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 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 the 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 lines
1205 (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
1733 This is because these files were not originally @emph{in} the parent
1734 directory @file{..}, where the archive is located; they were in the
1735 @file{practice} directory, and their file names reflect this:
1738 $ @kbd{tar -tvf music.tar}
1744 @FIXME{make sure the above works when going through the examples in
1748 Likewise, if you try to use this command,
1751 $ @kbd{tar -tvf music.tar folk jazz}
1755 you would get a similar response. Members with those names are not in the
1756 archive. You must use the correct member names, or wildcards, in order
1757 to extract the files from the archive.
1759 If you have forgotten the correct names of the files in the archive,
1760 use @w{@kbd{tar --list --verbose}} to list them correctly.
1762 @FIXME{more examples, here? hag thinks it's a good idea.}
1765 @section Going Further Ahead in this Manual
1768 @FIXME{need to write up a node here about the things that are going to
1769 be in the rest of the manual.}
1771 @node tar invocation
1772 @chapter Invoking @GNUTAR{}
1774 This chapter is about how one invokes the @GNUTAR{}
1775 command, from the command synopsis (@pxref{Synopsis}). There are
1776 numerous options, and many styles for writing them. One mandatory
1777 option specifies the operation @command{tar} should perform
1778 (@pxref{Operation Summary}), other options are meant to detail how
1779 this operation should be performed (@pxref{Option Summary}).
1780 Non-option arguments are not always interpreted the same way,
1781 depending on what the operation is.
1783 You will find in this chapter everything about option styles and rules for
1784 writing them (@pxref{Styles}). On the other hand, operations and options
1785 are fully described elsewhere, in other chapters. Here, you will find
1786 only synthetic descriptions for operations and options, together with
1787 pointers to other parts of the @command{tar} manual.
1789 Some options are so special they are fully described right in this
1790 chapter. They have the effect of inhibiting the normal operation of
1791 @command{tar} or else, they globally alter the amount of feedback the user
1792 receives about what is going on. These are the @option{--help} and
1793 @option{--version} (@pxref{help}), @option{--verbose} (@pxref{verbose})
1794 and @option{--interactive} options (@pxref{interactive}).
1798 * using tar options::
1810 @section General Synopsis of @command{tar}
1812 The @GNUTAR{} program is invoked as either one of:
1815 @kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
1816 @kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
1819 The second form is for when old options are being used.
1821 You can use @command{tar} to store files in an archive, to extract them from
1822 an archive, and to do other types of archive manipulation. The primary
1823 argument to @command{tar}, which is called the @dfn{operation}, specifies
1824 which action to take. The other arguments to @command{tar} are either
1825 @dfn{options}, which change the way @command{tar} performs an operation,
1826 or file names or archive members, which specify the files or members
1827 @command{tar} is to act on.
1829 You can actually type in arguments in any order, even if in this manual
1830 the options always precede the other arguments, to make examples easier
1831 to understand. Further, the option stating the main operation mode
1832 (the @command{tar} main command) is usually given first.
1834 Each @var{name} in the synopsis above is interpreted as an archive member
1835 name when the main command is one of @option{--compare}
1836 (@option{--diff}, @option{-d}), @option{--delete}, @option{--extract}
1837 (@option{--get}, @option{-x}), @option{--list} (@option{-t}) or
1838 @option{--update} (@option{-u}). When naming archive members, you
1839 must give the exact name of the member in the archive, as it is
1840 printed by @option{--list}. For @option{--append} (@option{-r}) and
1841 @option{--create} (@option{-c}), these @var{name} arguments specify
1842 the names of either files or directory hierarchies to place in the archive.
1843 These files or hierarchies should already exist in the file system,
1844 prior to the execution of the @command{tar} command.
1846 @command{tar} interprets relative file names as being relative to the
1847 working directory. @command{tar} will make all file names relative
1848 (by removing leading slashes when archiving or restoring files),
1849 unless you specify otherwise (using the @option{--absolute-names}
1850 option). @xref{absolute}, for more information about
1851 @option{--absolute-names}.
1853 If you give the name of a directory as either a file name or a member
1854 name, then @command{tar} acts recursively on all the files and directories
1855 beneath that directory. For example, the name @file{/} identifies all
1856 the files in the file system to @command{tar}.
1858 The distinction between file names and archive member names is especially
1859 important when shell globbing is used, and sometimes a source of confusion
1860 for newcomers. @xref{wildcards}, for more information about globbing.
1861 The problem is that shells may only glob using existing files in the
1862 file system. Only @command{tar} itself may glob on archive members, so when
1863 needed, you must ensure that wildcard characters reach @command{tar} without
1864 being interpreted by the shell first. Using a backslash before @samp{*}
1865 or @samp{?}, or putting the whole argument between quotes, is usually
1866 sufficient for this.
1868 Even if @var{name}s are often specified on the command line, they
1869 can also be read from a text file in the file system, using the
1870 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option.
1872 If you don't use any file name arguments, @option{--append} (@option{-r}),
1873 @option{--delete} and @option{--concatenate} (@option{--catenate},
1874 @option{-A}) will do nothing, while @option{--create} (@option{-c})
1875 will usually yield a diagnostic and inhibit @command{tar} execution.
1876 The other operations of @command{tar} (@option{--list},
1877 @option{--extract}, @option{--compare}, and @option{--update})
1878 will act on the entire contents of the archive.
1881 @cindex return status
1882 Besides successful exits, @GNUTAR{} may fail for
1883 many reasons. Some reasons correspond to bad usage, that is, when the
1884 @command{tar} command line is improperly written. Errors may be
1885 encountered later, while processing the archive or the files. Some
1886 errors are recoverable, in which case the failure is delayed until
1887 @command{tar} has completed all its work. Some errors are such that
1888 it would be not meaningful, or at least risky, to continue processing:
1889 @command{tar} then aborts processing immediately. All abnormal exits,
1890 whether immediate or delayed, should always be clearly diagnosed on
1891 @code{stderr}, after a line stating the nature of the error.
1893 Possible exit codes of @GNUTAR{} are summarized in the following
1898 @samp{Successful termination}.
1901 @samp{Some files differ}. If tar was invoked with @option{--compare}
1902 (@option{--diff}, @option{-d}) command line option, this means that
1903 some files in the archive differ from their disk counterparts
1904 (@pxref{compare}). If tar was given @option{--create},
1905 @option{--append} or @option{--update} option, this exit code means
1906 that some files were changed while being archived and so the resulting
1907 archive does not contain the exact copy of the file set.
1910 @samp{Fatal error}. This means that some fatal, unrecoverable error
1914 If @command{tar} has invoked a subprocess and that subprocess exited with a
1915 nonzero exit code, @command{tar} exits with that code as well.
1916 This can happen, for example, if @command{tar} was given some
1917 compression option (@pxref{gzip}) and the external compressor program
1918 failed. Another example is @command{rmt} failure during backup to the
1919 remote device (@pxref{Remote Tape Server}).
1921 @node using tar options
1922 @section Using @command{tar} Options
1924 @GNUTAR{} has a total of eight operating modes which
1925 allow you to perform a variety of tasks. You are required to choose
1926 one operating mode each time you employ the @command{tar} program by
1927 specifying one, and only one operation as an argument to the
1928 @command{tar} command (the corresponding options may be found
1929 at @ref{frequent operations} and @ref{Operations}). Depending on
1930 circumstances, you may also wish to customize how the chosen operating
1931 mode behaves. For example, you may wish to change the way the output
1932 looks, or the format of the files that you wish to archive may require
1933 you to do something special in order to make the archive look right.
1935 You can customize and control @command{tar}'s performance by running
1936 @command{tar} with one or more options (such as @option{--verbose}
1937 (@option{-v}), which we used in the tutorial). As we said in the
1938 tutorial, @dfn{options} are arguments to @command{tar} which are (as
1939 their name suggests) optional. Depending on the operating mode, you
1940 may specify one or more options. Different options will have different
1941 effects, but in general they all change details of the operation, such
1942 as archive format, archive name, or level of user interaction. Some
1943 options make sense with all operating modes, while others are
1944 meaningful only with particular modes. You will likely use some
1945 options frequently, while you will only use others infrequently, or
1946 not at all. (A full list of options is available in @pxref{All Options}.)
1948 @vrindex TAR_OPTIONS, environment variable
1949 @anchor{TAR_OPTIONS}
1950 The @env{TAR_OPTIONS} environment variable specifies default options to
1951 be placed in front of any explicit options. For example, if
1952 @code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as
1953 if the two options @option{-v} and @option{--unlink-first} had been
1954 specified before any explicit options. Option specifications are
1955 separated by whitespace. A backslash escapes the next character, so it
1956 can be used to specify an option containing whitespace or a backslash.
1958 Note that @command{tar} options are case sensitive. For example, the
1959 options @option{-T} and @option{-t} are different; the first requires an
1960 argument for stating the name of a file providing a list of @var{name}s,
1961 while the second does not require an argument and is another way to
1962 write @option{--list} (@option{-t}).
1964 In addition to the eight operations, there are many options to
1965 @command{tar}, and three different styles for writing both: long (mnemonic)
1966 form, short form, and old style. These styles are discussed below.
1967 Both the options and the operations can be written in any of these three
1970 @FIXME{menu at end of this node. need to think of an actual outline
1971 for this chapter; probably do that after stuff from chapter 4 is
1975 @section The Three Option Styles
1977 There are three styles for writing operations and options to the command
1978 line invoking @command{tar}. The different styles were developed at
1979 different times during the history of @command{tar}. These styles will be
1980 presented below, from the most recent to the oldest.
1982 Some options must take an argument. (For example, @option{--file}
1983 (@option{-f})) takes the name of an archive file as an argument. If
1984 you do not supply an archive file name, @command{tar} will use a
1985 default, but this can be confusing; thus, we recommend that you always
1986 supply a specific archive file name.) Where you @emph{place} the
1987 arguments generally depends on which style of options you choose. We
1988 will detail specific information relevant to each option style in the
1989 sections on the different option styles, below. The differences are
1990 subtle, yet can often be very important; incorrect option placement
1991 can cause you to overwrite a number of important files. We urge you
1992 to note these differences, and only use the option style(s) which
1993 makes the most sense to you until you feel comfortable with the others.
1995 Some options @emph{may} take an argument. Such options may have at
1996 most long and short forms, they do not have old style equivalent. The
1997 rules for specifying an argument for such options are stricter than
1998 those for specifying mandatory arguments. Please, pay special
2002 * Long Options:: Long Option Style
2003 * Short Options:: Short Option Style
2004 * Old Options:: Old Option Style
2005 * Mixing:: Mixing Option Styles
2009 @subsection Long Option Style
2011 @cindex long options
2012 @cindex options, long style
2013 @cindex options, GNU style
2014 @cindex options, mnemonic names
2015 Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
2016 dashes in a row, e.g., @option{--list}. The long names are more clear than
2017 their corresponding short or old names. It sometimes happens that a
2018 single long option has many different names which are
2019 synonymous, such as @option{--compare} and @option{--diff}. In addition,
2020 long option names can be given unique abbreviations. For example,
2021 @option{--cre} can be used in place of @option{--create} because there is no
2022 other long option which begins with @samp{cre}. (One way to find
2023 this out is by trying it and seeing what happens; if a particular
2024 abbreviation could represent more than one option, @command{tar} will tell
2025 you that that abbreviation is ambiguous and you'll know that that
2026 abbreviation won't work. You may also choose to run @samp{tar --help}
2027 to see a list of options. Be aware that if you run @command{tar} with a
2028 unique abbreviation for the long name of an option you didn't want to
2029 use, you are stuck; @command{tar} will perform the command as ordered.)
2031 Long options are meant to be obvious and easy to remember, and their
2032 meanings are generally easier to discern than those of their
2033 corresponding short options (see below). For example:
2036 $ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
2040 gives a fairly good set of hints about what the command does, even
2041 for those not fully acquainted with @command{tar}.
2043 @cindex arguments to long options
2044 @cindex long options with mandatory arguments
2045 Long options which require arguments take those arguments
2046 immediately following the option name. There are two ways of
2047 specifying a mandatory argument. It can be separated from the
2048 option name either by an equal sign, or by any amount of
2049 white space characters. For example, the @option{--file} option (which
2050 tells the name of the @command{tar} archive) is given a file such as
2051 @file{archive.tar} as argument by using any of the following notations:
2052 @option{--file=archive.tar} or @option{--file archive.tar}.
2054 @cindex optional arguments to long options
2055 @cindex long options with optional arguments
2056 In contrast, optional arguments must always be introduced using
2057 an equal sign. For example, the @option{--backup} option takes
2058 an optional argument specifying backup type. It must be used
2059 as @option{--backup=@var{backup-type}}.
2062 @subsection Short Option Style
2064 @cindex short options
2065 @cindex options, short style
2066 @cindex options, traditional
2067 Most options also have a @dfn{short option} name. Short options start with
2068 a single dash, and are followed by a single character, e.g., @option{-t}
2069 (which is equivalent to @option{--list}). The forms are absolutely
2070 identical in function; they are interchangeable.
2072 The short option names are faster to type than long option names.
2074 @cindex arguments to short options
2075 @cindex short options with mandatory arguments
2076 Short options which require arguments take their arguments immediately
2077 following the option, usually separated by white space. It is also
2078 possible to stick the argument right after the short option name, using
2079 no intervening space. For example, you might write @w{@option{-f
2080 archive.tar}} or @option{-farchive.tar} instead of using
2081 @option{--file=archive.tar}. Both @option{--file=@var{archive-name}} and
2082 @w{@option{-f @var{archive-name}}} denote the option which indicates a
2083 specific archive, here named @file{archive.tar}.
2085 @cindex optional arguments to short options
2086 @cindex short options with optional arguments
2087 Short options which take optional arguments take their arguments
2088 immediately following the option letter, @emph{without any intervening
2089 white space characters}.
2091 Short options' letters may be clumped together, but you are not
2092 required to do this (as compared to old options; see below). When
2093 short options are clumped as a set, use one (single) dash for them
2094 all, e.g., @w{@samp{@command{tar} -cvf}}. Only the last option in
2095 such a set is allowed to have an argument@footnote{Clustering many
2096 options, the last of which has an argument, is a rather opaque way to
2097 write options. Some wonder if @acronym{GNU} @code{getopt} should not
2098 even be made helpful enough for considering such usages as invalid.}.
2100 When the options are separated, the argument for each option which requires
2101 an argument directly follows that option, as is usual for Unix programs.
2105 $ @kbd{tar -c -v -b 20 -f /dev/rmt0}
2108 If you reorder short options' locations, be sure to move any arguments
2109 that belong to them. If you do not move the arguments properly, you may
2110 end up overwriting files.
2113 @subsection Old Option Style
2114 @cindex options, old style
2115 @cindex old option style
2117 Like short options, @dfn{old options} are single letters. However, old options
2118 must be written together as a single clumped set, without spaces separating
2119 them or dashes preceding them@footnote{Beware that if you precede options
2120 with a dash, you are announcing the short option style instead of the
2121 old option style; short options are decoded differently.}. This set
2122 of letters must be the first to appear on the command line, after the
2123 @command{tar} program name and some white space; old options cannot appear
2124 anywhere else. The letter of an old option is exactly the same letter as
2125 the corresponding short option. For example, the old option @samp{t} is
2126 the same as the short option @option{-t}, and consequently, the same as the
2127 long option @option{--list}. So for example, the command @w{@samp{tar
2128 cv}} specifies the option @option{-v} in addition to the operation @option{-c}.
2130 @cindex arguments to old options
2131 @cindex old options with mandatory arguments
2132 When options that need arguments are given together with the command,
2133 all the associated arguments follow, in the same order as the options.
2134 Thus, the example given previously could also be written in the old
2138 $ @kbd{tar cvbf 20 /dev/rmt0}
2142 Here, @samp{20} is the argument of @option{-b} and @samp{/dev/rmt0} is
2143 the argument of @option{-f}.
2145 On the other hand, this old style syntax makes it difficult to match
2146 option letters with their corresponding arguments, and is often
2147 confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example,
2148 @samp{20} is the argument for @option{-b}, @samp{/dev/rmt0} is the
2149 argument for @option{-f}, and @option{-v} does not have a corresponding
2150 argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f
2151 /dev/rmt0}} is clearer, putting all arguments next to the option they
2154 If you want to reorder the letters in the old option argument, be
2155 sure to reorder any corresponding argument appropriately.
2157 This old way of writing @command{tar} options can surprise even experienced
2158 users. For example, the two commands:
2161 @kbd{tar cfz archive.tar.gz file}
2162 @kbd{tar -cfz archive.tar.gz file}
2166 are quite different. The first example uses @file{archive.tar.gz} as
2167 the value for option @samp{f} and recognizes the option @samp{z}. The
2168 second example, however, uses @file{z} as the value for option
2169 @samp{f} --- probably not what was intended.
2171 Old options are kept for compatibility with old versions of @command{tar}.
2173 This second example could be corrected in many ways, among which the
2174 following are equivalent:
2177 @kbd{tar -czf archive.tar.gz file}
2178 @kbd{tar -cf archive.tar.gz -z file}
2179 @kbd{tar cf archive.tar.gz -z file}
2182 @cindex option syntax, traditional
2183 As far as we know, all @command{tar} programs, @acronym{GNU} and
2184 non-@acronym{GNU}, support old options. @GNUTAR{}
2185 supports them not only for historical reasons, but also because many
2186 people are used to them. For compatibility with Unix @command{tar},
2187 the first argument is always treated as containing command and option
2188 letters even if it doesn't start with @samp{-}. Thus, @samp{tar c} is
2189 equivalent to @w{@samp{tar -c}:} both of them specify the
2190 @option{--create} (@option{-c}) command to create an archive.
2193 @subsection Mixing Option Styles
2195 @cindex options, mixing different styles
2196 All three styles may be intermixed in a single @command{tar} command,
2197 so long as the rules for each style are fully
2198 respected@footnote{Before @GNUTAR{} version 1.11.6,
2199 a bug prevented intermixing old style options with long options in
2200 some cases.}. Old style options and either of the modern styles of
2201 options may be mixed within a single @command{tar} command. However,
2202 old style options must be introduced as the first arguments only,
2203 following the rule for old options (old options must appear directly
2204 after the @command{tar} command and some white space). Modern options
2205 may be given only after all arguments to the old options have been
2206 collected. If this rule is not respected, a modern option might be
2207 falsely interpreted as the value of the argument to one of the old
2210 For example, all the following commands are wholly equivalent, and
2211 illustrate the many combinations and orderings of option styles.
2214 @kbd{tar --create --file=archive.tar}
2215 @kbd{tar --create -f archive.tar}
2216 @kbd{tar --create -farchive.tar}
2217 @kbd{tar --file=archive.tar --create}
2218 @kbd{tar --file=archive.tar -c}
2219 @kbd{tar -c --file=archive.tar}
2220 @kbd{tar -c -f archive.tar}
2221 @kbd{tar -c -farchive.tar}
2222 @kbd{tar -cf archive.tar}
2223 @kbd{tar -cfarchive.tar}
2224 @kbd{tar -f archive.tar --create}
2225 @kbd{tar -f archive.tar -c}
2226 @kbd{tar -farchive.tar --create}
2227 @kbd{tar -farchive.tar -c}
2228 @kbd{tar c --file=archive.tar}
2229 @kbd{tar c -f archive.tar}
2230 @kbd{tar c -farchive.tar}
2231 @kbd{tar cf archive.tar}
2232 @kbd{tar f archive.tar --create}
2233 @kbd{tar f archive.tar -c}
2234 @kbd{tar fc archive.tar}
2237 On the other hand, the following commands are @emph{not} equivalent to
2241 @kbd{tar -f -c archive.tar}
2242 @kbd{tar -fc archive.tar}
2243 @kbd{tar -fcarchive.tar}
2244 @kbd{tar -farchive.tarc}
2245 @kbd{tar cfarchive.tar}
2249 These last examples mean something completely different from what the
2250 user intended (judging based on the example in the previous set which
2251 uses long options, whose intent is therefore very clear). The first
2252 four specify that the @command{tar} archive would be a file named
2253 @option{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc},
2254 respectively. The first two examples also specify a single non-option,
2255 @var{name} argument having the value @samp{archive.tar}. The last
2256 example contains only old style option letters (repeating option
2257 @samp{c} twice), not all of which are meaningful (eg., @samp{.},
2258 @samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked
2259 the first sentence of this paragraph..}
2262 @section All @command{tar} Options
2264 The coming manual sections contain an alphabetical listing of all
2265 @command{tar} operations and options, with brief descriptions and cross
2266 references to more in-depth explanations in the body of the manual.
2267 They also contain an alphabetically arranged table of the short option
2268 forms with their corresponding long option. You can use this table as
2269 a reference for deciphering @command{tar} commands in scripts.
2272 * Operation Summary::
2274 * Short Option Summary::
2277 @node Operation Summary
2278 @subsection Operations
2286 Appends files to the end of the archive. @xref{append}.
2288 @opsummary{catenate}
2292 Same as @option{--concatenate}. @xref{concatenate}.
2298 Compares archive members with their counterparts in the file
2299 system, and reports differences in file size, mode, owner,
2300 modification date and contents. @xref{compare}.
2302 @opsummary{concatenate}
2306 Appends other @command{tar} archives to the end of the archive.
2313 Creates a new @command{tar} archive. @xref{create}.
2318 Deletes members from the archive. Don't try this on a archive on a
2319 tape! @xref{delete}.
2325 Same @option{--compare}. @xref{compare}.
2331 Extracts members from the archive into the file system. @xref{extract}.
2337 Same as @option{--extract}. @xref{extract}.
2343 Lists the members in an archive. @xref{list}.
2349 Adds files to the end of the archive, but only if they are newer than
2350 their counterparts already in the archive, or if they do not already
2351 exist in the archive. @xref{update}.
2355 @node Option Summary
2356 @subsection @command{tar} Options
2360 @opsummary{absolute-names}
2361 @item --absolute-names
2364 Normally when creating an archive, @command{tar} strips an initial
2365 @samp{/} from member names. This option disables that behavior.
2368 @opsummary{after-date}
2371 (See @option{--newer}, @pxref{after})
2373 @opsummary{anchored}
2375 A pattern must match an initial subsequence of the name's components.
2376 @xref{controlling pattern-matching}.
2378 @opsummary{atime-preserve}
2379 @item --atime-preserve
2380 @itemx --atime-preserve=replace
2381 @itemx --atime-preserve=system
2383 Attempt to preserve the access time of files when reading them. This
2384 option currently is effective only on files that you own, unless you
2385 have superuser privileges.
2387 @option{--atime-preserve=replace} remembers the access time of a file
2388 before reading it, and then restores the access time afterwards. This
2389 may cause problems if other programs are reading the file at the same
2390 time, as the times of their accesses will be lost. On most platforms
2391 restoring the access time also requires @command{tar} to restore the
2392 data modification time too, so this option may also cause problems if
2393 other programs are writing the file at the same time. (Tar attempts
2394 to detect this situation, but cannot do so reliably due to race
2395 conditions.) Worse, on most platforms restoring the access time also
2396 updates the status change time, which means that this option is
2397 incompatible with incremental backups.
2399 @option{--atime-preserve=system} avoids changing time stamps on files,
2400 without interfering with time stamp updates
2401 caused by other programs, so it works better with incremental backups.
2402 However, it requires a special @code{O_NOATIME} option from the
2403 underlying operating and file system implementation, and it also requires
2404 that searching directories does not update their access times. As of
2405 this writing (November 2005) this works only with Linux, and only with
2406 Linux kernels 2.6.8 and later. Worse, there is currently no reliable
2407 way to know whether this feature actually works. Sometimes
2408 @command{tar} knows that it does not work, and if you use
2409 @option{--atime-preserve=system} then @command{tar} complains and
2410 exits right away. But other times @command{tar} might think that the
2411 option works when it actually does not.
2413 Currently @option{--atime-preserve} with no operand defaults to
2414 @option{--atime-preserve=replace}, but this may change in the future
2415 as support for @option{--atime-preserve=system} improves.
2417 If your operating system does not support
2418 @option{--atime-preserve=@-system}, you might be able to preserve access
2419 times reliably by by using the @command{mount} command. For example,
2420 you can mount the file system read-only, or access the file system via
2421 a read-only loopback mount, or use the @samp{noatime} mount option
2422 available on some systems. However, mounting typically requires
2423 superuser privileges and can be a pain to manage.
2425 @opsummary{auto-compress}
2426 @item --auto-compress
2429 During a @option{--create} operation, enables automatic compressed
2430 format recognition based on the archive suffix. The effect of this
2431 option is cancelled by @option{--no-auto-compress}. @xref{gzip}.
2434 @item --backup=@var{backup-type}
2436 Rather than deleting files from the file system, @command{tar} will
2437 back them up using simple or numbered backups, depending upon
2438 @var{backup-type}. @xref{backup}.
2440 @opsummary{block-number}
2441 @item --block-number
2444 With this option present, @command{tar} prints error messages for read errors
2445 with the block number in the archive file. @xref{block-number}.
2447 @opsummary{blocking-factor}
2448 @item --blocking-factor=@var{blocking}
2449 @itemx -b @var{blocking}
2451 Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
2452 record. @xref{Blocking Factor}.
2458 This option tells @command{tar} to read or write archives through
2459 @code{bzip2}. @xref{gzip}.
2461 @opsummary{check-device}
2462 @item --check-device
2463 Check device numbers when creating a list of modified files for
2464 incremental archiving. This is the default. @xref{device numbers},
2465 for a detailed description.
2467 @opsummary{checkpoint}
2468 @item --checkpoint[=@var{number}]
2470 This option directs @command{tar} to print periodic checkpoint
2471 messages as it reads through the archive. It is intended for when you
2472 want a visual indication that @command{tar} is still running, but
2473 don't want to see @option{--verbose} output. You can also instruct
2474 @command{tar} to execute a list of actions on each checkpoint, see
2475 @option{--checkpoint-action} below. For a detailed description, see
2478 @opsummary{checkpoint-action}
2479 @item --checkpoint-action=@var{action}
2480 Instruct @command{tar} to execute an action upon hitting a
2481 breakpoint. Here we give only a brief outline. @xref{checkpoints},
2482 for a complete description.
2484 The @var{action} argument can be one of the following:
2488 Produce an audible bell on the console.
2492 Print a single dot on the standard listing stream.
2495 Display a textual message on the standard error, with the status and
2496 number of the checkpoint. This is the default.
2498 @item echo=@var{string}
2499 Display @var{string} on the standard error. Before output, the string
2500 is subject to meta-character expansion.
2502 @item exec=@var{command}
2503 Execute the given @var{command}.
2505 @item sleep=@var{time}
2506 Wait for @var{time} seconds.
2508 @item ttyout=@var{string}
2509 Output @var{string} on the current console (@file{/dev/tty}).
2512 Several @option{--checkpoint-action} options can be specified. The
2513 supplied actions will be executed in order of their appearance in the
2516 Using @option{--checkpoint-action} without @option{--checkpoint}
2517 assumes default checkpoint frequency of one checkpoint per 10 records.
2519 @opsummary{check-links}
2522 If this option was given, @command{tar} will check the number of links
2523 dumped for each processed file. If this number does not match the
2524 total number of hard links for the file, a warning message will be
2525 output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2526 synonym for @option{--one-file-system}. The current semantics, which
2527 complies to UNIX98, was introduced with version
2528 1.15.91. @xref{Changes}, for more information.}.
2532 @opsummary{compress}
2533 @opsummary{uncompress}
2538 @command{tar} will use the @command{compress} program when reading or
2539 writing the archive. This allows you to directly act on archives
2540 while saving space. @xref{gzip}.
2542 @opsummary{confirmation}
2543 @item --confirmation
2545 (See @option{--interactive}.) @xref{interactive}.
2547 @opsummary{delay-directory-restore}
2548 @item --delay-directory-restore
2550 Delay setting modification times and permissions of extracted
2551 directories until the end of extraction. @xref{Directory Modification Times and Permissions}.
2553 @opsummary{dereference}
2557 When creating a @command{tar} archive, @command{tar} will archive the
2558 file that a symbolic link points to, rather than archiving the
2559 symlink. @xref{dereference}.
2561 @opsummary{directory}
2562 @item --directory=@var{dir}
2565 When this option is specified, @command{tar} will change its current directory
2566 to @var{dir} before performing any operations. When this option is used
2567 during archive creation, it is order sensitive. @xref{directory}.
2570 @item --exclude=@var{pattern}
2572 When performing operations, @command{tar} will skip files that match
2573 @var{pattern}. @xref{exclude}.
2575 @opsummary{exclude-backups}
2576 @item --exclude-backups
2577 Exclude backup and lock files. @xref{exclude,, exclude-backups}.
2579 @opsummary{exclude-from}
2580 @item --exclude-from=@var{file}
2581 @itemx -X @var{file}
2583 Similar to @option{--exclude}, except @command{tar} will use the list of
2584 patterns in the file @var{file}. @xref{exclude}.
2586 @opsummary{exclude-caches}
2587 @item --exclude-caches
2589 Exclude from dump any directory containing a valid cache directory
2590 tag file, but still dump the directory node and the tag file itself.
2592 @xref{exclude,, exclude-caches}.
2594 @opsummary{exclude-caches-under}
2595 @item --exclude-caches-under
2597 Exclude from dump any directory containing a valid cache directory
2598 tag file, but still dump the directory node itself.
2602 @opsummary{exclude-caches-all}
2603 @item --exclude-caches-all
2605 Exclude from dump any directory containing a valid cache directory
2606 tag file. @xref{exclude}.
2608 @opsummary{exclude-tag}
2609 @item --exclude-tag=@var{file}
2611 Exclude from dump any directory containing file named @var{file}, but
2612 dump the directory node and @var{file} itself. @xref{exclude,, exclude-tag}.
2614 @opsummary{exclude-tag-under}
2615 @item --exclude-tag-under=@var{file}
2617 Exclude from dump the contents of any directory containing file
2618 named @var{file}, but dump the directory node itself. @xref{exclude,,
2621 @opsummary{exclude-tag-all}
2622 @item --exclude-tag-all=@var{file}
2624 Exclude from dump any directory containing file named @var{file}.
2625 @xref{exclude,,exclude-tag-all}.
2627 @opsummary{exclude-vcs}
2630 Exclude from dump directories and files, that are internal for some
2631 widely used version control systems.
2633 @xref{exclude,,exclude-vcs}.
2636 @item --file=@var{archive}
2637 @itemx -f @var{archive}
2639 @command{tar} will use the file @var{archive} as the @command{tar} archive it
2640 performs operations on, rather than @command{tar}'s compilation dependent
2641 default. @xref{file tutorial}.
2643 @opsummary{files-from}
2644 @item --files-from=@var{file}
2645 @itemx -T @var{file}
2647 @command{tar} will use the contents of @var{file} as a list of archive members
2648 or files to operate on, in addition to those specified on the
2649 command-line. @xref{files}.
2651 @opsummary{force-local}
2654 Forces @command{tar} to interpret the file name given to @option{--file}
2655 as a local file, even if it looks like a remote tape drive name.
2656 @xref{local and remote archives}.
2659 @item --format=@var{format}
2660 @itemx -H @var{format}
2662 Selects output archive format. @var{Format} may be one of the
2667 Creates an archive that is compatible with Unix V7 @command{tar}.
2670 Creates an archive that is compatible with GNU @command{tar} version
2674 Creates archive in GNU tar 1.13 format. Basically it is the same as
2675 @samp{oldgnu} with the only difference in the way it handles long
2679 Creates a @acronym{POSIX.1-1988} compatible archive.
2682 Creates a @acronym{POSIX.1-2001 archive}.
2686 @xref{Formats}, for a detailed discussion of these formats.
2689 @item --group=@var{group}
2691 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
2692 rather than the group from the source file. @var{group} is first decoded
2693 as a group symbolic name, but if this interpretation fails, it has to be
2694 a decimal numeric group @acronym{ID}. @xref{override}.
2696 Also see the comments for the @option{--owner=@var{user}} option.
2706 This option tells @command{tar} to read or write archives through
2707 @command{gzip}, allowing @command{tar} to directly operate on several
2708 kinds of compressed archives transparently. @xref{gzip}.
2710 @opsummary{hard-dereference}
2711 @item --hard-dereference
2712 When creating an archive, dereference hard links and store the files
2713 they refer to, instead of creating usual hard link members.
2721 @command{tar} will print out a short message summarizing the operations and
2722 options to @command{tar} and exit. @xref{help}.
2724 @opsummary{ignore-case}
2726 Ignore case when matching member or file names with
2727 patterns. @xref{controlling pattern-matching}.
2729 @opsummary{ignore-command-error}
2730 @item --ignore-command-error
2731 Ignore exit codes of subprocesses. @xref{Writing to an External Program}.
2733 @opsummary{ignore-failed-read}
2734 @item --ignore-failed-read
2736 Do not exit unsuccessfully merely because an unreadable file was encountered.
2739 @opsummary{ignore-zeros}
2740 @item --ignore-zeros
2743 With this option, @command{tar} will ignore zeroed blocks in the
2744 archive, which normally signals EOF. @xref{Reading}.
2746 @opsummary{incremental}
2750 Informs @command{tar} that it is working with an old
2751 @acronym{GNU}-format incremental backup archive. It is intended
2752 primarily for backwards compatibility only. @xref{Incremental Dumps},
2753 for a detailed discussion of incremental archives.
2755 @opsummary{index-file}
2756 @item --index-file=@var{file}
2758 Send verbose output to @var{file} instead of to standard output.
2760 @opsummary{info-script}
2761 @opsummary{new-volume-script}
2762 @item --info-script=@var{script-file}
2763 @itemx --new-volume-script=@var{script-file}
2764 @itemx -F @var{script-file}
2766 When @command{tar} is performing multi-tape backups, @var{script-file} is run
2767 at the end of each tape. If @var{script-file} exits with nonzero status,
2768 @command{tar} fails immediately. @xref{info-script}, for a detailed
2769 discussion of @var{script-file}.
2771 @opsummary{interactive}
2773 @itemx --confirmation
2776 Specifies that @command{tar} should ask the user for confirmation before
2777 performing potentially destructive options, such as overwriting files.
2780 @opsummary{keep-newer-files}
2781 @item --keep-newer-files
2783 Do not replace existing files that are newer than their archive copies
2784 when extracting files from an archive.
2786 @opsummary{keep-old-files}
2787 @item --keep-old-files
2790 Do not overwrite existing files when extracting files from an archive.
2791 @xref{Keep Old Files}.
2794 @item --label=@var{name}
2795 @itemx -V @var{name}
2797 When creating an archive, instructs @command{tar} to write @var{name}
2798 as a name record in the archive. When extracting or listing archives,
2799 @command{tar} will only operate on archives that have a label matching
2800 the pattern specified in @var{name}. @xref{Tape Files}.
2803 @item --level=@var{n}
2804 Force incremental backup of level @var{n}. As of @GNUTAR version
2805 @value{VERSION}, the option @option{--level=0} truncates the snapshot
2806 file, thereby forcing the level 0 dump. Other values of @var{n} are
2807 effectively ignored. @xref{--level=0}, for details and examples.
2809 The use of this option is valid only in conjunction with the
2810 @option{--listed-incremental} option. @xref{Incremental Dumps},
2811 for a detailed description.
2813 @opsummary{listed-incremental}
2814 @item --listed-incremental=@var{snapshot-file}
2815 @itemx -g @var{snapshot-file}
2817 During a @option{--create} operation, specifies that the archive that
2818 @command{tar} creates is a new @acronym{GNU}-format incremental
2819 backup, using @var{snapshot-file} to determine which files to backup.
2820 With other operations, informs @command{tar} that the archive is in
2821 incremental format. @xref{Incremental Dumps}.
2826 This option tells @command{tar} to read or write archives through
2827 @command{lzma}. @xref{gzip}.
2831 This option tells @command{tar} to read or write archives through
2832 @command{lzop}. @xref{gzip}.
2835 @item --mode=@var{permissions}
2837 When adding files to an archive, @command{tar} will use
2838 @var{permissions} for the archive members, rather than the permissions
2839 from the files. @var{permissions} can be specified either as an octal
2840 number or as symbolic permissions, like with
2841 @command{chmod}. @xref{override}.
2844 @item --mtime=@var{date}
2846 When adding files to an archive, @command{tar} will use @var{date} as
2847 the modification time of members when creating archives, instead of
2848 their actual modification times. The value of @var{date} can be
2849 either a textual date representation (@pxref{Date input formats}) or a
2850 name of the existing file, starting with @samp{/} or @samp{.}. In the
2851 latter case, the modification time of that file is used. @xref{override}.
2853 @opsummary{multi-volume}
2854 @item --multi-volume
2857 Informs @command{tar} that it should create or otherwise operate on a
2858 multi-volume @command{tar} archive. @xref{Using Multiple Tapes}.
2860 @opsummary{new-volume-script}
2861 @item --new-volume-script
2866 @item --newer=@var{date}
2867 @itemx --after-date=@var{date}
2870 When creating an archive, @command{tar} will only add files that have changed
2871 since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it
2872 is taken to be the name of a file whose data modification time specifies
2873 the date. @xref{after}.
2875 @opsummary{newer-mtime}
2876 @item --newer-mtime=@var{date}
2878 Like @option{--newer}, but add only files whose
2879 contents have changed (as opposed to just @option{--newer}, which will
2880 also back up files for which any status information has
2881 changed). @xref{after}.
2883 @opsummary{no-anchored}
2885 An exclude pattern can match any subsequence of the name's components.
2886 @xref{controlling pattern-matching}.
2888 @opsummary{no-auto-compress}
2889 @item --no-auto-compress
2891 Disables automatic compressed format recognition based on the archive
2892 suffix. @xref{--auto-compress}. @xref{gzip}.
2894 @opsummary{no-check-device}
2895 @item --no-check-device
2896 Do not check device numbers when creating a list of modified files
2897 for incremental archiving. @xref{device numbers}, for
2898 a detailed description.
2900 @opsummary{no-delay-directory-restore}
2901 @item --no-delay-directory-restore
2903 Modification times and permissions of extracted
2904 directories are set when all files from this directory have been
2905 extracted. This is the default.
2906 @xref{Directory Modification Times and Permissions}.
2908 @opsummary{no-ignore-case}
2909 @item --no-ignore-case
2910 Use case-sensitive matching.
2911 @xref{controlling pattern-matching}.
2913 @opsummary{no-ignore-command-error}
2914 @item --no-ignore-command-error
2915 Print warnings about subprocesses that terminated with a nonzero exit
2916 code. @xref{Writing to an External Program}.
2921 If the @option{--null} option was given previously, this option
2922 cancels its effect, so that any following @option{--files-from}
2923 options will expect their file lists to be newline-terminated.
2925 @opsummary{no-overwrite-dir}
2926 @item --no-overwrite-dir
2928 Preserve metadata of existing directories when extracting files
2929 from an archive. @xref{Overwrite Old Files}.
2931 @opsummary{no-quote-chars}
2932 @item --no-quote-chars=@var{string}
2933 Remove characters listed in @var{string} from the list of quoted
2934 characters set by the previous @option{--quote-chars} option
2935 (@pxref{quoting styles}).
2937 @opsummary{no-recursion}
2938 @item --no-recursion
2940 With this option, @command{tar} will not recurse into directories.
2943 @opsummary{no-same-owner}
2944 @item --no-same-owner
2947 When extracting an archive, do not attempt to preserve the owner
2948 specified in the @command{tar} archive. This the default behavior
2951 @opsummary{no-same-permissions}
2952 @item --no-same-permissions
2954 When extracting an archive, subtract the user's umask from files from
2955 the permissions specified in the archive. This is the default behavior
2961 The archive media does not support seeks to arbitrary
2962 locations. Usually @command{tar} determines automatically whether
2963 the archive can be seeked or not. Use this option to disable this
2966 @opsummary{no-unquote}
2968 Treat all input file or member names literally, do not interpret
2969 escape sequences. @xref{input name quoting}.
2971 @opsummary{no-wildcards}
2972 @item --no-wildcards
2973 Do not use wildcards.
2974 @xref{controlling pattern-matching}.
2976 @opsummary{no-wildcards-match-slash}
2977 @item --no-wildcards-match-slash
2978 Wildcards do not match @samp{/}.
2979 @xref{controlling pattern-matching}.
2984 When @command{tar} is using the @option{--files-from} option, this option
2985 instructs @command{tar} to expect file names terminated with @acronym{NUL}, so
2986 @command{tar} can correctly work with file names that contain newlines.
2989 @opsummary{numeric-owner}
2990 @item --numeric-owner
2992 This option will notify @command{tar} that it should use numeric user
2993 and group IDs when creating a @command{tar} file, rather than names.
2997 The function of this option depends on the action @command{tar} is
2998 performing. When extracting files, @option{-o} is a synonym for
2999 @option{--no-same-owner}, i.e., it prevents @command{tar} from
3000 restoring ownership of files being extracted.
3002 When creating an archive, it is a synonym for
3003 @option{--old-archive}. This behavior is for compatibility
3004 with previous versions of @GNUTAR{}, and will be
3005 removed in future releases.
3007 @xref{Changes}, for more information.
3009 @opsummary{occurrence}
3010 @item --occurrence[=@var{number}]
3012 This option can be used in conjunction with one of the subcommands
3013 @option{--delete}, @option{--diff}, @option{--extract} or
3014 @option{--list} when a list of files is given either on the command
3015 line or via @option{-T} option.
3017 This option instructs @command{tar} to process only the @var{number}th
3018 occurrence of each named file. @var{Number} defaults to 1, so
3021 tar -x -f archive.tar --occurrence filename
3025 will extract the first occurrence of the member @file{filename} from @file{archive.tar}
3026 and will terminate without scanning to the end of the archive.
3028 @opsummary{old-archive}
3030 Synonym for @option{--format=v7}.
3032 @opsummary{one-file-system}
3033 @item --one-file-system
3034 Used when creating an archive. Prevents @command{tar} from recursing into
3035 directories that are on different file systems from the current
3038 @opsummary{overwrite}
3041 Overwrite existing files and directory metadata when extracting files
3042 from an archive. @xref{Overwrite Old Files}.
3044 @opsummary{overwrite-dir}
3045 @item --overwrite-dir
3047 Overwrite the metadata of existing directories when extracting files
3048 from an archive. @xref{Overwrite Old Files}.
3051 @item --owner=@var{user}
3053 Specifies that @command{tar} should use @var{user} as the owner of members
3054 when creating archives, instead of the user associated with the source
3055 file. @var{user} is first decoded as a user symbolic name, but if
3056 this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
3059 This option does not affect extraction from archives.
3061 @opsummary{pax-option}
3062 @item --pax-option=@var{keyword-list}
3063 This option enables creation of the archive in @acronym{POSIX.1-2001}
3064 format (@pxref{posix}) and modifies the way @command{tar} handles the
3065 extended header keywords. @var{Keyword-list} is a comma-separated
3066 list of keyword options. @xref{PAX keywords}, for a detailed
3069 @opsummary{portability}
3071 @itemx --old-archive
3072 Synonym for @option{--format=v7}.
3076 Same as @option{--format=posix}.
3078 @opsummary{preserve}
3081 Synonymous with specifying both @option{--preserve-permissions} and
3082 @option{--same-order}. @xref{Setting Access Permissions}.
3084 @opsummary{preserve-order}
3085 @item --preserve-order
3087 (See @option{--same-order}; @pxref{Reading}.)
3089 @opsummary{preserve-permissions}
3090 @opsummary{same-permissions}
3091 @item --preserve-permissions
3092 @itemx --same-permissions
3095 When @command{tar} is extracting an archive, it normally subtracts the
3096 users' umask from the permissions specified in the archive and uses
3097 that number as the permissions to create the destination file.
3098 Specifying this option instructs @command{tar} that it should use the
3099 permissions directly from the archive. @xref{Setting Access Permissions}.
3101 @opsummary{quote-chars}
3102 @item --quote-chars=@var{string}
3103 Always quote characters from @var{string}, even if the selected
3104 quoting style would not quote them (@pxref{quoting styles}).
3106 @opsummary{quoting-style}
3107 @item --quoting-style=@var{style}
3108 Set quoting style to use when printing member and file names
3109 (@pxref{quoting styles}). Valid @var{style} values are:
3110 @code{literal}, @code{shell}, @code{shell-always}, @code{c},
3111 @code{escape}, @code{locale}, and @code{clocale}. Default quoting
3112 style is @code{escape}, unless overridden while configuring the
3115 @opsummary{read-full-records}
3116 @item --read-full-records
3119 Specifies that @command{tar} should reblock its input, for reading
3120 from pipes on systems with buggy implementations. @xref{Reading}.
3122 @opsummary{record-size}
3123 @item --record-size=@var{size}
3125 Instructs @command{tar} to use @var{size} bytes per record when accessing the
3126 archive. @xref{Blocking Factor}.
3128 @opsummary{recursion}
3131 With this option, @command{tar} recurses into directories (default).
3134 @opsummary{recursive-unlink}
3135 @item --recursive-unlink
3138 directory hierarchies before extracting directories of the same name
3139 from the archive. @xref{Recursive Unlink}.
3141 @opsummary{remove-files}
3142 @item --remove-files
3144 Directs @command{tar} to remove the source file from the file system after
3145 appending it to an archive. @xref{remove files}.
3147 @opsummary{restrict}
3150 Disable use of some potentially harmful @command{tar} options.
3151 Currently this option disables shell invocation from multi-volume menu
3152 (@pxref{Using Multiple Tapes}).
3154 @opsummary{rmt-command}
3155 @item --rmt-command=@var{cmd}
3157 Notifies @command{tar} that it should use @var{cmd} instead of
3158 the default @file{/usr/libexec/rmt} (@pxref{Remote Tape Server}).
3160 @opsummary{rsh-command}
3161 @item --rsh-command=@var{cmd}
3163 Notifies @command{tar} that is should use @var{cmd} to communicate with remote
3164 devices. @xref{Device}.
3166 @opsummary{same-order}
3168 @itemx --preserve-order
3171 This option is an optimization for @command{tar} when running on machines with
3172 small amounts of memory. It informs @command{tar} that the list of file
3173 arguments has already been sorted to match the order of files in the
3174 archive. @xref{Reading}.
3176 @opsummary{same-owner}
3179 When extracting an archive, @command{tar} will attempt to preserve the owner
3180 specified in the @command{tar} archive with this option present.
3181 This is the default behavior for the superuser; this option has an
3182 effect only for ordinary users. @xref{Attributes}.
3184 @opsummary{same-permissions}
3185 @item --same-permissions
3187 (See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
3193 Assume that the archive media supports seeks to arbitrary
3194 locations. Usually @command{tar} determines automatically whether
3195 the archive can be seeked or not. This option is intended for use
3196 in cases when such recognition fails. It takes effect only if the
3197 archive is open for reading (e.g. with @option{--list} or
3198 @option{--extract} options).
3200 @opsummary{show-defaults}
3201 @item --show-defaults
3203 Displays the default options used by @command{tar} and exits
3204 successfully. This option is intended for use in shell scripts.
3205 Here is an example of what you can see using this option:
3208 $ tar --show-defaults
3209 --format=gnu -f- -b20 --quoting-style=escape \
3210 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
3213 @opsummary{show-omitted-dirs}
3214 @item --show-omitted-dirs
3216 Instructs @command{tar} to mention the directories it is skipping when
3217 operating on a @command{tar} archive. @xref{show-omitted-dirs}.
3219 @opsummary{show-transformed-names}
3220 @opsummary{show-stored-names}
3221 @item --show-transformed-names
3222 @itemx --show-stored-names
3224 Display file or member names after applying any transformations
3225 (@pxref{transform}). In particular, when used in conjunction with one of
3226 the archive creation operations it instructs @command{tar} to list the
3227 member names stored in the archive, as opposed to the actual file
3228 names. @xref{listing member and file names}.
3234 Invokes a @acronym{GNU} extension when adding files to an archive that handles
3235 sparse files efficiently. @xref{sparse}.
3237 @opsummary{sparse-version}
3238 @item --sparse-version=@var{version}
3240 Specifies the @dfn{format version} to use when archiving sparse
3241 files. Implies @option{--sparse}. @xref{sparse}. For the description
3242 of the supported sparse formats, @xref{Sparse Formats}.
3244 @opsummary{starting-file}
3245 @item --starting-file=@var{name}
3246 @itemx -K @var{name}
3248 This option affects extraction only; @command{tar} will skip extracting
3249 files in the archive until it finds one that matches @var{name}.
3252 @opsummary{strip-components}
3253 @item --strip-components=@var{number}
3254 Strip given @var{number} of leading components from file names before
3255 extraction. For example, if archive @file{archive.tar} contained
3256 @file{/some/file/name}, then running
3259 tar --extract --file archive.tar --strip-components=2
3263 would extract this file to file @file{name}.
3265 @opsummary{suffix}, summary
3266 @item --suffix=@var{suffix}
3268 Alters the suffix @command{tar} uses when backing up files from the default
3269 @samp{~}. @xref{backup}.
3271 @opsummary{tape-length}
3272 @item --tape-length=@var{num}
3275 Specifies the length of tapes that @command{tar} is writing as being
3276 @w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
3278 @opsummary{test-label}
3281 Reads the volume label. If an argument is specified, test whether it
3282 matches the volume label. @xref{--test-label option}.
3284 @opsummary{to-command}
3285 @item --to-command=@var{command}
3287 During extraction @command{tar} will pipe extracted files to the
3288 standard input of @var{command}. @xref{Writing to an External Program}.
3290 @opsummary{to-stdout}
3294 During extraction, @command{tar} will extract files to stdout rather
3295 than to the file system. @xref{Writing to Standard Output}.
3298 @item --totals[=@var{signo}]
3300 Displays the total number of bytes transferred when processing an
3301 archive. If an argument is given, these data are displayed on
3302 request, when signal @var{signo} is delivered to @command{tar}.
3309 Sets the data modification time of extracted files to the extraction time,
3310 rather than the data modification time stored in the archive.
3311 @xref{Data Modification Times}.
3313 @opsummary{transform}
3315 @item --transform=@var{sed-expr}
3316 @itemx --xform=@var{sed-expr}
3317 Transform file or member names using @command{sed} replacement expression
3318 @var{sed-expr}. For example,
3321 $ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
3325 will add to @file{archive} files from the current working directory,
3326 replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
3327 discussion, @xref{transform}.
3329 To see transformed member names in verbose listings, use
3330 @option{--show-transformed-names} option
3331 (@pxref{show-transformed-names}).
3333 @opsummary{uncompress}
3336 (See @option{--compress}. @pxref{gzip})
3341 (See @option{--gzip}. @pxref{gzip})
3343 @opsummary{unlink-first}
3344 @item --unlink-first
3347 Directs @command{tar} to remove the corresponding file from the file
3348 system before extracting it from the archive. @xref{Unlink First}.
3352 Enable unquoting input file or member names (default). @xref{input
3355 @opsummary{use-compress-program}
3356 @item --use-compress-program=@var{prog}
3357 @itemx -I=@var{prog}
3359 Instructs @command{tar} to access the archive through @var{prog}, which is
3360 presumed to be a compression program of some sort. @xref{gzip}.
3365 Display file modification dates in @acronym{UTC}. This option implies
3372 Specifies that @command{tar} should be more verbose about the
3373 operations it is performing. This option can be specified multiple
3374 times for some operations to increase the amount of information displayed.
3381 Verifies that the archive was correctly written when creating an
3382 archive. @xref{verify}.
3387 Print information about the program's name, version, origin and legal
3388 status, all on standard output, and then exit successfully.
3391 @opsummary{volno-file}
3392 @item --volno-file=@var{file}
3394 Used in conjunction with @option{--multi-volume}. @command{tar} will
3395 keep track of which volume of a multi-volume archive it is working in
3396 @var{file}. @xref{volno-file}.
3399 @item --warning=@var{keyword}
3401 Enable or disable warning messages identified by @var{keyword}. The
3402 messages are suppressed if @var{keyword} is prefixed with @samp{no-}.
3405 @opsummary{wildcards}
3407 Use wildcards when matching member names with patterns.
3408 @xref{controlling pattern-matching}.
3410 @opsummary{wildcards-match-slash}
3411 @item --wildcards-match-slash
3412 Wildcards match @samp{/}.
3413 @xref{controlling pattern-matching}.
3418 Use @command{xz} for compressing or decompressing the archives. @xref{gzip}.
3422 @node Short Option Summary
3423 @subsection Short Options Cross Reference
3425 Here is an alphabetized list of all of the short option forms, matching
3426 them with the equivalent long option.
3428 @multitable @columnfractions 0.20 0.80
3429 @headitem Short Option @tab Reference
3431 @item -A @tab @ref{--concatenate}.
3433 @item -B @tab @ref{--read-full-records}.
3435 @item -C @tab @ref{--directory}.
3437 @item -F @tab @ref{--info-script}.
3439 @item -G @tab @ref{--incremental}.
3441 @item -J @tab @ref{--xz}.
3443 @item -K @tab @ref{--starting-file}.
3445 @item -L @tab @ref{--tape-length}.
3447 @item -M @tab @ref{--multi-volume}.
3449 @item -N @tab @ref{--newer}.
3451 @item -O @tab @ref{--to-stdout}.
3453 @item -P @tab @ref{--absolute-names}.
3455 @item -R @tab @ref{--block-number}.
3457 @item -S @tab @ref{--sparse}.
3459 @item -T @tab @ref{--files-from}.
3461 @item -U @tab @ref{--unlink-first}.
3463 @item -V @tab @ref{--label}.
3465 @item -W @tab @ref{--verify}.
3467 @item -X @tab @ref{--exclude-from}.
3469 @item -Z @tab @ref{--compress}.
3471 @item -b @tab @ref{--blocking-factor}.
3473 @item -c @tab @ref{--create}.
3475 @item -d @tab @ref{--compare}.
3477 @item -f @tab @ref{--file}.
3479 @item -g @tab @ref{--listed-incremental}.
3481 @item -h @tab @ref{--dereference}.
3483 @item -i @tab @ref{--ignore-zeros}.
3485 @item -j @tab @ref{--bzip2}.
3487 @item -k @tab @ref{--keep-old-files}.
3489 @item -l @tab @ref{--check-links}.
3491 @item -m @tab @ref{--touch}.
3493 @item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
3494 @ref{--portability}.
3496 The latter usage is deprecated. It is retained for compatibility with
3497 the earlier versions of @GNUTAR{}. In future releases
3498 @option{-o} will be equivalent to @option{--no-same-owner} only.
3500 @item -p @tab @ref{--preserve-permissions}.
3502 @item -r @tab @ref{--append}.
3504 @item -s @tab @ref{--same-order}.
3506 @item -t @tab @ref{--list}.
3508 @item -u @tab @ref{--update}.
3510 @item -v @tab @ref{--verbose}.
3512 @item -w @tab @ref{--interactive}.
3514 @item -x @tab @ref{--extract}.
3516 @item -z @tab @ref{--gzip}.
3521 @section @GNUTAR{} documentation
3523 @cindex Getting program version number
3525 @cindex Version of the @command{tar} program
3526 Being careful, the first thing is really checking that you are using
3527 @GNUTAR{}, indeed. The @option{--version} option
3528 causes @command{tar} to print information about its name, version,
3529 origin and legal status, all on standard output, and then exit
3530 successfully. For example, @w{@samp{tar --version}} might print:
3533 tar (GNU tar) @value{VERSION}
3534 Copyright (C) 2008 Free Software Foundation, Inc.
3535 This is free software. You may redistribute copies of it under the terms
3536 of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
3537 There is NO WARRANTY, to the extent permitted by law.
3539 Written by John Gilmore and Jay Fenlason.
3543 The first occurrence of @samp{tar} in the result above is the program
3544 name in the package (for example, @command{rmt} is another program),
3545 while the second occurrence of @samp{tar} is the name of the package
3546 itself, containing possibly many programs. The package is currently
3547 named @samp{tar}, after the name of the main program it
3548 contains@footnote{There are plans to merge the @command{cpio} and
3549 @command{tar} packages into a single one which would be called
3550 @code{paxutils}. So, who knows if, one of this days, the
3551 @option{--version} would not output @w{@samp{tar (@acronym{GNU}
3554 @cindex Obtaining help
3555 @cindex Listing all @command{tar} options
3556 @xopindex{help, introduction}
3557 Another thing you might want to do is checking the spelling or meaning
3558 of some particular @command{tar} option, without resorting to this
3559 manual, for once you have carefully read it. @GNUTAR{}
3560 has a short help feature, triggerable through the
3561 @option{--help} option. By using this option, @command{tar} will
3562 print a usage message listing all available options on standard
3563 output, then exit successfully, without doing anything else and
3564 ignoring all other options. Even if this is only a brief summary, it
3565 may be several screens long. So, if you are not using some kind of
3566 scrollable window, you might prefer to use something like:
3569 $ @kbd{tar --help | less}
3573 presuming, here, that you like using @command{less} for a pager. Other
3574 popular pagers are @command{more} and @command{pg}. If you know about some
3575 @var{keyword} which interests you and do not want to read all the
3576 @option{--help} output, another common idiom is doing:
3579 tar --help | grep @var{keyword}
3583 for getting only the pertinent lines. Notice, however, that some
3584 @command{tar} options have long description lines and the above
3585 command will list only the first of them.
3587 The exact look of the option summary displayed by @kbd{tar --help} is
3588 configurable. @xref{Configuring Help Summary}, for a detailed description.
3591 If you only wish to check the spelling of an option, running @kbd{tar
3592 --usage} may be a better choice. This will display a terse list of
3593 @command{tar} option without accompanying explanations.
3595 The short help output is quite succinct, and you might have to get
3596 back to the full documentation for precise points. If you are reading
3597 this paragraph, you already have the @command{tar} manual in some
3598 form. This manual is available in a variety of forms from
3599 @url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{}
3600 distribution, provided you have @TeX{} already installed somewhere,
3601 and a laser printer around. Just configure the distribution, execute
3602 the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the
3603 usual way (contact your local guru to know how). If @GNUTAR{}
3604 has been conveniently installed at your place, this
3605 manual is also available in interactive, hypertextual form as an Info
3606 file. Just call @w{@samp{info tar}} or, if you do not have the
3607 @command{info} program handy, use the Info reader provided within
3608 @acronym{GNU} Emacs, calling @samp{tar} from the main Info menu.
3610 There is currently no @code{man} page for @GNUTAR{}.
3611 If you observe such a @code{man} page on the system you are running,
3612 either it does not belong to @GNUTAR{}, or it has not
3613 been produced by @acronym{GNU}. Some package maintainers convert
3614 @kbd{tar --help} output to a man page, using @command{help2man}. In
3615 any case, please bear in mind that the authoritative source of
3616 information about @GNUTAR{} is this Texinfo documentation.
3619 @section Obtaining @GNUTAR{} default values
3621 @opindex show-defaults
3622 @GNUTAR{} has some predefined defaults that are used when you do not
3623 explicitly specify another values. To obtain a list of such
3624 defaults, use @option{--show-defaults} option. This will output the
3625 values in the form of @command{tar} command line options:
3629 @kbd{tar --show-defaults}
3630 --format=gnu -f- -b20 --quoting-style=escape
3631 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3636 Notice, that this option outputs only one line. The example output above
3637 has been split to fit page boundaries.
3640 The above output shows that this version of @GNUTAR{} defaults to
3641 using @samp{gnu} archive format (@pxref{Formats}), it uses standard
3642 output as the archive, if no @option{--file} option has been given
3643 (@pxref{file tutorial}), the default blocking factor is 20
3644 (@pxref{Blocking Factor}). It also shows the default locations where
3645 @command{tar} will look for @command{rmt} and @command{rsh} binaries.
3648 @section Checking @command{tar} progress
3650 Typically, @command{tar} performs most operations without reporting any
3651 information to the user except error messages. When using @command{tar}
3652 with many options, particularly ones with complicated or
3653 difficult-to-predict behavior, it is possible to make serious mistakes.
3654 @command{tar} provides several options that make observing @command{tar}
3655 easier. These options cause @command{tar} to print information as it
3656 progresses in its job, and you might want to use them just for being
3657 more careful about what is going on, or merely for entertaining
3658 yourself. If you have encountered a problem when operating on an
3659 archive, however, you may need more information than just an error
3660 message in order to solve the problem. The following options can be
3661 helpful diagnostic tools.
3663 @cindex Verbose operation
3665 Normally, the @option{--list} (@option{-t}) command to list an archive
3666 prints just the file names (one per line) and the other commands are
3667 silent. When used with most operations, the @option{--verbose}
3668 (@option{-v}) option causes @command{tar} to print the name of each
3669 file or archive member as it is processed. This and the other options
3670 which make @command{tar} print status information can be useful in
3671 monitoring @command{tar}.
3673 With @option{--create} or @option{--extract}, @option{--verbose} used
3674 once just prints the names of the files or members as they are processed.
3675 Using it twice causes @command{tar} to print a longer listing
3676 (@xref{verbose member listing}, for the description) for each member.
3677 Since @option{--list} already prints the names of the members,
3678 @option{--verbose} used once with @option{--list} causes @command{tar}
3679 to print an @samp{ls -l} type listing of the files in the archive.
3680 The following examples both extract members with long list output:
3683 $ @kbd{tar --extract --file=archive.tar --verbose --verbose}
3684 $ @kbd{tar xvvf archive.tar}
3687 Verbose output appears on the standard output except when an archive is
3688 being written to the standard output, as with @samp{tar --create
3689 --file=- --verbose} (@samp{tar cfv -}, or even @samp{tar cv}---if the
3690 installer let standard output be the default archive). In that case
3691 @command{tar} writes verbose output to the standard error stream.
3693 If @option{--index-file=@var{file}} is specified, @command{tar} sends
3694 verbose output to @var{file} rather than to standard output or standard
3698 @cindex Obtaining total status information
3700 The @option{--totals} option causes @command{tar} to print on the
3701 standard error the total amount of bytes transferred when processing
3702 an archive. When creating or appending to an archive, this option
3703 prints the number of bytes written to the archive and the average
3704 speed at which they have been written, e.g.:
3708 $ @kbd{tar -c -f archive.tar --totals /home}
3709 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3713 When reading an archive, this option displays the number of bytes
3718 $ @kbd{tar -x -f archive.tar --totals}
3719 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3723 Finally, when deleting from an archive, the @option{--totals} option
3724 displays both numbers plus number of bytes removed from the archive:
3728 $ @kbd{tar --delete -f foo.tar --totals --wildcards '*~'}
3729 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3730 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3731 Total bytes deleted: 1474048
3735 You can also obtain this information on request. When
3736 @option{--totals} is used with an argument, this argument is
3737 interpreted as a symbolic name of a signal, upon delivery of which the
3738 statistics is to be printed:
3741 @item --totals=@var{signo}
3742 Print statistics upon delivery of signal @var{signo}. Valid arguments
3743 are: @code{SIGHUP}, @code{SIGQUIT}, @code{SIGINT}, @code{SIGUSR1} and
3744 @code{SIGUSR2}. Shortened names without @samp{SIG} prefix are also
3748 Both forms of @option{--totals} option can be used simultaneously.
3749 Thus, @kbd{tar -x --totals --totals=USR1} instructs @command{tar} to
3750 extract all members from its default archive and print statistics
3751 after finishing the extraction, as well as when receiving signal
3754 @anchor{Progress information}
3755 @cindex Progress information
3756 The @option{--checkpoint} option prints an occasional message
3757 as @command{tar} reads or writes the archive. It is designed for
3758 those who don't need the more detailed (and voluminous) output of
3759 @option{--block-number} (@option{-R}), but do want visual confirmation
3760 that @command{tar} is actually making forward progress. By default it
3761 prints a message each 10 records read or written. This can be changed
3762 by giving it a numeric argument after an equal sign:
3765 $ @kbd{tar -c --checkpoint=1000} /var
3766 tar: Write checkpoint 1000
3767 tar: Write checkpoint 2000
3768 tar: Write checkpoint 3000
3771 This example shows the default checkpoint message used by
3772 @command{tar}. If you place a dot immediately after the equal
3773 sign, it will print a @samp{.} at each checkpoint@footnote{This is
3774 actually a shortcut for @option{--checkpoint=@var{n}
3775 --checkpoint-action=dot}. @xref{checkpoints, dot}.}. For example:
3778 $ @kbd{tar -c --checkpoint=.1000} /var
3782 The @option{--checkpoint} option provides a flexible mechanism for
3783 executing arbitrary actions upon hitting checkpoints, see the next
3784 section (@pxref{checkpoints}), for more information on it.
3786 @opindex show-omitted-dirs
3787 @anchor{show-omitted-dirs}
3788 The @option{--show-omitted-dirs} option, when reading an archive---with
3789 @option{--list} or @option{--extract}, for example---causes a message
3790 to be printed for each directory in the archive which is skipped.
3791 This happens regardless of the reason for skipping: the directory might
3792 not have been named on the command line (implicitly or explicitly),
3793 it might be excluded by the use of the
3794 @option{--exclude=@var{pattern}} option, or some other reason.
3796 @opindex block-number
3797 @cindex Block number where error occurred
3798 @anchor{block-number}
3799 If @option{--block-number} (@option{-R}) is used, @command{tar} prints, along with
3800 every message it would normally produce, the block number within the
3801 archive where the message was triggered. Also, supplementary messages
3802 are triggered when reading blocks full of NULs, or when hitting end of
3803 file on the archive. As of now, if the archive is properly terminated
3804 with a NUL block, the reading of the file may stop before end of file
3805 is met, so the position of end of file will not usually show when
3806 @option{--block-number} (@option{-R}) is used. Note that @GNUTAR{}
3807 drains the archive before exiting when reading the
3808 archive from a pipe.
3810 @cindex Error message, block number of
3811 This option is especially useful when reading damaged archives, since
3812 it helps pinpoint the damaged sections. It can also be used with
3813 @option{--list} (@option{-t}) when listing a file-system backup tape, allowing you to
3814 choose among several backup tapes when retrieving a file later, in
3815 favor of the tape where the file appears earliest (closest to the
3816 front of the tape). @xref{backup}.
3819 @section Checkpoints
3820 @cindex checkpoints, defined
3822 @opindex checkpoint-action
3824 A @dfn{checkpoint} is a moment of time before writing @var{n}th record to
3825 the archive (a @dfn{write checkpoint}), or before reading @var{n}th record
3826 from the archive (a @dfn{read checkpoint}). Checkpoints allow to
3827 periodically execute arbitrary actions.
3829 The checkpoint facility is enabled using the following option:
3832 @xopindex{checkpoint, defined}
3833 @item --checkpoint[=@var{n}]
3834 Schedule checkpoints before writing or reading each @var{n}th record.
3835 The default value for @var{n} is 10.
3838 A list of arbitrary @dfn{actions} can be executed at each checkpoint.
3839 These actions include: pausing, displaying textual messages, and
3840 executing arbitrary external programs. Actions are defined using
3841 the @option{--checkpoint-action} option.
3844 @xopindex{checkpoint-action, defined}
3845 @item --checkpoint-action=@var{action}
3846 Execute an @var{action} at each checkpoint.
3849 @cindex @code{echo}, checkpoint action
3850 The simplest value of @var{action} is @samp{echo}. It instructs
3851 @command{tar} to display the default message on the standard error
3852 stream upon arriving at each checkpoint. The default message is (in
3853 @acronym{POSIX} locale) @samp{Write checkpoint @var{n}}, for write
3854 checkpoints, and @samp{Read checkpoint @var{n}}, for read checkpoints.
3855 Here, @var{n} represents ordinal number of the checkpoint.
3857 In another locales, translated versions of this message are used.
3859 This is the default action, so running:
3862 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=echo} /var
3869 $ @kbd{tar -c --checkpoint=1000} /var
3872 The @samp{echo} action also allows to supply a customized message.
3873 You do so by placing an equals sign and the message right after it,
3877 --checkpoint-action="echo=Hit %s checkpoint #%u"
3880 The @samp{%s} and @samp{%u} in the above example are
3881 @dfn{meta-characters}. The @samp{%s} meta-character is replaced with
3882 the @dfn{type} of the checkpoint: @samp{write} or
3883 @samp{read} (or a corresponding translated version in locales other
3884 than @acronym{POSIX}). The @samp{%u} meta-character is replaced with
3885 the ordinal number of the checkpoint. Thus, the above example could
3886 produce the following output when used with the @option{--create}
3890 tar: Hit write checkpoint #10
3891 tar: Hit write checkpoint #20
3892 tar: Hit write checkpoint #30
3895 Aside from meta-character expansion, the message string is subject to
3896 @dfn{unquoting}, during which the backslash @dfn{escape sequences} are
3897 replaced with their corresponding @acronym{ASCII} characters
3898 (@pxref{escape sequences}). E.g. the following action will produce an
3899 audible bell and the message described above at each checkpoint:
3902 --checkpoint-action='echo=\aHit %s checkpoint #%u'
3905 @cindex @code{bell}, checkpoint action
3906 There is also a special action which produces an audible signal:
3907 @samp{bell}. It is not equivalent to @samp{echo='\a'}, because
3908 @samp{bell} sends the bell directly to the console (@file{/dev/tty}),
3909 whereas @samp{echo='\a'} sends it to the standard error.
3911 @cindex @code{ttyout}, checkpoint action
3912 The @samp{ttyout=@var{string}} action outputs @var{string} to
3913 @file{/dev/tty}, so it can be used even if the standard output is
3914 redirected elsewhere. The @var{string} is subject to the same
3915 modifications as with @samp{echo} action. In contrast to the latter,
3916 @samp{ttyout} does not prepend @command{tar} executable name to the
3917 string, nor does it output a newline after it. For example, the
3918 following action will print the checkpoint message at the same screen
3919 line, overwriting any previous message:
3922 --checkpoint-action="ttyout=\rHit %s checkpoint #%u"
3925 @cindex @code{dot}, checkpoint action
3926 Another available checkpoint action is @samp{dot} (or @samp{.}). It
3927 instructs @command{tar} to print a single dot on the standard listing
3931 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=dot} /var
3935 For compatibility with previous @GNUTAR{} versions, this action can
3936 be abbreviated by placing a dot in front of the checkpoint frequency,
3937 as shown in the previous section.
3939 @cindex @code{sleep}, checkpoint action
3940 Yet another action, @samp{sleep}, pauses @command{tar} for a specified
3941 amount of seconds. The following example will stop for 30 seconds at each
3945 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=sleep=30}
3948 @cindex @code{exec}, checkpoint action
3949 Finally, the @code{exec} action executes a given external program.
3953 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint}
3956 This program is executed using @command{/bin/sh -c}, with no
3957 additional arguments. Its exit code is ignored. It gets a copy of
3958 @command{tar}'s environment plus the following variables:
3961 @vrindex TAR_VERSION, checkpoint script environment
3963 @GNUTAR{} version number.
3965 @vrindex TAR_ARCHIVE, checkpoint script environment
3967 The name of the archive @command{tar} is processing.
3969 @vrindex TAR_BLOCKING_FACTOR, checkpoint script environment
3970 @item TAR_BLOCKING_FACTOR
3971 Current blocking factor (@pxref{Blocking}).
3973 @vrindex TAR_CHECKPOINT, checkpoint script environment
3974 @item TAR_CHECKPOINT
3975 Number of the checkpoint.
3977 @vrindex TAR_SUBCOMMAND, checkpoint script environment
3978 @item TAR_SUBCOMMAND
3979 A short option describing the operation @command{tar} is executing.
3980 @xref{Operations}, for a complete list of subcommand options.
3982 @vrindex TAR_FORMAT, checkpoint script environment
3984 Format of the archive being processed. @xref{Formats}, for a complete
3985 list of archive format names.
3988 Any number of actions can be defined, by supplying several
3989 @option{--checkpoint-action} options in the command line. For
3990 example, the command below displays two messages, pauses
3991 execution for 30 seconds and executes the @file{/sbin/cpoint} script:
3995 $ @kbd{tar -c -f arc.tar \
3996 --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
3997 --checkpoint-action='echo=Sleeping for 30 seconds' \
3998 --checkpoint-action='sleep=30' \
3999 --checkpoint-action='exec=/sbin/cpoint'}
4003 This example also illustrates the fact that
4004 @option{--checkpoint-action} can be used without
4005 @option{--checkpoint}. In this case, the default checkpoint frequency
4006 (at each 10th record) is assumed.
4009 @section Controlling Warning Messages
4011 Sometimes, while performing the requested task, @GNUTAR{} notices
4012 some conditions that are not exactly erros, but which the user
4013 should be aware of. When this happens, @command{tar} issues a
4014 @dfn{warning message} describing the condition. Warning messages
4015 are output to the standard error and they do not affect the exit
4016 code of @command{tar} command.
4018 @xopindex{warning, explained}
4019 @GNUTAR{} allows the user to suppress some or all of its warning
4023 @item --warning=@var{keyword}
4024 Control display of the warning messages identified by @var{keyword}.
4025 If @var{keyword} starts with the prefix @samp{no-}, such messages are
4026 suppressed. Otherwise, they are enabled.
4028 Multiple @option{--warning} messages accumulate.
4030 The tables below list allowed values for @var{keyword} along with the
4031 warning messages they control.
4034 @subheading Keywords controlling @command{tar} operation
4038 Enable all warning messages. This is the default.
4041 Disable all warning messages.
4042 @kwindex filename-with-nuls
4043 @cindex @samp{file name read contains nul character}, warning message
4044 @item filename-with-nuls
4045 @samp{%s: file name read contains nul character}
4046 @kwindex alone-zero-block
4047 @cindex @samp{A lone zero block at}, warning message
4048 @item alone-zero-block
4049 @samp{A lone zero block at %s}
4052 @subheading Keywords applicable for @command{tar --create}
4055 @cindex @samp{contains a cache directory tag}, warning message
4057 @samp{%s: contains a cache directory tag %s; %s}
4058 @kwindex file-shrank
4059 @cindex @samp{File shrank by %s bytes}, warning message
4061 @samp{%s: File shrank by %s bytes; padding with zeros}
4063 @cindex @samp{file is on a different filesystem}, warning message
4065 @samp{%s: file is on a different filesystem; not dumped}
4066 @kwindex file-ignored
4067 @cindex @samp{Unknown file type; file ignored}, warning message
4068 @cindex @samp{socket ignored}, warning message
4069 @cindex @samp{door ignored}, warning message
4071 @samp{%s: Unknown file type; file ignored}
4072 @samp{%s: socket ignored}
4073 @*@samp{%s: door ignored}
4074 @kwindex file-unchanged
4075 @cindex @samp{file is unchanged; not dumped}, warning message
4076 @item file-unchanged
4077 @samp{%s: file is unchanged; not dumped}
4078 @kwindex ignore-archive
4079 @cindex @samp{file is the archive; not dumped}, warning message
4080 @kwindex ignore-archive
4081 @cindex @samp{file is the archive; not dumped}, warning message
4082 @item ignore-archive
4083 @samp{%s: file is the archive; not dumped}
4084 @kwindex file-removed
4085 @cindex @samp{File removed before we read it}, warning message
4087 @samp{%s: File removed before we read it}
4088 @kwindex file-changed
4089 @cindex @samp{file changed as we read it}, warning message
4091 @samp{%s: file changed as we read it}
4094 @subheading Keywords applicable for @command{tar --extract}
4097 @cindex @samp{implausibly old time stamp %s}, warning message
4098 @cindex @samp{time stamp %s is %s s in the future}, warning message
4100 @samp{%s: implausibly old time stamp %s}
4101 @*@samp{%s: time stamp %s is %s s in the future}
4102 @kwindex contiguous-cast
4103 @cindex @samp{Extracting contiguous files as regular files}, warning message
4104 @item contiguous-cast
4105 @samp{Extracting contiguous files as regular files}
4106 @kwindex symlink-cast
4107 @cindex @samp{Attempting extraction of symbolic links as hard links}, warning message
4109 @samp{Attempting extraction of symbolic links as hard links}
4110 @kwindex unknown-cast
4111 @cindex @samp{Unknown file type `%c', extracted as normal file}, warning message
4113 @samp{%s: Unknown file type `%c', extracted as normal file}
4114 @kwindex ignore-newer
4115 @cindex @samp{Current %s is newer or same age}, warning message
4117 @samp{Current %s is newer or same age}
4118 @kwindex unknown-keyword
4119 @cindex @samp{Ignoring unknown extended header keyword `%s'}, warning message
4120 @item unknown-keyword
4121 @samp{Ignoring unknown extended header keyword `%s'}
4124 @subheading Keywords controlling incremental extraction:
4126 @kwindex rename-directory
4127 @cindex @samp{%s: Directory has been renamed from %s}, warning message
4128 @cindex @samp{%s: Directory has been renamed}, warning message
4129 @item rename-directory
4130 @samp{%s: Directory has been renamed from %s}
4131 @*@samp{%s: Directory has been renamed}
4132 @kwindex new-directory
4133 @cindex @samp{%s: Directory is new}, warning message
4135 @samp{%s: Directory is new}
4137 @cindex @samp{%s: directory is on a different device: not purging}, warning message
4139 @samp{%s: directory is on a different device: not purging}
4140 @kwindex bad-dumpdir
4141 @cindex @samp{Malformed dumpdir: 'X' never used}, warning message
4143 @samp{Malformed dumpdir: 'X' never used}
4147 @section Asking for Confirmation During Operations
4148 @cindex Interactive operation
4150 Typically, @command{tar} carries out a command without stopping for
4151 further instructions. In some situations however, you may want to
4152 exclude some files and archive members from the operation (for instance
4153 if disk or storage space is tight). You can do this by excluding
4154 certain files automatically (@pxref{Choosing}), or by performing
4155 an operation interactively, using the @option{--interactive} (@option{-w}) option.
4156 @command{tar} also accepts @option{--confirmation} for this option.
4158 @opindex interactive
4159 When the @option{--interactive} (@option{-w}) option is specified, before
4160 reading, writing, or deleting files, @command{tar} first prints a message
4161 for each such file, telling what operation it intends to take, then asks
4162 for confirmation on the terminal. The actions which require
4163 confirmation include adding a file to the archive, extracting a file
4164 from the archive, deleting a file from the archive, and deleting a file
4165 from disk. To confirm the action, you must type a line of input
4166 beginning with @samp{y}. If your input line begins with anything other
4167 than @samp{y}, @command{tar} skips that file.
4169 If @command{tar} is reading the archive from the standard input,
4170 @command{tar} opens the file @file{/dev/tty} to support the interactive
4173 Verbose output is normally sent to standard output, separate from
4174 other error messages. However, if the archive is produced directly
4175 on standard output, then verbose output is mixed with errors on
4176 @code{stderr}. Producing the archive on standard output may be used
4177 as a way to avoid using disk space, when the archive is soon to be
4178 consumed by another process reading it, say. Some people felt the need
4179 of producing an archive on stdout, still willing to segregate between
4180 verbose output and error output. A possible approach would be using a
4181 named pipe to receive the archive, and having the consumer process to
4182 read from that named pipe. This has the advantage of letting standard
4183 output free to receive verbose output, all separate from errors.
4186 @chapter @GNUTAR{} Operations
4199 @section Basic @GNUTAR{} Operations
4201 The basic @command{tar} operations, @option{--create} (@option{-c}),
4202 @option{--list} (@option{-t}) and @option{--extract} (@option{--get},
4203 @option{-x}), are currently presented and described in the tutorial
4204 chapter of this manual. This section provides some complementary notes
4205 for these operations.
4208 @xopindex{create, complementary notes}
4212 Creating an empty archive would have some kind of elegance. One can
4213 initialize an empty archive and later use @option{--append}
4214 (@option{-r}) for adding all members. Some applications would not
4215 welcome making an exception in the way of adding the first archive
4216 member. On the other hand, many people reported that it is
4217 dangerously too easy for @command{tar} to destroy a magnetic tape with
4218 an empty archive@footnote{This is well described in @cite{Unix-haters
4219 Handbook}, by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG
4220 Books, ISBN 1-56884-203-1.}. The two most common errors are:
4224 Mistakingly using @code{create} instead of @code{extract}, when the
4225 intent was to extract the full contents of an archive. This error
4226 is likely: keys @kbd{c} and @kbd{x} are right next to each other on
4227 the QWERTY keyboard. Instead of being unpacked, the archive then
4228 gets wholly destroyed. When users speak about @dfn{exploding} an
4229 archive, they usually mean something else :-).
4232 Forgetting the argument to @code{file}, when the intent was to create
4233 an archive with a single file in it. This error is likely because a
4234 tired user can easily add the @kbd{f} key to the cluster of option
4235 letters, by the mere force of habit, without realizing the full
4236 consequence of doing so. The usual consequence is that the single
4237 file, which was meant to be saved, is rather destroyed.
4240 So, recognizing the likelihood and the catastrophic nature of these
4241 errors, @GNUTAR{} now takes some distance from elegance, and
4242 cowardly refuses to create an archive when @option{--create} option is
4243 given, there are no arguments besides options, and
4244 @option{--files-from} (@option{-T}) option is @emph{not} used. To get
4245 around the cautiousness of @GNUTAR{} and nevertheless create an
4246 archive with nothing in it, one may still use, as the value for the
4247 @option{--files-from} option, a file with no names in it, as shown in
4248 the following commands:
4251 @kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
4252 @kbd{tar cfT empty-archive.tar /dev/null}
4255 @xopindex{extract, complementary notes}
4260 A socket is stored, within a @GNUTAR{} archive, as a pipe.
4262 @item @option{--list} (@option{-t})
4264 @GNUTAR{} now shows dates as @samp{1996-08-30},
4265 while it used to show them as @samp{Aug 30 1996}. Preferably,
4266 people should get used to ISO 8601 dates. Local American dates should
4267 be made available again with full date localization support, once
4268 ready. In the meantime, programs not being localizable for dates
4269 should prefer international dates, that's really the way to go.
4271 Look up @url{http://www.cl.cam.ac.uk/@/~mgk25/@/iso-time.html} if you
4272 are curious, it contains a detailed explanation of the ISO 8601 standard.
4277 @section Advanced @GNUTAR{} Operations
4279 Now that you have learned the basics of using @GNUTAR{}, you may want
4280 to learn about further ways in which @command{tar} can help you.
4282 This chapter presents five, more advanced operations which you probably
4283 won't use on a daily basis, but which serve more specialized functions.
4284 We also explain the different styles of options and why you might want
4285 to use one or another, or a combination of them in your @command{tar}
4286 commands. Additionally, this chapter includes options which allow you to
4287 define the output from @command{tar} more carefully, and provide help and
4288 error correction in special circumstances.
4290 @FIXME{check this after the chapter is actually revised to make sure
4291 it still introduces the info in the chapter correctly : ).}
4303 @subsection The Five Advanced @command{tar} Operations
4305 @cindex basic operations
4306 In the last chapter, you learned about the first three operations to
4307 @command{tar}. This chapter presents the remaining five operations to
4308 @command{tar}: @option{--append}, @option{--update}, @option{--concatenate},
4309 @option{--delete}, and @option{--compare}.
4311 You are not likely to use these operations as frequently as those
4312 covered in the last chapter; however, since they perform specialized
4313 functions, they are quite useful when you do need to use them. We
4314 will give examples using the same directory and files that you created
4315 in the last chapter. As you may recall, the directory is called
4316 @file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk},
4317 @samp{rock}, and the two archive files you created are
4318 @samp{collection.tar} and @samp{music.tar}.
4320 We will also use the archive files @samp{afiles.tar} and
4321 @samp{bfiles.tar}. The archive @samp{afiles.tar} contains the members @samp{apple},
4322 @samp{angst}, and @samp{aspic}; @samp{bfiles.tar} contains the members
4323 @samp{./birds}, @samp{baboon}, and @samp{./box}.
4325 Unless we state otherwise, all practicing you do and examples you follow
4326 in this chapter will take place in the @file{practice} directory that
4327 you created in the previous chapter; see @ref{prepare for examples}.
4328 (Below in this section, we will remind you of the state of the examples
4329 where the last chapter left them.)
4331 The five operations that we will cover in this chapter are:
4336 Add new entries to an archive that already exists.
4339 Add more recent copies of archive members to the end of an archive, if
4344 Add one or more pre-existing archives to the end of another archive.
4346 Delete items from an archive (does not work on tapes).
4350 Compare archive members to their counterparts in the file system.
4354 @subsection How to Add Files to Existing Archives: @option{--append}
4356 @cindex appending files to existing archive
4358 If you want to add files to an existing archive, you don't need to
4359 create a new archive; you can use @option{--append} (@option{-r}).
4360 The archive must already exist in order to use @option{--append}. (A
4361 related operation is the @option{--update} operation; you can use this
4362 to add newer versions of archive members to an existing archive. To learn how to
4363 do this with @option{--update}, @pxref{update}.)
4365 If you use @option{--append} to add a file that has the same name as an
4366 archive member to an archive containing that archive member, then the
4367 old member is not deleted. What does happen, however, is somewhat
4368 complex. @command{tar} @emph{allows} you to have infinite number of files
4369 with the same name. Some operations treat these same-named members no
4370 differently than any other set of archive members: for example, if you
4371 view an archive with @option{--list} (@option{-t}), you will see all
4372 of those members listed, with their data modification times, owners, etc.
4374 Other operations don't deal with these members as perfectly as you might
4375 prefer; if you were to use @option{--extract} to extract the archive,
4376 only the most recently added copy of a member with the same name as four
4377 other members would end up in the working directory. This is because
4378 @option{--extract} extracts an archive in the order the members appeared
4379 in the archive; the most recently archived members will be extracted
4380 last. Additionally, an extracted member will @emph{replace} a file of
4381 the same name which existed in the directory already, and @command{tar}
4382 will not prompt you about this@footnote{Unless you give it
4383 @option{--keep-old-files} option, or the disk copy is newer than the
4384 the one in the archive and you invoke @command{tar} with
4385 @option{--keep-newer-files} option}. Thus, only the most recently archived
4386 member will end up being extracted, as it will replace the one
4387 extracted before it, and so on.
4389 @cindex extracting @var{n}th copy of the file
4390 @xopindex{occurrence, described}
4391 There exists a special option that allows you to get around this
4392 behavior and extract (or list) only a particular copy of the file.
4393 This is @option{--occurrence} option. If you run @command{tar} with
4394 this option, it will extract only the first copy of the file. You
4395 may also give this option an argument specifying the number of
4396 copy to be extracted. Thus, for example if the archive
4397 @file{archive.tar} contained three copies of file @file{myfile}, then
4401 tar --extract --file archive.tar --occurrence=2 myfile
4405 would extract only the second copy. @xref{Option
4406 Summary,---occurrence}, for the description of @option{--occurrence}
4409 @FIXME{ hag -- you might want to incorporate some of the above into the
4410 MMwtSN node; not sure. i didn't know how to make it simpler...
4412 There are a few ways to get around this. (maybe xref Multiple Members
4413 with the Same Name.}
4415 @cindex Members, replacing with other members
4416 @cindex Replacing members with other members
4417 @xopindex{delete, using before --append}
4418 If you want to replace an archive member, use @option{--delete} to
4419 delete the member you want to remove from the archive, and then use
4420 @option{--append} to add the member you want to be in the archive. Note
4421 that you can not change the order of the archive; the most recently
4422 added member will still appear last. In this sense, you cannot truly
4423 ``replace'' one member with another. (Replacing one member with another
4424 will not work on certain types of media, such as tapes; see @ref{delete}
4425 and @ref{Media}, for more information.)
4428 * appending files:: Appending Files to an Archive
4432 @node appending files
4433 @subsubsection Appending Files to an Archive
4434 @cindex Adding files to an Archive
4435 @cindex Appending files to an Archive
4436 @cindex Archives, Appending files to
4439 The simplest way to add a file to an already existing archive is the
4440 @option{--append} (@option{-r}) operation, which writes specified
4441 files into the archive whether or not they are already among the
4444 When you use @option{--append}, you @emph{must} specify file name
4445 arguments, as there is no default. If you specify a file that already
4446 exists in the archive, another copy of the file will be added to the
4447 end of the archive. As with other operations, the member names of the
4448 newly added files will be exactly the same as their names given on the
4449 command line. The @option{--verbose} (@option{-v}) option will print
4450 out the names of the files as they are written into the archive.
4452 @option{--append} cannot be performed on some tape drives, unfortunately,
4453 due to deficiencies in the formats those tape drives use. The archive
4454 must be a valid @command{tar} archive, or else the results of using this
4455 operation will be unpredictable. @xref{Media}.
4457 To demonstrate using @option{--append} to add a file to an archive,
4458 create a file called @file{rock} in the @file{practice} directory.
4459 Make sure you are in the @file{practice} directory. Then, run the
4460 following @command{tar} command to add @file{rock} to
4461 @file{collection.tar}:
4464 $ @kbd{tar --append --file=collection.tar rock}
4468 If you now use the @option{--list} (@option{-t}) operation, you will see that
4469 @file{rock} has been added to the archive:
4472 $ @kbd{tar --list --file=collection.tar}
4473 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4474 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4475 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4476 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4480 @subsubsection Multiple Members with the Same Name
4481 @cindex members, multiple
4482 @cindex multiple members
4484 You can use @option{--append} (@option{-r}) to add copies of files
4485 which have been updated since the archive was created. (However, we
4486 do not recommend doing this since there is another @command{tar}
4487 option called @option{--update}; @xref{update}, for more information.
4488 We describe this use of @option{--append} here for the sake of
4489 completeness.) When you extract the archive, the older version will
4490 be effectively lost. This works because files are extracted from an
4491 archive in the order in which they were archived. Thus, when the
4492 archive is extracted, a file archived later in time will replace a
4493 file of the same name which was archived earlier, even though the
4494 older version of the file will remain in the archive unless you delete
4495 all versions of the file.
4497 Supposing you change the file @file{blues} and then append the changed
4498 version to @file{collection.tar}. As you saw above, the original
4499 @file{blues} is in the archive @file{collection.tar}. If you change the
4500 file and append the new version of the file to the archive, there will
4501 be two copies in the archive. When you extract the archive, the older
4502 version of the file will be extracted first, and then replaced by the
4503 newer version when it is extracted.
4505 You can append the new, changed copy of the file @file{blues} to the
4506 archive in this way:
4509 $ @kbd{tar --append --verbose --file=collection.tar blues}
4514 Because you specified the @option{--verbose} option, @command{tar} has
4515 printed the name of the file being appended as it was acted on. Now
4516 list the contents of the archive:
4519 $ @kbd{tar --list --verbose --file=collection.tar}
4520 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4521 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4522 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4523 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4524 -rw-r--r-- me user 58 1996-10-24 18:30 blues
4528 The newest version of @file{blues} is now at the end of the archive
4529 (note the different creation dates and file sizes). If you extract
4530 the archive, the older version of the file @file{blues} will be
4531 replaced by the newer version. You can confirm this by extracting
4532 the archive and running @samp{ls} on the directory.
4534 If you wish to extract the first occurrence of the file @file{blues}
4535 from the archive, use @option{--occurrence} option, as shown in
4536 the following example:
4539 $ @kbd{tar --extract -vv --occurrence --file=collection.tar blues}
4540 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4543 @xref{Writing}, for more information on @option{--extract} and
4544 @xref{Option Summary, --occurrence}, for the description of
4545 @option{--occurrence} option.
4548 @subsection Updating an Archive
4549 @cindex Updating an archive
4552 In the previous section, you learned how to use @option{--append} to
4553 add a file to an existing archive. A related operation is
4554 @option{--update} (@option{-u}). The @option{--update} operation
4555 updates a @command{tar} archive by comparing the date of the specified
4556 archive members against the date of the file with the same name. If
4557 the file has been modified more recently than the archive member, then
4558 the newer version of the file is added to the archive (as with
4561 Unfortunately, you cannot use @option{--update} with magnetic tape drives.
4562 The operation will fail.
4564 @FIXME{other examples of media on which --update will fail? need to ask
4565 charles and/or mib/thomas/dave shevett..}
4567 Both @option{--update} and @option{--append} work by adding to the end
4568 of the archive. When you extract a file from the archive, only the
4569 version stored last will wind up in the file system, unless you use
4570 the @option{--backup} option. @xref{multiple}, for a detailed discussion.
4577 @subsubsection How to Update an Archive Using @option{--update}
4580 You must use file name arguments with the @option{--update}
4581 (@option{-u}) operation. If you don't specify any files,
4582 @command{tar} won't act on any files and won't tell you that it didn't
4583 do anything (which may end up confusing you).
4585 @c note: the above parenthetical added because in fact, this
4586 @c behavior just confused the author. :-)
4588 To see the @option{--update} option at work, create a new file,
4589 @file{classical}, in your practice directory, and some extra text to the
4590 file @file{blues}, using any text editor. Then invoke @command{tar} with
4591 the @samp{update} operation and the @option{--verbose} (@option{-v})
4592 option specified, using the names of all the files in the practice
4593 directory as file name arguments:
4596 $ @kbd{tar --update -v -f collection.tar blues folk rock classical}
4603 Because we have specified verbose mode, @command{tar} prints out the names
4604 of the files it is working on, which in this case are the names of the
4605 files that needed to be updated. If you run @samp{tar --list} and look
4606 at the archive, you will see @file{blues} and @file{classical} at its
4607 end. There will be a total of two versions of the member @samp{blues};
4608 the one at the end will be newer and larger, since you added text before
4611 (The reason @command{tar} does not overwrite the older file when updating
4612 it is because writing to the middle of a section of tape is a difficult
4613 process. Tapes are not designed to go backward. @xref{Media}, for more
4614 information about tapes.
4616 @option{--update} (@option{-u}) is not suitable for performing backups for two
4617 reasons: it does not change directory content entries, and it
4618 lengthens the archive every time it is used. The @GNUTAR{}
4619 options intended specifically for backups are more
4620 efficient. If you need to run backups, please consult @ref{Backups}.
4623 @subsection Combining Archives with @option{--concatenate}
4625 @cindex Adding archives to an archive
4626 @cindex Concatenating Archives
4627 @opindex concatenate
4629 @c @cindex @option{-A} described
4630 Sometimes it may be convenient to add a second archive onto the end of
4631 an archive rather than adding individual files to the archive. To add
4632 one or more archives to the end of another archive, you should use the
4633 @option{--concatenate} (@option{--catenate}, @option{-A}) operation.
4635 To use @option{--concatenate}, give the first archive with
4636 @option{--file} option and name the rest of archives to be
4637 concatenated on the command line. The members, and their member
4638 names, will be copied verbatim from those archives to the first one.
4639 @footnote{This can cause multiple members to have the same name, for
4640 information on how this affects reading the archive, @ref{multiple}.}
4641 The new, concatenated archive will be called by the same name as the
4642 one given with the @option{--file} option. As usual, if you omit
4643 @option{--file}, @command{tar} will use the value of the environment
4644 variable @env{TAPE}, or, if this has not been set, the default archive name.
4646 @FIXME{There is no way to specify a new name...}
4648 To demonstrate how @option{--concatenate} works, create two small archives
4649 called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
4650 files from @file{practice}:
4653 $ @kbd{tar -cvf bluesrock.tar blues rock}
4656 $ @kbd{tar -cvf folkjazz.tar folk jazz}
4662 If you like, You can run @samp{tar --list} to make sure the archives
4663 contain what they are supposed to:
4666 $ @kbd{tar -tvf bluesrock.tar}
4667 -rw-r--r-- melissa user 105 1997-01-21 19:42 blues
4668 -rw-r--r-- melissa user 33 1997-01-20 15:34 rock
4669 $ @kbd{tar -tvf jazzfolk.tar}
4670 -rw-r--r-- melissa user 20 1996-09-23 16:44 folk
4671 -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
4674 We can concatenate these two archives with @command{tar}:
4678 $ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
4681 If you now list the contents of the @file{bluesrock.tar}, you will see
4682 that now it also contains the archive members of @file{jazzfolk.tar}:
4685 $ @kbd{tar --list --file=bluesrock.tar}
4692 When you use @option{--concatenate}, the source and target archives must
4693 already exist and must have been created using compatible format
4694 parameters. Notice, that @command{tar} does not check whether the
4695 archives it concatenates have compatible formats, it does not
4696 even check if the files are really tar archives.
4698 Like @option{--append} (@option{-r}), this operation cannot be performed on some
4699 tape drives, due to deficiencies in the formats those tape drives use.
4701 @cindex @code{concatenate} vs @command{cat}
4702 @cindex @command{cat} vs @code{concatenate}
4703 It may seem more intuitive to you to want or try to use @command{cat} to
4704 concatenate two archives instead of using the @option{--concatenate}
4705 operation; after all, @command{cat} is the utility for combining files.
4707 However, @command{tar} archives incorporate an end-of-file marker which
4708 must be removed if the concatenated archives are to be read properly as
4709 one archive. @option{--concatenate} removes the end-of-archive marker
4710 from the target archive before each new archive is appended. If you use
4711 @command{cat} to combine the archives, the result will not be a valid
4712 @command{tar} format archive. If you need to retrieve files from an
4713 archive that was added to using the @command{cat} utility, use the
4714 @option{--ignore-zeros} (@option{-i}) option. @xref{Ignore Zeros}, for further
4715 information on dealing with archives improperly combined using the
4716 @command{cat} shell utility.
4719 @subsection Removing Archive Members Using @option{--delete}
4720 @cindex Deleting files from an archive
4721 @cindex Removing files from an archive
4724 You can remove members from an archive by using the @option{--delete}
4725 option. Specify the name of the archive with @option{--file}
4726 (@option{-f}) and then specify the names of the members to be deleted;
4727 if you list no member names, nothing will be deleted. The
4728 @option{--verbose} option will cause @command{tar} to print the names
4729 of the members as they are deleted. As with @option{--extract}, you
4730 must give the exact member names when using @samp{tar --delete}.
4731 @option{--delete} will remove all versions of the named file from the
4732 archive. The @option{--delete} operation can run very slowly.
4734 Unlike other operations, @option{--delete} has no short form.
4736 @cindex Tapes, using @option{--delete} and
4737 @cindex Deleting from tape archives
4738 This operation will rewrite the archive. You can only use
4739 @option{--delete} on an archive if the archive device allows you to
4740 write to any point on the media, such as a disk; because of this, it
4741 does not work on magnetic tapes. Do not try to delete an archive member
4742 from a magnetic tape; the action will not succeed, and you will be
4743 likely to scramble the archive and damage your tape. There is no safe
4744 way (except by completely re-writing the archive) to delete files from
4745 most kinds of magnetic tape. @xref{Media}.
4747 To delete all versions of the file @file{blues} from the archive
4748 @file{collection.tar} in the @file{practice} directory, make sure you
4749 are in that directory, and then,
4752 $ @kbd{tar --list --file=collection.tar}
4757 $ @kbd{tar --delete --file=collection.tar blues}
4758 $ @kbd{tar --list --file=collection.tar}
4765 @FIXME{Check if the above listing is actually produced after running
4766 all the examples on collection.tar.}
4768 The @option{--delete} option has been reported to work properly when
4769 @command{tar} acts as a filter from @code{stdin} to @code{stdout}.
4772 @subsection Comparing Archive Members with the File System
4773 @cindex Verifying the currency of an archive
4776 The @option{--compare} (@option{-d}), or @option{--diff} operation compares
4777 specified archive members against files with the same names, and then
4778 reports differences in file size, mode, owner, modification date and
4779 contents. You should @emph{only} specify archive member names, not file
4780 names. If you do not name any members, then @command{tar} will compare the
4781 entire archive. If a file is represented in the archive but does not
4782 exist in the file system, @command{tar} reports a difference.
4784 You have to specify the record size of the archive when modifying an
4785 archive with a non-default record size.
4787 @command{tar} ignores files in the file system that do not have
4788 corresponding members in the archive.
4790 The following example compares the archive members @file{rock},
4791 @file{blues} and @file{funk} in the archive @file{bluesrock.tar} with
4792 files of the same name in the file system. (Note that there is no file,
4793 @file{funk}; @command{tar} will report an error message.)
4796 $ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
4799 tar: funk not found in archive
4802 The spirit behind the @option{--compare} (@option{--diff},
4803 @option{-d}) option is to check whether the archive represents the
4804 current state of files on disk, more than validating the integrity of
4805 the archive media. For this later goal, @xref{verify}.
4807 @node create options
4808 @section Options Used by @option{--create}
4810 @xopindex{create, additional options}
4811 The previous chapter described the basics of how to use
4812 @option{--create} (@option{-c}) to create an archive from a set of files.
4813 @xref{create}. This section described advanced options to be used with
4817 * override:: Overriding File Metadata.
4818 * Ignore Failed Read::
4822 @subsection Overriding File Metadata
4824 As described above, a @command{tar} archive keeps, for each member it contains,
4825 its @dfn{metadata}, such as modification time, mode and ownership of
4826 the file. @GNUTAR{} allows to replace these data with other values
4827 when adding files to the archive. The options described in this
4828 section affect creation of archives of any type. For POSIX archives,
4829 see also @ref{PAX keywords}, for additional ways of controlling
4830 metadata, stored in the archive.
4834 @item --mode=@var{permissions}
4836 When adding files to an archive, @command{tar} will use
4837 @var{permissions} for the archive members, rather than the permissions
4838 from the files. @var{permissions} can be specified either as an octal
4839 number or as symbolic permissions, like with
4840 @command{chmod} (@xref{File permissions, Permissions, File
4841 permissions, fileutils, @acronym{GNU} file utilities}. This reference
4842 also has useful information for those not being overly familiar with
4843 the UNIX permission system). Using latter syntax allows for
4844 more flexibility. For example, the value @samp{a+rw} adds read and write
4845 permissions for everybody, while retaining executable bits on directories
4846 or on any other file already marked as executable:
4849 $ @kbd{tar -c -f archive.tar --mode='a+rw' .}
4852 @item --mtime=@var{date}
4855 When adding files to an archive, @command{tar} will use @var{date} as
4856 the modification time of members when creating archives, instead of
4857 their actual modification times. The argument @var{date} can be
4858 either a textual date representation in almost arbitrary format
4859 (@pxref{Date input formats}) or a name of the existing file, starting
4860 with @samp{/} or @samp{.}. In the latter case, the modification time
4861 of that file will be used.
4863 The following example will set the modification date to 00:00:00 UTC,
4867 $ @kbd{tar -c -f archive.tar --mtime='1970-01-01' .}
4871 When used with @option{--verbose} (@pxref{verbose tutorial}) @GNUTAR{}
4872 will try to convert the specified date back to its textual
4873 representation and compare it with the one given with
4874 @option{--mtime} options. If the two dates differ, @command{tar} will
4875 print a warning saying what date it will use. This is to help user
4876 ensure he is using the right date.
4881 $ @kbd{tar -c -f archive.tar -v --mtime=yesterday .}
4882 tar: Option --mtime: Treating date `yesterday' as 2006-06-20
4887 @item --owner=@var{user}
4890 Specifies that @command{tar} should use @var{user} as the owner of members
4891 when creating archives, instead of the user associated with the source
4892 file. The argument @var{user} can be either an existing user symbolic
4893 name, or a decimal numeric user @acronym{ID}.
4895 There is no value indicating a missing number, and @samp{0} usually means
4896 @code{root}. Some people like to force @samp{0} as the value to offer in
4897 their distributions for the owner of files, because the @code{root} user is
4898 anonymous anyway, so that might as well be the owner of anonymous
4899 archives. For example:
4903 $ @kbd{tar -c -f archive.tar --owner=0 .}
4905 $ @kbd{tar -c -f archive.tar --owner=root .}
4909 @item --group=@var{group}
4912 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
4913 rather than the group from the source file. The argument @var{group}
4914 can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
4917 @node Ignore Failed Read
4918 @subsection Ignore Fail Read
4921 @item --ignore-failed-read
4922 @opindex ignore-failed-read
4923 Do not exit with nonzero on unreadable files or directories.
4926 @node extract options
4927 @section Options Used by @option{--extract}
4928 @cindex options for use with @option{--extract}
4930 @xopindex{extract, additional options}
4931 The previous chapter showed how to use @option{--extract} to extract
4932 an archive into the file system. Various options cause @command{tar} to
4933 extract more information than just file contents, such as the owner,
4934 the permissions, the modification date, and so forth. This section
4935 presents options to be used with @option{--extract} when certain special
4936 considerations arise. You may review the information presented in
4937 @ref{extract} for more basic information about the
4938 @option{--extract} operation.
4941 * Reading:: Options to Help Read Archives
4942 * Writing:: Changing How @command{tar} Writes Files
4943 * Scarce:: Coping with Scarce Resources
4947 @subsection Options to Help Read Archives
4948 @cindex Options when reading archives
4950 @cindex Reading incomplete records
4951 @cindex Records, incomplete
4952 @opindex read-full-records
4953 Normally, @command{tar} will request data in full record increments from
4954 an archive storage device. If the device cannot return a full record,
4955 @command{tar} will report an error. However, some devices do not always
4956 return full records, or do not require the last record of an archive to
4957 be padded out to the next record boundary. To keep reading until you
4958 obtain a full record, or to accept an incomplete record if it contains
4959 an end-of-archive marker, specify the @option{--read-full-records} (@option{-B}) option
4960 in conjunction with the @option{--extract} or @option{--list} operations.
4963 The @option{--read-full-records} (@option{-B}) option is turned on by default when
4964 @command{tar} reads an archive from standard input, or from a remote
4965 machine. This is because on @acronym{BSD} Unix systems, attempting to read a
4966 pipe returns however much happens to be in the pipe, even if it is
4967 less than was requested. If this option were not enabled, @command{tar}
4968 would fail as soon as it read an incomplete record from the pipe.
4970 If you're not sure of the blocking factor of an archive, you can
4971 read the archive by specifying @option{--read-full-records} (@option{-B}) and
4972 @option{--blocking-factor=@var{512-size}} (@option{-b
4973 @var{512-size}}), using a blocking factor larger than what the archive
4974 uses. This lets you avoid having to determine the blocking factor
4975 of an archive. @xref{Blocking Factor}.
4978 * read full records::
4982 @node read full records
4983 @unnumberedsubsubsec Reading Full Records
4985 @FIXME{need sentence or so of intro here}
4988 @opindex read-full-records
4989 @item --read-full-records
4991 Use in conjunction with @option{--extract} (@option{--get},
4992 @option{-x}) to read an archive which contains incomplete records, or
4993 one which has a blocking factor less than the one specified.
4997 @unnumberedsubsubsec Ignoring Blocks of Zeros
4999 @cindex End-of-archive blocks, ignoring
5000 @cindex Ignoring end-of-archive blocks
5001 @opindex ignore-zeros
5002 Normally, @command{tar} stops reading when it encounters a block of zeros
5003 between file entries (which usually indicates the end of the archive).
5004 @option{--ignore-zeros} (@option{-i}) allows @command{tar} to
5005 completely read an archive which contains a block of zeros before the
5006 end (i.e., a damaged archive, or one that was created by concatenating
5007 several archives together).
5009 The @option{--ignore-zeros} (@option{-i}) option is turned off by default because many
5010 versions of @command{tar} write garbage after the end-of-archive entry,
5011 since that part of the media is never supposed to be read. @GNUTAR{}
5012 does not write after the end of an archive, but seeks to
5013 maintain compatibility among archiving utilities.
5016 @item --ignore-zeros
5018 To ignore blocks of zeros (i.e., end-of-archive entries) which may be
5019 encountered while reading an archive. Use in conjunction with
5020 @option{--extract} or @option{--list}.
5024 @subsection Changing How @command{tar} Writes Files
5027 @FIXME{Introductory paragraph}
5030 * Dealing with Old Files::
5031 * Overwrite Old Files::
5033 * Keep Newer Files::
5035 * Recursive Unlink::
5036 * Data Modification Times::
5037 * Setting Access Permissions::
5038 * Directory Modification Times and Permissions::
5039 * Writing to Standard Output::
5040 * Writing to an External Program::
5044 @node Dealing with Old Files
5045 @unnumberedsubsubsec Options Controlling the Overwriting of Existing Files
5047 @xopindex{overwrite-dir, introduced}
5048 When extracting files, if @command{tar} discovers that the extracted
5049 file already exists, it normally replaces the file by removing it before
5050 extracting it, to prevent confusion in the presence of hard or symbolic
5051 links. (If the existing file is a symbolic link, it is removed, not
5052 followed.) However, if a directory cannot be removed because it is
5053 nonempty, @command{tar} normally overwrites its metadata (ownership,
5054 permission, etc.). The @option{--overwrite-dir} option enables this
5055 default behavior. To be more cautious and preserve the metadata of
5056 such a directory, use the @option{--no-overwrite-dir} option.
5058 @cindex Overwriting old files, prevention
5059 @xopindex{keep-old-files, introduced}
5060 To be even more cautious and prevent existing files from being replaced, use
5061 the @option{--keep-old-files} (@option{-k}) option. It causes @command{tar} to refuse
5062 to replace or update a file that already exists, i.e., a file with the
5063 same name as an archive member prevents extraction of that archive
5064 member. Instead, it reports an error.
5066 @xopindex{overwrite, introduced}
5067 To be more aggressive about altering existing files, use the
5068 @option{--overwrite} option. It causes @command{tar} to overwrite
5069 existing files and to follow existing symbolic links when extracting.
5071 @cindex Protecting old files
5072 Some people argue that @GNUTAR{} should not hesitate
5073 to overwrite files with other files when extracting. When extracting
5074 a @command{tar} archive, they expect to see a faithful copy of the
5075 state of the file system when the archive was created. It is debatable
5076 that this would always be a proper behavior. For example, suppose one
5077 has an archive in which @file{usr/local} is a link to
5078 @file{usr/local2}. Since then, maybe the site removed the link and
5079 renamed the whole hierarchy from @file{/usr/local2} to
5080 @file{/usr/local}. Such things happen all the time. I guess it would
5081 not be welcome at all that @GNUTAR{} removes the
5082 whole hierarchy just to make room for the link to be reinstated
5083 (unless it @emph{also} simultaneously restores the full
5084 @file{/usr/local2}, of course!) @GNUTAR{} is indeed
5085 able to remove a whole hierarchy to reestablish a symbolic link, for
5086 example, but @emph{only if} @option{--recursive-unlink} is specified
5087 to allow this behavior. In any case, single files are silently
5090 @xopindex{unlink-first, introduced}
5091 Finally, the @option{--unlink-first} (@option{-U}) option can improve performance in
5092 some cases by causing @command{tar} to remove files unconditionally
5093 before extracting them.
5095 @node Overwrite Old Files
5096 @unnumberedsubsubsec Overwrite Old Files
5101 Overwrite existing files and directory metadata when extracting files
5104 This causes @command{tar} to write extracted files into the file system without
5105 regard to the files already on the system; i.e., files with the same
5106 names as archive members are overwritten when the archive is extracted.
5107 It also causes @command{tar} to extract the ownership, permissions,
5108 and time stamps onto any preexisting files or directories.
5109 If the name of a corresponding file name is a symbolic link, the file
5110 pointed to by the symbolic link will be overwritten instead of the
5111 symbolic link itself (if this is possible). Moreover, special devices,
5112 empty directories and even symbolic links are automatically removed if
5113 they are in the way of extraction.
5115 Be careful when using the @option{--overwrite} option, particularly when
5116 combined with the @option{--absolute-names} (@option{-P}) option, as this combination
5117 can change the contents, ownership or permissions of any file on your
5118 system. Also, many systems do not take kindly to overwriting files that
5119 are currently being executed.
5121 @opindex overwrite-dir
5122 @item --overwrite-dir
5123 Overwrite the metadata of directories when extracting files from an
5124 archive, but remove other files before extracting.
5127 @node Keep Old Files
5128 @unnumberedsubsubsec Keep Old Files
5131 @opindex keep-old-files
5132 @item --keep-old-files
5134 Do not replace existing files from archive. The
5135 @option{--keep-old-files} (@option{-k}) option prevents @command{tar}
5136 from replacing existing files with files with the same name from the
5137 archive. The @option{--keep-old-files} option is meaningless with
5138 @option{--list} (@option{-t}). Prevents @command{tar} from replacing
5139 files in the file system during extraction.
5142 @node Keep Newer Files
5143 @unnumberedsubsubsec Keep Newer Files
5146 @opindex keep-newer-files
5147 @item --keep-newer-files
5148 Do not replace existing files that are newer than their archive
5149 copies. This option is meaningless with @option{--list} (@option{-t}).
5153 @unnumberedsubsubsec Unlink First
5156 @opindex unlink-first
5157 @item --unlink-first
5159 Remove files before extracting over them.
5160 This can make @command{tar} run a bit faster if you know in advance
5161 that the extracted files all need to be removed. Normally this option
5162 slows @command{tar} down slightly, so it is disabled by default.
5165 @node Recursive Unlink
5166 @unnumberedsubsubsec Recursive Unlink
5169 @opindex recursive-unlink
5170 @item --recursive-unlink
5171 When this option is specified, try removing files and directory hierarchies
5172 before extracting over them. @emph{This is a dangerous option!}
5175 If you specify the @option{--recursive-unlink} option,
5176 @command{tar} removes @emph{anything} that keeps you from extracting a file
5177 as far as current permissions will allow it. This could include removal
5178 of the contents of a full directory hierarchy.
5180 @node Data Modification Times
5181 @unnumberedsubsubsec Setting Data Modification Times
5183 @cindex Data modification times of extracted files
5184 @cindex Modification times of extracted files
5185 Normally, @command{tar} sets the data modification times of extracted
5186 files to the corresponding times recorded for the files in the archive, but
5187 limits the permissions of extracted files by the current @code{umask}
5190 To set the data modification times of extracted files to the time when
5191 the files were extracted, use the @option{--touch} (@option{-m}) option in
5192 conjunction with @option{--extract} (@option{--get}, @option{-x}).
5198 Sets the data modification time of extracted archive members to the time
5199 they were extracted, not the time recorded for them in the archive.
5200 Use in conjunction with @option{--extract} (@option{--get}, @option{-x}).
5203 @node Setting Access Permissions
5204 @unnumberedsubsubsec Setting Access Permissions
5206 @cindex Permissions of extracted files
5207 @cindex Modes of extracted files
5208 To set the modes (access permissions) of extracted files to those
5209 recorded for those files in the archive, use @option{--same-permissions}
5210 in conjunction with the @option{--extract} (@option{--get},
5211 @option{-x}) operation.
5214 @opindex preserve-permissions
5215 @opindex same-permissions
5216 @item --preserve-permissions
5217 @itemx --same-permissions
5218 @c @itemx --ignore-umask
5220 Set modes of extracted archive members to those recorded in the
5221 archive, instead of current umask settings. Use in conjunction with
5222 @option{--extract} (@option{--get}, @option{-x}).
5225 @node Directory Modification Times and Permissions
5226 @unnumberedsubsubsec Directory Modification Times and Permissions
5228 After successfully extracting a file member, @GNUTAR{} normally
5229 restores its permissions and modification times, as described in the
5230 previous sections. This cannot be done for directories, because
5231 after extracting a directory @command{tar} will almost certainly
5232 extract files into that directory and this will cause the directory
5233 modification time to be updated. Moreover, restoring that directory
5234 permissions may not permit file creation within it. Thus, restoring
5235 directory permissions and modification times must be delayed at least
5236 until all files have been extracted into that directory. @GNUTAR{}
5237 restores directories using the following approach.
5239 The extracted directories are created with the mode specified in the
5240 archive, as modified by the umask of the user, which gives sufficient
5241 permissions to allow file creation. The meta-information about the
5242 directory is recorded in the temporary list of directories. When
5243 preparing to extract next archive member, @GNUTAR{} checks if the
5244 directory prefix of this file contains the remembered directory. If
5245 it does not, the program assumes that all files have been extracted
5246 into that directory, restores its modification time and permissions
5247 and removes its entry from the internal list. This approach allows
5248 to correctly restore directory meta-information in the majority of
5249 cases, while keeping memory requirements sufficiently small. It is
5250 based on the fact, that most @command{tar} archives use the predefined
5251 order of members: first the directory, then all the files and
5252 subdirectories in that directory.
5254 However, this is not always true. The most important exception are
5255 incremental archives (@pxref{Incremental Dumps}). The member order in
5256 an incremental archive is reversed: first all directory members are
5257 stored, followed by other (non-directory) members. So, when extracting
5258 from incremental archives, @GNUTAR{} alters the above procedure. It
5259 remembers all restored directories, and restores their meta-data
5260 only after the entire archive has been processed. Notice, that you do
5261 not need to specify any special options for that, as @GNUTAR{}
5262 automatically detects archives in incremental format.
5264 There may be cases, when such processing is required for normal archives
5265 too. Consider the following example:
5269 $ @kbd{tar --no-recursion -cvf archive \
5270 foo foo/file1 bar bar/file foo/file2}
5279 During the normal operation, after encountering @file{bar}
5280 @GNUTAR{} will assume that all files from the directory @file{foo}
5281 were already extracted and will therefore restore its timestamp and
5282 permission bits. However, after extracting @file{foo/file2} the
5283 directory timestamp will be offset again.
5285 To correctly restore directory meta-information in such cases, use
5286 @option{delay-directory-restore} command line option:
5289 @opindex delay-directory-restore
5290 @item --delay-directory-restore
5291 Delays restoring of the modification times and permissions of extracted
5292 directories until the end of extraction. This way, correct
5293 meta-information is restored even if the archive has unusual member
5296 @opindex no-delay-directory-restore
5297 @item --no-delay-directory-restore
5298 Cancel the effect of the previous @option{--delay-directory-restore}.
5299 Use this option if you have used @option{--delay-directory-restore} in
5300 @env{TAR_OPTIONS} variable (@pxref{TAR_OPTIONS}) and wish to
5301 temporarily disable it.
5304 @node Writing to Standard Output
5305 @unnumberedsubsubsec Writing to Standard Output
5307 @cindex Writing extracted files to standard output
5308 @cindex Standard output, writing extracted files to
5309 To write the extracted files to the standard output, instead of
5310 creating the files on the file system, use @option{--to-stdout} (@option{-O}) in
5311 conjunction with @option{--extract} (@option{--get}, @option{-x}). This option is useful if you are
5312 extracting files to send them through a pipe, and do not need to
5313 preserve them in the file system. If you extract multiple members,
5314 they appear on standard output concatenated, in the order they are
5315 found in the archive.
5321 Writes files to the standard output. Use only in conjunction with
5322 @option{--extract} (@option{--get}, @option{-x}). When this option is
5323 used, instead of creating the files specified, @command{tar} writes
5324 the contents of the files extracted to its standard output. This may
5325 be useful if you are only extracting the files in order to send them
5326 through a pipe. This option is meaningless with @option{--list}
5330 This can be useful, for example, if you have a tar archive containing
5331 a big file and don't want to store the file on disk before processing
5332 it. You can use a command like this:
5335 tar -xOzf foo.tgz bigfile | process
5338 or even like this if you want to process the concatenation of the files:
5341 tar -xOzf foo.tgz bigfile1 bigfile2 | process
5344 However, @option{--to-command} may be more convenient for use with
5345 multiple files. See the next section.
5347 @node Writing to an External Program
5348 @unnumberedsubsubsec Writing to an External Program
5350 You can instruct @command{tar} to send the contents of each extracted
5351 file to the standard input of an external program:
5355 @item --to-command=@var{command}
5356 Extract files and pipe their contents to the standard input of
5357 @var{command}. When this option is used, instead of creating the
5358 files specified, @command{tar} invokes @var{command} and pipes the
5359 contents of the files to its standard output. @var{Command} may
5360 contain command line arguments. The program is executed via
5361 @code{sh -c}. Notice, that @var{command} is executed once for each regular file
5362 extracted. Non-regular files (directories, etc.) are ignored when this
5366 The command can obtain the information about the file it processes
5367 from the following environment variables:
5370 @vrindex TAR_FILETYPE, to-command environment
5372 Type of the file. It is a single letter with the following meaning:
5374 @multitable @columnfractions 0.10 0.90
5375 @item f @tab Regular file
5376 @item d @tab Directory
5377 @item l @tab Symbolic link
5378 @item h @tab Hard link
5379 @item b @tab Block device
5380 @item c @tab Character device
5383 Currently only regular files are supported.
5385 @vrindex TAR_MODE, to-command environment
5387 File mode, an octal number.
5389 @vrindex TAR_FILENAME, to-command environment
5391 The name of the file.
5393 @vrindex TAR_REALNAME, to-command environment
5395 Name of the file as stored in the archive.
5397 @vrindex TAR_UNAME, to-command environment
5399 Name of the file owner.
5401 @vrindex TAR_GNAME, to-command environment
5403 Name of the file owner group.
5405 @vrindex TAR_ATIME, to-command environment
5407 Time of last access. It is a decimal number, representing seconds
5408 since the Epoch. If the archive provides times with nanosecond
5409 precision, the nanoseconds are appended to the timestamp after a
5412 @vrindex TAR_MTIME, to-command environment
5414 Time of last modification.
5416 @vrindex TAR_CTIME, to-command environment
5418 Time of last status change.
5420 @vrindex TAR_SIZE, to-command environment
5424 @vrindex TAR_UID, to-command environment
5426 UID of the file owner.
5428 @vrindex TAR_GID, to-command environment
5430 GID of the file owner.
5433 Additionally, the following variables contain information about
5434 tar mode and the archive being processed:
5437 @vrindex TAR_VERSION, to-command environment
5439 @GNUTAR{} version number.
5441 @vrindex TAR_ARCHIVE, to-command environment
5443 The name of the archive @command{tar} is processing.
5445 @vrindex TAR_BLOCKING_FACTOR, to-command environment
5446 @item TAR_BLOCKING_FACTOR
5447 Current blocking factor (@pxref{Blocking}.
5449 @vrindex TAR_VOLUME, to-command environment
5451 Ordinal number of the volume @command{tar} is processing.
5453 @vrindex TAR_FORMAT, to-command environment
5455 Format of the archive being processed. @xref{Formats}, for a complete
5456 list of archive format names.
5459 If @var{command} exits with a non-0 status, @command{tar} will print
5460 an error message similar to the following:
5463 tar: 2345: Child returned status 1
5466 Here, @samp{2345} is the PID of the finished process.
5468 If this behavior is not wanted, use @option{--ignore-command-error}:
5471 @opindex ignore-command-error
5472 @item --ignore-command-error
5473 Ignore exit codes of subprocesses. Notice that if the program
5474 exits on signal or otherwise terminates abnormally, the error message
5475 will be printed even if this option is used.
5477 @opindex no-ignore-command-error
5478 @item --no-ignore-command-error
5479 Cancel the effect of any previous @option{--ignore-command-error}
5480 option. This option is useful if you have set
5481 @option{--ignore-command-error} in @env{TAR_OPTIONS}
5482 (@pxref{TAR_OPTIONS}) and wish to temporarily cancel it.
5486 @unnumberedsubsubsec Removing Files
5488 @FIXME{The section is too terse. Something more to add? An example,
5492 @opindex remove-files
5493 @item --remove-files
5494 Remove files after adding them to the archive.
5498 @subsection Coping with Scarce Resources
5501 @cindex Small memory
5502 @cindex Running out of space
5510 @unnumberedsubsubsec Starting File
5513 @opindex starting-file
5514 @item --starting-file=@var{name}
5515 @itemx -K @var{name}
5516 Starts an operation in the middle of an archive. Use in conjunction
5517 with @option{--extract} (@option{--get}, @option{-x}) or @option{--list} (@option{-t}).
5520 @cindex Middle of the archive, starting in the
5521 If a previous attempt to extract files failed due to lack of disk
5522 space, you can use @option{--starting-file=@var{name}} (@option{-K
5523 @var{name}}) to start extracting only after member @var{name} of the
5524 archive. This assumes, of course, that there is now free space, or
5525 that you are now extracting into a different file system. (You could
5526 also choose to suspend @command{tar}, remove unnecessary files from
5527 the file system, and then restart the same @command{tar} operation.
5528 In this case, @option{--starting-file} is not necessary.
5529 @xref{Incremental Dumps}, @xref{interactive}, and @ref{exclude}.)
5532 @unnumberedsubsubsec Same Order
5535 @cindex Large lists of file names on small machines
5537 @opindex preserve-order
5539 @itemx --preserve-order
5541 To process large lists of file names on machines with small amounts of
5542 memory. Use in conjunction with @option{--compare} (@option{--diff},
5543 @option{-d}), @option{--list} (@option{-t}) or @option{--extract}
5544 (@option{--get}, @option{-x}).
5547 The @option{--same-order} (@option{--preserve-order}, @option{-s}) option tells @command{tar} that the list of file
5548 names to be listed or extracted is sorted in the same order as the
5549 files in the archive. This allows a large list of names to be used,
5550 even on a small machine that would not otherwise be able to hold all
5551 the names in memory at the same time. Such a sorted list can easily be
5552 created by running @samp{tar -t} on the archive and editing its output.
5554 This option is probably never needed on modern computer systems.
5557 @section Backup options
5559 @cindex backup options
5561 @GNUTAR{} offers options for making backups of files
5562 before writing new versions. These options control the details of
5563 these backups. They may apply to the archive itself before it is
5564 created or rewritten, as well as individual extracted members. Other
5565 @acronym{GNU} programs (@command{cp}, @command{install}, @command{ln},
5566 and @command{mv}, for example) offer similar options.
5568 Backup options may prove unexpectedly useful when extracting archives
5569 containing many members having identical name, or when extracting archives
5570 on systems having file name limitations, making different members appear
5571 as having similar names through the side-effect of name truncation.
5572 @FIXME{This is true only if we have a good scheme for truncated backup names,
5573 which I'm not sure at all: I suspect work is needed in this area.}
5574 When any existing file is backed up before being overwritten by extraction,
5575 then clashing files are automatically be renamed to be unique, and the
5576 true name is kept for only the last file of a series of clashing files.
5577 By using verbose mode, users may track exactly what happens.
5579 At the detail level, some decisions are still experimental, and may
5580 change in the future, we are waiting comments from our users. So, please
5581 do not learn to depend blindly on the details of the backup features.
5582 For example, currently, directories themselves are never renamed through
5583 using these options, so, extracting a file over a directory still has
5584 good chances to fail. Also, backup options apply to created archives,
5585 not only to extracted members. For created archives, backups will not
5586 be attempted when the archive is a block or character device, or when it
5587 refers to a remote file.
5589 For the sake of simplicity and efficiency, backups are made by renaming old
5590 files prior to creation or extraction, and not by copying. The original
5591 name is restored if the file creation fails. If a failure occurs after a
5592 partial extraction of a file, both the backup and the partially extracted
5596 @item --backup[=@var{method}]
5598 @vindex VERSION_CONTROL
5600 Back up files that are about to be overwritten or removed.
5601 Without this option, the original versions are destroyed.
5603 Use @var{method} to determine the type of backups made.
5604 If @var{method} is not specified, use the value of the @env{VERSION_CONTROL}
5605 environment variable. And if @env{VERSION_CONTROL} is not set,
5606 use the @samp{existing} method.
5608 @vindex version-control @r{Emacs variable}
5609 This option corresponds to the Emacs variable @samp{version-control};
5610 the same values for @var{method} are accepted as in Emacs. This option
5611 also allows more descriptive names. The valid @var{method}s are:
5616 @cindex numbered @r{backup method}
5617 Always make numbered backups.
5621 @cindex existing @r{backup method}
5622 Make numbered backups of files that already have them, simple backups
5627 @cindex simple @r{backup method}
5628 Always make simple backups.
5632 @item --suffix=@var{suffix}
5634 @cindex backup suffix
5635 @vindex SIMPLE_BACKUP_SUFFIX
5636 Append @var{suffix} to each backup file made with @option{--backup}. If this
5637 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
5638 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
5639 set, the default is @samp{~}, just as in Emacs.
5644 @section Notable @command{tar} Usages
5647 @FIXME{Using Unix file linking capability to recreate directory
5648 structures---linking files into one subdirectory and then
5649 @command{tar}ring that directory.}
5651 @FIXME{Nice hairy example using absolute-names, newer, etc.}
5654 You can easily use archive files to transport a group of files from
5655 one system to another: put all relevant files into an archive on one
5656 computer system, transfer the archive to another system, and extract
5657 the contents there. The basic transfer medium might be magnetic tape,
5658 Internet FTP, or even electronic mail (though you must encode the
5659 archive with @command{uuencode} in order to transport it properly by
5660 mail). Both machines do not have to use the same operating system, as
5661 long as they both support the @command{tar} program.
5663 For example, here is how you might copy a directory's contents from
5664 one disk to another, while preserving the dates, modes, owners and
5665 link-structure of all the files therein. In this case, the transfer
5666 medium is a @dfn{pipe}, which is one a Unix redirection mechanism:
5669 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
5673 You can avoid subshells by using @option{-C} option:
5676 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xf -}
5680 The command also works using short option forms:
5683 $ @kbd{(cd sourcedir; tar --create --file=- . ) \
5684 | (cd targetdir; tar --extract --file=-)}
5686 $ @kbd{tar --directory sourcedir --create --file=- . ) \
5687 | tar --directory targetdir --extract --file=-}
5691 This is one of the easiest methods to transfer a @command{tar} archive.
5694 @section Looking Ahead: The Rest of this Manual
5696 You have now seen how to use all eight of the operations available to
5697 @command{tar}, and a number of the possible options. The next chapter
5698 explains how to choose and change file and archive names, how to use
5699 files to store names of other files which you can then call as
5700 arguments to @command{tar} (this can help you save time if you expect to
5701 archive the same list of files a number of times), and so forth.
5702 @FIXME{in case it's not obvious, i'm making this up in some sense
5703 based on my limited memory of what the next chapter *really* does. i
5704 just wanted to flesh out this final section a little bit so i'd
5705 remember to stick it in here. :-)}
5707 If there are too many files to conveniently list on the command line,
5708 you can list the names in a file, and @command{tar} will read that file.
5711 There are various ways of causing @command{tar} to skip over some files,
5712 and not archive them. @xref{Choosing}.
5715 @chapter Performing Backups and Restoring Files
5718 @GNUTAR{} is distributed along with the scripts for performing backups
5719 and restores. Even if there is a good chance those scripts may be
5720 satisfying to you, they are not the only scripts or methods available for doing
5721 backups and restore. You may well create your own, or use more
5722 sophisticated packages dedicated to that purpose.
5724 Some users are enthusiastic about @code{Amanda} (The Advanced Maryland
5725 Automatic Network Disk Archiver), a backup system developed by James
5726 da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
5727 This is free software, and it is available from @uref{http://www.amanda.org}.
5731 Here is a possible plan for a future documentation about the backuping
5732 scripts which are provided within the @GNUTAR{}
5738 @item what are dumps
5739 @item different levels of dumps
5741 @item full dump = dump everything
5742 @item level 1, level 2 dumps etc
5743 A level @var{n} dump dumps everything changed since the last level
5746 @item how to use scripts for dumps (ie, the concept)
5748 @item scripts to run after editing backup specs (details)
5750 @item Backup Specs, what is it.
5752 @item how to customize
5753 @item actual text of script [/sp/dump/backup-specs]
5757 @item rsh doesn't work
5758 @item rtape isn't installed
5761 @item the @option{--incremental} option of tar
5764 @item write protection
5765 @item types of media, different sizes and types, useful for different things
5766 @item files and tape marks
5767 one tape mark between files, two at end.
5768 @item positioning the tape
5769 MT writes two at end of write,
5770 backspaces over one when writing again.
5776 This chapter documents both the provided shell scripts and @command{tar}
5777 options which are more specific to usage as a backup tool.
5779 To @dfn{back up} a file system means to create archives that contain
5780 all the files in that file system. Those archives can then be used to
5781 restore any or all of those files (for instance if a disk crashes or a
5782 file is accidentally deleted). File system @dfn{backups} are also
5786 * Full Dumps:: Using @command{tar} to Perform Full Dumps
5787 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
5788 * Backup Levels:: Levels of Backups
5789 * Backup Parameters:: Setting Parameters for Backups and Restoration
5790 * Scripted Backups:: Using the Backup Scripts
5791 * Scripted Restoration:: Using the Restore Script
5795 @section Using @command{tar} to Perform Full Dumps
5801 @cindex corrupted archives
5802 Full dumps should only be made when no other people or programs
5803 are modifying files in the file system. If files are modified while
5804 @command{tar} is making the backup, they may not be stored properly in
5805 the archive, in which case you won't be able to restore them if you
5806 have to. (Files not being modified are written with no trouble, and do
5807 not corrupt the entire archive.)
5809 You will want to use the @option{--label=@var{archive-label}}
5810 (@option{-V @var{archive-label}}) option to give the archive a
5811 volume label, so you can tell what this archive is even if the label
5812 falls off the tape, or anything like that.
5814 Unless the file system you are dumping is guaranteed to fit on
5815 one volume, you will need to use the @option{--multi-volume} (@option{-M}) option.
5816 Make sure you have enough tapes on hand to complete the backup.
5818 If you want to dump each file system separately you will need to use
5819 the @option{--one-file-system} option to prevent
5820 @command{tar} from crossing file system boundaries when storing
5823 The @option{--incremental} (@option{-G}) (@pxref{Incremental Dumps})
5824 option is not needed, since this is a complete copy of everything in
5825 the file system, and a full restore from this backup would only be
5826 done onto a completely
5829 Unless you are in a hurry, and trust the @command{tar} program (and your
5830 tapes), it is a good idea to use the @option{--verify} (@option{-W})
5831 option, to make sure your files really made it onto the dump properly.
5832 This will also detect cases where the file was modified while (or just
5833 after) it was being archived. Not all media (notably cartridge tapes)
5834 are capable of being verified, unfortunately.
5836 @node Incremental Dumps
5837 @section Using @command{tar} to Perform Incremental Dumps
5839 @dfn{Incremental backup} is a special form of @GNUTAR{} archive that
5840 stores additional metadata so that exact state of the file system
5841 can be restored when extracting the archive.
5843 @GNUTAR{} currently offers two options for handling incremental
5844 backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
5845 @var{snapshot-file}}) and @option{--incremental} (@option{-G}).
5847 @xopindex{listed-incremental, described}
5848 The option @option{--listed-incremental} instructs tar to operate on
5849 an incremental archive with additional metadata stored in a standalone
5850 file, called a @dfn{snapshot file}. The purpose of this file is to help
5851 determine which files have been changed, added or deleted since the
5852 last backup, so that the next incremental backup will contain only
5853 modified files. The name of the snapshot file is given as an argument
5857 @item --listed-incremental=@var{file}
5858 @itemx -g @var{file}
5859 Handle incremental backups with snapshot data in @var{file}.
5862 To create an incremental backup, you would use
5863 @option{--listed-incremental} together with @option{--create}
5864 (@pxref{create}). For example:
5867 $ @kbd{tar --create \
5868 --file=archive.1.tar \
5869 --listed-incremental=/var/log/usr.snar \
5873 This will create in @file{archive.1.tar} an incremental backup of
5874 the @file{/usr} file system, storing additional metadata in the file
5875 @file{/var/log/usr.snar}. If this file does not exist, it will be
5876 created. The created archive will then be a @dfn{level 0 backup};
5877 please see the next section for more on backup levels.
5879 Otherwise, if the file @file{/var/log/usr.snar} exists, it
5880 determines which files are modified. In this case only these files will be
5881 stored in the archive. Suppose, for example, that after running the
5882 above command, you delete file @file{/usr/doc/old} and create
5883 directory @file{/usr/local/db} with the following contents:
5886 $ @kbd{ls /usr/local/db}
5891 Some time later you create another incremental backup. You will
5895 $ @kbd{tar --create \
5896 --file=archive.2.tar \
5897 --listed-incremental=/var/log/usr.snar \
5899 tar: usr/local/db: Directory is new
5906 The created archive @file{archive.2.tar} will contain only these
5907 three members. This archive is called a @dfn{level 1 backup}. Notice
5908 that @file{/var/log/usr.snar} will be updated with the new data, so if
5909 you plan to create more @samp{level 1} backups, it is necessary to
5910 create a working copy of the snapshot file before running
5911 @command{tar}. The above example will then be modified as follows:
5914 $ @kbd{cp /var/log/usr.snar /var/log/usr.snar-1}
5915 $ @kbd{tar --create \
5916 --file=archive.2.tar \
5917 --listed-incremental=/var/log/usr.snar-1 \
5922 @xopindex{level, described}
5923 You can force @samp{level 0} backups either by removing the snapshot
5924 file before running @command{tar}, or by supplying the
5925 @option{--level=0} option, e.g.:
5928 $ @kbd{tar --create \
5929 --file=archive.2.tar \
5930 --listed-incremental=/var/log/usr.snar-0 \
5935 Incremental dumps depend crucially on time stamps, so the results are
5936 unreliable if you modify a file's time stamps during dumping (e.g.,
5937 with the @option{--atime-preserve=replace} option), or if you set the clock
5940 @anchor{device numbers}
5941 @cindex Device numbers, using in incremental backups
5942 Metadata stored in snapshot files include device numbers, which,
5943 obviously are supposed to be a non-volatile values. However, it turns
5944 out that @acronym{NFS} devices have undependable values when an automounter
5945 gets in the picture. This can lead to a great deal of spurious
5946 redumping in incremental dumps, so it is somewhat useless to compare
5947 two @acronym{NFS} devices numbers over time. The solution implemented
5948 currently is to considers all @acronym{NFS} devices as being equal
5949 when it comes to comparing directories; this is fairly gross, but
5950 there does not seem to be a better way to go.
5952 Apart from using @acronym{NFS}, there are a number of cases where
5953 relying on device numbers can cause spurious redumping of unmodified
5954 files. For example, this occurs when archiving @acronym{LVM} snapshot
5955 volumes. To avoid this, use @option{--no-check-device} option:
5958 @xopindex{no-check-device, described}
5959 @item --no-check-device
5960 Do not rely on device numbers when preparing a list of changed files
5961 for an incremental dump.
5963 @xopindex{check-device, described}
5964 @item --check-device
5965 Use device numbers when preparing a list of changed files
5966 for an incremental dump. This is the default behavior. The purpose
5967 of this option is to undo the effect of the @option{--no-check-device}
5968 if it was given in @env{TAR_OPTIONS} environment variable
5969 (@pxref{TAR_OPTIONS}).
5972 There is also another way to cope with changing device numbers. It is
5973 described in detail in @ref{Fixing Snapshot Files}.
5975 Note that incremental archives use @command{tar} extensions and may
5976 not be readable by non-@acronym{GNU} versions of the @command{tar} program.
5978 @xopindex{listed-incremental, using with @option{--extract}}
5979 @xopindex{extract, using with @option{--listed-incremental}}
5980 To extract from the incremental dumps, use
5981 @option{--listed-incremental} together with @option{--extract}
5982 option (@pxref{extracting files}). In this case, @command{tar} does
5983 not need to access snapshot file, since all the data necessary for
5984 extraction are stored in the archive itself. So, when extracting, you
5985 can give whatever argument to @option{--listed-incremental}, the usual
5986 practice is to use @option{--listed-incremental=/dev/null}.
5987 Alternatively, you can use @option{--incremental}, which needs no
5988 arguments. In general, @option{--incremental} (@option{-G}) can be
5989 used as a shortcut for @option{--listed-incremental} when listing or
5990 extracting incremental backups (for more information, regarding this
5991 option, @pxref{incremental-op}).
5993 When extracting from the incremental backup @GNUTAR{} attempts to
5994 restore the exact state the file system had when the archive was
5995 created. In particular, it will @emph{delete} those files in the file
5996 system that did not exist in their directories when the archive was
5997 created. If you have created several levels of incremental files,
5998 then in order to restore the exact contents the file system had when
5999 the last level was created, you will need to restore from all backups
6000 in turn. Continuing our example, to restore the state of @file{/usr}
6001 file system, one would do@footnote{Notice, that since both archives
6002 were created without @option{-P} option (@pxref{absolute}), these
6003 commands should be run from the root file system.}:
6006 $ @kbd{tar --extract \
6007 --listed-incremental=/dev/null \
6008 --file archive.1.tar}
6009 $ @kbd{tar --extract \
6010 --listed-incremental=/dev/null \
6011 --file archive.2.tar}
6014 To list the contents of an incremental archive, use @option{--list}
6015 (@pxref{list}), as usual. To obtain more information about the
6016 archive, use @option{--listed-incremental} or @option{--incremental}
6017 combined with two @option{--verbose} options@footnote{Two
6018 @option{--verbose} options were selected to avoid breaking usual
6019 verbose listing output (@option{--list --verbose}) when using in
6022 @xopindex{incremental, using with @option{--list}}
6023 @xopindex{listed-incremental, using with @option{--list}}
6024 @xopindex{list, using with @option{--incremental}}
6025 @xopindex{list, using with @option{--listed-incremental}}
6026 Versions of @GNUTAR{} up to 1.15.1 used to dump verbatim binary
6027 contents of the DUMPDIR header (with terminating nulls) when
6028 @option{--incremental} or @option{--listed-incremental} option was
6029 given, no matter what the verbosity level. This behavior, and,
6030 especially, the binary output it produced were considered inconvenient
6031 and were changed in version 1.16}:
6034 @kbd{tar --list --incremental --verbose --verbose archive.tar}
6037 This command will print, for each directory in the archive, the list
6038 of files in that directory at the time the archive was created. This
6039 information is put out in a format which is both human-readable and
6040 unambiguous for a program: each file name is printed as
6047 where @var{x} is a letter describing the status of the file: @samp{Y}
6048 if the file is present in the archive, @samp{N} if the file is not
6049 included in the archive, or a @samp{D} if the file is a directory (and
6050 is included in the archive). @xref{Dumpdir}, for the detailed
6051 description of dumpdirs and status codes. Each such
6052 line is terminated by a newline character. The last line is followed
6053 by an additional newline to indicate the end of the data.
6055 @anchor{incremental-op}The option @option{--incremental} (@option{-G})
6056 gives the same behavior as @option{--listed-incremental} when used
6057 with @option{--list} and @option{--extract} options. When used with
6058 @option{--create} option, it creates an incremental archive without
6059 creating snapshot file. Thus, it is impossible to create several
6060 levels of incremental backups with @option{--incremental} option.
6063 @section Levels of Backups
6065 An archive containing all the files in the file system is called a
6066 @dfn{full backup} or @dfn{full dump}. You could insure your data by
6067 creating a full dump every day. This strategy, however, would waste a
6068 substantial amount of archive media and user time, as unchanged files
6069 are daily re-archived.
6071 It is more efficient to do a full dump only occasionally. To back up
6072 files between full dumps, you can use @dfn{incremental dumps}. A @dfn{level
6073 one} dump archives all the files that have changed since the last full
6076 A typical dump strategy would be to perform a full dump once a week,
6077 and a level one dump once a day. This means some versions of files
6078 will in fact be archived more than once, but this dump strategy makes
6079 it possible to restore a file system to within one day of accuracy by
6080 only extracting two archives---the last weekly (full) dump and the
6081 last daily (level one) dump. The only information lost would be in
6082 files changed or created since the last daily backup. (Doing dumps
6083 more than once a day is usually not worth the trouble).
6085 @GNUTAR{} comes with scripts you can use to do full
6086 and level-one (actually, even level-two and so on) dumps. Using
6087 scripts (shell programs) to perform backups and restoration is a
6088 convenient and reliable alternative to typing out file name lists
6089 and @command{tar} commands by hand.
6091 Before you use these scripts, you need to edit the file
6092 @file{backup-specs}, which specifies parameters used by the backup
6093 scripts and by the restore script. This file is usually located
6094 in @file{/etc/backup} directory. @xref{Backup Parameters}, for its
6095 detailed description. Once the backup parameters are set, you can
6096 perform backups or restoration by running the appropriate script.
6098 The name of the backup script is @code{backup}. The name of the
6099 restore script is @code{restore}. The following sections describe
6100 their use in detail.
6102 @emph{Please Note:} The backup and restoration scripts are
6103 designed to be used together. While it is possible to restore files by
6104 hand from an archive which was created using a backup script, and to create
6105 an archive by hand which could then be extracted using the restore script,
6106 it is easier to use the scripts. @xref{Incremental Dumps}, before
6107 making such an attempt.
6109 @node Backup Parameters
6110 @section Setting Parameters for Backups and Restoration
6112 The file @file{backup-specs} specifies backup parameters for the
6113 backup and restoration scripts provided with @command{tar}. You must
6114 edit @file{backup-specs} to fit your system configuration and schedule
6115 before using these scripts.
6117 Syntactically, @file{backup-specs} is a shell script, containing
6118 mainly variable assignments. However, any valid shell construct
6119 is allowed in this file. Particularly, you may wish to define
6120 functions within that script (e.g., see @code{RESTORE_BEGIN} below).
6121 For more information about shell script syntax, please refer to
6122 @url{http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
6123 g_02, the definition of the Shell Command Language}. See also
6124 @ref{Top,,Bash Features,bashref,Bash Reference Manual}.
6126 The shell variables controlling behavior of @code{backup} and
6127 @code{restore} are described in the following subsections.
6130 * General-Purpose Variables::
6131 * Magnetic Tape Control::
6133 * backup-specs example:: An Example Text of @file{Backup-specs}
6136 @node General-Purpose Variables
6137 @subsection General-Purpose Variables
6139 @defvr {Backup variable} ADMINISTRATOR
6140 The user name of the backup administrator. @code{Backup} scripts
6141 sends a backup report to this address.
6144 @defvr {Backup variable} BACKUP_HOUR
6145 The hour at which the backups are done. This can be a number from 0
6146 to 23, or the time specification in form @var{hours}:@var{minutes},
6147 or the string @samp{now}.
6149 This variable is used by @code{backup}. Its value may be overridden
6150 using @option{--time} option (@pxref{Scripted Backups}).
6153 @defvr {Backup variable} TAPE_FILE
6155 The device @command{tar} writes the archive to. If @var{TAPE_FILE}
6156 is a remote archive (@pxref{remote-dev}), backup script will suppose
6157 that your @command{mt} is able to access remote devices. If @var{RSH}
6158 (@pxref{RSH}) is set, @option{--rsh-command} option will be added to
6159 invocations of @command{mt}.
6162 @defvr {Backup variable} BLOCKING
6164 The blocking factor @command{tar} will use when writing the dump archive.
6165 @xref{Blocking Factor}.
6168 @defvr {Backup variable} BACKUP_DIRS
6170 A list of file systems to be dumped (for @code{backup}), or restored
6171 (for @code{restore}). You can include any directory
6172 name in the list --- subdirectories on that file system will be
6173 included, regardless of how they may look to other networked machines.
6174 Subdirectories on other file systems will be ignored.
6176 The host name specifies which host to run @command{tar} on, and should
6177 normally be the host that actually contains the file system. However,
6178 the host machine must have @GNUTAR{} installed, and
6179 must be able to access the directory containing the backup scripts and
6180 their support files using the same file name that is used on the
6181 machine where the scripts are run (i.e., what @command{pwd} will print
6182 when in that directory on that machine). If the host that contains
6183 the file system does not have this capability, you can specify another
6184 host as long as it can access the file system through @acronym{NFS}.
6186 If the list of file systems is very long you may wish to put it
6187 in a separate file. This file is usually named
6188 @file{/etc/backup/dirs}, but this name may be overridden in
6189 @file{backup-specs} using @code{DIRLIST} variable.
6192 @defvr {Backup variable} DIRLIST
6194 The name of the file that contains a list of file systems to backup
6195 or restore. By default it is @file{/etc/backup/dirs}.
6198 @defvr {Backup variable} BACKUP_FILES
6200 A list of individual files to be dumped (for @code{backup}), or restored
6201 (for @code{restore}). These should be accessible from the machine on
6202 which the backup script is run.
6204 If the list of file systems is very long you may wish to store it
6205 in a separate file. This file is usually named
6206 @file{/etc/backup/files}, but this name may be overridden in
6207 @file{backup-specs} using @code{FILELIST} variable.
6210 @defvr {Backup variable} FILELIST
6212 The name of the file that contains a list of individual files to backup
6213 or restore. By default it is @file{/etc/backup/files}.
6216 @defvr {Backup variable} MT
6218 Full file name of @command{mt} binary.
6221 @defvr {Backup variable} RSH
6223 Full file name of @command{rsh} binary or its equivalent. You may wish to
6224 set it to @code{ssh}, to improve security. In this case you will have
6225 to use public key authentication.
6228 @defvr {Backup variable} RSH_COMMAND
6230 Full file name of @command{rsh} binary on remote machines. This will
6231 be passed via @option{--rsh-command} option to the remote invocation
6235 @defvr {Backup variable} VOLNO_FILE
6237 Name of temporary file to hold volume numbers. This needs to be accessible
6238 by all the machines which have file systems to be dumped.
6241 @defvr {Backup variable} XLIST
6243 Name of @dfn{exclude file list}. An @dfn{exclude file list} is a file
6244 located on the remote machine and containing the list of files to
6245 be excluded from the backup. Exclude file lists are searched in
6246 /etc/tar-backup directory. A common use for exclude file lists
6247 is to exclude files containing security-sensitive information
6248 (e.g., @file{/etc/shadow} from backups).
6250 This variable affects only @code{backup}.
6253 @defvr {Backup variable} SLEEP_TIME
6255 Time to sleep between dumps of any two successive file systems
6257 This variable affects only @code{backup}.
6260 @defvr {Backup variable} DUMP_REMIND_SCRIPT
6262 Script to be run when it's time to insert a new tape in for the next
6263 volume. Administrators may want to tailor this script for their site.
6264 If this variable isn't set, @GNUTAR{} will display its built-in
6265 prompt, and will expect confirmation from the console. For the
6266 description of the default prompt, see @ref{change volume prompt}.
6270 @defvr {Backup variable} SLEEP_MESSAGE
6272 Message to display on the terminal while waiting for dump time. Usually
6273 this will just be some literal text.
6276 @defvr {Backup variable} TAR
6278 Full file name of the @GNUTAR{} executable. If this is not set, backup
6279 scripts will search @command{tar} in the current shell path.
6282 @node Magnetic Tape Control
6283 @subsection Magnetic Tape Control
6285 Backup scripts access tape device using special @dfn{hook functions}.
6286 These functions take a single argument -- the name of the tape
6287 device. Their names are kept in the following variables:
6289 @defvr {Backup variable} MT_BEGIN
6290 The name of @dfn{begin} function. This function is called before
6291 accessing the drive. By default it retensions the tape:
6297 mt -f "$1" retension
6302 @defvr {Backup variable} MT_REWIND
6303 The name of @dfn{rewind} function. The default definition is as
6316 @defvr {Backup variable} MT_OFFLINE
6317 The name of the function switching the tape off line. By default
6318 it is defined as follows:
6321 MT_OFFLINE=mt_offline
6329 @defvr {Backup variable} MT_STATUS
6330 The name of the function used to obtain the status of the archive device,
6331 including error count. Default definition:
6343 @subsection User Hooks
6345 @dfn{User hooks} are shell functions executed before and after
6346 each @command{tar} invocation. Thus, there are @dfn{backup
6347 hooks}, which are executed before and after dumping each file
6348 system, and @dfn{restore hooks}, executed before and
6349 after restoring a file system. Each user hook is a shell function
6350 taking four arguments:
6352 @deffn {User Hook Function} hook @var{level} @var{host} @var{fs} @var{fsname}
6357 Current backup or restore level.
6360 Name or IP address of the host machine being dumped or restored.
6363 Full file name of the file system being dumped or restored.
6366 File system name with directory separators replaced with colons. This
6367 is useful, e.g., for creating unique files.
6371 Following variables keep the names of user hook functions
6373 @defvr {Backup variable} DUMP_BEGIN
6374 Dump begin function. It is executed before dumping the file system.
6377 @defvr {Backup variable} DUMP_END
6378 Executed after dumping the file system.
6381 @defvr {Backup variable} RESTORE_BEGIN
6382 Executed before restoring the file system.
6385 @defvr {Backup variable} RESTORE_END
6386 Executed after restoring the file system.
6389 @node backup-specs example
6390 @subsection An Example Text of @file{Backup-specs}
6392 The following is an example of @file{backup-specs}:
6395 # site-specific parameters for file system backup.
6397 ADMINISTRATOR=friedman
6399 TAPE_FILE=/dev/nrsmt0
6401 # Use @code{ssh} instead of the less secure @code{rsh}
6403 RSH_COMMAND=/usr/bin/ssh
6405 # Override MT_STATUS function:
6411 # Disable MT_OFFLINE function
6428 apple-gunkies:/com/mailer/gnu
6429 apple-gunkies:/com/archive/gnu"
6431 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
6435 @node Scripted Backups
6436 @section Using the Backup Scripts
6438 The syntax for running a backup script is:
6441 backup --level=@var{level} --time=@var{time}
6444 The @option{level} option requests the dump level. Thus, to produce
6445 a full dump, specify @code{--level=0} (this is the default, so
6446 @option{--level} may be omitted if its value is @code{0}).
6447 @footnote{For backward compatibility, the @code{backup} will also
6448 try to deduce the requested dump level from the name of the
6449 script itself. If the name consists of a string @samp{level-}
6450 followed by a single decimal digit, that digit is taken as
6451 the dump level number. Thus, you may create a link from @code{backup}
6452 to @code{level-1} and then run @code{level-1} whenever you need to
6453 create a level one dump.}
6455 The @option{--time} option determines when should the backup be
6456 run. @var{Time} may take three forms:
6459 @item @var{hh}:@var{mm}
6461 The dump must be run at @var{hh} hours @var{mm} minutes.
6465 The dump must be run at @var{hh} hours
6469 The dump must be run immediately.
6472 You should start a script with a tape or disk mounted. Once you
6473 start a script, it prompts you for new tapes or disks as it
6474 needs them. Media volumes don't have to correspond to archive
6475 files --- a multi-volume archive can be started in the middle of a
6476 tape that already contains the end of another multi-volume archive.
6477 The @code{restore} script prompts for media by its archive volume,
6478 so to avoid an error message you should keep track of which tape
6479 (or disk) contains which volume of the archive (@pxref{Scripted
6482 The backup scripts write two files on the file system. The first is a
6483 record file in @file{/etc/tar-backup/}, which is used by the scripts
6484 to store and retrieve information about which files were dumped. This
6485 file is not meant to be read by humans, and should not be deleted by
6486 them. @xref{Snapshot Files}, for a more detailed explanation of this
6489 The second file is a log file containing the names of the file systems
6490 and files dumped, what time the backup was made, and any error
6491 messages that were generated, as well as how much space was left in
6492 the media volume after the last volume of the archive was written.
6493 You should check this log file after every backup. The file name is
6494 @file{log-@var{mm-dd-yyyy}-level-@var{n}}, where @var{mm-dd-yyyy}
6495 represents current date, and @var{n} represents current dump level number.
6497 The script also prints the name of each system being dumped to the
6500 Following is the full list of options accepted by @code{backup}
6504 @item -l @var{level}
6505 @itemx --level=@var{level}
6506 Do backup level @var{level} (default 0).
6510 Force backup even if today's log file already exists.
6512 @item -v[@var{level}]
6513 @itemx --verbose[=@var{level}]
6514 Set verbosity level. The higher the level is, the more debugging
6515 information will be output during execution. Default @var{level}
6516 is 100, which means the highest debugging level.
6518 @item -t @var{start-time}
6519 @itemx --time=@var{start-time}
6520 Wait till @var{time}, then do backup.
6524 Display short help message and exit.
6528 Display information about the program's name, version, origin and legal
6529 status, all on standard output, and then exit successfully.
6533 @node Scripted Restoration
6534 @section Using the Restore Script
6536 To restore files that were archived using a scripted backup, use the
6537 @code{restore} script. Its usage is quite straightforward. In the
6538 simplest form, invoke @code{restore --all}, it will
6539 then restore all the file systems and files specified in
6540 @file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
6542 You may select the file systems (and/or files) to restore by
6543 giving @code{restore} list of @dfn{patterns} in its command
6544 line. For example, running
6551 will restore all file systems on the machine @samp{albert}. A more
6552 complicated example:
6555 restore 'albert:*' '*:/var'
6559 This command will restore all file systems on the machine @samp{albert}
6560 as well as @file{/var} file system on all machines.
6562 By default @code{restore} will start restoring files from the lowest
6563 available dump level (usually zero) and will continue through
6564 all available dump levels. There may be situations where such a
6565 thorough restore is not necessary. For example, you may wish to
6566 restore only files from the recent level one backup. To do so,
6567 use @option{--level} option, as shown in the example below:
6573 The full list of options accepted by @code{restore} follows:
6578 Restore all file systems and files specified in @file{backup-specs}
6580 @item -l @var{level}
6581 @itemx --level=@var{level}
6582 Start restoring from the given backup level, instead of the default 0.
6584 @item -v[@var{level}]
6585 @itemx --verbose[=@var{level}]
6586 Set verbosity level. The higher the level is, the more debugging
6587 information will be output during execution. Default @var{level}
6588 is 100, which means the highest debugging level.
6592 Display short help message and exit.
6596 Display information about the program's name, version, origin and legal
6597 status, all on standard output, and then exit successfully.
6600 You should start the restore script with the media containing the
6601 first volume of the archive mounted. The script will prompt for other
6602 volumes as they are needed. If the archive is on tape, you don't need
6603 to rewind the tape to to its beginning---if the tape head is
6604 positioned past the beginning of the archive, the script will rewind
6605 the tape as needed. @xref{Tape Positioning}, for a discussion of tape
6609 @strong{Warning:} The script will delete files from the active file
6610 system if they were not in the file system when the archive was made.
6613 @xref{Incremental Dumps}, for an explanation of how the script makes
6617 @chapter Choosing Files and Names for @command{tar}
6619 Certain options to @command{tar} enable you to specify a name for your
6620 archive. Other options let you decide which files to include or exclude
6621 from the archive, based on when or whether files were modified, whether
6622 the file names do or don't match specified patterns, or whether files
6623 are in specified directories.
6625 This chapter discusses these options in detail.
6628 * file:: Choosing the Archive's Name
6629 * Selecting Archive Members::
6630 * files:: Reading Names from a File
6631 * exclude:: Excluding Some Files
6632 * wildcards:: Wildcards Patterns and Matching
6633 * quoting styles:: Ways of Quoting Special Characters in Names
6634 * transform:: Modifying File and Member Names
6635 * after:: Operating Only on New Files
6636 * recurse:: Descending into Directories
6637 * one:: Crossing File System Boundaries
6641 @section Choosing and Naming Archive Files
6643 @cindex Naming an archive
6644 @cindex Archive Name
6645 @cindex Choosing an archive file
6646 @cindex Where is the archive?
6648 By default, @command{tar} uses an archive file name that was compiled when
6649 it was built on the system; usually this name refers to some physical
6650 tape drive on the machine. However, the person who installed @command{tar}
6651 on the system may not have set the default to a meaningful value as far as
6652 most users are concerned. As a result, you will usually want to tell
6653 @command{tar} where to find (or create) the archive. The
6654 @option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
6655 option allows you to either specify or name a file to use as the archive
6656 instead of the default archive file location.
6659 @xopindex{file, short description}
6660 @item --file=@var{archive-name}
6661 @itemx -f @var{archive-name}
6662 Name the archive to create or operate on. Use in conjunction with
6666 For example, in this @command{tar} command,
6669 $ @kbd{tar -cvf collection.tar blues folk jazz}
6673 @file{collection.tar} is the name of the archive. It must directly
6674 follow the @option{-f} option, since whatever directly follows @option{-f}
6675 @emph{will} end up naming the archive. If you neglect to specify an
6676 archive name, you may end up overwriting a file in the working directory
6677 with the archive you create since @command{tar} will use this file's name
6678 for the archive name.
6680 An archive can be saved as a file in the file system, sent through a
6681 pipe or over a network, or written to an I/O device such as a tape,
6682 floppy disk, or CD write drive.
6684 @cindex Writing new archives
6685 @cindex Archive creation
6686 If you do not name the archive, @command{tar} uses the value of the
6687 environment variable @env{TAPE} as the file name for the archive. If
6688 that is not available, @command{tar} uses a default, compiled-in archive
6689 name, usually that for tape unit zero (i.e., @file{/dev/tu00}).
6691 @cindex Standard input and output
6692 @cindex tar to standard input and output
6693 If you use @file{-} as an @var{archive-name}, @command{tar} reads the
6694 archive from standard input (when listing or extracting files), or
6695 writes it to standard output (when creating an archive). If you use
6696 @file{-} as an @var{archive-name} when modifying an archive,
6697 @command{tar} reads the original archive from its standard input and
6698 writes the entire new archive to its standard output.
6700 The following example is a convenient way of copying directory
6701 hierarchy from @file{sourcedir} to @file{targetdir}.
6704 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)}
6707 The @option{-C} option allows to avoid using subshells:
6710 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xpf -}
6713 In both examples above, the leftmost @command{tar} invocation archives
6714 the contents of @file{sourcedir} to the standard output, while the
6715 rightmost one reads this archive from its standard input and
6716 extracts it. The @option{-p} option tells it to restore permissions
6717 of the extracted files.
6719 @cindex Remote devices
6720 @cindex tar to a remote device
6722 To specify an archive file on a device attached to a remote machine,
6726 @kbd{--file=@var{hostname}:/@var{dev}/@var{file-name}}
6730 @command{tar} will complete the remote connection, if possible, and
6731 prompt you for a username and password. If you use
6732 @option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
6733 will complete the remote connection, if possible, using your username
6734 as the username on the remote machine.
6736 @cindex Local and remote archives
6737 @anchor{local and remote archives}
6738 If the archive file name includes a colon (@samp{:}), then it is assumed
6739 to be a file on another machine. If the archive file is
6740 @samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the
6741 host @var{host}. The remote host is accessed using the @command{rsh}
6742 program, with a username of @var{user}. If the username is omitted
6743 (along with the @samp{@@} sign), then your user name will be used.
6744 (This is the normal @command{rsh} behavior.) It is necessary for the
6745 remote machine, in addition to permitting your @command{rsh} access, to
6746 have the @file{rmt} program installed (This command is included in
6747 the @GNUTAR{} distribution and by default is installed under
6748 @file{@var{prefix}/libexec/rmt}, were @var{prefix} means your
6749 installation prefix). If you need to use a file whose name includes a
6750 colon, then the remote tape drive behavior
6751 can be inhibited by using the @option{--force-local} option.
6753 When the archive is being created to @file{/dev/null}, @GNUTAR{}
6754 tries to minimize input and output operations. The Amanda backup
6755 system, when used with @GNUTAR{}, has an initial sizing pass which
6758 @node Selecting Archive Members
6759 @section Selecting Archive Members
6760 @cindex Specifying files to act on
6761 @cindex Specifying archive members
6763 @dfn{File Name arguments} specify which files in the file system
6764 @command{tar} operates on, when creating or adding to an archive, or which
6765 archive members @command{tar} operates on, when reading or deleting from
6766 an archive. @xref{Operations}.
6768 To specify file names, you can include them as the last arguments on
6769 the command line, as follows:
6771 @kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
6774 If a file name begins with dash (@samp{-}), precede it with
6775 @option{--add-file} option to prevent it from being treated as an
6778 @anchor{input name quoting}
6779 By default @GNUTAR{} attempts to @dfn{unquote} each file or member
6780 name, replacing @dfn{escape sequences} according to the following
6783 @multitable @columnfractions 0.20 0.60
6784 @headitem Escape @tab Replaced with
6785 @item \a @tab Audible bell (@acronym{ASCII} 7)
6786 @item \b @tab Backspace (@acronym{ASCII} 8)
6787 @item \f @tab Form feed (@acronym{ASCII} 12)
6788 @item \n @tab New line (@acronym{ASCII} 10)
6789 @item \r @tab Carriage return (@acronym{ASCII} 13)
6790 @item \t @tab Horizontal tabulation (@acronym{ASCII} 9)
6791 @item \v @tab Vertical tabulation (@acronym{ASCII} 11)
6792 @item \? @tab @acronym{ASCII} 127
6793 @item \@var{n} @tab @acronym{ASCII} @var{n} (@var{n} should be an octal number
6797 A backslash followed by any other symbol is retained.
6799 This default behavior is controlled by the following command line
6805 Enable unquoting input file or member names (default).
6809 Disable unquoting input file or member names.
6812 If you specify a directory name as a file name argument, all the files
6813 in that directory are operated on by @command{tar}.
6815 If you do not specify files, @command{tar} behavior differs depending
6816 on the operation mode as described below:
6818 When @command{tar} is invoked with @option{--create} (@option{-c}),
6819 @command{tar} will stop immediately, reporting the following:
6823 $ @kbd{tar cf a.tar}
6824 tar: Cowardly refusing to create an empty archive
6825 Try `tar --help' or `tar --usage' for more information.
6829 If you specify either @option{--list} (@option{-t}) or
6830 @option{--extract} (@option{--get}, @option{-x}), @command{tar}
6831 operates on all the archive members in the archive.
6833 If run with @option{--diff} option, tar will compare the archive with
6834 the contents of the current working directory.
6836 If you specify any other operation, @command{tar} does nothing.
6838 By default, @command{tar} takes file names from the command line. However,
6839 there are other ways to specify file or member names, or to modify the
6840 manner in which @command{tar} selects the files or members upon which to
6841 operate. In general, these methods work both for specifying the names
6842 of files and archive members.
6845 @section Reading Names from a File
6847 @cindex Reading file names from a file
6848 @cindex Lists of file names
6849 @cindex File Name arguments, alternatives
6850 @cindex @command{find}, using with @command{tar}
6851 Instead of giving the names of files or archive members on the command
6852 line, you can put the names into a file, and then use the
6853 @option{--files-from=@var{file-of-names}} (@option{-T
6854 @var{file-of-names}}) option to @command{tar}. Give the name of the
6855 file which contains the list of files to include as the argument to
6856 @option{--files-from}. In the list, the file names should be separated by
6857 newlines. You will frequently use this option when you have generated
6858 the list of files to archive with the @command{find} utility.
6862 @item --files-from=@var{file-name}
6863 @itemx -T @var{file-name}
6864 Get names to extract or create from file @var{file-name}.
6867 If you give a single dash as a file name for @option{--files-from}, (i.e.,
6868 you specify either @code{--files-from=-} or @code{-T -}), then the file
6869 names are read from standard input.
6871 Unless you are running @command{tar} with @option{--create}, you can not use
6872 both @code{--files-from=-} and @code{--file=-} (@code{-f -}) in the same
6875 Any number of @option{-T} options can be given in the command line.
6877 The following example shows how to use @command{find} to generate a list of
6878 files smaller than 400K in length and put that list into a file
6879 called @file{small-files}. You can then use the @option{-T} option to
6880 @command{tar} to specify the files from that file, @file{small-files}, to
6881 create the archive @file{little.tgz}. (The @option{-z} option to
6882 @command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for
6886 $ @kbd{find . -size -400 -print > small-files}
6887 $ @kbd{tar -c -v -z -T small-files -f little.tgz}
6891 In the file list given by @option{-T} option, any file name beginning
6892 with @samp{-} character is considered a @command{tar} option and is
6893 processed accordingly.@footnote{Versions of @GNUTAR{} up to 1.15.1
6894 recognized only @option{-C} option in file lists, and only if the
6895 option and its argument occupied two consecutive lines.} For example,
6896 the common use of this feature is to change to another directory by
6897 specifying @option{-C} option:
6907 $ @kbd{tar -c -f foo.tar --files-from list}
6912 In this example, @command{tar} will first switch to @file{/etc}
6913 directory and add files @file{passwd} and @file{hosts} to the
6914 archive. Then it will change to @file{/lib} directory and will archive
6915 the file @file{libc.a}. Thus, the resulting archive @file{foo.tar} will
6920 $ @kbd{tar tf foo.tar}
6928 @xopindex{directory, using in @option{--files-from} argument}
6929 Notice that the option parsing algorithm used with @option{-T} is
6930 stricter than the one used by shell. Namely, when specifying option
6931 arguments, you should observe the following rules:
6935 When using short (single-letter) option form, its argument must
6936 immediately follow the option letter, without any intervening
6937 whitespace. For example: @code{-Cdir}.
6940 When using long option form, the option argument must be separated
6941 from the option by a single equal sign. No whitespace is allowed on
6942 any side of the equal sign. For example: @code{--directory=dir}.
6945 For both short and long option forms, the option argument can be given
6946 on the next line after the option name, e.g.:
6967 If you happen to have a file whose name starts with @samp{-},
6968 precede it with @option{--add-file} option to prevent it from
6969 being recognized as an option. For example: @code{--add-file=--my-file}.
6976 @subsection @code{NUL} Terminated File Names
6978 @cindex File names, terminated by @code{NUL}
6979 @cindex @code{NUL} terminated file names
6980 The @option{--null} option causes
6981 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
6982 to read file names terminated by a @code{NUL} instead of a newline, so
6983 files whose names contain newlines can be archived using
6984 @option{--files-from}.
6987 @xopindex{null, described}
6989 Only consider @code{NUL} terminated file names, instead of files that
6990 terminate in a newline.
6992 @xopindex{no-null, described}
6994 Undo the effect of any previous @option{--null} option.
6997 The @option{--null} option is just like the one in @acronym{GNU}
6998 @command{xargs} and @command{cpio}, and is useful with the
6999 @option{-print0} predicate of @acronym{GNU} @command{find}. In
7000 @command{tar}, @option{--null} also disables special handling for
7001 file names that begin with dash.
7003 This example shows how to use @command{find} to generate a list of files
7004 larger than 800K in length and put that list into a file called
7005 @file{long-files}. The @option{-print0} option to @command{find} is just
7006 like @option{-print}, except that it separates files with a @code{NUL}
7007 rather than with a newline. You can then run @command{tar} with both the
7008 @option{--null} and @option{-T} options to specify that @command{tar} get the
7009 files from that file, @file{long-files}, to create the archive
7010 @file{big.tgz}. The @option{--null} option to @command{tar} will cause
7011 @command{tar} to recognize the @code{NUL} separator between files.
7014 $ @kbd{find . -size +800 -print0 > long-files}
7015 $ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
7018 The @option{--no-null} option can be used if you need to read both
7019 zero-terminated and newline-terminated files on the same command line.
7020 For example, if @file{flist} is a newline-terminated file, then the
7021 following command can be used to combine it with the above command:
7025 $ @kbd{find . -size +800 -print0 |
7026 tar -c -f big.tar --null -T - --no-null -T flist}
7030 This example uses short options for typographic reasons, to avoid
7033 @GNUTAR is able to automatically detect null-terminated file lists, so
7034 it is safe to use them even without the @option{--null} option. In
7035 this case @command{tar} will print a warning and continue reading such
7036 a file as if @option{--null} were actually given:
7040 $ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
7041 tar: -: file name read contains nul character
7045 The null terminator, however, remains in effect only for this
7046 particular file, any following @option{-T} options will assume
7047 newline termination. Of course, the null autodetection applies
7048 to these eventual surplus @option{-T} options as well.
7051 @section Excluding Some Files
7053 @cindex File names, excluding files by
7054 @cindex Excluding files by name and pattern
7055 @cindex Excluding files by file system
7057 @opindex exclude-from
7058 To avoid operating on files whose names match a particular pattern,
7059 use the @option{--exclude} or @option{--exclude-from} options.
7063 @item --exclude=@var{pattern}
7064 Causes @command{tar} to ignore files that match the @var{pattern}.
7068 The @option{--exclude=@var{pattern}} option prevents any file or
7069 member whose name matches the shell wildcard (@var{pattern}) from
7071 For example, to create an archive with all the contents of the directory
7072 @file{src} except for files whose names end in @file{.o}, use the
7073 command @samp{tar -cf src.tar --exclude='*.o' src}.
7075 You may give multiple @option{--exclude} options.
7078 @opindex exclude-from
7079 @item --exclude-from=@var{file}
7080 @itemx -X @var{file}
7081 Causes @command{tar} to ignore files that match the patterns listed in
7085 @findex exclude-from
7086 Use the @option{--exclude-from} option to read a
7087 list of patterns, one per line, from @var{file}; @command{tar} will
7088 ignore files matching those patterns. Thus if @command{tar} is
7089 called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a
7090 single line @file{*.o}, no files whose names end in @file{.o} will be
7091 added to the archive.
7093 Notice, that lines from @var{file} are read verbatim. One of the
7094 frequent errors is leaving some extra whitespace after a file name,
7095 which is difficult to catch using text editors.
7097 However, empty lines are OK.
7100 @cindex version control system, excluding files
7101 @cindex VCS, excluding files
7102 @cindex SCCS, excluding files
7103 @cindex RCS, excluding files
7104 @cindex CVS, excluding files
7105 @cindex SVN, excluding files
7106 @cindex git, excluding files
7107 @cindex Bazaar, excluding files
7108 @cindex Arch, excluding files
7109 @cindex Mercurial, excluding files
7110 @cindex Darcs, excluding files
7111 @opindex exclude-vcs
7113 Exclude files and directories used by following version control
7114 systems: @samp{CVS}, @samp{RCS}, @samp{SCCS}, @samp{SVN}, @samp{Arch},
7115 @samp{Bazaar}, @samp{Mercurial}, and @samp{Darcs}.
7117 As of version @value{VERSION}, the following files are excluded:
7120 @item @file{CVS/}, and everything under it
7121 @item @file{RCS/}, and everything under it
7122 @item @file{SCCS/}, and everything under it
7123 @item @file{.git/}, and everything under it
7124 @item @file{.gitignore}
7125 @item @file{.cvsignore}
7126 @item @file{.svn/}, and everything under it
7127 @item @file{.arch-ids/}, and everything under it
7128 @item @file{@{arch@}/}, and everything under it
7129 @item @file{=RELEASE-ID}
7130 @item @file{=meta-update}
7131 @item @file{=update}
7133 @item @file{.bzrignore}
7134 @item @file{.bzrtags}
7136 @item @file{.hgignore}
7137 @item @file{.hgrags}
7141 @opindex exclude-backups
7142 @item --exclude-backups
7143 Exclude backup and lock files. This option causes exclusion of files
7144 that match the following shell globbing patterns:
7154 @findex exclude-caches
7155 When creating an archive, the @option{--exclude-caches} option family
7156 causes @command{tar} to exclude all directories that contain a @dfn{cache
7157 directory tag}. A cache directory tag is a short file with the
7158 well-known name @file{CACHEDIR.TAG} and having a standard header
7159 specified in @url{http://www.brynosaurus.com/cachedir/spec.html}.
7160 Various applications write cache directory tags into directories they
7161 use to hold regenerable, non-precious data, so that such data can be
7162 more easily excluded from backups.
7164 There are three @samp{exclude-caches} options, each providing a different
7165 exclusion semantics:
7168 @opindex exclude-caches
7169 @item --exclude-caches
7170 Do not archive the contents of the directory, but archive the
7171 directory itself and the @file{CACHEDIR.TAG} file.
7173 @opindex exclude-caches-under
7174 @item --exclude-caches-under
7175 Do not archive the contents of the directory, nor the
7176 @file{CACHEDIR.TAG} file, archive only the directory itself.
7178 @opindex exclude-caches-all
7179 @item --exclude-caches-all
7180 Omit directories containing @file{CACHEDIR.TAG} file entirely.
7184 Another option family, @option{--exclude-tag}, provides a generalization of
7185 this concept. It takes a single argument, a file name to look for.
7186 Any directory that contains this file will be excluded from the dump.
7187 Similarly to @samp{exclude-caches}, there are three options in this
7191 @opindex exclude-tag
7192 @item --exclude-tag=@var{file}
7193 Do not dump the contents of the directory, but dump the
7194 directory itself and the @var{file}.
7196 @opindex exclude-tag-under
7197 @item --exclude-tag-under=@var{file}
7198 Do not dump the contents of the directory, nor the
7199 @var{file}, archive only the directory itself.
7201 @opindex exclude-tag-all
7202 @item --exclude-tag-all=@var{file}
7203 Omit directories containing @var{file} file entirely.
7206 Multiple @option{--exclude-tag*} options can be given.
7208 For example, given this directory:
7223 The @option{--exclude-tag} will produce the following:
7226 $ @kbd{tar -cf archive.tar --exclude-tag=tagfile -v dir}
7231 tar: dir/folk/: contains a cache directory tag tagfile;
7236 Both the @file{dir/folk} directory and its tagfile are preserved in
7237 the archive, however the rest of files in this directory are not.
7239 Now, using the @option{--exclude-tag-under} option will exclude
7240 @file{tagfile} from the dump, while still preserving the directory
7241 itself, as shown in this example:
7244 $ @kbd{tar -cf archive.tar --exclude-tag-under=tagfile -v dir}
7249 ./tar: dir/folk/: contains a cache directory tag tagfile;
7253 Finally, using @option{--exclude-tag-all} omits the @file{dir/folk}
7257 $ @kbd{tar -cf archive.tar --exclude-tag-all=tagfile -v dir}
7261 ./tar: dir/folk/: contains a cache directory tag tagfile;
7262 directory not dumped
7266 * problems with exclude::
7269 @node problems with exclude
7270 @unnumberedsubsec Problems with Using the @code{exclude} Options
7272 @xopindex{exclude, potential problems with}
7273 Some users find @samp{exclude} options confusing. Here are some common
7278 The main operating mode of @command{tar} does not act on a file name
7279 explicitly listed on the command line, if one of its file name
7280 components is excluded. In the example above, if
7281 you create an archive and exclude files that end with @samp{*.o}, but
7282 explicitly name the file @samp{dir.o/foo} after all the options have been
7283 listed, @samp{dir.o/foo} will be excluded from the archive.
7286 You can sometimes confuse the meanings of @option{--exclude} and
7287 @option{--exclude-from}. Be careful: use @option{--exclude} when files
7288 to be excluded are given as a pattern on the command line. Use
7289 @option{--exclude-from} to introduce the name of a file which contains
7290 a list of patterns, one per line; each of these patterns can exclude
7291 zero, one, or many files.
7294 When you use @option{--exclude=@var{pattern}}, be sure to quote the
7295 @var{pattern} parameter, so @GNUTAR{} sees wildcard characters
7296 like @samp{*}. If you do not do this, the shell might expand the
7297 @samp{*} itself using files at hand, so @command{tar} might receive a
7298 list of files instead of one pattern, or none at all, making the
7299 command somewhat illegal. This might not correspond to what you want.
7304 $ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}}
7312 $ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
7316 You must use use shell syntax, or globbing, rather than @code{regexp}
7317 syntax, when using exclude options in @command{tar}. If you try to use
7318 @code{regexp} syntax to describe files to be excluded, your command
7322 @FIXME{The change in semantics must have occurred before 1.11,
7323 so I doubt if it is worth mentioning at all. Anyway, should at
7324 least specify in which version the semantics changed.}
7325 In earlier versions of @command{tar}, what is now the
7326 @option{--exclude-from} option was called @option{--exclude} instead.
7327 Now, @option{--exclude} applies to patterns listed on the command
7328 line and @option{--exclude-from} applies to patterns listed in a
7334 @section Wildcards Patterns and Matching
7336 @dfn{Globbing} is the operation by which @dfn{wildcard} characters,
7337 @samp{*} or @samp{?} for example, are replaced and expanded into all
7338 existing files matching the given pattern. @GNUTAR{} can use wildcard
7339 patterns for matching (or globbing) archive members when extracting
7340 from or listing an archive. Wildcard patterns are also used for
7341 verifying volume labels of @command{tar} archives. This section has the
7342 purpose of explaining wildcard syntax for @command{tar}.
7344 @FIXME{the next few paragraphs need work.}
7346 A @var{pattern} should be written according to shell syntax, using wildcard
7347 characters to effect globbing. Most characters in the pattern stand
7348 for themselves in the matched string, and case is significant: @samp{a}
7349 will match only @samp{a}, and not @samp{A}. The character @samp{?} in the
7350 pattern matches any single character in the matched string. The character
7351 @samp{*} in the pattern matches zero, one, or more single characters in
7352 the matched string. The character @samp{\} says to take the following
7353 character of the pattern @emph{literally}; it is useful when one needs to
7354 match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves.
7356 The character @samp{[}, up to the matching @samp{]}, introduces a character
7357 class. A @dfn{character class} is a list of acceptable characters
7358 for the next single character of the matched string. For example,
7359 @samp{[abcde]} would match any of the first five letters of the alphabet.
7360 Note that within a character class, all of the ``special characters''
7361 listed above other than @samp{\} lose their special meaning; for example,
7362 @samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\},
7363 @samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints,
7364 the characters @samp{-} and @samp{]} must either come @emph{first} or
7365 @emph{last} in a character class.)
7367 @cindex Excluding characters from a character class
7368 @cindex Character class, excluding characters from
7369 If the first character of the class after the opening @samp{[}
7370 is @samp{!} or @samp{^}, then the meaning of the class is reversed.
7371 Rather than listing character to match, it lists those characters which
7372 are @emph{forbidden} as the next single character of the matched string.
7374 Other characters of the class stand for themselves. The special
7375 construction @samp{[@var{a}-@var{e}]}, using an hyphen between two
7376 letters, is meant to represent all characters between @var{a} and
7379 @FIXME{need to add a sentence or so here to make this clear for those
7380 who don't have dan around.}
7382 Periods (@samp{.}) or forward slashes (@samp{/}) are not considered
7383 special for wildcard matches. However, if a pattern completely matches
7384 a directory prefix of a matched string, then it matches the full matched
7385 string: thus, excluding a directory also excludes all the files beneath it.
7388 * controlling pattern-matching::
7391 @node controlling pattern-matching
7392 @unnumberedsubsec Controlling Pattern-Matching
7394 For the purposes of this section, we call @dfn{exclusion members} all
7395 member names obtained while processing @option{--exclude} and
7396 @option{--exclude-from} options, and @dfn{inclusion members} those
7397 member names that were given in the command line or read from the file
7398 specified with @option{--files-from} option.
7400 These two pairs of member lists are used in the following operations:
7401 @option{--diff}, @option{--extract}, @option{--list},
7404 There are no inclusion members in create mode (@option{--create} and
7405 @option{--append}), since in this mode the names obtained from the
7406 command line refer to @emph{files}, not archive members.
7408 By default, inclusion members are compared with archive members
7409 literally @footnote{Notice that earlier @GNUTAR{} versions used
7410 globbing for inclusion members, which contradicted to UNIX98
7411 specification and was not documented. @xref{Changes}, for more
7412 information on this and other changes.} and exclusion members are
7413 treated as globbing patterns. For example:
7417 $ @kbd{tar tf foo.tar}
7422 # @i{Member names are used verbatim:}
7423 $ @kbd{tar -xf foo.tar -v '[remarks]'}
7425 # @i{Exclude member names are globbed:}
7426 $ @kbd{tar -xf foo.tar -v --exclude '*.c'}
7432 This behavior can be altered by using the following options:
7437 Treat all member names as wildcards.
7439 @opindex no-wildcards
7440 @item --no-wildcards
7441 Treat all member names as literal strings.
7444 Thus, to extract files whose names end in @samp{.c}, you can use:
7447 $ @kbd{tar -xf foo.tar -v --wildcards '*.c'}
7453 Notice quoting of the pattern to prevent the shell from interpreting
7456 The effect of @option{--wildcards} option is canceled by
7457 @option{--no-wildcards}. This can be used to pass part of
7458 the command line arguments verbatim and other part as globbing
7459 patterns. For example, the following invocation:
7462 $ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'}
7466 instructs @command{tar} to extract from @file{foo.tar} all files whose
7467 names end in @samp{.txt} and the file named @file{[remarks]}.
7469 Normally, a pattern matches a name if an initial subsequence of the
7470 name's components matches the pattern, where @samp{*}, @samp{?}, and
7471 @samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
7472 and wildcards can match @samp{/}.
7474 Other than optionally stripping leading @samp{/} from names
7475 (@pxref{absolute}), patterns and names are used as-is. For
7476 example, trailing @samp{/} is not trimmed from a user-specified name
7477 before deciding whether to exclude it.
7479 However, this matching procedure can be altered by the options listed
7480 below. These options accumulate. For example:
7483 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
7487 ignores case when excluding @samp{makefile}, but not when excluding
7492 @opindex no-anchored
7494 @itemx --no-anchored
7495 If anchored, a pattern must match an initial subsequence
7496 of the name's components. Otherwise, the pattern can match any
7497 subsequence. Default is @option{--no-anchored} for exclusion members
7498 and @option{--anchored} inclusion members.
7500 @opindex ignore-case
7501 @opindex no-ignore-case
7503 @itemx --no-ignore-case
7504 When ignoring case, upper-case patterns match lower-case names and vice versa.
7505 When not ignoring case (the default), matching is case-sensitive.
7507 @opindex wildcards-match-slash
7508 @opindex no-wildcards-match-slash
7509 @item --wildcards-match-slash
7510 @itemx --no-wildcards-match-slash
7511 When wildcards match slash (the default for exclusion members), a
7512 wildcard like @samp{*} in the pattern can match a @samp{/} in the
7513 name. Otherwise, @samp{/} is matched only by @samp{/}.
7517 The @option{--recursion} and @option{--no-recursion} options
7518 (@pxref{recurse}) also affect how member patterns are interpreted. If
7519 recursion is in effect, a pattern matches a name if it matches any of
7520 the name's parent directories.
7522 The following table summarizes pattern-matching default values:
7524 @multitable @columnfractions .3 .7
7525 @headitem Members @tab Default settings
7526 @item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash}
7527 @item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash}
7530 @node quoting styles
7531 @section Quoting Member Names
7533 When displaying member names, @command{tar} takes care to avoid
7534 ambiguities caused by certain characters. This is called @dfn{name
7535 quoting}. The characters in question are:
7538 @item Non-printable control characters:
7539 @anchor{escape sequences}
7540 @multitable @columnfractions 0.20 0.10 0.60
7541 @headitem Character @tab @acronym{ASCII} @tab Character name
7542 @item \a @tab 7 @tab Audible bell
7543 @item \b @tab 8 @tab Backspace
7544 @item \f @tab 12 @tab Form feed
7545 @item \n @tab 10 @tab New line
7546 @item \r @tab 13 @tab Carriage return
7547 @item \t @tab 9 @tab Horizontal tabulation
7548 @item \v @tab 11 @tab Vertical tabulation
7551 @item Space (@acronym{ASCII} 32)
7553 @item Single and double quotes (@samp{'} and @samp{"})
7555 @item Backslash (@samp{\})
7558 The exact way @command{tar} uses to quote these characters depends on
7559 the @dfn{quoting style}. The default quoting style, called
7560 @dfn{escape} (see below), uses backslash notation to represent control
7561 characters, space and backslash. Using this quoting style, control
7562 characters are represented as listed in column @samp{Character} in the
7563 above table, a space is printed as @samp{\ } and a backslash as @samp{\\}.
7565 @GNUTAR{} offers seven distinct quoting styles, which can be selected
7566 using @option{--quoting-style} option:
7569 @item --quoting-style=@var{style}
7570 @opindex quoting-style
7572 Sets quoting style. Valid values for @var{style} argument are:
7573 literal, shell, shell-always, c, escape, locale, clocale.
7576 These styles are described in detail below. To illustrate their
7577 effect, we will use an imaginary tar archive @file{arch.tar}
7578 containing the following members:
7582 # 1. Contains horizontal tabulation character.
7584 # 2. Contains newline character
7587 # 3. Contains a space
7589 # 4. Contains double quotes
7591 # 5. Contains single quotes
7593 # 6. Contains a backslash character:
7598 Here is how usual @command{ls} command would have listed them, if they
7599 had existed in the current working directory:
7617 No quoting, display each character as is:
7621 $ @kbd{tar tf arch.tar --quoting-style=literal}
7634 Display characters the same way Bourne shell does:
7635 control characters, except @samp{\t} and @samp{\n}, are printed using
7636 backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a
7637 single quote is printed as @samp{\'}. If a name contains any quoted
7638 characters, it is enclosed in single quotes. In particular, if a name
7639 contains single quotes, it is printed as several single-quoted strings:
7643 $ @kbd{tar tf arch.tar --quoting-style=shell}
7646 './a'\''single'\''quote'
7656 Same as @samp{shell}, but the names are always enclosed in single
7661 $ @kbd{tar tf arch.tar --quoting-style=shell-always}
7664 './a'\''single'\''quote'
7674 Use the notation of the C programming language. All names are
7675 enclosed in double quotes. Control characters are quoted using
7676 backslash notations, double quotes are represented as @samp{\"},
7677 backslash characters are represented as @samp{\\}. Single quotes and
7678 spaces are not quoted:
7682 $ @kbd{tar tf arch.tar --quoting-style=c}
7686 "./a\"double\"quote"
7694 Control characters are printed using backslash notation, a space is
7695 printed as @samp{\ } and a backslash as @samp{\\}. This is the
7696 default quoting style, unless it was changed when configured the
7701 $ @kbd{tar tf arch.tar --quoting-style=escape}
7713 Control characters, single quote and backslash are printed using
7714 backslash notation. All names are quoted using left and right
7715 quotation marks, appropriate to the current locale. If it does not
7716 define quotation marks, use @samp{`} as left and @samp{'} as right
7717 quotation marks. Any occurrences of the right quotation mark in a
7718 name are escaped with @samp{\}, for example:
7724 $ @kbd{tar tf arch.tar --quoting-style=locale}
7727 `./a\'single\'quote'
7736 Same as @samp{locale}, but @samp{"} is used for both left and right
7737 quotation marks, if not provided by the currently selected locale:
7741 $ @kbd{tar tf arch.tar --quoting-style=clocale}
7745 "./a\"double\"quote"
7753 You can specify which characters should be quoted in addition to those
7754 implied by the current quoting style:
7757 @item --quote-chars=@var{string}
7758 Always quote characters from @var{string}, even if the selected
7759 quoting style would not quote them.
7762 For example, using @samp{escape} quoting (compare with the usual
7763 escape listing above):
7767 $ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'}
7778 To disable quoting of such additional characters, use the following
7782 @item --no-quote-chars=@var{string}
7783 Remove characters listed in @var{string} from the list of quoted
7784 characters set by the previous @option{--quote-chars} option.
7787 This option is particularly useful if you have added
7788 @option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS})
7789 and wish to disable it for the current invocation.
7791 Note, that @option{--no-quote-chars} does @emph{not} disable those
7792 characters that are quoted by default in the selected quoting style.
7795 @section Modifying File and Member Names
7797 @command{Tar} archives contain detailed information about files stored
7798 in them and full file names are part of that information. When
7799 storing file to an archive, its file name is recorded in it,
7800 along with the actual file contents. When restoring from an archive,
7801 a file is created on disk with exactly the same name as that stored
7802 in the archive. In the majority of cases this is the desired behavior
7803 of a file archiver. However, there are some cases when it is not.
7805 First of all, it is often unsafe to extract archive members with
7806 absolute file names or those that begin with a @file{../}. @GNUTAR{}
7807 takes special precautions when extracting such names and provides a
7808 special option for handling them, which is described in
7811 Secondly, you may wish to extract file names without some leading
7812 directory components, or with otherwise modified names. In other
7813 cases it is desirable to store files under differing names in the
7816 @GNUTAR{} provides several options for these needs.
7819 @opindex strip-components
7820 @item --strip-components=@var{number}
7821 Strip given @var{number} of leading components from file names before
7825 For example, suppose you have archived whole @file{/usr} hierarchy to
7826 a tar archive named @file{usr.tar}. Among other files, this archive
7827 contains @file{usr/include/stdlib.h}, which you wish to extract to
7828 the current working directory. To do so, you type:
7831 $ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h}
7834 The option @option{--strip=2} instructs @command{tar} to strip the
7835 two leading components (@file{usr/} and @file{include/}) off the file
7838 If you add the @option{--verbose} (@option{-v}) option to the invocation
7839 above, you will note that the verbose listing still contains the
7840 full file name, with the two removed components still in place. This
7841 can be inconvenient, so @command{tar} provides a special option for
7842 altering this behavior:
7844 @anchor{show-transformed-names}
7846 @opindex show-transformed-names
7847 @item --show-transformed-names
7848 Display file or member names with all requested transformations
7857 $ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h}
7858 usr/include/stdlib.h
7859 $ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h}
7864 Notice that in both cases the file @file{stdlib.h} is extracted to the
7865 current working directory, @option{--show-transformed-names} affects
7866 only the way its name is displayed.
7868 This option is especially useful for verifying whether the invocation
7869 will have the desired effect. Thus, before running
7872 $ @kbd{tar -x --strip=@var{n}}
7876 it is often advisable to run
7879 $ @kbd{tar -t -v --show-transformed --strip=@var{n}}
7883 to make sure the command will produce the intended results.
7885 In case you need to apply more complex modifications to the file name,
7886 @GNUTAR{} provides a general-purpose transformation option:
7891 @item --transform=@var{expression}
7892 @itemx --xform=@var{expression}
7893 Modify file names using supplied @var{expression}.
7897 The @var{expression} is a @command{sed}-like replace expression of the
7901 s/@var{regexp}/@var{replace}/[@var{flags}]
7905 where @var{regexp} is a @dfn{regular expression}, @var{replace} is a
7906 replacement for each file name part that matches @var{regexp}. Both
7907 @var{regexp} and @var{replace} are described in detail in
7908 @ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
7910 Any delimiter can be used in lieue of @samp{/}, the only requirement being
7911 that it be used consistently throughout the expression. For example,
7912 the following two expressions are equivalent:
7921 Changing delimiters is often useful when the @var{regex} contains
7922 slashes. For example, it is more convenient to write @code{s,/,-,} than
7925 As in @command{sed}, you can give several replace expressions,
7926 separated by a semicolon.
7928 Supported @var{flags} are:
7932 Apply the replacement to @emph{all} matches to the @var{regexp}, not
7936 Use case-insensitive matching
7939 @var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
7940 regexps, Extended regular expressions, Extended regular expressions,
7944 Only replace the @var{number}th match of the @var{regexp}.
7946 Note: the @acronym{POSIX} standard does not specify what should happen
7947 when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
7948 follows the GNU @command{sed} implementation in this regard, so
7949 the interaction is defined to be: ignore matches before the
7950 @var{number}th, and then match and replace all matches from the
7955 In addition, several @dfn{transformation scope} flags are supported,
7956 that control to what files transformations apply. These are:
7960 Apply transformation to regular archive members.
7963 Do not apply transformation to regular archive members.
7966 Apply transformation to symbolic link targets.
7969 Do not apply transformation to symbolic link targets.
7972 Apply transformation to hard link targets.
7975 Do not apply transformation to hard link targets.
7978 Default is @samp{rsh}, which means to apply tranformations to both archive
7979 members and targets of symbolic and hard links.
7981 Default scope flags can also be changed using @samp{flags=} statement
7982 in the transform expression. The flags set this way remain in force
7983 until next @samp{flags=} statement or end of expression, whichever
7984 occurs first. For example:
7987 --transform 'flags=S;s|^|/usr/local/|'
7990 Here are several examples of @option{--transform} usage:
7993 @item Extract @file{usr/} hierarchy into @file{usr/local/}:
7996 $ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar}
7999 @item Strip two leading directory components (equivalent to
8000 @option{--strip-components=2}):
8003 $ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
8006 @item Convert each file name to lower case:
8009 $ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
8012 @item Prepend @file{/prefix/} to each file name:
8015 $ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
8018 @item Archive the @file{/lib} directory, prepending @samp{/usr/local}
8019 to each archive member:
8022 $ @kbd{tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib}
8026 Notice the use of flags in the last example. The @file{/lib}
8027 directory often contains many symbolic links to files within it.
8028 It may look, for example, like this:
8032 drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
8033 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
8034 lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
8038 Using the expression @samp{s,^,/usr/local/,} would mean adding
8039 @samp{/usr/local} to both regular archive members and to link
8040 targets. In this case, @file{/lib/libc.so.6} would become:
8043 /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
8046 This is definitely not desired. To avoid this, the @samp{S} flag
8047 are used, which excludes symbolic link targets from filename
8048 transformations. The result is:
8051 $ @kbd{tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
8052 --show-transformed /lib}
8053 drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
8054 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
8055 lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 ->
8059 Unlike @option{--strip-components}, @option{--transform} can be used
8060 in any @GNUTAR{} operation mode. For example, the following command
8061 adds files to the archive while replacing the leading @file{usr/}
8062 component with @file{var/}:
8065 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /}
8068 To test @option{--transform} effect we suggest using
8069 @option{--show-transformed-names} option:
8072 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \
8073 --verbose --show-transformed-names /}
8076 If both @option{--strip-components} and @option{--transform} are used
8077 together, then @option{--transform} is applied first, and the required
8078 number of components is then stripped from its result.
8080 You can use as many @option{--transform} options in a single command
8081 line as you want. The specified expressions will then be applied in
8082 order of their appearance. For example, the following two invocations
8086 $ @kbd{tar -cf arch.tar --transform='s,/usr/var,/var/' \
8087 --transform='s,/usr/local,/usr/,'}
8088 $ @kbd{tar -cf arch.tar \
8089 --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'}
8093 @section Operating Only on New Files
8095 @cindex Excluding file by age
8096 @cindex Data Modification time, excluding files by
8097 @cindex Modification time, excluding files by
8098 @cindex Age, excluding files by
8099 The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
8100 @option{-N @var{date}}) option causes @command{tar} to only work on
8101 files whose data modification or status change times are newer than
8102 the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
8103 it is taken to be a file name; the data modification time of that file
8104 is used as the date. If you use this option when creating or appending
8105 to an archive, the archive will only include new files. If you use
8106 @option{--after-date} when extracting an archive, @command{tar} will
8107 only extract files newer than the @var{date} you specify.
8109 If you only want @command{tar} to make the date comparison based on
8110 modification of the file's data (rather than status
8111 changes), then use the @option{--newer-mtime=@var{date}} option.
8113 @cindex --after-date and --update compared
8114 @cindex --newer-mtime and --update compared
8115 You may use these options with any operation. Note that these options
8116 differ from the @option{--update} (@option{-u}) operation in that they
8117 allow you to specify a particular date against which @command{tar} can
8118 compare when deciding whether or not to archive the files.
8123 @item --after-date=@var{date}
8124 @itemx --newer=@var{date}
8125 @itemx -N @var{date}
8126 Only store files newer than @var{date}.
8128 Acts on files only if their data modification or status change times are
8129 later than @var{date}. Use in conjunction with any operation.
8131 If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
8132 name; the data modification time of that file is used as the date.
8134 @opindex newer-mtime
8135 @item --newer-mtime=@var{date}
8136 Acts like @option{--after-date}, but only looks at data modification times.
8139 These options limit @command{tar} to operate only on files which have
8140 been modified after the date specified. A file's status is considered to have
8141 changed if its contents have been modified, or if its owner,
8142 permissions, and so forth, have been changed. (For more information on
8143 how to specify a date, see @ref{Date input formats}; remember that the
8144 entire date argument must be quoted if it contains any spaces.)
8146 Gurus would say that @option{--after-date} tests both the data
8147 modification time (@code{mtime}, the time the contents of the file
8148 were last modified) and the status change time (@code{ctime}, the time
8149 the file's status was last changed: owner, permissions, etc.@:)
8150 fields, while @option{--newer-mtime} tests only the @code{mtime}
8153 To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
8154 @code{ctime} and processes the file if either one is more recent than
8155 @var{date}, while @option{--newer-mtime} only checks @code{mtime} and
8156 disregards @code{ctime}. Neither does it use @code{atime} (the last time the
8157 contents of the file were looked at).
8159 Date specifiers can have embedded spaces. Because of this, you may need
8160 to quote date arguments to keep the shell from parsing them as separate
8161 arguments. For example, the following command will add to the archive
8162 all the files modified less than two days ago:
8165 $ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'}
8168 When any of these options is used with the option @option{--verbose}
8169 (@pxref{verbose tutorial}) @GNUTAR{} will try to convert the specified
8170 date back to its textual representation and compare that with the
8171 one given with the option. If the two dates differ, @command{tar} will
8172 print a warning saying what date it will use. This is to help user
8173 ensure he is using the right date. For example:
8177 $ @kbd{tar -c -f archive.tar --after-date='10 days ago' .}
8178 tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
8184 @strong{Please Note:} @option{--after-date} and @option{--newer-mtime}
8185 should not be used for incremental backups. @xref{Incremental Dumps},
8186 for proper way of creating incremental backups.
8190 @section Descending into Directories
8191 @cindex Avoiding recursion in directories
8192 @cindex Descending directories, avoiding
8193 @cindex Directories, avoiding recursion
8194 @cindex Recursion in directories, avoiding
8196 Usually, @command{tar} will recursively explore all directories (either
8197 those given on the command line or through the @option{--files-from}
8198 option) for the various files they contain. However, you may not always
8199 want @command{tar} to act this way.
8201 @opindex no-recursion
8202 @cindex @command{find}, using with @command{tar}
8203 The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
8204 into specified directories. If you specify @option{--no-recursion}, you can
8205 use the @command{find} (@pxref{Top,, find, find, GNU Find Manual})
8206 utility for hunting through levels of directories to
8207 construct a list of file names which you could then pass to @command{tar}.
8208 @command{find} allows you to be more selective when choosing which files to
8209 archive; see @ref{files}, for more information on using @command{find} with
8213 @item --no-recursion
8214 Prevents @command{tar} from recursively descending directories.
8218 Requires @command{tar} to recursively descend directories.
8219 This is the default.
8222 When you use @option{--no-recursion}, @GNUTAR{} grabs
8223 directory entries themselves, but does not descend on them
8224 recursively. Many people use @command{find} for locating files they
8225 want to back up, and since @command{tar} @emph{usually} recursively
8226 descends on directories, they have to use the @samp{@w{-not -type d}}
8227 test in their @command{find} invocation (@pxref{Type, Type, Type test,
8228 find, Finding Files}), as they usually do not want all the files in a
8229 directory. They then use the @option{--files-from} option to archive
8230 the files located via @command{find}.
8232 The problem when restoring files archived in this manner is that the
8233 directories themselves are not in the archive; so the
8234 @option{--same-permissions} (@option{--preserve-permissions},
8235 @option{-p}) option does not affect them---while users might really
8236 like it to. Specifying @option{--no-recursion} is a way to tell
8237 @command{tar} to grab only the directory entries given to it, adding
8238 no new files on its own. To summarize, if you use @command{find} to
8239 create a list of files to be stored in an archive, use it as follows:
8243 $ @kbd{find @var{dir} @var{tests} | \
8244 tar -cf @var{archive} -T - --no-recursion}
8248 The @option{--no-recursion} option also applies when extracting: it
8249 causes @command{tar} to extract only the matched directory entries, not
8250 the files under those directories.
8252 The @option{--no-recursion} option also affects how globbing patterns
8253 are interpreted (@pxref{controlling pattern-matching}).
8255 The @option{--no-recursion} and @option{--recursion} options apply to
8256 later options and operands, and can be overridden by later occurrences
8257 of @option{--no-recursion} and @option{--recursion}. For example:
8260 $ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
8264 creates an archive with one entry for @file{grape}, and the recursive
8265 contents of @file{grape/concord}, but no entries under @file{grape}
8266 other than @file{grape/concord}.
8269 @section Crossing File System Boundaries
8270 @cindex File system boundaries, not crossing
8272 @command{tar} will normally automatically cross file system boundaries in
8273 order to archive files which are part of a directory tree. You can
8274 change this behavior by running @command{tar} and specifying
8275 @option{--one-file-system}. This option only affects files that are
8276 archived because they are in a directory that is being archived;
8277 @command{tar} will still archive files explicitly named on the command line
8278 or through @option{--files-from}, regardless of where they reside.
8281 @opindex one-file-system
8282 @item --one-file-system
8283 Prevents @command{tar} from crossing file system boundaries when
8284 archiving. Use in conjunction with any write operation.
8287 The @option{--one-file-system} option causes @command{tar} to modify its
8288 normal behavior in archiving the contents of directories. If a file in
8289 a directory is not on the same file system as the directory itself, then
8290 @command{tar} will not archive that file. If the file is a directory
8291 itself, @command{tar} will not archive anything beneath it; in other words,
8292 @command{tar} will not cross mount points.
8294 This option is useful for making full or incremental archival backups of
8295 a file system. If this option is used in conjunction with
8296 @option{--verbose} (@option{-v}), files that are excluded are
8297 mentioned by name on the standard error.
8300 * directory:: Changing Directory
8301 * absolute:: Absolute File Names
8305 @subsection Changing the Working Directory
8307 @FIXME{need to read over this node now for continuity; i've switched
8308 things around some.}
8310 @cindex Changing directory mid-stream
8311 @cindex Directory, changing mid-stream
8312 @cindex Working directory, specifying
8313 To change the working directory in the middle of a list of file names,
8314 either on the command line or in a file specified using
8315 @option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
8316 This will change the working directory to the specified directory
8317 after that point in the list.
8321 @item --directory=@var{directory}
8322 @itemx -C @var{directory}
8323 Changes the working directory in the middle of a command line.
8329 $ @kbd{tar -c -f jams.tar grape prune -C food cherry}
8333 will place the files @file{grape} and @file{prune} from the current
8334 directory into the archive @file{jams.tar}, followed by the file
8335 @file{cherry} from the directory @file{food}. This option is especially
8336 useful when you have several widely separated files that you want to
8337 store in the same archive.
8339 Note that the file @file{cherry} is recorded in the archive under the
8340 precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the
8341 archive will contain three files that all appear to have come from the
8342 same directory; if the archive is extracted with plain @samp{tar
8343 --extract}, all three files will be written in the current directory.
8345 Contrast this with the command,
8348 $ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
8352 which records the third file in the archive under the name
8353 @file{red/cherry} so that, if the archive is extracted using
8354 @samp{tar --extract}, the third file will be written in a subdirectory
8355 named @file{orange-colored}.
8357 You can use the @option{--directory} option to make the archive
8358 independent of the original name of the directory holding the files.
8359 The following command places the files @file{/etc/passwd},
8360 @file{/etc/hosts}, and @file{/lib/libc.a} into the archive
8364 $ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
8368 However, the names of the archive members will be exactly what they were
8369 on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}.
8370 They will not appear to be related by file name to the original
8371 directories where those files were located.
8373 Note that @option{--directory} options are interpreted consecutively. If
8374 @option{--directory} specifies a relative file name, it is interpreted
8375 relative to the then current directory, which might not be the same as
8376 the original current working directory of @command{tar}, due to a previous
8377 @option{--directory} option.
8379 When using @option{--files-from} (@pxref{files}), you can put various
8380 @command{tar} options (including @option{-C}) in the file list. Notice,
8381 however, that in this case the option and its argument may not be
8382 separated by whitespace. If you use short option, its argument must
8383 either follow the option letter immediately, without any intervening
8384 whitespace, or occupy the next line. Otherwise, if you use long
8385 option, separate its argument by an equal sign.
8387 For instance, the file list for the above example will be:
8400 To use it, you would invoke @command{tar} as follows:
8403 $ @kbd{tar -c -f foo.tar --files-from list}
8406 The interpretation of @option{--directory} is disabled by
8407 @option{--null} option.
8410 @subsection Absolute File Names
8411 @cindex absolute file names
8412 @cindex file names, absolute
8414 By default, @GNUTAR{} drops a leading @samp{/} on
8415 input or output, and complains about file names containing a @file{..}
8416 component. There is an option that turns off this behavior:
8419 @opindex absolute-names
8420 @item --absolute-names
8422 Do not strip leading slashes from file names, and permit file names
8423 containing a @file{..} file name component.
8426 When @command{tar} extracts archive members from an archive, it strips any
8427 leading slashes (@samp{/}) from the member name. This causes absolute
8428 member names in the archive to be treated as relative file names. This
8429 allows you to have such members extracted wherever you want, instead of
8430 being restricted to extracting the member in the exact directory named
8431 in the archive. For example, if the archive member has the name
8432 @file{/etc/passwd}, @command{tar} will extract it as if the name were
8433 really @file{etc/passwd}.
8435 File names containing @file{..} can cause problems when extracting, so
8436 @command{tar} normally warns you about such files when creating an
8437 archive, and rejects attempts to extracts such files.
8439 Other @command{tar} programs do not do this. As a result, if you
8440 create an archive whose member names start with a slash, they will be
8441 difficult for other people with a non-@GNUTAR{}
8442 program to use. Therefore, @GNUTAR{} also strips
8443 leading slashes from member names when putting members into the
8444 archive. For example, if you ask @command{tar} to add the file
8445 @file{/bin/ls} to an archive, it will do so, but the member name will
8446 be @file{bin/ls}.@footnote{A side effect of this is that when
8447 @option{--create} is used with @option{--verbose} the resulting output
8448 is not, generally speaking, the same as the one you'd get running
8449 @kbd{tar --list} command. This may be important if you use some
8450 scripts for comparing both outputs. @xref{listing member and file names},
8451 for the information on how to handle this case.}
8453 If you use the @option{--absolute-names} (@option{-P}) option,
8454 @command{tar} will do none of these transformations.
8456 To archive or extract files relative to the root directory, specify
8457 the @option{--absolute-names} (@option{-P}) option.
8459 Normally, @command{tar} acts on files relative to the working
8460 directory---ignoring superior directory names when archiving, and
8461 ignoring leading slashes when extracting.
8463 When you specify @option{--absolute-names} (@option{-P}),
8464 @command{tar} stores file names including all superior directory
8465 names, and preserves leading slashes. If you only invoked
8466 @command{tar} from the root directory you would never need the
8467 @option{--absolute-names} option, but using this option
8468 may be more convenient than switching to root.
8470 @FIXME{Should be an example in the tutorial/wizardry section using this
8471 to transfer files between systems.}
8474 @item --absolute-names
8475 Preserves full file names (including superior directory names) when
8476 archiving files. Preserves leading slash when extracting files.
8480 @command{tar} prints out a message about removing the @samp{/} from
8481 file names. This message appears once per @GNUTAR{}
8482 invocation. It represents something which ought to be told; ignoring
8483 what it means can cause very serious surprises, later.
8485 Some people, nevertheless, do not want to see this message. Wanting to
8486 play really dangerously, one may of course redirect @command{tar} standard
8487 error to the sink. For example, under @command{sh}:
8490 $ @kbd{tar -c -f archive.tar /home 2> /dev/null}
8494 Another solution, both nicer and simpler, would be to change to
8495 the @file{/} directory first, and then avoid absolute notation.
8499 $ @kbd{tar -c -f archive.tar -C / home}
8502 @include getdate.texi
8505 @chapter Controlling the Archive Format
8507 @cindex Tar archive formats
8508 Due to historical reasons, there are several formats of tar archives.
8509 All of them are based on the same principles, but have some subtle
8510 differences that often make them incompatible with each other.
8512 GNU tar is able to create and handle archives in a variety of formats.
8513 The most frequently used formats are (in alphabetical order):
8517 Format used by @GNUTAR{} versions up to 1.13.25. This format derived
8518 from an early @acronym{POSIX} standard, adding some improvements such as
8519 sparse file handling and incremental archives. Unfortunately these
8520 features were implemented in a way incompatible with other archive
8523 Archives in @samp{gnu} format are able to hold file names of unlimited
8527 Format used by @GNUTAR{} of versions prior to 1.12.
8530 Archive format, compatible with the V7 implementation of tar. This
8531 format imposes a number of limitations. The most important of them
8535 @item The maximum length of a file name is limited to 99 characters.
8536 @item The maximum length of a symbolic link is limited to 99 characters.
8537 @item It is impossible to store special files (block and character
8538 devices, fifos etc.)
8539 @item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777
8541 @item V7 archives do not contain symbolic ownership information (user
8542 and group name of the file owner).
8545 This format has traditionally been used by Automake when producing
8546 Makefiles. This practice will change in the future, in the meantime,
8547 however this means that projects containing file names more than 99
8548 characters long will not be able to use @GNUTAR{} @value{VERSION} and
8549 Automake prior to 1.9.
8552 Archive format defined by @acronym{POSIX.1-1988} specification. It stores
8553 symbolic ownership information. It is also able to store
8554 special files. However, it imposes several restrictions as well:
8557 @item The maximum length of a file name is limited to 256 characters,
8558 provided that the file name can be split at a directory separator in
8559 two parts, first of them being at most 155 bytes long. So, in most
8560 cases the maximum file name length will be shorter than 256
8562 @item The maximum length of a symbolic link name is limited to
8564 @item Maximum size of a file the archive is able to accommodate
8566 @item Maximum value of UID/GID is 2097151.
8567 @item Maximum number of bits in device major and minor numbers is 21.
8571 Format used by J@"org Schilling @command{star}
8572 implementation. @GNUTAR{} is able to read @samp{star} archives but
8573 currently does not produce them.
8576 Archive format defined by @acronym{POSIX.1-2001} specification. This is the
8577 most flexible and feature-rich format. It does not impose any
8578 restrictions on file sizes or file name lengths. This format is quite
8579 recent, so not all tar implementations are able to handle it properly.
8580 However, this format is designed in such a way that any tar
8581 implementation able to read @samp{ustar} archives will be able to read
8582 most @samp{posix} archives as well, with the only exception that any
8583 additional information (such as long file names etc.) will in such
8584 case be extracted as plain text files along with the files it refers to.
8586 This archive format will be the default format for future versions
8591 The following table summarizes the limitations of each of these
8594 @multitable @columnfractions .10 .20 .20 .20 .20
8595 @headitem Format @tab UID @tab File Size @tab File Name @tab Devn
8596 @item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8597 @item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8598 @item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
8599 @item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
8600 @item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
8603 The default format for @GNUTAR{} is defined at compilation
8604 time. You may check it by running @command{tar --help}, and examining
8605 the last lines of its output. Usually, @GNUTAR{} is configured
8606 to create archives in @samp{gnu} format, however, future version will
8607 switch to @samp{posix}.
8610 * Compression:: Using Less Space through Compression
8611 * Attributes:: Handling File Attributes
8612 * Portability:: Making @command{tar} Archives More Portable
8613 * cpio:: Comparison of @command{tar} and @command{cpio}
8617 @section Using Less Space through Compression
8620 * gzip:: Creating and Reading Compressed Archives
8621 * sparse:: Archiving Sparse Files
8625 @subsection Creating and Reading Compressed Archives
8626 @cindex Compressed archives
8627 @cindex Storing archives in compressed format
8634 @GNUTAR{} is able to create and read compressed archives. It supports
8635 @command{gzip}, @command{bzip2}, @command{lzma} and @command{lzop} compression
8636 programs. For backward compatibility, it also supports
8637 @command{compress} command, although we strongly recommend against
8638 using it, because it is by far less effective than other compression
8639 programs@footnote{It also had patent problems in the past.}.
8641 Creating a compressed archive is simple: you just specify a
8642 @dfn{compression option} along with the usual archive creation
8643 commands. The compression option is @option{-z} (@option{--gzip}) to
8644 create a @command{gzip} compressed archive, @option{-j}
8645 (@option{--bzip2}) to create a @command{bzip2} compressed archive,
8646 @option{-J} (@option{--xz}) to create an @asis{XZ} archive,
8647 @option{--lzma} to create an @asis{LZMA} compressed
8648 archive, @option{--lzop} to create an @asis{LSOP} archive, and
8649 @option{-Z} (@option{--compress}) to use @command{compress} program.
8653 $ @kbd{tar cfz archive.tar.gz .}
8656 You can also let @GNUTAR{} select the compression program basing on
8657 the suffix of the archive file name. This is done using
8658 @option{--auto-compress} (@option{-a}) command line option. For
8659 example, the following invocation will use @command{bzip2} for
8663 $ @kbd{tar cfa archive.tar.bz2 .}
8667 whereas the following one will use @command{lzma}:
8670 $ @kbd{tar cfa archive.tar.lzma .}
8673 For a complete list of file name suffixes recognized by @GNUTAR{},
8674 @ref{auto-compress}.
8676 Reading compressed archive is even simpler: you don't need to specify
8677 any additional options as @GNUTAR{} recognizes its format
8678 automatically. Thus, the following commands will list and extract the
8679 archive created in previous example:
8682 # List the compressed archive
8683 $ @kbd{tar tf archive.tar.gz}
8684 # Extract the compressed archive
8685 $ @kbd{tar xf archive.tar.gz}
8688 The format recognition algorithm is based on @dfn{signatures}, a
8689 special byte sequences in the beginning of file, that are specific for
8690 certain compression formats. If this approach fails, @command{tar}
8691 falls back to using archive name suffix to determine its format
8692 (@xref{auto-compress}, for a list of recognized suffixes).
8694 The only case when you have to specify a decompression option while
8695 reading the archive is when reading from a pipe or from a tape drive
8696 that does not support random access. However, in this case @GNUTAR{}
8697 will indicate which option you should use. For example:
8700 $ @kbd{cat archive.tar.gz | tar tf -}
8701 tar: Archive is compressed. Use -z option
8702 tar: Error is not recoverable: exiting now
8705 If you see such diagnostics, just add the suggested option to the
8706 invocation of @GNUTAR{}:
8709 $ @kbd{cat archive.tar.gz | tar tfz -}
8712 Notice also, that there are several restrictions on operations on
8713 compressed archives. First of all, compressed archives cannot be
8714 modified, i.e., you cannot update (@option{--update} (@option{-u}))
8715 them or delete (@option{--delete}) members from them or
8716 add (@option{--append} (@option{-r})) members to them. Likewise, you
8717 cannot append another @command{tar} archive to a compressed archive using
8718 @option{--concatenate} (@option{-A})). Secondly, multi-volume
8719 archives cannot be compressed.
8721 The following table summarizes compression options used by @GNUTAR{}.
8724 @anchor{auto-compress}
8725 @opindex auto-compress
8726 @item --auto-compress
8728 Select a compression program to use by the archive file name
8729 suffix. The following suffixes are recognized:
8731 @multitable @columnfractions 0.3 0.6
8732 @headitem Suffix @tab Compression program
8733 @item @samp{.gz} @tab @command{gzip}
8734 @item @samp{.tgz} @tab @command{gzip}
8735 @item @samp{.taz} @tab @command{gzip}
8736 @item @samp{.Z} @tab @command{compress}
8737 @item @samp{.taZ} @tab @command{compress}
8738 @item @samp{.bz2} @tab @command{bzip2}
8739 @item @samp{.tz2} @tab @command{bzip2}
8740 @item @samp{.tbz2} @tab @command{bzip2}
8741 @item @samp{.tbz} @tab @command{bzip2}
8742 @item @samp{.lzma} @tab @command{lzma}
8743 @item @samp{.tlz} @tab @command{lzma}
8744 @item @samp{.lzo} @tab @command{lzop}
8745 @item @samp{.xz} @tab @command{xz}
8753 Filter the archive through @command{gzip}.
8755 You can use @option{--gzip} and @option{--gunzip} on physical devices
8756 (tape drives, etc.) and remote files as well as on normal files; data
8757 to or from such devices or remote files is reblocked by another copy
8758 of the @command{tar} program to enforce the specified (or default) record
8759 size. The default compression parameters are used; if you need to
8760 override them, set @env{GZIP} environment variable, e.g.:
8763 $ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
8767 Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
8768 @command{gzip} explicitly:
8771 $ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
8774 @cindex corrupted archives
8775 About corrupted compressed archives: @command{gzip}'ed files have no
8776 redundancy, for maximum compression. The adaptive nature of the
8777 compression scheme means that the compression tables are implicitly
8778 spread all over the archive. If you lose a few blocks, the dynamic
8779 construction of the compression tables becomes unsynchronized, and there
8780 is little chance that you could recover later in the archive.
8782 There are pending suggestions for having a per-volume or per-file
8783 compression in @GNUTAR{}. This would allow for viewing the
8784 contents without decompression, and for resynchronizing decompression at
8785 every volume or file, in case of corrupted archives. Doing so, we might
8786 lose some compressibility. But this would have make recovering easier.
8787 So, there are pros and cons. We'll see!
8792 Filter the archive through @code{xz}. Otherwise like
8797 Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
8801 Filter the archive through @command{lzma}. Otherwise like @option{--gzip}.
8805 Filter the archive through @command{lzop}. Otherwise like
8813 Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
8815 @opindex use-compress-program
8816 @item --use-compress-program=@var{prog}
8817 @itemx -I=@var{prog}
8818 Use external compression program @var{prog}. Use this option if you
8819 have a compression program that @GNUTAR{} does not support. There
8820 are two requirements to which @var{prog} should comply:
8822 First, when called without options, it should read data from standard
8823 input, compress it and output it on standard output.
8825 Secondly, if called with @option{-d} argument, it should do exactly
8826 the opposite, i.e., read the compressed data from the standard input
8827 and produce uncompressed data on the standard output.
8830 @cindex gpg, using with tar
8831 @cindex gnupg, using with tar
8832 @cindex Using encrypted archives
8833 The @option{--use-compress-program} option, in particular, lets you
8834 implement your own filters, not necessarily dealing with
8835 compression/decompression. For example, suppose you wish to implement
8836 PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
8837 gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard
8838 Manual}). The following script does that:
8844 -d) gpg --decrypt - | gzip -d -c;;
8845 '') gzip -c | gpg -s ;;
8846 *) echo "Unknown option $1">&2; exit 1;;
8851 Suppose you name it @file{gpgz} and save it somewhere in your
8852 @env{PATH}. Then the following command will create a compressed
8853 archive signed with your private key:
8856 $ @kbd{tar -cf foo.tar.gpgz -Igpgz .}
8860 Likewise, the command below will list its contents:
8863 $ @kbd{tar -tf foo.tar.gpgz -Igpgz .}
8867 The above is based on the following discussion:
8869 I have one question, or maybe it's a suggestion if there isn't a way
8870 to do it now. I would like to use @option{--gzip}, but I'd also like
8871 the output to be fed through a program like @acronym{GNU}
8872 @command{ecc} (actually, right now that's @samp{exactly} what I'd like
8873 to use :-)), basically adding ECC protection on top of compression.
8874 It seems as if this should be quite easy to do, but I can't work out
8875 exactly how to go about it. Of course, I can pipe the standard output
8876 of @command{tar} through @command{ecc}, but then I lose (though I
8877 haven't started using it yet, I confess) the ability to have
8878 @command{tar} use @command{rmt} for it's I/O (I think).
8880 I think the most straightforward thing would be to let me specify a
8881 general set of filters outboard of compression (preferably ordered,
8882 so the order can be automatically reversed on input operations, and
8883 with the options they require specifiable), but beggars shouldn't be
8884 choosers and anything you decide on would be fine with me.
8886 By the way, I like @command{ecc} but if (as the comments say) it can't
8887 deal with loss of block sync, I'm tempted to throw some time at adding
8888 that capability. Supposing I were to actually do such a thing and
8889 get it (apparently) working, do you accept contributed changes to
8890 utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
8892 Isn't that exactly the role of the
8893 @option{--use-compress-prog=@var{program}} option?
8894 I never tried it myself, but I suspect you may want to write a
8895 @var{prog} script or program able to filter stdin to stdout to
8896 way you want. It should recognize the @option{-d} option, for when
8897 extraction is needed rather than creation.
8899 It has been reported that if one writes compressed data (through the
8900 @option{--gzip} or @option{--compress} options) to a DLT and tries to use
8901 the DLT compression mode, the data will actually get bigger and one will
8902 end up with less space on the tape.
8906 @subsection Archiving Sparse Files
8907 @cindex Sparse Files
8909 Files in the file system occasionally have @dfn{holes}. A @dfn{hole}
8910 in a file is a section of the file's contents which was never written.
8911 The contents of a hole reads as all zeros. On many operating systems,
8912 actual disk storage is not allocated for holes, but they are counted
8913 in the length of the file. If you archive such a file, @command{tar}
8914 could create an archive longer than the original. To have @command{tar}
8915 attempt to recognize the holes in a file, use @option{--sparse}
8916 (@option{-S}). When you use this option, then, for any file using
8917 less disk space than would be expected from its length, @command{tar}
8918 searches the file for consecutive stretches of zeros. It then records
8919 in the archive for the file where the consecutive stretches of zeros
8920 are, and only archives the ``real contents'' of the file. On
8921 extraction (using @option{--sparse} is not needed on extraction) any
8922 such files have holes created wherever the continuous stretches of zeros
8923 were found. Thus, if you use @option{--sparse}, @command{tar} archives
8924 won't take more space than the original.
8930 This option instructs @command{tar} to test each file for sparseness
8931 before attempting to archive it. If the file is found to be sparse it
8932 is treated specially, thus allowing to decrease the amount of space
8933 used by its image in the archive.
8935 This option is meaningful only when creating or updating archives. It
8936 has no effect on extraction.
8939 Consider using @option{--sparse} when performing file system backups,
8940 to avoid archiving the expanded forms of files stored sparsely in the
8943 Even if your system has no sparse files currently, some may be
8944 created in the future. If you use @option{--sparse} while making file
8945 system backups as a matter of course, you can be assured the archive
8946 will never take more space on the media than the files take on disk
8947 (otherwise, archiving a disk filled with sparse files might take
8948 hundreds of tapes). @xref{Incremental Dumps}.
8950 However, be aware that @option{--sparse} option presents a serious
8951 drawback. Namely, in order to determine if the file is sparse
8952 @command{tar} has to read it before trying to archive it, so in total
8953 the file is read @strong{twice}. So, always bear in mind that the
8954 time needed to process all files with this option is roughly twice
8955 the time needed to archive them without it.
8956 @FIXME{A technical note:
8958 Programs like @command{dump} do not have to read the entire file; by
8959 examining the file system directly, they can determine in advance
8960 exactly where the holes are and thus avoid reading through them. The
8961 only data it need read are the actual allocated data blocks.
8962 @GNUTAR{} uses a more portable and straightforward
8963 archiving approach, it would be fairly difficult that it does
8964 otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, on
8968 What I did say is that you cannot tell the difference between a hole and an
8969 equivalent number of nulls without reading raw blocks. @code{st_blocks} at
8970 best tells you how many holes there are; it doesn't tell you @emph{where}.
8971 Just as programs may, conceivably, care what @code{st_blocks} is (care
8972 to name one that does?), they may also care where the holes are (I have
8973 no examples of this one either, but it's equally imaginable).
8975 I conclude from this that good archivers are not portable. One can
8976 arguably conclude that if you want a portable program, you can in good
8977 conscience restore files with as many holes as possible, since you can't
8982 @cindex sparse formats, defined
8983 When using @samp{POSIX} archive format, @GNUTAR{} is able to store
8984 sparse files using in three distinct ways, called @dfn{sparse
8985 formats}. A sparse format is identified by its @dfn{number},
8986 consisting, as usual of two decimal numbers, delimited by a dot. By
8987 default, format @samp{1.0} is used. If, for some reason, you wish to
8988 use an earlier format, you can select it using
8989 @option{--sparse-version} option.
8992 @opindex sparse-version
8993 @item --sparse-version=@var{version}
8995 Select the format to store sparse files in. Valid @var{version} values
8996 are: @samp{0.0}, @samp{0.1} and @samp{1.0}. @xref{Sparse Formats},
8997 for a detailed description of each format.
9000 Using @option{--sparse-format} option implies @option{--sparse}.
9003 @section Handling File Attributes
9004 @cindex atrributes, files
9005 @cindex file attributes
9007 When @command{tar} reads files, it updates their access times. To
9008 avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
9009 reset the access time retroactively or avoid changing it in the first
9013 @opindex atime-preserve
9014 @item --atime-preserve
9015 @itemx --atime-preserve=replace
9016 @itemx --atime-preserve=system
9017 Preserve the access times of files that are read. This works only for
9018 files that you own, unless you have superuser privileges.
9020 @option{--atime-preserve=replace} works on most systems, but it also
9021 restores the data modification time and updates the status change
9022 time. Hence it doesn't interact with incremental dumps nicely
9023 (@pxref{Incremental Dumps}), and it can set access or data modification times
9024 incorrectly if other programs access the file while @command{tar} is
9027 @option{--atime-preserve=system} avoids changing the access time in
9028 the first place, if the operating system supports this.
9029 Unfortunately, this may or may not work on any given operating system
9030 or file system. If @command{tar} knows for sure it won't work, it
9031 complains right away.
9033 Currently @option{--atime-preserve} with no operand defaults to
9034 @option{--atime-preserve=replace}, but this is intended to change to
9035 @option{--atime-preserve=system} when the latter is better-supported.
9040 Do not extract data modification time.
9042 When this option is used, @command{tar} leaves the data modification times
9043 of the files it extracts as the times when the files were extracted,
9044 instead of setting it to the times recorded in the archive.
9046 This option is meaningless with @option{--list} (@option{-t}).
9050 Create extracted files with the same ownership they have in the
9053 This is the default behavior for the superuser,
9054 so this option is meaningful only for non-root users, when @command{tar}
9055 is executed on those systems able to give files away. This is
9056 considered as a security flaw by many people, at least because it
9057 makes quite difficult to correctly account users for the disk space
9058 they occupy. Also, the @code{suid} or @code{sgid} attributes of
9059 files are easily and silently lost when files are given away.
9061 When writing an archive, @command{tar} writes the user @acronym{ID} and user name
9062 separately. If it can't find a user name (because the user @acronym{ID} is not
9063 in @file{/etc/passwd}), then it does not write one. When restoring,
9064 it tries to look the name (if one was written) up in
9065 @file{/etc/passwd}. If it fails, then it uses the user @acronym{ID} stored in
9066 the archive instead.
9068 @opindex no-same-owner
9069 @item --no-same-owner
9071 Do not attempt to restore ownership when extracting. This is the
9072 default behavior for ordinary users, so this option has an effect
9073 only for the superuser.
9075 @opindex numeric-owner
9076 @item --numeric-owner
9077 The @option{--numeric-owner} option allows (ANSI) archives to be written
9078 without user/group name information or such information to be ignored
9079 when extracting. It effectively disables the generation and/or use
9080 of user/group name information. This option forces extraction using
9081 the numeric ids from the archive, ignoring the names.
9083 This is useful in certain circumstances, when restoring a backup from
9084 an emergency floppy with different passwd/group files for example.
9085 It is otherwise impossible to extract files with the right ownerships
9086 if the password file in use during the extraction does not match the
9087 one belonging to the file system(s) being extracted. This occurs,
9088 for example, if you are restoring your files after a major crash and
9089 had booted from an emergency floppy with no password file or put your
9090 disk into another machine to do the restore.
9092 The numeric ids are @emph{always} saved into @command{tar} archives.
9093 The identifying names are added at create time when provided by the
9094 system, unless @option{--old-archive} (@option{-o}) is used. Numeric ids could be
9095 used when moving archives between a collection of machines using
9096 a centralized management for attribution of numeric ids to users
9097 and groups. This is often made through using the NIS capabilities.
9099 When making a @command{tar} file for distribution to other sites, it
9100 is sometimes cleaner to use a single owner for all files in the
9101 distribution, and nicer to specify the write permission bits of the
9102 files as stored in the archive independently of their actual value on
9103 the file system. The way to prepare a clean distribution is usually
9104 to have some Makefile rule creating a directory, copying all needed
9105 files in that directory, then setting ownership and permissions as
9106 wanted (there are a lot of possible schemes), and only then making a
9107 @command{tar} archive out of this directory, before cleaning
9108 everything out. Of course, we could add a lot of options to
9109 @GNUTAR{} for fine tuning permissions and ownership.
9110 This is not the good way, I think. @GNUTAR{} is
9111 already crowded with options and moreover, the approach just explained
9112 gives you a great deal of control already.
9114 @xopindex{same-permissions, short description}
9115 @xopindex{preserve-permissions, short description}
9117 @itemx --same-permissions
9118 @itemx --preserve-permissions
9119 Extract all protection information.
9121 This option causes @command{tar} to set the modes (access permissions) of
9122 extracted files exactly as recorded in the archive. If this option
9123 is not used, the current @code{umask} setting limits the permissions
9124 on extracted files. This option is by default enabled when
9125 @command{tar} is executed by a superuser.
9128 This option is meaningless with @option{--list} (@option{-t}).
9132 Same as both @option{--same-permissions} and @option{--same-order}.
9134 This option is deprecated, and will be removed in @GNUTAR{} version 1.23.
9139 @section Making @command{tar} Archives More Portable
9141 Creating a @command{tar} archive on a particular system that is meant to be
9142 useful later on many other machines and with other versions of @command{tar}
9143 is more challenging than you might think. @command{tar} archive formats
9144 have been evolving since the first versions of Unix. Many such formats
9145 are around, and are not always compatible with each other. This section
9146 discusses a few problems, and gives some advice about making @command{tar}
9147 archives more portable.
9149 One golden rule is simplicity. For example, limit your @command{tar}
9150 archives to contain only regular files and directories, avoiding
9151 other kind of special files. Do not attempt to save sparse files or
9152 contiguous files as such. Let's discuss a few more problems, in turn.
9154 @FIXME{Discuss GNU extensions (incremental backups, multi-volume
9155 archives and archive labels) in GNU and PAX formats.}
9158 * Portable Names:: Portable Names
9159 * dereference:: Symbolic Links
9160 * hard links:: Hard Links
9161 * old:: Old V7 Archives
9162 * ustar:: Ustar Archives
9163 * gnu:: GNU and old GNU format archives.
9164 * posix:: @acronym{POSIX} archives
9165 * Checksumming:: Checksumming Problems
9166 * Large or Negative Values:: Large files, negative time stamps, etc.
9167 * Other Tars:: How to Extract GNU-Specific Data Using
9168 Other @command{tar} Implementations
9171 @node Portable Names
9172 @subsection Portable Names
9174 Use portable file and member names. A name is portable if it contains
9175 only @acronym{ASCII} letters and digits, @samp{/}, @samp{.}, @samp{_}, and
9176 @samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
9177 contain @samp{/-}. Avoid deep directory nesting. For portability to
9178 old Unix hosts, limit your file name components to 14 characters or
9181 If you intend to have your @command{tar} archives to be read under
9182 MSDOS, you should not rely on case distinction for file names, and you
9183 might use the @acronym{GNU} @command{doschk} program for helping you
9184 further diagnosing illegal MSDOS names, which are even more limited
9188 @subsection Symbolic Links
9189 @cindex File names, using symbolic links
9190 @cindex Symbolic link as file name
9192 @opindex dereference
9193 Normally, when @command{tar} archives a symbolic link, it writes a
9194 block to the archive naming the target of the link. In that way, the
9195 @command{tar} archive is a faithful record of the file system contents.
9196 @option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
9197 @command{tar} to archive the files symbolic links point to, instead of
9198 the links themselves. When this option is used, when @command{tar}
9199 encounters a symbolic link, it will archive the linked-to file,
9200 instead of simply recording the presence of a symbolic link.
9202 The name under which the file is stored in the file system is not
9203 recorded in the archive. To record both the symbolic link name and
9204 the file name in the system, archive the file under both names. If
9205 all links were recorded automatically by @command{tar}, an extracted file
9206 might be linked to a file name that no longer exists in the file
9209 If a linked-to file is encountered again by @command{tar} while creating
9210 the same archive, an entire second copy of it will be stored. (This
9211 @emph{might} be considered a bug.)
9213 So, for portable archives, do not archive symbolic links as such,
9214 and use @option{--dereference} (@option{-h}): many systems do not support
9215 symbolic links, and moreover, your distribution might be unusable if
9216 it contains unresolved symbolic links.
9219 @subsection Hard Links
9220 @cindex File names, using hard links
9221 @cindex hard links, dereferencing
9222 @cindex dereferencing hard links
9224 Normally, when @command{tar} archives a hard link, it writes a
9225 block to the archive naming the target of the link (a @samp{1} type
9226 block). In that way, the actual file contents is stored in file only
9227 once. For example, consider the following two files:
9232 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 one
9233 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 jeden
9237 Here, @file{jeden} is a link to @file{one}. When archiving this
9238 directory with a verbose level 2, you will get an output similar to
9242 $ tar cfvv ../archive.tar .
9243 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9244 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9245 hrw-r--r-- gray/staff 0 2007-10-30 15:11 ./one link to ./jeden
9248 The last line shows that, instead of storing two copies of the file,
9249 @command{tar} stored it only once, under the name @file{jeden}, and
9250 stored file @file{one} as a hard link to this file.
9252 It may be important to know that all hard links to the given file are
9253 stored in the archive. For example, this may be necessary for exact
9254 reproduction of the file system. The following option does that:
9257 @xopindex{check-links, described}
9260 Check the number of links dumped for each processed file. If this
9261 number does not match the total number of hard links for the file, print
9265 For example, trying to archive only file @file{jeden} with this option
9266 produces the following diagnostics:
9269 $ tar -c -f ../archive.tar jeden
9270 tar: Missing links to `jeden'.
9273 Although creating special records for hard links helps keep a faithful
9274 record of the file system contents and makes archives more compact, it
9275 may present some difficulties when extracting individual members from
9276 the archive. For example, trying to extract file @file{one} from the
9277 archive created in previous examples produces, in the absense of file
9281 $ tar xf archive.tar ./one
9282 tar: ./one: Cannot hard link to `./jeden': No such file or directory
9283 tar: Error exit delayed from previous errors
9286 The reason for this behavior is that @command{tar} cannot seek back in
9287 the archive to the previous member (in this case, @file{one}), to
9288 extract it@footnote{There are plans to fix this in future releases.}.
9289 If you wish to avoid such problems at the cost of a bigger archive,
9290 use the following option:
9293 @xopindex{hard-dereference, described}
9294 @item --hard-dereference
9295 Dereference hard links and store the files they refer to.
9298 For example, trying this option on our two sample files, we get two
9299 copies in the archive, each of which can then be extracted
9300 independently of the other:
9304 $ tar -c -vv -f ../archive.tar --hard-dereference .
9305 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9306 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9307 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./one
9312 @subsection Old V7 Archives
9313 @cindex Format, old style
9314 @cindex Old style format
9315 @cindex Old style archives
9316 @cindex v7 archive format
9318 Certain old versions of @command{tar} cannot handle additional
9319 information recorded by newer @command{tar} programs. To create an
9320 archive in V7 format (not ANSI), which can be read by these old
9321 versions, specify the @option{--format=v7} option in
9322 conjunction with the @option{--create} (@option{-c}) (@command{tar} also
9323 accepts @option{--portability} or @option{--old-archive} for this
9324 option). When you specify it,
9325 @command{tar} leaves out information about directories, pipes, fifos,
9326 contiguous files, and device files, and specifies file ownership by
9327 group and user IDs instead of group and user names.
9329 When updating an archive, do not use @option{--format=v7}
9330 unless the archive was created using this option.
9332 In most cases, a @emph{new} format archive can be read by an @emph{old}
9333 @command{tar} program without serious trouble, so this option should
9334 seldom be needed. On the other hand, most modern @command{tar}s are
9335 able to read old format archives, so it might be safer for you to
9336 always use @option{--format=v7} for your distributions. Notice,
9337 however, that @samp{ustar} format is a better alternative, as it is
9338 free from many of @samp{v7}'s drawbacks.
9341 @subsection Ustar Archive Format
9343 @cindex ustar archive format
9344 Archive format defined by @acronym{POSIX}.1-1988 specification is called
9345 @code{ustar}. Although it is more flexible than the V7 format, it
9346 still has many restrictions (@xref{Formats,ustar}, for the detailed
9347 description of @code{ustar} format). Along with V7 format,
9348 @code{ustar} format is a good choice for archives intended to be read
9349 with other implementations of @command{tar}.
9351 To create archive in @code{ustar} format, use @option{--format=ustar}
9352 option in conjunction with the @option{--create} (@option{-c}).
9355 @subsection @acronym{GNU} and old @GNUTAR{} format
9357 @cindex GNU archive format
9358 @cindex Old GNU archive format
9359 @GNUTAR{} was based on an early draft of the
9360 @acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
9361 @command{tar}, such as the support for file names longer than 100
9362 characters, use portions of the @command{tar} header record which were
9363 specified in that @acronym{POSIX} draft as unused. Subsequent changes in
9364 @acronym{POSIX} have allocated the same parts of the header record for
9365 other purposes. As a result, @GNUTAR{} format is
9366 incompatible with the current @acronym{POSIX} specification, and with
9367 @command{tar} programs that follow it.
9369 In the majority of cases, @command{tar} will be configured to create
9370 this format by default. This will change in future releases, since
9371 we plan to make @samp{POSIX} format the default.
9373 To force creation a @GNUTAR{} archive, use option
9374 @option{--format=gnu}.
9377 @subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
9379 @cindex POSIX archive format
9380 @cindex PAX archive format
9381 Starting from version 1.14 @GNUTAR{} features full support for
9382 @acronym{POSIX.1-2001} archives.
9384 A @acronym{POSIX} conformant archive will be created if @command{tar}
9385 was given @option{--format=posix} (@option{--format=pax}) option. No
9386 special option is required to read and extract from a @acronym{POSIX}
9390 * PAX keywords:: Controlling Extended Header Keywords.
9394 @subsubsection Controlling Extended Header Keywords
9398 @item --pax-option=@var{keyword-list}
9399 Handle keywords in @acronym{PAX} extended headers. This option is
9400 equivalent to @option{-o} option of the @command{pax} utility.
9403 @var{Keyword-list} is a comma-separated
9404 list of keyword options, each keyword option taking one of
9405 the following forms:
9408 @item delete=@var{pattern}
9409 When used with one of archive-creation commands,
9410 this option instructs @command{tar} to omit from extended header records
9411 that it produces any keywords matching the string @var{pattern}.
9413 When used in extract or list mode, this option instructs tar
9414 to ignore any keywords matching the given @var{pattern} in the extended
9415 header records. In both cases, matching is performed using the pattern
9416 matching notation described in @acronym{POSIX 1003.2}, 3.13
9417 (@pxref{wildcards}). For example:
9420 --pax-option delete=security.*
9423 would suppress security-related information.
9425 @item exthdr.name=@var{string}
9427 This keyword allows user control over the name that is written into the
9428 ustar header blocks for the extended headers. The name is obtained
9429 from @var{string} after making the following substitutions:
9431 @multitable @columnfractions .25 .55
9432 @headitem Meta-character @tab Replaced By
9433 @item %d @tab The directory name of the file, equivalent to the
9434 result of the @command{dirname} utility on the translated file name.
9435 @item %f @tab The name of the file with the directory information
9436 stripped, equivalent to the result of the @command{basename} utility
9437 on the translated file name.
9438 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9439 @item %% @tab A @samp{%} character.
9442 Any other @samp{%} characters in @var{string} produce undefined
9445 If no option @samp{exthdr.name=string} is specified, @command{tar}
9446 will use the following default value:
9452 @item exthdr.mtime=@var{value}
9454 This keyword defines the value of the @samp{mtime} field that
9455 is written into the ustar header blocks for the extended headers.
9456 By default, the @samp{mtime} field is set to the modification time
9457 of the archive member described by that extended headers.
9459 @item globexthdr.name=@var{string}
9460 This keyword allows user control over the name that is written into
9461 the ustar header blocks for global extended header records. The name
9462 is obtained from the contents of @var{string}, after making
9463 the following substitutions:
9465 @multitable @columnfractions .25 .55
9466 @headitem Meta-character @tab Replaced By
9467 @item %n @tab An integer that represents the
9468 sequence number of the global extended header record in the archive,
9470 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9471 @item %% @tab A @samp{%} character.
9474 Any other @samp{%} characters in @var{string} produce undefined results.
9476 If no option @samp{globexthdr.name=string} is specified, @command{tar}
9477 will use the following default value:
9480 $TMPDIR/GlobalHead.%p.%n
9484 where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
9485 environment variable. If @var{TMPDIR} is not set, @command{tar}
9488 @item exthdr.mtime=@var{value}
9490 This keyword defines the value of the @samp{mtime} field that
9491 is written into the ustar header blocks for the global extended headers.
9492 By default, the @samp{mtime} field is set to the time when
9493 @command{tar} was invoked.
9495 @item @var{keyword}=@var{value}
9496 When used with one of archive-creation commands, these keyword/value pairs
9497 will be included at the beginning of the archive in a global extended
9498 header record. When used with one of archive-reading commands,
9499 @command{tar} will behave as if it has encountered these keyword/value
9500 pairs at the beginning of the archive in a global extended header
9503 @item @var{keyword}:=@var{value}
9504 When used with one of archive-creation commands, these keyword/value pairs
9505 will be included as records at the beginning of an extended header for
9506 each file. This is effectively equivalent to @var{keyword}=@var{value}
9507 form except that it creates no global extended header records.
9509 When used with one of archive-reading commands, @command{tar} will
9510 behave as if these keyword/value pairs were included as records at the
9511 end of each extended header; thus, they will override any global or
9512 file-specific extended header record keywords of the same names.
9513 For example, in the command:
9516 tar --format=posix --create \
9517 --file archive --pax-option gname:=user .
9520 the group name will be forced to a new value for all files
9521 stored in the archive.
9524 In any of the forms described above, the @var{value} may be
9525 a string enclosed in curly braces. In that case, the string
9526 between the braces is understood either as a textual time
9527 representation, as described in @ref{Date input formats}, or a name of
9528 the existing file, starting with @samp{/} or @samp{.}. In the latter
9529 case, the modification time of that file is used.
9531 For example, to set all modification times to the current date, you
9532 use the following option:
9535 --pax-option='mtime:=@{now@}'
9538 Note quoting of the option's argument.
9540 @cindex archives, binary equivalent
9541 @cindex binary equivalent archives, creating
9542 As another example, here is the option that ensures that any two
9543 archives created using it, will be binary equivalent if they have the
9547 --pax-option=exthdr.name=%d/PaxHeaders/%f,atime:=0
9551 @subsection Checksumming Problems
9553 SunOS and HP-UX @command{tar} fail to accept archives created using
9554 @GNUTAR{} and containing non-@acronym{ASCII} file names, that
9555 is, file names having characters with the eight bit set, because they
9556 use signed checksums, while @GNUTAR{} uses unsigned
9557 checksums while creating archives, as per @acronym{POSIX} standards. On
9558 reading, @GNUTAR{} computes both checksums and
9559 accepts any. It is somewhat worrying that a lot of people may go
9560 around doing backup of their files using faulty (or at least
9561 non-standard) software, not learning about it until it's time to
9562 restore their missing files with an incompatible file extractor, or
9565 @GNUTAR{} compute checksums both ways, and accept
9566 any on read, so @acronym{GNU} tar can read Sun tapes even with their
9567 wrong checksums. @GNUTAR{} produces the standard
9568 checksum, however, raising incompatibilities with Sun. That is to
9569 say, @GNUTAR{} has not been modified to
9570 @emph{produce} incorrect archives to be read by buggy @command{tar}'s.
9571 I've been told that more recent Sun @command{tar} now read standard
9572 archives, so maybe Sun did a similar patch, after all?
9574 The story seems to be that when Sun first imported @command{tar}
9575 sources on their system, they recompiled it without realizing that
9576 the checksums were computed differently, because of a change in
9577 the default signing of @code{char}'s in their compiler. So they
9578 started computing checksums wrongly. When they later realized their
9579 mistake, they merely decided to stay compatible with it, and with
9580 themselves afterwards. Presumably, but I do not really know, HP-UX
9581 has chosen that their @command{tar} archives to be compatible with Sun's.
9582 The current standards do not favor Sun @command{tar} format. In any
9583 case, it now falls on the shoulders of SunOS and HP-UX users to get
9584 a @command{tar} able to read the good archives they receive.
9586 @node Large or Negative Values
9587 @subsection Large or Negative Values
9588 @cindex large values
9589 @cindex future time stamps
9590 @cindex negative time stamps
9593 The above sections suggest to use @samp{oldest possible} archive
9594 format if in doubt. However, sometimes it is not possible. If you
9595 attempt to archive a file whose metadata cannot be represented using
9596 required format, @GNUTAR{} will print error message and ignore such a
9597 file. You will than have to switch to a format that is able to
9598 handle such values. The format summary table (@pxref{Formats}) will
9601 In particular, when trying to archive files larger than 8GB or with
9602 timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
9603 12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
9604 @acronym{POSIX} archive formats. When considering which format to
9605 choose, bear in mind that the @acronym{GNU} format uses
9606 two's-complement base-256 notation to store values that do not fit
9607 into standard @acronym{ustar} range. Such archives can generally be
9608 read only by a @GNUTAR{} implementation. Moreover, they sometimes
9609 cannot be correctly restored on another hosts even by @GNUTAR{}. For
9610 example, using two's complement representation for negative time
9611 stamps that assumes a signed 32-bit @code{time_t} generates archives
9612 that are not portable to hosts with differing @code{time_t}
9615 On the other hand, @acronym{POSIX} archives, generally speaking, can
9616 be extracted by any tar implementation that understands older
9617 @acronym{ustar} format. The only exception are files larger than 8GB.
9619 @FIXME{Describe how @acronym{POSIX} archives are extracted by non
9623 @subsection How to Extract GNU-Specific Data Using Other @command{tar} Implementations
9625 In previous sections you became acquainted with various quirks
9626 necessary to make your archives portable. Sometimes you may need to
9627 extract archives containing GNU-specific members using some
9628 third-party @command{tar} implementation or an older version of
9629 @GNUTAR{}. Of course your best bet is to have @GNUTAR{} installed,
9630 but if it is for some reason impossible, this section will explain
9631 how to cope without it.
9633 When we speak about @dfn{GNU-specific} members we mean two classes of
9634 them: members split between the volumes of a multi-volume archive and
9635 sparse members. You will be able to always recover such members if
9636 the archive is in PAX format. In addition split members can be
9637 recovered from archives in old GNU format. The following subsections
9638 describe the required procedures in detail.
9641 * Split Recovery:: Members Split Between Volumes
9642 * Sparse Recovery:: Sparse Members
9645 @node Split Recovery
9646 @subsubsection Extracting Members Split Between Volumes
9648 @cindex Mutli-volume archives, extracting using non-GNU tars
9649 If a member is split between several volumes of an old GNU format archive
9650 most third party @command{tar} implementation will fail to extract
9651 it. To extract it, use @command{tarcat} program (@pxref{Tarcat}).
9652 This program is available from
9653 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tarcat.html, @GNUTAR{}
9654 home page}. It concatenates several archive volumes into a single
9655 valid archive. For example, if you have three volumes named from
9656 @file{vol-1.tar} to @file{vol-3.tar}, you can do the following to
9657 extract them using a third-party @command{tar}:
9660 $ @kbd{tarcat vol-1.tar vol-2.tar vol-3.tar | tar xf -}
9663 @cindex Mutli-volume archives in PAX format, extracting using non-GNU tars
9664 You could use this approach for most (although not all) PAX
9665 format archives as well. However, extracting split members from a PAX
9666 archive is a much easier task, because PAX volumes are constructed in
9667 such a way that each part of a split member is extracted to a
9668 different file by @command{tar} implementations that are not aware of
9669 GNU extensions. More specifically, the very first part retains its
9670 original name, and all subsequent parts are named using the pattern:
9673 %d/GNUFileParts.%p/%f.%n
9677 where symbols preceeded by @samp{%} are @dfn{macro characters} that
9678 have the following meaning:
9680 @multitable @columnfractions .25 .55
9681 @headitem Meta-character @tab Replaced By
9682 @item %d @tab The directory name of the file, equivalent to the
9683 result of the @command{dirname} utility on its full name.
9684 @item %f @tab The file name of the file, equivalent to the result
9685 of the @command{basename} utility on its full name.
9686 @item %p @tab The process @acronym{ID} of the @command{tar} process that
9687 created the archive.
9688 @item %n @tab Ordinal number of this particular part.
9691 For example, if the file @file{var/longfile} was split during archive
9692 creation between three volumes, and the creator @command{tar} process
9693 had process @acronym{ID} @samp{27962}, then the member names will be:
9697 var/GNUFileParts.27962/longfile.1
9698 var/GNUFileParts.27962/longfile.2
9701 When you extract your archive using a third-party @command{tar}, these
9702 files will be created on your disk, and the only thing you will need
9703 to do to restore your file in its original form is concatenate them in
9704 the proper order, for example:
9709 $ @kbd{cat GNUFileParts.27962/longfile.1 \
9710 GNUFileParts.27962/longfile.2 >> longfile}
9711 $ rm -f GNUFileParts.27962
9715 Notice, that if the @command{tar} implementation you use supports PAX
9716 format archives, it will probably emit warnings about unknown keywords
9717 during extraction. They will look like this:
9722 Unknown extended header keyword 'GNU.volume.filename' ignored.
9723 Unknown extended header keyword 'GNU.volume.size' ignored.
9724 Unknown extended header keyword 'GNU.volume.offset' ignored.
9729 You can safely ignore these warnings.
9731 If your @command{tar} implementation is not PAX-aware, you will get
9732 more warnings and more files generated on your disk, e.g.:
9736 $ @kbd{tar xf vol-1.tar}
9737 var/PaxHeaders.27962/longfile: Unknown file type 'x', extracted as
9739 Unexpected EOF in archive
9740 $ @kbd{tar xf vol-2.tar}
9741 tmp/GlobalHead.27962.1: Unknown file type 'g', extracted as normal file
9742 GNUFileParts.27962/PaxHeaders.27962/sparsefile.1: Unknown file type
9743 'x', extracted as normal file
9747 Ignore these warnings. The @file{PaxHeaders.*} directories created
9748 will contain files with @dfn{extended header keywords} describing the
9749 extracted files. You can delete them, unless they describe sparse
9750 members. Read further to learn more about them.
9752 @node Sparse Recovery
9753 @subsubsection Extracting Sparse Members
9755 @cindex sparse files, extracting with non-GNU tars
9756 Any @command{tar} implementation will be able to extract sparse members from a
9757 PAX archive. However, the extracted files will be @dfn{condensed},
9758 i.e., any zero blocks will be removed from them. When we restore such
9759 a condensed file to its original form, by adding zero blocks (or
9760 @dfn{holes}) back to their original locations, we call this process
9761 @dfn{expanding} a compressed sparse file.
9764 To expand a file, you will need a simple auxiliary program called
9765 @command{xsparse}. It is available in source form from
9766 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/xsparse.html, @GNUTAR{}
9769 @cindex sparse files v.1.0, extracting with non-GNU tars
9770 Let's begin with archive members in @dfn{sparse format
9771 version 1.0}@footnote{@xref{PAX 1}.}, which are the easiest to expand.
9772 The condensed file will contain both file map and file data, so no
9773 additional data will be needed to restore it. If the original file
9774 name was @file{@var{dir}/@var{name}}, then the condensed file will be
9775 named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
9776 @var{n} is a decimal number@footnote{technically speaking, @var{n} is a
9777 @dfn{process @acronym{ID}} of the @command{tar} process which created the
9778 archive (@pxref{PAX keywords}).}.
9780 To expand a version 1.0 file, run @command{xsparse} as follows:
9783 $ @kbd{xsparse @file{cond-file}}
9787 where @file{cond-file} is the name of the condensed file. The utility
9788 will deduce the name for the resulting expanded file using the
9789 following algorithm:
9792 @item If @file{cond-file} does not contain any directories,
9793 @file{../cond-file} will be used;
9795 @item If @file{cond-file} has the form
9796 @file{@var{dir}/@var{t}/@var{name}}, where both @var{t} and @var{name}
9797 are simple names, with no @samp{/} characters in them, the output file
9798 name will be @file{@var{dir}/@var{name}}.
9800 @item Otherwise, if @file{cond-file} has the form
9801 @file{@var{dir}/@var{name}}, the output file name will be
9805 In the unlikely case when this algorithm does not suit your needs,
9806 you can explicitly specify output file name as a second argument to
9810 $ @kbd{xsparse @file{cond-file} @file{out-file}}
9813 It is often a good idea to run @command{xsparse} in @dfn{dry run} mode
9814 first. In this mode, the command does not actually expand the file,
9815 but verbosely lists all actions it would be taking to do so. The dry
9816 run mode is enabled by @option{-n} command line argument:
9820 $ @kbd{xsparse -n /home/gray/GNUSparseFile.6058/sparsefile}
9821 Reading v.1.0 sparse map
9822 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9823 `/home/gray/sparsefile'
9828 To actually expand the file, you would run:
9831 $ @kbd{xsparse /home/gray/GNUSparseFile.6058/sparsefile}
9835 The program behaves the same way all UNIX utilities do: it will keep
9836 quiet unless it has simething important to tell you (e.g. an error
9837 condition or something). If you wish it to produce verbose output,
9838 similar to that from the dry run mode, use @option{-v} option:
9842 $ @kbd{xsparse -v /home/gray/GNUSparseFile.6058/sparsefile}
9843 Reading v.1.0 sparse map
9844 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9845 `/home/gray/sparsefile'
9850 Additionally, if your @command{tar} implementation has extracted the
9851 @dfn{extended headers} for this file, you can instruct @command{xstar}
9852 to use them in order to verify the integrity of the expanded file.
9853 The option @option{-x} sets the name of the extended header file to
9854 use. Continuing our example:
9858 $ @kbd{xsparse -v -x /home/gray/PaxHeaders.6058/sparsefile \
9859 /home/gray/GNUSparseFile.6058/sparsefile}
9860 Reading extended header file
9861 Found variable GNU.sparse.major = 1
9862 Found variable GNU.sparse.minor = 0
9863 Found variable GNU.sparse.name = sparsefile
9864 Found variable GNU.sparse.realsize = 217481216
9865 Reading v.1.0 sparse map
9866 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9867 `/home/gray/sparsefile'
9872 @anchor{extracting sparse v.0.x}
9873 @cindex sparse files v.0.1, extracting with non-GNU tars
9874 @cindex sparse files v.0.0, extracting with non-GNU tars
9875 An @dfn{extended header} is a special @command{tar} archive header
9876 that precedes an archive member and contains a set of
9877 @dfn{variables}, describing the member properties that cannot be
9878 stored in the standard @code{ustar} header. While optional for
9879 expanding sparse version 1.0 members, the use of extended headers is
9880 mandatory when expanding sparse members in older sparse formats: v.0.0
9881 and v.0.1 (The sparse formats are described in detail in @ref{Sparse
9882 Formats}.) So, for these formats, the question is: how to obtain
9883 extended headers from the archive?
9885 If you use a @command{tar} implementation that does not support PAX
9886 format, extended headers for each member will be extracted as a
9887 separate file. If we represent the member name as
9888 @file{@var{dir}/@var{name}}, then the extended header file will be
9889 named @file{@var{dir}/@/PaxHeaders.@var{n}/@/@var{name}}, where
9890 @var{n} is an integer number.
9892 Things become more difficult if your @command{tar} implementation
9893 does support PAX headers, because in this case you will have to
9894 manually extract the headers. We recommend the following algorithm:
9898 Consult the documentation of your @command{tar} implementation for an
9899 option that prints @dfn{block numbers} along with the archive
9900 listing (analogous to @GNUTAR{}'s @option{-R} option). For example,
9901 @command{star} has @option{-block-number}.
9904 Obtain verbose listing using the @samp{block number} option, and
9905 find block numbers of the sparse member in question and the member
9906 immediately following it. For example, running @command{star} on our
9911 $ @kbd{star -t -v -block-number -f arc.tar}
9913 star: Unknown extended header keyword 'GNU.sparse.size' ignored.
9914 star: Unknown extended header keyword 'GNU.sparse.numblocks' ignored.
9915 star: Unknown extended header keyword 'GNU.sparse.name' ignored.
9916 star: Unknown extended header keyword 'GNU.sparse.map' ignored.
9917 block 56: 425984 -rw-r--r-- gray/users Jun 25 14:46 2006 GNUSparseFile.28124/sparsefile
9918 block 897: 65391 -rw-r--r-- gray/users Jun 24 20:06 2006 README
9924 (as usual, ignore the warnings about unknown keywords.)
9927 Let @var{size} be the size of the sparse member, @var{Bs} be its block number
9928 and @var{Bn} be the block number of the next member.
9932 @var{N} = @var{Bs} - @var{Bn} - @var{size}/512 - 2
9936 This number gives the size of the extended header part in tar @dfn{blocks}.
9937 In our example, this formula gives: @code{897 - 56 - 425984 / 512 - 2
9941 Use @command{dd} to extract the headers:
9944 @kbd{dd if=@var{archive} of=@var{hname} bs=512 skip=@var{Bs} count=@var{N}}
9948 where @var{archive} is the archive name, @var{hname} is a name of the
9949 file to store the extended header in, @var{Bs} and @var{N} are
9950 computed in previous steps.
9952 In our example, this command will be
9955 $ @kbd{dd if=arc.tar of=xhdr bs=512 skip=56 count=7}
9959 Finally, you can expand the condensed file, using the obtained header:
9963 $ @kbd{xsparse -v -x xhdr GNUSparseFile.6058/sparsefile}
9964 Reading extended header file
9965 Found variable GNU.sparse.size = 217481216
9966 Found variable GNU.sparse.numblocks = 208
9967 Found variable GNU.sparse.name = sparsefile
9968 Found variable GNU.sparse.map = 0,2048,1050624,2048,@dots{}
9969 Expanding file `GNUSparseFile.28124/sparsefile' to `sparsefile'
9975 @section Comparison of @command{tar} and @command{cpio}
9978 @FIXME{Reorganize the following material}
9980 The @command{cpio} archive formats, like @command{tar}, do have maximum
9981 file name lengths. The binary and old @acronym{ASCII} formats have a maximum file
9982 length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max
9983 file length of 1024. @acronym{GNU} @command{cpio} can read and write archives
9984 with arbitrary file name lengths, but other @command{cpio} implementations
9985 may crash unexplainedly trying to read them.
9987 @command{tar} handles symbolic links in the form in which it comes in @acronym{BSD};
9988 @command{cpio} doesn't handle symbolic links in the form in which it comes
9989 in System V prior to SVR4, and some vendors may have added symlinks
9990 to their system without enhancing @command{cpio} to know about them.
9991 Others may have enhanced it in a way other than the way I did it
9992 at Sun, and which was adopted by AT&T (and which is, I think, also
9993 present in the @command{cpio} that Berkeley picked up from AT&T and put
9994 into a later @acronym{BSD} release---I think I gave them my changes).
9996 (SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
9997 can handle @command{tar} format input, and write it on output, and it
9998 probably handles symbolic links. They may not have bothered doing
9999 anything to enhance @command{tar} as a result.)
10001 @command{cpio} handles special files; traditional @command{tar} doesn't.
10003 @command{tar} comes with V7, System III, System V, and @acronym{BSD} source;
10004 @command{cpio} comes only with System III, System V, and later @acronym{BSD}
10005 (4.3-tahoe and later).
10007 @command{tar}'s way of handling multiple hard links to a file can handle
10008 file systems that support 32-bit inumbers (e.g., the @acronym{BSD} file system);
10009 @command{cpio}s way requires you to play some games (in its ``binary''
10010 format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
10011 they're 18 bits---it would have to play games with the "file system @acronym{ID}"
10012 field of the header to make sure that the file system @acronym{ID}/i-number pairs
10013 of different files were always different), and I don't know which
10014 @command{cpio}s, if any, play those games. Those that don't might get
10015 confused and think two files are the same file when they're not, and
10016 make hard links between them.
10018 @command{tar}s way of handling multiple hard links to a file places only
10019 one copy of the link on the tape, but the name attached to that copy
10020 is the @emph{only} one you can use to retrieve the file; @command{cpio}s
10021 way puts one copy for every link, but you can retrieve it using any
10025 What type of check sum (if any) is used, and how is this calculated.
10028 See the attached manual pages for @command{tar} and @command{cpio} format.
10029 @command{tar} uses a checksum which is the sum of all the bytes in the
10030 @command{tar} header for a file; @command{cpio} uses no checksum.
10033 If anyone knows why @command{cpio} was made when @command{tar} was present
10037 It wasn't. @command{cpio} first showed up in PWB/UNIX 1.0; no
10038 generally-available version of UNIX had @command{tar} at the time. I don't
10039 know whether any version that was generally available @emph{within AT&T}
10040 had @command{tar}, or, if so, whether the people within AT&T who did
10041 @command{cpio} knew about it.
10043 On restore, if there is a corruption on a tape @command{tar} will stop at
10044 that point, while @command{cpio} will skip over it and try to restore the
10047 The main difference is just in the command syntax and header format.
10049 @command{tar} is a little more tape-oriented in that everything is blocked
10050 to start on a record boundary.
10053 Is there any differences between the ability to recover crashed
10054 archives between the two of them. (Is there any chance of recovering
10055 crashed archives at all.)
10058 Theoretically it should be easier under @command{tar} since the blocking
10059 lets you find a header with some variation of @samp{dd skip=@var{nn}}.
10060 However, modern @command{cpio}'s and variations have an option to just
10061 search for the next file header after an error with a reasonable chance
10062 of resyncing. However, lots of tape driver software won't allow you to
10063 continue past a media error which should be the only reason for getting
10064 out of sync unless a file changed sizes while you were writing the
10068 If anyone knows why @command{cpio} was made when @command{tar} was present
10069 at the unix scene, please tell me about this too.
10072 Probably because it is more media efficient (by not blocking everything
10073 and using only the space needed for the headers where @command{tar}
10074 always uses 512 bytes per file header) and it knows how to archive
10077 You might want to look at the freely available alternatives. The
10078 major ones are @command{afio}, @GNUTAR{}, and
10079 @command{pax}, each of which have their own extensions with some
10080 backwards compatibility.
10082 Sparse files were @command{tar}red as sparse files (which you can
10083 easily test, because the resulting archive gets smaller, and
10084 @acronym{GNU} @command{cpio} can no longer read it).
10087 @chapter Tapes and Other Archive Media
10090 A few special cases about tape handling warrant more detailed
10091 description. These special cases are discussed below.
10093 Many complexities surround the use of @command{tar} on tape drives. Since
10094 the creation and manipulation of archives located on magnetic tape was
10095 the original purpose of @command{tar}, it contains many features making
10096 such manipulation easier.
10098 Archives are usually written on dismountable media---tape cartridges,
10099 mag tapes, or floppy disks.
10101 The amount of data a tape or disk holds depends not only on its size,
10102 but also on how it is formatted. A 2400 foot long reel of mag tape
10103 holds 40 megabytes of data when formatted at 1600 bits per inch. The
10104 physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
10106 Magnetic media are re-usable---once the archive on a tape is no longer
10107 needed, the archive can be erased and the tape or disk used over.
10108 Media quality does deteriorate with use, however. Most tapes or disks
10109 should be discarded when they begin to produce data errors. EXABYTE
10110 tape cartridges should be discarded when they generate an @dfn{error
10111 count} (number of non-usable bits) of more than 10k.
10113 Magnetic media are written and erased using magnetic fields, and
10114 should be protected from such fields to avoid damage to stored data.
10115 Sticking a floppy disk to a filing cabinet using a magnet is probably
10119 * Device:: Device selection and switching
10120 * Remote Tape Server::
10121 * Common Problems and Solutions::
10122 * Blocking:: Blocking
10123 * Many:: Many archives on one tape
10124 * Using Multiple Tapes:: Using Multiple Tapes
10125 * label:: Including a Label in the Archive
10127 * Write Protection::
10131 @section Device Selection and Switching
10135 @item -f [@var{hostname}:]@var{file}
10136 @itemx --file=[@var{hostname}:]@var{file}
10137 Use archive file or device @var{file} on @var{hostname}.
10140 This option is used to specify the file name of the archive @command{tar}
10143 If the file name is @samp{-}, @command{tar} reads the archive from standard
10144 input (when listing or extracting), or writes it to standard output
10145 (when creating). If the @samp{-} file name is given when updating an
10146 archive, @command{tar} will read the original archive from its standard
10147 input, and will write the entire new archive to its standard output.
10149 If the file name contains a @samp{:}, it is interpreted as
10150 @samp{hostname:file name}. If the @var{hostname} contains an @dfn{at}
10151 sign (@samp{@@}), it is treated as @samp{user@@hostname:file name}. In
10152 either case, @command{tar} will invoke the command @command{rsh} (or
10153 @command{remsh}) to start up an @command{/usr/libexec/rmt} on the remote
10154 machine. If you give an alternate login name, it will be given to the
10156 Naturally, the remote machine must have an executable
10157 @command{/usr/libexec/rmt}. This program is free software from the
10158 University of California, and a copy of the source code can be found
10159 with the sources for @command{tar}; it's compiled and installed by default.
10160 The exact path to this utility is determined when configuring the package.
10161 It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for
10162 your installation prefix. This location may also be overridden at
10163 runtime by using @option{rmt-command=@var{command}} option (@xref{Option Summary,
10164 ---rmt-command}, for detailed description of this option. @xref{Remote
10165 Tape Server}, for the description of @command{rmt} command).
10167 If this option is not given, but the environment variable @env{TAPE}
10168 is set, its value is used; otherwise, old versions of @command{tar}
10169 used a default archive name (which was picked when @command{tar} was
10170 compiled). The default is normally set up to be the @dfn{first} tape
10171 drive or other transportable I/O medium on the system.
10173 Starting with version 1.11.5, @GNUTAR{} uses
10174 standard input and standard output as the default device, and I will
10175 not try anymore supporting automatic device detection at installation
10176 time. This was failing really in too many cases, it was hopeless.
10177 This is now completely left to the installer to override standard
10178 input and standard output for default device, if this seems
10179 preferable. Further, I think @emph{most} actual usages of
10180 @command{tar} are done with pipes or disks, not really tapes,
10181 cartridges or diskettes.
10183 Some users think that using standard input and output is running
10184 after trouble. This could lead to a nasty surprise on your screen if
10185 you forget to specify an output file name---especially if you are going
10186 through a network or terminal server capable of buffering large amounts
10187 of output. We had so many bug reports in that area of configuring
10188 default tapes automatically, and so many contradicting requests, that
10189 we finally consider the problem to be portably intractable. We could
10190 of course use something like @samp{/dev/tape} as a default, but this
10191 is @emph{also} running after various kind of trouble, going from hung
10192 processes to accidental destruction of real tapes. After having seen
10193 all this mess, using standard input and output as a default really
10194 sounds like the only clean choice left, and a very useful one too.
10196 @GNUTAR{} reads and writes archive in records, I
10197 suspect this is the main reason why block devices are preferred over
10198 character devices. Most probably, block devices are more efficient
10199 too. The installer could also check for @samp{DEFTAPE} in
10200 @file{<sys/mtio.h>}.
10203 @xopindex{force-local, short description}
10204 @item --force-local
10205 Archive file is local even if it contains a colon.
10207 @opindex rsh-command
10208 @item --rsh-command=@var{command}
10209 Use remote @var{command} instead of @command{rsh}. This option exists
10210 so that people who use something other than the standard @command{rsh}
10211 (e.g., a Kerberized @command{rsh}) can access a remote device.
10213 When this command is not used, the shell command found when
10214 the @command{tar} program was installed is used instead. This is
10215 the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh},
10216 @file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}.
10217 The installer may have overridden this by defining the environment
10218 variable @env{RSH} @emph{at installation time}.
10221 Specify drive and density.
10223 @xopindex{multi-volume, short description}
10225 @itemx --multi-volume
10226 Create/list/extract multi-volume archive.
10228 This option causes @command{tar} to write a @dfn{multi-volume} archive---one
10229 that may be larger than will fit on the medium used to hold it.
10230 @xref{Multi-Volume Archives}.
10232 @xopindex{tape-length, short description}
10234 @itemx --tape-length=@var{num}
10235 Change tape after writing @var{num} x 1024 bytes.
10237 This option might be useful when your tape drivers do not properly
10238 detect end of physical tapes. By being slightly conservative on the
10239 maximum tape length, you might avoid the problem entirely.
10241 @xopindex{info-script, short description}
10242 @xopindex{new-volume-script, short description}
10243 @item -F @var{file}
10244 @itemx --info-script=@var{file}
10245 @itemx --new-volume-script=@var{file}
10246 Execute @file{file} at end of each tape. This implies
10247 @option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed
10248 description of this option.
10251 @node Remote Tape Server
10252 @section The Remote Tape Server
10254 @cindex remote tape drive
10256 In order to access the tape drive on a remote machine, @command{tar}
10257 uses the remote tape server written at the University of California at
10258 Berkeley. The remote tape server must be installed as
10259 @file{@var{prefix}/libexec/rmt} on any machine whose tape drive you
10260 want to use. @command{tar} calls @command{rmt} by running an
10261 @command{rsh} or @command{remsh} to the remote machine, optionally
10262 using a different login name if one is supplied.
10264 A copy of the source for the remote tape server is provided. It is
10265 Copyright @copyright{} 1983 by the Regents of the University of
10266 California, but can be freely distributed. It is compiled and
10267 installed by default.
10269 @cindex absolute file names
10270 Unless you use the @option{--absolute-names} (@option{-P}) option,
10271 @GNUTAR{} will not allow you to create an archive that contains
10272 absolute file names (a file name beginning with @samp{/}.) If you try,
10273 @command{tar} will automatically remove the leading @samp{/} from the
10274 file names it stores in the archive. It will also type a warning
10275 message telling you what it is doing.
10277 When reading an archive that was created with a different
10278 @command{tar} program, @GNUTAR{} automatically
10279 extracts entries in the archive which have absolute file names as if
10280 the file names were not absolute. This is an important feature. A
10281 visitor here once gave a @command{tar} tape to an operator to restore;
10282 the operator used Sun @command{tar} instead of @GNUTAR{},
10283 and the result was that it replaced large portions of
10284 our @file{/bin} and friends with versions from the tape; needless to
10285 say, we were unhappy about having to recover the file system from
10288 For example, if the archive contained a file @file{/usr/bin/computoy},
10289 @GNUTAR{} would extract the file to @file{usr/bin/computoy},
10290 relative to the current directory. If you want to extract the files in
10291 an archive to the same absolute names that they had when the archive
10292 was created, you should do a @samp{cd /} before extracting the files
10293 from the archive, or you should either use the @option{--absolute-names}
10294 option, or use the command @samp{tar -C / @dots{}}.
10296 @cindex Ultrix 3.1 and write failure
10297 Some versions of Unix (Ultrix 3.1 is known to have this problem),
10298 can claim that a short write near the end of a tape succeeded,
10299 when it actually failed. This will result in the -M option not
10300 working correctly. The best workaround at the moment is to use a
10301 significantly larger blocking factor than the default 20.
10303 In order to update an archive, @command{tar} must be able to backspace the
10304 archive in order to reread or rewrite a record that was just read (or
10305 written). This is currently possible only on two kinds of files: normal
10306 disk files (or any other file that can be backspaced with @samp{lseek}),
10307 and industry-standard 9-track magnetic tape (or any other kind of tape
10308 that can be backspaced with the @code{MTIOCTOP} @code{ioctl}.
10310 This means that the @option{--append}, @option{--concatenate}, and
10311 @option{--delete} commands will not work on any other kind of file.
10312 Some media simply cannot be backspaced, which means these commands and
10313 options will never be able to work on them. These non-backspacing
10314 media include pipes and cartridge tape drives.
10316 Some other media can be backspaced, and @command{tar} will work on them
10317 once @command{tar} is modified to do so.
10319 Archives created with the @option{--multi-volume}, @option{--label}, and
10320 @option{--incremental} (@option{-G}) options may not be readable by other version
10321 of @command{tar}. In particular, restoring a file that was split over
10322 a volume boundary will require some careful work with @command{dd}, if
10323 it can be done at all. Other versions of @command{tar} may also create
10324 an empty file whose name is that of the volume header. Some versions
10325 of @command{tar} may create normal files instead of directories archived
10326 with the @option{--incremental} (@option{-G}) option.
10328 @node Common Problems and Solutions
10329 @section Some Common Problems and their Solutions
10334 errors from system:
10336 no such file or directory
10339 errors from @command{tar}:
10340 directory checksum error
10341 header format error
10343 errors from media/system:
10355 @dfn{Block} and @dfn{record} terminology is rather confused, and it
10356 is also confusing to the expert reader. On the other hand, readers
10357 who are new to the field have a fresh mind, and they may safely skip
10358 the next two paragraphs, as the remainder of this manual uses those
10359 two terms in a quite consistent way.
10361 John Gilmore, the writer of the public domain @command{tar} from which
10362 @GNUTAR{} was originally derived, wrote (June 1995):
10365 The nomenclature of tape drives comes from IBM, where I believe
10366 they were invented for the IBM 650 or so. On IBM mainframes, what
10367 is recorded on tape are tape blocks. The logical organization of
10368 data is into records. There are various ways of putting records into
10369 blocks, including @code{F} (fixed sized records), @code{V} (variable
10370 sized records), @code{FB} (fixed blocked: fixed size records, @var{n}
10371 to a block), @code{VB} (variable size records, @var{n} to a block),
10372 @code{VSB} (variable spanned blocked: variable sized records that can
10373 occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=}
10374 parameter specified this to the operating system.
10376 The Unix man page on @command{tar} was totally confused about this.
10377 When I wrote @code{PD TAR}, I used the historically correct terminology
10378 (@command{tar} writes data records, which are grouped into blocks).
10379 It appears that the bogus terminology made it into @acronym{POSIX} (no surprise
10380 here), and now Fran@,{c}ois has migrated that terminology back
10381 into the source code too.
10384 The term @dfn{physical block} means the basic transfer chunk from or
10385 to a device, after which reading or writing may stop without anything
10386 being lost. In this manual, the term @dfn{block} usually refers to
10387 a disk physical block, @emph{assuming} that each disk block is 512
10388 bytes in length. It is true that some disk devices have different
10389 physical blocks, but @command{tar} ignore these differences in its own
10390 format, which is meant to be portable, so a @command{tar} block is always
10391 512 bytes in length, and @dfn{block} always mean a @command{tar} block.
10392 The term @dfn{logical block} often represents the basic chunk of
10393 allocation of many disk blocks as a single entity, which the operating
10394 system treats somewhat atomically; this concept is only barely used
10397 The term @dfn{physical record} is another way to speak of a physical
10398 block, those two terms are somewhat interchangeable. In this manual,
10399 the term @dfn{record} usually refers to a tape physical block,
10400 @emph{assuming} that the @command{tar} archive is kept on magnetic tape.
10401 It is true that archives may be put on disk or used with pipes,
10402 but nevertheless, @command{tar} tries to read and write the archive one
10403 @dfn{record} at a time, whatever the medium in use. One record is made
10404 up of an integral number of blocks, and this operation of putting many
10405 disk blocks into a single tape block is called @dfn{reblocking}, or
10406 more simply, @dfn{blocking}. The term @dfn{logical record} refers to
10407 the logical organization of many characters into something meaningful
10408 to the application. The term @dfn{unit record} describes a small set
10409 of characters which are transmitted whole to or by the application,
10410 and often refers to a line of text. Those two last terms are unrelated
10411 to what we call a @dfn{record} in @GNUTAR{}.
10413 When writing to tapes, @command{tar} writes the contents of the archive
10414 in chunks known as @dfn{records}. To change the default blocking
10415 factor, use the @option{--blocking-factor=@var{512-size}} (@option{-b
10416 @var{512-size}}) option. Each record will then be composed of
10417 @var{512-size} blocks. (Each @command{tar} block is 512 bytes.
10418 @xref{Standard}.) Each file written to the archive uses at least one
10419 full record. As a result, using a larger record size can result in
10420 more wasted space for small files. On the other hand, a larger record
10421 size can often be read and written much more efficiently.
10423 Further complicating the problem is that some tape drives ignore the
10424 blocking entirely. For these, a larger record size can still improve
10425 performance (because the software layers above the tape drive still
10426 honor the blocking), but not as dramatically as on tape drives that
10429 When reading an archive, @command{tar} can usually figure out the
10430 record size on itself. When this is the case, and a non-standard
10431 record size was used when the archive was created, @command{tar} will
10432 print a message about a non-standard blocking factor, and then operate
10433 normally. On some tape devices, however, @command{tar} cannot figure
10434 out the record size itself. On most of those, you can specify a
10435 blocking factor (with @option{--blocking-factor}) larger than the
10436 actual blocking factor, and then use the @option{--read-full-records}
10437 (@option{-B}) option. (If you specify a blocking factor with
10438 @option{--blocking-factor} and don't use the
10439 @option{--read-full-records} option, then @command{tar} will not
10440 attempt to figure out the recording size itself.) On some devices,
10441 you must always specify the record size exactly with
10442 @option{--blocking-factor} when reading, because @command{tar} cannot
10443 figure it out. In any case, use @option{--list} (@option{-t}) before
10444 doing any extractions to see whether @command{tar} is reading the archive
10447 @command{tar} blocks are all fixed size (512 bytes), and its scheme for
10448 putting them into records is to put a whole number of them (one or
10449 more) into each record. @command{tar} records are all the same size;
10450 at the end of the file there's a block containing all zeros, which
10451 is how you tell that the remainder of the last record(s) are garbage.
10453 In a standard @command{tar} file (no options), the block size is 512
10454 and the record size is 10240, for a blocking factor of 20. What the
10455 @option{--blocking-factor} option does is sets the blocking factor,
10456 changing the record size while leaving the block size at 512 bytes.
10457 20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives;
10458 most tape drives these days prefer much bigger records in order to
10459 stream and not waste tape. When writing tapes for myself, some tend
10460 to use a factor of the order of 2048, say, giving a record size of
10461 around one megabyte.
10463 If you use a blocking factor larger than 20, older @command{tar}
10464 programs might not be able to read the archive, so we recommend this
10465 as a limit to use in practice. @GNUTAR{}, however,
10466 will support arbitrarily large record sizes, limited only by the
10467 amount of virtual memory or the physical characteristics of the tape
10471 * Format Variations:: Format Variations
10472 * Blocking Factor:: The Blocking Factor of an Archive
10475 @node Format Variations
10476 @subsection Format Variations
10477 @cindex Format Parameters
10478 @cindex Format Options
10479 @cindex Options, archive format specifying
10480 @cindex Options, format specifying
10483 Format parameters specify how an archive is written on the archive
10484 media. The best choice of format parameters will vary depending on
10485 the type and number of files being archived, and on the media used to
10488 To specify format parameters when accessing or creating an archive,
10489 you can use the options described in the following sections.
10490 If you do not specify any format parameters, @command{tar} uses
10491 default parameters. You cannot modify a compressed archive.
10492 If you create an archive with the @option{--blocking-factor} option
10493 specified (@pxref{Blocking Factor}), you must specify that
10494 blocking-factor when operating on the archive. @xref{Formats}, for other
10495 examples of format parameter considerations.
10497 @node Blocking Factor
10498 @subsection The Blocking Factor of an Archive
10499 @cindex Blocking Factor
10500 @cindex Record Size
10501 @cindex Number of blocks per record
10502 @cindex Number of bytes per record
10503 @cindex Bytes per record
10504 @cindex Blocks per record
10507 @opindex blocking-factor
10508 The data in an archive is grouped into blocks, which are 512 bytes.
10509 Blocks are read and written in whole number multiples called
10510 @dfn{records}. The number of blocks in a record (i.e., the size of a
10511 record in units of 512 bytes) is called the @dfn{blocking factor}.
10512 The @option{--blocking-factor=@var{512-size}} (@option{-b
10513 @var{512-size}}) option specifies the blocking factor of an archive.
10514 The default blocking factor is typically 20 (i.e., 10240 bytes), but
10515 can be specified at installation. To find out the blocking factor of
10516 an existing archive, use @samp{tar --list --file=@var{archive-name}}.
10517 This may not work on some devices.
10519 Records are separated by gaps, which waste space on the archive media.
10520 If you are archiving on magnetic tape, using a larger blocking factor
10521 (and therefore larger records) provides faster throughput and allows you
10522 to fit more data on a tape (because there are fewer gaps). If you are
10523 archiving on cartridge, a very large blocking factor (say 126 or more)
10524 greatly increases performance. A smaller blocking factor, on the other
10525 hand, may be useful when archiving small files, to avoid archiving lots
10526 of nulls as @command{tar} fills out the archive to the end of the record.
10527 In general, the ideal record size depends on the size of the
10528 inter-record gaps on the tape you are using, and the average size of the
10529 files you are archiving. @xref{create}, for information on
10532 @FIXME{Need example of using a cartridge with blocking factor=126 or more.}
10534 Archives with blocking factors larger than 20 cannot be read
10535 by very old versions of @command{tar}, or by some newer versions
10536 of @command{tar} running on old machines with small address spaces.
10537 With @GNUTAR{}, the blocking factor of an archive is limited
10538 only by the maximum record size of the device containing the archive,
10539 or by the amount of available virtual memory.
10541 Also, on some systems, not using adequate blocking factors, as sometimes
10542 imposed by the device drivers, may yield unexpected diagnostics. For
10543 example, this has been reported:
10546 Cannot write to /dev/dlt: Invalid argument
10550 In such cases, it sometimes happen that the @command{tar} bundled by
10551 the system is aware of block size idiosyncrasies, while @GNUTAR{}
10552 requires an explicit specification for the block size,
10553 which it cannot guess. This yields some people to consider
10554 @GNUTAR{} is misbehaving, because by comparison,
10555 @cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}},
10556 for example, might resolve the problem.
10558 If you use a non-default blocking factor when you create an archive, you
10559 must specify the same blocking factor when you modify that archive. Some
10560 archive devices will also require you to specify the blocking factor when
10561 reading that archive, however this is not typically the case. Usually, you
10562 can use @option{--list} (@option{-t}) without specifying a blocking factor---@command{tar}
10563 reports a non-default record size and then lists the archive members as
10564 it would normally. To extract files from an archive with a non-standard
10565 blocking factor (particularly if you're not sure what the blocking factor
10566 is), you can usually use the @option{--read-full-records} (@option{-B}) option while
10567 specifying a blocking factor larger then the blocking factor of the archive
10568 (i.e., @samp{tar --extract --read-full-records --blocking-factor=300}.
10569 @xref{list}, for more information on the @option{--list} (@option{-t})
10570 operation. @xref{Reading}, for a more detailed explanation of that option.
10573 @item --blocking-factor=@var{number}
10574 @itemx -b @var{number}
10575 Specifies the blocking factor of an archive. Can be used with any
10576 operation, but is usually not necessary with @option{--list} (@option{-t}).
10582 @item -b @var{blocks}
10583 @itemx --blocking-factor=@var{blocks}
10584 Set record size to @math{@var{blocks} * 512} bytes.
10586 This option is used to specify a @dfn{blocking factor} for the archive.
10587 When reading or writing the archive, @command{tar}, will do reads and writes
10588 of the archive in records of @math{@var{block}*512} bytes. This is true
10589 even when the archive is compressed. Some devices requires that all
10590 write operations be a multiple of a certain size, and so, @command{tar}
10591 pads the archive out to the next record boundary.
10593 The default blocking factor is set when @command{tar} is compiled, and is
10594 typically 20. Blocking factors larger than 20 cannot be read by very
10595 old versions of @command{tar}, or by some newer versions of @command{tar}
10596 running on old machines with small address spaces.
10598 With a magnetic tape, larger records give faster throughput and fit
10599 more data on a tape (because there are fewer inter-record gaps).
10600 If the archive is in a disk file or a pipe, you may want to specify
10601 a smaller blocking factor, since a large one will result in a large
10602 number of null bytes at the end of the archive.
10604 When writing cartridge or other streaming tapes, a much larger
10605 blocking factor (say 126 or more) will greatly increase performance.
10606 However, you must specify the same blocking factor when reading or
10607 updating the archive.
10609 Apparently, Exabyte drives have a physical block size of 8K bytes.
10610 If we choose our blocksize as a multiple of 8k bytes, then the problem
10611 seems to disappear. Id est, we are using block size of 112 right
10612 now, and we haven't had the problem since we switched@dots{}
10614 With @GNUTAR{} the blocking factor is limited only
10615 by the maximum record size of the device containing the archive, or by
10616 the amount of available virtual memory.
10618 However, deblocking or reblocking is virtually avoided in a special
10619 case which often occurs in practice, but which requires all the
10620 following conditions to be simultaneously true:
10623 the archive is subject to a compression option,
10625 the archive is not handled through standard input or output, nor
10626 redirected nor piped,
10628 the archive is directly handled to a local disk, instead of any special
10631 @option{--blocking-factor} is not explicitly specified on the @command{tar}
10635 If the output goes directly to a local disk, and not through
10636 stdout, then the last write is not extended to a full record size.
10637 Otherwise, reblocking occurs. Here are a few other remarks on this
10643 @command{gzip} will complain about trailing garbage if asked to
10644 uncompress a compressed archive on tape, there is an option to turn
10645 the message off, but it breaks the regularity of simply having to use
10646 @samp{@var{prog} -d} for decompression. It would be nice if gzip was
10647 silently ignoring any number of trailing zeros. I'll ask Jean-loup
10648 Gailly, by sending a copy of this message to him.
10651 @command{compress} does not show this problem, but as Jean-loup pointed
10652 out to Michael, @samp{compress -d} silently adds garbage after
10653 the result of decompression, which tar ignores because it already
10654 recognized its end-of-file indicator. So this bug may be safely
10658 @samp{gzip -d -q} will be silent about the trailing zeros indeed,
10659 but will still return an exit status of 2 which tar reports in turn.
10660 @command{tar} might ignore the exit status returned, but I hate doing
10661 that, as it weakens the protection @command{tar} offers users against
10662 other possible problems at decompression time. If @command{gzip} was
10663 silently skipping trailing zeros @emph{and} also avoiding setting the
10664 exit status in this innocuous case, that would solve this situation.
10667 @command{tar} should become more solid at not stopping to read a pipe at
10668 the first null block encountered. This inelegantly breaks the pipe.
10669 @command{tar} should rather drain the pipe out before exiting itself.
10672 @xopindex{ignore-zeros, short description}
10674 @itemx --ignore-zeros
10675 Ignore blocks of zeros in archive (means EOF).
10677 The @option{--ignore-zeros} (@option{-i}) option causes @command{tar} to ignore blocks
10678 of zeros in the archive. Normally a block of zeros indicates the
10679 end of the archive, but when reading a damaged archive, or one which
10680 was created by concatenating several archives together, this option
10681 allows @command{tar} to read the entire archive. This option is not on
10682 by default because many versions of @command{tar} write garbage after
10685 Note that this option causes @command{tar} to read to the end of the
10686 archive file, which may sometimes avoid problems when multiple files
10687 are stored on a single physical tape.
10689 @xopindex{read-full-records, short description}
10691 @itemx --read-full-records
10692 Reblock as we read (for reading 4.2@acronym{BSD} pipes).
10694 If @option{--read-full-records} is used, @command{tar}
10695 will not panic if an attempt to read a record from the archive does
10696 not return a full record. Instead, @command{tar} will keep reading
10697 until it has obtained a full
10700 This option is turned on by default when @command{tar} is reading
10701 an archive from standard input, or from a remote machine. This is
10702 because on @acronym{BSD} Unix systems, a read of a pipe will return however
10703 much happens to be in the pipe, even if it is less than @command{tar}
10704 requested. If this option was not used, @command{tar} would fail as
10705 soon as it read an incomplete record from the pipe.
10707 This option is also useful with the commands for updating an archive.
10713 @FIXME{Appropriate options should be moved here from elsewhere.}
10715 @cindex blocking factor
10716 @cindex tape blocking
10718 When handling various tapes or cartridges, you have to take care of
10719 selecting a proper blocking, that is, the number of disk blocks you
10720 put together as a single tape block on the tape, without intervening
10721 tape gaps. A @dfn{tape gap} is a small landing area on the tape
10722 with no information on it, used for decelerating the tape to a
10723 full stop, and for later regaining the reading or writing speed.
10724 When the tape driver starts reading a record, the record has to
10725 be read whole without stopping, as a tape gap is needed to stop the
10726 tape motion without loosing information.
10728 @cindex Exabyte blocking
10729 @cindex DAT blocking
10730 Using higher blocking (putting more disk blocks per tape block) will use
10731 the tape more efficiently as there will be less tape gaps. But reading
10732 such tapes may be more difficult for the system, as more memory will be
10733 required to receive at once the whole record. Further, if there is a
10734 reading error on a huge record, this is less likely that the system will
10735 succeed in recovering the information. So, blocking should not be too
10736 low, nor it should be too high. @command{tar} uses by default a blocking of
10737 20 for historical reasons, and it does not really matter when reading or
10738 writing to disk. Current tape technology would easily accommodate higher
10739 blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs.
10740 We were told that for some DLT drives, the blocking should be a multiple
10741 of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance.
10742 Other manufacturers may use different recommendations for the same tapes.
10743 This might also depends of the buffering techniques used inside modern
10744 tape controllers. Some imposes a minimum blocking, or a maximum blocking.
10745 Others request blocking to be some exponent of two.
10747 So, there is no fixed rule for blocking. But blocking at read time
10748 should ideally be the same as blocking used at write time. At one place
10749 I know, with a wide variety of equipment, they found it best to use a
10750 blocking of 32 to guarantee that their tapes are fully interchangeable.
10752 I was also told that, for recycled tapes, prior erasure (by the same
10753 drive unit that will be used to create the archives) sometimes lowers
10754 the error rates observed at rewriting time.
10756 I might also use @option{--number-blocks} instead of
10757 @option{--block-number}, so @option{--block} will then expand to
10758 @option{--blocking-factor} unambiguously.
10761 @section Many Archives on One Tape
10763 @FIXME{Appropriate options should be moved here from elsewhere.}
10765 @findex ntape @r{device}
10766 Most tape devices have two entries in the @file{/dev} directory, or
10767 entries that come in pairs, which differ only in the minor number for
10768 this device. Let's take for example @file{/dev/tape}, which often
10769 points to the only or usual tape device of a given system. There might
10770 be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler
10771 name is the @emph{rewinding} version of the device, while the name
10772 having @samp{nr} in it is the @emph{no rewinding} version of the same
10775 A rewinding tape device will bring back the tape to its beginning point
10776 automatically when this device is opened or closed. Since @command{tar}
10777 opens the archive file before using it and closes it afterwards, this
10778 means that a simple:
10781 $ @kbd{tar cf /dev/tape @var{directory}}
10785 will reposition the tape to its beginning both prior and after saving
10786 @var{directory} contents to it, thus erasing prior tape contents and
10787 making it so that any subsequent write operation will destroy what has
10790 @cindex tape positioning
10791 So, a rewinding device is normally meant to hold one and only one file.
10792 If you want to put more than one @command{tar} archive on a given tape, you
10793 will need to avoid using the rewinding version of the tape device. You
10794 will also have to pay special attention to tape positioning. Errors in
10795 positioning may overwrite the valuable data already on your tape. Many
10796 people, burnt by past experiences, will only use rewinding devices and
10797 limit themselves to one file per tape, precisely to avoid the risk of
10798 such errors. Be fully aware that writing at the wrong position on a
10799 tape loses all information past this point and most probably until the
10800 end of the tape, and this destroyed information @emph{cannot} be
10803 To save @var{directory-1} as a first archive at the beginning of a
10804 tape, and leave that tape ready for a second archive, you should use:
10807 $ @kbd{mt -f /dev/nrtape rewind}
10808 $ @kbd{tar cf /dev/nrtape @var{directory-1}}
10812 @dfn{Tape marks} are special magnetic patterns written on the tape
10813 media, which are later recognizable by the reading hardware. These
10814 marks are used after each file, when there are many on a single tape.
10815 An empty file (that is to say, two tape marks in a row) signal the
10816 logical end of the tape, after which no file exist. Usually,
10817 non-rewinding tape device drivers will react to the close request issued
10818 by @command{tar} by first writing two tape marks after your archive, and by
10819 backspacing over one of these. So, if you remove the tape at that time
10820 from the tape drive, it is properly terminated. But if you write
10821 another file at the current position, the second tape mark will be
10822 erased by the new information, leaving only one tape mark between files.
10824 So, you may now save @var{directory-2} as a second archive after the
10825 first on the same tape by issuing the command:
10828 $ @kbd{tar cf /dev/nrtape @var{directory-2}}
10832 and so on for all the archives you want to put on the same tape.
10834 Another usual case is that you do not write all the archives the same
10835 day, and you need to remove and store the tape between two archive
10836 sessions. In general, you must remember how many files are already
10837 saved on your tape. Suppose your tape already has 16 files on it, and
10838 that you are ready to write the 17th. You have to take care of skipping
10839 the first 16 tape marks before saving @var{directory-17}, say, by using
10843 $ @kbd{mt -f /dev/nrtape rewind}
10844 $ @kbd{mt -f /dev/nrtape fsf 16}
10845 $ @kbd{tar cf /dev/nrtape @var{directory-17}}
10848 In all the previous examples, we put aside blocking considerations, but
10849 you should do the proper things for that as well. @xref{Blocking}.
10852 * Tape Positioning:: Tape Positions and Tape Marks
10853 * mt:: The @command{mt} Utility
10856 @node Tape Positioning
10857 @subsection Tape Positions and Tape Marks
10860 Just as archives can store more than one file from the file system,
10861 tapes can store more than one archive file. To keep track of where
10862 archive files (or any other type of file stored on tape) begin and
10863 end, tape archive devices write magnetic @dfn{tape marks} on the
10864 archive media. Tape drives write one tape mark between files,
10865 two at the end of all the file entries.
10867 If you think of data as a series of records "rrrr"'s, and tape marks as
10868 "*"'s, a tape might look like the following:
10871 rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
10874 Tape devices read and write tapes using a read/write @dfn{tape
10875 head}---a physical part of the device which can only access one
10876 point on the tape at a time. When you use @command{tar} to read or
10877 write archive data from a tape device, the device will begin reading
10878 or writing from wherever on the tape the tape head happens to be,
10879 regardless of which archive or what part of the archive the tape
10880 head is on. Before writing an archive, you should make sure that no
10881 data on the tape will be overwritten (unless it is no longer needed).
10882 Before reading an archive, you should make sure the tape head is at
10883 the beginning of the archive you want to read. You can do it manually
10884 via @code{mt} utility (@pxref{mt}). The @code{restore} script does
10885 that automatically (@pxref{Scripted Restoration}).
10887 If you want to add new archive file entries to a tape, you should
10888 advance the tape to the end of the existing file entries, backspace
10889 over the last tape mark, and write the new archive file. If you were
10890 to add two archives to the example above, the tape might look like the
10894 rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
10898 @subsection The @command{mt} Utility
10901 @FIXME{Is it true that this only works on non-block devices?
10902 should explain the difference, (fixed or variable).}
10903 @xref{Blocking Factor}.
10905 You can use the @command{mt} utility to advance or rewind a tape past a
10906 specified number of archive files on the tape. This will allow you
10907 to move to the beginning of an archive before extracting or reading
10908 it, or to the end of all the archives before writing a new one.
10909 @FIXME{Why isn't there an "advance 'til you find two tape marks
10912 The syntax of the @command{mt} command is:
10915 @kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
10918 where @var{tapename} is the name of the tape device, @var{number} is
10919 the number of times an operation is performed (with a default of one),
10920 and @var{operation} is one of the following:
10922 @FIXME{is there any use for record operations?}
10927 Writes @var{number} tape marks at the current position on the tape.
10930 Moves tape position forward @var{number} files.
10933 Moves tape position back @var{number} files.
10936 Rewinds the tape. (Ignores @var{number}).
10940 Rewinds the tape and takes the tape device off-line. (Ignores @var{number}).
10943 Prints status information about the tape unit.
10947 If you don't specify a @var{tapename}, @command{mt} uses the environment
10948 variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
10949 the default device specified in your @file{sys/mtio.h} file
10950 (@code{DEFTAPE} variable). If this is not defined, the program will
10951 display a descriptive error message and exit with code 1.
10953 @command{mt} returns a 0 exit status when the operation(s) were
10954 successful, 1 if the command was unrecognized, and 2 if an operation
10957 @node Using Multiple Tapes
10958 @section Using Multiple Tapes
10960 Often you might want to write a large archive, one larger than will fit
10961 on the actual tape you are using. In such a case, you can run multiple
10962 @command{tar} commands, but this can be inconvenient, particularly if you
10963 are using options like @option{--exclude=@var{pattern}} or dumping entire file systems.
10964 Therefore, @command{tar} provides a special mode for creating
10965 multi-volume archives.
10967 @dfn{Multi-volume} archive is a single @command{tar} archive, stored
10968 on several media volumes of fixed size. Although in this section we will
10969 often call @samp{volume} a @dfn{tape}, there is absolutely no
10970 requirement for multi-volume archives to be stored on tapes. Instead,
10971 they can use whatever media type the user finds convenient, they can
10972 even be located on files.
10974 When creating a multi-volume archive, @GNUTAR{} continues to fill
10975 current volume until it runs out of space, then it switches to
10976 next volume (usually the operator is queried to replace the tape on
10977 this point), and continues working on the new volume. This operation
10978 continues until all requested files are dumped. If @GNUTAR{} detects
10979 end of media while dumping a file, such a file is archived in split
10980 form. Some very big files can even be split across several volumes.
10982 Each volume is itself a valid @GNUTAR{} archive, so it can be read
10983 without any special options. Consequently any file member residing
10984 entirely on one volume can be extracted or otherwise operated upon
10985 without needing the other volume. Sure enough, to extract a split
10986 member you would need all volumes its parts reside on.
10988 Multi-volume archives suffer from several limitations. In particular,
10989 they cannot be compressed.
10991 @GNUTAR{} is able to create multi-volume archives of two formats
10992 (@pxref{Formats}): @samp{GNU} and @samp{POSIX}.
10995 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
10996 * Tape Files:: Tape Files
10997 * Tarcat:: Concatenate Volumes into a Single Archive
11001 @node Multi-Volume Archives
11002 @subsection Archives Longer than One Tape or Disk
11003 @cindex Multi-volume archives
11005 @opindex multi-volume
11006 To create an archive that is larger than will fit on a single unit of
11007 the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
11008 the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
11009 archive can be manipulated like any other archive (provided the
11010 @option{--multi-volume} option is specified), but is stored on more
11011 than one tape or disk.
11013 When you specify @option{--multi-volume}, @command{tar} does not report an
11014 error when it comes to the end of an archive volume (when reading), or
11015 the end of the media (when writing). Instead, it prompts you to load
11016 a new storage volume. If the archive is on a magnetic tape, you
11017 should change tapes when you see the prompt; if the archive is on a
11018 floppy disk, you should change disks; etc.
11021 @item --multi-volume
11023 Creates a multi-volume archive, when used in conjunction with
11024 @option{--create} (@option{-c}). To perform any other operation on a multi-volume
11025 archive, specify @option{--multi-volume} in conjunction with that
11030 $ @kbd{tar --create --multi-volume --file=/dev/tape @var{files}}
11034 The method @command{tar} uses to detect end of tape is not perfect, and
11035 fails on some operating systems or on some devices. If @command{tar}
11036 cannot detect the end of the tape itself, you can use
11037 @option{--tape-length} option to inform it about the capacity of the
11040 @anchor{tape-length}
11042 @opindex tape-length
11043 @item --tape-length=@var{size}
11044 @itemx -L @var{size}
11045 Set maximum length of a volume. The @var{size} argument should then
11046 be the usable size of the tape in units of 1024 bytes. This option
11047 selects @option{--multi-volume} automatically. For example:
11050 $ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}}
11054 @anchor{change volume prompt}
11055 When @GNUTAR{} comes to the end of a storage media, it asks you to
11056 change the volume. The built-in prompt for POSIX locale
11057 is@footnote{If you run @GNUTAR{} under a different locale, the
11058 translation to the locale's language will be used.}:
11061 Prepare volume #@var{n} for `@var{archive}' and hit return:
11065 where @var{n} is the ordinal number of the volume to be created and
11066 @var{archive} is archive file or device name.
11068 When prompting for a new tape, @command{tar} accepts any of the following
11073 Request @command{tar} to explain possible responses
11075 Request @command{tar} to exit immediately.
11076 @item n @var{file-name}
11077 Request @command{tar} to write the next volume on the file @var{file-name}.
11079 Request @command{tar} to run a subshell. This option can be disabled
11080 by giving @option{--restrict} command line option to
11081 @command{tar}@footnote{@xref{--restrict}, for more information about
11084 Request @command{tar} to begin writing the next volume.
11087 (You should only type @samp{y} after you have changed the tape;
11088 otherwise @command{tar} will write over the volume it just finished.)
11090 @cindex Volume number file
11092 @anchor{volno-file}
11093 @opindex volno-file
11094 The volume number used by @command{tar} in its tape-changing prompt
11095 can be changed; if you give the
11096 @option{--volno-file=@var{file-of-number}} option, then
11097 @var{file-of-number} should be an non-existing file to be created, or
11098 else, a file already containing a decimal number. That number will be
11099 used as the volume number of the first volume written. When
11100 @command{tar} is finished, it will rewrite the file with the
11101 now-current volume number. (This does not change the volume number
11102 written on a tape label, as per @ref{label}, it @emph{only} affects
11103 the number used in the prompt.)
11105 @cindex End-of-archive info script
11106 @cindex Info script
11107 @anchor{info-script}
11108 @opindex info-script
11109 @opindex new-volume-script
11110 If you want more elaborate behavior than this, you can write a special
11111 @dfn{new volume script}, that will be responsible for changing the
11112 volume, and instruct @command{tar} to use it instead of its normal
11113 prompting procedure:
11116 @item --info-script=@var{script-name}
11117 @itemx --new-volume-script=@var{script-name}
11118 @itemx -F @var{script-name}
11119 Specify the full name of the volume script to use. The script can be
11120 used to eject cassettes, or to broadcast messages such as
11121 @samp{Someone please come change my tape} when performing unattended
11125 The @var{script-name} is executed without any command line
11126 arguments. It inherits @command{tar}'s shell environment.
11127 Additional data is passed to it via the following
11128 environment variables:
11131 @vrindex TAR_VERSION, info script environment variable
11133 @GNUTAR{} version number.
11135 @vrindex TAR_ARCHIVE, info script environment variable
11137 The name of the archive @command{tar} is processing.
11139 @vrindex TAR_BLOCKING_FACTOR, info script environment variable
11140 @item TAR_BLOCKING_FACTOR
11141 Current blocking factor (@pxref{Blocking}.
11143 @vrindex TAR_VOLUME, info script environment variable
11145 Ordinal number of the volume @command{tar} is about to start.
11147 @vrindex TAR_SUBCOMMAND, info script environment variable
11148 @item TAR_SUBCOMMAND
11149 A short option describing the operation @command{tar} is executing
11150 @xref{Operations}, for a complete list of subcommand options.
11152 @vrindex TAR_FORMAT, info script environment variable
11154 Format of the archive being processed. @xref{Formats}, for a complete
11155 list of archive format names.
11157 @vrindex TAR_FD, info script environment variable
11159 File descriptor which can be used to communicate the new volume
11160 name to @command{tar}.
11163 The volume script can instruct @command{tar} to use new archive name,
11164 by writing in to file descriptor @env{$TAR_FD} (see below for an example).
11166 If the info script fails, @command{tar} exits; otherwise, it begins
11167 writing the next volume.
11169 If you want @command{tar} to cycle through a series of files or tape
11170 drives, there are three approaches to choose from. First of all, you
11171 can give @command{tar} multiple @option{--file} options. In this case
11172 the specified files will be used, in sequence, as the successive
11173 volumes of the archive. Only when the first one in the sequence needs
11174 to be used again will @command{tar} prompt for a tape change (or run
11175 the info script). For example, suppose someone has two tape drives on
11176 a system named @file{/dev/tape0} and @file{/dev/tape1}. For having
11177 @GNUTAR{} to switch to the second drive when it needs to write the
11178 second tape, and then back to the first tape, etc., just do either of:
11181 $ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
11182 $ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
11185 The second method is to use the @samp{n} response to the tape-change
11188 Finally, the most flexible approach is to use a volume script, that
11189 writes new archive name to the file descriptor @env{$TAR_FD}. For example, the
11190 following volume script will create a series of archive files, named
11191 @file{@var{archive}-@var{vol}}, where @var{archive} is the name of the
11192 archive being created (as given by @option{--file} option) and
11193 @var{vol} is the ordinal number of the archive being created:
11198 echo Preparing volume $TAR_VOLUME of $TAR_ARCHIVE.
11200 name=`expr $TAR_ARCHIVE : '\(.*\)-.*'`
11201 case $TAR_SUBCOMMAND in
11203 -d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
11208 echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&$TAR_FD
11212 The same script can be used while listing, comparing or extracting
11213 from the created archive. For example:
11217 # @r{Create a multi-volume archive:}
11218 $ @kbd{tar -c -L1024 -f archive.tar -F new-volume .}
11219 # @r{Extract from the created archive:}
11220 $ @kbd{tar -x -f archive.tar -F new-volume .}
11225 Notice, that the first command had to use @option{-L} option, since
11226 otherwise @GNUTAR{} will end up writing everything to file
11227 @file{archive.tar}.
11229 You can read each individual volume of a multi-volume archive as if it
11230 were an archive by itself. For example, to list the contents of one
11231 volume, use @option{--list}, without @option{--multi-volume} specified.
11232 To extract an archive member from one volume (assuming it is described
11233 that volume), use @option{--extract}, again without
11234 @option{--multi-volume}.
11236 If an archive member is split across volumes (i.e., its entry begins on
11237 one volume of the media and ends on another), you need to specify
11238 @option{--multi-volume} to extract it successfully. In this case, you
11239 should load the volume where the archive member starts, and use
11240 @samp{tar --extract --multi-volume}---@command{tar} will prompt for later
11241 volumes as it needs them. @xref{extracting archives}, for more
11242 information about extracting archives.
11244 Multi-volume archives can be modified like any other archive. To add
11245 files to a multi-volume archive, you need to only mount the last
11246 volume of the archive media (and new volumes, if needed). For all
11247 other operations, you need to use the entire archive.
11249 If a multi-volume archive was labeled using
11250 @option{--label=@var{archive-label}} (@pxref{label}) when it was
11251 created, @command{tar} will not automatically label volumes which are
11252 added later. To label subsequent volumes, specify
11253 @option{--label=@var{archive-label}} again in conjunction with the
11254 @option{--append}, @option{--update} or @option{--concatenate} operation.
11256 Notice that multi-volume support is a GNU extension and the archives
11257 created in this mode should be read only using @GNUTAR{}. If you
11258 absolutely have to process such archives using a third-party @command{tar}
11259 implementation, read @ref{Split Recovery}.
11262 @subsection Tape Files
11263 @cindex labeling archives
11267 To give the archive a name which will be recorded in it, use the
11268 @option{--label=@var{volume-label}} (@option{-V @var{volume-label}})
11269 option. This will write a special block identifying
11270 @var{volume-label} as the name of the archive to the front of the
11271 archive which will be displayed when the archive is listed with
11272 @option{--list}. If you are creating a multi-volume archive with
11273 @option{--multi-volume} (@pxref{Using Multiple Tapes}), then the
11274 volume label will have @samp{Volume @var{nnn}} appended to the name
11275 you give, where @var{nnn} is the number of the volume of the archive.
11276 (If you use the @option{--label=@var{volume-label}}) option when
11277 reading an archive, it checks to make sure the label on the tape
11278 matches the one you give. @xref{label}.
11280 When @command{tar} writes an archive to tape, it creates a single
11281 tape file. If multiple archives are written to the same tape, one
11282 after the other, they each get written as separate tape files. When
11283 extracting, it is necessary to position the tape at the right place
11284 before running @command{tar}. To do this, use the @command{mt} command.
11285 For more information on the @command{mt} command and on the organization
11286 of tapes into a sequence of tape files, see @ref{mt}.
11288 People seem to often do:
11291 @kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
11294 or such, for pushing a common date in all volumes or an archive set.
11297 @subsection Concatenate Volumes into a Single Archive
11300 Sometimes it is necessary to convert existing @GNUTAR{} multi-volume
11301 archive to a single @command{tar} archive. Simply concatenating all
11302 volumes into one will not work, since each volume carries an additional
11303 information at the beginning. @GNUTAR{} is shipped with the shell
11304 script @command{tarcat} designed for this purpose.
11306 The script takes a list of files comprising a multi-volume archive
11307 and creates the resulting archive at the standard output. For example:
11310 @kbd{tarcat vol.1 vol.2 vol.3 | tar tf -}
11313 The script implements a simple heuristics to determine the format of
11314 the first volume file and to decide how to process the rest of the
11315 files. However, it makes no attempt to verify whether the files are
11316 given in order or even if they are valid @command{tar} archives.
11317 It uses @command{dd} and does not filter its standard error, so you
11318 will usually see lots of spurious messages.
11320 @FIXME{The script is not installed. Should we install it?}
11323 @section Including a Label in the Archive
11324 @cindex Labeling an archive
11325 @cindex Labels on the archive media
11326 @cindex Labeling multi-volume archives
11330 To avoid problems caused by misplaced paper labels on the archive
11331 media, you can include a @dfn{label} entry---an archive member which
11332 contains the name of the archive---in the archive itself. Use the
11333 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11334 option in conjunction with the @option{--create} operation to include
11335 a label entry in the archive as it is being created.
11338 @item --label=@var{archive-label}
11339 @itemx -V @var{archive-label}
11340 Includes an @dfn{archive-label} at the beginning of the archive when
11341 the archive is being created, when used in conjunction with the
11342 @option{--create} operation. Checks to make sure the archive label
11343 matches the one specified (when used in conjunction with any other
11347 If you create an archive using both
11348 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11349 and @option{--multi-volume} (@option{-M}), each volume of the archive
11350 will have an archive label of the form @samp{@var{archive-label}
11351 Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the
11352 next, and so on. @xref{Using Multiple Tapes}, for information on
11353 creating multiple volume archives.
11355 @cindex Volume label, listing
11356 @cindex Listing volume label
11357 The volume label will be displayed by @option{--list} along with
11358 the file contents. If verbose display is requested, it will also be
11359 explicitly marked as in the example below:
11363 $ @kbd{tar --verbose --list --file=iamanarchive}
11364 V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
11365 -rw-r--r-- ringo user 40 1990-05-21 13:30 iamafilename
11369 @opindex test-label
11370 @anchor{--test-label option}
11371 However, @option{--list} option will cause listing entire
11372 contents of the archive, which may be undesirable (for example, if the
11373 archive is stored on a tape). You can request checking only the volume
11374 by specifying @option{--test-label} option. This option reads only the
11375 first block of an archive, so it can be used with slow storage
11376 devices. For example:
11380 $ @kbd{tar --test-label --file=iamanarchive}
11385 If @option{--test-label} is used with a single command line
11386 argument, @command{tar} compares the volume label with the
11387 argument. It exits with code 0 if the two strings match, and with code
11388 2 otherwise. In this case no output is displayed. For example:
11392 $ @kbd{tar --test-label --file=iamanarchive 'iamalable'}
11394 $ @kbd{tar --test-label --file=iamanarchive 'iamalable' alabel}
11399 If you request any operation, other than @option{--create}, along
11400 with using @option{--label} option, @command{tar} will first check if
11401 the archive label matches the one specified and will refuse to proceed
11402 if it does not. Use this as a safety precaution to avoid accidentally
11403 overwriting existing archives. For example, if you wish to add files
11404 to @file{archive}, presumably labeled with string @samp{My volume},
11409 $ @kbd{tar -rf archive --label 'My volume' .}
11410 tar: Archive not labeled to match `My volume'
11415 in case its label does not match. This will work even if
11416 @file{archive} is not labeled at all.
11418 Similarly, @command{tar} will refuse to list or extract the
11419 archive if its label doesn't match the @var{archive-label}
11420 specified. In those cases, @var{archive-label} argument is interpreted
11421 as a globbing-style pattern which must match the actual magnetic
11422 volume label. @xref{exclude}, for a precise description of how match
11423 is attempted@footnote{Previous versions of @command{tar} used full
11424 regular expression matching, or before that, only exact string
11425 matching, instead of wildcard matchers. We decided for the sake of
11426 simplicity to use a uniform matching device through
11427 @command{tar}.}. If the switch @option{--multi-volume} (@option{-M}) is being used,
11428 the volume label matcher will also suffix @var{archive-label} by
11429 @w{@samp{ Volume [1-9]*}} if the initial match fails, before giving
11430 up. Since the volume numbering is automatically added in labels at
11431 creation time, it sounded logical to equally help the user taking care
11432 of it when the archive is being read.
11434 The @option{--label} was once called @option{--volume}, but is not
11435 available under that name anymore.
11437 You can also use @option{--label} to get a common information on
11438 all tapes of a series. For having this information different in each
11439 series created through a single script used on a regular basis, just
11440 manage to get some date string as part of the label. For example:
11444 $ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
11445 $ @kbd{tar --create --file=/dev/tape --multi-volume \
11446 --volume="Daily backup for `date +%Y-%m-%d`"}
11450 Also note that each label has its own date and time, which corresponds
11451 to when @GNUTAR{} initially attempted to write it,
11452 often soon after the operator launches @command{tar} or types the
11453 carriage return telling that the next tape is ready. Comparing date
11454 labels does give an idea of tape throughput only if the delays for
11455 rewinding tapes and the operator switching them were negligible, which
11456 is usually not the case.
11459 @section Verifying Data as It is Stored
11460 @cindex Verifying a write operation
11461 @cindex Double-checking a write operation
11466 @opindex verify, short description
11467 Attempt to verify the archive after writing.
11470 This option causes @command{tar} to verify the archive after writing it.
11471 Each volume is checked after it is written, and any discrepancies
11472 are recorded on the standard error output.
11474 Verification requires that the archive be on a back-space-able medium.
11475 This means pipes, some cartridge tape drives, and some other devices
11476 cannot be verified.
11478 You can insure the accuracy of an archive by comparing files in the
11479 system with archive members. @command{tar} can compare an archive to the
11480 file system as the archive is being written, to verify a write
11481 operation, or can compare a previously written archive, to insure that
11484 @xopindex{verify, using with @option{--create}}
11485 @xopindex{create, using with @option{--verify}}
11486 To check for discrepancies in an archive immediately after it is
11487 written, use the @option{--verify} (@option{-W}) option in conjunction with
11488 the @option{--create} operation. When this option is
11489 specified, @command{tar} checks archive members against their counterparts
11490 in the file system, and reports discrepancies on the standard error.
11492 To verify an archive, you must be able to read it from before the end
11493 of the last written entry. This option is useful for detecting data
11494 errors on some tapes. Archives written to pipes, some cartridge tape
11495 drives, and some other devices cannot be verified.
11497 One can explicitly compare an already made archive with the file
11498 system by using the @option{--compare} (@option{--diff}, @option{-d})
11499 option, instead of using the more automatic @option{--verify} option.
11502 Note that these two options have a slightly different intent. The
11503 @option{--compare} option checks how identical are the logical contents of some
11504 archive with what is on your disks, while the @option{--verify} option is
11505 really for checking if the physical contents agree and if the recording
11506 media itself is of dependable quality. So, for the @option{--verify}
11507 operation, @command{tar} tries to defeat all in-memory cache pertaining to
11508 the archive, while it lets the speed optimization undisturbed for the
11509 @option{--compare} option. If you nevertheless use @option{--compare} for
11510 media verification, you may have to defeat the in-memory cache yourself,
11511 maybe by opening and reclosing the door latch of your recording unit,
11512 forcing some doubt in your operating system about the fact this is really
11513 the same volume as the one just written or read.
11515 The @option{--verify} option would not be necessary if drivers were indeed
11516 able to detect dependably all write failures. This sometimes require many
11517 magnetic heads, some able to read after the writes occurred. One would
11518 not say that drivers unable to detect all cases are necessarily flawed,
11519 as long as programming is concerned.
11521 The @option{--verify} (@option{-W}) option will not work in
11522 conjunction with the @option{--multi-volume} (@option{-M}) option or
11523 the @option{--append} (@option{-r}), @option{--update} (@option{-u})
11524 and @option{--delete} operations. @xref{Operations}, for more
11525 information on these operations.
11527 Also, since @command{tar} normally strips leading @samp{/} from file
11528 names (@pxref{absolute}), a command like @samp{tar --verify -cf
11529 /tmp/foo.tar /etc} will work as desired only if the working directory is
11530 @file{/}, as @command{tar} uses the archive's relative member names
11531 (e.g., @file{etc/motd}) when verifying the archive.
11533 @node Write Protection
11534 @section Write Protection
11536 Almost all tapes and diskettes, and in a few rare cases, even disks can
11537 be @dfn{write protected}, to protect data on them from being changed.
11538 Once an archive is written, you should write protect the media to prevent
11539 the archive from being accidentally overwritten or deleted. (This will
11540 protect the archive from being changed with a tape or floppy drive---it
11541 will not protect it from magnet fields or other physical hazards).
11543 The write protection device itself is usually an integral part of the
11544 physical media, and can be a two position (write enabled/write
11545 disabled) switch, a notch which can be popped out or covered, a ring
11546 which can be removed from the center of a tape reel, or some other
11547 changeable feature.
11552 This appendix lists some important user-visible changes between
11553 version @GNUTAR{} @value{VERSION} and previous versions. An up-to-date
11554 version of this document is available at
11555 @uref{http://www.gnu.org/@/software/@/tar/manual/changes.html,the
11556 @GNUTAR{} documentation page}.
11559 @item Use of globbing patterns when listing and extracting.
11561 Previous versions of GNU tar assumed shell-style globbing when
11562 extracting from or listing an archive. For example:
11565 $ @kbd{tar xf foo.tar '*.c'}
11568 would extract all files whose names end in @samp{.c}. This behavior
11569 was not documented and was incompatible with traditional tar
11570 implementations. Therefore, starting from version 1.15.91, GNU tar
11571 no longer uses globbing by default. For example, the above invocation
11572 is now interpreted as a request to extract from the archive the file
11575 To facilitate transition to the new behavior for those users who got
11576 used to the previous incorrect one, @command{tar} will print a warning
11577 if it finds out that a requested member was not found in the archive
11578 and its name looks like a globbing pattern. For example:
11581 $ @kbd{tar xf foo.tar '*.c'}
11582 tar: Pattern matching characters used in file names. Please,
11583 tar: use --wildcards to enable pattern matching, or --no-wildcards to
11584 tar: suppress this warning.
11585 tar: *.c: Not found in archive
11586 tar: Error exit delayed from previous errors
11589 To treat member names as globbing patterns, use --wildcards option.
11590 If you want to tar to mimic the behavior of versions prior to 1.15.91,
11591 add this option to your @env{TAR_OPTIONS} variable.
11593 @xref{wildcards}, for the detailed discussion of the use of globbing
11594 patterns by @GNUTAR{}.
11596 @item Use of short option @option{-o}.
11598 Earlier versions of @GNUTAR{} understood @option{-o} command line
11599 option as a synonym for @option{--old-archive}.
11601 @GNUTAR{} starting from version 1.13.90 understands this option as
11602 a synonym for @option{--no-same-owner}. This is compatible with
11603 UNIX98 @command{tar} implementations.
11605 However, to facilitate transition, @option{-o} option retains its
11606 old semantics when it is used with one of archive-creation commands.
11607 Users are encouraged to use @option{--format=oldgnu} instead.
11609 It is especially important, since versions of @acronym{GNU} Automake
11610 up to and including 1.8.4 invoke tar with this option to produce
11611 distribution tarballs. @xref{Formats,v7}, for the detailed discussion
11612 of this issue and its implications.
11614 @xref{Options, tar-formats, Changing Automake's Behavior,
11615 automake, GNU Automake}, for a description on how to use various
11616 archive formats with @command{automake}.
11618 Future versions of @GNUTAR{} will understand @option{-o} only as a
11619 synonym for @option{--no-same-owner}.
11621 @item Use of short option @option{-l}
11623 Earlier versions of @GNUTAR{} understood @option{-l} option as a
11624 synonym for @option{--one-file-system}. Since such usage contradicted
11625 to UNIX98 specification and harmed compatibility with other
11626 implementation, it was declared deprecated in version 1.14. However,
11627 to facilitate transition to its new semantics, it was supported by
11628 versions 1.15 and 1.15.90. The present use of @option{-l} as a short
11629 variant of @option{--check-links} was introduced in version 1.15.91.
11631 @item Use of options @option{--portability} and @option{--old-archive}
11633 These options are deprecated. Please use @option{--format=v7} instead.
11635 @item Use of option @option{--posix}
11637 This option is deprecated. Please use @option{--format=posix} instead.
11640 @node Configuring Help Summary
11641 @appendix Configuring Help Summary
11643 Running @kbd{tar --help} displays the short @command{tar} option
11644 summary (@pxref{help}). This summary is organized by @dfn{groups} of
11645 semantically close options. The options within each group are printed
11646 in the following order: a short option, eventually followed by a list
11647 of corresponding long option names, followed by a short description of
11648 the option. For example, here is an excerpt from the actual @kbd{tar
11652 Main operation mode:
11654 -A, --catenate, --concatenate append tar files to an archive
11655 -c, --create create a new archive
11656 -d, --diff, --compare find differences between archive and
11658 --delete delete from the archive
11661 @vrindex ARGP_HELP_FMT, environment variable
11662 The exact visual representation of the help output is configurable via
11663 @env{ARGP_HELP_FMT} environment variable. The value of this variable
11664 is a comma-separated list of @dfn{format variable} assignments. There
11665 are two kinds of format variables. An @dfn{offset variable} keeps the
11666 offset of some part of help output text from the leftmost column on
11667 the screen. A @dfn{boolean} variable is a flag that toggles some
11668 output feature on or off. Depending on the type of the corresponding
11669 variable, there are two kinds of assignments:
11672 @item Offset assignment
11674 The assignment to an offset variable has the following syntax:
11677 @var{variable}=@var{value}
11681 where @var{variable} is the variable name, and @var{value} is a
11682 numeric value to be assigned to the variable.
11684 @item Boolean assignment
11686 To assign @code{true} value to a variable, simply put this variable name. To
11687 assign @code{false} value, prefix the variable name with @samp{no-}. For
11692 # Assign @code{true} value:
11694 # Assign @code{false} value:
11700 Following variables are declared:
11702 @deftypevr {Help Output} boolean dup-args
11703 If true, arguments for an option are shown with both short and long
11704 options, even when a given option has both forms, for example:
11707 -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE
11710 If false, then if an option has both short and long forms, the
11711 argument is only shown with the long one, for example:
11714 -f, --file=ARCHIVE use archive file or device ARCHIVE
11718 and a message indicating that the argument is applicable to both
11719 forms is printed below the options. This message can be disabled
11720 using @code{dup-args-note} (see below).
11722 The default is false.
11725 @deftypevr {Help Output} boolean dup-args-note
11726 If this variable is true, which is the default, the following notice
11727 is displayed at the end of the help output:
11730 Mandatory or optional arguments to long options are also mandatory or
11731 optional for any corresponding short options.
11734 Setting @code{no-dup-args-note} inhibits this message. Normally, only one of
11735 variables @code{dup-args} or @code{dup-args-note} should be set.
11738 @deftypevr {Help Output} offset short-opt-col
11739 Column in which short options start. Default is 2.
11743 $ @kbd{tar --help|grep ARCHIVE}
11744 -f, --file=ARCHIVE use archive file or device ARCHIVE
11745 $ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE}
11746 -f, --file=ARCHIVE use archive file or device ARCHIVE
11751 @deftypevr {Help Output} offset long-opt-col
11752 Column in which long options start. Default is 6. For example:
11756 $ @kbd{tar --help|grep ARCHIVE}
11757 -f, --file=ARCHIVE use archive file or device ARCHIVE
11758 $ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE}
11759 -f, --file=ARCHIVE use archive file or device ARCHIVE
11764 @deftypevr {Help Output} offset doc-opt-col
11765 Column in which @dfn{doc options} start. A doc option isn't actually
11766 an option, but rather an arbitrary piece of documentation that is
11767 displayed in much the same manner as the options. For example, in
11768 the description of @option{--format} option:
11772 -H, --format=FORMAT create archive of the given format.
11774 FORMAT is one of the following:
11776 gnu GNU tar 1.13.x format
11777 oldgnu GNU format as per tar <= 1.12
11778 pax POSIX 1003.1-2001 (pax) format
11780 ustar POSIX 1003.1-1988 (ustar) format
11781 v7 old V7 tar format
11786 the format names are doc options. Thus, if you set
11787 @kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output
11788 will look as follows:
11792 -H, --format=FORMAT create archive of the given format.
11794 FORMAT is one of the following:
11796 gnu GNU tar 1.13.x format
11797 oldgnu GNU format as per tar <= 1.12
11798 pax POSIX 1003.1-2001 (pax) format
11800 ustar POSIX 1003.1-1988 (ustar) format
11801 v7 old V7 tar format
11806 @deftypevr {Help Output} offset opt-doc-col
11807 Column in which option description starts. Default is 29.
11811 $ @kbd{tar --help|grep ARCHIVE}
11812 -f, --file=ARCHIVE use archive file or device ARCHIVE
11813 $ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE}
11814 -f, --file=ARCHIVE use archive file or device ARCHIVE
11815 $ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE}
11817 use archive file or device ARCHIVE
11822 Notice, that the description starts on a separate line if
11823 @code{opt-doc-col} value is too small.
11826 @deftypevr {Help Output} offset header-col
11827 Column in which @dfn{group headers} are printed. A group header is a
11828 descriptive text preceding an option group. For example, in the
11832 Main operation mode:
11834 -A, --catenate, --concatenate append tar files to
11836 -c, --create create a new archive
11839 @samp{Main operation mode:} is the group header.
11841 The default value is 1.
11844 @deftypevr {Help Output} offset usage-indent
11845 Indentation of wrapped usage lines. Affects @option{--usage}
11846 output. Default is 12.
11849 @deftypevr {Help Output} offset rmargin
11850 Right margin of the text output. Used for wrapping.
11853 @node Fixing Snapshot Files
11854 @appendix Fixing Snapshot Files
11855 @include tar-snapshot-edit.texi
11857 @node Tar Internals
11858 @appendix Tar Internals
11859 @include intern.texi
11863 @include genfile.texi
11865 @node Free Software Needs Free Documentation
11866 @appendix Free Software Needs Free Documentation
11867 @include freemanuals.texi
11869 @node Copying This Manual
11870 @appendix Copying This Manual
11873 * GNU Free Documentation License:: License for copying this manual
11878 @node Index of Command Line Options
11879 @appendix Index of Command Line Options
11881 This appendix contains an index of all @GNUTAR{} long command line
11882 options. The options are listed without the preceding double-dash.
11883 For a cross-reference of short command line options, @ref{Short Option Summary}.
11896 @c Local variables:
11897 @c texinfo-column-for-description: 32
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