting in the
5533 If a previous attempt to extract files failed due to lack of disk
5534 space, you can use @option{--starting-file=@var{name}} (@option{-K
5535 @var{name}}) to start extracting only after member @var{name} of the
5536 archive. This assumes, of course, that there is now free space, or
5537 that you are now extracting into a different file system. (You could
5538 also choose to suspend @command{tar}, remove unnecessary files from
5539 the file system, and then resume the same @command{tar} operation.
5540 In this case, @option{--starting-file} is not necessary.) See also
5541 @ref{interactive}, and @ref{exclude}.
5544 @unnumberedsubsubsec Same Order
5547 @cindex Large lists of file names on small machines
5549 @opindex preserve-order
5551 @itemx --preserve-order
5553 To process large lists of file names on machines with small amounts of
5554 memory. Use in conjunction with @option{--compare} (@option{--diff},
5555 @option{-d}), @option{--list} (@option{-t}) or @option{--extract}
5556 (@option{--get}, @option{-x}).
5559 The @option{--same-order} (@option{--preserve-order}, @option{-s}) option tells @command{tar} that the list of file
5560 names to be listed or extracted is sorted in the same order as the
5561 files in the archive. This allows a large list of names to be used,
5562 even on a small machine that would not otherwise be able to hold all
5563 the names in memory at the same time. Such a sorted list can easily be
5564 created by running @samp{tar -t} on the archive and editing its output.
5566 This option is probably never needed on modern computer systems.
5569 @section Backup options
5571 @cindex backup options
5573 @GNUTAR{} offers options for making backups of files
5574 before writing new versions. These options control the details of
5575 these backups. They may apply to the archive itself before it is
5576 created or rewritten, as well as individual extracted members. Other
5577 @acronym{GNU} programs (@command{cp}, @command{install}, @command{ln},
5578 and @command{mv}, for example) offer similar options.
5580 Backup options may prove unexpectedly useful when extracting archives
5581 containing many members having identical name, or when extracting archives
5582 on systems having file name limitations, making different members appear
5583 as having similar names through the side-effect of name truncation.
5584 @FIXME{This is true only if we have a good scheme for truncated backup names,
5585 which I'm not sure at all: I suspect work is needed in this area.}
5586 When any existing file is backed up before being overwritten by extraction,
5587 then clashing files are automatically be renamed to be unique, and the
5588 true name is kept for only the last file of a series of clashing files.
5589 By using verbose mode, users may track exactly what happens.
5591 At the detail level, some decisions are still experimental, and may
5592 change in the future, we are waiting comments from our users. So, please
5593 do not learn to depend blindly on the details of the backup features.
5594 For example, currently, directories themselves are never renamed through
5595 using these options, so, extracting a file over a directory still has
5596 good chances to fail. Also, backup options apply to created archives,
5597 not only to extracted members. For created archives, backups will not
5598 be attempted when the archive is a block or character device, or when it
5599 refers to a remote file.
5601 For the sake of simplicity and efficiency, backups are made by renaming old
5602 files prior to creation or extraction, and not by copying. The original
5603 name is restored if the file creation fails. If a failure occurs after a
5604 partial extraction of a file, both the backup and the partially extracted
5608 @item --backup[=@var{method}]
5610 @vindex VERSION_CONTROL
5612 Back up files that are about to be overwritten or removed.
5613 Without this option, the original versions are destroyed.
5615 Use @var{method} to determine the type of backups made.
5616 If @var{method} is not specified, use the value of the @env{VERSION_CONTROL}
5617 environment variable. And if @env{VERSION_CONTROL} is not set,
5618 use the @samp{existing} method.
5620 @vindex version-control @r{Emacs variable}
5621 This option corresponds to the Emacs variable @samp{version-control};
5622 the same values for @var{method} are accepted as in Emacs. This option
5623 also allows more descriptive names. The valid @var{method}s are:
5628 @cindex numbered @r{backup method}
5629 Always make numbered backups.
5633 @cindex existing @r{backup method}
5634 Make numbered backups of files that already have them, simple backups
5639 @cindex simple @r{backup method}
5640 Always make simple backups.
5644 @item --suffix=@var{suffix}
5646 @cindex backup suffix
5647 @vindex SIMPLE_BACKUP_SUFFIX
5648 Append @var{suffix} to each backup file made with @option{--backup}. If this
5649 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
5650 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
5651 set, the default is @samp{~}, just as in Emacs.
5656 @section Notable @command{tar} Usages
5659 @FIXME{Using Unix file linking capability to recreate directory
5660 structures---linking files into one subdirectory and then
5661 @command{tar}ring that directory.}
5663 @FIXME{Nice hairy example using absolute-names, newer, etc.}
5666 You can easily use archive files to transport a group of files from
5667 one system to another: put all relevant files into an archive on one
5668 computer system, transfer the archive to another system, and extract
5669 the contents there. The basic transfer medium might be magnetic tape,
5670 Internet FTP, or even electronic mail (though you must encode the
5671 archive with @command{uuencode} in order to transport it properly by
5672 mail). Both machines do not have to use the same operating system, as
5673 long as they both support the @command{tar} program.
5675 For example, here is how you might copy a directory's contents from
5676 one disk to another, while preserving the dates, modes, owners and
5677 link-structure of all the files therein. In this case, the transfer
5678 medium is a @dfn{pipe}:
5681 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
5685 You can avoid subshells by using @option{-C} option:
5688 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xf -}
5692 The command also works using long option forms:
5696 $ @kbd{(cd sourcedir; tar --create --file=- . ) \
5697 | (cd targetdir; tar --extract --file=-)}
5706 $ @kbd{tar --directory sourcedir --create --file=- . \
5707 | tar --directory targetdir --extract --file=-}
5712 This is one of the easiest methods to transfer a @command{tar} archive.
5715 @section Looking Ahead: The Rest of this Manual
5717 You have now seen how to use all eight of the operations available to
5718 @command{tar}, and a number of the possible options. The next chapter
5719 explains how to choose and change file and archive names, how to use
5720 files to store names of other files which you can then call as
5721 arguments to @command{tar} (this can help you save time if you expect to
5722 archive the same list of files a number of times), and so forth.
5723 @FIXME{in case it's not obvious, i'm making this up in some sense
5724 based on my limited memory of what the next chapter *really* does. i
5725 just wanted to flesh out this final section a little bit so i'd
5726 remember to stick it in here. :-)}
5728 If there are too many files to conveniently list on the command line,
5729 you can list the names in a file, and @command{tar} will read that file.
5732 There are various ways of causing @command{tar} to skip over some files,
5733 and not archive them. @xref{Choosing}.
5736 @chapter Performing Backups and Restoring Files
5739 @GNUTAR{} is distributed along with the scripts for performing backups
5740 and restores. Even if there is a good chance those scripts may be
5741 satisfying to you, they are not the only scripts or methods available for doing
5742 backups and restore. You may well create your own, or use more
5743 sophisticated packages dedicated to that purpose.
5745 Some users are enthusiastic about @code{Amanda} (The Advanced Maryland
5746 Automatic Network Disk Archiver), a backup system developed by James
5747 da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
5748 This is free software, and it is available from @uref{http://www.amanda.org}.
5752 Here is a possible plan for a future documentation about the backuping
5753 scripts which are provided within the @GNUTAR{}
5759 @item what are dumps
5760 @item different levels of dumps
5762 @item full dump = dump everything
5763 @item level 1, level 2 dumps etc
5764 A level @var{n} dump dumps everything changed since the last level
5767 @item how to use scripts for dumps (ie, the concept)
5769 @item scripts to run after editing backup specs (details)
5771 @item Backup Specs, what is it.
5773 @item how to customize
5774 @item actual text of script [/sp/dump/backup-specs]
5778 @item rsh doesn't work
5779 @item rtape isn't installed
5782 @item the @option{--incremental} option of tar
5785 @item write protection
5786 @item types of media, different sizes and types, useful for different things
5787 @item files and tape marks
5788 one tape mark between files, two at end.
5789 @item positioning the tape
5790 MT writes two at end of write,
5791 backspaces over one when writing again.
5797 This chapter documents both the provided shell scripts and @command{tar}
5798 options which are more specific to usage as a backup tool.
5800 To @dfn{back up} a file system means to create archives that contain
5801 all the files in that file system. Those archives can then be used to
5802 restore any or all of those files (for instance if a disk crashes or a
5803 file is accidentally deleted). File system @dfn{backups} are also
5807 * Full Dumps:: Using @command{tar} to Perform Full Dumps
5808 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
5809 * Backup Levels:: Levels of Backups
5810 * Backup Parameters:: Setting Parameters for Backups and Restoration
5811 * Scripted Backups:: Using the Backup Scripts
5812 * Scripted Restoration:: Using the Restore Script
5816 @section Using @command{tar} to Perform Full Dumps
5822 @cindex corrupted archives
5823 Full dumps should only be made when no other people or programs
5824 are modifying files in the file system. If files are modified while
5825 @command{tar} is making the backup, they may not be stored properly in
5826 the archive, in which case you won't be able to restore them if you
5827 have to. (Files not being modified are written with no trouble, and do
5828 not corrupt the entire archive.)
5830 You will want to use the @option{--label=@var{archive-label}}
5831 (@option{-V @var{archive-label}}) option to give the archive a
5832 volume label, so you can tell what this archive is even if the label
5833 falls off the tape, or anything like that.
5835 Unless the file system you are dumping is guaranteed to fit on
5836 one volume, you will need to use the @option{--multi-volume} (@option{-M}) option.
5837 Make sure you have enough tapes on hand to complete the backup.
5839 If you want to dump each file system separately you will need to use
5840 the @option{--one-file-system} option to prevent
5841 @command{tar} from crossing file system boundaries when storing
5844 The @option{--incremental} (@option{-G}) (@pxref{Incremental Dumps})
5845 option is not needed, since this is a complete copy of everything in
5846 the file system, and a full restore from this backup would only be
5847 done onto a completely
5850 Unless you are in a hurry, and trust the @command{tar} program (and your
5851 tapes), it is a good idea to use the @option{--verify} (@option{-W})
5852 option, to make sure your files really made it onto the dump properly.
5853 This will also detect cases where the file was modified while (or just
5854 after) it was being archived. Not all media (notably cartridge tapes)
5855 are capable of being verified, unfortunately.
5857 @node Incremental Dumps
5858 @section Using @command{tar} to Perform Incremental Dumps
5860 @dfn{Incremental backup} is a special form of @GNUTAR{} archive that
5861 stores additional metadata so that exact state of the file system
5862 can be restored when extracting the archive.
5864 @GNUTAR{} currently offers two options for handling incremental
5865 backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
5866 @var{snapshot-file}}) and @option{--incremental} (@option{-G}).
5868 @xopindex{listed-incremental, described}
5869 The option @option{--listed-incremental} instructs tar to operate on
5870 an incremental archive with additional metadata stored in a standalone
5871 file, called a @dfn{snapshot file}. The purpose of this file is to help
5872 determine which files have been changed, added or deleted since the
5873 last backup, so that the next incremental backup will contain only
5874 modified files. The name of the snapshot file is given as an argument
5878 @item --listed-incremental=@var{file}
5879 @itemx -g @var{file}
5880 Handle incremental backups with snapshot data in @var{file}.
5883 To create an incremental backup, you would use
5884 @option{--listed-incremental} together with @option{--create}
5885 (@pxref{create}). For example:
5888 $ @kbd{tar --create \
5889 --file=archive.1.tar \
5890 --listed-incremental=/var/log/usr.snar \
5894 This will create in @file{archive.1.tar} an incremental backup of
5895 the @file{/usr} file system, storing additional metadata in the file
5896 @file{/var/log/usr.snar}. If this file does not exist, it will be
5897 created. The created archive will then be a @dfn{level 0 backup};
5898 please see the next section for more on backup levels.
5900 Otherwise, if the file @file{/var/log/usr.snar} exists, it
5901 determines which files are modified. In this case only these files will be
5902 stored in the archive. Suppose, for example, that after running the
5903 above command, you delete file @file{/usr/doc/old} and create
5904 directory @file{/usr/local/db} with the following contents:
5907 $ @kbd{ls /usr/local/db}
5912 Some time later you create another incremental backup. You will
5916 $ @kbd{tar --create \
5917 --file=archive.2.tar \
5918 --listed-incremental=/var/log/usr.snar \
5920 tar: usr/local/db: Directory is new
5927 The created archive @file{archive.2.tar} will contain only these
5928 three members. This archive is called a @dfn{level 1 backup}. Notice
5929 that @file{/var/log/usr.snar} will be updated with the new data, so if
5930 you plan to create more @samp{level 1} backups, it is necessary to
5931 create a working copy of the snapshot file before running
5932 @command{tar}. The above example will then be modified as follows:
5935 $ @kbd{cp /var/log/usr.snar /var/log/usr.snar-1}
5936 $ @kbd{tar --create \
5937 --file=archive.2.tar \
5938 --listed-incremental=/var/log/usr.snar-1 \
5943 @xopindex{level, described}
5944 You can force @samp{level 0} backups either by removing the snapshot
5945 file before running @command{tar}, or by supplying the
5946 @option{--level=0} option, e.g.:
5949 $ @kbd{tar --create \
5950 --file=archive.2.tar \
5951 --listed-incremental=/var/log/usr.snar-0 \
5956 Incremental dumps depend crucially on time stamps, so the results are
5957 unreliable if you modify a file's time stamps during dumping (e.g.,
5958 with the @option{--atime-preserve=replace} option), or if you set the clock
5961 @anchor{device numbers}
5962 @cindex Device numbers, using in incremental backups
5963 Metadata stored in snapshot files include device numbers, which,
5964 obviously are supposed to be non-volatile values. However, it turns
5965 out that @acronym{NFS} devices have undependable values when an automounter
5966 gets in the picture. This can lead to a great deal of spurious
5967 redumping in incremental dumps, so it is somewhat useless to compare
5968 two @acronym{NFS} devices numbers over time. The solution implemented
5969 currently is to consider all @acronym{NFS} devices as being equal
5970 when it comes to comparing directories; this is fairly gross, but
5971 there does not seem to be a better way to go.
5973 Apart from using @acronym{NFS}, there are a number of cases where
5974 relying on device numbers can cause spurious redumping of unmodified
5975 files. For example, this occurs when archiving @acronym{LVM} snapshot
5976 volumes. To avoid this, use @option{--no-check-device} option:
5979 @xopindex{no-check-device, described}
5980 @item --no-check-device
5981 Do not rely on device numbers when preparing a list of changed files
5982 for an incremental dump.
5984 @xopindex{check-device, described}
5985 @item --check-device
5986 Use device numbers when preparing a list of changed files
5987 for an incremental dump. This is the default behavior. The purpose
5988 of this option is to undo the effect of the @option{--no-check-device}
5989 if it was given in @env{TAR_OPTIONS} environment variable
5990 (@pxref{TAR_OPTIONS}).
5993 There is also another way to cope with changing device numbers. It is
5994 described in detail in @ref{Fixing Snapshot Files}.
5996 Note that incremental archives use @command{tar} extensions and may
5997 not be readable by non-@acronym{GNU} versions of the @command{tar} program.
5999 @xopindex{listed-incremental, using with @option{--extract}}
6000 @xopindex{extract, using with @option{--listed-incremental}}
6001 To extract from the incremental dumps, use
6002 @option{--listed-incremental} together with @option{--extract}
6003 option (@pxref{extracting files}). In this case, @command{tar} does
6004 not need to access snapshot file, since all the data necessary for
6005 extraction are stored in the archive itself. So, when extracting, you
6006 can give whatever argument to @option{--listed-incremental}, the usual
6007 practice is to use @option{--listed-incremental=/dev/null}.
6008 Alternatively, you can use @option{--incremental}, which needs no
6009 arguments. In general, @option{--incremental} (@option{-G}) can be
6010 used as a shortcut for @option{--listed-incremental} when listing or
6011 extracting incremental backups (for more information regarding this
6012 option, @pxref{incremental-op}).
6014 When extracting from the incremental backup @GNUTAR{} attempts to
6015 restore the exact state the file system had when the archive was
6016 created. In particular, it will @emph{delete} those files in the file
6017 system that did not exist in their directories when the archive was
6018 created. If you have created several levels of incremental files,
6019 then in order to restore the exact contents the file system had when
6020 the last level was created, you will need to restore from all backups
6021 in turn. Continuing our example, to restore the state of @file{/usr}
6022 file system, one would do@footnote{Notice, that since both archives
6023 were created without @option{-P} option (@pxref{absolute}), these
6024 commands should be run from the root file system.}:
6027 $ @kbd{tar --extract \
6028 --listed-incremental=/dev/null \
6029 --file archive.1.tar}
6030 $ @kbd{tar --extract \
6031 --listed-incremental=/dev/null \
6032 --file archive.2.tar}
6035 To list the contents of an incremental archive, use @option{--list}
6036 (@pxref{list}), as usual. To obtain more information about the
6037 archive, use @option{--listed-incremental} or @option{--incremental}
6038 combined with two @option{--verbose} options@footnote{Two
6039 @option{--verbose} options were selected to avoid breaking usual
6040 verbose listing output (@option{--list --verbose}) when using in
6043 @xopindex{incremental, using with @option{--list}}
6044 @xopindex{listed-incremental, using with @option{--list}}
6045 @xopindex{list, using with @option{--incremental}}
6046 @xopindex{list, using with @option{--listed-incremental}}
6047 Versions of @GNUTAR{} up to 1.15.1 used to dump verbatim binary
6048 contents of the DUMPDIR header (with terminating nulls) when
6049 @option{--incremental} or @option{--listed-incremental} option was
6050 given, no matter what the verbosity level. This behavior, and,
6051 especially, the binary output it produced were considered inconvenient
6052 and were changed in version 1.16.}:
6055 @kbd{tar --list --incremental --verbose --verbose archive.tar}
6058 This command will print, for each directory in the archive, the list
6059 of files in that directory at the time the archive was created. This
6060 information is put out in a format which is both human-readable and
6061 unambiguous for a program: each file name is printed as
6068 where @var{x} is a letter describing the status of the file: @samp{Y}
6069 if the file is present in the archive, @samp{N} if the file is not
6070 included in the archive, or a @samp{D} if the file is a directory (and
6071 is included in the archive). @xref{Dumpdir}, for the detailed
6072 description of dumpdirs and status codes. Each such
6073 line is terminated by a newline character. The last line is followed
6074 by an additional newline to indicate the end of the data.
6076 @anchor{incremental-op}The option @option{--incremental} (@option{-G})
6077 gives the same behavior as @option{--listed-incremental} when used
6078 with @option{--list} and @option{--extract} options. When used with
6079 @option{--create} option, it creates an incremental archive without
6080 creating snapshot file. Thus, it is impossible to create several
6081 levels of incremental backups with @option{--incremental} option.
6084 @section Levels of Backups
6086 An archive containing all the files in the file system is called a
6087 @dfn{full backup} or @dfn{full dump}. You could insure your data by
6088 creating a full dump every day. This strategy, however, would waste a
6089 substantial amount of archive media and user time, as unchanged files
6090 are daily re-archived.
6092 It is more efficient to do a full dump only occasionally. To back up
6093 files between full dumps, you can use @dfn{incremental dumps}. A @dfn{level
6094 one} dump archives all the files that have changed since the last full
6097 A typical dump strategy would be to perform a full dump once a week,
6098 and a level one dump once a day. This means some versions of files
6099 will in fact be archived more than once, but this dump strategy makes
6100 it possible to restore a file system to within one day of accuracy by
6101 only extracting two archives---the last weekly (full) dump and the
6102 last daily (level one) dump. The only information lost would be in
6103 files changed or created since the last daily backup. (Doing dumps
6104 more than once a day is usually not worth the trouble.)
6106 @GNUTAR{} comes with scripts you can use to do full
6107 and level-one (actually, even level-two and so on) dumps. Using
6108 scripts (shell programs) to perform backups and restoration is a
6109 convenient and reliable alternative to typing out file name lists
6110 and @command{tar} commands by hand.
6112 Before you use these scripts, you need to edit the file
6113 @file{backup-specs}, which specifies parameters used by the backup
6114 scripts and by the restore script. This file is usually located
6115 in @file{/etc/backup} directory. @xref{Backup Parameters}, for its
6116 detailed description. Once the backup parameters are set, you can
6117 perform backups or restoration by running the appropriate script.
6119 The name of the backup script is @code{backup}. The name of the
6120 restore script is @code{restore}. The following sections describe
6121 their use in detail.
6123 @emph{Please Note:} The backup and restoration scripts are
6124 designed to be used together. While it is possible to restore files by
6125 hand from an archive which was created using a backup script, and to create
6126 an archive by hand which could then be extracted using the restore script,
6127 it is easier to use the scripts. @xref{Incremental Dumps}, before
6128 making such an attempt.
6130 @node Backup Parameters
6131 @section Setting Parameters for Backups and Restoration
6133 The file @file{backup-specs} specifies backup parameters for the
6134 backup and restoration scripts provided with @command{tar}. You must
6135 edit @file{backup-specs} to fit your system configuration and schedule
6136 before using these scripts.
6138 Syntactically, @file{backup-specs} is a shell script, containing
6139 mainly variable assignments. However, any valid shell construct
6140 is allowed in this file. Particularly, you may wish to define
6141 functions within that script (e.g., see @code{RESTORE_BEGIN} below).
6142 For more information about shell script syntax, please refer to
6143 @url{http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
6144 g_02, the definition of the Shell Command Language}. See also
6145 @ref{Top,,Bash Features,bashref,Bash Reference Manual}.
6147 The shell variables controlling behavior of @code{backup} and
6148 @code{restore} are described in the following subsections.
6151 * General-Purpose Variables::
6152 * Magnetic Tape Control::
6154 * backup-specs example:: An Example Text of @file{Backup-specs}
6157 @node General-Purpose Variables
6158 @subsection General-Purpose Variables
6160 @defvr {Backup variable} ADMINISTRATOR
6161 The user name of the backup administrator. @code{Backup} scripts
6162 sends a backup report to this address.
6165 @defvr {Backup variable} BACKUP_HOUR
6166 The hour at which the backups are done. This can be a number from 0
6167 to 23, or the time specification in form @var{hours}:@var{minutes},
6168 or the string @samp{now}.
6170 This variable is used by @code{backup}. Its value may be overridden
6171 using @option{--time} option (@pxref{Scripted Backups}).
6174 @defvr {Backup variable} TAPE_FILE
6176 The device @command{tar} writes the archive to. If @var{TAPE_FILE}
6177 is a remote archive (@pxref{remote-dev}), backup script will suppose
6178 that your @command{mt} is able to access remote devices. If @var{RSH}
6179 (@pxref{RSH}) is set, @option{--rsh-command} option will be added to
6180 invocations of @command{mt}.
6183 @defvr {Backup variable} BLOCKING
6185 The blocking factor @command{tar} will use when writing the dump archive.
6186 @xref{Blocking Factor}.
6189 @defvr {Backup variable} BACKUP_DIRS
6191 A list of file systems to be dumped (for @code{backup}), or restored
6192 (for @code{restore}). You can include any directory
6193 name in the list --- subdirectories on that file system will be
6194 included, regardless of how they may look to other networked machines.
6195 Subdirectories on other file systems will be ignored.
6197 The host name specifies which host to run @command{tar} on, and should
6198 normally be the host that actually contains the file system. However,
6199 the host machine must have @GNUTAR{} installed, and
6200 must be able to access the directory containing the backup scripts and
6201 their support files using the same file name that is used on the
6202 machine where the scripts are run (i.e., what @command{pwd} will print
6203 when in that directory on that machine). If the host that contains
6204 the file system does not have this capability, you can specify another
6205 host as long as it can access the file system through @acronym{NFS}.
6207 If the list of file systems is very long you may wish to put it
6208 in a separate file. This file is usually named
6209 @file{/etc/backup/dirs}, but this name may be overridden in
6210 @file{backup-specs} using @code{DIRLIST} variable.
6213 @defvr {Backup variable} DIRLIST
6215 The name of the file that contains a list of file systems to backup
6216 or restore. By default it is @file{/etc/backup/dirs}.
6219 @defvr {Backup variable} BACKUP_FILES
6221 A list of individual files to be dumped (for @code{backup}), or restored
6222 (for @code{restore}). These should be accessible from the machine on
6223 which the backup script is run.
6225 If the list of individual files is very long you may wish to store it
6226 in a separate file. This file is usually named
6227 @file{/etc/backup/files}, but this name may be overridden in
6228 @file{backup-specs} using @code{FILELIST} variable.
6231 @defvr {Backup variable} FILELIST
6233 The name of the file that contains a list of individual files to backup
6234 or restore. By default it is @file{/etc/backup/files}.
6237 @defvr {Backup variable} MT
6239 Full file name of @command{mt} binary.
6242 @defvr {Backup variable} RSH
6244 Full file name of @command{rsh} binary or its equivalent. You may wish to
6245 set it to @code{ssh}, to improve security. In this case you will have
6246 to use public key authentication.
6249 @defvr {Backup variable} RSH_COMMAND
6251 Full file name of @command{rsh} binary on remote machines. This will
6252 be passed via @option{--rsh-command} option to the remote invocation
6256 @defvr {Backup variable} VOLNO_FILE
6258 Name of temporary file to hold volume numbers. This needs to be accessible
6259 by all the machines which have file systems to be dumped.
6262 @defvr {Backup variable} XLIST
6264 Name of @dfn{exclude file list}. An @dfn{exclude file list} is a file
6265 located on the remote machine and containing the list of files to
6266 be excluded from the backup. Exclude file lists are searched in
6267 /etc/tar-backup directory. A common use for exclude file lists
6268 is to exclude files containing security-sensitive information
6269 (e.g., @file{/etc/shadow} from backups).
6271 This variable affects only @code{backup}.
6274 @defvr {Backup variable} SLEEP_TIME
6276 Time to sleep between dumps of any two successive file systems
6278 This variable affects only @code{backup}.
6281 @defvr {Backup variable} DUMP_REMIND_SCRIPT
6283 Script to be run when it's time to insert a new tape in for the next
6284 volume. Administrators may want to tailor this script for their site.
6285 If this variable isn't set, @GNUTAR{} will display its built-in
6286 prompt, and will expect confirmation from the console. For the
6287 description of the default prompt, see @ref{change volume prompt}.
6291 @defvr {Backup variable} SLEEP_MESSAGE
6293 Message to display on the terminal while waiting for dump time. Usually
6294 this will just be some literal text.
6297 @defvr {Backup variable} TAR
6299 Full file name of the @GNUTAR{} executable. If this is not set, backup
6300 scripts will search @command{tar} in the current shell path.
6303 @node Magnetic Tape Control
6304 @subsection Magnetic Tape Control
6306 Backup scripts access tape device using special @dfn{hook functions}.
6307 These functions take a single argument --- the name of the tape
6308 device. Their names are kept in the following variables:
6310 @defvr {Backup variable} MT_BEGIN
6311 The name of @dfn{begin} function. This function is called before
6312 accessing the drive. By default it retensions the tape:
6318 mt -f "$1" retension
6323 @defvr {Backup variable} MT_REWIND
6324 The name of @dfn{rewind} function. The default definition is as
6337 @defvr {Backup variable} MT_OFFLINE
6338 The name of the function switching the tape off line. By default
6339 it is defined as follows:
6342 MT_OFFLINE=mt_offline
6350 @defvr {Backup variable} MT_STATUS
6351 The name of the function used to obtain the status of the archive device,
6352 including error count. Default definition:
6364 @subsection User Hooks
6366 @dfn{User hooks} are shell functions executed before and after
6367 each @command{tar} invocation. Thus, there are @dfn{backup
6368 hooks}, which are executed before and after dumping each file
6369 system, and @dfn{restore hooks}, executed before and
6370 after restoring a file system. Each user hook is a shell function
6371 taking four arguments:
6373 @deffn {User Hook Function} hook @var{level} @var{host} @var{fs} @var{fsname}
6378 Current backup or restore level.
6381 Name or IP address of the host machine being dumped or restored.
6384 Full file name of the file system being dumped or restored.
6387 File system name with directory separators replaced with colons. This
6388 is useful, e.g., for creating unique files.
6392 Following variables keep the names of user hook functions:
6394 @defvr {Backup variable} DUMP_BEGIN
6395 Dump begin function. It is executed before dumping the file system.
6398 @defvr {Backup variable} DUMP_END
6399 Executed after dumping the file system.
6402 @defvr {Backup variable} RESTORE_BEGIN
6403 Executed before restoring the file system.
6406 @defvr {Backup variable} RESTORE_END
6407 Executed after restoring the file system.
6410 @node backup-specs example
6411 @subsection An Example Text of @file{Backup-specs}
6413 The following is an example of @file{backup-specs}:
6416 # site-specific parameters for file system backup.
6418 ADMINISTRATOR=friedman
6420 TAPE_FILE=/dev/nrsmt0
6422 # Use @code{ssh} instead of the less secure @code{rsh}
6424 RSH_COMMAND=/usr/bin/ssh
6426 # Override MT_STATUS function:
6432 # Disable MT_OFFLINE function
6449 apple-gunkies:/com/mailer/gnu
6450 apple-gunkies:/com/archive/gnu"
6452 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
6456 @node Scripted Backups
6457 @section Using the Backup Scripts
6459 The syntax for running a backup script is:
6462 backup --level=@var{level} --time=@var{time}
6465 The @option{--level} option requests the dump level. Thus, to produce
6466 a full dump, specify @code{--level=0} (this is the default, so
6467 @option{--level} may be omitted if its value is
6468 @code{0})@footnote{For backward compatibility, the @code{backup} will also
6469 try to deduce the requested dump level from the name of the
6470 script itself. If the name consists of a string @samp{level-}
6471 followed by a single decimal digit, that digit is taken as
6472 the dump level number. Thus, you may create a link from @code{backup}
6473 to @code{level-1} and then run @code{level-1} whenever you need to
6474 create a level one dump.}.
6476 The @option{--time} option determines when should the backup be
6477 run. @var{Time} may take three forms:
6480 @item @var{hh}:@var{mm}
6482 The dump must be run at @var{hh} hours @var{mm} minutes.
6486 The dump must be run at @var{hh} hours.
6490 The dump must be run immediately.
6493 You should start a script with a tape or disk mounted. Once you
6494 start a script, it prompts you for new tapes or disks as it
6495 needs them. Media volumes don't have to correspond to archive
6496 files --- a multi-volume archive can be started in the middle of a
6497 tape that already contains the end of another multi-volume archive.
6498 The @code{restore} script prompts for media by its archive volume,
6499 so to avoid an error message you should keep track of which tape
6500 (or disk) contains which volume of the archive (@pxref{Scripted
6503 The backup scripts write two files on the file system. The first is a
6504 record file in @file{/etc/tar-backup/}, which is used by the scripts
6505 to store and retrieve information about which files were dumped. This
6506 file is not meant to be read by humans, and should not be deleted by
6507 them. @xref{Snapshot Files}, for a more detailed explanation of this
6510 The second file is a log file containing the names of the file systems
6511 and files dumped, what time the backup was made, and any error
6512 messages that were generated, as well as how much space was left in
6513 the media volume after the last volume of the archive was written.
6514 You should check this log file after every backup. The file name is
6515 @file{log-@var{mm-dd-yyyy}-level-@var{n}}, where @var{mm-dd-yyyy}
6516 represents current date, and @var{n} represents current dump level number.
6518 The script also prints the name of each system being dumped to the
6521 Following is the full list of options accepted by @code{backup}
6525 @item -l @var{level}
6526 @itemx --level=@var{level}
6527 Do backup level @var{level} (default 0).
6531 Force backup even if today's log file already exists.
6533 @item -v[@var{level}]
6534 @itemx --verbose[=@var{level}]
6535 Set verbosity level. The higher the level is, the more debugging
6536 information will be output during execution. Default @var{level}
6537 is 100, which means the highest debugging level.
6539 @item -t @var{start-time}
6540 @itemx --time=@var{start-time}
6541 Wait till @var{time}, then do backup.
6545 Display short help message and exit.
6549 Display information about the program's name, version, origin and legal
6550 status, all on standard output, and then exit successfully.
6554 @node Scripted Restoration
6555 @section Using the Restore Script
6557 To restore files that were archived using a scripted backup, use the
6558 @code{restore} script. Its usage is quite straightforward. In the
6559 simplest form, invoke @code{restore --all}, it will
6560 then restore all the file systems and files specified in
6561 @file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
6563 You may select the file systems (and/or files) to restore by
6564 giving @code{restore} a list of @dfn{patterns} in its command
6565 line. For example, running
6572 will restore all file systems on the machine @samp{albert}. A more
6573 complicated example:
6576 restore 'albert:*' '*:/var'
6580 This command will restore all file systems on the machine @samp{albert}
6581 as well as @file{/var} file system on all machines.
6583 By default @code{restore} will start restoring files from the lowest
6584 available dump level (usually zero) and will continue through
6585 all available dump levels. There may be situations where such a
6586 thorough restore is not necessary. For example, you may wish to
6587 restore only files from the recent level one backup. To do so,
6588 use @option{--level} option, as shown in the example below:
6594 The full list of options accepted by @code{restore} follows:
6599 Restore all file systems and files specified in @file{backup-specs}.
6601 @item -l @var{level}
6602 @itemx --level=@var{level}
6603 Start restoring from the given backup level, instead of the default 0.
6605 @item -v[@var{level}]
6606 @itemx --verbose[=@var{level}]
6607 Set verbosity level. The higher the level is, the more debugging
6608 information will be output during execution. Default @var{level}
6609 is 100, which means the highest debugging level.
6613 Display short help message and exit.
6617 Display information about the program's name, version, origin and legal
6618 status, all on standard output, and then exit successfully.
6621 You should start the restore script with the media containing the
6622 first volume of the archive mounted. The script will prompt for other
6623 volumes as they are needed. If the archive is on tape, you don't need
6624 to rewind the tape to to its beginning---if the tape head is
6625 positioned past the beginning of the archive, the script will rewind
6626 the tape as needed. @xref{Tape Positioning}, for a discussion of tape
6630 @strong{Warning:} The script will delete files from the active file
6631 system if they were not in the file system when the archive was made.
6634 @xref{Incremental Dumps}, for an explanation of how the script makes
6638 @chapter Choosing Files and Names for @command{tar}
6640 Certain options to @command{tar} enable you to specify a name for your
6641 archive. Other options let you decide which files to include or exclude
6642 from the archive, based on when or whether files were modified, whether
6643 the file names do or don't match specified patterns, or whether files
6644 are in specified directories.
6646 This chapter discusses these options in detail.
6649 * file:: Choosing the Archive's Name
6650 * Selecting Archive Members::
6651 * files:: Reading Names from a File
6652 * exclude:: Excluding Some Files
6653 * wildcards:: Wildcards Patterns and Matching
6654 * quoting styles:: Ways of Quoting Special Characters in Names
6655 * transform:: Modifying File and Member Names
6656 * after:: Operating Only on New Files
6657 * recurse:: Descending into Directories
6658 * one:: Crossing File System Boundaries
6662 @section Choosing and Naming Archive Files
6664 @cindex Naming an archive
6665 @cindex Archive Name
6666 @cindex Choosing an archive file
6667 @cindex Where is the archive?
6669 By default, @command{tar} uses an archive file name that was compiled when
6670 it was built on the system; usually this name refers to some physical
6671 tape drive on the machine. However, the person who installed @command{tar}
6672 on the system may not have set the default to a meaningful value as far as
6673 most users are concerned. As a result, you will usually want to tell
6674 @command{tar} where to find (or create) the archive. The
6675 @option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
6676 option allows you to either specify or name a file to use as the archive
6677 instead of the default archive file location.
6680 @xopindex{file, short description}
6681 @item --file=@var{archive-name}
6682 @itemx -f @var{archive-name}
6683 Name the archive to create or operate on. Use in conjunction with
6687 For example, in this @command{tar} command,
6690 $ @kbd{tar -cvf collection.tar blues folk jazz}
6694 @file{collection.tar} is the name of the archive. It must directly
6695 follow the @option{-f} option, since whatever directly follows @option{-f}
6696 @emph{will} end up naming the archive. If you neglect to specify an
6697 archive name, you may end up overwriting a file in the working directory
6698 with the archive you create since @command{tar} will use this file's name
6699 for the archive name.
6701 An archive can be saved as a file in the file system, sent through a
6702 pipe or over a network, or written to an I/O device such as a tape,
6703 floppy disk, or CD write drive.
6705 @cindex Writing new archives
6706 @cindex Archive creation
6707 If you do not name the archive, @command{tar} uses the value of the
6708 environment variable @env{TAPE} as the file name for the archive. If
6709 that is not available, @command{tar} uses a default, compiled-in archive
6710 name, usually that for tape unit zero (i.e., @file{/dev/tu00}).
6712 @cindex Standard input and output
6713 @cindex tar to standard input and output
6714 If you use @file{-} as an @var{archive-name}, @command{tar} reads the
6715 archive from standard input (when listing or extracting files), or
6716 writes it to standard output (when creating an archive). If you use
6717 @file{-} as an @var{archive-name} when modifying an archive,
6718 @command{tar} reads the original archive from its standard input and
6719 writes the entire new archive to its standard output.
6721 The following example is a convenient way of copying directory
6722 hierarchy from @file{sourcedir} to @file{targetdir}.
6725 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)}
6728 The @option{-C} option allows to avoid using subshells:
6731 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xpf -}
6734 In both examples above, the leftmost @command{tar} invocation archives
6735 the contents of @file{sourcedir} to the standard output, while the
6736 rightmost one reads this archive from its standard input and
6737 extracts it. The @option{-p} option tells it to restore permissions
6738 of the extracted files.
6740 @cindex Remote devices
6741 @cindex tar to a remote device
6743 To specify an archive file on a device attached to a remote machine,
6747 @kbd{--file=@var{hostname}:/@var{dev}/@var{file-name}}
6751 @command{tar} will set up the remote connection, if possible, and
6752 prompt you for a username and password. If you use
6753 @option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
6754 will attempt to set up the remote connection using your username
6755 as the username on the remote machine.
6757 @cindex Local and remote archives
6758 @anchor{local and remote archives}
6759 If the archive file name includes a colon (@samp{:}), then it is assumed
6760 to be a file on another machine. If the archive file is
6761 @samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the
6762 host @var{host}. The remote host is accessed using the @command{rsh}
6763 program, with a username of @var{user}. If the username is omitted
6764 (along with the @samp{@@} sign), then your user name will be used.
6765 (This is the normal @command{rsh} behavior.) It is necessary for the
6766 remote machine, in addition to permitting your @command{rsh} access, to
6767 have the @file{rmt} program installed (this command is included in
6768 the @GNUTAR{} distribution and by default is installed under
6769 @file{@var{prefix}/libexec/rmt}, where @var{prefix} means your
6770 installation prefix). If you need to use a file whose name includes a
6771 colon, then the remote tape drive behavior
6772 can be inhibited by using the @option{--force-local} option.
6774 When the archive is being created to @file{/dev/null}, @GNUTAR{}
6775 tries to minimize input and output operations. The Amanda backup
6776 system, when used with @GNUTAR{}, has an initial sizing pass which
6779 @node Selecting Archive Members
6780 @section Selecting Archive Members
6781 @cindex Specifying files to act on
6782 @cindex Specifying archive members
6784 @dfn{File Name arguments} specify which files in the file system
6785 @command{tar} operates on, when creating or adding to an archive, or which
6786 archive members @command{tar} operates on, when reading or deleting from
6787 an archive. @xref{Operations}.
6789 To specify file names, you can include them as the last arguments on
6790 the command line, as follows:
6792 @kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
6795 If a file name begins with dash (@samp{-}), precede it with
6796 @option{--add-file} option to prevent it from being treated as an
6799 @anchor{input name quoting}
6800 By default @GNUTAR{} attempts to @dfn{unquote} each file or member
6801 name, replacing @dfn{escape sequences} according to the following
6804 @multitable @columnfractions 0.20 0.60
6805 @headitem Escape @tab Replaced with
6806 @item \a @tab Audible bell (@acronym{ASCII} 7)
6807 @item \b @tab Backspace (@acronym{ASCII} 8)
6808 @item \f @tab Form feed (@acronym{ASCII} 12)
6809 @item \n @tab New line (@acronym{ASCII} 10)
6810 @item \r @tab Carriage return (@acronym{ASCII} 13)
6811 @item \t @tab Horizontal tabulation (@acronym{ASCII} 9)
6812 @item \v @tab Vertical tabulation (@acronym{ASCII} 11)
6813 @item \? @tab @acronym{ASCII} 127
6814 @item \@var{n} @tab @acronym{ASCII} @var{n} (@var{n} should be an octal number
6818 A backslash followed by any other symbol is retained.
6820 This default behavior is controlled by the following command line
6826 Enable unquoting input file or member names (default).
6830 Disable unquoting input file or member names.
6833 If you specify a directory name as a file name argument, all the files
6834 in that directory are operated on by @command{tar}.
6836 If you do not specify files, @command{tar} behavior differs depending
6837 on the operation mode as described below:
6839 When @command{tar} is invoked with @option{--create} (@option{-c}),
6840 @command{tar} will stop immediately, reporting the following:
6844 $ @kbd{tar cf a.tar}
6845 tar: Cowardly refusing to create an empty archive
6846 Try `tar --help' or `tar --usage' for more information.
6850 If you specify either @option{--list} (@option{-t}) or
6851 @option{--extract} (@option{--get}, @option{-x}), @command{tar}
6852 operates on all the archive members in the archive.
6854 If run with @option{--diff} option, tar will compare the archive with
6855 the contents of the current working directory.
6857 If you specify any other operation, @command{tar} does nothing.
6859 By default, @command{tar} takes file names from the command line. However,
6860 there are other ways to specify file or member names, or to modify the
6861 manner in which @command{tar} selects the files or members upon which to
6862 operate. In general, these methods work both for specifying the names
6863 of files and archive members.
6866 @section Reading Names from a File
6868 @cindex Reading file names from a file
6869 @cindex Lists of file names
6870 @cindex File Name arguments, alternatives
6871 @cindex @command{find}, using with @command{tar}
6872 Instead of giving the names of files or archive members on the command
6873 line, you can put the names into a file, and then use the
6874 @option{--files-from=@var{file-of-names}} (@option{-T
6875 @var{file-of-names}}) option to @command{tar}. Give the name of the
6876 file which contains the list of files to include as the argument to
6877 @option{--files-from}. In the list, the file names should be separated by
6878 newlines. You will frequently use this option when you have generated
6879 the list of files to archive with the @command{find} utility.
6883 @item --files-from=@var{file-name}
6884 @itemx -T @var{file-name}
6885 Get names to extract or create from file @var{file-name}.
6888 If you give a single dash as a file name for @option{--files-from}, (i.e.,
6889 you specify either @code{--files-from=-} or @code{-T -}), then the file
6890 names are read from standard input.
6892 Unless you are running @command{tar} with @option{--create}, you can not use
6893 both @code{--files-from=-} and @code{--file=-} (@code{-f -}) in the same
6896 Any number of @option{-T} options can be given in the command line.
6898 The following example shows how to use @command{find} to generate a list of
6899 files smaller than 400K in length and put that list into a file
6900 called @file{small-files}. You can then use the @option{-T} option to
6901 @command{tar} to specify the files from that file, @file{small-files}, to
6902 create the archive @file{little.tgz}. (The @option{-z} option to
6903 @command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for
6907 $ @kbd{find . -size -400 -print > small-files}
6908 $ @kbd{tar -c -v -z -T small-files -f little.tgz}
6912 In the file list given by @option{-T} option, any file name beginning
6913 with @samp{-} character is considered a @command{tar} option and is
6914 processed accordingly@footnote{Versions of @GNUTAR{} up to 1.15.1
6915 recognized only @option{-C} option in file lists, and only if the
6916 option and its argument occupied two consecutive lines.}. For example,
6917 the common use of this feature is to change to another directory by
6918 specifying @option{-C} option:
6928 $ @kbd{tar -c -f foo.tar --files-from list}
6933 In this example, @command{tar} will first switch to @file{/etc}
6934 directory and add files @file{passwd} and @file{hosts} to the
6935 archive. Then it will change to @file{/lib} directory and will archive
6936 the file @file{libc.a}. Thus, the resulting archive @file{foo.tar} will
6941 $ @kbd{tar tf foo.tar}
6949 @xopindex{directory, using in @option{--files-from} argument}
6950 Notice that the option parsing algorithm used with @option{-T} is
6951 stricter than the one used by shell. Namely, when specifying option
6952 arguments, you should observe the following rules:
6956 When using short (single-letter) option form, its argument must
6957 immediately follow the option letter, without any intervening
6958 whitespace. For example: @code{-Cdir}.
6961 When using long option form, the option argument must be separated
6962 from the option by a single equal sign. No whitespace is allowed on
6963 any side of the equal sign. For example: @code{--directory=dir}.
6966 For both short and long option forms, the option argument can be given
6967 on the next line after the option name, e.g.:
6988 If you happen to have a file whose name starts with @samp{-},
6989 precede it with @option{--add-file} option to prevent it from
6990 being recognized as an option. For example: @code{--add-file=--my-file}.
6997 @subsection @code{NUL}-Terminated File Names
6999 @cindex File names, terminated by @code{NUL}
7000 @cindex @code{NUL}-terminated file names
7001 The @option{--null} option causes
7002 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
7003 to read file names terminated by a @code{NUL} instead of a newline, so
7004 files whose names contain newlines can be archived using
7005 @option{--files-from}.
7008 @xopindex{null, described}
7010 Only consider @code{NUL}-terminated file names, instead of files that
7011 terminate in a newline.
7013 @xopindex{no-null, described}
7015 Undo the effect of any previous @option{--null} option.
7018 The @option{--null} option is just like the one in @acronym{GNU}
7019 @command{xargs} and @command{cpio}, and is useful with the
7020 @option{-print0} predicate of @acronym{GNU} @command{find}. In
7021 @command{tar}, @option{--null} also disables special handling for
7022 file names that begin with dash.
7024 This example shows how to use @command{find} to generate a list of files
7025 larger than 800K in length and put that list into a file called
7026 @file{long-files}. The @option{-print0} option to @command{find} is just
7027 like @option{-print}, except that it separates files with a @code{NUL}
7028 rather than with a newline. You can then run @command{tar} with both the
7029 @option{--null} and @option{-T} options to specify that @command{tar} gets the
7030 files from that file, @file{long-files}, to create the archive
7031 @file{big.tgz}. The @option{--null} option to @command{tar} will cause
7032 @command{tar} to recognize the @code{NUL} separator between files.
7035 $ @kbd{find . -size +800 -print0 > long-files}
7036 $ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
7039 The @option{--no-null} option can be used if you need to read both
7040 @code{NUL}-terminated and newline-terminated files on the same command line.
7041 For example, if @file{flist} is a newline-terminated file, then the
7042 following command can be used to combine it with the above command:
7046 $ @kbd{find . -size +800 -print0 |
7047 tar -c -f big.tar --null -T - --no-null -T flist}
7051 This example uses short options for typographic reasons, to avoid
7054 @GNUTAR is able to automatically detect @code{NUL}-terminated file lists, so
7055 it is safe to use them even without the @option{--null} option. In
7056 this case @command{tar} will print a warning and continue reading such
7057 a file as if @option{--null} were actually given:
7061 $ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
7062 tar: -: file name read contains nul character
7066 The null terminator, however, remains in effect only for this
7067 particular file, any following @option{-T} options will assume
7068 newline termination. Of course, the null autodetection applies
7069 to these eventual surplus @option{-T} options as well.
7072 @section Excluding Some Files
7074 @cindex File names, excluding files by
7075 @cindex Excluding files by name and pattern
7076 @cindex Excluding files by file system
7078 @opindex exclude-from
7079 To avoid operating on files whose names match a particular pattern,
7080 use the @option{--exclude} or @option{--exclude-from} options.
7084 @item --exclude=@var{pattern}
7085 Causes @command{tar} to ignore files that match the @var{pattern}.
7089 The @option{--exclude=@var{pattern}} option prevents any file or
7090 member whose name matches the shell wildcard (@var{pattern}) from
7092 For example, to create an archive with all the contents of the directory
7093 @file{src} except for files whose names end in @file{.o}, use the
7094 command @samp{tar -cf src.tar --exclude='*.o' src}.
7096 You may give multiple @option{--exclude} options.
7099 @opindex exclude-from
7100 @item --exclude-from=@var{file}
7101 @itemx -X @var{file}
7102 Causes @command{tar} to ignore files that match the patterns listed in
7106 @findex exclude-from
7107 Use the @option{--exclude-from} option to read a
7108 list of patterns, one per line, from @var{file}; @command{tar} will
7109 ignore files matching those patterns. Thus if @command{tar} is
7110 called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a
7111 single line @file{*.o}, no files whose names end in @file{.o} will be
7112 added to the archive.
7114 Notice, that lines from @var{file} are read verbatim. One of the
7115 frequent errors is leaving some extra whitespace after a file name,
7116 which is difficult to catch using text editors.
7118 However, empty lines are OK.
7121 @cindex version control system, excluding files
7122 @cindex VCS, excluding files
7123 @cindex SCCS, excluding files
7124 @cindex RCS, excluding files
7125 @cindex CVS, excluding files
7126 @cindex SVN, excluding files
7127 @cindex git, excluding files
7128 @cindex Bazaar, excluding files
7129 @cindex Arch, excluding files
7130 @cindex Mercurial, excluding files
7131 @cindex Darcs, excluding files
7132 @opindex exclude-vcs
7134 Exclude files and directories used by following version control
7135 systems: @samp{CVS}, @samp{RCS}, @samp{SCCS}, @samp{SVN}, @samp{Arch},
7136 @samp{Bazaar}, @samp{Mercurial}, and @samp{Darcs}.
7138 As of version @value{VERSION}, the following files are excluded:
7141 @item @file{CVS/}, and everything under it
7142 @item @file{RCS/}, and everything under it
7143 @item @file{SCCS/}, and everything under it
7144 @item @file{.git/}, and everything under it
7145 @item @file{.gitignore}
7146 @item @file{.cvsignore}
7147 @item @file{.svn/}, and everything under it
7148 @item @file{.arch-ids/}, and everything under it
7149 @item @file{@{arch@}/}, and everything under it
7150 @item @file{=RELEASE-ID}
7151 @item @file{=meta-update}
7152 @item @file{=update}
7154 @item @file{.bzrignore}
7155 @item @file{.bzrtags}
7157 @item @file{.hgignore}
7158 @item @file{.hgrags}
7162 @opindex exclude-backups
7163 @item --exclude-backups
7164 Exclude backup and lock files. This option causes exclusion of files
7165 that match the following shell globbing patterns:
7175 @findex exclude-caches
7176 When creating an archive, the @option{--exclude-caches} option family
7177 causes @command{tar} to exclude all directories that contain a @dfn{cache
7178 directory tag}. A cache directory tag is a short file with the
7179 well-known name @file{CACHEDIR.TAG} and having a standard header
7180 specified in @url{http://www.brynosaurus.com/cachedir/spec.html}.
7181 Various applications write cache directory tags into directories they
7182 use to hold regenerable, non-precious data, so that such data can be
7183 more easily excluded from backups.
7185 There are three @samp{exclude-caches} options, each providing a different
7186 exclusion semantics:
7189 @opindex exclude-caches
7190 @item --exclude-caches
7191 Do not archive the contents of the directory, but archive the
7192 directory itself and the @file{CACHEDIR.TAG} file.
7194 @opindex exclude-caches-under
7195 @item --exclude-caches-under
7196 Do not archive the contents of the directory, nor the
7197 @file{CACHEDIR.TAG} file, archive only the directory itself.
7199 @opindex exclude-caches-all
7200 @item --exclude-caches-all
7201 Omit directories containing @file{CACHEDIR.TAG} file entirely.
7205 Another option family, @option{--exclude-tag}, provides a generalization of
7206 this concept. It takes a single argument, a file name to look for.
7207 Any directory that contains this file will be excluded from the dump.
7208 Similarly to @samp{exclude-caches}, there are three options in this
7212 @opindex exclude-tag
7213 @item --exclude-tag=@var{file}
7214 Do not dump the contents of the directory, but dump the
7215 directory itself and the @var{file}.
7217 @opindex exclude-tag-under
7218 @item --exclude-tag-under=@var{file}
7219 Do not dump the contents of the directory, nor the
7220 @var{file}, archive only the directory itself.
7222 @opindex exclude-tag-all
7223 @item --exclude-tag-all=@var{file}
7224 Omit directories containing @var{file} file entirely.
7227 Multiple @option{--exclude-tag*} options can be given.
7229 For example, given this directory:
7244 The @option{--exclude-tag} will produce the following:
7247 $ @kbd{tar -cf archive.tar --exclude-tag=tagfile -v dir}
7252 tar: dir/folk/: contains a cache directory tag tagfile;
7257 Both the @file{dir/folk} directory and its tagfile are preserved in
7258 the archive, however the rest of files in this directory are not.
7260 Now, using the @option{--exclude-tag-under} option will exclude
7261 @file{tagfile} from the dump, while still preserving the directory
7262 itself, as shown in this example:
7265 $ @kbd{tar -cf archive.tar --exclude-tag-under=tagfile -v dir}
7270 ./tar: dir/folk/: contains a cache directory tag tagfile;
7274 Finally, using @option{--exclude-tag-all} omits the @file{dir/folk}
7278 $ @kbd{tar -cf archive.tar --exclude-tag-all=tagfile -v dir}
7282 ./tar: dir/folk/: contains a cache directory tag tagfile;
7283 directory not dumped
7287 * problems with exclude::
7290 @node problems with exclude
7291 @unnumberedsubsec Problems with Using the @code{exclude} Options
7293 @xopindex{exclude, potential problems with}
7294 Some users find @samp{exclude} options confusing. Here are some common
7299 The main operating mode of @command{tar} does not act on a file name
7300 explicitly listed on the command line, if one of its file name
7301 components is excluded. In the example above, if
7302 you create an archive and exclude files that end with @samp{*.o}, but
7303 explicitly name the file @samp{dir.o/foo} after all the options have been
7304 listed, @samp{dir.o/foo} will be excluded from the archive.
7307 You can sometimes confuse the meanings of @option{--exclude} and
7308 @option{--exclude-from}. Be careful: use @option{--exclude} when files
7309 to be excluded are given as a pattern on the command line. Use
7310 @option{--exclude-from} to introduce the name of a file which contains
7311 a list of patterns, one per line; each of these patterns can exclude
7312 zero, one, or many files.
7315 When you use @option{--exclude=@var{pattern}}, be sure to quote the
7316 @var{pattern} parameter, so @GNUTAR{} sees wildcard characters
7317 like @samp{*}. If you do not do this, the shell might expand the
7318 @samp{*} itself using files at hand, so @command{tar} might receive a
7319 list of files instead of one pattern, or none at all, making the
7320 command somewhat illegal. This might not correspond to what you want.
7325 $ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}}
7333 $ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
7337 You must use use shell syntax, or globbing, rather than @code{regexp}
7338 syntax, when using exclude options in @command{tar}. If you try to use
7339 @code{regexp} syntax to describe files to be excluded, your command
7343 @FIXME{The change in semantics must have occurred before 1.11,
7344 so I doubt if it is worth mentioning at all. Anyway, should at
7345 least specify in which version the semantics changed.}
7346 In earlier versions of @command{tar}, what is now the
7347 @option{--exclude-from} option was called @option{--exclude} instead.
7348 Now, @option{--exclude} applies to patterns listed on the command
7349 line and @option{--exclude-from} applies to patterns listed in a
7355 @section Wildcards Patterns and Matching
7357 @dfn{Globbing} is the operation by which @dfn{wildcard} characters,
7358 @samp{*} or @samp{?} for example, are replaced and expanded into all
7359 existing files matching the given pattern. @GNUTAR{} can use wildcard
7360 patterns for matching (or globbing) archive members when extracting
7361 from or listing an archive. Wildcard patterns are also used for
7362 verifying volume labels of @command{tar} archives. This section has the
7363 purpose of explaining wildcard syntax for @command{tar}.
7365 @FIXME{the next few paragraphs need work.}
7367 A @var{pattern} should be written according to shell syntax, using wildcard
7368 characters to effect globbing. Most characters in the pattern stand
7369 for themselves in the matched string, and case is significant: @samp{a}
7370 will match only @samp{a}, and not @samp{A}. The character @samp{?} in the
7371 pattern matches any single character in the matched string. The character
7372 @samp{*} in the pattern matches zero, one, or more single characters in
7373 the matched string. The character @samp{\} says to take the following
7374 character of the pattern @emph{literally}; it is useful when one needs to
7375 match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves.
7377 The character @samp{[}, up to the matching @samp{]}, introduces a character
7378 class. A @dfn{character class} is a list of acceptable characters
7379 for the next single character of the matched string. For example,
7380 @samp{[abcde]} would match any of the first five letters of the alphabet.
7381 Note that within a character class, all of the ``special characters''
7382 listed above other than @samp{\} lose their special meaning; for example,
7383 @samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\},
7384 @samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints,
7385 the characters @samp{-} and @samp{]} must either come @emph{first} or
7386 @emph{last} in a character class.)
7388 @cindex Excluding characters from a character class
7389 @cindex Character class, excluding characters from
7390 If the first character of the class after the opening @samp{[}
7391 is @samp{!} or @samp{^}, then the meaning of the class is reversed.
7392 Rather than listing character to match, it lists those characters which
7393 are @emph{forbidden} as the next single character of the matched string.
7395 Other characters of the class stand for themselves. The special
7396 construction @samp{[@var{a}-@var{e}]}, using an hyphen between two
7397 letters, is meant to represent all characters between @var{a} and
7400 @FIXME{need to add a sentence or so here to make this clear for those
7401 who don't have dan around.}
7403 Periods (@samp{.}) or forward slashes (@samp{/}) are not considered
7404 special for wildcard matches. However, if a pattern completely matches
7405 a directory prefix of a matched string, then it matches the full matched
7406 string: thus, excluding a directory also excludes all the files beneath it.
7409 * controlling pattern-matching::
7412 @node controlling pattern-matching
7413 @unnumberedsubsec Controlling Pattern-Matching
7415 For the purposes of this section, we call @dfn{exclusion members} all
7416 member names obtained while processing @option{--exclude} and
7417 @option{--exclude-from} options, and @dfn{inclusion members} those
7418 member names that were given in the command line or read from the file
7419 specified with @option{--files-from} option.
7421 These two pairs of member lists are used in the following operations:
7422 @option{--diff}, @option{--extract}, @option{--list},
7425 There are no inclusion members in create mode (@option{--create} and
7426 @option{--append}), since in this mode the names obtained from the
7427 command line refer to @emph{files}, not archive members.
7429 By default, inclusion members are compared with archive members
7430 literally @footnote{Notice that earlier @GNUTAR{} versions used
7431 globbing for inclusion members, which contradicted to UNIX98
7432 specification and was not documented. @xref{Changes}, for more
7433 information on this and other changes.} and exclusion members are
7434 treated as globbing patterns. For example:
7438 $ @kbd{tar tf foo.tar}
7443 # @i{Member names are used verbatim:}
7444 $ @kbd{tar -xf foo.tar -v '[remarks]'}
7446 # @i{Exclude member names are globbed:}
7447 $ @kbd{tar -xf foo.tar -v --exclude '*.c'}
7453 This behavior can be altered by using the following options:
7458 Treat all member names as wildcards.
7460 @opindex no-wildcards
7461 @item --no-wildcards
7462 Treat all member names as literal strings.
7465 Thus, to extract files whose names end in @samp{.c}, you can use:
7468 $ @kbd{tar -xf foo.tar -v --wildcards '*.c'}
7474 Notice quoting of the pattern to prevent the shell from interpreting
7477 The effect of @option{--wildcards} option is canceled by
7478 @option{--no-wildcards}. This can be used to pass part of
7479 the command line arguments verbatim and other part as globbing
7480 patterns. For example, the following invocation:
7483 $ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'}
7487 instructs @command{tar} to extract from @file{foo.tar} all files whose
7488 names end in @samp{.txt} and the file named @file{[remarks]}.
7490 Normally, a pattern matches a name if an initial subsequence of the
7491 name's components matches the pattern, where @samp{*}, @samp{?}, and
7492 @samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
7493 and wildcards can match @samp{/}.
7495 Other than optionally stripping leading @samp{/} from names
7496 (@pxref{absolute}), patterns and names are used as-is. For
7497 example, trailing @samp{/} is not trimmed from a user-specified name
7498 before deciding whether to exclude it.
7500 However, this matching procedure can be altered by the options listed
7501 below. These options accumulate. For example:
7504 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
7508 ignores case when excluding @samp{makefile}, but not when excluding
7513 @opindex no-anchored
7515 @itemx --no-anchored
7516 If anchored, a pattern must match an initial subsequence
7517 of the name's components. Otherwise, the pattern can match any
7518 subsequence. Default is @option{--no-anchored} for exclusion members
7519 and @option{--anchored} inclusion members.
7521 @opindex ignore-case
7522 @opindex no-ignore-case
7524 @itemx --no-ignore-case
7525 When ignoring case, upper-case patterns match lower-case names and vice versa.
7526 When not ignoring case (the default), matching is case-sensitive.
7528 @opindex wildcards-match-slash
7529 @opindex no-wildcards-match-slash
7530 @item --wildcards-match-slash
7531 @itemx --no-wildcards-match-slash
7532 When wildcards match slash (the default for exclusion members), a
7533 wildcard like @samp{*} in the pattern can match a @samp{/} in the
7534 name. Otherwise, @samp{/} is matched only by @samp{/}.
7538 The @option{--recursion} and @option{--no-recursion} options
7539 (@pxref{recurse}) also affect how member patterns are interpreted. If
7540 recursion is in effect, a pattern matches a name if it matches any of
7541 the name's parent directories.
7543 The following table summarizes pattern-matching default values:
7545 @multitable @columnfractions .3 .7
7546 @headitem Members @tab Default settings
7547 @item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash}
7548 @item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash}
7551 @node quoting styles
7552 @section Quoting Member Names
7554 When displaying member names, @command{tar} takes care to avoid
7555 ambiguities caused by certain characters. This is called @dfn{name
7556 quoting}. The characters in question are:
7559 @item Non-printable control characters:
7560 @anchor{escape sequences}
7561 @multitable @columnfractions 0.20 0.10 0.60
7562 @headitem Character @tab @acronym{ASCII} @tab Character name
7563 @item \a @tab 7 @tab Audible bell
7564 @item \b @tab 8 @tab Backspace
7565 @item \f @tab 12 @tab Form feed
7566 @item \n @tab 10 @tab New line
7567 @item \r @tab 13 @tab Carriage return
7568 @item \t @tab 9 @tab Horizontal tabulation
7569 @item \v @tab 11 @tab Vertical tabulation
7572 @item Space (@acronym{ASCII} 32)
7574 @item Single and double quotes (@samp{'} and @samp{"})
7576 @item Backslash (@samp{\})
7579 The exact way @command{tar} uses to quote these characters depends on
7580 the @dfn{quoting style}. The default quoting style, called
7581 @dfn{escape} (see below), uses backslash notation to represent control
7582 characters, space and backslash. Using this quoting style, control
7583 characters are represented as listed in column @samp{Character} in the
7584 above table, a space is printed as @samp{\ } and a backslash as @samp{\\}.
7586 @GNUTAR{} offers seven distinct quoting styles, which can be selected
7587 using @option{--quoting-style} option:
7590 @item --quoting-style=@var{style}
7591 @opindex quoting-style
7593 Sets quoting style. Valid values for @var{style} argument are:
7594 literal, shell, shell-always, c, escape, locale, clocale.
7597 These styles are described in detail below. To illustrate their
7598 effect, we will use an imaginary tar archive @file{arch.tar}
7599 containing the following members:
7603 # 1. Contains horizontal tabulation character.
7605 # 2. Contains newline character
7608 # 3. Contains a space
7610 # 4. Contains double quotes
7612 # 5. Contains single quotes
7614 # 6. Contains a backslash character:
7619 Here is how usual @command{ls} command would have listed them, if they
7620 had existed in the current working directory:
7638 No quoting, display each character as is:
7642 $ @kbd{tar tf arch.tar --quoting-style=literal}
7655 Display characters the same way Bourne shell does:
7656 control characters, except @samp{\t} and @samp{\n}, are printed using
7657 backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a
7658 single quote is printed as @samp{\'}. If a name contains any quoted
7659 characters, it is enclosed in single quotes. In particular, if a name
7660 contains single quotes, it is printed as several single-quoted strings:
7664 $ @kbd{tar tf arch.tar --quoting-style=shell}
7667 './a'\''single'\''quote'
7677 Same as @samp{shell}, but the names are always enclosed in single
7682 $ @kbd{tar tf arch.tar --quoting-style=shell-always}
7685 './a'\''single'\''quote'
7695 Use the notation of the C programming language. All names are
7696 enclosed in double quotes. Control characters are quoted using
7697 backslash notations, double quotes are represented as @samp{\"},
7698 backslash characters are represented as @samp{\\}. Single quotes and
7699 spaces are not quoted:
7703 $ @kbd{tar tf arch.tar --quoting-style=c}
7707 "./a\"double\"quote"
7715 Control characters are printed using backslash notation, a space is
7716 printed as @samp{\ } and a backslash as @samp{\\}. This is the
7717 default quoting style, unless it was changed when configured the
7722 $ @kbd{tar tf arch.tar --quoting-style=escape}
7734 Control characters, single quote and backslash are printed using
7735 backslash notation. All names are quoted using left and right
7736 quotation marks, appropriate to the current locale. If it does not
7737 define quotation marks, use @samp{`} as left and @samp{'} as right
7738 quotation marks. Any occurrences of the right quotation mark in a
7739 name are escaped with @samp{\}, for example:
7745 $ @kbd{tar tf arch.tar --quoting-style=locale}
7748 `./a\'single\'quote'
7757 Same as @samp{locale}, but @samp{"} is used for both left and right
7758 quotation marks, if not provided by the currently selected locale:
7762 $ @kbd{tar tf arch.tar --quoting-style=clocale}
7766 "./a\"double\"quote"
7774 You can specify which characters should be quoted in addition to those
7775 implied by the current quoting style:
7778 @item --quote-chars=@var{string}
7779 Always quote characters from @var{string}, even if the selected
7780 quoting style would not quote them.
7783 For example, using @samp{escape} quoting (compare with the usual
7784 escape listing above):
7788 $ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'}
7799 To disable quoting of such additional characters, use the following
7803 @item --no-quote-chars=@var{string}
7804 Remove characters listed in @var{string} from the list of quoted
7805 characters set by the previous @option{--quote-chars} option.
7808 This option is particularly useful if you have added
7809 @option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS})
7810 and wish to disable it for the current invocation.
7812 Note, that @option{--no-quote-chars} does @emph{not} disable those
7813 characters that are quoted by default in the selected quoting style.
7816 @section Modifying File and Member Names
7818 @command{Tar} archives contain detailed information about files stored
7819 in them and full file names are part of that information. When
7820 storing a file to an archive, its file name is recorded in it,
7821 along with the actual file contents. When restoring from an archive,
7822 a file is created on disk with exactly the same name as that stored
7823 in the archive. In the majority of cases this is the desired behavior
7824 of a file archiver. However, there are some cases when it is not.
7826 First of all, it is often unsafe to extract archive members with
7827 absolute file names or those that begin with a @file{../}. @GNUTAR{}
7828 takes special precautions when extracting such names and provides a
7829 special option for handling them, which is described in
7832 Secondly, you may wish to extract file names without some leading
7833 directory components, or with otherwise modified names. In other
7834 cases it is desirable to store files under differing names in the
7837 @GNUTAR{} provides several options for these needs.
7840 @opindex strip-components
7841 @item --strip-components=@var{number}
7842 Strip given @var{number} of leading components from file names before
7846 For example, suppose you have archived whole @file{/usr} hierarchy to
7847 a tar archive named @file{usr.tar}. Among other files, this archive
7848 contains @file{usr/include/stdlib.h}, which you wish to extract to
7849 the current working directory. To do so, you type:
7852 $ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h}
7855 The option @option{--strip=2} instructs @command{tar} to strip the
7856 two leading components (@file{usr/} and @file{include/}) off the file
7859 If you add the @option{--verbose} (@option{-v}) option to the invocation
7860 above, you will note that the verbose listing still contains the
7861 full file name, with the two removed components still in place. This
7862 can be inconvenient, so @command{tar} provides a special option for
7863 altering this behavior:
7865 @anchor{show-transformed-names}
7867 @opindex show-transformed-names
7868 @item --show-transformed-names
7869 Display file or member names with all requested transformations
7878 $ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h}
7879 usr/include/stdlib.h
7880 $ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h}
7885 Notice that in both cases the file @file{stdlib.h} is extracted to the
7886 current working directory, @option{--show-transformed-names} affects
7887 only the way its name is displayed.
7889 This option is especially useful for verifying whether the invocation
7890 will have the desired effect. Thus, before running
7893 $ @kbd{tar -x --strip=@var{n}}
7897 it is often advisable to run
7900 $ @kbd{tar -t -v --show-transformed --strip=@var{n}}
7904 to make sure the command will produce the intended results.
7906 In case you need to apply more complex modifications to the file name,
7907 @GNUTAR{} provides a general-purpose transformation option:
7912 @item --transform=@var{expression}
7913 @itemx --xform=@var{expression}
7914 Modify file names using supplied @var{expression}.
7918 The @var{expression} is a @command{sed}-like replace expression of the
7922 s/@var{regexp}/@var{replace}/[@var{flags}]
7926 where @var{regexp} is a @dfn{regular expression}, @var{replace} is a
7927 replacement for each file name part that matches @var{regexp}. Both
7928 @var{regexp} and @var{replace} are described in detail in
7929 @ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
7931 Any delimiter can be used in lieu of @samp{/}, the only requirement being
7932 that it be used consistently throughout the expression. For example,
7933 the following two expressions are equivalent:
7942 Changing delimiters is often useful when the @var{regex} contains
7943 slashes. For example, it is more convenient to write @code{s,/,-,} than
7946 As in @command{sed}, you can give several replace expressions,
7947 separated by a semicolon.
7949 Supported @var{flags} are:
7953 Apply the replacement to @emph{all} matches to the @var{regexp}, not
7957 Use case-insensitive matching.
7960 @var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
7961 regexps, Extended regular expressions, Extended regular expressions,
7965 Only replace the @var{number}th match of the @var{regexp}.
7967 Note: the @acronym{POSIX} standard does not specify what should happen
7968 when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
7969 follows the GNU @command{sed} implementation in this regard, so
7970 the interaction is defined to be: ignore matches before the
7971 @var{number}th, and then match and replace all matches from the
7976 In addition, several @dfn{transformation scope} flags are supported,
7977 that control to what files transformations apply. These are:
7981 Apply transformation to regular archive members.
7984 Do not apply transformation to regular archive members.
7987 Apply transformation to symbolic link targets.
7990 Do not apply transformation to symbolic link targets.
7993 Apply transformation to hard link targets.
7996 Do not apply transformation to hard link targets.
7999 Default is @samp{rsh}, which means to apply tranformations to both archive
8000 members and targets of symbolic and hard links.
8002 Default scope flags can also be changed using @samp{flags=} statement
8003 in the transform expression. The flags set this way remain in force
8004 until next @samp{flags=} statement or end of expression, whichever
8005 occurs first. For example:
8008 --transform 'flags=S;s|^|/usr/local/|'
8011 Here are several examples of @option{--transform} usage:
8014 @item Extract @file{usr/} hierarchy into @file{usr/local/}:
8017 $ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar}
8020 @item Strip two leading directory components (equivalent to
8021 @option{--strip-components=2}):
8024 $ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
8027 @item Convert each file name to lower case:
8030 $ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
8033 @item Prepend @file{/prefix/} to each file name:
8036 $ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
8039 @item Archive the @file{/lib} directory, prepending @samp{/usr/local}
8040 to each archive member:
8043 $ @kbd{tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib}
8047 Notice the use of flags in the last example. The @file{/lib}
8048 directory often contains many symbolic links to files within it.
8049 It may look, for example, like this:
8053 drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
8054 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
8055 lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
8059 Using the expression @samp{s,^,/usr/local/,} would mean adding
8060 @samp{/usr/local} to both regular archive members and to link
8061 targets. In this case, @file{/lib/libc.so.6} would become:
8064 /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
8067 This is definitely not desired. To avoid this, the @samp{S} flag
8068 is used, which excludes symbolic link targets from filename
8069 transformations. The result is:
8072 $ @kbd{tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
8073 --show-transformed /lib}
8074 drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
8075 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
8076 lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 \
8080 Unlike @option{--strip-components}, @option{--transform} can be used
8081 in any @GNUTAR{} operation mode. For example, the following command
8082 adds files to the archive while replacing the leading @file{usr/}
8083 component with @file{var/}:
8086 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /}
8089 To test @option{--transform} effect we suggest using
8090 @option{--show-transformed-names} option:
8093 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \
8094 --verbose --show-transformed-names /}
8097 If both @option{--strip-components} and @option{--transform} are used
8098 together, then @option{--transform} is applied first, and the required
8099 number of components is then stripped from its result.
8101 You can use as many @option{--transform} options in a single command
8102 line as you want. The specified expressions will then be applied in
8103 order of their appearance. For example, the following two invocations
8107 $ @kbd{tar -cf arch.tar --transform='s,/usr/var,/var/' \
8108 --transform='s,/usr/local,/usr/,'}
8109 $ @kbd{tar -cf arch.tar \
8110 --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'}
8114 @section Operating Only on New Files
8116 @cindex Excluding file by age
8117 @cindex Data Modification time, excluding files by
8118 @cindex Modification time, excluding files by
8119 @cindex Age, excluding files by
8120 The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
8121 @option{-N @var{date}}) option causes @command{tar} to only work on
8122 files whose data modification or status change times are newer than
8123 the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
8124 it is taken to be a file name; the data modification time of that file
8125 is used as the date. If you use this option when creating or appending
8126 to an archive, the archive will only include new files. If you use
8127 @option{--after-date} when extracting an archive, @command{tar} will
8128 only extract files newer than the @var{date} you specify.
8130 If you only want @command{tar} to make the date comparison based on
8131 modification of the file's data (rather than status
8132 changes), then use the @option{--newer-mtime=@var{date}} option.
8134 @cindex --after-date and --update compared
8135 @cindex --newer-mtime and --update compared
8136 You may use these options with any operation. Note that these options
8137 differ from the @option{--update} (@option{-u}) operation in that they
8138 allow you to specify a particular date against which @command{tar} can
8139 compare when deciding whether or not to archive the files.
8144 @item --after-date=@var{date}
8145 @itemx --newer=@var{date}
8146 @itemx -N @var{date}
8147 Only store files newer than @var{date}.
8149 Acts on files only if their data modification or status change times are
8150 later than @var{date}. Use in conjunction with any operation.
8152 If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
8153 name; the data modification time of that file is used as the date.
8155 @opindex newer-mtime
8156 @item --newer-mtime=@var{date}
8157 Acts like @option{--after-date}, but only looks at data modification times.
8160 These options limit @command{tar} to operate only on files which have
8161 been modified after the date specified. A file's status is considered to have
8162 changed if its contents have been modified, or if its owner,
8163 permissions, and so forth, have been changed. (For more information on
8164 how to specify a date, see @ref{Date input formats}; remember that the
8165 entire date argument must be quoted if it contains any spaces.)
8167 Gurus would say that @option{--after-date} tests both the data
8168 modification time (@code{mtime}, the time the contents of the file
8169 were last modified) and the status change time (@code{ctime}, the time
8170 the file's status was last changed: owner, permissions, etc.@:)
8171 fields, while @option{--newer-mtime} tests only the @code{mtime}
8174 To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
8175 @code{ctime} and processes the file if either one is more recent than
8176 @var{date}, while @option{--newer-mtime} only checks @code{mtime} and
8177 disregards @code{ctime}. Neither does it use @code{atime} (the last time the
8178 contents of the file were looked at).
8180 Date specifiers can have embedded spaces. Because of this, you may need
8181 to quote date arguments to keep the shell from parsing them as separate
8182 arguments. For example, the following command will add to the archive
8183 all the files modified less than two days ago:
8186 $ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'}
8189 When any of these options is used with the option @option{--verbose}
8190 (@pxref{verbose tutorial}) @GNUTAR{} will try to convert the specified
8191 date back to its textual representation and compare that with the
8192 one given with the option. If the two dates differ, @command{tar} will
8193 print a warning saying what date it will use. This is to help user
8194 ensure he is using the right date. For example:
8198 $ @kbd{tar -c -f archive.tar --after-date='10 days ago' .}
8199 tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
8205 @strong{Please Note:} @option{--after-date} and @option{--newer-mtime}
8206 should not be used for incremental backups. @xref{Incremental Dumps},
8207 for proper way of creating incremental backups.
8211 @section Descending into Directories
8212 @cindex Avoiding recursion in directories
8213 @cindex Descending directories, avoiding
8214 @cindex Directories, avoiding recursion
8215 @cindex Recursion in directories, avoiding
8217 Usually, @command{tar} will recursively explore all directories (either
8218 those given on the command line or through the @option{--files-from}
8219 option) for the various files they contain. However, you may not always
8220 want @command{tar} to act this way.
8222 @opindex no-recursion
8223 @cindex @command{find}, using with @command{tar}
8224 The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
8225 into specified directories. If you specify @option{--no-recursion}, you can
8226 use the @command{find} (@pxref{Top,, find, find, GNU Find Manual})
8227 utility for hunting through levels of directories to
8228 construct a list of file names which you could then pass to @command{tar}.
8229 @command{find} allows you to be more selective when choosing which files to
8230 archive; see @ref{files}, for more information on using @command{find} with
8234 @item --no-recursion
8235 Prevents @command{tar} from recursively descending directories.
8239 Requires @command{tar} to recursively descend directories.
8240 This is the default.
8243 When you use @option{--no-recursion}, @GNUTAR{} grabs
8244 directory entries themselves, but does not descend on them
8245 recursively. Many people use @command{find} for locating files they
8246 want to back up, and since @command{tar} @emph{usually} recursively
8247 descends on directories, they have to use the @samp{@w{-not -type d}}
8248 test in their @command{find} invocation (@pxref{Type, Type, Type test,
8249 find, Finding Files}), as they usually do not want all the files in a
8250 directory. They then use the @option{--files-from} option to archive
8251 the files located via @command{find}.
8253 The problem when restoring files archived in this manner is that the
8254 directories themselves are not in the archive; so the
8255 @option{--same-permissions} (@option{--preserve-permissions},
8256 @option{-p}) option does not affect them---while users might really
8257 like it to. Specifying @option{--no-recursion} is a way to tell
8258 @command{tar} to grab only the directory entries given to it, adding
8259 no new files on its own. To summarize, if you use @command{find} to
8260 create a list of files to be stored in an archive, use it as follows:
8264 $ @kbd{find @var{dir} @var{tests} | \
8265 tar -cf @var{archive} -T - --no-recursion}
8269 The @option{--no-recursion} option also applies when extracting: it
8270 causes @command{tar} to extract only the matched directory entries, not
8271 the files under those directories.
8273 The @option{--no-recursion} option also affects how globbing patterns
8274 are interpreted (@pxref{controlling pattern-matching}).
8276 The @option{--no-recursion} and @option{--recursion} options apply to
8277 later options and operands, and can be overridden by later occurrences
8278 of @option{--no-recursion} and @option{--recursion}. For example:
8281 $ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
8285 creates an archive with one entry for @file{grape}, and the recursive
8286 contents of @file{grape/concord}, but no entries under @file{grape}
8287 other than @file{grape/concord}.
8290 @section Crossing File System Boundaries
8291 @cindex File system boundaries, not crossing
8293 @command{tar} will normally automatically cross file system boundaries in
8294 order to archive files which are part of a directory tree. You can
8295 change this behavior by running @command{tar} and specifying
8296 @option{--one-file-system}. This option only affects files that are
8297 archived because they are in a directory that is being archived;
8298 @command{tar} will still archive files explicitly named on the command line
8299 or through @option{--files-from}, regardless of where they reside.
8302 @opindex one-file-system
8303 @item --one-file-system
8304 Prevents @command{tar} from crossing file system boundaries when
8305 archiving. Use in conjunction with any write operation.
8308 The @option{--one-file-system} option causes @command{tar} to modify its
8309 normal behavior in archiving the contents of directories. If a file in
8310 a directory is not on the same file system as the directory itself, then
8311 @command{tar} will not archive that file. If the file is a directory
8312 itself, @command{tar} will not archive anything beneath it; in other words,
8313 @command{tar} will not cross mount points.
8315 This option is useful for making full or incremental archival backups of
8316 a file system. If this option is used in conjunction with
8317 @option{--verbose} (@option{-v}), files that are excluded are
8318 mentioned by name on the standard error.
8321 * directory:: Changing Directory
8322 * absolute:: Absolute File Names
8326 @subsection Changing the Working Directory
8328 @FIXME{need to read over this node now for continuity; i've switched
8329 things around some.}
8331 @cindex Changing directory mid-stream
8332 @cindex Directory, changing mid-stream
8333 @cindex Working directory, specifying
8334 To change the working directory in the middle of a list of file names,
8335 either on the command line or in a file specified using
8336 @option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
8337 This will change the working directory to the specified directory
8338 after that point in the list.
8342 @item --directory=@var{directory}
8343 @itemx -C @var{directory}
8344 Changes the working directory in the middle of a command line.
8350 $ @kbd{tar -c -f jams.tar grape prune -C food cherry}
8354 will place the files @file{grape} and @file{prune} from the current
8355 directory into the archive @file{jams.tar}, followed by the file
8356 @file{cherry} from the directory @file{food}. This option is especially
8357 useful when you have several widely separated files that you want to
8358 store in the same archive.
8360 Note that the file @file{cherry} is recorded in the archive under the
8361 precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the
8362 archive will contain three files that all appear to have come from the
8363 same directory; if the archive is extracted with plain @samp{tar
8364 --extract}, all three files will be written in the current directory.
8366 Contrast this with the command,
8369 $ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
8373 which records the third file in the archive under the name
8374 @file{red/cherry} so that, if the archive is extracted using
8375 @samp{tar --extract}, the third file will be written in a subdirectory
8378 You can use the @option{--directory} option to make the archive
8379 independent of the original name of the directory holding the files.
8380 The following command places the files @file{/etc/passwd},
8381 @file{/etc/hosts}, and @file{/lib/libc.a} into the archive
8385 $ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
8389 However, the names of the archive members will be exactly what they were
8390 on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}.
8391 They will not appear to be related by file name to the original
8392 directories where those files were located.
8394 Note that @option{--directory} options are interpreted consecutively. If
8395 @option{--directory} specifies a relative file name, it is interpreted
8396 relative to the then current directory, which might not be the same as
8397 the original current working directory of @command{tar}, due to a previous
8398 @option{--directory} option.
8400 When using @option{--files-from} (@pxref{files}), you can put various
8401 @command{tar} options (including @option{-C}) in the file list. Notice,
8402 however, that in this case the option and its argument may not be
8403 separated by whitespace. If you use short option, its argument must
8404 either follow the option letter immediately, without any intervening
8405 whitespace, or occupy the next line. Otherwise, if you use long
8406 option, separate its argument by an equal sign.
8408 For instance, the file list for the above example will be:
8421 To use it, you would invoke @command{tar} as follows:
8424 $ @kbd{tar -c -f foo.tar --files-from list}
8427 The interpretation of @option{--directory} is disabled by
8428 @option{--null} option.
8431 @subsection Absolute File Names
8432 @cindex absolute file names
8433 @cindex file names, absolute
8435 By default, @GNUTAR{} drops a leading @samp{/} on
8436 input or output, and complains about file names containing a @file{..}
8437 component. There is an option that turns off this behavior:
8440 @opindex absolute-names
8441 @item --absolute-names
8443 Do not strip leading slashes from file names, and permit file names
8444 containing a @file{..} file name component.
8447 When @command{tar} extracts archive members from an archive, it strips any
8448 leading slashes (@samp{/}) from the member name. This causes absolute
8449 member names in the archive to be treated as relative file names. This
8450 allows you to have such members extracted wherever you want, instead of
8451 being restricted to extracting the member in the exact directory named
8452 in the archive. For example, if the archive member has the name
8453 @file{/etc/passwd}, @command{tar} will extract it as if the name were
8454 really @file{etc/passwd}.
8456 File names containing @file{..} can cause problems when extracting, so
8457 @command{tar} normally warns you about such files when creating an
8458 archive, and rejects attempts to extracts such files.
8460 Other @command{tar} programs do not do this. As a result, if you
8461 create an archive whose member names start with a slash, they will be
8462 difficult for other people with a non-@GNUTAR{}
8463 program to use. Therefore, @GNUTAR{} also strips
8464 leading slashes from member names when putting members into the
8465 archive. For example, if you ask @command{tar} to add the file
8466 @file{/bin/ls} to an archive, it will do so, but the member name will
8467 be @file{bin/ls}@footnote{A side effect of this is that when
8468 @option{--create} is used with @option{--verbose} the resulting output
8469 is not, generally speaking, the same as the one you'd get running
8470 @kbd{tar --list} command. This may be important if you use some
8471 scripts for comparing both outputs. @xref{listing member and file names},
8472 for the information on how to handle this case.}.
8474 If you use the @option{--absolute-names} (@option{-P}) option,
8475 @command{tar} will do none of these transformations.
8477 To archive or extract files relative to the root directory, specify
8478 the @option{--absolute-names} (@option{-P}) option.
8480 Normally, @command{tar} acts on files relative to the working
8481 directory---ignoring superior directory names when archiving, and
8482 ignoring leading slashes when extracting.
8484 When you specify @option{--absolute-names} (@option{-P}),
8485 @command{tar} stores file names including all superior directory
8486 names, and preserves leading slashes. If you only invoked
8487 @command{tar} from the root directory you would never need the
8488 @option{--absolute-names} option, but using this option
8489 may be more convenient than switching to root.
8491 @FIXME{Should be an example in the tutorial/wizardry section using this
8492 to transfer files between systems.}
8495 @item --absolute-names
8496 Preserves full file names (including superior directory names) when
8497 archiving files. Preserves leading slash when extracting files.
8501 @command{tar} prints out a message about removing the @samp{/} from
8502 file names. This message appears once per @GNUTAR{}
8503 invocation. It represents something which ought to be told; ignoring
8504 what it means can cause very serious surprises, later.
8506 Some people, nevertheless, do not want to see this message. Wanting to
8507 play really dangerously, one may of course redirect @command{tar} standard
8508 error to the sink. For example, under @command{sh}:
8511 $ @kbd{tar -c -f archive.tar /home 2> /dev/null}
8515 Another solution, both nicer and simpler, would be to change to
8516 the @file{/} directory first, and then avoid absolute notation.
8520 $ @kbd{tar -c -f archive.tar -C / home}
8523 @include getdate.texi
8526 @chapter Controlling the Archive Format
8528 @cindex Tar archive formats
8529 Due to historical reasons, there are several formats of tar archives.
8530 All of them are based on the same principles, but have some subtle
8531 differences that often make them incompatible with each other.
8533 GNU tar is able to create and handle archives in a variety of formats.
8534 The most frequently used formats are (in alphabetical order):
8538 Format used by @GNUTAR{} versions up to 1.13.25. This format derived
8539 from an early @acronym{POSIX} standard, adding some improvements such as
8540 sparse file handling and incremental archives. Unfortunately these
8541 features were implemented in a way incompatible with other archive
8544 Archives in @samp{gnu} format are able to hold file names of unlimited
8548 Format used by @GNUTAR{} of versions prior to 1.12.
8551 Archive format, compatible with the V7 implementation of tar. This
8552 format imposes a number of limitations. The most important of them
8556 @item The maximum length of a file name is limited to 99 characters.
8557 @item The maximum length of a symbolic link is limited to 99 characters.
8558 @item It is impossible to store special files (block and character
8559 devices, fifos etc.)
8560 @item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777
8562 @item V7 archives do not contain symbolic ownership information (user
8563 and group name of the file owner).
8566 This format has traditionally been used by Automake when producing
8567 Makefiles. This practice will change in the future, in the meantime,
8568 however this means that projects containing file names more than 99
8569 characters long will not be able to use @GNUTAR{} @value{VERSION} and
8570 Automake prior to 1.9.
8573 Archive format defined by @acronym{POSIX.1-1988} specification. It stores
8574 symbolic ownership information. It is also able to store
8575 special files. However, it imposes several restrictions as well:
8578 @item The maximum length of a file name is limited to 256 characters,
8579 provided that the file name can be split at a directory separator in
8580 two parts, first of them being at most 155 bytes long. So, in most
8581 cases the maximum file name length will be shorter than 256
8583 @item The maximum length of a symbolic link name is limited to
8585 @item Maximum size of a file the archive is able to accommodate
8587 @item Maximum value of UID/GID is 2097151.
8588 @item Maximum number of bits in device major and minor numbers is 21.
8592 Format used by J@"org Schilling @command{star}
8593 implementation. @GNUTAR{} is able to read @samp{star} archives but
8594 currently does not produce them.
8597 Archive format defined by @acronym{POSIX.1-2001} specification. This is the
8598 most flexible and feature-rich format. It does not impose any
8599 restrictions on file sizes or file name lengths. This format is quite
8600 recent, so not all tar implementations are able to handle it properly.
8601 However, this format is designed in such a way that any tar
8602 implementation able to read @samp{ustar} archives will be able to read
8603 most @samp{posix} archives as well, with the only exception that any
8604 additional information (such as long file names etc.) will in such
8605 case be extracted as plain text files along with the files it refers to.
8607 This archive format will be the default format for future versions
8612 The following table summarizes the limitations of each of these
8615 @multitable @columnfractions .10 .20 .20 .20 .20
8616 @headitem Format @tab UID @tab File Size @tab File Name @tab Devn
8617 @item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8618 @item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8619 @item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
8620 @item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
8621 @item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
8624 The default format for @GNUTAR{} is defined at compilation
8625 time. You may check it by running @command{tar --help}, and examining
8626 the last lines of its output. Usually, @GNUTAR{} is configured
8627 to create archives in @samp{gnu} format, however, future version will
8628 switch to @samp{posix}.
8631 * Compression:: Using Less Space through Compression
8632 * Attributes:: Handling File Attributes
8633 * Portability:: Making @command{tar} Archives More Portable
8634 * cpio:: Comparison of @command{tar} and @command{cpio}
8638 @section Using Less Space through Compression
8641 * gzip:: Creating and Reading Compressed Archives
8642 * sparse:: Archiving Sparse Files
8646 @subsection Creating and Reading Compressed Archives
8647 @cindex Compressed archives
8648 @cindex Storing archives in compressed format
8656 @GNUTAR{} is able to create and read compressed archives. It supports
8657 a wide variety of compression programs, namely: @command{gzip},
8658 @command{bzip2}, @command{lzip}, @command{lzma}, @command{lzop},
8659 @command{xz} and traditional @command{compress}. The latter is
8660 supported mostly for backward compatibility, and we recommend
8661 against using it, because it is by far less effective than the other
8662 compression programs@footnote{It also had patent problems in the past.}.
8664 Creating a compressed archive is simple: you just specify a
8665 @dfn{compression option} along with the usual archive creation
8666 commands. The compression option is @option{-z} (@option{--gzip}) to
8667 create a @command{gzip} compressed archive, @option{-j}
8668 (@option{--bzip2}) to create a @command{bzip2} compressed archive,
8669 @option{--lzip} to create an @asis{lzip} compressed archive,
8670 @option{-J} (@option{--xz}) to create an @asis{XZ} archive,
8671 @option{--lzma} to create an @asis{LZMA} compressed
8672 archive, @option{--lzop} to create an @asis{LSOP} archive, and
8673 @option{-Z} (@option{--compress}) to use @command{compress} program.
8677 $ @kbd{tar cfz archive.tar.gz .}
8680 You can also let @GNUTAR{} select the compression program basing on
8681 the suffix of the archive file name. This is done using
8682 @option{--auto-compress} (@option{-a}) command line option. For
8683 example, the following invocation will use @command{bzip2} for
8687 $ @kbd{tar cfa archive.tar.bz2 .}
8691 whereas the following one will use @command{lzma}:
8694 $ @kbd{tar cfa archive.tar.lzma .}
8697 For a complete list of file name suffixes recognized by @GNUTAR{},
8698 see @ref{auto-compress}.
8700 Reading compressed archive is even simpler: you don't need to specify
8701 any additional options as @GNUTAR{} recognizes its format
8702 automatically. Thus, the following commands will list and extract the
8703 archive created in previous example:
8706 # List the compressed archive
8707 $ @kbd{tar tf archive.tar.gz}
8708 # Extract the compressed archive
8709 $ @kbd{tar xf archive.tar.gz}
8712 The format recognition algorithm is based on @dfn{signatures}, a
8713 special byte sequences in the beginning of file, that are specific for
8714 certain compression formats. If this approach fails, @command{tar}
8715 falls back to using archive name suffix to determine its format
8716 (@pxref{auto-compress}, for a list of recognized suffixes).
8718 The only case when you have to specify a decompression option while
8719 reading the archive is when reading from a pipe or from a tape drive
8720 that does not support random access. However, in this case @GNUTAR{}
8721 will indicate which option you should use. For example:
8724 $ @kbd{cat archive.tar.gz | tar tf -}
8725 tar: Archive is compressed. Use -z option
8726 tar: Error is not recoverable: exiting now
8729 If you see such diagnostics, just add the suggested option to the
8730 invocation of @GNUTAR{}:
8733 $ @kbd{cat archive.tar.gz | tar tfz -}
8736 Notice also, that there are several restrictions on operations on
8737 compressed archives. First of all, compressed archives cannot be
8738 modified, i.e., you cannot update (@option{--update}, alias @option{-u})
8739 them or delete (@option{--delete}) members from them or
8740 add (@option{--append}, alias @option{-r}) members to them. Likewise, you
8741 cannot append another @command{tar} archive to a compressed archive using
8742 @option{--concatenate} (@option{-A}). Secondly, multi-volume
8743 archives cannot be compressed.
8745 The following table summarizes compression options used by @GNUTAR{}.
8748 @anchor{auto-compress}
8749 @opindex auto-compress
8750 @item --auto-compress
8752 Select a compression program to use by the archive file name
8753 suffix. The following suffixes are recognized:
8755 @multitable @columnfractions 0.3 0.6
8756 @headitem Suffix @tab Compression program
8757 @item @samp{.gz} @tab @command{gzip}
8758 @item @samp{.tgz} @tab @command{gzip}
8759 @item @samp{.taz} @tab @command{gzip}
8760 @item @samp{.Z} @tab @command{compress}
8761 @item @samp{.taZ} @tab @command{compress}
8762 @item @samp{.bz2} @tab @command{bzip2}
8763 @item @samp{.tz2} @tab @command{bzip2}
8764 @item @samp{.tbz2} @tab @command{bzip2}
8765 @item @samp{.tbz} @tab @command{bzip2}
8766 @item @samp{.lz} @tab @command{lzip}
8767 @item @samp{.lzma} @tab @command{lzma}
8768 @item @samp{.tlz} @tab @command{lzma}
8769 @item @samp{.lzo} @tab @command{lzop}
8770 @item @samp{.xz} @tab @command{xz}
8778 Filter the archive through @command{gzip}.
8780 You can use @option{--gzip} and @option{--gunzip} on physical devices
8781 (tape drives, etc.) and remote files as well as on normal files; data
8782 to or from such devices or remote files is reblocked by another copy
8783 of the @command{tar} program to enforce the specified (or default) record
8784 size. The default compression parameters are used; if you need to
8785 override them, set @env{GZIP} environment variable, e.g.:
8788 $ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
8792 Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
8793 @command{gzip} explicitly:
8796 $ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
8799 @cindex corrupted archives
8800 About corrupted compressed archives: @command{gzip}'ed files have no
8801 redundancy, for maximum compression. The adaptive nature of the
8802 compression scheme means that the compression tables are implicitly
8803 spread all over the archive. If you lose a few blocks, the dynamic
8804 construction of the compression tables becomes unsynchronized, and there
8805 is little chance that you could recover later in the archive.
8807 There are pending suggestions for having a per-volume or per-file
8808 compression in @GNUTAR{}. This would allow for viewing the
8809 contents without decompression, and for resynchronizing decompression at
8810 every volume or file, in case of corrupted archives. Doing so, we might
8811 lose some compressibility. But this would have make recovering easier.
8812 So, there are pros and cons. We'll see!
8817 Filter the archive through @code{xz}. Otherwise like
8822 Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
8826 Filter the archive through @command{lzip}. Otherwise like @option{--gzip}.
8830 Filter the archive through @command{lzma}. Otherwise like @option{--gzip}.
8834 Filter the archive through @command{lzop}. Otherwise like
8842 Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
8844 @opindex use-compress-program
8845 @item --use-compress-program=@var{prog}
8846 @itemx -I=@var{prog}
8847 Use external compression program @var{prog}. Use this option if you
8848 are not happy with the compression program associated with the suffix
8849 at compile time or if you have a compression program that @GNUTAR{}
8850 does not support. There are two requirements to which @var{prog}
8853 First, when called without options, it should read data from standard
8854 input, compress it and output it on standard output.
8856 Secondly, if called with @option{-d} argument, it should do exactly
8857 the opposite, i.e., read the compressed data from the standard input
8858 and produce uncompressed data on the standard output.
8861 @cindex gpg, using with tar
8862 @cindex gnupg, using with tar
8863 @cindex Using encrypted archives
8864 The @option{--use-compress-program} option, in particular, lets you
8865 implement your own filters, not necessarily dealing with
8866 compression/decompression. For example, suppose you wish to implement
8867 PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
8868 gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard
8869 Manual}). The following script does that:
8875 -d) gpg --decrypt - | gzip -d -c;;
8876 '') gzip -c | gpg -s;;
8877 *) echo "Unknown option $1">&2; exit 1;;
8882 Suppose you name it @file{gpgz} and save it somewhere in your
8883 @env{PATH}. Then the following command will create a compressed
8884 archive signed with your private key:
8887 $ @kbd{tar -cf foo.tar.gpgz -Igpgz .}
8891 Likewise, the command below will list its contents:
8894 $ @kbd{tar -tf foo.tar.gpgz -Igpgz .}
8898 The above is based on the following discussion:
8900 I have one question, or maybe it's a suggestion if there isn't a way
8901 to do it now. I would like to use @option{--gzip}, but I'd also like
8902 the output to be fed through a program like @acronym{GNU}
8903 @command{ecc} (actually, right now that's @samp{exactly} what I'd like
8904 to use :-)), basically adding ECC protection on top of compression.
8905 It seems as if this should be quite easy to do, but I can't work out
8906 exactly how to go about it. Of course, I can pipe the standard output
8907 of @command{tar} through @command{ecc}, but then I lose (though I
8908 haven't started using it yet, I confess) the ability to have
8909 @command{tar} use @command{rmt} for it's I/O (I think).
8911 I think the most straightforward thing would be to let me specify a
8912 general set of filters outboard of compression (preferably ordered,
8913 so the order can be automatically reversed on input operations, and
8914 with the options they require specifiable), but beggars shouldn't be
8915 choosers and anything you decide on would be fine with me.
8917 By the way, I like @command{ecc} but if (as the comments say) it can't
8918 deal with loss of block sync, I'm tempted to throw some time at adding
8919 that capability. Supposing I were to actually do such a thing and
8920 get it (apparently) working, do you accept contributed changes to
8921 utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
8923 Isn't that exactly the role of the
8924 @option{--use-compress-prog=@var{program}} option?
8925 I never tried it myself, but I suspect you may want to write a
8926 @var{prog} script or program able to filter stdin to stdout to
8927 way you want. It should recognize the @option{-d} option, for when
8928 extraction is needed rather than creation.
8930 It has been reported that if one writes compressed data (through the
8931 @option{--gzip} or @option{--compress} options) to a DLT and tries to use
8932 the DLT compression mode, the data will actually get bigger and one will
8933 end up with less space on the tape.
8937 @subsection Archiving Sparse Files
8938 @cindex Sparse Files
8940 Files in the file system occasionally have @dfn{holes}. A @dfn{hole}
8941 in a file is a section of the file's contents which was never written.
8942 The contents of a hole reads as all zeros. On many operating systems,
8943 actual disk storage is not allocated for holes, but they are counted
8944 in the length of the file. If you archive such a file, @command{tar}
8945 could create an archive longer than the original. To have @command{tar}
8946 attempt to recognize the holes in a file, use @option{--sparse}
8947 (@option{-S}). When you use this option, then, for any file using
8948 less disk space than would be expected from its length, @command{tar}
8949 searches the file for consecutive stretches of zeros. It then records
8950 in the archive for the file where the consecutive stretches of zeros
8951 are, and only archives the ``real contents'' of the file. On
8952 extraction (using @option{--sparse} is not needed on extraction) any
8953 such files have holes created wherever the continuous stretches of zeros
8954 were found. Thus, if you use @option{--sparse}, @command{tar} archives
8955 won't take more space than the original.
8961 This option instructs @command{tar} to test each file for sparseness
8962 before attempting to archive it. If the file is found to be sparse it
8963 is treated specially, thus allowing to decrease the amount of space
8964 used by its image in the archive.
8966 This option is meaningful only when creating or updating archives. It
8967 has no effect on extraction.
8970 Consider using @option{--sparse} when performing file system backups,
8971 to avoid archiving the expanded forms of files stored sparsely in the
8974 Even if your system has no sparse files currently, some may be
8975 created in the future. If you use @option{--sparse} while making file
8976 system backups as a matter of course, you can be assured the archive
8977 will never take more space on the media than the files take on disk
8978 (otherwise, archiving a disk filled with sparse files might take
8979 hundreds of tapes). @xref{Incremental Dumps}.
8981 However, be aware that @option{--sparse} option presents a serious
8982 drawback. Namely, in order to determine if the file is sparse
8983 @command{tar} has to read it before trying to archive it, so in total
8984 the file is read @strong{twice}. So, always bear in mind that the
8985 time needed to process all files with this option is roughly twice
8986 the time needed to archive them without it.
8987 @FIXME{A technical note:
8989 Programs like @command{dump} do not have to read the entire file; by
8990 examining the file system directly, they can determine in advance
8991 exactly where the holes are and thus avoid reading through them. The
8992 only data it need read are the actual allocated data blocks.
8993 @GNUTAR{} uses a more portable and straightforward
8994 archiving approach, it would be fairly difficult that it does
8995 otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, on
8999 What I did say is that you cannot tell the difference between a hole and an
9000 equivalent number of nulls without reading raw blocks. @code{st_blocks} at
9001 best tells you how many holes there are; it doesn't tell you @emph{where}.
9002 Just as programs may, conceivably, care what @code{st_blocks} is (care
9003 to name one that does?), they may also care where the holes are (I have
9004 no examples of this one either, but it's equally imaginable).
9006 I conclude from this that good archivers are not portable. One can
9007 arguably conclude that if you want a portable program, you can in good
9008 conscience restore files with as many holes as possible, since you can't
9013 @cindex sparse formats, defined
9014 When using @samp{POSIX} archive format, @GNUTAR{} is able to store
9015 sparse files using in three distinct ways, called @dfn{sparse
9016 formats}. A sparse format is identified by its @dfn{number},
9017 consisting, as usual of two decimal numbers, delimited by a dot. By
9018 default, format @samp{1.0} is used. If, for some reason, you wish to
9019 use an earlier format, you can select it using
9020 @option{--sparse-version} option.
9023 @opindex sparse-version
9024 @item --sparse-version=@var{version}
9026 Select the format to store sparse files in. Valid @var{version} values
9027 are: @samp{0.0}, @samp{0.1} and @samp{1.0}. @xref{Sparse Formats},
9028 for a detailed description of each format.
9031 Using @option{--sparse-format} option implies @option{--sparse}.
9034 @section Handling File Attributes
9035 @cindex atrributes, files
9036 @cindex file attributes
9038 When @command{tar} reads files, it updates their access times. To
9039 avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
9040 reset the access time retroactively or avoid changing it in the first
9044 @opindex atime-preserve
9045 @item --atime-preserve
9046 @itemx --atime-preserve=replace
9047 @itemx --atime-preserve=system
9048 Preserve the access times of files that are read. This works only for
9049 files that you own, unless you have superuser privileges.
9051 @option{--atime-preserve=replace} works on most systems, but it also
9052 restores the data modification time and updates the status change
9053 time. Hence it doesn't interact with incremental dumps nicely
9054 (@pxref{Incremental Dumps}), and it can set access or data modification times
9055 incorrectly if other programs access the file while @command{tar} is
9058 @option{--atime-preserve=system} avoids changing the access time in
9059 the first place, if the operating system supports this.
9060 Unfortunately, this may or may not work on any given operating system
9061 or file system. If @command{tar} knows for sure it won't work, it
9062 complains right away.
9064 Currently @option{--atime-preserve} with no operand defaults to
9065 @option{--atime-preserve=replace}, but this is intended to change to
9066 @option{--atime-preserve=system} when the latter is better-supported.
9071 Do not extract data modification time.
9073 When this option is used, @command{tar} leaves the data modification times
9074 of the files it extracts as the times when the files were extracted,
9075 instead of setting it to the times recorded in the archive.
9077 This option is meaningless with @option{--list} (@option{-t}).
9081 Create extracted files with the same ownership they have in the
9084 This is the default behavior for the superuser,
9085 so this option is meaningful only for non-root users, when @command{tar}
9086 is executed on those systems able to give files away. This is
9087 considered as a security flaw by many people, at least because it
9088 makes quite difficult to correctly account users for the disk space
9089 they occupy. Also, the @code{suid} or @code{sgid} attributes of
9090 files are easily and silently lost when files are given away.
9092 When writing an archive, @command{tar} writes the user @acronym{ID} and user name
9093 separately. If it can't find a user name (because the user @acronym{ID} is not
9094 in @file{/etc/passwd}), then it does not write one. When restoring,
9095 it tries to look the name (if one was written) up in
9096 @file{/etc/passwd}. If it fails, then it uses the user @acronym{ID} stored in
9097 the archive instead.
9099 @opindex no-same-owner
9100 @item --no-same-owner
9102 Do not attempt to restore ownership when extracting. This is the
9103 default behavior for ordinary users, so this option has an effect
9104 only for the superuser.
9106 @opindex numeric-owner
9107 @item --numeric-owner
9108 The @option{--numeric-owner} option allows (ANSI) archives to be written
9109 without user/group name information or such information to be ignored
9110 when extracting. It effectively disables the generation and/or use
9111 of user/group name information. This option forces extraction using
9112 the numeric ids from the archive, ignoring the names.
9114 This is useful in certain circumstances, when restoring a backup from
9115 an emergency floppy with different passwd/group files for example.
9116 It is otherwise impossible to extract files with the right ownerships
9117 if the password file in use during the extraction does not match the
9118 one belonging to the file system(s) being extracted. This occurs,
9119 for example, if you are restoring your files after a major crash and
9120 had booted from an emergency floppy with no password file or put your
9121 disk into another machine to do the restore.
9123 The numeric ids are @emph{always} saved into @command{tar} archives.
9124 The identifying names are added at create time when provided by the
9125 system, unless @option{--format=oldgnu} is used. Numeric ids could be
9126 used when moving archives between a collection of machines using
9127 a centralized management for attribution of numeric ids to users
9128 and groups. This is often made through using the NIS capabilities.
9130 When making a @command{tar} file for distribution to other sites, it
9131 is sometimes cleaner to use a single owner for all files in the
9132 distribution, and nicer to specify the write permission bits of the
9133 files as stored in the archive independently of their actual value on
9134 the file system. The way to prepare a clean distribution is usually
9135 to have some Makefile rule creating a directory, copying all needed
9136 files in that directory, then setting ownership and permissions as
9137 wanted (there are a lot of possible schemes), and only then making a
9138 @command{tar} archive out of this directory, before cleaning
9139 everything out. Of course, we could add a lot of options to
9140 @GNUTAR{} for fine tuning permissions and ownership.
9141 This is not the good way, I think. @GNUTAR{} is
9142 already crowded with options and moreover, the approach just explained
9143 gives you a great deal of control already.
9145 @xopindex{same-permissions, short description}
9146 @xopindex{preserve-permissions, short description}
9148 @itemx --same-permissions
9149 @itemx --preserve-permissions
9150 Extract all protection information.
9152 This option causes @command{tar} to set the modes (access permissions) of
9153 extracted files exactly as recorded in the archive. If this option
9154 is not used, the current @code{umask} setting limits the permissions
9155 on extracted files. This option is by default enabled when
9156 @command{tar} is executed by a superuser.
9159 This option is meaningless with @option{--list} (@option{-t}).
9163 Same as both @option{--same-permissions} and @option{--same-order}.
9165 This option is deprecated, and will be removed in @GNUTAR{} version 1.23.
9170 @section Making @command{tar} Archives More Portable
9172 Creating a @command{tar} archive on a particular system that is meant to be
9173 useful later on many other machines and with other versions of @command{tar}
9174 is more challenging than you might think. @command{tar} archive formats
9175 have been evolving since the first versions of Unix. Many such formats
9176 are around, and are not always compatible with each other. This section
9177 discusses a few problems, and gives some advice about making @command{tar}
9178 archives more portable.
9180 One golden rule is simplicity. For example, limit your @command{tar}
9181 archives to contain only regular files and directories, avoiding
9182 other kind of special files. Do not attempt to save sparse files or
9183 contiguous files as such. Let's discuss a few more problems, in turn.
9185 @FIXME{Discuss GNU extensions (incremental backups, multi-volume
9186 archives and archive labels) in GNU and PAX formats.}
9189 * Portable Names:: Portable Names
9190 * dereference:: Symbolic Links
9191 * hard links:: Hard Links
9192 * old:: Old V7 Archives
9193 * ustar:: Ustar Archives
9194 * gnu:: GNU and old GNU format archives.
9195 * posix:: @acronym{POSIX} archives
9196 * Checksumming:: Checksumming Problems
9197 * Large or Negative Values:: Large files, negative time stamps, etc.
9198 * Other Tars:: How to Extract GNU-Specific Data Using
9199 Other @command{tar} Implementations
9202 @node Portable Names
9203 @subsection Portable Names
9205 Use portable file and member names. A name is portable if it contains
9206 only @acronym{ASCII} letters and digits, @samp{/}, @samp{.}, @samp{_}, and
9207 @samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
9208 contain @samp{/-}. Avoid deep directory nesting. For portability to
9209 old Unix hosts, limit your file name components to 14 characters or
9212 If you intend to have your @command{tar} archives to be read under
9213 MSDOS, you should not rely on case distinction for file names, and you
9214 might use the @acronym{GNU} @command{doschk} program for helping you
9215 further diagnosing illegal MSDOS names, which are even more limited
9219 @subsection Symbolic Links
9220 @cindex File names, using symbolic links
9221 @cindex Symbolic link as file name
9223 @opindex dereference
9224 Normally, when @command{tar} archives a symbolic link, it writes a
9225 block to the archive naming the target of the link. In that way, the
9226 @command{tar} archive is a faithful record of the file system contents.
9227 @option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
9228 @command{tar} to archive the files symbolic links point to, instead of
9229 the links themselves. When this option is used, when @command{tar}
9230 encounters a symbolic link, it will archive the linked-to file,
9231 instead of simply recording the presence of a symbolic link.
9233 The name under which the file is stored in the file system is not
9234 recorded in the archive. To record both the symbolic link name and
9235 the file name in the system, archive the file under both names. If
9236 all links were recorded automatically by @command{tar}, an extracted file
9237 might be linked to a file name that no longer exists in the file
9240 If a linked-to file is encountered again by @command{tar} while creating
9241 the same archive, an entire second copy of it will be stored. (This
9242 @emph{might} be considered a bug.)
9244 So, for portable archives, do not archive symbolic links as such,
9245 and use @option{--dereference} (@option{-h}): many systems do not support
9246 symbolic links, and moreover, your distribution might be unusable if
9247 it contains unresolved symbolic links.
9250 @subsection Hard Links
9251 @cindex File names, using hard links
9252 @cindex hard links, dereferencing
9253 @cindex dereferencing hard links
9255 Normally, when @command{tar} archives a hard link, it writes a
9256 block to the archive naming the target of the link (a @samp{1} type
9257 block). In that way, the actual file contents is stored in file only
9258 once. For example, consider the following two files:
9263 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 one
9264 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 jeden
9268 Here, @file{jeden} is a link to @file{one}. When archiving this
9269 directory with a verbose level 2, you will get an output similar to
9273 $ tar cfvv ../archive.tar .
9274 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9275 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9276 hrw-r--r-- gray/staff 0 2007-10-30 15:11 ./one link to ./jeden
9279 The last line shows that, instead of storing two copies of the file,
9280 @command{tar} stored it only once, under the name @file{jeden}, and
9281 stored file @file{one} as a hard link to this file.
9283 It may be important to know that all hard links to the given file are
9284 stored in the archive. For example, this may be necessary for exact
9285 reproduction of the file system. The following option does that:
9288 @xopindex{check-links, described}
9291 Check the number of links dumped for each processed file. If this
9292 number does not match the total number of hard links for the file, print
9296 For example, trying to archive only file @file{jeden} with this option
9297 produces the following diagnostics:
9300 $ tar -c -f ../archive.tar -l jeden
9301 tar: Missing links to `jeden'.
9304 Although creating special records for hard links helps keep a faithful
9305 record of the file system contents and makes archives more compact, it
9306 may present some difficulties when extracting individual members from
9307 the archive. For example, trying to extract file @file{one} from the
9308 archive created in previous examples produces, in the absense of file
9312 $ tar xf archive.tar ./one
9313 tar: ./one: Cannot hard link to `./jeden': No such file or directory
9314 tar: Error exit delayed from previous errors
9317 The reason for this behavior is that @command{tar} cannot seek back in
9318 the archive to the previous member (in this case, @file{one}), to
9319 extract it@footnote{There are plans to fix this in future releases.}.
9320 If you wish to avoid such problems at the cost of a bigger archive,
9321 use the following option:
9324 @xopindex{hard-dereference, described}
9325 @item --hard-dereference
9326 Dereference hard links and store the files they refer to.
9329 For example, trying this option on our two sample files, we get two
9330 copies in the archive, each of which can then be extracted
9331 independently of the other:
9335 $ tar -c -vv -f ../archive.tar --hard-dereference .
9336 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9337 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9338 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./one
9343 @subsection Old V7 Archives
9344 @cindex Format, old style
9345 @cindex Old style format
9346 @cindex Old style archives
9347 @cindex v7 archive format
9349 Certain old versions of @command{tar} cannot handle additional
9350 information recorded by newer @command{tar} programs. To create an
9351 archive in V7 format (not ANSI), which can be read by these old
9352 versions, specify the @option{--format=v7} option in
9353 conjunction with the @option{--create} (@option{-c}) (@command{tar} also
9354 accepts @option{--portability} or @option{--old-archive} for this
9355 option). When you specify it,
9356 @command{tar} leaves out information about directories, pipes, fifos,
9357 contiguous files, and device files, and specifies file ownership by
9358 group and user IDs instead of group and user names.
9360 When updating an archive, do not use @option{--format=v7}
9361 unless the archive was created using this option.
9363 In most cases, a @emph{new} format archive can be read by an @emph{old}
9364 @command{tar} program without serious trouble, so this option should
9365 seldom be needed. On the other hand, most modern @command{tar}s are
9366 able to read old format archives, so it might be safer for you to
9367 always use @option{--format=v7} for your distributions. Notice,
9368 however, that @samp{ustar} format is a better alternative, as it is
9369 free from many of @samp{v7}'s drawbacks.
9372 @subsection Ustar Archive Format
9374 @cindex ustar archive format
9375 Archive format defined by @acronym{POSIX}.1-1988 specification is called
9376 @code{ustar}. Although it is more flexible than the V7 format, it
9377 still has many restrictions (@pxref{Formats,ustar}, for the detailed
9378 description of @code{ustar} format). Along with V7 format,
9379 @code{ustar} format is a good choice for archives intended to be read
9380 with other implementations of @command{tar}.
9382 To create archive in @code{ustar} format, use @option{--format=ustar}
9383 option in conjunction with the @option{--create} (@option{-c}).
9386 @subsection @acronym{GNU} and old @GNUTAR{} format
9388 @cindex GNU archive format
9389 @cindex Old GNU archive format
9390 @GNUTAR{} was based on an early draft of the
9391 @acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
9392 @command{tar}, such as the support for file names longer than 100
9393 characters, use portions of the @command{tar} header record which were
9394 specified in that @acronym{POSIX} draft as unused. Subsequent changes in
9395 @acronym{POSIX} have allocated the same parts of the header record for
9396 other purposes. As a result, @GNUTAR{} format is
9397 incompatible with the current @acronym{POSIX} specification, and with
9398 @command{tar} programs that follow it.
9400 In the majority of cases, @command{tar} will be configured to create
9401 this format by default. This will change in future releases, since
9402 we plan to make @samp{POSIX} format the default.
9404 To force creation a @GNUTAR{} archive, use option
9405 @option{--format=gnu}.
9408 @subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
9410 @cindex POSIX archive format
9411 @cindex PAX archive format
9412 Starting from version 1.14 @GNUTAR{} features full support for
9413 @acronym{POSIX.1-2001} archives.
9415 A @acronym{POSIX} conformant archive will be created if @command{tar}
9416 was given @option{--format=posix} (@option{--format=pax}) option. No
9417 special option is required to read and extract from a @acronym{POSIX}
9421 * PAX keywords:: Controlling Extended Header Keywords.
9425 @subsubsection Controlling Extended Header Keywords
9429 @item --pax-option=@var{keyword-list}
9430 Handle keywords in @acronym{PAX} extended headers. This option is
9431 equivalent to @option{-o} option of the @command{pax} utility.
9434 @var{Keyword-list} is a comma-separated
9435 list of keyword options, each keyword option taking one of
9436 the following forms:
9439 @item delete=@var{pattern}
9440 When used with one of archive-creation commands,
9441 this option instructs @command{tar} to omit from extended header records
9442 that it produces any keywords matching the string @var{pattern}.
9444 When used in extract or list mode, this option instructs tar
9445 to ignore any keywords matching the given @var{pattern} in the extended
9446 header records. In both cases, matching is performed using the pattern
9447 matching notation described in @acronym{POSIX 1003.2}, 3.13
9448 (@pxref{wildcards}). For example:
9451 --pax-option delete=security.*
9454 would suppress security-related information.
9456 @item exthdr.name=@var{string}
9458 This keyword allows user control over the name that is written into the
9459 ustar header blocks for the extended headers. The name is obtained
9460 from @var{string} after making the following substitutions:
9462 @multitable @columnfractions .25 .55
9463 @headitem Meta-character @tab Replaced By
9464 @item %d @tab The directory name of the file, equivalent to the
9465 result of the @command{dirname} utility on the translated file name.
9466 @item %f @tab The name of the file with the directory information
9467 stripped, equivalent to the result of the @command{basename} utility
9468 on the translated file name.
9469 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9470 @item %% @tab A @samp{%} character.
9473 Any other @samp{%} characters in @var{string} produce undefined
9476 If no option @samp{exthdr.name=string} is specified, @command{tar}
9477 will use the following default value:
9483 @item exthdr.mtime=@var{value}
9485 This keyword defines the value of the @samp{mtime} field that
9486 is written into the ustar header blocks for the extended headers.
9487 By default, the @samp{mtime} field is set to the modification time
9488 of the archive member described by that extended headers.
9490 @item globexthdr.name=@var{string}
9491 This keyword allows user control over the name that is written into
9492 the ustar header blocks for global extended header records. The name
9493 is obtained from the contents of @var{string}, after making
9494 the following substitutions:
9496 @multitable @columnfractions .25 .55
9497 @headitem Meta-character @tab Replaced By
9498 @item %n @tab An integer that represents the
9499 sequence number of the global extended header record in the archive,
9501 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9502 @item %% @tab A @samp{%} character.
9505 Any other @samp{%} characters in @var{string} produce undefined results.
9507 If no option @samp{globexthdr.name=string} is specified, @command{tar}
9508 will use the following default value:
9511 $TMPDIR/GlobalHead.%p.%n
9515 where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
9516 environment variable. If @var{TMPDIR} is not set, @command{tar}
9519 @item globexthdr.mtime=@var{value}
9521 This keyword defines the value of the @samp{mtime} field that
9522 is written into the ustar header blocks for the global extended headers.
9523 By default, the @samp{mtime} field is set to the time when
9524 @command{tar} was invoked.
9526 @item @var{keyword}=@var{value}
9527 When used with one of archive-creation commands, these keyword/value pairs
9528 will be included at the beginning of the archive in a global extended
9529 header record. When used with one of archive-reading commands,
9530 @command{tar} will behave as if it has encountered these keyword/value
9531 pairs at the beginning of the archive in a global extended header
9534 @item @var{keyword}:=@var{value}
9535 When used with one of archive-creation commands, these keyword/value pairs
9536 will be included as records at the beginning of an extended header for
9537 each file. This is effectively equivalent to @var{keyword}=@var{value}
9538 form except that it creates no global extended header records.
9540 When used with one of archive-reading commands, @command{tar} will
9541 behave as if these keyword/value pairs were included as records at the
9542 end of each extended header; thus, they will override any global or
9543 file-specific extended header record keywords of the same names.
9544 For example, in the command:
9547 tar --format=posix --create \
9548 --file archive --pax-option gname:=user .
9551 the group name will be forced to a new value for all files
9552 stored in the archive.
9555 In any of the forms described above, the @var{value} may be
9556 a string enclosed in curly braces. In that case, the string
9557 between the braces is understood either as a textual time
9558 representation, as described in @ref{Date input formats}, or a name of
9559 the existing file, starting with @samp{/} or @samp{.}. In the latter
9560 case, the modification time of that file is used.
9562 For example, to set all modification times to the current date, you
9563 use the following option:
9566 --pax-option='mtime:=@{now@}'
9569 Note quoting of the option's argument.
9571 @cindex archives, binary equivalent
9572 @cindex binary equivalent archives, creating
9573 As another example, here is the option that ensures that any two
9574 archives created using it, will be binary equivalent if they have the
9578 --pax-option=exthdr.name=%d/PaxHeaders/%f,atime:=0
9582 @subsection Checksumming Problems
9584 SunOS and HP-UX @command{tar} fail to accept archives created using
9585 @GNUTAR{} and containing non-@acronym{ASCII} file names, that
9586 is, file names having characters with the eight bit set, because they
9587 use signed checksums, while @GNUTAR{} uses unsigned
9588 checksums while creating archives, as per @acronym{POSIX} standards. On
9589 reading, @GNUTAR{} computes both checksums and
9590 accepts any. It is somewhat worrying that a lot of people may go
9591 around doing backup of their files using faulty (or at least
9592 non-standard) software, not learning about it until it's time to
9593 restore their missing files with an incompatible file extractor, or
9596 @GNUTAR{} computes checksums both ways, and accept
9597 any on read, so @acronym{GNU} tar can read Sun tapes even with their
9598 wrong checksums. @GNUTAR{} produces the standard
9599 checksum, however, raising incompatibilities with Sun. That is to
9600 say, @GNUTAR{} has not been modified to
9601 @emph{produce} incorrect archives to be read by buggy @command{tar}'s.
9602 I've been told that more recent Sun @command{tar} now read standard
9603 archives, so maybe Sun did a similar patch, after all?
9605 The story seems to be that when Sun first imported @command{tar}
9606 sources on their system, they recompiled it without realizing that
9607 the checksums were computed differently, because of a change in
9608 the default signing of @code{char}'s in their compiler. So they
9609 started computing checksums wrongly. When they later realized their
9610 mistake, they merely decided to stay compatible with it, and with
9611 themselves afterwards. Presumably, but I do not really know, HP-UX
9612 has chosen that their @command{tar} archives to be compatible with Sun's.
9613 The current standards do not favor Sun @command{tar} format. In any
9614 case, it now falls on the shoulders of SunOS and HP-UX users to get
9615 a @command{tar} able to read the good archives they receive.
9617 @node Large or Negative Values
9618 @subsection Large or Negative Values
9619 @cindex large values
9620 @cindex future time stamps
9621 @cindex negative time stamps
9624 The above sections suggest to use @samp{oldest possible} archive
9625 format if in doubt. However, sometimes it is not possible. If you
9626 attempt to archive a file whose metadata cannot be represented using
9627 required format, @GNUTAR{} will print error message and ignore such a
9628 file. You will than have to switch to a format that is able to
9629 handle such values. The format summary table (@pxref{Formats}) will
9632 In particular, when trying to archive files larger than 8GB or with
9633 timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
9634 12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
9635 @acronym{POSIX} archive formats. When considering which format to
9636 choose, bear in mind that the @acronym{GNU} format uses
9637 two's-complement base-256 notation to store values that do not fit
9638 into standard @acronym{ustar} range. Such archives can generally be
9639 read only by a @GNUTAR{} implementation. Moreover, they sometimes
9640 cannot be correctly restored on another hosts even by @GNUTAR{}. For
9641 example, using two's complement representation for negative time
9642 stamps that assumes a signed 32-bit @code{time_t} generates archives
9643 that are not portable to hosts with differing @code{time_t}
9646 On the other hand, @acronym{POSIX} archives, generally speaking, can
9647 be extracted by any tar implementation that understands older
9648 @acronym{ustar} format. The only exception are files larger than 8GB.
9650 @FIXME{Describe how @acronym{POSIX} archives are extracted by non
9654 @subsection How to Extract GNU-Specific Data Using Other @command{tar} Implementations
9656 In previous sections you became acquainted with various quirks
9657 necessary to make your archives portable. Sometimes you may need to
9658 extract archives containing GNU-specific members using some
9659 third-party @command{tar} implementation or an older version of
9660 @GNUTAR{}. Of course your best bet is to have @GNUTAR{} installed,
9661 but if it is for some reason impossible, this section will explain
9662 how to cope without it.
9664 When we speak about @dfn{GNU-specific} members we mean two classes of
9665 them: members split between the volumes of a multi-volume archive and
9666 sparse members. You will be able to always recover such members if
9667 the archive is in PAX format. In addition split members can be
9668 recovered from archives in old GNU format. The following subsections
9669 describe the required procedures in detail.
9672 * Split Recovery:: Members Split Between Volumes
9673 * Sparse Recovery:: Sparse Members
9676 @node Split Recovery
9677 @subsubsection Extracting Members Split Between Volumes
9679 @cindex Mutli-volume archives, extracting using non-GNU tars
9680 If a member is split between several volumes of an old GNU format archive
9681 most third party @command{tar} implementation will fail to extract
9682 it. To extract it, use @command{tarcat} program (@pxref{Tarcat}).
9683 This program is available from
9684 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tarcat.html, @GNUTAR{}
9685 home page}. It concatenates several archive volumes into a single
9686 valid archive. For example, if you have three volumes named from
9687 @file{vol-1.tar} to @file{vol-3.tar}, you can do the following to
9688 extract them using a third-party @command{tar}:
9691 $ @kbd{tarcat vol-1.tar vol-2.tar vol-3.tar | tar xf -}
9694 @cindex Mutli-volume archives in PAX format, extracting using non-GNU tars
9695 You could use this approach for most (although not all) PAX
9696 format archives as well. However, extracting split members from a PAX
9697 archive is a much easier task, because PAX volumes are constructed in
9698 such a way that each part of a split member is extracted to a
9699 different file by @command{tar} implementations that are not aware of
9700 GNU extensions. More specifically, the very first part retains its
9701 original name, and all subsequent parts are named using the pattern:
9704 %d/GNUFileParts.%p/%f.%n
9708 where symbols preceeded by @samp{%} are @dfn{macro characters} that
9709 have the following meaning:
9711 @multitable @columnfractions .25 .55
9712 @headitem Meta-character @tab Replaced By
9713 @item %d @tab The directory name of the file, equivalent to the
9714 result of the @command{dirname} utility on its full name.
9715 @item %f @tab The file name of the file, equivalent to the result
9716 of the @command{basename} utility on its full name.
9717 @item %p @tab The process @acronym{ID} of the @command{tar} process that
9718 created the archive.
9719 @item %n @tab Ordinal number of this particular part.
9722 For example, if the file @file{var/longfile} was split during archive
9723 creation between three volumes, and the creator @command{tar} process
9724 had process @acronym{ID} @samp{27962}, then the member names will be:
9728 var/GNUFileParts.27962/longfile.1
9729 var/GNUFileParts.27962/longfile.2
9732 When you extract your archive using a third-party @command{tar}, these
9733 files will be created on your disk, and the only thing you will need
9734 to do to restore your file in its original form is concatenate them in
9735 the proper order, for example:
9740 $ @kbd{cat GNUFileParts.27962/longfile.1 \
9741 GNUFileParts.27962/longfile.2 >> longfile}
9742 $ rm -f GNUFileParts.27962
9746 Notice, that if the @command{tar} implementation you use supports PAX
9747 format archives, it will probably emit warnings about unknown keywords
9748 during extraction. They will look like this:
9753 Unknown extended header keyword 'GNU.volume.filename' ignored.
9754 Unknown extended header keyword 'GNU.volume.size' ignored.
9755 Unknown extended header keyword 'GNU.volume.offset' ignored.
9760 You can safely ignore these warnings.
9762 If your @command{tar} implementation is not PAX-aware, you will get
9763 more warnings and more files generated on your disk, e.g.:
9767 $ @kbd{tar xf vol-1.tar}
9768 var/PaxHeaders.27962/longfile: Unknown file type 'x', extracted as
9770 Unexpected EOF in archive
9771 $ @kbd{tar xf vol-2.tar}
9772 tmp/GlobalHead.27962.1: Unknown file type 'g', extracted as normal file
9773 GNUFileParts.27962/PaxHeaders.27962/sparsefile.1: Unknown file type
9774 'x', extracted as normal file
9778 Ignore these warnings. The @file{PaxHeaders.*} directories created
9779 will contain files with @dfn{extended header keywords} describing the
9780 extracted files. You can delete them, unless they describe sparse
9781 members. Read further to learn more about them.
9783 @node Sparse Recovery
9784 @subsubsection Extracting Sparse Members
9786 @cindex sparse files, extracting with non-GNU tars
9787 Any @command{tar} implementation will be able to extract sparse members from a
9788 PAX archive. However, the extracted files will be @dfn{condensed},
9789 i.e., any zero blocks will be removed from them. When we restore such
9790 a condensed file to its original form, by adding zero blocks (or
9791 @dfn{holes}) back to their original locations, we call this process
9792 @dfn{expanding} a compressed sparse file.
9795 To expand a file, you will need a simple auxiliary program called
9796 @command{xsparse}. It is available in source form from
9797 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/xsparse.html, @GNUTAR{}
9800 @cindex sparse files v.1.0, extracting with non-GNU tars
9801 Let's begin with archive members in @dfn{sparse format
9802 version 1.0}@footnote{@xref{PAX 1}.}, which are the easiest to expand.
9803 The condensed file will contain both file map and file data, so no
9804 additional data will be needed to restore it. If the original file
9805 name was @file{@var{dir}/@var{name}}, then the condensed file will be
9806 named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
9807 @var{n} is a decimal number@footnote{Technically speaking, @var{n} is a
9808 @dfn{process @acronym{ID}} of the @command{tar} process which created the
9809 archive (@pxref{PAX keywords}).}.
9811 To expand a version 1.0 file, run @command{xsparse} as follows:
9814 $ @kbd{xsparse @file{cond-file}}
9818 where @file{cond-file} is the name of the condensed file. The utility
9819 will deduce the name for the resulting expanded file using the
9820 following algorithm:
9823 @item If @file{cond-file} does not contain any directories,
9824 @file{../cond-file} will be used;
9826 @item If @file{cond-file} has the form
9827 @file{@var{dir}/@var{t}/@var{name}}, where both @var{t} and @var{name}
9828 are simple names, with no @samp{/} characters in them, the output file
9829 name will be @file{@var{dir}/@var{name}}.
9831 @item Otherwise, if @file{cond-file} has the form
9832 @file{@var{dir}/@var{name}}, the output file name will be
9836 In the unlikely case when this algorithm does not suit your needs,
9837 you can explicitly specify output file name as a second argument to
9841 $ @kbd{xsparse @file{cond-file} @file{out-file}}
9844 It is often a good idea to run @command{xsparse} in @dfn{dry run} mode
9845 first. In this mode, the command does not actually expand the file,
9846 but verbosely lists all actions it would be taking to do so. The dry
9847 run mode is enabled by @option{-n} command line argument:
9851 $ @kbd{xsparse -n /home/gray/GNUSparseFile.6058/sparsefile}
9852 Reading v.1.0 sparse map
9853 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9854 `/home/gray/sparsefile'
9859 To actually expand the file, you would run:
9862 $ @kbd{xsparse /home/gray/GNUSparseFile.6058/sparsefile}
9866 The program behaves the same way all UNIX utilities do: it will keep
9867 quiet unless it has simething important to tell you (e.g. an error
9868 condition or something). If you wish it to produce verbose output,
9869 similar to that from the dry run mode, use @option{-v} option:
9873 $ @kbd{xsparse -v /home/gray/GNUSparseFile.6058/sparsefile}
9874 Reading v.1.0 sparse map
9875 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9876 `/home/gray/sparsefile'
9881 Additionally, if your @command{tar} implementation has extracted the
9882 @dfn{extended headers} for this file, you can instruct @command{xstar}
9883 to use them in order to verify the integrity of the expanded file.
9884 The option @option{-x} sets the name of the extended header file to
9885 use. Continuing our example:
9889 $ @kbd{xsparse -v -x /home/gray/PaxHeaders.6058/sparsefile \
9890 /home/gray/GNUSparseFile.6058/sparsefile}
9891 Reading extended header file
9892 Found variable GNU.sparse.major = 1
9893 Found variable GNU.sparse.minor = 0
9894 Found variable GNU.sparse.name = sparsefile
9895 Found variable GNU.sparse.realsize = 217481216
9896 Reading v.1.0 sparse map
9897 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9898 `/home/gray/sparsefile'
9903 @anchor{extracting sparse v.0.x}
9904 @cindex sparse files v.0.1, extracting with non-GNU tars
9905 @cindex sparse files v.0.0, extracting with non-GNU tars
9906 An @dfn{extended header} is a special @command{tar} archive header
9907 that precedes an archive member and contains a set of
9908 @dfn{variables}, describing the member properties that cannot be
9909 stored in the standard @code{ustar} header. While optional for
9910 expanding sparse version 1.0 members, the use of extended headers is
9911 mandatory when expanding sparse members in older sparse formats: v.0.0
9912 and v.0.1 (The sparse formats are described in detail in @ref{Sparse
9913 Formats}.) So, for these formats, the question is: how to obtain
9914 extended headers from the archive?
9916 If you use a @command{tar} implementation that does not support PAX
9917 format, extended headers for each member will be extracted as a
9918 separate file. If we represent the member name as
9919 @file{@var{dir}/@var{name}}, then the extended header file will be
9920 named @file{@var{dir}/@/PaxHeaders.@var{n}/@/@var{name}}, where
9921 @var{n} is an integer number.
9923 Things become more difficult if your @command{tar} implementation
9924 does support PAX headers, because in this case you will have to
9925 manually extract the headers. We recommend the following algorithm:
9929 Consult the documentation of your @command{tar} implementation for an
9930 option that prints @dfn{block numbers} along with the archive
9931 listing (analogous to @GNUTAR{}'s @option{-R} option). For example,
9932 @command{star} has @option{-block-number}.
9935 Obtain verbose listing using the @samp{block number} option, and
9936 find block numbers of the sparse member in question and the member
9937 immediately following it. For example, running @command{star} on our
9942 $ @kbd{star -t -v -block-number -f arc.tar}
9944 star: Unknown extended header keyword 'GNU.sparse.size' ignored.
9945 star: Unknown extended header keyword 'GNU.sparse.numblocks' ignored.
9946 star: Unknown extended header keyword 'GNU.sparse.name' ignored.
9947 star: Unknown extended header keyword 'GNU.sparse.map' ignored.
9948 block 56: 425984 -rw-r--r-- gray/users Jun 25 14:46 2006 GNUSparseFile.28124/sparsefile
9949 block 897: 65391 -rw-r--r-- gray/users Jun 24 20:06 2006 README
9955 (as usual, ignore the warnings about unknown keywords.)
9958 Let @var{size} be the size of the sparse member, @var{Bs} be its block number
9959 and @var{Bn} be the block number of the next member.
9963 @var{N} = @var{Bs} - @var{Bn} - @var{size}/512 - 2
9967 This number gives the size of the extended header part in tar @dfn{blocks}.
9968 In our example, this formula gives: @code{897 - 56 - 425984 / 512 - 2
9972 Use @command{dd} to extract the headers:
9975 @kbd{dd if=@var{archive} of=@var{hname} bs=512 skip=@var{Bs} count=@var{N}}
9979 where @var{archive} is the archive name, @var{hname} is a name of the
9980 file to store the extended header in, @var{Bs} and @var{N} are
9981 computed in previous steps.
9983 In our example, this command will be
9986 $ @kbd{dd if=arc.tar of=xhdr bs=512 skip=56 count=7}
9990 Finally, you can expand the condensed file, using the obtained header:
9994 $ @kbd{xsparse -v -x xhdr GNUSparseFile.6058/sparsefile}
9995 Reading extended header file
9996 Found variable GNU.sparse.size = 217481216
9997 Found variable GNU.sparse.numblocks = 208
9998 Found variable GNU.sparse.name = sparsefile
9999 Found variable GNU.sparse.map = 0,2048,1050624,2048,@dots{}
10000 Expanding file `GNUSparseFile.28124/sparsefile' to `sparsefile'
10006 @section Comparison of @command{tar} and @command{cpio}
10009 @FIXME{Reorganize the following material}
10011 The @command{cpio} archive formats, like @command{tar}, do have maximum
10012 file name lengths. The binary and old @acronym{ASCII} formats have a maximum file
10013 length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max
10014 file length of 1024. @acronym{GNU} @command{cpio} can read and write archives
10015 with arbitrary file name lengths, but other @command{cpio} implementations
10016 may crash unexplainedly trying to read them.
10018 @command{tar} handles symbolic links in the form in which it comes in @acronym{BSD};
10019 @command{cpio} doesn't handle symbolic links in the form in which it comes
10020 in System V prior to SVR4, and some vendors may have added symlinks
10021 to their system without enhancing @command{cpio} to know about them.
10022 Others may have enhanced it in a way other than the way I did it
10023 at Sun, and which was adopted by AT&T (and which is, I think, also
10024 present in the @command{cpio} that Berkeley picked up from AT&T and put
10025 into a later @acronym{BSD} release---I think I gave them my changes).
10027 (SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
10028 can handle @command{tar} format input, and write it on output, and it
10029 probably handles symbolic links. They may not have bothered doing
10030 anything to enhance @command{tar} as a result.)
10032 @command{cpio} handles special files; traditional @command{tar} doesn't.
10034 @command{tar} comes with V7, System III, System V, and @acronym{BSD} source;
10035 @command{cpio} comes only with System III, System V, and later @acronym{BSD}
10036 (4.3-tahoe and later).
10038 @command{tar}'s way of handling multiple hard links to a file can handle
10039 file systems that support 32-bit i-numbers (e.g., the @acronym{BSD} file system);
10040 @command{cpio}s way requires you to play some games (in its ``binary''
10041 format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
10042 they're 18 bits---it would have to play games with the "file system @acronym{ID}"
10043 field of the header to make sure that the file system @acronym{ID}/i-number pairs
10044 of different files were always different), and I don't know which
10045 @command{cpio}s, if any, play those games. Those that don't might get
10046 confused and think two files are the same file when they're not, and
10047 make hard links between them.
10049 @command{tar}s way of handling multiple hard links to a file places only
10050 one copy of the link on the tape, but the name attached to that copy
10051 is the @emph{only} one you can use to retrieve the file; @command{cpio}s
10052 way puts one copy for every link, but you can retrieve it using any
10056 What type of check sum (if any) is used, and how is this calculated.
10059 See the attached manual pages for @command{tar} and @command{cpio} format.
10060 @command{tar} uses a checksum which is the sum of all the bytes in the
10061 @command{tar} header for a file; @command{cpio} uses no checksum.
10064 If anyone knows why @command{cpio} was made when @command{tar} was present
10068 It wasn't. @command{cpio} first showed up in PWB/UNIX 1.0; no
10069 generally-available version of UNIX had @command{tar} at the time. I don't
10070 know whether any version that was generally available @emph{within AT&T}
10071 had @command{tar}, or, if so, whether the people within AT&T who did
10072 @command{cpio} knew about it.
10074 On restore, if there is a corruption on a tape @command{tar} will stop at
10075 that point, while @command{cpio} will skip over it and try to restore the
10078 The main difference is just in the command syntax and header format.
10080 @command{tar} is a little more tape-oriented in that everything is blocked
10081 to start on a record boundary.
10084 Is there any differences between the ability to recover crashed
10085 archives between the two of them. (Is there any chance of recovering
10086 crashed archives at all.)
10089 Theoretically it should be easier under @command{tar} since the blocking
10090 lets you find a header with some variation of @samp{dd skip=@var{nn}}.
10091 However, modern @command{cpio}'s and variations have an option to just
10092 search for the next file header after an error with a reasonable chance
10093 of resyncing. However, lots of tape driver software won't allow you to
10094 continue past a media error which should be the only reason for getting
10095 out of sync unless a file changed sizes while you were writing the
10099 If anyone knows why @command{cpio} was made when @command{tar} was present
10100 at the unix scene, please tell me about this too.
10103 Probably because it is more media efficient (by not blocking everything
10104 and using only the space needed for the headers where @command{tar}
10105 always uses 512 bytes per file header) and it knows how to archive
10108 You might want to look at the freely available alternatives. The
10109 major ones are @command{afio}, @GNUTAR{}, and
10110 @command{pax}, each of which have their own extensions with some
10111 backwards compatibility.
10113 Sparse files were @command{tar}red as sparse files (which you can
10114 easily test, because the resulting archive gets smaller, and
10115 @acronym{GNU} @command{cpio} can no longer read it).
10118 @chapter Tapes and Other Archive Media
10121 A few special cases about tape handling warrant more detailed
10122 description. These special cases are discussed below.
10124 Many complexities surround the use of @command{tar} on tape drives. Since
10125 the creation and manipulation of archives located on magnetic tape was
10126 the original purpose of @command{tar}, it contains many features making
10127 such manipulation easier.
10129 Archives are usually written on dismountable media---tape cartridges,
10130 mag tapes, or floppy disks.
10132 The amount of data a tape or disk holds depends not only on its size,
10133 but also on how it is formatted. A 2400 foot long reel of mag tape
10134 holds 40 megabytes of data when formatted at 1600 bits per inch. The
10135 physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
10137 Magnetic media are re-usable---once the archive on a tape is no longer
10138 needed, the archive can be erased and the tape or disk used over.
10139 Media quality does deteriorate with use, however. Most tapes or disks
10140 should be discarded when they begin to produce data errors. EXABYTE
10141 tape cartridges should be discarded when they generate an @dfn{error
10142 count} (number of non-usable bits) of more than 10k.
10144 Magnetic media are written and erased using magnetic fields, and
10145 should be protected from such fields to avoid damage to stored data.
10146 Sticking a floppy disk to a filing cabinet using a magnet is probably
10150 * Device:: Device selection and switching
10151 * Remote Tape Server::
10152 * Common Problems and Solutions::
10153 * Blocking:: Blocking
10154 * Many:: Many archives on one tape
10155 * Using Multiple Tapes:: Using Multiple Tapes
10156 * label:: Including a Label in the Archive
10158 * Write Protection::
10162 @section Device Selection and Switching
10166 @item -f [@var{hostname}:]@var{file}
10167 @itemx --file=[@var{hostname}:]@var{file}
10168 Use archive file or device @var{file} on @var{hostname}.
10171 This option is used to specify the file name of the archive @command{tar}
10174 If the file name is @samp{-}, @command{tar} reads the archive from standard
10175 input (when listing or extracting), or writes it to standard output
10176 (when creating). If the @samp{-} file name is given when updating an
10177 archive, @command{tar} will read the original archive from its standard
10178 input, and will write the entire new archive to its standard output.
10180 If the file name contains a @samp{:}, it is interpreted as
10181 @samp{hostname:file name}. If the @var{hostname} contains an @dfn{at}
10182 sign (@samp{@@}), it is treated as @samp{user@@hostname:file name}. In
10183 either case, @command{tar} will invoke the command @command{rsh} (or
10184 @command{remsh}) to start up an @command{/usr/libexec/rmt} on the remote
10185 machine. If you give an alternate login name, it will be given to the
10187 Naturally, the remote machine must have an executable
10188 @command{/usr/libexec/rmt}. This program is free software from the
10189 University of California, and a copy of the source code can be found
10190 with the sources for @command{tar}; it's compiled and installed by default.
10191 The exact path to this utility is determined when configuring the package.
10192 It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for
10193 your installation prefix. This location may also be overridden at
10194 runtime by using the @option{--rmt-command=@var{command}} option (@xref{Option Summary,
10195 ---rmt-command}, for detailed description of this option. @xref{Remote
10196 Tape Server}, for the description of @command{rmt} command).
10198 If this option is not given, but the environment variable @env{TAPE}
10199 is set, its value is used; otherwise, old versions of @command{tar}
10200 used a default archive name (which was picked when @command{tar} was
10201 compiled). The default is normally set up to be the @dfn{first} tape
10202 drive or other transportable I/O medium on the system.
10204 Starting with version 1.11.5, @GNUTAR{} uses
10205 standard input and standard output as the default device, and I will
10206 not try anymore supporting automatic device detection at installation
10207 time. This was failing really in too many cases, it was hopeless.
10208 This is now completely left to the installer to override standard
10209 input and standard output for default device, if this seems
10210 preferable. Further, I think @emph{most} actual usages of
10211 @command{tar} are done with pipes or disks, not really tapes,
10212 cartridges or diskettes.
10214 Some users think that using standard input and output is running
10215 after trouble. This could lead to a nasty surprise on your screen if
10216 you forget to specify an output file name---especially if you are going
10217 through a network or terminal server capable of buffering large amounts
10218 of output. We had so many bug reports in that area of configuring
10219 default tapes automatically, and so many contradicting requests, that
10220 we finally consider the problem to be portably intractable. We could
10221 of course use something like @samp{/dev/tape} as a default, but this
10222 is @emph{also} running after various kind of trouble, going from hung
10223 processes to accidental destruction of real tapes. After having seen
10224 all this mess, using standard input and output as a default really
10225 sounds like the only clean choice left, and a very useful one too.
10227 @GNUTAR{} reads and writes archive in records, I
10228 suspect this is the main reason why block devices are preferred over
10229 character devices. Most probably, block devices are more efficient
10230 too. The installer could also check for @samp{DEFTAPE} in
10231 @file{<sys/mtio.h>}.
10234 @xopindex{force-local, short description}
10235 @item --force-local
10236 Archive file is local even if it contains a colon.
10238 @opindex rsh-command
10239 @item --rsh-command=@var{command}
10240 Use remote @var{command} instead of @command{rsh}. This option exists
10241 so that people who use something other than the standard @command{rsh}
10242 (e.g., a Kerberized @command{rsh}) can access a remote device.
10244 When this command is not used, the shell command found when
10245 the @command{tar} program was installed is used instead. This is
10246 the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh},
10247 @file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}.
10248 The installer may have overridden this by defining the environment
10249 variable @env{RSH} @emph{at installation time}.
10252 Specify drive and density.
10254 @xopindex{multi-volume, short description}
10256 @itemx --multi-volume
10257 Create/list/extract multi-volume archive.
10259 This option causes @command{tar} to write a @dfn{multi-volume} archive---one
10260 that may be larger than will fit on the medium used to hold it.
10261 @xref{Multi-Volume Archives}.
10263 @xopindex{tape-length, short description}
10265 @itemx --tape-length=@var{num}
10266 Change tape after writing @var{num} x 1024 bytes.
10268 This option might be useful when your tape drivers do not properly
10269 detect end of physical tapes. By being slightly conservative on the
10270 maximum tape length, you might avoid the problem entirely.
10272 @xopindex{info-script, short description}
10273 @xopindex{new-volume-script, short description}
10274 @item -F @var{file}
10275 @itemx --info-script=@var{file}
10276 @itemx --new-volume-script=@var{file}
10277 Execute @file{file} at end of each tape. This implies
10278 @option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed
10279 description of this option.
10282 @node Remote Tape Server
10283 @section Remote Tape Server
10285 @cindex remote tape drive
10287 In order to access the tape drive on a remote machine, @command{tar}
10288 uses the remote tape server written at the University of California at
10289 Berkeley. The remote tape server must be installed as
10290 @file{@var{prefix}/libexec/rmt} on any machine whose tape drive you
10291 want to use. @command{tar} calls @command{rmt} by running an
10292 @command{rsh} or @command{remsh} to the remote machine, optionally
10293 using a different login name if one is supplied.
10295 A copy of the source for the remote tape server is provided. It is
10296 Copyright @copyright{} 1983 by the Regents of the University of
10297 California, but can be freely distributed. It is compiled and
10298 installed by default.
10300 @cindex absolute file names
10301 Unless you use the @option{--absolute-names} (@option{-P}) option,
10302 @GNUTAR{} will not allow you to create an archive that contains
10303 absolute file names (a file name beginning with @samp{/}.) If you try,
10304 @command{tar} will automatically remove the leading @samp{/} from the
10305 file names it stores in the archive. It will also type a warning
10306 message telling you what it is doing.
10308 When reading an archive that was created with a different
10309 @command{tar} program, @GNUTAR{} automatically
10310 extracts entries in the archive which have absolute file names as if
10311 the file names were not absolute. This is an important feature. A
10312 visitor here once gave a @command{tar} tape to an operator to restore;
10313 the operator used Sun @command{tar} instead of @GNUTAR{},
10314 and the result was that it replaced large portions of
10315 our @file{/bin} and friends with versions from the tape; needless to
10316 say, we were unhappy about having to recover the file system from
10319 For example, if the archive contained a file @file{/usr/bin/computoy},
10320 @GNUTAR{} would extract the file to @file{usr/bin/computoy},
10321 relative to the current directory. If you want to extract the files in
10322 an archive to the same absolute names that they had when the archive
10323 was created, you should do a @samp{cd /} before extracting the files
10324 from the archive, or you should either use the @option{--absolute-names}
10325 option, or use the command @samp{tar -C / @dots{}}.
10327 @cindex Ultrix 3.1 and write failure
10328 Some versions of Unix (Ultrix 3.1 is known to have this problem),
10329 can claim that a short write near the end of a tape succeeded,
10330 when it actually failed. This will result in the -M option not
10331 working correctly. The best workaround at the moment is to use a
10332 significantly larger blocking factor than the default 20.
10334 In order to update an archive, @command{tar} must be able to backspace the
10335 archive in order to reread or rewrite a record that was just read (or
10336 written). This is currently possible only on two kinds of files: normal
10337 disk files (or any other file that can be backspaced with @samp{lseek}),
10338 and industry-standard 9-track magnetic tape (or any other kind of tape
10339 that can be backspaced with the @code{MTIOCTOP} @code{ioctl}).
10341 This means that the @option{--append}, @option{--concatenate}, and
10342 @option{--delete} commands will not work on any other kind of file.
10343 Some media simply cannot be backspaced, which means these commands and
10344 options will never be able to work on them. These non-backspacing
10345 media include pipes and cartridge tape drives.
10347 Some other media can be backspaced, and @command{tar} will work on them
10348 once @command{tar} is modified to do so.
10350 Archives created with the @option{--multi-volume}, @option{--label}, and
10351 @option{--incremental} (@option{-G}) options may not be readable by other version
10352 of @command{tar}. In particular, restoring a file that was split over
10353 a volume boundary will require some careful work with @command{dd}, if
10354 it can be done at all. Other versions of @command{tar} may also create
10355 an empty file whose name is that of the volume header. Some versions
10356 of @command{tar} may create normal files instead of directories archived
10357 with the @option{--incremental} (@option{-G}) option.
10359 @node Common Problems and Solutions
10360 @section Some Common Problems and their Solutions
10365 errors from system:
10367 no such file or directory
10370 errors from @command{tar}:
10371 directory checksum error
10372 header format error
10374 errors from media/system:
10386 @dfn{Block} and @dfn{record} terminology is rather confused, and it
10387 is also confusing to the expert reader. On the other hand, readers
10388 who are new to the field have a fresh mind, and they may safely skip
10389 the next two paragraphs, as the remainder of this manual uses those
10390 two terms in a quite consistent way.
10392 John Gilmore, the writer of the public domain @command{tar} from which
10393 @GNUTAR{} was originally derived, wrote (June 1995):
10396 The nomenclature of tape drives comes from IBM, where I believe
10397 they were invented for the IBM 650 or so. On IBM mainframes, what
10398 is recorded on tape are tape blocks. The logical organization of
10399 data is into records. There are various ways of putting records into
10400 blocks, including @code{F} (fixed sized records), @code{V} (variable
10401 sized records), @code{FB} (fixed blocked: fixed size records, @var{n}
10402 to a block), @code{VB} (variable size records, @var{n} to a block),
10403 @code{VSB} (variable spanned blocked: variable sized records that can
10404 occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=}
10405 parameter specified this to the operating system.
10407 The Unix man page on @command{tar} was totally confused about this.
10408 When I wrote @code{PD TAR}, I used the historically correct terminology
10409 (@command{tar} writes data records, which are grouped into blocks).
10410 It appears that the bogus terminology made it into @acronym{POSIX} (no surprise
10411 here), and now Fran@,{c}ois has migrated that terminology back
10412 into the source code too.
10415 The term @dfn{physical block} means the basic transfer chunk from or
10416 to a device, after which reading or writing may stop without anything
10417 being lost. In this manual, the term @dfn{block} usually refers to
10418 a disk physical block, @emph{assuming} that each disk block is 512
10419 bytes in length. It is true that some disk devices have different
10420 physical blocks, but @command{tar} ignore these differences in its own
10421 format, which is meant to be portable, so a @command{tar} block is always
10422 512 bytes in length, and @dfn{block} always mean a @command{tar} block.
10423 The term @dfn{logical block} often represents the basic chunk of
10424 allocation of many disk blocks as a single entity, which the operating
10425 system treats somewhat atomically; this concept is only barely used
10428 The term @dfn{physical record} is another way to speak of a physical
10429 block, those two terms are somewhat interchangeable. In this manual,
10430 the term @dfn{record} usually refers to a tape physical block,
10431 @emph{assuming} that the @command{tar} archive is kept on magnetic tape.
10432 It is true that archives may be put on disk or used with pipes,
10433 but nevertheless, @command{tar} tries to read and write the archive one
10434 @dfn{record} at a time, whatever the medium in use. One record is made
10435 up of an integral number of blocks, and this operation of putting many
10436 disk blocks into a single tape block is called @dfn{reblocking}, or
10437 more simply, @dfn{blocking}. The term @dfn{logical record} refers to
10438 the logical organization of many characters into something meaningful
10439 to the application. The term @dfn{unit record} describes a small set
10440 of characters which are transmitted whole to or by the application,
10441 and often refers to a line of text. Those two last terms are unrelated
10442 to what we call a @dfn{record} in @GNUTAR{}.
10444 When writing to tapes, @command{tar} writes the contents of the archive
10445 in chunks known as @dfn{records}. To change the default blocking
10446 factor, use the @option{--blocking-factor=@var{512-size}} (@option{-b
10447 @var{512-size}}) option. Each record will then be composed of
10448 @var{512-size} blocks. (Each @command{tar} block is 512 bytes.
10449 @xref{Standard}.) Each file written to the archive uses at least one
10450 full record. As a result, using a larger record size can result in
10451 more wasted space for small files. On the other hand, a larger record
10452 size can often be read and written much more efficiently.
10454 Further complicating the problem is that some tape drives ignore the
10455 blocking entirely. For these, a larger record size can still improve
10456 performance (because the software layers above the tape drive still
10457 honor the blocking), but not as dramatically as on tape drives that
10460 When reading an archive, @command{tar} can usually figure out the
10461 record size on itself. When this is the case, and a non-standard
10462 record size was used when the archive was created, @command{tar} will
10463 print a message about a non-standard blocking factor, and then operate
10464 normally. On some tape devices, however, @command{tar} cannot figure
10465 out the record size itself. On most of those, you can specify a
10466 blocking factor (with @option{--blocking-factor}) larger than the
10467 actual blocking factor, and then use the @option{--read-full-records}
10468 (@option{-B}) option. (If you specify a blocking factor with
10469 @option{--blocking-factor} and don't use the
10470 @option{--read-full-records} option, then @command{tar} will not
10471 attempt to figure out the recording size itself.) On some devices,
10472 you must always specify the record size exactly with
10473 @option{--blocking-factor} when reading, because @command{tar} cannot
10474 figure it out. In any case, use @option{--list} (@option{-t}) before
10475 doing any extractions to see whether @command{tar} is reading the archive
10478 @command{tar} blocks are all fixed size (512 bytes), and its scheme for
10479 putting them into records is to put a whole number of them (one or
10480 more) into each record. @command{tar} records are all the same size;
10481 at the end of the file there's a block containing all zeros, which
10482 is how you tell that the remainder of the last record(s) are garbage.
10484 In a standard @command{tar} file (no options), the block size is 512
10485 and the record size is 10240, for a blocking factor of 20. What the
10486 @option{--blocking-factor} option does is sets the blocking factor,
10487 changing the record size while leaving the block size at 512 bytes.
10488 20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives;
10489 most tape drives these days prefer much bigger records in order to
10490 stream and not waste tape. When writing tapes for myself, some tend
10491 to use a factor of the order of 2048, say, giving a record size of
10492 around one megabyte.
10494 If you use a blocking factor larger than 20, older @command{tar}
10495 programs might not be able to read the archive, so we recommend this
10496 as a limit to use in practice. @GNUTAR{}, however,
10497 will support arbitrarily large record sizes, limited only by the
10498 amount of virtual memory or the physical characteristics of the tape
10502 * Format Variations:: Format Variations
10503 * Blocking Factor:: The Blocking Factor of an Archive
10506 @node Format Variations
10507 @subsection Format Variations
10508 @cindex Format Parameters
10509 @cindex Format Options
10510 @cindex Options, archive format specifying
10511 @cindex Options, format specifying
10514 Format parameters specify how an archive is written on the archive
10515 media. The best choice of format parameters will vary depending on
10516 the type and number of files being archived, and on the media used to
10519 To specify format parameters when accessing or creating an archive,
10520 you can use the options described in the following sections.
10521 If you do not specify any format parameters, @command{tar} uses
10522 default parameters. You cannot modify a compressed archive.
10523 If you create an archive with the @option{--blocking-factor} option
10524 specified (@pxref{Blocking Factor}), you must specify that
10525 blocking-factor when operating on the archive. @xref{Formats}, for other
10526 examples of format parameter considerations.
10528 @node Blocking Factor
10529 @subsection The Blocking Factor of an Archive
10530 @cindex Blocking Factor
10531 @cindex Record Size
10532 @cindex Number of blocks per record
10533 @cindex Number of bytes per record
10534 @cindex Bytes per record
10535 @cindex Blocks per record
10538 @opindex blocking-factor
10539 The data in an archive is grouped into blocks, which are 512 bytes.
10540 Blocks are read and written in whole number multiples called
10541 @dfn{records}. The number of blocks in a record (i.e., the size of a
10542 record in units of 512 bytes) is called the @dfn{blocking factor}.
10543 The @option{--blocking-factor=@var{512-size}} (@option{-b
10544 @var{512-size}}) option specifies the blocking factor of an archive.
10545 The default blocking factor is typically 20 (i.e., 10240 bytes), but
10546 can be specified at installation. To find out the blocking factor of
10547 an existing archive, use @samp{tar --list --file=@var{archive-name}}.
10548 This may not work on some devices.
10550 Records are separated by gaps, which waste space on the archive media.
10551 If you are archiving on magnetic tape, using a larger blocking factor
10552 (and therefore larger records) provides faster throughput and allows you
10553 to fit more data on a tape (because there are fewer gaps). If you are
10554 archiving on cartridge, a very large blocking factor (say 126 or more)
10555 greatly increases performance. A smaller blocking factor, on the other
10556 hand, may be useful when archiving small files, to avoid archiving lots
10557 of nulls as @command{tar} fills out the archive to the end of the record.
10558 In general, the ideal record size depends on the size of the
10559 inter-record gaps on the tape you are using, and the average size of the
10560 files you are archiving. @xref{create}, for information on
10563 @FIXME{Need example of using a cartridge with blocking factor=126 or more.}
10565 Archives with blocking factors larger than 20 cannot be read
10566 by very old versions of @command{tar}, or by some newer versions
10567 of @command{tar} running on old machines with small address spaces.
10568 With @GNUTAR{}, the blocking factor of an archive is limited
10569 only by the maximum record size of the device containing the archive,
10570 or by the amount of available virtual memory.
10572 Also, on some systems, not using adequate blocking factors, as sometimes
10573 imposed by the device drivers, may yield unexpected diagnostics. For
10574 example, this has been reported:
10577 Cannot write to /dev/dlt: Invalid argument
10581 In such cases, it sometimes happen that the @command{tar} bundled by
10582 the system is aware of block size idiosyncrasies, while @GNUTAR{}
10583 requires an explicit specification for the block size,
10584 which it cannot guess. This yields some people to consider
10585 @GNUTAR{} is misbehaving, because by comparison,
10586 @cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}},
10587 for example, might resolve the problem.
10589 If you use a non-default blocking factor when you create an archive, you
10590 must specify the same blocking factor when you modify that archive. Some
10591 archive devices will also require you to specify the blocking factor when
10592 reading that archive, however this is not typically the case. Usually, you
10593 can use @option{--list} (@option{-t}) without specifying a blocking factor---@command{tar}
10594 reports a non-default record size and then lists the archive members as
10595 it would normally. To extract files from an archive with a non-standard
10596 blocking factor (particularly if you're not sure what the blocking factor
10597 is), you can usually use the @option{--read-full-records} (@option{-B}) option while
10598 specifying a blocking factor larger then the blocking factor of the archive
10599 (i.e., @samp{tar --extract --read-full-records --blocking-factor=300}).
10600 @xref{list}, for more information on the @option{--list} (@option{-t})
10601 operation. @xref{Reading}, for a more detailed explanation of that option.
10604 @item --blocking-factor=@var{number}
10605 @itemx -b @var{number}
10606 Specifies the blocking factor of an archive. Can be used with any
10607 operation, but is usually not necessary with @option{--list} (@option{-t}).
10613 @item -b @var{blocks}
10614 @itemx --blocking-factor=@var{blocks}
10615 Set record size to @math{@var{blocks}*512} bytes.
10617 This option is used to specify a @dfn{blocking factor} for the archive.
10618 When reading or writing the archive, @command{tar}, will do reads and writes
10619 of the archive in records of @math{@var{block}*512} bytes. This is true
10620 even when the archive is compressed. Some devices requires that all
10621 write operations be a multiple of a certain size, and so, @command{tar}
10622 pads the archive out to the next record boundary.
10624 The default blocking factor is set when @command{tar} is compiled, and is
10625 typically 20. Blocking factors larger than 20 cannot be read by very
10626 old versions of @command{tar}, or by some newer versions of @command{tar}
10627 running on old machines with small address spaces.
10629 With a magnetic tape, larger records give faster throughput and fit
10630 more data on a tape (because there are fewer inter-record gaps).
10631 If the archive is in a disk file or a pipe, you may want to specify
10632 a smaller blocking factor, since a large one will result in a large
10633 number of null bytes at the end of the archive.
10635 When writing cartridge or other streaming tapes, a much larger
10636 blocking factor (say 126 or more) will greatly increase performance.
10637 However, you must specify the same blocking factor when reading or
10638 updating the archive.
10640 Apparently, Exabyte drives have a physical block size of 8K bytes.
10641 If we choose our blocksize as a multiple of 8k bytes, then the problem
10642 seems to disappear. Id est, we are using block size of 112 right
10643 now, and we haven't had the problem since we switched@dots{}
10645 With @GNUTAR{} the blocking factor is limited only
10646 by the maximum record size of the device containing the archive, or by
10647 the amount of available virtual memory.
10649 However, deblocking or reblocking is virtually avoided in a special
10650 case which often occurs in practice, but which requires all the
10651 following conditions to be simultaneously true:
10654 the archive is subject to a compression option,
10656 the archive is not handled through standard input or output, nor
10657 redirected nor piped,
10659 the archive is directly handled to a local disk, instead of any special
10662 @option{--blocking-factor} is not explicitly specified on the @command{tar}
10666 If the output goes directly to a local disk, and not through
10667 stdout, then the last write is not extended to a full record size.
10668 Otherwise, reblocking occurs. Here are a few other remarks on this
10674 @command{gzip} will complain about trailing garbage if asked to
10675 uncompress a compressed archive on tape, there is an option to turn
10676 the message off, but it breaks the regularity of simply having to use
10677 @samp{@var{prog} -d} for decompression. It would be nice if gzip was
10678 silently ignoring any number of trailing zeros. I'll ask Jean-loup
10679 Gailly, by sending a copy of this message to him.
10682 @command{compress} does not show this problem, but as Jean-loup pointed
10683 out to Michael, @samp{compress -d} silently adds garbage after
10684 the result of decompression, which tar ignores because it already
10685 recognized its end-of-file indicator. So this bug may be safely
10689 @samp{gzip -d -q} will be silent about the trailing zeros indeed,
10690 but will still return an exit status of 2 which tar reports in turn.
10691 @command{tar} might ignore the exit status returned, but I hate doing
10692 that, as it weakens the protection @command{tar} offers users against
10693 other possible problems at decompression time. If @command{gzip} was
10694 silently skipping trailing zeros @emph{and} also avoiding setting the
10695 exit status in this innocuous case, that would solve this situation.
10698 @command{tar} should become more solid at not stopping to read a pipe at
10699 the first null block encountered. This inelegantly breaks the pipe.
10700 @command{tar} should rather drain the pipe out before exiting itself.
10703 @xopindex{ignore-zeros, short description}
10705 @itemx --ignore-zeros
10706 Ignore blocks of zeros in archive (means EOF).
10708 The @option{--ignore-zeros} (@option{-i}) option causes @command{tar} to ignore blocks
10709 of zeros in the archive. Normally a block of zeros indicates the
10710 end of the archive, but when reading a damaged archive, or one which
10711 was created by concatenating several archives together, this option
10712 allows @command{tar} to read the entire archive. This option is not on
10713 by default because many versions of @command{tar} write garbage after
10716 Note that this option causes @command{tar} to read to the end of the
10717 archive file, which may sometimes avoid problems when multiple files
10718 are stored on a single physical tape.
10720 @xopindex{read-full-records, short description}
10722 @itemx --read-full-records
10723 Reblock as we read (for reading 4.2@acronym{BSD} pipes).
10725 If @option{--read-full-records} is used, @command{tar}
10726 will not panic if an attempt to read a record from the archive does
10727 not return a full record. Instead, @command{tar} will keep reading
10728 until it has obtained a full
10731 This option is turned on by default when @command{tar} is reading
10732 an archive from standard input, or from a remote machine. This is
10733 because on @acronym{BSD} Unix systems, a read of a pipe will return however
10734 much happens to be in the pipe, even if it is less than @command{tar}
10735 requested. If this option was not used, @command{tar} would fail as
10736 soon as it read an incomplete record from the pipe.
10738 This option is also useful with the commands for updating an archive.
10744 @FIXME{Appropriate options should be moved here from elsewhere.}
10746 @cindex blocking factor
10747 @cindex tape blocking
10749 When handling various tapes or cartridges, you have to take care of
10750 selecting a proper blocking, that is, the number of disk blocks you
10751 put together as a single tape block on the tape, without intervening
10752 tape gaps. A @dfn{tape gap} is a small landing area on the tape
10753 with no information on it, used for decelerating the tape to a
10754 full stop, and for later regaining the reading or writing speed.
10755 When the tape driver starts reading a record, the record has to
10756 be read whole without stopping, as a tape gap is needed to stop the
10757 tape motion without losing information.
10759 @cindex Exabyte blocking
10760 @cindex DAT blocking
10761 Using higher blocking (putting more disk blocks per tape block) will use
10762 the tape more efficiently as there will be less tape gaps. But reading
10763 such tapes may be more difficult for the system, as more memory will be
10764 required to receive at once the whole record. Further, if there is a
10765 reading error on a huge record, this is less likely that the system will
10766 succeed in recovering the information. So, blocking should not be too
10767 low, nor it should be too high. @command{tar} uses by default a blocking of
10768 20 for historical reasons, and it does not really matter when reading or
10769 writing to disk. Current tape technology would easily accommodate higher
10770 blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs.
10771 We were told that for some DLT drives, the blocking should be a multiple
10772 of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance.
10773 Other manufacturers may use different recommendations for the same tapes.
10774 This might also depends of the buffering techniques used inside modern
10775 tape controllers. Some imposes a minimum blocking, or a maximum blocking.
10776 Others request blocking to be some exponent of two.
10778 So, there is no fixed rule for blocking. But blocking at read time
10779 should ideally be the same as blocking used at write time. At one place
10780 I know, with a wide variety of equipment, they found it best to use a
10781 blocking of 32 to guarantee that their tapes are fully interchangeable.
10783 I was also told that, for recycled tapes, prior erasure (by the same
10784 drive unit that will be used to create the archives) sometimes lowers
10785 the error rates observed at rewriting time.
10787 I might also use @option{--number-blocks} instead of
10788 @option{--block-number}, so @option{--block} will then expand to
10789 @option{--blocking-factor} unambiguously.
10792 @section Many Archives on One Tape
10794 @FIXME{Appropriate options should be moved here from elsewhere.}
10796 @findex ntape @r{device}
10797 Most tape devices have two entries in the @file{/dev} directory, or
10798 entries that come in pairs, which differ only in the minor number for
10799 this device. Let's take for example @file{/dev/tape}, which often
10800 points to the only or usual tape device of a given system. There might
10801 be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler
10802 name is the @emph{rewinding} version of the device, while the name
10803 having @samp{nr} in it is the @emph{no rewinding} version of the same
10806 A rewinding tape device will bring back the tape to its beginning point
10807 automatically when this device is opened or closed. Since @command{tar}
10808 opens the archive file before using it and closes it afterwards, this
10809 means that a simple:
10812 $ @kbd{tar cf /dev/tape @var{directory}}
10816 will reposition the tape to its beginning both prior and after saving
10817 @var{directory} contents to it, thus erasing prior tape contents and
10818 making it so that any subsequent write operation will destroy what has
10821 @cindex tape positioning
10822 So, a rewinding device is normally meant to hold one and only one file.
10823 If you want to put more than one @command{tar} archive on a given tape, you
10824 will need to avoid using the rewinding version of the tape device. You
10825 will also have to pay special attention to tape positioning. Errors in
10826 positioning may overwrite the valuable data already on your tape. Many
10827 people, burnt by past experiences, will only use rewinding devices and
10828 limit themselves to one file per tape, precisely to avoid the risk of
10829 such errors. Be fully aware that writing at the wrong position on a
10830 tape loses all information past this point and most probably until the
10831 end of the tape, and this destroyed information @emph{cannot} be
10834 To save @var{directory-1} as a first archive at the beginning of a
10835 tape, and leave that tape ready for a second archive, you should use:
10838 $ @kbd{mt -f /dev/nrtape rewind}
10839 $ @kbd{tar cf /dev/nrtape @var{directory-1}}
10843 @dfn{Tape marks} are special magnetic patterns written on the tape
10844 media, which are later recognizable by the reading hardware. These
10845 marks are used after each file, when there are many on a single tape.
10846 An empty file (that is to say, two tape marks in a row) signal the
10847 logical end of the tape, after which no file exist. Usually,
10848 non-rewinding tape device drivers will react to the close request issued
10849 by @command{tar} by first writing two tape marks after your archive, and by
10850 backspacing over one of these. So, if you remove the tape at that time
10851 from the tape drive, it is properly terminated. But if you write
10852 another file at the current position, the second tape mark will be
10853 erased by the new information, leaving only one tape mark between files.
10855 So, you may now save @var{directory-2} as a second archive after the
10856 first on the same tape by issuing the command:
10859 $ @kbd{tar cf /dev/nrtape @var{directory-2}}
10863 and so on for all the archives you want to put on the same tape.
10865 Another usual case is that you do not write all the archives the same
10866 day, and you need to remove and store the tape between two archive
10867 sessions. In general, you must remember how many files are already
10868 saved on your tape. Suppose your tape already has 16 files on it, and
10869 that you are ready to write the 17th. You have to take care of skipping
10870 the first 16 tape marks before saving @var{directory-17}, say, by using
10874 $ @kbd{mt -f /dev/nrtape rewind}
10875 $ @kbd{mt -f /dev/nrtape fsf 16}
10876 $ @kbd{tar cf /dev/nrtape @var{directory-17}}
10879 In all the previous examples, we put aside blocking considerations, but
10880 you should do the proper things for that as well. @xref{Blocking}.
10883 * Tape Positioning:: Tape Positions and Tape Marks
10884 * mt:: The @command{mt} Utility
10887 @node Tape Positioning
10888 @subsection Tape Positions and Tape Marks
10891 Just as archives can store more than one file from the file system,
10892 tapes can store more than one archive file. To keep track of where
10893 archive files (or any other type of file stored on tape) begin and
10894 end, tape archive devices write magnetic @dfn{tape marks} on the
10895 archive media. Tape drives write one tape mark between files,
10896 two at the end of all the file entries.
10898 If you think of data as a series of records "rrrr"'s, and tape marks as
10899 "*"'s, a tape might look like the following:
10902 rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
10905 Tape devices read and write tapes using a read/write @dfn{tape
10906 head}---a physical part of the device which can only access one
10907 point on the tape at a time. When you use @command{tar} to read or
10908 write archive data from a tape device, the device will begin reading
10909 or writing from wherever on the tape the tape head happens to be,
10910 regardless of which archive or what part of the archive the tape
10911 head is on. Before writing an archive, you should make sure that no
10912 data on the tape will be overwritten (unless it is no longer needed).
10913 Before reading an archive, you should make sure the tape head is at
10914 the beginning of the archive you want to read. You can do it manually
10915 via @code{mt} utility (@pxref{mt}). The @code{restore} script does
10916 that automatically (@pxref{Scripted Restoration}).
10918 If you want to add new archive file entries to a tape, you should
10919 advance the tape to the end of the existing file entries, backspace
10920 over the last tape mark, and write the new archive file. If you were
10921 to add two archives to the example above, the tape might look like the
10925 rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
10929 @subsection The @command{mt} Utility
10932 @FIXME{Is it true that this only works on non-block devices?
10933 should explain the difference, (fixed or variable).}
10934 @xref{Blocking Factor}.
10936 You can use the @command{mt} utility to advance or rewind a tape past a
10937 specified number of archive files on the tape. This will allow you
10938 to move to the beginning of an archive before extracting or reading
10939 it, or to the end of all the archives before writing a new one.
10940 @FIXME{Why isn't there an "advance 'til you find two tape marks
10943 The syntax of the @command{mt} command is:
10946 @kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
10949 where @var{tapename} is the name of the tape device, @var{number} is
10950 the number of times an operation is performed (with a default of one),
10951 and @var{operation} is one of the following:
10953 @FIXME{is there any use for record operations?}
10958 Writes @var{number} tape marks at the current position on the tape.
10961 Moves tape position forward @var{number} files.
10964 Moves tape position back @var{number} files.
10967 Rewinds the tape. (Ignores @var{number}.)
10971 Rewinds the tape and takes the tape device off-line. (Ignores @var{number}.)
10974 Prints status information about the tape unit.
10978 If you don't specify a @var{tapename}, @command{mt} uses the environment
10979 variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
10980 the default device specified in your @file{sys/mtio.h} file
10981 (@code{DEFTAPE} variable). If this is not defined, the program will
10982 display a descriptive error message and exit with code 1.
10984 @command{mt} returns a 0 exit status when the operation(s) were
10985 successful, 1 if the command was unrecognized, and 2 if an operation
10988 @node Using Multiple Tapes
10989 @section Using Multiple Tapes
10991 Often you might want to write a large archive, one larger than will fit
10992 on the actual tape you are using. In such a case, you can run multiple
10993 @command{tar} commands, but this can be inconvenient, particularly if you
10994 are using options like @option{--exclude=@var{pattern}} or dumping entire file systems.
10995 Therefore, @command{tar} provides a special mode for creating
10996 multi-volume archives.
10998 @dfn{Multi-volume} archive is a single @command{tar} archive, stored
10999 on several media volumes of fixed size. Although in this section we will
11000 often call @samp{volume} a @dfn{tape}, there is absolutely no
11001 requirement for multi-volume archives to be stored on tapes. Instead,
11002 they can use whatever media type the user finds convenient, they can
11003 even be located on files.
11005 When creating a multi-volume archive, @GNUTAR{} continues to fill
11006 current volume until it runs out of space, then it switches to
11007 next volume (usually the operator is queried to replace the tape on
11008 this point), and continues working on the new volume. This operation
11009 continues until all requested files are dumped. If @GNUTAR{} detects
11010 end of media while dumping a file, such a file is archived in split
11011 form. Some very big files can even be split across several volumes.
11013 Each volume is itself a valid @GNUTAR{} archive, so it can be read
11014 without any special options. Consequently any file member residing
11015 entirely on one volume can be extracted or otherwise operated upon
11016 without needing the other volume. Sure enough, to extract a split
11017 member you would need all volumes its parts reside on.
11019 Multi-volume archives suffer from several limitations. In particular,
11020 they cannot be compressed.
11022 @GNUTAR{} is able to create multi-volume archives of two formats
11023 (@pxref{Formats}): @samp{GNU} and @samp{POSIX}.
11026 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
11027 * Tape Files:: Tape Files
11028 * Tarcat:: Concatenate Volumes into a Single Archive
11032 @node Multi-Volume Archives
11033 @subsection Archives Longer than One Tape or Disk
11034 @cindex Multi-volume archives
11036 @opindex multi-volume
11037 To create an archive that is larger than will fit on a single unit of
11038 the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
11039 the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
11040 archive can be manipulated like any other archive (provided the
11041 @option{--multi-volume} option is specified), but is stored on more
11042 than one tape or file.
11044 When you specify @option{--multi-volume}, @command{tar} does not report an
11045 error when it comes to the end of an archive volume (when reading), or
11046 the end of the media (when writing). Instead, it prompts you to load
11047 a new storage volume. If the archive is on a magnetic tape, you
11048 should change tapes when you see the prompt; if the archive is on a
11049 floppy disk, you should change disks; etc.
11052 @item --multi-volume
11054 Creates a multi-volume archive, when used in conjunction with
11055 @option{--create} (@option{-c}). To perform any other operation on a multi-volume
11056 archive, specify @option{--multi-volume} in conjunction with that
11061 $ @kbd{tar --create --multi-volume --file=/dev/tape @var{files}}
11065 The method @command{tar} uses to detect end of tape is not perfect, and
11066 fails on some operating systems or on some devices. If @command{tar}
11067 cannot detect the end of the tape itself, you can use
11068 @option{--tape-length} option to inform it about the capacity of the
11071 @anchor{tape-length}
11073 @opindex tape-length
11074 @item --tape-length=@var{size}
11075 @itemx -L @var{size}
11076 Set maximum length of a volume. The @var{size} argument should then
11077 be the usable size of the tape in units of 1024 bytes. This option
11078 selects @option{--multi-volume} automatically. For example:
11081 $ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}}
11085 @anchor{change volume prompt}
11086 When @GNUTAR{} comes to the end of a storage media, it asks you to
11087 change the volume. The built-in prompt for POSIX locale
11088 is@footnote{If you run @GNUTAR{} under a different locale, the
11089 translation to the locale's language will be used.}:
11092 Prepare volume #@var{n} for `@var{archive}' and hit return:
11096 where @var{n} is the ordinal number of the volume to be created and
11097 @var{archive} is archive file or device name.
11099 When prompting for a new tape, @command{tar} accepts any of the following
11104 Request @command{tar} to explain possible responses.
11106 Request @command{tar} to exit immediately.
11107 @item n @var{file-name}
11108 Request @command{tar} to write the next volume on the file @var{file-name}.
11110 Request @command{tar} to run a subshell. This option can be disabled
11111 by giving @option{--restrict} command line option to
11112 @command{tar}@footnote{@xref{--restrict}, for more information about
11115 Request @command{tar} to begin writing the next volume.
11118 (You should only type @samp{y} after you have changed the tape;
11119 otherwise @command{tar} will write over the volume it just finished.)
11121 @cindex Volume number file
11123 @anchor{volno-file}
11124 @opindex volno-file
11125 The volume number used by @command{tar} in its tape-changing prompt
11126 can be changed; if you give the
11127 @option{--volno-file=@var{file-of-number}} option, then
11128 @var{file-of-number} should be an non-existing file to be created, or
11129 else, a file already containing a decimal number. That number will be
11130 used as the volume number of the first volume written. When
11131 @command{tar} is finished, it will rewrite the file with the
11132 now-current volume number. (This does not change the volume number
11133 written on a tape label, as per @ref{label}, it @emph{only} affects
11134 the number used in the prompt.)
11136 @cindex End-of-archive info script
11137 @cindex Info script
11138 @anchor{info-script}
11139 @opindex info-script
11140 @opindex new-volume-script
11141 If you want more elaborate behavior than this, you can write a special
11142 @dfn{new volume script}, that will be responsible for changing the
11143 volume, and instruct @command{tar} to use it instead of its normal
11144 prompting procedure:
11147 @item --info-script=@var{script-name}
11148 @itemx --new-volume-script=@var{script-name}
11149 @itemx -F @var{script-name}
11150 Specify the full name of the volume script to use. The script can be
11151 used to eject cassettes, or to broadcast messages such as
11152 @samp{Someone please come change my tape} when performing unattended
11156 The @var{script-name} is executed without any command line
11157 arguments. It inherits @command{tar}'s shell environment.
11158 Additional data is passed to it via the following
11159 environment variables:
11162 @vrindex TAR_VERSION, info script environment variable
11164 @GNUTAR{} version number.
11166 @vrindex TAR_ARCHIVE, info script environment variable
11168 The name of the archive @command{tar} is processing.
11170 @vrindex TAR_BLOCKING_FACTOR, info script environment variable
11171 @item TAR_BLOCKING_FACTOR
11172 Current blocking factor (@pxref{Blocking}).
11174 @vrindex TAR_VOLUME, info script environment variable
11176 Ordinal number of the volume @command{tar} is about to start.
11178 @vrindex TAR_SUBCOMMAND, info script environment variable
11179 @item TAR_SUBCOMMAND
11180 A short option describing the operation @command{tar} is executing.
11181 @xref{Operations}, for a complete list of subcommand options.
11183 @vrindex TAR_FORMAT, info script environment variable
11185 Format of the archive being processed. @xref{Formats}, for a complete
11186 list of archive format names.
11188 @vrindex TAR_FD, info script environment variable
11190 File descriptor which can be used to communicate the new volume
11191 name to @command{tar}.
11194 The volume script can instruct @command{tar} to use new archive name,
11195 by writing in to file descriptor @env{$TAR_FD} (see below for an example).
11197 If the info script fails, @command{tar} exits; otherwise, it begins
11198 writing the next volume.
11200 If you want @command{tar} to cycle through a series of files or tape
11201 drives, there are three approaches to choose from. First of all, you
11202 can give @command{tar} multiple @option{--file} options. In this case
11203 the specified files will be used, in sequence, as the successive
11204 volumes of the archive. Only when the first one in the sequence needs
11205 to be used again will @command{tar} prompt for a tape change (or run
11206 the info script). For example, suppose someone has two tape drives on
11207 a system named @file{/dev/tape0} and @file{/dev/tape1}. For having
11208 @GNUTAR{} to switch to the second drive when it needs to write the
11209 second tape, and then back to the first tape, etc., just do either of:
11212 $ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
11213 $ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
11216 The second method is to use the @samp{n} response to the tape-change
11219 Finally, the most flexible approach is to use a volume script, that
11220 writes new archive name to the file descriptor @env{$TAR_FD}. For example, the
11221 following volume script will create a series of archive files, named
11222 @file{@var{archive}-@var{vol}}, where @var{archive} is the name of the
11223 archive being created (as given by @option{--file} option) and
11224 @var{vol} is the ordinal number of the archive being created:
11229 echo Preparing volume $TAR_VOLUME of $TAR_ARCHIVE.
11231 name=`expr $TAR_ARCHIVE : '\(.*\)-.*'`
11232 case $TAR_SUBCOMMAND in
11234 -d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
11239 echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&$TAR_FD
11243 The same script can be used while listing, comparing or extracting
11244 from the created archive. For example:
11248 # @r{Create a multi-volume archive:}
11249 $ @kbd{tar -c -L1024 -f archive.tar -F new-volume .}
11250 # @r{Extract from the created archive:}
11251 $ @kbd{tar -x -f archive.tar -F new-volume .}
11256 Notice, that the first command had to use @option{-L} option, since
11257 otherwise @GNUTAR{} will end up writing everything to file
11258 @file{archive.tar}.
11260 You can read each individual volume of a multi-volume archive as if it
11261 were an archive by itself. For example, to list the contents of one
11262 volume, use @option{--list}, without @option{--multi-volume} specified.
11263 To extract an archive member from one volume (assuming it is described
11264 that volume), use @option{--extract}, again without
11265 @option{--multi-volume}.
11267 If an archive member is split across volumes (i.e., its entry begins on
11268 one volume of the media and ends on another), you need to specify
11269 @option{--multi-volume} to extract it successfully. In this case, you
11270 should load the volume where the archive member starts, and use
11271 @samp{tar --extract --multi-volume}---@command{tar} will prompt for later
11272 volumes as it needs them. @xref{extracting archives}, for more
11273 information about extracting archives.
11275 Multi-volume archives can be modified like any other archive. To add
11276 files to a multi-volume archive, you need to only mount the last
11277 volume of the archive media (and new volumes, if needed). For all
11278 other operations, you need to use the entire archive.
11280 If a multi-volume archive was labeled using
11281 @option{--label=@var{archive-label}} (@pxref{label}) when it was
11282 created, @command{tar} will not automatically label volumes which are
11283 added later. To label subsequent volumes, specify
11284 @option{--label=@var{archive-label}} again in conjunction with the
11285 @option{--append}, @option{--update} or @option{--concatenate} operation.
11287 Notice that multi-volume support is a GNU extension and the archives
11288 created in this mode should be read only using @GNUTAR{}. If you
11289 absolutely have to process such archives using a third-party @command{tar}
11290 implementation, read @ref{Split Recovery}.
11293 @subsection Tape Files
11294 @cindex labeling archives
11298 To give the archive a name which will be recorded in it, use the
11299 @option{--label=@var{volume-label}} (@option{-V @var{volume-label}})
11300 option. This will write a special block identifying
11301 @var{volume-label} as the name of the archive to the front of the
11302 archive which will be displayed when the archive is listed with
11303 @option{--list}. If you are creating a multi-volume archive with
11304 @option{--multi-volume} (@pxref{Using Multiple Tapes}), then the
11305 volume label will have @samp{Volume @var{nnn}} appended to the name
11306 you give, where @var{nnn} is the number of the volume of the archive.
11307 If you use the @option{--label=@var{volume-label}} option when
11308 reading an archive, it checks to make sure the label on the tape
11309 matches the one you gave. @xref{label}.
11311 When @command{tar} writes an archive to tape, it creates a single
11312 tape file. If multiple archives are written to the same tape, one
11313 after the other, they each get written as separate tape files. When
11314 extracting, it is necessary to position the tape at the right place
11315 before running @command{tar}. To do this, use the @command{mt} command.
11316 For more information on the @command{mt} command and on the organization
11317 of tapes into a sequence of tape files, see @ref{mt}.
11319 People seem to often do:
11322 @kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
11325 or such, for pushing a common date in all volumes or an archive set.
11328 @subsection Concatenate Volumes into a Single Archive
11331 Sometimes it is necessary to convert existing @GNUTAR{} multi-volume
11332 archive to a single @command{tar} archive. Simply concatenating all
11333 volumes into one will not work, since each volume carries an additional
11334 information at the beginning. @GNUTAR{} is shipped with the shell
11335 script @command{tarcat} designed for this purpose.
11337 The script takes a list of files comprising a multi-volume archive
11338 and creates the resulting archive at the standard output. For example:
11341 @kbd{tarcat vol.1 vol.2 vol.3 | tar tf -}
11344 The script implements a simple heuristics to determine the format of
11345 the first volume file and to decide how to process the rest of the
11346 files. However, it makes no attempt to verify whether the files are
11347 given in order or even if they are valid @command{tar} archives.
11348 It uses @command{dd} and does not filter its standard error, so you
11349 will usually see lots of spurious messages.
11351 @FIXME{The script is not installed. Should we install it?}
11354 @section Including a Label in the Archive
11355 @cindex Labeling an archive
11356 @cindex Labels on the archive media
11357 @cindex Labeling multi-volume archives
11360 To avoid problems caused by misplaced paper labels on the archive
11361 media, you can include a @dfn{label} entry --- an archive member which
11362 contains the name of the archive --- in the archive itself. Use the
11363 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11364 option@footnote{Until version 1.10, that option was called
11365 @option{--volume}, but is not available under that name anymore.} in
11366 conjunction with the @option{--create} operation to include a label
11367 entry in the archive as it is being created.
11370 @item --label=@var{archive-label}
11371 @itemx -V @var{archive-label}
11372 Includes an @dfn{archive-label} at the beginning of the archive when
11373 the archive is being created, when used in conjunction with the
11374 @option{--create} operation. Checks to make sure the archive label
11375 matches the one specified (when used in conjunction with any other
11379 If you create an archive using both
11380 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11381 and @option{--multi-volume} (@option{-M}), each volume of the archive
11382 will have an archive label of the form @samp{@var{archive-label}
11383 Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the
11384 next, and so on. @xref{Using Multiple Tapes}, for information on
11385 creating multiple volume archives.
11387 @cindex Volume label, listing
11388 @cindex Listing volume label
11389 The volume label will be displayed by @option{--list} along with
11390 the file contents. If verbose display is requested, it will also be
11391 explicitly marked as in the example below:
11395 $ @kbd{tar --verbose --list --file=iamanarchive}
11396 V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
11397 -rw-r--r-- ringo user 40 1990-05-21 13:30 iamafilename
11401 @opindex test-label
11402 @anchor{--test-label option}
11403 However, @option{--list} option will cause listing entire
11404 contents of the archive, which may be undesirable (for example, if the
11405 archive is stored on a tape). You can request checking only the volume
11406 label by specifying @option{--test-label} option. This option reads only the
11407 first block of an archive, so it can be used with slow storage
11408 devices. For example:
11412 $ @kbd{tar --test-label --file=iamanarchive}
11417 If @option{--test-label} is used with one or more command line
11418 arguments, @command{tar} compares the volume label with each
11419 argument. It exits with code 0 if a match is found, and with code 1
11420 otherwise@footnote{Note that @GNUTAR{} versions up to 1.23 indicated
11421 mismatch with an exit code 2 and printed a spurious diagnostics on
11422 stderr.}. No output is displayed, unless you also used the
11423 @option{--verbose} option. For example:
11427 $ @kbd{tar --test-label --file=iamanarchive 'iamalabel'}
11429 $ @kbd{tar --test-label --file=iamanarchive 'alabel'}
11434 When used with the @option{--verbose} option, @command{tar}
11435 prints the actual volume label (if any), and a verbose diagnostics in
11436 case of a mismatch:
11440 $ @kbd{tar --test-label --verbose --file=iamanarchive 'iamalabel'}
11443 $ @kbd{tar --test-label --verbose --file=iamanarchive 'alabel'}
11445 tar: Archive label mismatch
11450 If you request any operation, other than @option{--create}, along
11451 with using @option{--label} option, @command{tar} will first check if
11452 the archive label matches the one specified and will refuse to proceed
11453 if it does not. Use this as a safety precaution to avoid accidentally
11454 overwriting existing archives. For example, if you wish to add files
11455 to @file{archive}, presumably labeled with string @samp{My volume},
11460 $ @kbd{tar -rf archive --label 'My volume' .}
11461 tar: Archive not labeled to match `My volume'
11466 in case its label does not match. This will work even if
11467 @file{archive} is not labeled at all.
11469 Similarly, @command{tar} will refuse to list or extract the
11470 archive if its label doesn't match the @var{archive-label}
11471 specified. In those cases, @var{archive-label} argument is interpreted
11472 as a globbing-style pattern which must match the actual magnetic
11473 volume label. @xref{exclude}, for a precise description of how match
11474 is attempted@footnote{Previous versions of @command{tar} used full
11475 regular expression matching, or before that, only exact string
11476 matching, instead of wildcard matchers. We decided for the sake of
11477 simplicity to use a uniform matching device through
11478 @command{tar}.}. If the switch @option{--multi-volume} (@option{-M}) is being used,
11479 the volume label matcher will also suffix @var{archive-label} by
11480 @w{@samp{ Volume [1-9]*}} if the initial match fails, before giving
11481 up. Since the volume numbering is automatically added in labels at
11482 creation time, it sounded logical to equally help the user taking care
11483 of it when the archive is being read.
11485 You can also use @option{--label} to get a common information on
11486 all tapes of a series. For having this information different in each
11487 series created through a single script used on a regular basis, just
11488 manage to get some date string as part of the label. For example:
11492 $ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
11493 $ @kbd{tar --create --file=/dev/tape --multi-volume \
11494 --label="Daily backup for `date +%Y-%m-%d`"}
11498 Some more notes about volume labels:
11501 @item Each label has its own date and time, which corresponds
11502 to the time when @GNUTAR{} initially attempted to write it,
11503 often soon after the operator launches @command{tar} or types the
11504 carriage return telling that the next tape is ready.
11506 @item Comparing date labels to get an idea of tape throughput is
11507 unreliable. It gives correct results only if the delays for rewinding
11508 tapes and the operator switching them were negligible, which is
11509 usually not the case.
11513 @section Verifying Data as It is Stored
11514 @cindex Verifying a write operation
11515 @cindex Double-checking a write operation
11520 @opindex verify, short description
11521 Attempt to verify the archive after writing.
11524 This option causes @command{tar} to verify the archive after writing it.
11525 Each volume is checked after it is written, and any discrepancies
11526 are recorded on the standard error output.
11528 Verification requires that the archive be on a back-space-able medium.
11529 This means pipes, some cartridge tape drives, and some other devices
11530 cannot be verified.
11532 You can insure the accuracy of an archive by comparing files in the
11533 system with archive members. @command{tar} can compare an archive to the
11534 file system as the archive is being written, to verify a write
11535 operation, or can compare a previously written archive, to insure that
11538 @xopindex{verify, using with @option{--create}}
11539 @xopindex{create, using with @option{--verify}}
11540 To check for discrepancies in an archive immediately after it is
11541 written, use the @option{--verify} (@option{-W}) option in conjunction with
11542 the @option{--create} operation. When this option is
11543 specified, @command{tar} checks archive members against their counterparts
11544 in the file system, and reports discrepancies on the standard error.
11546 To verify an archive, you must be able to read it from before the end
11547 of the last written entry. This option is useful for detecting data
11548 errors on some tapes. Archives written to pipes, some cartridge tape
11549 drives, and some other devices cannot be verified.
11551 One can explicitly compare an already made archive with the file
11552 system by using the @option{--compare} (@option{--diff}, @option{-d})
11553 option, instead of using the more automatic @option{--verify} option.
11556 Note that these two options have a slightly different intent. The
11557 @option{--compare} option checks how identical are the logical contents of some
11558 archive with what is on your disks, while the @option{--verify} option is
11559 really for checking if the physical contents agree and if the recording
11560 media itself is of dependable quality. So, for the @option{--verify}
11561 operation, @command{tar} tries to defeat all in-memory cache pertaining to
11562 the archive, while it lets the speed optimization undisturbed for the
11563 @option{--compare} option. If you nevertheless use @option{--compare} for
11564 media verification, you may have to defeat the in-memory cache yourself,
11565 maybe by opening and reclosing the door latch of your recording unit,
11566 forcing some doubt in your operating system about the fact this is really
11567 the same volume as the one just written or read.
11569 The @option{--verify} option would not be necessary if drivers were indeed
11570 able to detect dependably all write failures. This sometimes require many
11571 magnetic heads, some able to read after the writes occurred. One would
11572 not say that drivers unable to detect all cases are necessarily flawed,
11573 as long as programming is concerned.
11575 The @option{--verify} (@option{-W}) option will not work in
11576 conjunction with the @option{--multi-volume} (@option{-M}) option or
11577 the @option{--append} (@option{-r}), @option{--update} (@option{-u})
11578 and @option{--delete} operations. @xref{Operations}, for more
11579 information on these operations.
11581 Also, since @command{tar} normally strips leading @samp{/} from file
11582 names (@pxref{absolute}), a command like @samp{tar --verify -cf
11583 /tmp/foo.tar /etc} will work as desired only if the working directory is
11584 @file{/}, as @command{tar} uses the archive's relative member names
11585 (e.g., @file{etc/motd}) when verifying the archive.
11587 @node Write Protection
11588 @section Write Protection
11590 Almost all tapes and diskettes, and in a few rare cases, even disks can
11591 be @dfn{write protected}, to protect data on them from being changed.
11592 Once an archive is written, you should write protect the media to prevent
11593 the archive from being accidentally overwritten or deleted. (This will
11594 protect the archive from being changed with a tape or floppy drive---it
11595 will not protect it from magnet fields or other physical hazards.)
11597 The write protection device itself is usually an integral part of the
11598 physical media, and can be a two position (write enabled/write
11599 disabled) switch, a notch which can be popped out or covered, a ring
11600 which can be removed from the center of a tape reel, or some other
11601 changeable feature.
11606 This appendix lists some important user-visible changes between
11607 version @GNUTAR{} @value{VERSION} and previous versions. An up-to-date
11608 version of this document is available at
11609 @uref{http://www.gnu.org/@/software/@/tar/manual/changes.html,the
11610 @GNUTAR{} documentation page}.
11613 @item Use of globbing patterns when listing and extracting.
11615 Previous versions of GNU tar assumed shell-style globbing when
11616 extracting from or listing an archive. For example:
11619 $ @kbd{tar xf foo.tar '*.c'}
11622 would extract all files whose names end in @samp{.c}. This behavior
11623 was not documented and was incompatible with traditional tar
11624 implementations. Therefore, starting from version 1.15.91, GNU tar
11625 no longer uses globbing by default. For example, the above invocation
11626 is now interpreted as a request to extract from the archive the file
11629 To facilitate transition to the new behavior for those users who got
11630 used to the previous incorrect one, @command{tar} will print a warning
11631 if it finds out that a requested member was not found in the archive
11632 and its name looks like a globbing pattern. For example:
11635 $ @kbd{tar xf foo.tar '*.c'}
11636 tar: Pattern matching characters used in file names. Please,
11637 tar: use --wildcards to enable pattern matching, or --no-wildcards to
11638 tar: suppress this warning.
11639 tar: *.c: Not found in archive
11640 tar: Error exit delayed from previous errors
11643 To treat member names as globbing patterns, use the @option{--wildcards} option.
11644 If you want to tar to mimic the behavior of versions prior to 1.15.91,
11645 add this option to your @env{TAR_OPTIONS} variable.
11647 @xref{wildcards}, for the detailed discussion of the use of globbing
11648 patterns by @GNUTAR{}.
11650 @item Use of short option @option{-o}.
11652 Earlier versions of @GNUTAR{} understood @option{-o} command line
11653 option as a synonym for @option{--old-archive}.
11655 @GNUTAR{} starting from version 1.13.90 understands this option as
11656 a synonym for @option{--no-same-owner}. This is compatible with
11657 UNIX98 @command{tar} implementations.
11659 However, to facilitate transition, @option{-o} option retains its
11660 old semantics when it is used with one of archive-creation commands.
11661 Users are encouraged to use @option{--format=oldgnu} instead.
11663 It is especially important, since versions of @acronym{GNU} Automake
11664 up to and including 1.8.4 invoke tar with this option to produce
11665 distribution tarballs. @xref{Formats,v7}, for the detailed discussion
11666 of this issue and its implications.
11668 @xref{Options, tar-formats, Changing Automake's Behavior,
11669 automake, GNU Automake}, for a description on how to use various
11670 archive formats with @command{automake}.
11672 Future versions of @GNUTAR{} will understand @option{-o} only as a
11673 synonym for @option{--no-same-owner}.
11675 @item Use of short option @option{-l}
11677 Earlier versions of @GNUTAR{} understood @option{-l} option as a
11678 synonym for @option{--one-file-system}. Since such usage contradicted
11679 to UNIX98 specification and harmed compatibility with other
11680 implementations, it was declared deprecated in version 1.14. However,
11681 to facilitate transition to its new semantics, it was supported by
11682 versions 1.15 and 1.15.90. The present use of @option{-l} as a short
11683 variant of @option{--check-links} was introduced in version 1.15.91.
11685 @item Use of options @option{--portability} and @option{--old-archive}
11687 These options are deprecated. Please use @option{--format=v7} instead.
11689 @item Use of option @option{--posix}
11691 This option is deprecated. Please use @option{--format=posix} instead.
11694 @node Configuring Help Summary
11695 @appendix Configuring Help Summary
11697 Running @kbd{tar --help} displays the short @command{tar} option
11698 summary (@pxref{help}). This summary is organized by @dfn{groups} of
11699 semantically close options. The options within each group are printed
11700 in the following order: a short option, eventually followed by a list
11701 of corresponding long option names, followed by a short description of
11702 the option. For example, here is an excerpt from the actual @kbd{tar
11706 Main operation mode:
11708 -A, --catenate, --concatenate append tar files to an archive
11709 -c, --create create a new archive
11710 -d, --diff, --compare find differences between archive and
11712 --delete delete from the archive
11715 @vrindex ARGP_HELP_FMT, environment variable
11716 The exact visual representation of the help output is configurable via
11717 @env{ARGP_HELP_FMT} environment variable. The value of this variable
11718 is a comma-separated list of @dfn{format variable} assignments. There
11719 are two kinds of format variables. An @dfn{offset variable} keeps the
11720 offset of some part of help output text from the leftmost column on
11721 the screen. A @dfn{boolean} variable is a flag that toggles some
11722 output feature on or off. Depending on the type of the corresponding
11723 variable, there are two kinds of assignments:
11726 @item Offset assignment
11728 The assignment to an offset variable has the following syntax:
11731 @var{variable}=@var{value}
11735 where @var{variable} is the variable name, and @var{value} is a
11736 numeric value to be assigned to the variable.
11738 @item Boolean assignment
11740 To assign @code{true} value to a variable, simply put this variable name. To
11741 assign @code{false} value, prefix the variable name with @samp{no-}. For
11746 # Assign @code{true} value:
11748 # Assign @code{false} value:
11754 Following variables are declared:
11756 @deftypevr {Help Output} boolean dup-args
11757 If true, arguments for an option are shown with both short and long
11758 options, even when a given option has both forms, for example:
11761 -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE
11764 If false, then if an option has both short and long forms, the
11765 argument is only shown with the long one, for example:
11768 -f, --file=ARCHIVE use archive file or device ARCHIVE
11772 and a message indicating that the argument is applicable to both
11773 forms is printed below the options. This message can be disabled
11774 using @code{dup-args-note} (see below).
11776 The default is false.
11779 @deftypevr {Help Output} boolean dup-args-note
11780 If this variable is true, which is the default, the following notice
11781 is displayed at the end of the help output:
11784 Mandatory or optional arguments to long options are also mandatory or
11785 optional for any corresponding short options.
11788 Setting @code{no-dup-args-note} inhibits this message. Normally, only one of
11789 variables @code{dup-args} or @code{dup-args-note} should be set.
11792 @deftypevr {Help Output} offset short-opt-col
11793 Column in which short options start. Default is 2.
11797 $ @kbd{tar --help|grep ARCHIVE}
11798 -f, --file=ARCHIVE use archive file or device ARCHIVE
11799 $ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE}
11800 -f, --file=ARCHIVE use archive file or device ARCHIVE
11805 @deftypevr {Help Output} offset long-opt-col
11806 Column in which long options start. Default is 6. For example:
11810 $ @kbd{tar --help|grep ARCHIVE}
11811 -f, --file=ARCHIVE use archive file or device ARCHIVE
11812 $ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE}
11813 -f, --file=ARCHIVE use archive file or device ARCHIVE
11818 @deftypevr {Help Output} offset doc-opt-col
11819 Column in which @dfn{doc options} start. A doc option isn't actually
11820 an option, but rather an arbitrary piece of documentation that is
11821 displayed in much the same manner as the options. For example, in
11822 the description of @option{--format} option:
11826 -H, --format=FORMAT create archive of the given format.
11828 FORMAT is one of the following:
11830 gnu GNU tar 1.13.x format
11831 oldgnu GNU format as per tar <= 1.12
11832 pax POSIX 1003.1-2001 (pax) format
11834 ustar POSIX 1003.1-1988 (ustar) format
11835 v7 old V7 tar format
11840 the format names are doc options. Thus, if you set
11841 @kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output
11842 will look as follows:
11846 -H, --format=FORMAT create archive of the given format.
11848 FORMAT is one of the following:
11850 gnu GNU tar 1.13.x format
11851 oldgnu GNU format as per tar <= 1.12
11852 pax POSIX 1003.1-2001 (pax) format
11854 ustar POSIX 1003.1-1988 (ustar) format
11855 v7 old V7 tar format
11860 @deftypevr {Help Output} offset opt-doc-col
11861 Column in which option description starts. Default is 29.
11865 $ @kbd{tar --help|grep ARCHIVE}
11866 -f, --file=ARCHIVE use archive file or device ARCHIVE
11867 $ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE}
11868 -f, --file=ARCHIVE use archive file or device ARCHIVE
11869 $ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE}
11871 use archive file or device ARCHIVE
11876 Notice, that the description starts on a separate line if
11877 @code{opt-doc-col} value is too small.
11880 @deftypevr {Help Output} offset header-col
11881 Column in which @dfn{group headers} are printed. A group header is a
11882 descriptive text preceding an option group. For example, in the
11886 Main operation mode:
11888 -A, --catenate, --concatenate append tar files to
11890 -c, --create create a new archive
11893 @samp{Main operation mode:} is the group header.
11895 The default value is 1.
11898 @deftypevr {Help Output} offset usage-indent
11899 Indentation of wrapped usage lines. Affects @option{--usage}
11900 output. Default is 12.
11903 @deftypevr {Help Output} offset rmargin
11904 Right margin of the text output. Used for wrapping.
11907 @node Fixing Snapshot Files
11908 @appendix Fixing Snapshot Files
11909 @include tar-snapshot-edit.texi
11911 @node Tar Internals
11912 @appendix Tar Internals
11913 @include intern.texi
11917 @include genfile.texi
11919 @node Free Software Needs Free Documentation
11920 @appendix Free Software Needs Free Documentation
11921 @include freemanuals.texi
11923 @node Copying This Manual
11924 @appendix Copying This Manual
11927 * GNU Free Documentation License:: License for copying this manual
11932 @node Index of Command Line Options
11933 @appendix Index of Command Line Options
11935 This appendix contains an index of all @GNUTAR{} long command line
11936 options. The options are listed without the preceding double-dash.
11937 For a cross-reference of short command line options, see
11938 @ref{Short Option Summary}.
11951 @c Local variables:
11952 @c texinfo-column-for-description: 32
projects / chaz / tar / blob