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
1524 @cindex Retrieving files from an archive
1525 @cindex Resurrecting files from an archive
1528 Creating an archive is only half the job---there is no point in storing
1529 files in an archive if you can't retrieve them. The act of retrieving
1530 members from an archive so they can be used and manipulated as
1531 unarchived files again is called @dfn{extraction}. To extract files
1532 from an archive, use the @option{--extract} (@option{--get} or
1533 @option{-x}) operation. As with @option{--create}, specify the name
1534 of the archive with @option{--file} (@option{-f}) option. Extracting
1535 an archive does not modify the archive in any way; you can extract it
1536 multiple times if you want or need to.
1538 Using @option{--extract}, you can extract an entire archive, or specific
1539 files. The files can be directories containing other files, or not. As
1540 with @option{--create} (@option{-c}) and @option{--list} (@option{-t}), you may use the short or the
1541 long form of the operation without affecting the performance.
1544 * extracting archives::
1545 * extracting files::
1547 * extracting untrusted archives::
1548 * failing commands::
1551 @node extracting archives
1552 @subsection Extracting an Entire Archive
1554 To extract an entire archive, specify the archive file name only, with
1555 no individual file names as arguments. For example,
1558 $ @kbd{tar -xvf collection.tar}
1565 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
1566 -rw-r--r-- me user 21 1996-09-23 16:44 blues
1567 -rw-r--r-- me user 20 1996-09-23 16:44 folk
1570 @node extracting files
1571 @subsection Extracting Specific Files
1573 To extract specific archive members, give their exact member names as
1574 arguments, as printed by @option{--list} (@option{-t}). If you had
1575 mistakenly deleted one of the files you had placed in the archive
1576 @file{collection.tar} earlier (say, @file{blues}), you can extract it
1577 from the archive without changing the archive's structure. Its
1578 contents will be identical to the original file @file{blues} that you
1581 First, make sure you are in the @file{practice} directory, and list the
1582 files in the directory. Now, delete the file, @samp{blues}, and list
1583 the files in the directory again.
1585 You can now extract the member @file{blues} from the archive file
1586 @file{collection.tar} like this:
1589 $ @kbd{tar --extract --file=collection.tar blues}
1593 If you list the files in the directory again, you will see that the file
1594 @file{blues} has been restored, with its original permissions, data
1595 modification times, and owner.@footnote{This is only accidentally
1596 true, but not in general. Whereas modification times are always
1597 restored, in most cases, one has to be root for restoring the owner,
1598 and use a special option for restoring permissions. Here, it just
1599 happens that the restoring user is also the owner of the archived
1600 members, and that the current @code{umask} is compatible with original
1601 permissions.} (These parameters will be identical to those which
1602 the file had when you originally placed it in the archive; any changes
1603 you may have made before deleting the file from the file system,
1604 however, will @emph{not} have been made to the archive member.) The
1605 archive file, @samp{collection.tar}, is the same as it was before you
1606 extracted @samp{blues}. You can confirm this by running @command{tar} with
1607 @option{--list} (@option{-t}).
1609 Remember that as with other operations, specifying the exact member
1610 name is important. @w{@kbd{tar --extract --file=bfiles.tar birds}}
1611 will fail, because there is no member named @file{birds}. To extract
1612 the member named @file{./birds}, you must specify @w{@kbd{tar
1613 --extract --file=bfiles.tar ./birds}}. If you don't remember the
1614 exact member names, use @option{--list} (@option{-t}) option
1615 (@pxref{list}). You can also extract those members that match a
1616 specific @dfn{globbing pattern}. For example, to extract from
1617 @file{bfiles.tar} all files that begin with @samp{b}, no matter their
1618 directory prefix, you could type:
1621 $ @kbd{tar -x -f bfiles.tar --wildcards --no-anchored 'b*'}
1625 Here, @option{--wildcards} instructs @command{tar} to treat
1626 command line arguments as globbing patterns and @option{--no-anchored}
1627 informs it that the patterns apply to member names after any @samp{/}
1628 delimiter. The use of globbing patterns is discussed in detail in
1631 You can extract a file to standard output by combining the above options
1632 with the @option{--to-stdout} (@option{-O}) option (@pxref{Writing to Standard
1635 If you give the @option{--verbose} option, then @option{--extract}
1636 will print the names of the archive members as it extracts them.
1639 @subsection Extracting Files that are Directories
1641 Extracting directories which are members of an archive is similar to
1642 extracting other files. The main difference to be aware of is that if
1643 the extracted directory has the same name as any directory already in
1644 the working directory, then files in the extracted directory will be
1645 placed into the directory of the same name. Likewise, if there are
1646 files in the pre-existing directory with the same names as the members
1647 which you extract, the files from the extracted archive will replace
1648 the files already in the working directory (and possible
1649 subdirectories). This will happen regardless of whether or not the
1650 files in the working directory were more recent than those extracted
1651 (there exist, however, special options that alter this behavior
1654 However, if a file was stored with a directory name as part of its file
1655 name, and that directory does not exist under the working directory when
1656 the file is extracted, @command{tar} will create the directory.
1658 We can demonstrate how to use @option{--extract} to extract a directory
1659 file with an example. Change to the @file{practice} directory if you
1660 weren't there, and remove the files @file{folk} and @file{jazz}. Then,
1661 go back to the parent directory and extract the archive
1662 @file{music.tar}. You may either extract the entire archive, or you may
1663 extract only the files you just deleted. To extract the entire archive,
1664 don't give any file names as arguments after the archive name
1665 @file{music.tar}. To extract only the files you deleted, use the
1669 $ @kbd{tar -xvf music.tar practice/folk practice/jazz}
1675 If you were to specify two @option{--verbose} (@option{-v}) options, @command{tar}
1676 would have displayed more detail about the extracted files, as shown
1677 in the example below:
1680 $ @kbd{tar -xvvf music.tar practice/folk practice/jazz}
1681 -rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz
1682 -rw-r--r-- me user 20 1996-09-23 16:44 practice/folk
1686 Because you created the directory with @file{practice} as part of the
1687 file names of each of the files by archiving the @file{practice}
1688 directory as @file{practice}, you must give @file{practice} as part
1689 of the file names when you extract those files from the archive.
1691 @node extracting untrusted archives
1692 @subsection Extracting Archives from Untrusted Sources
1694 Extracting files from archives can overwrite files that already exist.
1695 If you receive an archive from an untrusted source, you should make a
1696 new directory and extract into that directory, so that you don't have
1697 to worry about the extraction overwriting one of your existing files.
1698 For example, if @file{untrusted.tar} came from somewhere else on the
1699 Internet, and you don't necessarily trust its contents, you can
1700 extract it as follows:
1703 $ @kbd{mkdir newdir}
1705 $ @kbd{tar -xvf ../untrusted.tar}
1708 It is also a good practice to examine contents of the archive
1709 before extracting it, using @option{--list} (@option{-t}) option, possibly combined
1710 with @option{--verbose} (@option{-v}).
1712 @node failing commands
1713 @subsection Commands That Will Fail
1715 Here are some sample commands you might try which will not work, and why
1718 If you try to use this command,
1721 $ @kbd{tar -xvf music.tar folk jazz}
1725 you will get the following response:
1728 tar: folk: Not found in archive
1729 tar: jazz: Not found in archive
1734 This is because these files were not originally @emph{in} the parent
1735 directory @file{..}, where the archive is located; they were in the
1736 @file{practice} directory, and their file names reflect this:
1739 $ @kbd{tar -tvf music.tar}
1745 @FIXME{make sure the above works when going through the examples in
1749 Likewise, if you try to use this command,
1752 $ @kbd{tar -tvf music.tar folk jazz}
1756 you would get a similar response. Members with those names are not in the
1757 archive. You must use the correct member names, or wildcards, in order
1758 to extract the files from the archive.
1760 If you have forgotten the correct names of the files in the archive,
1761 use @w{@kbd{tar --list --verbose}} to list them correctly.
1763 @FIXME{more examples, here? hag thinks it's a good idea.}
1766 @section Going Further Ahead in this Manual
1769 @FIXME{need to write up a node here about the things that are going to
1770 be in the rest of the manual.}
1772 @node tar invocation
1773 @chapter Invoking @GNUTAR{}
1776 This chapter is about how one invokes the @GNUTAR{}
1777 command, from the command synopsis (@pxref{Synopsis}). There are
1778 numerous options, and many styles for writing them. One mandatory
1779 option specifies the operation @command{tar} should perform
1780 (@pxref{Operation Summary}), other options are meant to detail how
1781 this operation should be performed (@pxref{Option Summary}).
1782 Non-option arguments are not always interpreted the same way,
1783 depending on what the operation is.
1785 You will find in this chapter everything about option styles and rules for
1786 writing them (@pxref{Styles}). On the other hand, operations and options
1787 are fully described elsewhere, in other chapters. Here, you will find
1788 only synthetic descriptions for operations and options, together with
1789 pointers to other parts of the @command{tar} manual.
1791 Some options are so special they are fully described right in this
1792 chapter. They have the effect of inhibiting the normal operation of
1793 @command{tar} or else, they globally alter the amount of feedback the user
1794 receives about what is going on. These are the @option{--help} and
1795 @option{--version} (@pxref{help}), @option{--verbose} (@pxref{verbose})
1796 and @option{--interactive} options (@pxref{interactive}).
1800 * using tar options::
1812 @section General Synopsis of @command{tar}
1814 The @GNUTAR{} program is invoked as either one of:
1817 @kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
1818 @kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
1821 The second form is for when old options are being used.
1823 You can use @command{tar} to store files in an archive, to extract them from
1824 an archive, and to do other types of archive manipulation. The primary
1825 argument to @command{tar}, which is called the @dfn{operation}, specifies
1826 which action to take. The other arguments to @command{tar} are either
1827 @dfn{options}, which change the way @command{tar} performs an operation,
1828 or file names or archive members, which specify the files or members
1829 @command{tar} is to act on.
1831 You can actually type in arguments in any order, even if in this manual
1832 the options always precede the other arguments, to make examples easier
1833 to understand. Further, the option stating the main operation mode
1834 (the @command{tar} main command) is usually given first.
1836 Each @var{name} in the synopsis above is interpreted as an archive member
1837 name when the main command is one of @option{--compare}
1838 (@option{--diff}, @option{-d}), @option{--delete}, @option{--extract}
1839 (@option{--get}, @option{-x}), @option{--list} (@option{-t}) or
1840 @option{--update} (@option{-u}). When naming archive members, you
1841 must give the exact name of the member in the archive, as it is
1842 printed by @option{--list}. For @option{--append} (@option{-r}) and
1843 @option{--create} (@option{-c}), these @var{name} arguments specify
1844 the names of either files or directory hierarchies to place in the archive.
1845 These files or hierarchies should already exist in the file system,
1846 prior to the execution of the @command{tar} command.
1848 @command{tar} interprets relative file names as being relative to the
1849 working directory. @command{tar} will make all file names relative
1850 (by removing leading slashes when archiving or restoring files),
1851 unless you specify otherwise (using the @option{--absolute-names}
1852 option). @xref{absolute}, for more information about
1853 @option{--absolute-names}.
1855 If you give the name of a directory as either a file name or a member
1856 name, then @command{tar} acts recursively on all the files and directories
1857 beneath that directory. For example, the name @file{/} identifies all
1858 the files in the file system to @command{tar}.
1860 The distinction between file names and archive member names is especially
1861 important when shell globbing is used, and sometimes a source of confusion
1862 for newcomers. @xref{wildcards}, for more information about globbing.
1863 The problem is that shells may only glob using existing files in the
1864 file system. Only @command{tar} itself may glob on archive members, so when
1865 needed, you must ensure that wildcard characters reach @command{tar} without
1866 being interpreted by the shell first. Using a backslash before @samp{*}
1867 or @samp{?}, or putting the whole argument between quotes, is usually
1868 sufficient for this.
1870 Even if @var{name}s are often specified on the command line, they
1871 can also be read from a text file in the file system, using the
1872 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option.
1874 If you don't use any file name arguments, @option{--append} (@option{-r}),
1875 @option{--delete} and @option{--concatenate} (@option{--catenate},
1876 @option{-A}) will do nothing, while @option{--create} (@option{-c})
1877 will usually yield a diagnostic and inhibit @command{tar} execution.
1878 The other operations of @command{tar} (@option{--list},
1879 @option{--extract}, @option{--compare}, and @option{--update})
1880 will act on the entire contents of the archive.
1883 @cindex return status
1884 Besides successful exits, @GNUTAR{} may fail for
1885 many reasons. Some reasons correspond to bad usage, that is, when the
1886 @command{tar} command line is improperly written. Errors may be
1887 encountered later, while processing the archive or the files. Some
1888 errors are recoverable, in which case the failure is delayed until
1889 @command{tar} has completed all its work. Some errors are such that
1890 it would be not meaningful, or at least risky, to continue processing:
1891 @command{tar} then aborts processing immediately. All abnormal exits,
1892 whether immediate or delayed, should always be clearly diagnosed on
1893 @code{stderr}, after a line stating the nature of the error.
1895 Possible exit codes of @GNUTAR{} are summarized in the following
1900 @samp{Successful termination}.
1903 @samp{Some files differ}. If tar was invoked with @option{--compare}
1904 (@option{--diff}, @option{-d}) command line option, this means that
1905 some files in the archive differ from their disk counterparts
1906 (@pxref{compare}). If tar was given @option{--create},
1907 @option{--append} or @option{--update} option, this exit code means
1908 that some files were changed while being archived and so the resulting
1909 archive does not contain the exact copy of the file set.
1912 @samp{Fatal error}. This means that some fatal, unrecoverable error
1916 If @command{tar} has invoked a subprocess and that subprocess exited with a
1917 nonzero exit code, @command{tar} exits with that code as well.
1918 This can happen, for example, if @command{tar} was given some
1919 compression option (@pxref{gzip}) and the external compressor program
1920 failed. Another example is @command{rmt} failure during backup to the
1921 remote device (@pxref{Remote Tape Server}).
1923 @node using tar options
1924 @section Using @command{tar} Options
1926 @GNUTAR{} has a total of eight operating modes which
1927 allow you to perform a variety of tasks. You are required to choose
1928 one operating mode each time you employ the @command{tar} program by
1929 specifying one, and only one operation as an argument to the
1930 @command{tar} command (the corresponding options may be found
1931 at @ref{frequent operations} and @ref{Operations}). Depending on
1932 circumstances, you may also wish to customize how the chosen operating
1933 mode behaves. For example, you may wish to change the way the output
1934 looks, or the format of the files that you wish to archive may require
1935 you to do something special in order to make the archive look right.
1937 You can customize and control @command{tar}'s performance by running
1938 @command{tar} with one or more options (such as @option{--verbose}
1939 (@option{-v}), which we used in the tutorial). As we said in the
1940 tutorial, @dfn{options} are arguments to @command{tar} which are (as
1941 their name suggests) optional. Depending on the operating mode, you
1942 may specify one or more options. Different options will have different
1943 effects, but in general they all change details of the operation, such
1944 as archive format, archive name, or level of user interaction. Some
1945 options make sense with all operating modes, while others are
1946 meaningful only with particular modes. You will likely use some
1947 options frequently, while you will only use others infrequently, or
1948 not at all. (A full list of options is available in @pxref{All Options}.)
1950 @vrindex TAR_OPTIONS, environment variable
1951 @anchor{TAR_OPTIONS}
1952 The @env{TAR_OPTIONS} environment variable specifies default options to
1953 be placed in front of any explicit options. For example, if
1954 @code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as
1955 if the two options @option{-v} and @option{--unlink-first} had been
1956 specified before any explicit options. Option specifications are
1957 separated by whitespace. A backslash escapes the next character, so it
1958 can be used to specify an option containing whitespace or a backslash.
1960 Note that @command{tar} options are case sensitive. For example, the
1961 options @option{-T} and @option{-t} are different; the first requires an
1962 argument for stating the name of a file providing a list of @var{name}s,
1963 while the second does not require an argument and is another way to
1964 write @option{--list} (@option{-t}).
1966 In addition to the eight operations, there are many options to
1967 @command{tar}, and three different styles for writing both: long (mnemonic)
1968 form, short form, and old style. These styles are discussed below.
1969 Both the options and the operations can be written in any of these three
1972 @FIXME{menu at end of this node. need to think of an actual outline
1973 for this chapter; probably do that after stuff from chapter 4 is
1977 @section The Three Option Styles
1979 There are three styles for writing operations and options to the command
1980 line invoking @command{tar}. The different styles were developed at
1981 different times during the history of @command{tar}. These styles will be
1982 presented below, from the most recent to the oldest.
1984 Some options must take an argument. (For example, @option{--file}
1985 (@option{-f})) takes the name of an archive file as an argument. If
1986 you do not supply an archive file name, @command{tar} will use a
1987 default, but this can be confusing; thus, we recommend that you always
1988 supply a specific archive file name.) Where you @emph{place} the
1989 arguments generally depends on which style of options you choose. We
1990 will detail specific information relevant to each option style in the
1991 sections on the different option styles, below. The differences are
1992 subtle, yet can often be very important; incorrect option placement
1993 can cause you to overwrite a number of important files. We urge you
1994 to note these differences, and only use the option style(s) which
1995 makes the most sense to you until you feel comfortable with the others.
1997 Some options @emph{may} take an argument. Such options may have at
1998 most long and short forms, they do not have old style equivalent. The
1999 rules for specifying an argument for such options are stricter than
2000 those for specifying mandatory arguments. Please, pay special
2004 * Long Options:: Long Option Style
2005 * Short Options:: Short Option Style
2006 * Old Options:: Old Option Style
2007 * Mixing:: Mixing Option Styles
2011 @subsection Long Option Style
2013 Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
2014 dashes in a row, e.g., @option{--list}. The long names are more clear than
2015 their corresponding short or old names. It sometimes happens that a
2016 single long option has many different names which are
2017 synonymous, such as @option{--compare} and @option{--diff}. In addition,
2018 long option names can be given unique abbreviations. For example,
2019 @option{--cre} can be used in place of @option{--create} because there is no
2020 other long option which begins with @samp{cre}. (One way to find
2021 this out is by trying it and seeing what happens; if a particular
2022 abbreviation could represent more than one option, @command{tar} will tell
2023 you that that abbreviation is ambiguous and you'll know that that
2024 abbreviation won't work. You may also choose to run @samp{tar --help}
2025 to see a list of options. Be aware that if you run @command{tar} with a
2026 unique abbreviation for the long name of an option you didn't want to
2027 use, you are stuck; @command{tar} will perform the command as ordered.)
2029 Long options are meant to be obvious and easy to remember, and their
2030 meanings are generally easier to discern than those of their
2031 corresponding short options (see below). For example:
2034 $ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
2038 gives a fairly good set of hints about what the command does, even
2039 for those not fully acquainted with @command{tar}.
2041 Long options which require arguments take those arguments
2042 immediately following the option name. There are two ways of
2043 specifying a mandatory argument. It can be separated from the
2044 option name either by an equal sign, or by any amount of
2045 white space characters. For example, the @option{--file} option (which
2046 tells the name of the @command{tar} archive) is given a file such as
2047 @file{archive.tar} as argument by using any of the following notations:
2048 @option{--file=archive.tar} or @option{--file archive.tar}.
2050 In contrast, optional arguments must always be introduced using
2051 an equal sign. For example, the @option{--backup} option takes
2052 an optional argument specifying backup type. It must be used
2053 as @option{--backup=@var{backup-type}}.
2056 @subsection Short Option Style
2058 Most options also have a @dfn{short option} name. Short options start with
2059 a single dash, and are followed by a single character, e.g., @option{-t}
2060 (which is equivalent to @option{--list}). The forms are absolutely
2061 identical in function; they are interchangeable.
2063 The short option names are faster to type than long option names.
2065 Short options which require arguments take their arguments immediately
2066 following the option, usually separated by white space. It is also
2067 possible to stick the argument right after the short option name, using
2068 no intervening space. For example, you might write @w{@option{-f
2069 archive.tar}} or @option{-farchive.tar} instead of using
2070 @option{--file=archive.tar}. Both @option{--file=@var{archive-name}} and
2071 @w{@option{-f @var{archive-name}}} denote the option which indicates a
2072 specific archive, here named @file{archive.tar}.
2074 Short options which take optional arguments take their arguments
2075 immediately following the option letter, @emph{without any intervening
2076 white space characters}.
2078 Short options' letters may be clumped together, but you are not
2079 required to do this (as compared to old options; see below). When
2080 short options are clumped as a set, use one (single) dash for them
2081 all, e.g., @w{@samp{@command{tar} -cvf}}. Only the last option in
2082 such a set is allowed to have an argument@footnote{Clustering many
2083 options, the last of which has an argument, is a rather opaque way to
2084 write options. Some wonder if @acronym{GNU} @code{getopt} should not
2085 even be made helpful enough for considering such usages as invalid.}.
2087 When the options are separated, the argument for each option which requires
2088 an argument directly follows that option, as is usual for Unix programs.
2092 $ @kbd{tar -c -v -b 20 -f /dev/rmt0}
2095 If you reorder short options' locations, be sure to move any arguments
2096 that belong to them. If you do not move the arguments properly, you may
2097 end up overwriting files.
2100 @subsection Old Option Style
2103 Like short options, @dfn{old options} are single letters. However, old options
2104 must be written together as a single clumped set, without spaces separating
2105 them or dashes preceding them@footnote{Beware that if you precede options
2106 with a dash, you are announcing the short option style instead of the
2107 old option style; short options are decoded differently.}. This set
2108 of letters must be the first to appear on the command line, after the
2109 @command{tar} program name and some white space; old options cannot appear
2110 anywhere else. The letter of an old option is exactly the same letter as
2111 the corresponding short option. For example, the old option @samp{t} is
2112 the same as the short option @option{-t}, and consequently, the same as the
2113 long option @option{--list}. So for example, the command @w{@samp{tar
2114 cv}} specifies the option @option{-v} in addition to the operation @option{-c}.
2116 When options that need arguments are given together with the command,
2117 all the associated arguments follow, in the same order as the options.
2118 Thus, the example given previously could also be written in the old
2122 $ @kbd{tar cvbf 20 /dev/rmt0}
2126 Here, @samp{20} is the argument of @option{-b} and @samp{/dev/rmt0} is
2127 the argument of @option{-f}.
2129 On the other hand, this old style syntax makes it difficult to match
2130 option letters with their corresponding arguments, and is often
2131 confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example,
2132 @samp{20} is the argument for @option{-b}, @samp{/dev/rmt0} is the
2133 argument for @option{-f}, and @option{-v} does not have a corresponding
2134 argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f
2135 /dev/rmt0}} is clearer, putting all arguments next to the option they
2138 If you want to reorder the letters in the old option argument, be
2139 sure to reorder any corresponding argument appropriately.
2141 This old way of writing @command{tar} options can surprise even experienced
2142 users. For example, the two commands:
2145 @kbd{tar cfz archive.tar.gz file}
2146 @kbd{tar -cfz archive.tar.gz file}
2150 are quite different. The first example uses @file{archive.tar.gz} as
2151 the value for option @samp{f} and recognizes the option @samp{z}. The
2152 second example, however, uses @file{z} as the value for option
2153 @samp{f} --- probably not what was intended.
2155 Old options are kept for compatibility with old versions of @command{tar}.
2157 This second example could be corrected in many ways, among which the
2158 following are equivalent:
2161 @kbd{tar -czf archive.tar.gz file}
2162 @kbd{tar -cf archive.tar.gz -z file}
2163 @kbd{tar cf archive.tar.gz -z file}
2166 @cindex option syntax, traditional
2167 As far as we know, all @command{tar} programs, @acronym{GNU} and
2168 non-@acronym{GNU}, support old options. @GNUTAR{}
2169 supports them not only for historical reasons, but also because many
2170 people are used to them. For compatibility with Unix @command{tar},
2171 the first argument is always treated as containing command and option
2172 letters even if it doesn't start with @samp{-}. Thus, @samp{tar c} is
2173 equivalent to @w{@samp{tar -c}:} both of them specify the
2174 @option{--create} (@option{-c}) command to create an archive.
2177 @subsection Mixing Option Styles
2179 All three styles may be intermixed in a single @command{tar} command,
2180 so long as the rules for each style are fully
2181 respected@footnote{Before @GNUTAR{} version 1.11.6,
2182 a bug prevented intermixing old style options with long options in
2183 some cases.}. Old style options and either of the modern styles of
2184 options may be mixed within a single @command{tar} command. However,
2185 old style options must be introduced as the first arguments only,
2186 following the rule for old options (old options must appear directly
2187 after the @command{tar} command and some white space). Modern options
2188 may be given only after all arguments to the old options have been
2189 collected. If this rule is not respected, a modern option might be
2190 falsely interpreted as the value of the argument to one of the old
2193 For example, all the following commands are wholly equivalent, and
2194 illustrate the many combinations and orderings of option styles.
2197 @kbd{tar --create --file=archive.tar}
2198 @kbd{tar --create -f archive.tar}
2199 @kbd{tar --create -farchive.tar}
2200 @kbd{tar --file=archive.tar --create}
2201 @kbd{tar --file=archive.tar -c}
2202 @kbd{tar -c --file=archive.tar}
2203 @kbd{tar -c -f archive.tar}
2204 @kbd{tar -c -farchive.tar}
2205 @kbd{tar -cf archive.tar}
2206 @kbd{tar -cfarchive.tar}
2207 @kbd{tar -f archive.tar --create}
2208 @kbd{tar -f archive.tar -c}
2209 @kbd{tar -farchive.tar --create}
2210 @kbd{tar -farchive.tar -c}
2211 @kbd{tar c --file=archive.tar}
2212 @kbd{tar c -f archive.tar}
2213 @kbd{tar c -farchive.tar}
2214 @kbd{tar cf archive.tar}
2215 @kbd{tar f archive.tar --create}
2216 @kbd{tar f archive.tar -c}
2217 @kbd{tar fc archive.tar}
2220 On the other hand, the following commands are @emph{not} equivalent to
2224 @kbd{tar -f -c archive.tar}
2225 @kbd{tar -fc archive.tar}
2226 @kbd{tar -fcarchive.tar}
2227 @kbd{tar -farchive.tarc}
2228 @kbd{tar cfarchive.tar}
2232 These last examples mean something completely different from what the
2233 user intended (judging based on the example in the previous set which
2234 uses long options, whose intent is therefore very clear). The first
2235 four specify that the @command{tar} archive would be a file named
2236 @option{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc},
2237 respectively. The first two examples also specify a single non-option,
2238 @var{name} argument having the value @samp{archive.tar}. The last
2239 example contains only old style option letters (repeating option
2240 @samp{c} twice), not all of which are meaningful (eg., @samp{.},
2241 @samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked
2242 the first sentence of this paragraph..}
2245 @section All @command{tar} Options
2247 The coming manual sections contain an alphabetical listing of all
2248 @command{tar} operations and options, with brief descriptions and cross
2249 references to more in-depth explanations in the body of the manual.
2250 They also contain an alphabetically arranged table of the short option
2251 forms with their corresponding long option. You can use this table as
2252 a reference for deciphering @command{tar} commands in scripts.
2255 * Operation Summary::
2257 * Short Option Summary::
2260 @node Operation Summary
2261 @subsection Operations
2269 Appends files to the end of the archive. @xref{append}.
2271 @opsummary{catenate}
2275 Same as @option{--concatenate}. @xref{concatenate}.
2281 Compares archive members with their counterparts in the file
2282 system, and reports differences in file size, mode, owner,
2283 modification date and contents. @xref{compare}.
2285 @opsummary{concatenate}
2289 Appends other @command{tar} archives to the end of the archive.
2296 Creates a new @command{tar} archive. @xref{create}.
2301 Deletes members from the archive. Don't try this on a archive on a
2302 tape! @xref{delete}.
2308 Same @option{--compare}. @xref{compare}.
2314 Extracts members from the archive into the file system. @xref{extract}.
2320 Same as @option{--extract}. @xref{extract}.
2326 Lists the members in an archive. @xref{list}.
2332 Adds files to the end of the archive, but only if they are newer than
2333 their counterparts already in the archive, or if they do not already
2334 exist in the archive. @xref{update}.
2338 @node Option Summary
2339 @subsection @command{tar} Options
2343 @opsummary{absolute-names}
2344 @item --absolute-names
2347 Normally when creating an archive, @command{tar} strips an initial
2348 @samp{/} from member names. This option disables that behavior.
2351 @opsummary{after-date}
2354 (See @option{--newer}, @pxref{after})
2356 @opsummary{anchored}
2358 A pattern must match an initial subsequence of the name's components.
2359 @xref{controlling pattern-matching}.
2361 @opsummary{atime-preserve}
2362 @item --atime-preserve
2363 @itemx --atime-preserve=replace
2364 @itemx --atime-preserve=system
2366 Attempt to preserve the access time of files when reading them. This
2367 option currently is effective only on files that you own, unless you
2368 have superuser privileges.
2370 @option{--atime-preserve=replace} remembers the access time of a file
2371 before reading it, and then restores the access time afterwards. This
2372 may cause problems if other programs are reading the file at the same
2373 time, as the times of their accesses will be lost. On most platforms
2374 restoring the access time also requires @command{tar} to restore the
2375 data modification time too, so this option may also cause problems if
2376 other programs are writing the file at the same time. (Tar attempts
2377 to detect this situation, but cannot do so reliably due to race
2378 conditions.) Worse, on most platforms restoring the access time also
2379 updates the status change time, which means that this option is
2380 incompatible with incremental backups.
2382 @option{--atime-preserve=system} avoids changing time stamps on files,
2383 without interfering with time stamp updates
2384 caused by other programs, so it works better with incremental backups.
2385 However, it requires a special @code{O_NOATIME} option from the
2386 underlying operating and file system implementation, and it also requires
2387 that searching directories does not update their access times. As of
2388 this writing (November 2005) this works only with Linux, and only with
2389 Linux kernels 2.6.8 and later. Worse, there is currently no reliable
2390 way to know whether this feature actually works. Sometimes
2391 @command{tar} knows that it does not work, and if you use
2392 @option{--atime-preserve=system} then @command{tar} complains and
2393 exits right away. But other times @command{tar} might think that the
2394 option works when it actually does not.
2396 Currently @option{--atime-preserve} with no operand defaults to
2397 @option{--atime-preserve=replace}, but this may change in the future
2398 as support for @option{--atime-preserve=system} improves.
2400 If your operating system does not support
2401 @option{--atime-preserve=@-system}, you might be able to preserve access
2402 times reliably by by using the @command{mount} command. For example,
2403 you can mount the file system read-only, or access the file system via
2404 a read-only loopback mount, or use the @samp{noatime} mount option
2405 available on some systems. However, mounting typically requires
2406 superuser privileges and can be a pain to manage.
2408 @opsummary{auto-compress}
2409 @item --auto-compress
2412 During a @option{--create} operation, enables automatic compressed
2413 format recognition based on the archive suffix. The effect of this
2414 option is cancelled by @option{--no-auto-compress}. @xref{gzip}.
2417 @item --backup=@var{backup-type}
2419 Rather than deleting files from the file system, @command{tar} will
2420 back them up using simple or numbered backups, depending upon
2421 @var{backup-type}. @xref{backup}.
2423 @opsummary{block-number}
2424 @item --block-number
2427 With this option present, @command{tar} prints error messages for read errors
2428 with the block number in the archive file. @xref{block-number}.
2430 @opsummary{blocking-factor}
2431 @item --blocking-factor=@var{blocking}
2432 @itemx -b @var{blocking}
2434 Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
2435 record. @xref{Blocking Factor}.
2441 This option tells @command{tar} to read or write archives through
2442 @code{bzip2}. @xref{gzip}.
2444 @opsummary{check-device}
2445 @item --check-device
2446 Check device numbers when creating a list of modified files for
2447 incremental archiving. This is the default. @xref{device numbers},
2448 for a detailed description.
2450 @opsummary{checkpoint}
2451 @item --checkpoint[=@var{number}]
2453 This option directs @command{tar} to print periodic checkpoint
2454 messages as it reads through the archive. It is intended for when you
2455 want a visual indication that @command{tar} is still running, but
2456 don't want to see @option{--verbose} output. You can also instruct
2457 @command{tar} to execute a list of actions on each checkpoint, see
2458 @option{--checklist-action} below. For a detailed description, see
2461 @opsummary{checkpoint-action}
2462 @item --checkpoint-action=@var{action}
2463 Instruct @command{tar} to execute an action upon hitting a
2464 breakpoint. Here we give only a brief outline. @xref{checkpoints},
2465 for a complete description.
2467 The @var{action} argument can be one of the following:
2471 Produce an audible bell on the console.
2475 Print a single dot on the standard listing stream.
2478 Display a textual message on the standard error, with the status and
2479 number of the checkpoint. This is the default.
2481 @item echo=@var{string}
2482 Display @var{string} on the standard error. Before output, the string
2483 is subject to meta-character expansion.
2485 @item exec=@var{command}
2486 Execute the given @var{command}.
2488 @item sleep=@var{time}
2489 Wait for @var{time} seconds.
2491 @item ttyout=@var{string}
2492 Output @var{string} on the current console (@file{/dev/tty}).
2495 Several @option{--checkpoint-action} options can be specified. The
2496 supplied actions will be executed in order of their appearance in the
2499 Using @option{--checkpoint-action} without @option{--checkpoint}
2500 assumes default checkpoint frequency of one checkpoint per 10 records.
2502 @opsummary{check-links}
2505 If this option was given, @command{tar} will check the number of links
2506 dumped for each processed file. If this number does not match the
2507 total number of hard links for the file, a warning message will be
2508 output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2509 synonym for @option{--one-file-system}. The current semantics, which
2510 complies to UNIX98, was introduced with version
2511 1.15.91. @xref{Changes}, for more information.}.
2515 @opsummary{compress}
2516 @opsummary{uncompress}
2521 @command{tar} will use the @command{compress} program when reading or
2522 writing the archive. This allows you to directly act on archives
2523 while saving space. @xref{gzip}.
2525 @opsummary{confirmation}
2526 @item --confirmation
2528 (See @option{--interactive}.) @xref{interactive}.
2530 @opsummary{delay-directory-restore}
2531 @item --delay-directory-restore
2533 Delay setting modification times and permissions of extracted
2534 directories until the end of extraction. @xref{Directory Modification Times and Permissions}.
2536 @opsummary{dereference}
2540 When creating a @command{tar} archive, @command{tar} will archive the
2541 file that a symbolic link points to, rather than archiving the
2542 symlink. @xref{dereference}.
2544 @opsummary{directory}
2545 @item --directory=@var{dir}
2548 When this option is specified, @command{tar} will change its current directory
2549 to @var{dir} before performing any operations. When this option is used
2550 during archive creation, it is order sensitive. @xref{directory}.
2553 @item --exclude=@var{pattern}
2555 When performing operations, @command{tar} will skip files that match
2556 @var{pattern}. @xref{exclude}.
2558 @opsummary{exclude-from}
2559 @item --exclude-from=@var{file}
2560 @itemx -X @var{file}
2562 Similar to @option{--exclude}, except @command{tar} will use the list of
2563 patterns in the file @var{file}. @xref{exclude}.
2565 @opsummary{exclude-caches}
2566 @item --exclude-caches
2568 Exclude from dump any directory containing a valid cache directory
2569 tag file, but still dump the directory node and the tag file itself.
2573 @opsummary{exclude-caches-under}
2574 @item --exclude-caches-under
2576 Exclude from dump any directory containing a valid cache directory
2577 tag file, but still dump the directory node itself.
2581 @opsummary{exclude-caches-all}
2582 @item --exclude-caches-all
2584 Exclude from dump any directory containing a valid cache directory
2585 tag file. @xref{exclude}.
2587 @opsummary{exclude-tag}
2588 @item --exclude-tag=@var{file}
2590 Exclude from dump any directory containing file named @var{file}, but
2591 dump the directory node and @var{file} itself. @xref{exclude}.
2593 @opsummary{exclude-tag-under}
2594 @item --exclude-tag-under=@var{file}
2596 Exclude from dump the contents of any directory containing file
2597 named @var{file}, but dump the directory node itself. @xref{exclude}.
2599 @opsummary{exclude-tag-all}
2600 @item --exclude-tag-all=@var{file}
2602 Exclude from dump any directory containing file named @var{file}.
2605 @opsummary{exclude-vcs}
2608 Exclude from dump directories and files, that are internal for some
2609 widely used version control systems.
2614 @item --file=@var{archive}
2615 @itemx -f @var{archive}
2617 @command{tar} will use the file @var{archive} as the @command{tar} archive it
2618 performs operations on, rather than @command{tar}'s compilation dependent
2619 default. @xref{file tutorial}.
2621 @opsummary{files-from}
2622 @item --files-from=@var{file}
2623 @itemx -T @var{file}
2625 @command{tar} will use the contents of @var{file} as a list of archive members
2626 or files to operate on, in addition to those specified on the
2627 command-line. @xref{files}.
2629 @opsummary{force-local}
2632 Forces @command{tar} to interpret the file name given to @option{--file}
2633 as a local file, even if it looks like a remote tape drive name.
2634 @xref{local and remote archives}.
2637 @item --format=@var{format}
2638 @itemx -H @var{format}
2640 Selects output archive format. @var{Format} may be one of the
2645 Creates an archive that is compatible with Unix V7 @command{tar}.
2648 Creates an archive that is compatible with GNU @command{tar} version
2652 Creates archive in GNU tar 1.13 format. Basically it is the same as
2653 @samp{oldgnu} with the only difference in the way it handles long
2657 Creates a @acronym{POSIX.1-1988} compatible archive.
2660 Creates a @acronym{POSIX.1-2001 archive}.
2664 @xref{Formats}, for a detailed discussion of these formats.
2667 @item --group=@var{group}
2669 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
2670 rather than the group from the source file. @var{group} is first decoded
2671 as a group symbolic name, but if this interpretation fails, it has to be
2672 a decimal numeric group @acronym{ID}. @xref{override}.
2674 Also see the comments for the @option{--owner=@var{user}} option.
2684 This option tells @command{tar} to read or write archives through
2685 @command{gzip}, allowing @command{tar} to directly operate on several
2686 kinds of compressed archives transparently. @xref{gzip}.
2688 @opsummary{hard-dereference}
2689 @item --hard-dereference
2690 When creating an archive, dereference hard links and store the files
2691 they refer to, instead of creating usual hard link members.
2699 @command{tar} will print out a short message summarizing the operations and
2700 options to @command{tar} and exit. @xref{help}.
2702 @opsummary{ignore-case}
2704 Ignore case when matching member or file names with
2705 patterns. @xref{controlling pattern-matching}.
2707 @opsummary{ignore-command-error}
2708 @item --ignore-command-error
2709 Ignore exit codes of subprocesses. @xref{Writing to an External Program}.
2711 @opsummary{ignore-failed-read}
2712 @item --ignore-failed-read
2714 Do not exit unsuccessfully merely because an unreadable file was encountered.
2717 @opsummary{ignore-zeros}
2718 @item --ignore-zeros
2721 With this option, @command{tar} will ignore zeroed blocks in the
2722 archive, which normally signals EOF. @xref{Reading}.
2724 @opsummary{incremental}
2728 Informs @command{tar} that it is working with an old
2729 @acronym{GNU}-format incremental backup archive. It is intended
2730 primarily for backwards compatibility only. @xref{Incremental Dumps},
2731 for a detailed discussion of incremental archives.
2733 @opsummary{index-file}
2734 @item --index-file=@var{file}
2736 Send verbose output to @var{file} instead of to standard output.
2738 @opsummary{info-script}
2739 @opsummary{new-volume-script}
2740 @item --info-script=@var{script-file}
2741 @itemx --new-volume-script=@var{script-file}
2742 @itemx -F @var{script-file}
2744 When @command{tar} is performing multi-tape backups, @var{script-file} is run
2745 at the end of each tape. If @var{script-file} exits with nonzero status,
2746 @command{tar} fails immediately. @xref{info-script}, for a detailed
2747 discussion of @var{script-file}.
2749 @opsummary{interactive}
2751 @itemx --confirmation
2754 Specifies that @command{tar} should ask the user for confirmation before
2755 performing potentially destructive options, such as overwriting files.
2758 @opsummary{keep-newer-files}
2759 @item --keep-newer-files
2761 Do not replace existing files that are newer than their archive copies
2762 when extracting files from an archive.
2764 @opsummary{keep-old-files}
2765 @item --keep-old-files
2768 Do not overwrite existing files when extracting files from an archive.
2769 @xref{Keep Old Files}.
2772 @item --label=@var{name}
2773 @itemx -V @var{name}
2775 When creating an archive, instructs @command{tar} to write @var{name}
2776 as a name record in the archive. When extracting or listing archives,
2777 @command{tar} will only operate on archives that have a label matching
2778 the pattern specified in @var{name}. @xref{Tape Files}.
2780 @opsummary{listed-incremental}
2781 @item --listed-incremental=@var{snapshot-file}
2782 @itemx -g @var{snapshot-file}
2784 During a @option{--create} operation, specifies that the archive that
2785 @command{tar} creates is a new @acronym{GNU}-format incremental
2786 backup, using @var{snapshot-file} to determine which files to backup.
2787 With other operations, informs @command{tar} that the archive is in
2788 incremental format. @xref{Incremental Dumps}.
2793 This option tells @command{tar} to read or write archives through
2794 @command{lzma}. @xref{gzip}.
2798 This option tells @command{tar} to read or write archives through
2799 @command{lzop}. @xref{gzip}.
2802 @item --mode=@var{permissions}
2804 When adding files to an archive, @command{tar} will use
2805 @var{permissions} for the archive members, rather than the permissions
2806 from the files. @var{permissions} can be specified either as an octal
2807 number or as symbolic permissions, like with
2808 @command{chmod}. @xref{override}.
2811 @item --mtime=@var{date}
2813 When adding files to an archive, @command{tar} will use @var{date} as
2814 the modification time of members when creating archives, instead of
2815 their actual modification times. The value of @var{date} can be
2816 either a textual date representation (@pxref{Date input formats}) or a
2817 name of the existing file, starting with @samp{/} or @samp{.}. In the
2818 latter case, the modification time of that file is used. @xref{override}.
2820 @opsummary{multi-volume}
2821 @item --multi-volume
2824 Informs @command{tar} that it should create or otherwise operate on a
2825 multi-volume @command{tar} archive. @xref{Using Multiple Tapes}.
2827 @opsummary{new-volume-script}
2828 @item --new-volume-script
2833 @item --newer=@var{date}
2834 @itemx --after-date=@var{date}
2837 When creating an archive, @command{tar} will only add files that have changed
2838 since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it
2839 is taken to be the name of a file whose data modification time specifies
2840 the date. @xref{after}.
2842 @opsummary{newer-mtime}
2843 @item --newer-mtime=@var{date}
2845 Like @option{--newer}, but add only files whose
2846 contents have changed (as opposed to just @option{--newer}, which will
2847 also back up files for which any status information has
2848 changed). @xref{after}.
2850 @opsummary{no-anchored}
2852 An exclude pattern can match any subsequence of the name's components.
2853 @xref{controlling pattern-matching}.
2855 @opsummary{no-auto-compress}
2856 @item --no-auto-compress
2858 Disables automatic compressed format recognition based on the archive
2859 suffix. @xref{--auto-compress}. @xref{gzip}.
2861 @opsummary{no-check-device}
2862 @item --no-check-device
2863 Do not check device numbers when creating a list of modified files
2864 for incremental archiving. @xref{device numbers}, for
2865 a detailed description.
2867 @opsummary{no-delay-directory-restore}
2868 @item --no-delay-directory-restore
2870 Modification times and permissions of extracted
2871 directories are set when all files from this directory have been
2872 extracted. This is the default.
2873 @xref{Directory Modification Times and Permissions}.
2875 @opsummary{no-ignore-case}
2876 @item --no-ignore-case
2877 Use case-sensitive matching.
2878 @xref{controlling pattern-matching}.
2880 @opsummary{no-ignore-command-error}
2881 @item --no-ignore-command-error
2882 Print warnings about subprocesses that terminated with a nonzero exit
2883 code. @xref{Writing to an External Program}.
2888 If the @option{--null} option was given previously, this option
2889 cancels its effect, so that any following @option{--files-from}
2890 options will expect their file lists to be newline-terminated.
2892 @opsummary{no-overwrite-dir}
2893 @item --no-overwrite-dir
2895 Preserve metadata of existing directories when extracting files
2896 from an archive. @xref{Overwrite Old Files}.
2898 @opsummary{no-quote-chars}
2899 @item --no-quote-chars=@var{string}
2900 Remove characters listed in @var{string} from the list of quoted
2901 characters set by the previous @option{--quote-chars} option
2902 (@pxref{quoting styles}).
2904 @opsummary{no-recursion}
2905 @item --no-recursion
2907 With this option, @command{tar} will not recurse into directories.
2910 @opsummary{no-same-owner}
2911 @item --no-same-owner
2914 When extracting an archive, do not attempt to preserve the owner
2915 specified in the @command{tar} archive. This the default behavior
2918 @opsummary{no-same-permissions}
2919 @item --no-same-permissions
2921 When extracting an archive, subtract the user's umask from files from
2922 the permissions specified in the archive. This is the default behavior
2925 @opsummary{no-unquote}
2927 Treat all input file or member names literally, do not interpret
2928 escape sequences. @xref{input name quoting}.
2930 @opsummary{no-wildcards}
2931 @item --no-wildcards
2932 Do not use wildcards.
2933 @xref{controlling pattern-matching}.
2935 @opsummary{no-wildcards-match-slash}
2936 @item --no-wildcards-match-slash
2937 Wildcards do not match @samp{/}.
2938 @xref{controlling pattern-matching}.
2943 When @command{tar} is using the @option{--files-from} option, this option
2944 instructs @command{tar} to expect file names terminated with @acronym{NUL}, so
2945 @command{tar} can correctly work with file names that contain newlines.
2948 @opsummary{numeric-owner}
2949 @item --numeric-owner
2951 This option will notify @command{tar} that it should use numeric user
2952 and group IDs when creating a @command{tar} file, rather than names.
2956 The function of this option depends on the action @command{tar} is
2957 performing. When extracting files, @option{-o} is a synonym for
2958 @option{--no-same-owner}, i.e., it prevents @command{tar} from
2959 restoring ownership of files being extracted.
2961 When creating an archive, it is a synonym for
2962 @option{--old-archive}. This behavior is for compatibility
2963 with previous versions of @GNUTAR{}, and will be
2964 removed in future releases.
2966 @xref{Changes}, for more information.
2968 @opsummary{occurrence}
2969 @item --occurrence[=@var{number}]
2971 This option can be used in conjunction with one of the subcommands
2972 @option{--delete}, @option{--diff}, @option{--extract} or
2973 @option{--list} when a list of files is given either on the command
2974 line or via @option{-T} option.
2976 This option instructs @command{tar} to process only the @var{number}th
2977 occurrence of each named file. @var{Number} defaults to 1, so
2980 tar -x -f archive.tar --occurrence filename
2984 will extract the first occurrence of the member @file{filename} from @file{archive.tar}
2985 and will terminate without scanning to the end of the archive.
2987 @opsummary{old-archive}
2989 Synonym for @option{--format=v7}.
2991 @opsummary{one-file-system}
2992 @item --one-file-system
2993 Used when creating an archive. Prevents @command{tar} from recursing into
2994 directories that are on different file systems from the current
2997 @opsummary{overwrite}
3000 Overwrite existing files and directory metadata when extracting files
3001 from an archive. @xref{Overwrite Old Files}.
3003 @opsummary{overwrite-dir}
3004 @item --overwrite-dir
3006 Overwrite the metadata of existing directories when extracting files
3007 from an archive. @xref{Overwrite Old Files}.
3010 @item --owner=@var{user}
3012 Specifies that @command{tar} should use @var{user} as the owner of members
3013 when creating archives, instead of the user associated with the source
3014 file. @var{user} is first decoded as a user symbolic name, but if
3015 this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
3018 This option does not affect extraction from archives.
3020 @opsummary{pax-option}
3021 @item --pax-option=@var{keyword-list}
3022 This option is meaningful only with @acronym{POSIX.1-2001} archives
3023 (@pxref{posix}). It modifies the way @command{tar} handles the
3024 extended header keywords. @var{Keyword-list} is a comma-separated
3025 list of keyword options. @xref{PAX keywords}, for a detailed
3028 @opsummary{portability}
3030 @itemx --old-archive
3031 Synonym for @option{--format=v7}.
3035 Same as @option{--format=posix}.
3037 @opsummary{preserve}
3040 Synonymous with specifying both @option{--preserve-permissions} and
3041 @option{--same-order}. @xref{Setting Access Permissions}.
3043 @opsummary{preserve-order}
3044 @item --preserve-order
3046 (See @option{--same-order}; @pxref{Reading}.)
3048 @opsummary{preserve-permissions}
3049 @opsummary{same-permissions}
3050 @item --preserve-permissions
3051 @itemx --same-permissions
3054 When @command{tar} is extracting an archive, it normally subtracts the
3055 users' umask from the permissions specified in the archive and uses
3056 that number as the permissions to create the destination file.
3057 Specifying this option instructs @command{tar} that it should use the
3058 permissions directly from the archive. @xref{Setting Access Permissions}.
3060 @opsummary{quote-chars}
3061 @item --quote-chars=@var{string}
3062 Always quote characters from @var{string}, even if the selected
3063 quoting style would not quote them (@pxref{quoting styles}).
3065 @opsummary{quoting-style}
3066 @item --quoting-style=@var{style}
3067 Set quoting style to use when printing member and file names
3068 (@pxref{quoting styles}). Valid @var{style} values are:
3069 @code{literal}, @code{shell}, @code{shell-always}, @code{c},
3070 @code{escape}, @code{locale}, and @code{clocale}. Default quoting
3071 style is @code{escape}, unless overridden while configuring the
3074 @opsummary{read-full-records}
3075 @item --read-full-records
3078 Specifies that @command{tar} should reblock its input, for reading
3079 from pipes on systems with buggy implementations. @xref{Reading}.
3081 @opsummary{record-size}
3082 @item --record-size=@var{size}
3084 Instructs @command{tar} to use @var{size} bytes per record when accessing the
3085 archive. @xref{Blocking Factor}.
3087 @opsummary{recursion}
3090 With this option, @command{tar} recurses into directories (default).
3093 @opsummary{recursive-unlink}
3094 @item --recursive-unlink
3097 directory hierarchies before extracting directories of the same name
3098 from the archive. @xref{Recursive Unlink}.
3100 @opsummary{remove-files}
3101 @item --remove-files
3103 Directs @command{tar} to remove the source file from the file system after
3104 appending it to an archive. @xref{remove files}.
3106 @opsummary{restrict}
3109 Disable use of some potentially harmful @command{tar} options.
3110 Currently this option disables shell invocation from multi-volume menu
3111 (@pxref{Using Multiple Tapes}).
3113 @opsummary{rmt-command}
3114 @item --rmt-command=@var{cmd}
3116 Notifies @command{tar} that it should use @var{cmd} instead of
3117 the default @file{/usr/libexec/rmt} (@pxref{Remote Tape Server}).
3119 @opsummary{rsh-command}
3120 @item --rsh-command=@var{cmd}
3122 Notifies @command{tar} that is should use @var{cmd} to communicate with remote
3123 devices. @xref{Device}.
3125 @opsummary{same-order}
3127 @itemx --preserve-order
3130 This option is an optimization for @command{tar} when running on machines with
3131 small amounts of memory. It informs @command{tar} that the list of file
3132 arguments has already been sorted to match the order of files in the
3133 archive. @xref{Reading}.
3135 @opsummary{same-owner}
3138 When extracting an archive, @command{tar} will attempt to preserve the owner
3139 specified in the @command{tar} archive with this option present.
3140 This is the default behavior for the superuser; this option has an
3141 effect only for ordinary users. @xref{Attributes}.
3143 @opsummary{same-permissions}
3144 @item --same-permissions
3146 (See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
3152 Assume that the archive media supports seeks to arbitrary
3153 locations. Usually @command{tar} determines automatically whether
3154 the archive can be seeked or not. This option is intended for use
3155 in cases when such recognition fails.
3157 @opsummary{show-defaults}
3158 @item --show-defaults
3160 Displays the default options used by @command{tar} and exits
3161 successfully. This option is intended for use in shell scripts.
3162 Here is an example of what you can see using this option:
3165 $ tar --show-defaults
3166 --format=gnu -f- -b20 --quoting-style=escape \
3167 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
3170 @opsummary{show-omitted-dirs}
3171 @item --show-omitted-dirs
3173 Instructs @command{tar} to mention the directories it is skipping when
3174 operating on a @command{tar} archive. @xref{show-omitted-dirs}.
3176 @opsummary{show-transformed-names}
3177 @opsummary{show-stored-names}
3178 @item --show-transformed-names
3179 @itemx --show-stored-names
3181 Display file or member names after applying any transformations
3182 (@pxref{transform}). In particular, when used in conjunction with one of
3183 the archive creation operations it instructs @command{tar} to list the
3184 member names stored in the archive, as opposed to the actual file
3185 names. @xref{listing member and file names}.
3191 Invokes a @acronym{GNU} extension when adding files to an archive that handles
3192 sparse files efficiently. @xref{sparse}.
3194 @opsummary{sparse-version}
3195 @item --sparse-version=@var{version}
3197 Specifies the @dfn{format version} to use when archiving sparse
3198 files. Implies @option{--sparse}. @xref{sparse}. For the description
3199 of the supported sparse formats, @xref{Sparse Formats}.
3201 @opsummary{starting-file}
3202 @item --starting-file=@var{name}
3203 @itemx -K @var{name}
3205 This option affects extraction only; @command{tar} will skip extracting
3206 files in the archive until it finds one that matches @var{name}.
3209 @opsummary{strip-components}
3210 @item --strip-components=@var{number}
3211 Strip given @var{number} of leading components from file names before
3212 extraction. For example, if archive @file{archive.tar} contained
3213 @file{/some/file/name}, then running
3216 tar --extract --file archive.tar --strip-components=2
3220 would extract this file to file @file{name}.
3222 @opsummary{suffix}, summary
3223 @item --suffix=@var{suffix}
3225 Alters the suffix @command{tar} uses when backing up files from the default
3226 @samp{~}. @xref{backup}.
3228 @opsummary{tape-length}
3229 @item --tape-length=@var{num}
3232 Specifies the length of tapes that @command{tar} is writing as being
3233 @w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
3235 @opsummary{test-label}
3238 Reads the volume label. If an argument is specified, test whether it
3239 matches the volume label. @xref{--test-label option}.
3241 @opsummary{to-command}
3242 @item --to-command=@var{command}
3244 During extraction @command{tar} will pipe extracted files to the
3245 standard input of @var{command}. @xref{Writing to an External Program}.
3247 @opsummary{to-stdout}
3251 During extraction, @command{tar} will extract files to stdout rather
3252 than to the file system. @xref{Writing to Standard Output}.
3255 @item --totals[=@var{signo}]
3257 Displays the total number of bytes transferred when processing an
3258 archive. If an argument is given, these data are displayed on
3259 request, when signal @var{signo} is delivered to @command{tar}.
3266 Sets the data modification time of extracted files to the extraction time,
3267 rather than the data modification time stored in the archive.
3268 @xref{Data Modification Times}.
3270 @opsummary{transform}
3272 @item --transform=@var{sed-expr}
3273 @itemx --xform=@var{sed-expr}
3274 Transform file or member names using @command{sed} replacement expression
3275 @var{sed-expr}. For example,
3278 $ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
3282 will add to @file{archive} files from the current working directory,
3283 replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
3284 discussion, @xref{transform}.
3286 To see transformed member names in verbose listings, use
3287 @option{--show-transformed-names} option
3288 (@pxref{show-transformed-names}).
3290 @opsummary{uncompress}
3293 (See @option{--compress}. @pxref{gzip})
3298 (See @option{--gzip}. @pxref{gzip})
3300 @opsummary{unlink-first}
3301 @item --unlink-first
3304 Directs @command{tar} to remove the corresponding file from the file
3305 system before extracting it from the archive. @xref{Unlink First}.
3309 Enable unquoting input file or member names (default). @xref{input
3312 @opsummary{use-compress-program}
3313 @item --use-compress-program=@var{prog}
3314 @itemx -I=@var{prog}
3316 Instructs @command{tar} to access the archive through @var{prog}, which is
3317 presumed to be a compression program of some sort. @xref{gzip}.
3322 Display file modification dates in @acronym{UTC}. This option implies
3329 Specifies that @command{tar} should be more verbose about the
3330 operations it is performing. This option can be specified multiple
3331 times for some operations to increase the amount of information displayed.
3338 Verifies that the archive was correctly written when creating an
3339 archive. @xref{verify}.
3344 Print information about the program's name, version, origin and legal
3345 status, all on standard output, and then exit successfully.
3348 @opsummary{volno-file}
3349 @item --volno-file=@var{file}
3351 Used in conjunction with @option{--multi-volume}. @command{tar} will
3352 keep track of which volume of a multi-volume archive it is working in
3353 @var{file}. @xref{volno-file}.
3356 @item --warning=@var{keyword}
3358 Enable or disable warning messages identified by @var{keyword}. The
3359 messages are suppressed if @var{keyword} is prefixed with @samp{no-}.
3362 @opsummary{wildcards}
3364 Use wildcards when matching member names with patterns.
3365 @xref{controlling pattern-matching}.
3367 @opsummary{wildcards-match-slash}
3368 @item --wildcards-match-slash
3369 Wildcards match @samp{/}.
3370 @xref{controlling pattern-matching}.
3375 Use @command{xz} for compressing or decompressing the archives. @xref{gzip}.
3379 @node Short Option Summary
3380 @subsection Short Options Cross Reference
3382 Here is an alphabetized list of all of the short option forms, matching
3383 them with the equivalent long option.
3385 @multitable @columnfractions 0.20 0.80
3386 @headitem Short Option @tab Reference
3388 @item -A @tab @ref{--concatenate}.
3390 @item -B @tab @ref{--read-full-records}.
3392 @item -C @tab @ref{--directory}.
3394 @item -F @tab @ref{--info-script}.
3396 @item -G @tab @ref{--incremental}.
3398 @item -J @tab @ref{--xz}.
3400 @item -K @tab @ref{--starting-file}.
3402 @item -L @tab @ref{--tape-length}.
3404 @item -M @tab @ref{--multi-volume}.
3406 @item -N @tab @ref{--newer}.
3408 @item -O @tab @ref{--to-stdout}.
3410 @item -P @tab @ref{--absolute-names}.
3412 @item -R @tab @ref{--block-number}.
3414 @item -S @tab @ref{--sparse}.
3416 @item -T @tab @ref{--files-from}.
3418 @item -U @tab @ref{--unlink-first}.
3420 @item -V @tab @ref{--label}.
3422 @item -W @tab @ref{--verify}.
3424 @item -X @tab @ref{--exclude-from}.
3426 @item -Z @tab @ref{--compress}.
3428 @item -b @tab @ref{--blocking-factor}.
3430 @item -c @tab @ref{--create}.
3432 @item -d @tab @ref{--compare}.
3434 @item -f @tab @ref{--file}.
3436 @item -g @tab @ref{--listed-incremental}.
3438 @item -h @tab @ref{--dereference}.
3440 @item -i @tab @ref{--ignore-zeros}.
3442 @item -j @tab @ref{--bzip2}.
3444 @item -k @tab @ref{--keep-old-files}.
3446 @item -l @tab @ref{--check-links}.
3448 @item -m @tab @ref{--touch}.
3450 @item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
3451 @ref{--portability}.
3453 The latter usage is deprecated. It is retained for compatibility with
3454 the earlier versions of @GNUTAR{}. In future releases
3455 @option{-o} will be equivalent to @option{--no-same-owner} only.
3457 @item -p @tab @ref{--preserve-permissions}.
3459 @item -r @tab @ref{--append}.
3461 @item -s @tab @ref{--same-order}.
3463 @item -t @tab @ref{--list}.
3465 @item -u @tab @ref{--update}.
3467 @item -v @tab @ref{--verbose}.
3469 @item -w @tab @ref{--interactive}.
3471 @item -x @tab @ref{--extract}.
3473 @item -z @tab @ref{--gzip}.
3478 @section @GNUTAR{} documentation
3480 @cindex Getting program version number
3482 @cindex Version of the @command{tar} program
3483 Being careful, the first thing is really checking that you are using
3484 @GNUTAR{}, indeed. The @option{--version} option
3485 causes @command{tar} to print information about its name, version,
3486 origin and legal status, all on standard output, and then exit
3487 successfully. For example, @w{@samp{tar --version}} might print:
3490 tar (GNU tar) @value{VERSION}
3491 Copyright (C) 2008 Free Software Foundation, Inc.
3492 This is free software. You may redistribute copies of it under the terms
3493 of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
3494 There is NO WARRANTY, to the extent permitted by law.
3496 Written by John Gilmore and Jay Fenlason.
3500 The first occurrence of @samp{tar} in the result above is the program
3501 name in the package (for example, @command{rmt} is another program),
3502 while the second occurrence of @samp{tar} is the name of the package
3503 itself, containing possibly many programs. The package is currently
3504 named @samp{tar}, after the name of the main program it
3505 contains@footnote{There are plans to merge the @command{cpio} and
3506 @command{tar} packages into a single one which would be called
3507 @code{paxutils}. So, who knows if, one of this days, the
3508 @option{--version} would not output @w{@samp{tar (@acronym{GNU}
3511 @cindex Obtaining help
3512 @cindex Listing all @command{tar} options
3513 @xopindex{help, introduction}
3514 Another thing you might want to do is checking the spelling or meaning
3515 of some particular @command{tar} option, without resorting to this
3516 manual, for once you have carefully read it. @GNUTAR{}
3517 has a short help feature, triggerable through the
3518 @option{--help} option. By using this option, @command{tar} will
3519 print a usage message listing all available options on standard
3520 output, then exit successfully, without doing anything else and
3521 ignoring all other options. Even if this is only a brief summary, it
3522 may be several screens long. So, if you are not using some kind of
3523 scrollable window, you might prefer to use something like:
3526 $ @kbd{tar --help | less}
3530 presuming, here, that you like using @command{less} for a pager. Other
3531 popular pagers are @command{more} and @command{pg}. If you know about some
3532 @var{keyword} which interests you and do not want to read all the
3533 @option{--help} output, another common idiom is doing:
3536 tar --help | grep @var{keyword}
3540 for getting only the pertinent lines. Notice, however, that some
3541 @command{tar} options have long description lines and the above
3542 command will list only the first of them.
3544 The exact look of the option summary displayed by @kbd{tar --help} is
3545 configurable. @xref{Configuring Help Summary}, for a detailed description.
3548 If you only wish to check the spelling of an option, running @kbd{tar
3549 --usage} may be a better choice. This will display a terse list of
3550 @command{tar} option without accompanying explanations.
3552 The short help output is quite succinct, and you might have to get
3553 back to the full documentation for precise points. If you are reading
3554 this paragraph, you already have the @command{tar} manual in some
3555 form. This manual is available in a variety of forms from
3556 @url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{}
3557 distribution, provided you have @TeX{} already installed somewhere,
3558 and a laser printer around. Just configure the distribution, execute
3559 the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the
3560 usual way (contact your local guru to know how). If @GNUTAR{}
3561 has been conveniently installed at your place, this
3562 manual is also available in interactive, hypertextual form as an Info
3563 file. Just call @w{@samp{info tar}} or, if you do not have the
3564 @command{info} program handy, use the Info reader provided within
3565 @acronym{GNU} Emacs, calling @samp{tar} from the main Info menu.
3567 There is currently no @code{man} page for @GNUTAR{}.
3568 If you observe such a @code{man} page on the system you are running,
3569 either it does not belong to @GNUTAR{}, or it has not
3570 been produced by @acronym{GNU}. Some package maintainers convert
3571 @kbd{tar --help} output to a man page, using @command{help2man}. In
3572 any case, please bear in mind that the authoritative source of
3573 information about @GNUTAR{} is this Texinfo documentation.
3576 @section Obtaining @GNUTAR{} default values
3578 @opindex show-defaults
3579 @GNUTAR{} has some predefined defaults that are used when you do not
3580 explicitly specify another values. To obtain a list of such
3581 defaults, use @option{--show-defaults} option. This will output the
3582 values in the form of @command{tar} command line options:
3586 @kbd{tar --show-defaults}
3587 --format=gnu -f- -b20 --quoting-style=escape
3588 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3593 Notice, that this option outputs only one line. The example output above
3594 has been split to fit page boundaries.
3597 The above output shows that this version of @GNUTAR{} defaults to
3598 using @samp{gnu} archive format (@pxref{Formats}), it uses standard
3599 output as the archive, if no @option{--file} option has been given
3600 (@pxref{file tutorial}), the default blocking factor is 20
3601 (@pxref{Blocking Factor}). It also shows the default locations where
3602 @command{tar} will look for @command{rmt} and @command{rsh} binaries.
3605 @section Checking @command{tar} progress
3607 Typically, @command{tar} performs most operations without reporting any
3608 information to the user except error messages. When using @command{tar}
3609 with many options, particularly ones with complicated or
3610 difficult-to-predict behavior, it is possible to make serious mistakes.
3611 @command{tar} provides several options that make observing @command{tar}
3612 easier. These options cause @command{tar} to print information as it
3613 progresses in its job, and you might want to use them just for being
3614 more careful about what is going on, or merely for entertaining
3615 yourself. If you have encountered a problem when operating on an
3616 archive, however, you may need more information than just an error
3617 message in order to solve the problem. The following options can be
3618 helpful diagnostic tools.
3620 @cindex Verbose operation
3622 Normally, the @option{--list} (@option{-t}) command to list an archive
3623 prints just the file names (one per line) and the other commands are
3624 silent. When used with most operations, the @option{--verbose}
3625 (@option{-v}) option causes @command{tar} to print the name of each
3626 file or archive member as it is processed. This and the other options
3627 which make @command{tar} print status information can be useful in
3628 monitoring @command{tar}.
3630 With @option{--create} or @option{--extract}, @option{--verbose} used
3631 once just prints the names of the files or members as they are processed.
3632 Using it twice causes @command{tar} to print a longer listing
3633 (@xref{verbose member listing}, for the description) for each member.
3634 Since @option{--list} already prints the names of the members,
3635 @option{--verbose} used once with @option{--list} causes @command{tar}
3636 to print an @samp{ls -l} type listing of the files in the archive.
3637 The following examples both extract members with long list output:
3640 $ @kbd{tar --extract --file=archive.tar --verbose --verbose}
3641 $ @kbd{tar xvvf archive.tar}
3644 Verbose output appears on the standard output except when an archive is
3645 being written to the standard output, as with @samp{tar --create
3646 --file=- --verbose} (@samp{tar cfv -}, or even @samp{tar cv}---if the
3647 installer let standard output be the default archive). In that case
3648 @command{tar} writes verbose output to the standard error stream.
3650 If @option{--index-file=@var{file}} is specified, @command{tar} sends
3651 verbose output to @var{file} rather than to standard output or standard
3655 @cindex Obtaining total status information
3657 The @option{--totals} option causes @command{tar} to print on the
3658 standard error the total amount of bytes transferred when processing
3659 an archive. When creating or appending to an archive, this option
3660 prints the number of bytes written to the archive and the average
3661 speed at which they have been written, e.g.:
3665 $ @kbd{tar -c -f archive.tar --totals /home}
3666 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3670 When reading an archive, this option displays the number of bytes
3675 $ @kbd{tar -x -f archive.tar --totals}
3676 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3680 Finally, when deleting from an archive, the @option{--totals} option
3681 displays both numbers plus number of bytes removed from the archive:
3685 $ @kbd{tar --delete -f foo.tar --totals --wildcards '*~'}
3686 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3687 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3688 Total bytes deleted: 1474048
3692 You can also obtain this information on request. When
3693 @option{--totals} is used with an argument, this argument is
3694 interpreted as a symbolic name of a signal, upon delivery of which the
3695 statistics is to be printed:
3698 @item --totals=@var{signo}
3699 Print statistics upon delivery of signal @var{signo}. Valid arguments
3700 are: @code{SIGHUP}, @code{SIGQUIT}, @code{SIGINT}, @code{SIGUSR1} and
3701 @code{SIGUSR2}. Shortened names without @samp{SIG} prefix are also
3705 Both forms of @option{--totals} option can be used simultaneously.
3706 Thus, @kbd{tar -x --totals --totals=USR1} instructs @command{tar} to
3707 extract all members from its default archive and print statistics
3708 after finishing the extraction, as well as when receiving signal
3711 @anchor{Progress information}
3712 @cindex Progress information
3713 The @option{--checkpoint} option prints an occasional message
3714 as @command{tar} reads or writes the archive. It is designed for
3715 those who don't need the more detailed (and voluminous) output of
3716 @option{--block-number} (@option{-R}), but do want visual confirmation
3717 that @command{tar} is actually making forward progress. By default it
3718 prints a message each 10 records read or written. This can be changed
3719 by giving it a numeric argument after an equal sign:
3722 $ @kbd{tar -c --checkpoint=1000} /var
3723 tar: Write checkpoint 1000
3724 tar: Write checkpoint 2000
3725 tar: Write checkpoint 3000
3728 This example shows the default checkpoint message used by
3729 @command{tar}. If you place a dot immediately after the equal
3730 sign, it will print a @samp{.} at each checkpoint@footnote{This is
3731 actually a shortcut for @option{--checkpoint=@var{n}
3732 --checkpoint-action=dot}. @xref{checkpoints, dot}.}. For example:
3735 $ @kbd{tar -c --checkpoint=.1000} /var
3739 The @option{--checkpoint} option provides a flexible mechanism for
3740 executing arbitrary actions upon hitting checkpoints, see the next
3741 section (@pxref{checkpoints}), for more information on it.
3743 @opindex show-omitted-dirs
3744 @anchor{show-omitted-dirs}
3745 The @option{--show-omitted-dirs} option, when reading an archive---with
3746 @option{--list} or @option{--extract}, for example---causes a message
3747 to be printed for each directory in the archive which is skipped.
3748 This happens regardless of the reason for skipping: the directory might
3749 not have been named on the command line (implicitly or explicitly),
3750 it might be excluded by the use of the
3751 @option{--exclude=@var{pattern}} option, or some other reason.
3753 @opindex block-number
3754 @cindex Block number where error occurred
3755 @anchor{block-number}
3756 If @option{--block-number} (@option{-R}) is used, @command{tar} prints, along with
3757 every message it would normally produce, the block number within the
3758 archive where the message was triggered. Also, supplementary messages
3759 are triggered when reading blocks full of NULs, or when hitting end of
3760 file on the archive. As of now, if the archive is properly terminated
3761 with a NUL block, the reading of the file may stop before end of file
3762 is met, so the position of end of file will not usually show when
3763 @option{--block-number} (@option{-R}) is used. Note that @GNUTAR{}
3764 drains the archive before exiting when reading the
3765 archive from a pipe.
3767 @cindex Error message, block number of
3768 This option is especially useful when reading damaged archives, since
3769 it helps pinpoint the damaged sections. It can also be used with
3770 @option{--list} (@option{-t}) when listing a file-system backup tape, allowing you to
3771 choose among several backup tapes when retrieving a file later, in
3772 favor of the tape where the file appears earliest (closest to the
3773 front of the tape). @xref{backup}.
3776 @section Checkpoints
3777 @cindex checkpoints, defined
3779 @opindex checkpoint-action
3781 A @dfn{checkpoint} is a moment of time before writing @var{n}th record to
3782 the archive (a @dfn{write checkpoint}), or before reading @var{n}th record
3783 from the archive (a @dfn{read checkpoint}). Checkpoints allow to
3784 periodically execute arbitrary actions.
3786 The checkpoint facility is enabled using the following option:
3789 @xopindex{checkpoint, defined}
3790 @item --checkpoint[=@var{n}]
3791 Schedule checkpoints before writing or reading each @var{n}th record.
3792 The default value for @var{n} is 10.
3795 A list of arbitrary @dfn{actions} can be executed at each checkpoint.
3796 These actions include: pausing, displaying textual messages, and
3797 executing arbitrary external programs. Actions are defined using
3798 the @option{--checkpoint-action} option.
3801 @xopindex{checkpoint-action, defined}
3802 @item --checkpoint-action=@var{action}
3803 Execute an @var{action} at each checkpoint.
3806 @cindex @code{echo}, checkpoint action
3807 The simplest value of @var{action} is @samp{echo}. It instructs
3808 @command{tar} to display the default message on the standard error
3809 stream upon arriving at each checkpoint. The default message is (in
3810 @acronym{POSIX} locale) @samp{Write checkpoint @var{n}}, for write
3811 checkpoints, and @samp{Read checkpoint @var{n}}, for read checkpoints.
3812 Here, @var{n} represents ordinal number of the checkpoint.
3814 In another locales, translated versions of this message are used.
3816 This is the default action, so running:
3819 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=echo} /var
3826 $ @kbd{tar -c --checkpoint=1000} /var
3829 The @samp{echo} action also allows to supply a customized message.
3830 You do so by placing an equals sign and the message right after it,
3834 --checkpoint-action="echo=Hit %s checkpoint #%u"
3837 The @samp{%s} and @samp{%u} in the above example are
3838 @dfn{meta-characters}. The @samp{%s} meta-character is replaced with
3839 the @dfn{type} of the checkpoint: @samp{write} or
3840 @samp{read} (or a corresponding translated version in locales other
3841 than @acronym{POSIX}). The @samp{%u} meta-character is replaced with
3842 the ordinal number of the checkpoint. Thus, the above example could
3843 produce the following output when used with the @option{--create}
3847 tar: Hit write checkpoint #10
3848 tar: Hit write checkpoint #20
3849 tar: Hit write checkpoint #30
3852 Aside from meta-character expansion, the message string is subject to
3853 @dfn{unquoting}, during which the backslash @dfn{escape sequences} are
3854 replaced with their corresponding @acronym{ASCII} characters
3855 (@pxref{escape sequences}). E.g. the following action will produce an
3856 audible bell and the message described above at each checkpoint:
3859 --checkpoint-action='echo=\aHit %s checkpoint #%u'
3862 @cindex @code{bell}, checkpoint action
3863 There is also a special action which produces an audible signal:
3864 @samp{bell}. It is not equivalent to @samp{echo='\a'}, because
3865 @samp{bell} sends the bell directly to the console (@file{/dev/tty}),
3866 whereas @samp{echo='\a'} sends it to the standard error.
3868 @cindex @code{ttyout}, checkpoint action
3869 The @samp{ttyout=@var{string}} action outputs @var{string} to
3870 @file{/dev/tty}, so it can be used even if the standard output is
3871 redirected elsewhere. The @var{string} is subject to the same
3872 modifications as with @samp{echo} action. In contrast to the latter,
3873 @samp{ttyout} does not prepend @command{tar} executable name to the
3874 string, nor does it output a newline after it. For example, the
3875 following action will print the checkpoint message at the same screen
3876 line, overwriting any previous message:
3879 --checkpoint-action="ttyout=\rHit %s checkpoint #%u"
3882 @cindex @code{dot}, checkpoint action
3883 Another available checkpoint action is @samp{dot} (or @samp{.}). It
3884 instructs @command{tar} to print a single dot on the standard listing
3888 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=dot} /var
3892 For compatibility with previous @GNUTAR{} versions, this action can
3893 be abbreviated by placing a dot in front of the checkpoint frequency,
3894 as shown in the previous section.
3896 @cindex @code{sleep}, checkpoint action
3897 Yet another action, @samp{sleep}, pauses @command{tar} for a specified
3898 amount of seconds. The following example will stop for 30 seconds at each
3902 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=sleep=30}
3905 @cindex @code{exec}, checkpoint action
3906 Finally, the @code{exec} action executes a given external program.
3910 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint}
3913 This program is executed using @command{/bin/sh -c}, with no
3914 additional arguments. Its exit code is ignored. It gets a copy of
3915 @command{tar}'s environment plus the following variables:
3918 @vrindex TAR_VERSION, checkpoint script environment
3920 @GNUTAR{} version number.
3922 @vrindex TAR_ARCHIVE, checkpoint script environment
3924 The name of the archive @command{tar} is processing.
3926 @vrindex TAR_BLOCKING_FACTOR, checkpoint script environment
3927 @item TAR_BLOCKING_FACTOR
3928 Current blocking factor (@pxref{Blocking}).
3930 @vrindex TAR_CHECKPOINT, checkpoint script environment
3931 @item TAR_CHECKPOINT
3932 Number of the checkpoint.
3934 @vrindex TAR_SUBCOMMAND, checkpoint script environment
3935 @item TAR_SUBCOMMAND
3936 A short option describing the operation @command{tar} is executing.
3937 @xref{Operations}, for a complete list of subcommand options.
3939 @vrindex TAR_FORMAT, checkpoint script environment
3941 Format of the archive being processed. @xref{Formats}, for a complete
3942 list of archive format names.
3945 Any number of actions can be defined, by supplying several
3946 @option{--checkpoint-action} options in the command line. For
3947 example, the command below displays two messages, pauses
3948 execution for 30 seconds and executes the @file{/sbin/cpoint} script:
3952 $ @kbd{tar -c -f arc.tar \
3953 --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
3954 --checkpoint-action='echo=Sleeping for 30 seconds' \
3955 --checkpoint-action='sleep=30' \
3956 --checkpoint-action='exec=/sbin/cpoint'}
3960 This example also illustrates the fact that
3961 @option{--checkpoint-action} can be used without
3962 @option{--checkpoint}. In this case, the default checkpoint frequency
3963 (at each 10th record) is assumed.
3966 @section Controlling Warning Messages
3968 Sometimes, while performing the requested task, @GNUTAR{} notices
3969 some conditions that are not exactly erros, but which the user
3970 should be aware of. When this happens, @command{tar} issues a
3971 @dfn{warning message} describing the condition. Warning messages
3972 are output to the standard error and they do not affect the exit
3973 code of @command{tar} command.
3975 @xopindex{warning, explained}
3976 @GNUTAR{} allows the user to suppress some or all of its warning
3980 @item --warning=@var{keyword}
3981 Control display of the warning messages identified by @var{keyword}.
3982 If @var{keyword} starts with the prefix @samp{no-}, such messages are
3983 suppressed. Otherwise, they are enabled.
3985 Multiple @option{--warning} messages accumulate.
3987 The tables below list allowed values for @var{keyword} along with the
3988 warning messages they control.
3991 @subheading Keywords controlling @command{tar} operation
3995 Enable all warning messages. This is the default.
3998 Disable all warning messages.
3999 @kwindex filename-with-nuls
4000 @cindex @samp{file name read contains nul character}, warning message
4001 @item filename-with-nuls
4002 @samp{%s: file name read contains nul character}
4003 @kwindex alone-zero-block
4004 @cindex @samp{A lone zero block at}, warning message
4005 @item alone-zero-block
4006 @samp{A lone zero block at %s}
4009 @subheading Keywords applicable for @command{tar --create}
4012 @cindex @samp{contains a cache directory tag}, warning message
4014 @samp{%s: contains a cache directory tag %s; %s}
4015 @kwindex file-shrank
4016 @cindex @samp{File shrank by %s bytes}, warning message
4018 @samp{%s: File shrank by %s bytes; padding with zeros}
4020 @cindex @samp{file is on a different filesystem}, warning message
4022 @samp{%s: file is on a different filesystem; not dumped}
4023 @kwindex file-ignored
4024 @cindex @samp{Unknown file type; file ignored}, warning message
4025 @cindex @samp{socket ignored}, warning message
4026 @cindex @samp{door ignored}, warning message
4028 @samp{%s: Unknown file type; file ignored}
4029 @samp{%s: socket ignored}
4030 @*@samp{%s: door ignored}
4031 @kwindex file-unchanged
4032 @cindex @samp{file is unchanged; not dumped}, warning message
4033 @item file-unchanged
4034 @samp{%s: file is unchanged; not dumped}
4035 @kwindex ignore-archive
4036 @cindex @samp{file is the archive; not dumped}, warning message
4037 @kwindex ignore-archive
4038 @cindex @samp{file is the archive; not dumped}, warning message
4039 @item ignore-archive
4040 @samp{%s: file is the archive; not dumped}
4041 @kwindex file-removed
4042 @cindex @samp{File removed before we read it}, warning message
4044 @samp{%s: File removed before we read it}
4045 @kwindex file-changed
4046 @cindex @samp{file changed as we read it}, warning message
4048 @samp{%s: file changed as we read it}
4051 @subheading Keywords applicable for @command{tar --extract}
4054 @cindex @samp{implausibly old time stamp %s}, warning message
4055 @cindex @samp{time stamp %s is %s s in the future}, warning message
4057 @samp{%s: implausibly old time stamp %s}
4058 @*@samp{%s: time stamp %s is %s s in the future}
4059 @kwindex contiguous-cast
4060 @cindex @samp{Extracting contiguous files as regular files}, warning message
4061 @item contiguous-cast
4062 @samp{Extracting contiguous files as regular files}
4063 @kwindex symlink-cast
4064 @cindex @samp{Attempting extraction of symbolic links as hard links}, warning message
4066 @samp{Attempting extraction of symbolic links as hard links}
4067 @kwindex unknown-cast
4068 @cindex @samp{Unknown file type `%c', extracted as normal file}, warning message
4070 @samp{%s: Unknown file type `%c', extracted as normal file}
4071 @kwindex ignore-newer
4072 @cindex @samp{Current %s is newer or same age}, warning message
4074 @samp{Current %s is newer or same age}
4075 @kwindex unknown-keyword
4076 @cindex @samp{Ignoring unknown extended header keyword `%s'}, warning message
4077 @item unknown-keyword
4078 @samp{Ignoring unknown extended header keyword `%s'}
4081 @subheading Keywords controlling incremental extraction:
4083 @kwindex rename-directory
4084 @cindex @samp{%s: Directory has been renamed from %s}, warning message
4085 @cindex @samp{%s: Directory has been renamed}, warning message
4086 @item rename-directory
4087 @samp{%s: Directory has been renamed from %s}
4088 @*@samp{%s: Directory has been renamed}
4089 @kwindex new-directory
4090 @cindex @samp{%s: Directory is new}, warning message
4092 @samp{%s: Directory is new}
4094 @cindex @samp{%s: directory is on a different device: not purging}, warning message
4096 @samp{%s: directory is on a different device: not purging}
4097 @kwindex bad-dumpdir
4098 @cindex @samp{Malformed dumpdir: 'X' never used}, warning message
4100 @samp{Malformed dumpdir: 'X' never used}
4104 @section Asking for Confirmation During Operations
4105 @cindex Interactive operation
4107 Typically, @command{tar} carries out a command without stopping for
4108 further instructions. In some situations however, you may want to
4109 exclude some files and archive members from the operation (for instance
4110 if disk or storage space is tight). You can do this by excluding
4111 certain files automatically (@pxref{Choosing}), or by performing
4112 an operation interactively, using the @option{--interactive} (@option{-w}) option.
4113 @command{tar} also accepts @option{--confirmation} for this option.
4115 @opindex interactive
4116 When the @option{--interactive} (@option{-w}) option is specified, before
4117 reading, writing, or deleting files, @command{tar} first prints a message
4118 for each such file, telling what operation it intends to take, then asks
4119 for confirmation on the terminal. The actions which require
4120 confirmation include adding a file to the archive, extracting a file
4121 from the archive, deleting a file from the archive, and deleting a file
4122 from disk. To confirm the action, you must type a line of input
4123 beginning with @samp{y}. If your input line begins with anything other
4124 than @samp{y}, @command{tar} skips that file.
4126 If @command{tar} is reading the archive from the standard input,
4127 @command{tar} opens the file @file{/dev/tty} to support the interactive
4130 Verbose output is normally sent to standard output, separate from
4131 other error messages. However, if the archive is produced directly
4132 on standard output, then verbose output is mixed with errors on
4133 @code{stderr}. Producing the archive on standard output may be used
4134 as a way to avoid using disk space, when the archive is soon to be
4135 consumed by another process reading it, say. Some people felt the need
4136 of producing an archive on stdout, still willing to segregate between
4137 verbose output and error output. A possible approach would be using a
4138 named pipe to receive the archive, and having the consumer process to
4139 read from that named pipe. This has the advantage of letting standard
4140 output free to receive verbose output, all separate from errors.
4143 @chapter @GNUTAR{} Operations
4156 @section Basic @GNUTAR{} Operations
4158 The basic @command{tar} operations, @option{--create} (@option{-c}),
4159 @option{--list} (@option{-t}) and @option{--extract} (@option{--get},
4160 @option{-x}), are currently presented and described in the tutorial
4161 chapter of this manual. This section provides some complementary notes
4162 for these operations.
4165 @xopindex{create, complementary notes}
4169 Creating an empty archive would have some kind of elegance. One can
4170 initialize an empty archive and later use @option{--append}
4171 (@option{-r}) for adding all members. Some applications would not
4172 welcome making an exception in the way of adding the first archive
4173 member. On the other hand, many people reported that it is
4174 dangerously too easy for @command{tar} to destroy a magnetic tape with
4175 an empty archive@footnote{This is well described in @cite{Unix-haters
4176 Handbook}, by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG
4177 Books, ISBN 1-56884-203-1.}. The two most common errors are:
4181 Mistakingly using @code{create} instead of @code{extract}, when the
4182 intent was to extract the full contents of an archive. This error
4183 is likely: keys @kbd{c} and @kbd{x} are right next to each other on
4184 the QWERTY keyboard. Instead of being unpacked, the archive then
4185 gets wholly destroyed. When users speak about @dfn{exploding} an
4186 archive, they usually mean something else :-).
4189 Forgetting the argument to @code{file}, when the intent was to create
4190 an archive with a single file in it. This error is likely because a
4191 tired user can easily add the @kbd{f} key to the cluster of option
4192 letters, by the mere force of habit, without realizing the full
4193 consequence of doing so. The usual consequence is that the single
4194 file, which was meant to be saved, is rather destroyed.
4197 So, recognizing the likelihood and the catastrophic nature of these
4198 errors, @GNUTAR{} now takes some distance from elegance, and
4199 cowardly refuses to create an archive when @option{--create} option is
4200 given, there are no arguments besides options, and
4201 @option{--files-from} (@option{-T}) option is @emph{not} used. To get
4202 around the cautiousness of @GNUTAR{} and nevertheless create an
4203 archive with nothing in it, one may still use, as the value for the
4204 @option{--files-from} option, a file with no names in it, as shown in
4205 the following commands:
4208 @kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
4209 @kbd{tar cfT empty-archive.tar /dev/null}
4212 @xopindex{extract, complementary notes}
4217 A socket is stored, within a @GNUTAR{} archive, as a pipe.
4219 @item @option{--list} (@option{-t})
4221 @GNUTAR{} now shows dates as @samp{1996-08-30},
4222 while it used to show them as @samp{Aug 30 1996}. Preferably,
4223 people should get used to ISO 8601 dates. Local American dates should
4224 be made available again with full date localization support, once
4225 ready. In the meantime, programs not being localizable for dates
4226 should prefer international dates, that's really the way to go.
4228 Look up @url{http://www.cl.cam.ac.uk/@/~mgk25/@/iso-time.html} if you
4229 are curious, it contains a detailed explanation of the ISO 8601 standard.
4234 @section Advanced @GNUTAR{} Operations
4236 Now that you have learned the basics of using @GNUTAR{}, you may want
4237 to learn about further ways in which @command{tar} can help you.
4239 This chapter presents five, more advanced operations which you probably
4240 won't use on a daily basis, but which serve more specialized functions.
4241 We also explain the different styles of options and why you might want
4242 to use one or another, or a combination of them in your @command{tar}
4243 commands. Additionally, this chapter includes options which allow you to
4244 define the output from @command{tar} more carefully, and provide help and
4245 error correction in special circumstances.
4247 @FIXME{check this after the chapter is actually revised to make sure
4248 it still introduces the info in the chapter correctly : ).}
4260 @subsection The Five Advanced @command{tar} Operations
4263 In the last chapter, you learned about the first three operations to
4264 @command{tar}. This chapter presents the remaining five operations to
4265 @command{tar}: @option{--append}, @option{--update}, @option{--concatenate},
4266 @option{--delete}, and @option{--compare}.
4268 You are not likely to use these operations as frequently as those
4269 covered in the last chapter; however, since they perform specialized
4270 functions, they are quite useful when you do need to use them. We
4271 will give examples using the same directory and files that you created
4272 in the last chapter. As you may recall, the directory is called
4273 @file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk},
4274 @samp{rock}, and the two archive files you created are
4275 @samp{collection.tar} and @samp{music.tar}.
4277 We will also use the archive files @samp{afiles.tar} and
4278 @samp{bfiles.tar}. The archive @samp{afiles.tar} contains the members @samp{apple},
4279 @samp{angst}, and @samp{aspic}; @samp{bfiles.tar} contains the members
4280 @samp{./birds}, @samp{baboon}, and @samp{./box}.
4282 Unless we state otherwise, all practicing you do and examples you follow
4283 in this chapter will take place in the @file{practice} directory that
4284 you created in the previous chapter; see @ref{prepare for examples}.
4285 (Below in this section, we will remind you of the state of the examples
4286 where the last chapter left them.)
4288 The five operations that we will cover in this chapter are:
4293 Add new entries to an archive that already exists.
4296 Add more recent copies of archive members to the end of an archive, if
4301 Add one or more pre-existing archives to the end of another archive.
4303 Delete items from an archive (does not work on tapes).
4307 Compare archive members to their counterparts in the file system.
4311 @subsection How to Add Files to Existing Archives: @option{--append}
4315 If you want to add files to an existing archive, you don't need to
4316 create a new archive; you can use @option{--append} (@option{-r}).
4317 The archive must already exist in order to use @option{--append}. (A
4318 related operation is the @option{--update} operation; you can use this
4319 to add newer versions of archive members to an existing archive. To learn how to
4320 do this with @option{--update}, @pxref{update}.)
4322 If you use @option{--append} to add a file that has the same name as an
4323 archive member to an archive containing that archive member, then the
4324 old member is not deleted. What does happen, however, is somewhat
4325 complex. @command{tar} @emph{allows} you to have infinite number of files
4326 with the same name. Some operations treat these same-named members no
4327 differently than any other set of archive members: for example, if you
4328 view an archive with @option{--list} (@option{-t}), you will see all
4329 of those members listed, with their data modification times, owners, etc.
4331 Other operations don't deal with these members as perfectly as you might
4332 prefer; if you were to use @option{--extract} to extract the archive,
4333 only the most recently added copy of a member with the same name as four
4334 other members would end up in the working directory. This is because
4335 @option{--extract} extracts an archive in the order the members appeared
4336 in the archive; the most recently archived members will be extracted
4337 last. Additionally, an extracted member will @emph{replace} a file of
4338 the same name which existed in the directory already, and @command{tar}
4339 will not prompt you about this@footnote{Unless you give it
4340 @option{--keep-old-files} option, or the disk copy is newer than the
4341 the one in the archive and you invoke @command{tar} with
4342 @option{--keep-newer-files} option}. Thus, only the most recently archived
4343 member will end up being extracted, as it will replace the one
4344 extracted before it, and so on.
4346 There exists a special option that allows you to get around this
4347 behavior and extract (or list) only a particular copy of the file.
4348 This is @option{--occurrence} option. If you run @command{tar} with
4349 this option, it will extract only the first copy of the file. You
4350 may also give this option an argument specifying the number of
4351 copy to be extracted. Thus, for example if the archive
4352 @file{archive.tar} contained three copies of file @file{myfile}, then
4356 tar --extract --file archive.tar --occurrence=2 myfile
4360 would extract only the second copy. @xref{Option
4361 Summary,---occurrence}, for the description of @option{--occurrence}
4364 @FIXME{ hag -- you might want to incorporate some of the above into the
4365 MMwtSN node; not sure. i didn't know how to make it simpler...
4367 There are a few ways to get around this. (maybe xref Multiple Members
4368 with the Same Name.}
4370 @cindex Members, replacing with other members
4371 @cindex Replacing members with other members
4372 If you want to replace an archive member, use @option{--delete} to
4373 delete the member you want to remove from the archive, , and then use
4374 @option{--append} to add the member you want to be in the archive. Note
4375 that you can not change the order of the archive; the most recently
4376 added member will still appear last. In this sense, you cannot truly
4377 ``replace'' one member with another. (Replacing one member with another
4378 will not work on certain types of media, such as tapes; see @ref{delete}
4379 and @ref{Media}, for more information.)
4382 * appending files:: Appending Files to an Archive
4386 @node appending files
4387 @subsubsection Appending Files to an Archive
4389 @cindex Adding files to an Archive
4390 @cindex Appending files to an Archive
4391 @cindex Archives, Appending files to
4393 The simplest way to add a file to an already existing archive is the
4394 @option{--append} (@option{-r}) operation, which writes specified
4395 files into the archive whether or not they are already among the
4398 When you use @option{--append}, you @emph{must} specify file name
4399 arguments, as there is no default. If you specify a file that already
4400 exists in the archive, another copy of the file will be added to the
4401 end of the archive. As with other operations, the member names of the
4402 newly added files will be exactly the same as their names given on the
4403 command line. The @option{--verbose} (@option{-v}) option will print
4404 out the names of the files as they are written into the archive.
4406 @option{--append} cannot be performed on some tape drives, unfortunately,
4407 due to deficiencies in the formats those tape drives use. The archive
4408 must be a valid @command{tar} archive, or else the results of using this
4409 operation will be unpredictable. @xref{Media}.
4411 To demonstrate using @option{--append} to add a file to an archive,
4412 create a file called @file{rock} in the @file{practice} directory.
4413 Make sure you are in the @file{practice} directory. Then, run the
4414 following @command{tar} command to add @file{rock} to
4415 @file{collection.tar}:
4418 $ @kbd{tar --append --file=collection.tar rock}
4422 If you now use the @option{--list} (@option{-t}) operation, you will see that
4423 @file{rock} has been added to the archive:
4426 $ @kbd{tar --list --file=collection.tar}
4427 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4428 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4429 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4430 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4434 @subsubsection Multiple Members with the Same Name
4436 You can use @option{--append} (@option{-r}) to add copies of files
4437 which have been updated since the archive was created. (However, we
4438 do not recommend doing this since there is another @command{tar}
4439 option called @option{--update}; @xref{update}, for more information.
4440 We describe this use of @option{--append} here for the sake of
4441 completeness.) When you extract the archive, the older version will
4442 be effectively lost. This works because files are extracted from an
4443 archive in the order in which they were archived. Thus, when the
4444 archive is extracted, a file archived later in time will replace a
4445 file of the same name which was archived earlier, even though the
4446 older version of the file will remain in the archive unless you delete
4447 all versions of the file.
4449 Supposing you change the file @file{blues} and then append the changed
4450 version to @file{collection.tar}. As you saw above, the original
4451 @file{blues} is in the archive @file{collection.tar}. If you change the
4452 file and append the new version of the file to the archive, there will
4453 be two copies in the archive. When you extract the archive, the older
4454 version of the file will be extracted first, and then replaced by the
4455 newer version when it is extracted.
4457 You can append the new, changed copy of the file @file{blues} to the
4458 archive in this way:
4461 $ @kbd{tar --append --verbose --file=collection.tar blues}
4466 Because you specified the @option{--verbose} option, @command{tar} has
4467 printed the name of the file being appended as it was acted on. Now
4468 list the contents of the archive:
4471 $ @kbd{tar --list --verbose --file=collection.tar}
4472 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4473 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4474 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4475 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4476 -rw-r--r-- me user 58 1996-10-24 18:30 blues
4480 The newest version of @file{blues} is now at the end of the archive
4481 (note the different creation dates and file sizes). If you extract
4482 the archive, the older version of the file @file{blues} will be
4483 replaced by the newer version. You can confirm this by extracting
4484 the archive and running @samp{ls} on the directory.
4486 If you wish to extract the first occurrence of the file @file{blues}
4487 from the archive, use @option{--occurrence} option, as shown in
4488 the following example:
4491 $ @kbd{tar --extract -vv --occurrence --file=collection.tar blues}
4492 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4495 @xref{Writing}, for more information on @option{--extract} and
4496 @xref{Option Summary, --occurrence}, for the description of
4497 @option{--occurrence} option.
4500 @subsection Updating an Archive
4502 @cindex Updating an archive
4505 In the previous section, you learned how to use @option{--append} to
4506 add a file to an existing archive. A related operation is
4507 @option{--update} (@option{-u}). The @option{--update} operation
4508 updates a @command{tar} archive by comparing the date of the specified
4509 archive members against the date of the file with the same name. If
4510 the file has been modified more recently than the archive member, then
4511 the newer version of the file is added to the archive (as with
4514 Unfortunately, you cannot use @option{--update} with magnetic tape drives.
4515 The operation will fail.
4517 @FIXME{other examples of media on which --update will fail? need to ask
4518 charles and/or mib/thomas/dave shevett..}
4520 Both @option{--update} and @option{--append} work by adding to the end
4521 of the archive. When you extract a file from the archive, only the
4522 version stored last will wind up in the file system, unless you use
4523 the @option{--backup} option. @xref{multiple}, for a detailed discussion.
4530 @subsubsection How to Update an Archive Using @option{--update}
4532 You must use file name arguments with the @option{--update}
4533 (@option{-u}) operation. If you don't specify any files,
4534 @command{tar} won't act on any files and won't tell you that it didn't
4535 do anything (which may end up confusing you).
4537 @c note: the above parenthetical added because in fact, this
4538 @c behavior just confused the author. :-)
4540 To see the @option{--update} option at work, create a new file,
4541 @file{classical}, in your practice directory, and some extra text to the
4542 file @file{blues}, using any text editor. Then invoke @command{tar} with
4543 the @samp{update} operation and the @option{--verbose} (@option{-v})
4544 option specified, using the names of all the files in the practice
4545 directory as file name arguments:
4548 $ @kbd{tar --update -v -f collection.tar blues folk rock classical}
4555 Because we have specified verbose mode, @command{tar} prints out the names
4556 of the files it is working on, which in this case are the names of the
4557 files that needed to be updated. If you run @samp{tar --list} and look
4558 at the archive, you will see @file{blues} and @file{classical} at its
4559 end. There will be a total of two versions of the member @samp{blues};
4560 the one at the end will be newer and larger, since you added text before
4563 (The reason @command{tar} does not overwrite the older file when updating
4564 it is because writing to the middle of a section of tape is a difficult
4565 process. Tapes are not designed to go backward. @xref{Media}, for more
4566 information about tapes.
4568 @option{--update} (@option{-u}) is not suitable for performing backups for two
4569 reasons: it does not change directory content entries, and it
4570 lengthens the archive every time it is used. The @GNUTAR{}
4571 options intended specifically for backups are more
4572 efficient. If you need to run backups, please consult @ref{Backups}.
4575 @subsection Combining Archives with @option{--concatenate}
4577 @cindex Adding archives to an archive
4578 @cindex Concatenating Archives
4579 @opindex concatenate
4581 @c @cindex @option{-A} described
4582 Sometimes it may be convenient to add a second archive onto the end of
4583 an archive rather than adding individual files to the archive. To add
4584 one or more archives to the end of another archive, you should use the
4585 @option{--concatenate} (@option{--catenate}, @option{-A}) operation.
4587 To use @option{--concatenate}, give the first archive with
4588 @option{--file} option and name the rest of archives to be
4589 concatenated on the command line. The members, and their member
4590 names, will be copied verbatim from those archives to the first one.
4591 @footnote{This can cause multiple members to have the same name, for
4592 information on how this affects reading the archive, @ref{multiple}.}
4593 The new, concatenated archive will be called by the same name as the
4594 one given with the @option{--file} option. As usual, if you omit
4595 @option{--file}, @command{tar} will use the value of the environment
4596 variable @env{TAPE}, or, if this has not been set, the default archive name.
4598 @FIXME{There is no way to specify a new name...}
4600 To demonstrate how @option{--concatenate} works, create two small archives
4601 called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
4602 files from @file{practice}:
4605 $ @kbd{tar -cvf bluesrock.tar blues rock}
4608 $ @kbd{tar -cvf folkjazz.tar folk jazz}
4614 If you like, You can run @samp{tar --list} to make sure the archives
4615 contain what they are supposed to:
4618 $ @kbd{tar -tvf bluesrock.tar}
4619 -rw-r--r-- melissa user 105 1997-01-21 19:42 blues
4620 -rw-r--r-- melissa user 33 1997-01-20 15:34 rock
4621 $ @kbd{tar -tvf jazzfolk.tar}
4622 -rw-r--r-- melissa user 20 1996-09-23 16:44 folk
4623 -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
4626 We can concatenate these two archives with @command{tar}:
4630 $ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
4633 If you now list the contents of the @file{bluesrock.tar}, you will see
4634 that now it also contains the archive members of @file{jazzfolk.tar}:
4637 $ @kbd{tar --list --file=bluesrock.tar}
4644 When you use @option{--concatenate}, the source and target archives must
4645 already exist and must have been created using compatible format
4646 parameters. Notice, that @command{tar} does not check whether the
4647 archives it concatenates have compatible formats, it does not
4648 even check if the files are really tar archives.
4650 Like @option{--append} (@option{-r}), this operation cannot be performed on some
4651 tape drives, due to deficiencies in the formats those tape drives use.
4653 @cindex @code{concatenate} vs @command{cat}
4654 @cindex @command{cat} vs @code{concatenate}
4655 It may seem more intuitive to you to want or try to use @command{cat} to
4656 concatenate two archives instead of using the @option{--concatenate}
4657 operation; after all, @command{cat} is the utility for combining files.
4659 However, @command{tar} archives incorporate an end-of-file marker which
4660 must be removed if the concatenated archives are to be read properly as
4661 one archive. @option{--concatenate} removes the end-of-archive marker
4662 from the target archive before each new archive is appended. If you use
4663 @command{cat} to combine the archives, the result will not be a valid
4664 @command{tar} format archive. If you need to retrieve files from an
4665 archive that was added to using the @command{cat} utility, use the
4666 @option{--ignore-zeros} (@option{-i}) option. @xref{Ignore Zeros}, for further
4667 information on dealing with archives improperly combined using the
4668 @command{cat} shell utility.
4671 @subsection Removing Archive Members Using @option{--delete}
4673 @cindex Deleting files from an archive
4674 @cindex Removing files from an archive
4677 You can remove members from an archive by using the @option{--delete}
4678 option. Specify the name of the archive with @option{--file}
4679 (@option{-f}) and then specify the names of the members to be deleted;
4680 if you list no member names, nothing will be deleted. The
4681 @option{--verbose} option will cause @command{tar} to print the names
4682 of the members as they are deleted. As with @option{--extract}, you
4683 must give the exact member names when using @samp{tar --delete}.
4684 @option{--delete} will remove all versions of the named file from the
4685 archive. The @option{--delete} operation can run very slowly.
4687 Unlike other operations, @option{--delete} has no short form.
4689 @cindex Tapes, using @option{--delete} and
4690 @cindex Deleting from tape archives
4691 This operation will rewrite the archive. You can only use
4692 @option{--delete} on an archive if the archive device allows you to
4693 write to any point on the media, such as a disk; because of this, it
4694 does not work on magnetic tapes. Do not try to delete an archive member
4695 from a magnetic tape; the action will not succeed, and you will be
4696 likely to scramble the archive and damage your tape. There is no safe
4697 way (except by completely re-writing the archive) to delete files from
4698 most kinds of magnetic tape. @xref{Media}.
4700 To delete all versions of the file @file{blues} from the archive
4701 @file{collection.tar} in the @file{practice} directory, make sure you
4702 are in that directory, and then,
4705 $ @kbd{tar --list --file=collection.tar}
4710 $ @kbd{tar --delete --file=collection.tar blues}
4711 $ @kbd{tar --list --file=collection.tar}
4718 @FIXME{Check if the above listing is actually produced after running
4719 all the examples on collection.tar.}
4721 The @option{--delete} option has been reported to work properly when
4722 @command{tar} acts as a filter from @code{stdin} to @code{stdout}.
4725 @subsection Comparing Archive Members with the File System
4726 @cindex Verifying the currency of an archive
4730 The @option{--compare} (@option{-d}), or @option{--diff} operation compares
4731 specified archive members against files with the same names, and then
4732 reports differences in file size, mode, owner, modification date and
4733 contents. You should @emph{only} specify archive member names, not file
4734 names. If you do not name any members, then @command{tar} will compare the
4735 entire archive. If a file is represented in the archive but does not
4736 exist in the file system, @command{tar} reports a difference.
4738 You have to specify the record size of the archive when modifying an
4739 archive with a non-default record size.
4741 @command{tar} ignores files in the file system that do not have
4742 corresponding members in the archive.
4744 The following example compares the archive members @file{rock},
4745 @file{blues} and @file{funk} in the archive @file{bluesrock.tar} with
4746 files of the same name in the file system. (Note that there is no file,
4747 @file{funk}; @command{tar} will report an error message.)
4750 $ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
4753 tar: funk not found in archive
4756 The spirit behind the @option{--compare} (@option{--diff},
4757 @option{-d}) option is to check whether the archive represents the
4758 current state of files on disk, more than validating the integrity of
4759 the archive media. For this later goal, @xref{verify}.
4761 @node create options
4762 @section Options Used by @option{--create}
4764 @xopindex{create, additional options}
4765 The previous chapter described the basics of how to use
4766 @option{--create} (@option{-c}) to create an archive from a set of files.
4767 @xref{create}. This section described advanced options to be used with
4771 * override:: Overriding File Metadata.
4772 * Ignore Failed Read::
4776 @subsection Overriding File Metadata
4778 As described above, a @command{tar} archive keeps, for each member it contains,
4779 its @dfn{metadata}, such as modification time, mode and ownership of
4780 the file. @GNUTAR{} allows to replace these data with other values
4781 when adding files to the archive. The options described in this
4782 section affect creation of archives of any type. For POSIX archives,
4783 see also @ref{PAX keywords}, for additional ways of controlling
4784 metadata, stored in the archive.
4788 @item --mode=@var{permissions}
4790 When adding files to an archive, @command{tar} will use
4791 @var{permissions} for the archive members, rather than the permissions
4792 from the files. @var{permissions} can be specified either as an octal
4793 number or as symbolic permissions, like with
4794 @command{chmod} (@xref{File permissions, Permissions, File
4795 permissions, fileutils, @acronym{GNU} file utilities}. This reference
4796 also has useful information for those not being overly familiar with
4797 the UNIX permission system). Using latter syntax allows for
4798 more flexibility. For example, the value @samp{a+rw} adds read and write
4799 permissions for everybody, while retaining executable bits on directories
4800 or on any other file already marked as executable:
4803 $ @kbd{tar -c -f archive.tar --mode='a+rw' .}
4806 @item --mtime=@var{date}
4809 When adding files to an archive, @command{tar} will use @var{date} as
4810 the modification time of members when creating archives, instead of
4811 their actual modification times. The argument @var{date} can be
4812 either a textual date representation in almost arbitrary format
4813 (@pxref{Date input formats}) or a name of the existing file, starting
4814 with @samp{/} or @samp{.}. In the latter case, the modification time
4815 of that file will be used.
4817 The following example will set the modification date to 00:00:00 UTC,
4821 $ @kbd{tar -c -f archive.tar --mtime='1970-01-01' .}
4825 When used with @option{--verbose} (@pxref{verbose tutorial}) @GNUTAR{}
4826 will try to convert the specified date back to its textual
4827 representation and compare it with the one given with
4828 @option{--mtime} options. If the two dates differ, @command{tar} will
4829 print a warning saying what date it will use. This is to help user
4830 ensure he is using the right date.
4835 $ @kbd{tar -c -f archive.tar -v --mtime=yesterday .}
4836 tar: Option --mtime: Treating date `yesterday' as 2006-06-20
4841 @item --owner=@var{user}
4844 Specifies that @command{tar} should use @var{user} as the owner of members
4845 when creating archives, instead of the user associated with the source
4846 file. The argument @var{user} can be either an existing user symbolic
4847 name, or a decimal numeric user @acronym{ID}.
4849 There is no value indicating a missing number, and @samp{0} usually means
4850 @code{root}. Some people like to force @samp{0} as the value to offer in
4851 their distributions for the owner of files, because the @code{root} user is
4852 anonymous anyway, so that might as well be the owner of anonymous
4853 archives. For example:
4857 $ @kbd{tar -c -f archive.tar --owner=0 .}
4859 $ @kbd{tar -c -f archive.tar --owner=root .}
4863 @item --group=@var{group}
4866 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
4867 rather than the group from the source file. The argument @var{group}
4868 can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
4871 @node Ignore Failed Read
4872 @subsection Ignore Fail Read
4875 @item --ignore-failed-read
4876 @opindex ignore-failed-read
4877 Do not exit with nonzero on unreadable files or directories.
4880 @node extract options
4881 @section Options Used by @option{--extract}
4884 @xopindex{extract, additional options}
4885 The previous chapter showed how to use @option{--extract} to extract
4886 an archive into the file system. Various options cause @command{tar} to
4887 extract more information than just file contents, such as the owner,
4888 the permissions, the modification date, and so forth. This section
4889 presents options to be used with @option{--extract} when certain special
4890 considerations arise. You may review the information presented in
4891 @ref{extract} for more basic information about the
4892 @option{--extract} operation.
4895 * Reading:: Options to Help Read Archives
4896 * Writing:: Changing How @command{tar} Writes Files
4897 * Scarce:: Coping with Scarce Resources
4901 @subsection Options to Help Read Archives
4902 @cindex Options when reading archives
4905 @cindex Reading incomplete records
4906 @cindex Records, incomplete
4907 @opindex read-full-records
4908 Normally, @command{tar} will request data in full record increments from
4909 an archive storage device. If the device cannot return a full record,
4910 @command{tar} will report an error. However, some devices do not always
4911 return full records, or do not require the last record of an archive to
4912 be padded out to the next record boundary. To keep reading until you
4913 obtain a full record, or to accept an incomplete record if it contains
4914 an end-of-archive marker, specify the @option{--read-full-records} (@option{-B}) option
4915 in conjunction with the @option{--extract} or @option{--list} operations.
4918 The @option{--read-full-records} (@option{-B}) option is turned on by default when
4919 @command{tar} reads an archive from standard input, or from a remote
4920 machine. This is because on @acronym{BSD} Unix systems, attempting to read a
4921 pipe returns however much happens to be in the pipe, even if it is
4922 less than was requested. If this option were not enabled, @command{tar}
4923 would fail as soon as it read an incomplete record from the pipe.
4925 If you're not sure of the blocking factor of an archive, you can
4926 read the archive by specifying @option{--read-full-records} (@option{-B}) and
4927 @option{--blocking-factor=@var{512-size}} (@option{-b
4928 @var{512-size}}), using a blocking factor larger than what the archive
4929 uses. This lets you avoid having to determine the blocking factor
4930 of an archive. @xref{Blocking Factor}.
4933 * read full records::
4937 @node read full records
4938 @unnumberedsubsubsec Reading Full Records
4940 @FIXME{need sentence or so of intro here}
4943 @opindex read-full-records
4944 @item --read-full-records
4946 Use in conjunction with @option{--extract} (@option{--get},
4947 @option{-x}) to read an archive which contains incomplete records, or
4948 one which has a blocking factor less than the one specified.
4952 @unnumberedsubsubsec Ignoring Blocks of Zeros
4954 @cindex End-of-archive blocks, ignoring
4955 @cindex Ignoring end-of-archive blocks
4956 @opindex ignore-zeros
4957 Normally, @command{tar} stops reading when it encounters a block of zeros
4958 between file entries (which usually indicates the end of the archive).
4959 @option{--ignore-zeros} (@option{-i}) allows @command{tar} to
4960 completely read an archive which contains a block of zeros before the
4961 end (i.e., a damaged archive, or one that was created by concatenating
4962 several archives together).
4964 The @option{--ignore-zeros} (@option{-i}) option is turned off by default because many
4965 versions of @command{tar} write garbage after the end-of-archive entry,
4966 since that part of the media is never supposed to be read. @GNUTAR{}
4967 does not write after the end of an archive, but seeks to
4968 maintain compatibility among archiving utilities.
4971 @item --ignore-zeros
4973 To ignore blocks of zeros (i.e., end-of-archive entries) which may be
4974 encountered while reading an archive. Use in conjunction with
4975 @option{--extract} or @option{--list}.
4979 @subsection Changing How @command{tar} Writes Files
4982 @FIXME{Introductory paragraph}
4985 * Dealing with Old Files::
4986 * Overwrite Old Files::
4988 * Keep Newer Files::
4990 * Recursive Unlink::
4991 * Data Modification Times::
4992 * Setting Access Permissions::
4993 * Directory Modification Times and Permissions::
4994 * Writing to Standard Output::
4995 * Writing to an External Program::
4999 @node Dealing with Old Files
5000 @unnumberedsubsubsec Options Controlling the Overwriting of Existing Files
5002 @xopindex{overwrite-dir, introduced}
5003 When extracting files, if @command{tar} discovers that the extracted
5004 file already exists, it normally replaces the file by removing it before
5005 extracting it, to prevent confusion in the presence of hard or symbolic
5006 links. (If the existing file is a symbolic link, it is removed, not
5007 followed.) However, if a directory cannot be removed because it is
5008 nonempty, @command{tar} normally overwrites its metadata (ownership,
5009 permission, etc.). The @option{--overwrite-dir} option enables this
5010 default behavior. To be more cautious and preserve the metadata of
5011 such a directory, use the @option{--no-overwrite-dir} option.
5013 @cindex Overwriting old files, prevention
5014 @xopindex{keep-old-files, introduced}
5015 To be even more cautious and prevent existing files from being replaced, use
5016 the @option{--keep-old-files} (@option{-k}) option. It causes @command{tar} to refuse
5017 to replace or update a file that already exists, i.e., a file with the
5018 same name as an archive member prevents extraction of that archive
5019 member. Instead, it reports an error.
5021 @xopindex{overwrite, introduced}
5022 To be more aggressive about altering existing files, use the
5023 @option{--overwrite} option. It causes @command{tar} to overwrite
5024 existing files and to follow existing symbolic links when extracting.
5026 @cindex Protecting old files
5027 Some people argue that @GNUTAR{} should not hesitate
5028 to overwrite files with other files when extracting. When extracting
5029 a @command{tar} archive, they expect to see a faithful copy of the
5030 state of the file system when the archive was created. It is debatable
5031 that this would always be a proper behavior. For example, suppose one
5032 has an archive in which @file{usr/local} is a link to
5033 @file{usr/local2}. Since then, maybe the site removed the link and
5034 renamed the whole hierarchy from @file{/usr/local2} to
5035 @file{/usr/local}. Such things happen all the time. I guess it would
5036 not be welcome at all that @GNUTAR{} removes the
5037 whole hierarchy just to make room for the link to be reinstated
5038 (unless it @emph{also} simultaneously restores the full
5039 @file{/usr/local2}, of course!) @GNUTAR{} is indeed
5040 able to remove a whole hierarchy to reestablish a symbolic link, for
5041 example, but @emph{only if} @option{--recursive-unlink} is specified
5042 to allow this behavior. In any case, single files are silently
5045 @xopindex{unlink-first, introduced}
5046 Finally, the @option{--unlink-first} (@option{-U}) option can improve performance in
5047 some cases by causing @command{tar} to remove files unconditionally
5048 before extracting them.
5050 @node Overwrite Old Files
5051 @unnumberedsubsubsec Overwrite Old Files
5056 Overwrite existing files and directory metadata when extracting files
5059 This causes @command{tar} to write extracted files into the file system without
5060 regard to the files already on the system; i.e., files with the same
5061 names as archive members are overwritten when the archive is extracted.
5062 It also causes @command{tar} to extract the ownership, permissions,
5063 and time stamps onto any preexisting files or directories.
5064 If the name of a corresponding file name is a symbolic link, the file
5065 pointed to by the symbolic link will be overwritten instead of the
5066 symbolic link itself (if this is possible). Moreover, special devices,
5067 empty directories and even symbolic links are automatically removed if
5068 they are in the way of extraction.
5070 Be careful when using the @option{--overwrite} option, particularly when
5071 combined with the @option{--absolute-names} (@option{-P}) option, as this combination
5072 can change the contents, ownership or permissions of any file on your
5073 system. Also, many systems do not take kindly to overwriting files that
5074 are currently being executed.
5076 @opindex overwrite-dir
5077 @item --overwrite-dir
5078 Overwrite the metadata of directories when extracting files from an
5079 archive, but remove other files before extracting.
5082 @node Keep Old Files
5083 @unnumberedsubsubsec Keep Old Files
5086 @opindex keep-old-files
5087 @item --keep-old-files
5089 Do not replace existing files from archive. The
5090 @option{--keep-old-files} (@option{-k}) option prevents @command{tar}
5091 from replacing existing files with files with the same name from the
5092 archive. The @option{--keep-old-files} option is meaningless with
5093 @option{--list} (@option{-t}). Prevents @command{tar} from replacing
5094 files in the file system during extraction.
5097 @node Keep Newer Files
5098 @unnumberedsubsubsec Keep Newer Files
5101 @opindex keep-newer-files
5102 @item --keep-newer-files
5103 Do not replace existing files that are newer than their archive
5104 copies. This option is meaningless with @option{--list} (@option{-t}).
5108 @unnumberedsubsubsec Unlink First
5111 @opindex unlink-first
5112 @item --unlink-first
5114 Remove files before extracting over them.
5115 This can make @command{tar} run a bit faster if you know in advance
5116 that the extracted files all need to be removed. Normally this option
5117 slows @command{tar} down slightly, so it is disabled by default.
5120 @node Recursive Unlink
5121 @unnumberedsubsubsec Recursive Unlink
5124 @opindex recursive-unlink
5125 @item --recursive-unlink
5126 When this option is specified, try removing files and directory hierarchies
5127 before extracting over them. @emph{This is a dangerous option!}
5130 If you specify the @option{--recursive-unlink} option,
5131 @command{tar} removes @emph{anything} that keeps you from extracting a file
5132 as far as current permissions will allow it. This could include removal
5133 of the contents of a full directory hierarchy.
5135 @node Data Modification Times
5136 @unnumberedsubsubsec Setting Data Modification Times
5138 @cindex Data modification times of extracted files
5139 @cindex Modification times of extracted files
5140 Normally, @command{tar} sets the data modification times of extracted
5141 files to the corresponding times recorded for the files in the archive, but
5142 limits the permissions of extracted files by the current @code{umask}
5145 To set the data modification times of extracted files to the time when
5146 the files were extracted, use the @option{--touch} (@option{-m}) option in
5147 conjunction with @option{--extract} (@option{--get}, @option{-x}).
5153 Sets the data modification time of extracted archive members to the time
5154 they were extracted, not the time recorded for them in the archive.
5155 Use in conjunction with @option{--extract} (@option{--get}, @option{-x}).
5158 @node Setting Access Permissions
5159 @unnumberedsubsubsec Setting Access Permissions
5161 @cindex Permissions of extracted files
5162 @cindex Modes of extracted files
5163 To set the modes (access permissions) of extracted files to those
5164 recorded for those files in the archive, use @option{--same-permissions}
5165 in conjunction with the @option{--extract} (@option{--get},
5166 @option{-x}) operation.
5169 @opindex preserve-permissions
5170 @opindex same-permissions
5171 @item --preserve-permissions
5172 @itemx --same-permissions
5173 @c @itemx --ignore-umask
5175 Set modes of extracted archive members to those recorded in the
5176 archive, instead of current umask settings. Use in conjunction with
5177 @option{--extract} (@option{--get}, @option{-x}).
5180 @node Directory Modification Times and Permissions
5181 @unnumberedsubsubsec Directory Modification Times and Permissions
5183 After successfully extracting a file member, @GNUTAR{} normally
5184 restores its permissions and modification times, as described in the
5185 previous sections. This cannot be done for directories, because
5186 after extracting a directory @command{tar} will almost certainly
5187 extract files into that directory and this will cause the directory
5188 modification time to be updated. Moreover, restoring that directory
5189 permissions may not permit file creation within it. Thus, restoring
5190 directory permissions and modification times must be delayed at least
5191 until all files have been extracted into that directory. @GNUTAR{}
5192 restores directories using the following approach.
5194 The extracted directories are created with the mode specified in the
5195 archive, as modified by the umask of the user, which gives sufficient
5196 permissions to allow file creation. The meta-information about the
5197 directory is recorded in the temporary list of directories. When
5198 preparing to extract next archive member, @GNUTAR{} checks if the
5199 directory prefix of this file contains the remembered directory. If
5200 it does not, the program assumes that all files have been extracted
5201 into that directory, restores its modification time and permissions
5202 and removes its entry from the internal list. This approach allows
5203 to correctly restore directory meta-information in the majority of
5204 cases, while keeping memory requirements sufficiently small. It is
5205 based on the fact, that most @command{tar} archives use the predefined
5206 order of members: first the directory, then all the files and
5207 subdirectories in that directory.
5209 However, this is not always true. The most important exception are
5210 incremental archives (@pxref{Incremental Dumps}). The member order in
5211 an incremental archive is reversed: first all directory members are
5212 stored, followed by other (non-directory) members. So, when extracting
5213 from incremental archives, @GNUTAR{} alters the above procedure. It
5214 remembers all restored directories, and restores their meta-data
5215 only after the entire archive has been processed. Notice, that you do
5216 not need to specify any special options for that, as @GNUTAR{}
5217 automatically detects archives in incremental format.
5219 There may be cases, when such processing is required for normal archives
5220 too. Consider the following example:
5224 $ @kbd{tar --no-recursion -cvf archive \
5225 foo foo/file1 bar bar/file foo/file2}
5234 During the normal operation, after encountering @file{bar}
5235 @GNUTAR{} will assume that all files from the directory @file{foo}
5236 were already extracted and will therefore restore its timestamp and
5237 permission bits. However, after extracting @file{foo/file2} the
5238 directory timestamp will be offset again.
5240 To correctly restore directory meta-information in such cases, use
5241 @option{delay-directory-restore} command line option:
5244 @opindex delay-directory-restore
5245 @item --delay-directory-restore
5246 Delays restoring of the modification times and permissions of extracted
5247 directories until the end of extraction. This way, correct
5248 meta-information is restored even if the archive has unusual member
5251 @opindex no-delay-directory-restore
5252 @item --no-delay-directory-restore
5253 Cancel the effect of the previous @option{--delay-directory-restore}.
5254 Use this option if you have used @option{--delay-directory-restore} in
5255 @env{TAR_OPTIONS} variable (@pxref{TAR_OPTIONS}) and wish to
5256 temporarily disable it.
5259 @node Writing to Standard Output
5260 @unnumberedsubsubsec Writing to Standard Output
5262 @cindex Writing extracted files to standard output
5263 @cindex Standard output, writing extracted files to
5264 To write the extracted files to the standard output, instead of
5265 creating the files on the file system, use @option{--to-stdout} (@option{-O}) in
5266 conjunction with @option{--extract} (@option{--get}, @option{-x}). This option is useful if you are
5267 extracting files to send them through a pipe, and do not need to
5268 preserve them in the file system. If you extract multiple members,
5269 they appear on standard output concatenated, in the order they are
5270 found in the archive.
5276 Writes files to the standard output. Use only in conjunction with
5277 @option{--extract} (@option{--get}, @option{-x}). When this option is
5278 used, instead of creating the files specified, @command{tar} writes
5279 the contents of the files extracted to its standard output. This may
5280 be useful if you are only extracting the files in order to send them
5281 through a pipe. This option is meaningless with @option{--list}
5285 This can be useful, for example, if you have a tar archive containing
5286 a big file and don't want to store the file on disk before processing
5287 it. You can use a command like this:
5290 tar -xOzf foo.tgz bigfile | process
5293 or even like this if you want to process the concatenation of the files:
5296 tar -xOzf foo.tgz bigfile1 bigfile2 | process
5299 However, @option{--to-command} may be more convenient for use with
5300 multiple files. See the next section.
5302 @node Writing to an External Program
5303 @unnumberedsubsubsec Writing to an External Program
5305 You can instruct @command{tar} to send the contents of each extracted
5306 file to the standard input of an external program:
5310 @item --to-command=@var{command}
5311 Extract files and pipe their contents to the standard input of
5312 @var{command}. When this option is used, instead of creating the
5313 files specified, @command{tar} invokes @var{command} and pipes the
5314 contents of the files to its standard output. @var{Command} may
5315 contain command line arguments. The program is executed via
5316 @code{sh -c}. Notice, that @var{command} is executed once for each regular file
5317 extracted. Non-regular files (directories, etc.) are ignored when this
5321 The command can obtain the information about the file it processes
5322 from the following environment variables:
5325 @vrindex TAR_FILETYPE, to-command environment
5327 Type of the file. It is a single letter with the following meaning:
5329 @multitable @columnfractions 0.10 0.90
5330 @item f @tab Regular file
5331 @item d @tab Directory
5332 @item l @tab Symbolic link
5333 @item h @tab Hard link
5334 @item b @tab Block device
5335 @item c @tab Character device
5338 Currently only regular files are supported.
5340 @vrindex TAR_MODE, to-command environment
5342 File mode, an octal number.
5344 @vrindex TAR_FILENAME, to-command environment
5346 The name of the file.
5348 @vrindex TAR_REALNAME, to-command environment
5350 Name of the file as stored in the archive.
5352 @vrindex TAR_UNAME, to-command environment
5354 Name of the file owner.
5356 @vrindex TAR_GNAME, to-command environment
5358 Name of the file owner group.
5360 @vrindex TAR_ATIME, to-command environment
5362 Time of last access. It is a decimal number, representing seconds
5363 since the epoch. If the archive provides times with nanosecond
5364 precision, the nanoseconds are appended to the timestamp after a
5367 @vrindex TAR_MTIME, to-command environment
5369 Time of last modification.
5371 @vrindex TAR_CTIME, to-command environment
5373 Time of last status change.
5375 @vrindex TAR_SIZE, to-command environment
5379 @vrindex TAR_UID, to-command environment
5381 UID of the file owner.
5383 @vrindex TAR_GID, to-command environment
5385 GID of the file owner.
5388 In addition to these variables, @env{TAR_VERSION} contains the
5389 @GNUTAR{} version number.
5391 If @var{command} exits with a non-0 status, @command{tar} will print
5392 an error message similar to the following:
5395 tar: 2345: Child returned status 1
5398 Here, @samp{2345} is the PID of the finished process.
5400 If this behavior is not wanted, use @option{--ignore-command-error}:
5403 @opindex ignore-command-error
5404 @item --ignore-command-error
5405 Ignore exit codes of subprocesses. Notice that if the program
5406 exits on signal or otherwise terminates abnormally, the error message
5407 will be printed even if this option is used.
5409 @opindex no-ignore-command-error
5410 @item --no-ignore-command-error
5411 Cancel the effect of any previous @option{--ignore-command-error}
5412 option. This option is useful if you have set
5413 @option{--ignore-command-error} in @env{TAR_OPTIONS}
5414 (@pxref{TAR_OPTIONS}) and wish to temporarily cancel it.
5418 @unnumberedsubsubsec Removing Files
5420 @FIXME{The section is too terse. Something more to add? An example,
5424 @opindex remove-files
5425 @item --remove-files
5426 Remove files after adding them to the archive.
5430 @subsection Coping with Scarce Resources
5433 @cindex Small memory
5434 @cindex Running out of space
5442 @unnumberedsubsubsec Starting File
5445 @opindex starting-file
5446 @item --starting-file=@var{name}
5447 @itemx -K @var{name}
5448 Starts an operation in the middle of an archive. Use in conjunction
5449 with @option{--extract} (@option{--get}, @option{-x}) or @option{--list} (@option{-t}).
5452 @cindex Middle of the archive, starting in the
5453 If a previous attempt to extract files failed due to lack of disk
5454 space, you can use @option{--starting-file=@var{name}} (@option{-K
5455 @var{name}}) to start extracting only after member @var{name} of the
5456 archive. This assumes, of course, that there is now free space, or
5457 that you are now extracting into a different file system. (You could
5458 also choose to suspend @command{tar}, remove unnecessary files from
5459 the file system, and then restart the same @command{tar} operation.
5460 In this case, @option{--starting-file} is not necessary.
5461 @xref{Incremental Dumps}, @xref{interactive}, and @ref{exclude}.)
5464 @unnumberedsubsubsec Same Order
5467 @cindex Large lists of file names on small machines
5469 @opindex preserve-order
5471 @itemx --preserve-order
5473 To process large lists of file names on machines with small amounts of
5474 memory. Use in conjunction with @option{--compare} (@option{--diff},
5475 @option{-d}), @option{--list} (@option{-t}) or @option{--extract}
5476 (@option{--get}, @option{-x}).
5479 The @option{--same-order} (@option{--preserve-order}, @option{-s}) option tells @command{tar} that the list of file
5480 names to be listed or extracted is sorted in the same order as the
5481 files in the archive. This allows a large list of names to be used,
5482 even on a small machine that would not otherwise be able to hold all
5483 the names in memory at the same time. Such a sorted list can easily be
5484 created by running @samp{tar -t} on the archive and editing its output.
5486 This option is probably never needed on modern computer systems.
5489 @section Backup options
5491 @cindex backup options
5493 @GNUTAR{} offers options for making backups of files
5494 before writing new versions. These options control the details of
5495 these backups. They may apply to the archive itself before it is
5496 created or rewritten, as well as individual extracted members. Other
5497 @acronym{GNU} programs (@command{cp}, @command{install}, @command{ln},
5498 and @command{mv}, for example) offer similar options.
5500 Backup options may prove unexpectedly useful when extracting archives
5501 containing many members having identical name, or when extracting archives
5502 on systems having file name limitations, making different members appear
5503 as having similar names through the side-effect of name truncation.
5504 @FIXME{This is true only if we have a good scheme for truncated backup names,
5505 which I'm not sure at all: I suspect work is needed in this area.}
5506 When any existing file is backed up before being overwritten by extraction,
5507 then clashing files are automatically be renamed to be unique, and the
5508 true name is kept for only the last file of a series of clashing files.
5509 By using verbose mode, users may track exactly what happens.
5511 At the detail level, some decisions are still experimental, and may
5512 change in the future, we are waiting comments from our users. So, please
5513 do not learn to depend blindly on the details of the backup features.
5514 For example, currently, directories themselves are never renamed through
5515 using these options, so, extracting a file over a directory still has
5516 good chances to fail. Also, backup options apply to created archives,
5517 not only to extracted members. For created archives, backups will not
5518 be attempted when the archive is a block or character device, or when it
5519 refers to a remote file.
5521 For the sake of simplicity and efficiency, backups are made by renaming old
5522 files prior to creation or extraction, and not by copying. The original
5523 name is restored if the file creation fails. If a failure occurs after a
5524 partial extraction of a file, both the backup and the partially extracted
5528 @item --backup[=@var{method}]
5530 @vindex VERSION_CONTROL
5532 Back up files that are about to be overwritten or removed.
5533 Without this option, the original versions are destroyed.
5535 Use @var{method} to determine the type of backups made.
5536 If @var{method} is not specified, use the value of the @env{VERSION_CONTROL}
5537 environment variable. And if @env{VERSION_CONTROL} is not set,
5538 use the @samp{existing} method.
5540 @vindex version-control @r{Emacs variable}
5541 This option corresponds to the Emacs variable @samp{version-control};
5542 the same values for @var{method} are accepted as in Emacs. This option
5543 also allows more descriptive names. The valid @var{method}s are:
5548 @cindex numbered @r{backup method}
5549 Always make numbered backups.
5553 @cindex existing @r{backup method}
5554 Make numbered backups of files that already have them, simple backups
5559 @cindex simple @r{backup method}
5560 Always make simple backups.
5564 @item --suffix=@var{suffix}
5566 @cindex backup suffix
5567 @vindex SIMPLE_BACKUP_SUFFIX
5568 Append @var{suffix} to each backup file made with @option{--backup}. If this
5569 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
5570 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
5571 set, the default is @samp{~}, just as in Emacs.
5576 @section Notable @command{tar} Usages
5579 @FIXME{Using Unix file linking capability to recreate directory
5580 structures---linking files into one subdirectory and then
5581 @command{tar}ring that directory.}
5583 @FIXME{Nice hairy example using absolute-names, newer, etc.}
5586 You can easily use archive files to transport a group of files from
5587 one system to another: put all relevant files into an archive on one
5588 computer system, transfer the archive to another system, and extract
5589 the contents there. The basic transfer medium might be magnetic tape,
5590 Internet FTP, or even electronic mail (though you must encode the
5591 archive with @command{uuencode} in order to transport it properly by
5592 mail). Both machines do not have to use the same operating system, as
5593 long as they both support the @command{tar} program.
5595 For example, here is how you might copy a directory's contents from
5596 one disk to another, while preserving the dates, modes, owners and
5597 link-structure of all the files therein. In this case, the transfer
5598 medium is a @dfn{pipe}, which is one a Unix redirection mechanism:
5601 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
5605 You can avoid subshells by using @option{-C} option:
5608 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xf -}
5612 The command also works using short option forms:
5615 $ @kbd{(cd sourcedir; tar --create --file=- . ) \
5616 | (cd targetdir; tar --extract --file=-)}
5618 $ @kbd{tar --directory sourcedir --create --file=- . ) \
5619 | tar --directory targetdir --extract --file=-}
5623 This is one of the easiest methods to transfer a @command{tar} archive.
5626 @section Looking Ahead: The Rest of this Manual
5628 You have now seen how to use all eight of the operations available to
5629 @command{tar}, and a number of the possible options. The next chapter
5630 explains how to choose and change file and archive names, how to use
5631 files to store names of other files which you can then call as
5632 arguments to @command{tar} (this can help you save time if you expect to
5633 archive the same list of files a number of times), and so forth.
5634 @FIXME{in case it's not obvious, i'm making this up in some sense
5635 based on my limited memory of what the next chapter *really* does. i
5636 just wanted to flesh out this final section a little bit so i'd
5637 remember to stick it in here. :-)}
5639 If there are too many files to conveniently list on the command line,
5640 you can list the names in a file, and @command{tar} will read that file.
5643 There are various ways of causing @command{tar} to skip over some files,
5644 and not archive them. @xref{Choosing}.
5647 @chapter Performing Backups and Restoring Files
5650 @GNUTAR{} is distributed along with the scripts
5651 which the Free Software Foundation uses for performing backups. There
5652 is no corresponding scripts available yet for doing restoration of
5653 files. Even if there is a good chance those scripts may be satisfying
5654 to you, they are not the only scripts or methods available for doing
5655 backups and restore. You may well create your own, or use more
5656 sophisticated packages dedicated to that purpose.
5658 Some users are enthusiastic about @code{Amanda} (The Advanced Maryland
5659 Automatic Network Disk Archiver), a backup system developed by James
5660 da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
5661 This is free software, and it is available at these places:
5664 http://www.cs.umd.edu/projects/amanda/amanda.html
5665 ftp://ftp.cs.umd.edu/pub/amanda
5670 Here is a possible plan for a future documentation about the backuping
5671 scripts which are provided within the @GNUTAR{}
5677 @item what are dumps
5678 @item different levels of dumps
5680 @item full dump = dump everything
5681 @item level 1, level 2 dumps etc
5682 A level @var{n} dump dumps everything changed since the last level
5685 @item how to use scripts for dumps (ie, the concept)
5687 @item scripts to run after editing backup specs (details)
5689 @item Backup Specs, what is it.
5691 @item how to customize
5692 @item actual text of script [/sp/dump/backup-specs]
5696 @item rsh doesn't work
5697 @item rtape isn't installed
5700 @item the @option{--incremental} option of tar
5703 @item write protection
5704 @item types of media, different sizes and types, useful for different things
5705 @item files and tape marks
5706 one tape mark between files, two at end.
5707 @item positioning the tape
5708 MT writes two at end of write,
5709 backspaces over one when writing again.
5715 This chapter documents both the provided shell scripts and @command{tar}
5716 options which are more specific to usage as a backup tool.
5718 To @dfn{back up} a file system means to create archives that contain
5719 all the files in that file system. Those archives can then be used to
5720 restore any or all of those files (for instance if a disk crashes or a
5721 file is accidentally deleted). File system @dfn{backups} are also
5725 * Full Dumps:: Using @command{tar} to Perform Full Dumps
5726 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
5727 * Backup Levels:: Levels of Backups
5728 * Backup Parameters:: Setting Parameters for Backups and Restoration
5729 * Scripted Backups:: Using the Backup Scripts
5730 * Scripted Restoration:: Using the Restore Script
5734 @section Using @command{tar} to Perform Full Dumps
5740 @cindex corrupted archives
5741 Full dumps should only be made when no other people or programs
5742 are modifying files in the file system. If files are modified while
5743 @command{tar} is making the backup, they may not be stored properly in
5744 the archive, in which case you won't be able to restore them if you
5745 have to. (Files not being modified are written with no trouble, and do
5746 not corrupt the entire archive.)
5748 You will want to use the @option{--label=@var{archive-label}}
5749 (@option{-V @var{archive-label}}) option to give the archive a
5750 volume label, so you can tell what this archive is even if the label
5751 falls off the tape, or anything like that.
5753 Unless the file system you are dumping is guaranteed to fit on
5754 one volume, you will need to use the @option{--multi-volume} (@option{-M}) option.
5755 Make sure you have enough tapes on hand to complete the backup.
5757 If you want to dump each file system separately you will need to use
5758 the @option{--one-file-system} option to prevent
5759 @command{tar} from crossing file system boundaries when storing
5762 The @option{--incremental} (@option{-G}) (@pxref{Incremental Dumps})
5763 option is not needed, since this is a complete copy of everything in
5764 the file system, and a full restore from this backup would only be
5765 done onto a completely
5768 Unless you are in a hurry, and trust the @command{tar} program (and your
5769 tapes), it is a good idea to use the @option{--verify} (@option{-W})
5770 option, to make sure your files really made it onto the dump properly.
5771 This will also detect cases where the file was modified while (or just
5772 after) it was being archived. Not all media (notably cartridge tapes)
5773 are capable of being verified, unfortunately.
5775 @node Incremental Dumps
5776 @section Using @command{tar} to Perform Incremental Dumps
5778 @dfn{Incremental backup} is a special form of @GNUTAR{} archive that
5779 stores additional metadata so that exact state of the file system
5780 can be restored when extracting the archive.
5782 @GNUTAR{} currently offers two options for handling incremental
5783 backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
5784 @var{snapshot-file}}) and @option{--incremental} (@option{-G}).
5786 @opindex listed-incremental
5787 The option @option{--listed-incremental} instructs tar to operate on
5788 an incremental archive with additional metadata stored in a standalone
5789 file, called a @dfn{snapshot file}. The purpose of this file is to help
5790 determine which files have been changed, added or deleted since the
5791 last backup, so that the next incremental backup will contain only
5792 modified files. The name of the snapshot file is given as an argument
5796 @item --listed-incremental=@var{file}
5797 @itemx -g @var{file}
5798 Handle incremental backups with snapshot data in @var{file}.
5801 To create an incremental backup, you would use
5802 @option{--listed-incremental} together with @option{--create}
5803 (@pxref{create}). For example:
5806 $ @kbd{tar --create \
5807 --file=archive.1.tar \
5808 --listed-incremental=/var/log/usr.snar \
5812 This will create in @file{archive.1.tar} an incremental backup of
5813 the @file{/usr} file system, storing additional metadata in the file
5814 @file{/var/log/usr.snar}. If this file does not exist, it will be
5815 created. The created archive will then be a @dfn{level 0 backup};
5816 please see the next section for more on backup levels.
5818 Otherwise, if the file @file{/var/log/usr.snar} exists, it
5819 determines which files are modified. In this case only these files will be
5820 stored in the archive. Suppose, for example, that after running the
5821 above command, you delete file @file{/usr/doc/old} and create
5822 directory @file{/usr/local/db} with the following contents:
5825 $ @kbd{ls /usr/local/db}
5830 Some time later you create another incremental backup. You will
5834 $ @kbd{tar --create \
5835 --file=archive.2.tar \
5836 --listed-incremental=/var/log/usr.snar \
5838 tar: usr/local/db: Directory is new
5845 The created archive @file{archive.2.tar} will contain only these
5846 three members. This archive is called a @dfn{level 1 backup}. Notice
5847 that @file{/var/log/usr.snar} will be updated with the new data, so if
5848 you plan to create more @samp{level 1} backups, it is necessary to
5849 create a working copy of the snapshot file before running
5850 @command{tar}. The above example will then be modified as follows:
5853 $ @kbd{cp /var/log/usr.snar /var/log/usr.snar-1}
5854 $ @kbd{tar --create \
5855 --file=archive.2.tar \
5856 --listed-incremental=/var/log/usr.snar-1 \
5860 Incremental dumps depend crucially on time stamps, so the results are
5861 unreliable if you modify a file's time stamps during dumping (e.g.,
5862 with the @option{--atime-preserve=replace} option), or if you set the clock
5865 @anchor{device numbers}
5866 @cindex Device numbers, using in incremental backups
5867 Metadata stored in snapshot files include device numbers, which,
5868 obviously are supposed to be a non-volatile values. However, it turns
5869 out that @acronym{NFS} devices have undependable values when an automounter
5870 gets in the picture. This can lead to a great deal of spurious
5871 redumping in incremental dumps, so it is somewhat useless to compare
5872 two @acronym{NFS} devices numbers over time. The solution implemented
5873 currently is to considers all @acronym{NFS} devices as being equal
5874 when it comes to comparing directories; this is fairly gross, but
5875 there does not seem to be a better way to go.
5877 Apart from using @acronym{NFS}, there are a number of cases where
5878 relying on device numbers can cause spurious redumping of unmodified
5879 files. For example, this occurs when archiving @acronym{LVM} snapshot
5880 volumes. To avoid this, use @option{--no-check-device} option:
5883 @xopindex{no-check-device, described}
5884 @item --no-check-device
5885 Do not rely on device numbers when preparing a list of changed files
5886 for an incremental dump.
5888 @xopindex{check-device, described}
5889 @item --check-device
5890 Use device numbers when preparing a list of changed files
5891 for an incremental dump. This is the default behavior. The purpose
5892 of this option is to undo the effect of the @option{--no-check-device}
5893 if it was given in @env{TAR_OPTIONS} environment variable
5894 (@pxref{TAR_OPTIONS}).
5897 There is also another way to cope with changing device numbers. It is
5898 described in detail in @ref{Fixing Snapshot Files}.
5900 Note that incremental archives use @command{tar} extensions and may
5901 not be readable by non-@acronym{GNU} versions of the @command{tar} program.
5903 @xopindex{listed-incremental, using with @option{--extract}}
5904 @xopindex{extract, using with @option{--listed-incremental}}
5905 To extract from the incremental dumps, use
5906 @option{--listed-incremental} together with @option{--extract}
5907 option (@pxref{extracting files}). In this case, @command{tar} does
5908 not need to access snapshot file, since all the data necessary for
5909 extraction are stored in the archive itself. So, when extracting, you
5910 can give whatever argument to @option{--listed-incremental}, the usual
5911 practice is to use @option{--listed-incremental=/dev/null}.
5912 Alternatively, you can use @option{--incremental}, which needs no
5913 arguments. In general, @option{--incremental} (@option{-G}) can be
5914 used as a shortcut for @option{--listed-incremental} when listing or
5915 extracting incremental backups (for more information, regarding this
5916 option, @pxref{incremental-op}).
5918 When extracting from the incremental backup @GNUTAR{} attempts to
5919 restore the exact state the file system had when the archive was
5920 created. In particular, it will @emph{delete} those files in the file
5921 system that did not exist in their directories when the archive was
5922 created. If you have created several levels of incremental files,
5923 then in order to restore the exact contents the file system had when
5924 the last level was created, you will need to restore from all backups
5925 in turn. Continuing our example, to restore the state of @file{/usr}
5926 file system, one would do@footnote{Notice, that since both archives
5927 were created without @option{-P} option (@pxref{absolute}), these
5928 commands should be run from the root file system.}:
5931 $ @kbd{tar --extract \
5932 --listed-incremental=/dev/null \
5933 --file archive.1.tar}
5934 $ @kbd{tar --extract \
5935 --listed-incremental=/dev/null \
5936 --file archive.2.tar}
5939 To list the contents of an incremental archive, use @option{--list}
5940 (@pxref{list}), as usual. To obtain more information about the
5941 archive, use @option{--listed-incremental} or @option{--incremental}
5942 combined with two @option{--verbose} options@footnote{Two
5943 @option{--verbose} options were selected to avoid breaking usual
5944 verbose listing output (@option{--list --verbose}) when using in
5947 @xopindex{incremental, using with @option{--list}}
5948 @xopindex{listed-incremental, using with @option{--list}}
5949 @xopindex{list, using with @option{--incremental}}
5950 @xopindex{list, using with @option{--listed-incremental}}
5951 Versions of @GNUTAR{} up to 1.15.1 used to dump verbatim binary
5952 contents of the DUMPDIR header (with terminating nulls) when
5953 @option{--incremental} or @option{--listed-incremental} option was
5954 given, no matter what the verbosity level. This behavior, and,
5955 especially, the binary output it produced were considered inconvenient
5956 and were changed in version 1.16}:
5959 @kbd{tar --list --incremental --verbose --verbose archive.tar}
5962 This command will print, for each directory in the archive, the list
5963 of files in that directory at the time the archive was created. This
5964 information is put out in a format which is both human-readable and
5965 unambiguous for a program: each file name is printed as
5972 where @var{x} is a letter describing the status of the file: @samp{Y}
5973 if the file is present in the archive, @samp{N} if the file is not
5974 included in the archive, or a @samp{D} if the file is a directory (and
5975 is included in the archive). @xref{Dumpdir}, for the detailed
5976 description of dumpdirs and status codes. Each such
5977 line is terminated by a newline character. The last line is followed
5978 by an additional newline to indicate the end of the data.
5980 @anchor{incremental-op}The option @option{--incremental} (@option{-G})
5981 gives the same behavior as @option{--listed-incremental} when used
5982 with @option{--list} and @option{--extract} options. When used with
5983 @option{--create} option, it creates an incremental archive without
5984 creating snapshot file. Thus, it is impossible to create several
5985 levels of incremental backups with @option{--incremental} option.
5988 @section Levels of Backups
5990 An archive containing all the files in the file system is called a
5991 @dfn{full backup} or @dfn{full dump}. You could insure your data by
5992 creating a full dump every day. This strategy, however, would waste a
5993 substantial amount of archive media and user time, as unchanged files
5994 are daily re-archived.
5996 It is more efficient to do a full dump only occasionally. To back up
5997 files between full dumps, you can use @dfn{incremental dumps}. A @dfn{level
5998 one} dump archives all the files that have changed since the last full
6001 A typical dump strategy would be to perform a full dump once a week,
6002 and a level one dump once a day. This means some versions of files
6003 will in fact be archived more than once, but this dump strategy makes
6004 it possible to restore a file system to within one day of accuracy by
6005 only extracting two archives---the last weekly (full) dump and the
6006 last daily (level one) dump. The only information lost would be in
6007 files changed or created since the last daily backup. (Doing dumps
6008 more than once a day is usually not worth the trouble).
6010 @GNUTAR{} comes with scripts you can use to do full
6011 and level-one (actually, even level-two and so on) dumps. Using
6012 scripts (shell programs) to perform backups and restoration is a
6013 convenient and reliable alternative to typing out file name lists
6014 and @command{tar} commands by hand.
6016 Before you use these scripts, you need to edit the file
6017 @file{backup-specs}, which specifies parameters used by the backup
6018 scripts and by the restore script. This file is usually located
6019 in @file{/etc/backup} directory. @xref{Backup Parameters}, for its
6020 detailed description. Once the backup parameters are set, you can
6021 perform backups or restoration by running the appropriate script.
6023 The name of the backup script is @code{backup}. The name of the
6024 restore script is @code{restore}. The following sections describe
6025 their use in detail.
6027 @emph{Please Note:} The backup and restoration scripts are
6028 designed to be used together. While it is possible to restore files by
6029 hand from an archive which was created using a backup script, and to create
6030 an archive by hand which could then be extracted using the restore script,
6031 it is easier to use the scripts. @xref{Incremental Dumps}, before
6032 making such an attempt.
6034 @node Backup Parameters
6035 @section Setting Parameters for Backups and Restoration
6037 The file @file{backup-specs} specifies backup parameters for the
6038 backup and restoration scripts provided with @command{tar}. You must
6039 edit @file{backup-specs} to fit your system configuration and schedule
6040 before using these scripts.
6042 Syntactically, @file{backup-specs} is a shell script, containing
6043 mainly variable assignments. However, any valid shell construct
6044 is allowed in this file. Particularly, you may wish to define
6045 functions within that script (e.g., see @code{RESTORE_BEGIN} below).
6046 For more information about shell script syntax, please refer to
6047 @url{http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
6048 g_02, the definition of the Shell Command Language}. See also
6049 @ref{Top,,Bash Features,bashref,Bash Reference Manual}.
6051 The shell variables controlling behavior of @code{backup} and
6052 @code{restore} are described in the following subsections.
6055 * General-Purpose Variables::
6056 * Magnetic Tape Control::
6058 * backup-specs example:: An Example Text of @file{Backup-specs}
6061 @node General-Purpose Variables
6062 @subsection General-Purpose Variables
6064 @defvr {Backup variable} ADMINISTRATOR
6065 The user name of the backup administrator. @code{Backup} scripts
6066 sends a backup report to this address.
6069 @defvr {Backup variable} BACKUP_HOUR
6070 The hour at which the backups are done. This can be a number from 0
6071 to 23, or the time specification in form @var{hours}:@var{minutes},
6072 or the string @samp{now}.
6074 This variable is used by @code{backup}. Its value may be overridden
6075 using @option{--time} option (@pxref{Scripted Backups}).
6078 @defvr {Backup variable} TAPE_FILE
6080 The device @command{tar} writes the archive to. If @var{TAPE_FILE}
6081 is a remote archive (@pxref{remote-dev}), backup script will suppose
6082 that your @command{mt} is able to access remote devices. If @var{RSH}
6083 (@pxref{RSH}) is set, @option{--rsh-command} option will be added to
6084 invocations of @command{mt}.
6087 @defvr {Backup variable} BLOCKING
6089 The blocking factor @command{tar} will use when writing the dump archive.
6090 @xref{Blocking Factor}.
6093 @defvr {Backup variable} BACKUP_DIRS
6095 A list of file systems to be dumped (for @code{backup}), or restored
6096 (for @code{restore}). You can include any directory
6097 name in the list --- subdirectories on that file system will be
6098 included, regardless of how they may look to other networked machines.
6099 Subdirectories on other file systems will be ignored.
6101 The host name specifies which host to run @command{tar} on, and should
6102 normally be the host that actually contains the file system. However,
6103 the host machine must have @GNUTAR{} installed, and
6104 must be able to access the directory containing the backup scripts and
6105 their support files using the same file name that is used on the
6106 machine where the scripts are run (i.e., what @command{pwd} will print
6107 when in that directory on that machine). If the host that contains
6108 the file system does not have this capability, you can specify another
6109 host as long as it can access the file system through @acronym{NFS}.
6111 If the list of file systems is very long you may wish to put it
6112 in a separate file. This file is usually named
6113 @file{/etc/backup/dirs}, but this name may be overridden in
6114 @file{backup-specs} using @code{DIRLIST} variable.
6117 @defvr {Backup variable} DIRLIST
6119 The name of the file that contains a list of file systems to backup
6120 or restore. By default it is @file{/etc/backup/dirs}.
6123 @defvr {Backup variable} BACKUP_FILES
6125 A list of individual files to be dumped (for @code{backup}), or restored
6126 (for @code{restore}). These should be accessible from the machine on
6127 which the backup script is run.
6129 If the list of file systems is very long you may wish to store it
6130 in a separate file. This file is usually named
6131 @file{/etc/backup/files}, but this name may be overridden in
6132 @file{backup-specs} using @code{FILELIST} variable.
6135 @defvr {Backup variable} FILELIST
6137 The name of the file that contains a list of individual files to backup
6138 or restore. By default it is @file{/etc/backup/files}.
6141 @defvr {Backup variable} MT
6143 Full file name of @command{mt} binary.
6146 @defvr {Backup variable} RSH
6148 Full file name of @command{rsh} binary or its equivalent. You may wish to
6149 set it to @code{ssh}, to improve security. In this case you will have
6150 to use public key authentication.
6153 @defvr {Backup variable} RSH_COMMAND
6155 Full file name of @command{rsh} binary on remote machines. This will
6156 be passed via @option{--rsh-command} option to the remote invocation
6160 @defvr {Backup variable} VOLNO_FILE
6162 Name of temporary file to hold volume numbers. This needs to be accessible
6163 by all the machines which have file systems to be dumped.
6166 @defvr {Backup variable} XLIST
6168 Name of @dfn{exclude file list}. An @dfn{exclude file list} is a file
6169 located on the remote machine and containing the list of files to
6170 be excluded from the backup. Exclude file lists are searched in
6171 /etc/tar-backup directory. A common use for exclude file lists
6172 is to exclude files containing security-sensitive information
6173 (e.g., @file{/etc/shadow} from backups).
6175 This variable affects only @code{backup}.
6178 @defvr {Backup variable} SLEEP_TIME
6180 Time to sleep between dumps of any two successive file systems
6182 This variable affects only @code{backup}.
6185 @defvr {Backup variable} DUMP_REMIND_SCRIPT
6187 Script to be run when it's time to insert a new tape in for the next
6188 volume. Administrators may want to tailor this script for their site.
6189 If this variable isn't set, @GNUTAR{} will display its built-in
6190 prompt, and will expect confirmation from the console. For the
6191 description of the default prompt, see @ref{change volume prompt}.
6195 @defvr {Backup variable} SLEEP_MESSAGE
6197 Message to display on the terminal while waiting for dump time. Usually
6198 this will just be some literal text.
6201 @defvr {Backup variable} TAR
6203 Full file name of the @GNUTAR{} executable. If this is not set, backup
6204 scripts will search @command{tar} in the current shell path.
6207 @node Magnetic Tape Control
6208 @subsection Magnetic Tape Control
6210 Backup scripts access tape device using special @dfn{hook functions}.
6211 These functions take a single argument -- the name of the tape
6212 device. Their names are kept in the following variables:
6214 @defvr {Backup variable} MT_BEGIN
6215 The name of @dfn{begin} function. This function is called before
6216 accessing the drive. By default it retensions the tape:
6222 mt -f "$1" retension
6227 @defvr {Backup variable} MT_REWIND
6228 The name of @dfn{rewind} function. The default definition is as
6241 @defvr {Backup variable} MT_OFFLINE
6242 The name of the function switching the tape off line. By default
6243 it is defined as follows:
6246 MT_OFFLINE=mt_offline
6254 @defvr {Backup variable} MT_STATUS
6255 The name of the function used to obtain the status of the archive device,
6256 including error count. Default definition:
6268 @subsection User Hooks
6270 @dfn{User hooks} are shell functions executed before and after
6271 each @command{tar} invocation. Thus, there are @dfn{backup
6272 hooks}, which are executed before and after dumping each file
6273 system, and @dfn{restore hooks}, executed before and
6274 after restoring a file system. Each user hook is a shell function
6275 taking four arguments:
6277 @deffn {User Hook Function} hook @var{level} @var{host} @var{fs} @var{fsname}
6282 Current backup or restore level.
6285 Name or IP address of the host machine being dumped or restored.
6288 Full file name of the file system being dumped or restored.
6291 File system name with directory separators replaced with colons. This
6292 is useful, e.g., for creating unique files.
6296 Following variables keep the names of user hook functions
6298 @defvr {Backup variable} DUMP_BEGIN
6299 Dump begin function. It is executed before dumping the file system.
6302 @defvr {Backup variable} DUMP_END
6303 Executed after dumping the file system.
6306 @defvr {Backup variable} RESTORE_BEGIN
6307 Executed before restoring the file system.
6310 @defvr {Backup variable} RESTORE_END
6311 Executed after restoring the file system.
6314 @node backup-specs example
6315 @subsection An Example Text of @file{Backup-specs}
6317 The following is an example of @file{backup-specs}:
6320 # site-specific parameters for file system backup.
6322 ADMINISTRATOR=friedman
6324 TAPE_FILE=/dev/nrsmt0
6326 # Use @code{ssh} instead of the less secure @code{rsh}
6328 RSH_COMMAND=/usr/bin/ssh
6330 # Override MT_STATUS function:
6336 # Disable MT_OFFLINE function
6353 apple-gunkies:/com/mailer/gnu
6354 apple-gunkies:/com/archive/gnu"
6356 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
6360 @node Scripted Backups
6361 @section Using the Backup Scripts
6363 The syntax for running a backup script is:
6366 backup --level=@var{level} --time=@var{time}
6369 The @option{level} option requests the dump level. Thus, to produce
6370 a full dump, specify @code{--level=0} (this is the default, so
6371 @option{--level} may be omitted if its value is @code{0}).
6372 @footnote{For backward compatibility, the @code{backup} will also
6373 try to deduce the requested dump level from the name of the
6374 script itself. If the name consists of a string @samp{level-}
6375 followed by a single decimal digit, that digit is taken as
6376 the dump level number. Thus, you may create a link from @code{backup}
6377 to @code{level-1} and then run @code{level-1} whenever you need to
6378 create a level one dump.}
6380 The @option{--time} option determines when should the backup be
6381 run. @var{Time} may take three forms:
6384 @item @var{hh}:@var{mm}
6386 The dump must be run at @var{hh} hours @var{mm} minutes.
6390 The dump must be run at @var{hh} hours
6394 The dump must be run immediately.
6397 You should start a script with a tape or disk mounted. Once you
6398 start a script, it prompts you for new tapes or disks as it
6399 needs them. Media volumes don't have to correspond to archive
6400 files --- a multi-volume archive can be started in the middle of a
6401 tape that already contains the end of another multi-volume archive.
6402 The @code{restore} script prompts for media by its archive volume,
6403 so to avoid an error message you should keep track of which tape
6404 (or disk) contains which volume of the archive (@pxref{Scripted
6407 The backup scripts write two files on the file system. The first is a
6408 record file in @file{/etc/tar-backup/}, which is used by the scripts
6409 to store and retrieve information about which files were dumped. This
6410 file is not meant to be read by humans, and should not be deleted by
6411 them. @xref{Snapshot Files}, for a more detailed explanation of this
6414 The second file is a log file containing the names of the file systems
6415 and files dumped, what time the backup was made, and any error
6416 messages that were generated, as well as how much space was left in
6417 the media volume after the last volume of the archive was written.
6418 You should check this log file after every backup. The file name is
6419 @file{log-@var{mm-dd-yyyy}-level-@var{n}}, where @var{mm-dd-yyyy}
6420 represents current date, and @var{n} represents current dump level number.
6422 The script also prints the name of each system being dumped to the
6425 Following is the full list of options accepted by @code{backup}
6429 @item -l @var{level}
6430 @itemx --level=@var{level}
6431 Do backup level @var{level} (default 0).
6435 Force backup even if today's log file already exists.
6437 @item -v[@var{level}]
6438 @itemx --verbose[=@var{level}]
6439 Set verbosity level. The higher the level is, the more debugging
6440 information will be output during execution. Default @var{level}
6441 is 100, which means the highest debugging level.
6443 @item -t @var{start-time}
6444 @itemx --time=@var{start-time}
6445 Wait till @var{time}, then do backup.
6449 Display short help message and exit.
6453 Display information about the program's name, version, origin and legal
6454 status, all on standard output, and then exit successfully.
6458 @node Scripted Restoration
6459 @section Using the Restore Script
6461 To restore files that were archived using a scripted backup, use the
6462 @code{restore} script. Its usage is quite straightforward. In the
6463 simplest form, invoke @code{restore --all}, it will
6464 then restore all the file systems and files specified in
6465 @file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
6467 You may select the file systems (and/or files) to restore by
6468 giving @code{restore} list of @dfn{patterns} in its command
6469 line. For example, running
6476 will restore all file systems on the machine @samp{albert}. A more
6477 complicated example:
6480 restore 'albert:*' '*:/var'
6484 This command will restore all file systems on the machine @samp{albert}
6485 as well as @file{/var} file system on all machines.
6487 By default @code{restore} will start restoring files from the lowest
6488 available dump level (usually zero) and will continue through
6489 all available dump levels. There may be situations where such a
6490 thorough restore is not necessary. For example, you may wish to
6491 restore only files from the recent level one backup. To do so,
6492 use @option{--level} option, as shown in the example below:
6498 The full list of options accepted by @code{restore} follows:
6503 Restore all file systems and files specified in @file{backup-specs}
6505 @item -l @var{level}
6506 @itemx --level=@var{level}
6507 Start restoring from the given backup level, instead of the default 0.
6509 @item -v[@var{level}]
6510 @itemx --verbose[=@var{level}]
6511 Set verbosity level. The higher the level is, the more debugging
6512 information will be output during execution. Default @var{level}
6513 is 100, which means the highest debugging level.
6517 Display short help message and exit.
6521 Display information about the program's name, version, origin and legal
6522 status, all on standard output, and then exit successfully.
6525 You should start the restore script with the media containing the
6526 first volume of the archive mounted. The script will prompt for other
6527 volumes as they are needed. If the archive is on tape, you don't need
6528 to rewind the tape to to its beginning---if the tape head is
6529 positioned past the beginning of the archive, the script will rewind
6530 the tape as needed. @xref{Tape Positioning}, for a discussion of tape
6534 @strong{Warning:} The script will delete files from the active file
6535 system if they were not in the file system when the archive was made.
6538 @xref{Incremental Dumps}, for an explanation of how the script makes
6542 @chapter Choosing Files and Names for @command{tar}
6545 Certain options to @command{tar} enable you to specify a name for your
6546 archive. Other options let you decide which files to include or exclude
6547 from the archive, based on when or whether files were modified, whether
6548 the file names do or don't match specified patterns, or whether files
6549 are in specified directories.
6551 This chapter discusses these options in detail.
6554 * file:: Choosing the Archive's Name
6555 * Selecting Archive Members::
6556 * files:: Reading Names from a File
6557 * exclude:: Excluding Some Files
6558 * wildcards:: Wildcards Patterns and Matching
6559 * quoting styles:: Ways of Quoting Special Characters in Names
6560 * transform:: Modifying File and Member Names
6561 * after:: Operating Only on New Files
6562 * recurse:: Descending into Directories
6563 * one:: Crossing File System Boundaries
6567 @section Choosing and Naming Archive Files
6570 @cindex Naming an archive
6571 @cindex Archive Name
6572 @cindex Choosing an archive file
6573 @cindex Where is the archive?
6574 By default, @command{tar} uses an archive file name that was compiled when
6575 it was built on the system; usually this name refers to some physical
6576 tape drive on the machine. However, the person who installed @command{tar}
6577 on the system may not have set the default to a meaningful value as far as
6578 most users are concerned. As a result, you will usually want to tell
6579 @command{tar} where to find (or create) the archive. The
6580 @option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
6581 option allows you to either specify or name a file to use as the archive
6582 instead of the default archive file location.
6585 @xopindex{file, short description}
6586 @item --file=@var{archive-name}
6587 @itemx -f @var{archive-name}
6588 Name the archive to create or operate on. Use in conjunction with
6592 For example, in this @command{tar} command,
6595 $ @kbd{tar -cvf collection.tar blues folk jazz}
6599 @file{collection.tar} is the name of the archive. It must directly
6600 follow the @option{-f} option, since whatever directly follows @option{-f}
6601 @emph{will} end up naming the archive. If you neglect to specify an
6602 archive name, you may end up overwriting a file in the working directory
6603 with the archive you create since @command{tar} will use this file's name
6604 for the archive name.
6606 An archive can be saved as a file in the file system, sent through a
6607 pipe or over a network, or written to an I/O device such as a tape,
6608 floppy disk, or CD write drive.
6610 @cindex Writing new archives
6611 @cindex Archive creation
6612 If you do not name the archive, @command{tar} uses the value of the
6613 environment variable @env{TAPE} as the file name for the archive. If
6614 that is not available, @command{tar} uses a default, compiled-in archive
6615 name, usually that for tape unit zero (i.e., @file{/dev/tu00}).
6617 @cindex Standard input and output
6618 @cindex tar to standard input and output
6619 If you use @file{-} as an @var{archive-name}, @command{tar} reads the
6620 archive from standard input (when listing or extracting files), or
6621 writes it to standard output (when creating an archive). If you use
6622 @file{-} as an @var{archive-name} when modifying an archive,
6623 @command{tar} reads the original archive from its standard input and
6624 writes the entire new archive to its standard output.
6626 The following example is a convenient way of copying directory
6627 hierarchy from @file{sourcedir} to @file{targetdir}.
6630 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)}
6633 The @option{-C} option allows to avoid using subshells:
6636 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xpf -}
6639 In both examples above, the leftmost @command{tar} invocation archives
6640 the contents of @file{sourcedir} to the standard output, while the
6641 rightmost one reads this archive from its standard input and
6642 extracts it. The @option{-p} option tells it to restore permissions
6643 of the extracted files.
6645 @cindex Remote devices
6646 @cindex tar to a remote device
6648 To specify an archive file on a device attached to a remote machine,
6652 @kbd{--file=@var{hostname}:/@var{dev}/@var{file-name}}
6656 @command{tar} will complete the remote connection, if possible, and
6657 prompt you for a username and password. If you use
6658 @option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
6659 will complete the remote connection, if possible, using your username
6660 as the username on the remote machine.
6662 @cindex Local and remote archives
6663 @anchor{local and remote archives}
6664 If the archive file name includes a colon (@samp{:}), then it is assumed
6665 to be a file on another machine. If the archive file is
6666 @samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the
6667 host @var{host}. The remote host is accessed using the @command{rsh}
6668 program, with a username of @var{user}. If the username is omitted
6669 (along with the @samp{@@} sign), then your user name will be used.
6670 (This is the normal @command{rsh} behavior.) It is necessary for the
6671 remote machine, in addition to permitting your @command{rsh} access, to
6672 have the @file{rmt} program installed (This command is included in
6673 the @GNUTAR{} distribution and by default is installed under
6674 @file{@var{prefix}/libexec/rmt}, were @var{prefix} means your
6675 installation prefix). If you need to use a file whose name includes a
6676 colon, then the remote tape drive behavior
6677 can be inhibited by using the @option{--force-local} option.
6679 When the archive is being created to @file{/dev/null}, @GNUTAR{}
6680 tries to minimize input and output operations. The Amanda backup
6681 system, when used with @GNUTAR{}, has an initial sizing pass which
6684 @node Selecting Archive Members
6685 @section Selecting Archive Members
6686 @cindex Specifying files to act on
6687 @cindex Specifying archive members
6689 @dfn{File Name arguments} specify which files in the file system
6690 @command{tar} operates on, when creating or adding to an archive, or which
6691 archive members @command{tar} operates on, when reading or deleting from
6692 an archive. @xref{Operations}.
6694 To specify file names, you can include them as the last arguments on
6695 the command line, as follows:
6697 @kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
6700 If a file name begins with dash (@samp{-}), precede it with
6701 @option{--add-file} option to prevent it from being treated as an
6704 @anchor{input name quoting}
6705 By default @GNUTAR{} attempts to @dfn{unquote} each file or member
6706 name, replacing @dfn{escape sequences} according to the following
6709 @multitable @columnfractions 0.20 0.60
6710 @headitem Escape @tab Replaced with
6711 @item \a @tab Audible bell (@acronym{ASCII} 7)
6712 @item \b @tab Backspace (@acronym{ASCII} 8)
6713 @item \f @tab Form feed (@acronym{ASCII} 12)
6714 @item \n @tab New line (@acronym{ASCII} 10)
6715 @item \r @tab Carriage return (@acronym{ASCII} 13)
6716 @item \t @tab Horizontal tabulation (@acronym{ASCII} 9)
6717 @item \v @tab Vertical tabulation (@acronym{ASCII} 11)
6718 @item \? @tab @acronym{ASCII} 127
6719 @item \@var{n} @tab @acronym{ASCII} @var{n} (@var{n} should be an octal number
6723 A backslash followed by any other symbol is retained.
6725 This default behavior is controlled by the following command line
6731 Enable unquoting input file or member names (default).
6735 Disable unquoting input file or member names.
6738 If you specify a directory name as a file name argument, all the files
6739 in that directory are operated on by @command{tar}.
6741 If you do not specify files, @command{tar} behavior differs depending
6742 on the operation mode as described below:
6744 When @command{tar} is invoked with @option{--create} (@option{-c}),
6745 @command{tar} will stop immediately, reporting the following:
6749 $ @kbd{tar cf a.tar}
6750 tar: Cowardly refusing to create an empty archive
6751 Try `tar --help' or `tar --usage' for more information.
6755 If you specify either @option{--list} (@option{-t}) or
6756 @option{--extract} (@option{--get}, @option{-x}), @command{tar}
6757 operates on all the archive members in the archive.
6759 If run with @option{--diff} option, tar will compare the archive with
6760 the contents of the current working directory.
6762 If you specify any other operation, @command{tar} does nothing.
6764 By default, @command{tar} takes file names from the command line. However,
6765 there are other ways to specify file or member names, or to modify the
6766 manner in which @command{tar} selects the files or members upon which to
6767 operate. In general, these methods work both for specifying the names
6768 of files and archive members.
6771 @section Reading Names from a File
6773 @cindex Reading file names from a file
6774 @cindex Lists of file names
6775 @cindex File Name arguments, alternatives
6776 Instead of giving the names of files or archive members on the command
6777 line, you can put the names into a file, and then use the
6778 @option{--files-from=@var{file-of-names}} (@option{-T
6779 @var{file-of-names}}) option to @command{tar}. Give the name of the
6780 file which contains the list of files to include as the argument to
6781 @option{--files-from}. In the list, the file names should be separated by
6782 newlines. You will frequently use this option when you have generated
6783 the list of files to archive with the @command{find} utility.
6787 @item --files-from=@var{file-name}
6788 @itemx -T @var{file-name}
6789 Get names to extract or create from file @var{file-name}.
6792 If you give a single dash as a file name for @option{--files-from}, (i.e.,
6793 you specify either @code{--files-from=-} or @code{-T -}), then the file
6794 names are read from standard input.
6796 Unless you are running @command{tar} with @option{--create}, you can not use
6797 both @code{--files-from=-} and @code{--file=-} (@code{-f -}) in the same
6800 Any number of @option{-T} options can be given in the command line.
6802 The following example shows how to use @command{find} to generate a list of
6803 files smaller than 400K in length and put that list into a file
6804 called @file{small-files}. You can then use the @option{-T} option to
6805 @command{tar} to specify the files from that file, @file{small-files}, to
6806 create the archive @file{little.tgz}. (The @option{-z} option to
6807 @command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for
6811 $ @kbd{find . -size -400 -print > small-files}
6812 $ @kbd{tar -c -v -z -T small-files -f little.tgz}
6816 In the file list given by @option{-T} option, any file name beginning
6817 with @samp{-} character is considered a @command{tar} option and is
6818 processed accordingly.@footnote{Versions of @GNUTAR{} up to 1.15.1
6819 recognized only @option{-C} option in file lists, and only if the
6820 option and its argument occupied two consecutive lines.} For example,
6821 the common use of this feature is to change to another directory by
6822 specifying @option{-C} option:
6832 $ @kbd{tar -c -f foo.tar --files-from list}
6837 In this example, @command{tar} will first switch to @file{/etc}
6838 directory and add files @file{passwd} and @file{hosts} to the
6839 archive. Then it will change to @file{/lib} directory and will archive
6840 the file @file{libc.a}. Thus, the resulting archive @file{foo.tar} will
6845 $ @kbd{tar tf foo.tar}
6853 @xopindex{directory, using in @option{--files-from} argument}
6854 Notice that the option parsing algorithm used with @option{-T} is
6855 stricter than the one used by shell. Namely, when specifying option
6856 arguments, you should observe the following rules:
6860 When using short (single-letter) option form, its argument must
6861 immediately follow the option letter, without any intervening
6862 whitespace. For example: @code{-Cdir}.
6865 When using long option form, the option argument must be separated
6866 from the option by a single equal sign. No whitespace is allowed on
6867 any side of the equal sign. For example: @code{--directory=dir}.
6870 For both short and long option forms, the option argument can be given
6871 on the next line after the option name, e.g.:
6892 If you happen to have a file whose name starts with @samp{-},
6893 precede it with @option{--add-file} option to prevent it from
6894 being recognized as an option. For example: @code{--add-file=--my-file}.
6901 @subsection @code{NUL} Terminated File Names
6903 @cindex File names, terminated by @code{NUL}
6904 @cindex @code{NUL} terminated file names
6905 The @option{--null} option causes
6906 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
6907 to read file names terminated by a @code{NUL} instead of a newline, so
6908 files whose names contain newlines can be archived using
6909 @option{--files-from}.
6912 @xopindex{null, described}
6914 Only consider @code{NUL} terminated file names, instead of files that
6915 terminate in a newline.
6917 @xopindex{no-null, described}
6919 Undo the effect of any previous @option{--null} option.
6922 The @option{--null} option is just like the one in @acronym{GNU}
6923 @command{xargs} and @command{cpio}, and is useful with the
6924 @option{-print0} predicate of @acronym{GNU} @command{find}. In
6925 @command{tar}, @option{--null} also disables special handling for
6926 file names that begin with dash.
6928 This example shows how to use @command{find} to generate a list of files
6929 larger than 800K in length and put that list into a file called
6930 @file{long-files}. The @option{-print0} option to @command{find} is just
6931 like @option{-print}, except that it separates files with a @code{NUL}
6932 rather than with a newline. You can then run @command{tar} with both the
6933 @option{--null} and @option{-T} options to specify that @command{tar} get the
6934 files from that file, @file{long-files}, to create the archive
6935 @file{big.tgz}. The @option{--null} option to @command{tar} will cause
6936 @command{tar} to recognize the @code{NUL} separator between files.
6939 $ @kbd{find . -size +800 -print0 > long-files}
6940 $ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
6943 The @option{--no-null} option can be used if you need to read both
6944 zero-terminated and newline-terminated files on the same command line.
6945 For example, if @file{flist} is a newline-terminated file, then the
6946 following command can be used to combine it with the above command:
6950 $ @kbd{find . -size +800 -print0 |
6951 tar -c -f big.tar --null -T - --no-null -T flist}
6955 This example uses short options for typographic reasons, to avoid
6958 @GNUTAR is able to automatically detect null-terminated file lists, so
6959 it is safe to use them even without the @option{--null} option. In
6960 this case @command{tar} will print a warning and continue reading such
6961 a file as if @option{--null} were actually given:
6965 $ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
6966 tar: -: file name read contains nul character
6970 The null terminator, however, remains in effect only for this
6971 particular file, any following @option{-T} options will assume
6972 newline termination. Of course, the null autodetection applies
6973 to these eventual surplus @option{-T} options as well.
6976 @section Excluding Some Files
6979 @cindex File names, excluding files by
6980 @cindex Excluding files by name and pattern
6981 @cindex Excluding files by file system
6982 To avoid operating on files whose names match a particular pattern,
6983 use the @option{--exclude} or @option{--exclude-from} options.
6987 @item --exclude=@var{pattern}
6988 Causes @command{tar} to ignore files that match the @var{pattern}.
6992 The @option{--exclude=@var{pattern}} option prevents any file or
6993 member whose name matches the shell wildcard (@var{pattern}) from
6995 For example, to create an archive with all the contents of the directory
6996 @file{src} except for files whose names end in @file{.o}, use the
6997 command @samp{tar -cf src.tar --exclude='*.o' src}.
6999 You may give multiple @option{--exclude} options.
7002 @opindex exclude-from
7003 @item --exclude-from=@var{file}
7004 @itemx -X @var{file}
7005 Causes @command{tar} to ignore files that match the patterns listed in
7009 @findex exclude-from
7010 Use the @option{--exclude-from} option to read a
7011 list of patterns, one per line, from @var{file}; @command{tar} will
7012 ignore files matching those patterns. Thus if @command{tar} is
7013 called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a
7014 single line @file{*.o}, no files whose names end in @file{.o} will be
7015 added to the archive.
7017 Notice, that lines from @var{file} are read verbatim. One of the
7018 frequent errors is leaving some extra whitespace after a file name,
7019 which is difficult to catch using text editors.
7021 However, empty lines are OK.
7023 @cindex version control system, excluding files
7024 @cindex VCS, excluding files
7025 @cindex SCCS, excluding files
7026 @cindex RCS, excluding files
7027 @cindex CVS, excluding files
7028 @cindex SVN, excluding files
7029 @cindex git, excluding files
7030 @cindex Bazaar, excluding files
7031 @cindex Arch, excluding files
7032 @cindex Mercurial, excluding files
7033 @cindex Darcs, excluding files
7035 @opindex exclude-vcs
7037 Exclude files and directories used by following version control
7038 systems: @samp{CVS}, @samp{RCS}, @samp{SCCS}, @samp{SVN}, @samp{Arch},
7039 @samp{Bazaar}, @samp{Mercurial}, and @samp{Darcs}.
7042 As of version @value{VERSION}, the following files are excluded:
7045 @item @file{CVS/}, and everything under it
7046 @item @file{RCS/}, and everything under it
7047 @item @file{SCCS/}, and everything under it
7048 @item @file{.git/}, and everything under it
7049 @item @file{.gitignore}
7050 @item @file{.cvsignore}
7051 @item @file{.svn/}, and everything under it
7052 @item @file{.arch-ids/}, and everything under it
7053 @item @file{@{arch@}/}, and everything under it
7054 @item @file{=RELEASE-ID}
7055 @item @file{=meta-update}
7056 @item @file{=update}
7058 @item @file{.bzrignore}
7059 @item @file{.bzrtags}
7061 @item @file{.hgignore}
7062 @item @file{.hgrags}
7066 @findex exclude-caches
7067 When creating an archive, the @option{--exclude-caches} option family
7068 causes @command{tar} to exclude all directories that contain a @dfn{cache
7069 directory tag}. A cache directory tag is a short file with the
7070 well-known name @file{CACHEDIR.TAG} and having a standard header
7071 specified in @url{http://www.brynosaurus.com/cachedir/spec.html}.
7072 Various applications write cache directory tags into directories they
7073 use to hold regenerable, non-precious data, so that such data can be
7074 more easily excluded from backups.
7076 There are three @samp{exclude-caches} options, each providing a different
7077 exclusion semantics:
7080 @opindex exclude-caches
7081 @item --exclude-caches
7082 Do not archive the contents of the directory, but archive the
7083 directory itself and the @file{CACHEDIR.TAG} file.
7085 @opindex exclude-caches-under
7086 @item --exclude-caches-under
7087 Do not archive the contents of the directory, nor the
7088 @file{CACHEDIR.TAG} file, archive only the directory itself.
7090 @opindex exclude-caches-all
7091 @item --exclude-caches-all
7092 Omit directories containing @file{CACHEDIR.TAG} file entirely.
7096 Another option family, @option{--exclude-tag}, provides a generalization of
7097 this concept. It takes a single argument, a file name to look for.
7098 Any directory that contains this file will be excluded from the dump.
7099 Similarly to @samp{exclude-caches}, there are three options in this
7103 @opindex exclude-tag
7104 @item --exclude-tag=@var{file}
7105 Do not dump the contents of the directory, but dump the
7106 directory itself and the @var{file}.
7108 @opindex exclude-tag-under
7109 @item --exclude-tag-under=@var{file}
7110 Do not dump the contents of the directory, nor the
7111 @var{file}, archive only the directory itself.
7113 @opindex exclude-tag-all
7114 @item --exclude-tag-all=@var{file}
7115 Omit directories containing @var{file} file entirely.
7118 Multiple @option{--exclude-tag*} options can be given.
7120 For example, given this directory:
7135 The @option{--exclude-tag} will produce the following:
7138 $ @kbd{tar -cf archive.tar --exclude-tag=tagfile -v dir}
7143 tar: dir/folk/: contains a cache directory tag tagfile;
7148 Both the @file{dir/folk} directory and its tagfile are preserved in
7149 the archive, however the rest of files in this directory are not.
7151 Now, using the @option{--exclude-tag-under} option will exclude
7152 @file{tagfile} from the dump, while still preserving the directory
7153 itself, as shown in this example:
7156 $ @kbd{tar -cf archive.tar --exclude-tag-under=tagfile -v dir}
7161 ./tar: dir/folk/: contains a cache directory tag tagfile;
7165 Finally, using @option{--exclude-tag-all} omits the @file{dir/folk}
7169 $ @kbd{tar -cf archive.tar --exclude-tag-all=tagfile -v dir}
7173 ./tar: dir/folk/: contains a cache directory tag tagfile;
7174 directory not dumped
7178 * problems with exclude::
7181 @node problems with exclude
7182 @unnumberedsubsec Problems with Using the @code{exclude} Options
7184 @xopindex{exclude, potential problems with}
7185 Some users find @samp{exclude} options confusing. Here are some common
7190 The main operating mode of @command{tar} does not act on a file name
7191 explicitly listed on the command line, if one of its file name
7192 components is excluded. In the example above, if
7193 you create an archive and exclude files that end with @samp{*.o}, but
7194 explicitly name the file @samp{dir.o/foo} after all the options have been
7195 listed, @samp{dir.o/foo} will be excluded from the archive.
7198 You can sometimes confuse the meanings of @option{--exclude} and
7199 @option{--exclude-from}. Be careful: use @option{--exclude} when files
7200 to be excluded are given as a pattern on the command line. Use
7201 @option{--exclude-from} to introduce the name of a file which contains
7202 a list of patterns, one per line; each of these patterns can exclude
7203 zero, one, or many files.
7206 When you use @option{--exclude=@var{pattern}}, be sure to quote the
7207 @var{pattern} parameter, so @GNUTAR{} sees wildcard characters
7208 like @samp{*}. If you do not do this, the shell might expand the
7209 @samp{*} itself using files at hand, so @command{tar} might receive a
7210 list of files instead of one pattern, or none at all, making the
7211 command somewhat illegal. This might not correspond to what you want.
7216 $ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}}
7224 $ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
7228 You must use use shell syntax, or globbing, rather than @code{regexp}
7229 syntax, when using exclude options in @command{tar}. If you try to use
7230 @code{regexp} syntax to describe files to be excluded, your command
7234 @FIXME{The change in semantics must have occurred before 1.11,
7235 so I doubt if it is worth mentioning at all. Anyway, should at
7236 least specify in which version the semantics changed.}
7237 In earlier versions of @command{tar}, what is now the
7238 @option{--exclude-from} option was called @option{--exclude} instead.
7239 Now, @option{--exclude} applies to patterns listed on the command
7240 line and @option{--exclude-from} applies to patterns listed in a
7246 @section Wildcards Patterns and Matching
7248 @dfn{Globbing} is the operation by which @dfn{wildcard} characters,
7249 @samp{*} or @samp{?} for example, are replaced and expanded into all
7250 existing files matching the given pattern. @GNUTAR{} can use wildcard
7251 patterns for matching (or globbing) archive members when extracting
7252 from or listing an archive. Wildcard patterns are also used for
7253 verifying volume labels of @command{tar} archives. This section has the
7254 purpose of explaining wildcard syntax for @command{tar}.
7256 @FIXME{the next few paragraphs need work.}
7258 A @var{pattern} should be written according to shell syntax, using wildcard
7259 characters to effect globbing. Most characters in the pattern stand
7260 for themselves in the matched string, and case is significant: @samp{a}
7261 will match only @samp{a}, and not @samp{A}. The character @samp{?} in the
7262 pattern matches any single character in the matched string. The character
7263 @samp{*} in the pattern matches zero, one, or more single characters in
7264 the matched string. The character @samp{\} says to take the following
7265 character of the pattern @emph{literally}; it is useful when one needs to
7266 match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves.
7268 The character @samp{[}, up to the matching @samp{]}, introduces a character
7269 class. A @dfn{character class} is a list of acceptable characters
7270 for the next single character of the matched string. For example,
7271 @samp{[abcde]} would match any of the first five letters of the alphabet.
7272 Note that within a character class, all of the ``special characters''
7273 listed above other than @samp{\} lose their special meaning; for example,
7274 @samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\},
7275 @samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints,
7276 the characters @samp{-} and @samp{]} must either come @emph{first} or
7277 @emph{last} in a character class.)
7279 @cindex Excluding characters from a character class
7280 @cindex Character class, excluding characters from
7281 If the first character of the class after the opening @samp{[}
7282 is @samp{!} or @samp{^}, then the meaning of the class is reversed.
7283 Rather than listing character to match, it lists those characters which
7284 are @emph{forbidden} as the next single character of the matched string.
7286 Other characters of the class stand for themselves. The special
7287 construction @samp{[@var{a}-@var{e}]}, using an hyphen between two
7288 letters, is meant to represent all characters between @var{a} and
7291 @FIXME{need to add a sentence or so here to make this clear for those
7292 who don't have dan around.}
7294 Periods (@samp{.}) or forward slashes (@samp{/}) are not considered
7295 special for wildcard matches. However, if a pattern completely matches
7296 a directory prefix of a matched string, then it matches the full matched
7297 string: thus, excluding a directory also excludes all the files beneath it.
7300 * controlling pattern-matching::
7303 @node controlling pattern-matching
7304 @unnumberedsubsec Controlling Pattern-Matching
7306 For the purposes of this section, we call @dfn{exclusion members} all
7307 member names obtained while processing @option{--exclude} and
7308 @option{--exclude-from} options, and @dfn{inclusion members} those
7309 member names that were given in the command line or read from the file
7310 specified with @option{--files-from} option.
7312 These two pairs of member lists are used in the following operations:
7313 @option{--diff}, @option{--extract}, @option{--list},
7316 There are no inclusion members in create mode (@option{--create} and
7317 @option{--append}), since in this mode the names obtained from the
7318 command line refer to @emph{files}, not archive members.
7320 By default, inclusion members are compared with archive members
7321 literally @footnote{Notice that earlier @GNUTAR{} versions used
7322 globbing for inclusion members, which contradicted to UNIX98
7323 specification and was not documented. @xref{Changes}, for more
7324 information on this and other changes.} and exclusion members are
7325 treated as globbing patterns. For example:
7329 $ @kbd{tar tf foo.tar}
7334 # @i{Member names are used verbatim:}
7335 $ @kbd{tar -xf foo.tar -v '[remarks]'}
7337 # @i{Exclude member names are globbed:}
7338 $ @kbd{tar -xf foo.tar -v --exclude '*.c'}
7344 This behavior can be altered by using the following options:
7349 Treat all member names as wildcards.
7351 @opindex no-wildcards
7352 @item --no-wildcards
7353 Treat all member names as literal strings.
7356 Thus, to extract files whose names end in @samp{.c}, you can use:
7359 $ @kbd{tar -xf foo.tar -v --wildcards '*.c'}
7365 Notice quoting of the pattern to prevent the shell from interpreting
7368 The effect of @option{--wildcards} option is canceled by
7369 @option{--no-wildcards}. This can be used to pass part of
7370 the command line arguments verbatim and other part as globbing
7371 patterns. For example, the following invocation:
7374 $ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'}
7378 instructs @command{tar} to extract from @file{foo.tar} all files whose
7379 names end in @samp{.txt} and the file named @file{[remarks]}.
7381 Normally, a pattern matches a name if an initial subsequence of the
7382 name's components matches the pattern, where @samp{*}, @samp{?}, and
7383 @samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
7384 and wildcards can match @samp{/}.
7386 Other than optionally stripping leading @samp{/} from names
7387 (@pxref{absolute}), patterns and names are used as-is. For
7388 example, trailing @samp{/} is not trimmed from a user-specified name
7389 before deciding whether to exclude it.
7391 However, this matching procedure can be altered by the options listed
7392 below. These options accumulate. For example:
7395 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
7399 ignores case when excluding @samp{makefile}, but not when excluding
7404 @opindex no-anchored
7406 @itemx --no-anchored
7407 If anchored, a pattern must match an initial subsequence
7408 of the name's components. Otherwise, the pattern can match any
7409 subsequence. Default is @option{--no-anchored} for exclusion members
7410 and @option{--anchored} inclusion members.
7412 @opindex ignore-case
7413 @opindex no-ignore-case
7415 @itemx --no-ignore-case
7416 When ignoring case, upper-case patterns match lower-case names and vice versa.
7417 When not ignoring case (the default), matching is case-sensitive.
7419 @opindex wildcards-match-slash
7420 @opindex no-wildcards-match-slash
7421 @item --wildcards-match-slash
7422 @itemx --no-wildcards-match-slash
7423 When wildcards match slash (the default for exclusion members), a
7424 wildcard like @samp{*} in the pattern can match a @samp{/} in the
7425 name. Otherwise, @samp{/} is matched only by @samp{/}.
7429 The @option{--recursion} and @option{--no-recursion} options
7430 (@pxref{recurse}) also affect how member patterns are interpreted. If
7431 recursion is in effect, a pattern matches a name if it matches any of
7432 the name's parent directories.
7434 The following table summarizes pattern-matching default values:
7436 @multitable @columnfractions .3 .7
7437 @headitem Members @tab Default settings
7438 @item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash}
7439 @item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash}
7442 @node quoting styles
7443 @section Quoting Member Names
7445 When displaying member names, @command{tar} takes care to avoid
7446 ambiguities caused by certain characters. This is called @dfn{name
7447 quoting}. The characters in question are:
7450 @item Non-printable control characters:
7451 @anchor{escape sequences}
7452 @multitable @columnfractions 0.20 0.10 0.60
7453 @headitem Character @tab @acronym{ASCII} @tab Character name
7454 @item \a @tab 7 @tab Audible bell
7455 @item \b @tab 8 @tab Backspace
7456 @item \f @tab 12 @tab Form feed
7457 @item \n @tab 10 @tab New line
7458 @item \r @tab 13 @tab Carriage return
7459 @item \t @tab 9 @tab Horizontal tabulation
7460 @item \v @tab 11 @tab Vertical tabulation
7463 @item Space (@acronym{ASCII} 32)
7465 @item Single and double quotes (@samp{'} and @samp{"})
7467 @item Backslash (@samp{\})
7470 The exact way @command{tar} uses to quote these characters depends on
7471 the @dfn{quoting style}. The default quoting style, called
7472 @dfn{escape} (see below), uses backslash notation to represent control
7473 characters, space and backslash. Using this quoting style, control
7474 characters are represented as listed in column @samp{Character} in the
7475 above table, a space is printed as @samp{\ } and a backslash as @samp{\\}.
7477 @GNUTAR{} offers seven distinct quoting styles, which can be selected
7478 using @option{--quoting-style} option:
7481 @item --quoting-style=@var{style}
7482 @opindex quoting-style
7484 Sets quoting style. Valid values for @var{style} argument are:
7485 literal, shell, shell-always, c, escape, locale, clocale.
7488 These styles are described in detail below. To illustrate their
7489 effect, we will use an imaginary tar archive @file{arch.tar}
7490 containing the following members:
7494 # 1. Contains horizontal tabulation character.
7496 # 2. Contains newline character
7499 # 3. Contains a space
7501 # 4. Contains double quotes
7503 # 5. Contains single quotes
7505 # 6. Contains a backslash character:
7510 Here is how usual @command{ls} command would have listed them, if they
7511 had existed in the current working directory:
7529 No quoting, display each character as is:
7533 $ @kbd{tar tf arch.tar --quoting-style=literal}
7546 Display characters the same way Bourne shell does:
7547 control characters, except @samp{\t} and @samp{\n}, are printed using
7548 backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a
7549 single quote is printed as @samp{\'}. If a name contains any quoted
7550 characters, it is enclosed in single quotes. In particular, if a name
7551 contains single quotes, it is printed as several single-quoted strings:
7555 $ @kbd{tar tf arch.tar --quoting-style=shell}
7558 './a'\''single'\''quote'
7568 Same as @samp{shell}, but the names are always enclosed in single
7573 $ @kbd{tar tf arch.tar --quoting-style=shell-always}
7576 './a'\''single'\''quote'
7586 Use the notation of the C programming language. All names are
7587 enclosed in double quotes. Control characters are quoted using
7588 backslash notations, double quotes are represented as @samp{\"},
7589 backslash characters are represented as @samp{\\}. Single quotes and
7590 spaces are not quoted:
7594 $ @kbd{tar tf arch.tar --quoting-style=c}
7598 "./a\"double\"quote"
7606 Control characters are printed using backslash notation, a space is
7607 printed as @samp{\ } and a backslash as @samp{\\}. This is the
7608 default quoting style, unless it was changed when configured the
7613 $ @kbd{tar tf arch.tar --quoting-style=escape}
7625 Control characters, single quote and backslash are printed using
7626 backslash notation. All names are quoted using left and right
7627 quotation marks, appropriate to the current locale. If it does not
7628 define quotation marks, use @samp{`} as left and @samp{'} as right
7629 quotation marks. Any occurrences of the right quotation mark in a
7630 name are escaped with @samp{\}, for example:
7636 $ @kbd{tar tf arch.tar --quoting-style=locale}
7639 `./a\'single\'quote'
7648 Same as @samp{locale}, but @samp{"} is used for both left and right
7649 quotation marks, if not provided by the currently selected locale:
7653 $ @kbd{tar tf arch.tar --quoting-style=clocale}
7657 "./a\"double\"quote"
7665 You can specify which characters should be quoted in addition to those
7666 implied by the current quoting style:
7669 @item --quote-chars=@var{string}
7670 Always quote characters from @var{string}, even if the selected
7671 quoting style would not quote them.
7674 For example, using @samp{escape} quoting (compare with the usual
7675 escape listing above):
7679 $ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'}
7690 To disable quoting of such additional characters, use the following
7694 @item --no-quote-chars=@var{string}
7695 Remove characters listed in @var{string} from the list of quoted
7696 characters set by the previous @option{--quote-chars} option.
7699 This option is particularly useful if you have added
7700 @option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS})
7701 and wish to disable it for the current invocation.
7703 Note, that @option{--no-quote-chars} does @emph{not} disable those
7704 characters that are quoted by default in the selected quoting style.
7707 @section Modifying File and Member Names
7709 @command{Tar} archives contain detailed information about files stored
7710 in them and full file names are part of that information. When
7711 storing file to an archive, its file name is recorded in it,
7712 along with the actual file contents. When restoring from an archive,
7713 a file is created on disk with exactly the same name as that stored
7714 in the archive. In the majority of cases this is the desired behavior
7715 of a file archiver. However, there are some cases when it is not.
7717 First of all, it is often unsafe to extract archive members with
7718 absolute file names or those that begin with a @file{../}. @GNUTAR{}
7719 takes special precautions when extracting such names and provides a
7720 special option for handling them, which is described in
7723 Secondly, you may wish to extract file names without some leading
7724 directory components, or with otherwise modified names. In other
7725 cases it is desirable to store files under differing names in the
7728 @GNUTAR{} provides several options for these needs.
7731 @opindex strip-components
7732 @item --strip-components=@var{number}
7733 Strip given @var{number} of leading components from file names before
7737 For example, suppose you have archived whole @file{/usr} hierarchy to
7738 a tar archive named @file{usr.tar}. Among other files, this archive
7739 contains @file{usr/include/stdlib.h}, which you wish to extract to
7740 the current working directory. To do so, you type:
7743 $ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h}
7746 The option @option{--strip=2} instructs @command{tar} to strip the
7747 two leading components (@file{usr/} and @file{include/}) off the file
7750 If you add the @option{--verbose} (@option{-v}) option to the invocation
7751 above, you will note that the verbose listing still contains the
7752 full file name, with the two removed components still in place. This
7753 can be inconvenient, so @command{tar} provides a special option for
7754 altering this behavior:
7756 @anchor{show-transformed-names}
7758 @opindex show-transformed-names
7759 @item --show-transformed-names
7760 Display file or member names with all requested transformations
7769 $ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h}
7770 usr/include/stdlib.h
7771 $ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h}
7776 Notice that in both cases the file @file{stdlib.h} is extracted to the
7777 current working directory, @option{--show-transformed-names} affects
7778 only the way its name is displayed.
7780 This option is especially useful for verifying whether the invocation
7781 will have the desired effect. Thus, before running
7784 $ @kbd{tar -x --strip=@var{n}}
7788 it is often advisable to run
7791 $ @kbd{tar -t -v --show-transformed --strip=@var{n}}
7795 to make sure the command will produce the intended results.
7797 In case you need to apply more complex modifications to the file name,
7798 @GNUTAR{} provides a general-purpose transformation option:
7803 @item --transform=@var{expression}
7804 @itemx --xform=@var{expression}
7805 Modify file names using supplied @var{expression}.
7809 The @var{expression} is a @command{sed}-like replace expression of the
7813 s/@var{regexp}/@var{replace}/[@var{flags}]
7817 where @var{regexp} is a @dfn{regular expression}, @var{replace} is a
7818 replacement for each file name part that matches @var{regexp}. Both
7819 @var{regexp} and @var{replace} are described in detail in
7820 @ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
7822 Any delimiter can be used in lieue of @samp{/}, the only requirement being
7823 that it be used consistently throughout the expression. For example,
7824 the following two expressions are equivalent:
7833 Changing delimiters is often useful when the @var{regex} contains
7834 slashes. For example, it is more convenient to write @code{s,/,-,} than
7837 As in @command{sed}, you can give several replace expressions,
7838 separated by a semicolon.
7840 Supported @var{flags} are:
7844 Apply the replacement to @emph{all} matches to the @var{regexp}, not
7848 Use case-insensitive matching
7851 @var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
7852 regexps, Extended regular expressions, Extended regular expressions,
7856 Only replace the @var{number}th match of the @var{regexp}.
7858 Note: the @acronym{POSIX} standard does not specify what should happen
7859 when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
7860 follows the GNU @command{sed} implementation in this regard, so
7861 the interaction is defined to be: ignore matches before the
7862 @var{number}th, and then match and replace all matches from the
7867 In addition, several @dfn{transformation scope} flags are supported,
7868 that control to what files transformations apply. These are:
7872 Apply transformation to regular archive members.
7875 Do not apply transformation to regular archive members.
7878 Apply transformation to symbolic link targets.
7881 Do not apply transformation to symbolic link targets.
7884 Apply transformation to hard link targets.
7887 Do not apply transformation to hard link targets.
7890 Default is @samp{rsh}, which means to apply tranformations to both archive
7891 members and targets of symbolic and hard links.
7893 Default scope flags can also be changed using @samp{flags=} statement
7894 in the transform expression. The flags set this way remain in force
7895 until next @samp{flags=} statement or end of expression, whichever
7896 occurs first. For example:
7899 --transform 'flags=S;s|^|/usr/local/|'
7902 Here are several examples of @option{--transform} usage:
7905 @item Extract @file{usr/} hierarchy into @file{usr/local/}:
7908 $ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar}
7911 @item Strip two leading directory components (equivalent to
7912 @option{--strip-components=2}):
7915 $ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
7918 @item Convert each file name to lower case:
7921 $ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
7924 @item Prepend @file{/prefix/} to each file name:
7927 $ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
7930 @item Archive the @file{/lib} directory, prepending @samp{/usr/local}
7931 to each archive member:
7934 $ @kbd{tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib}
7938 Notice the use of flags in the last example. The @file{/lib}
7939 directory often contains many symbolic links to files within it.
7940 It may look, for example, like this:
7944 drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
7945 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
7946 lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
7950 Using the expression @samp{s,^,/usr/local/,} would mean adding
7951 @samp{/usr/local} to both regular archive members and to link
7952 targets. In this case, @file{/lib/libc.so.6} would become:
7955 /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
7958 This is definitely not desired. To avoid this, the @samp{S} flag
7959 are used, which excludes symbolic link targets from filename
7960 transformations. The result is:
7963 $ @kbd{tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
7964 --show-transformed /lib}
7965 drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
7966 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
7967 lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 ->
7971 Unlike @option{--strip-components}, @option{--transform} can be used
7972 in any @GNUTAR{} operation mode. For example, the following command
7973 adds files to the archive while replacing the leading @file{usr/}
7974 component with @file{var/}:
7977 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /}
7980 To test @option{--transform} effect we suggest using
7981 @option{--show-transformed-names} option:
7984 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \
7985 --verbose --show-transformed-names /}
7988 If both @option{--strip-components} and @option{--transform} are used
7989 together, then @option{--transform} is applied first, and the required
7990 number of components is then stripped from its result.
7992 You can use as many @option{--transform} options in a single command
7993 line as you want. The specified expressions will then be applied in
7994 order of their appearance. For example, the following two invocations
7998 $ @kbd{tar -cf arch.tar --transform='s,/usr/var,/var/' \
7999 --transform='s,/usr/local,/usr/,'}
8000 $ @kbd{tar -cf arch.tar \
8001 --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'}
8005 @section Operating Only on New Files
8008 @cindex Excluding file by age
8009 @cindex Data Modification time, excluding files by
8010 @cindex Modification time, excluding files by
8011 @cindex Age, excluding files by
8012 The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
8013 @option{-N @var{date}}) option causes @command{tar} to only work on
8014 files whose data modification or status change times are newer than
8015 the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
8016 it is taken to be a file name; the data modification time of that file
8017 is used as the date. If you use this option when creating or appending
8018 to an archive, the archive will only include new files. If you use
8019 @option{--after-date} when extracting an archive, @command{tar} will
8020 only extract files newer than the @var{date} you specify.
8022 If you only want @command{tar} to make the date comparison based on
8023 modification of the file's data (rather than status
8024 changes), then use the @option{--newer-mtime=@var{date}} option.
8026 You may use these options with any operation. Note that these options
8027 differ from the @option{--update} (@option{-u}) operation in that they
8028 allow you to specify a particular date against which @command{tar} can
8029 compare when deciding whether or not to archive the files.
8034 @item --after-date=@var{date}
8035 @itemx --newer=@var{date}
8036 @itemx -N @var{date}
8037 Only store files newer than @var{date}.
8039 Acts on files only if their data modification or status change times are
8040 later than @var{date}. Use in conjunction with any operation.
8042 If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
8043 name; the data modification time of that file is used as the date.
8045 @opindex newer-mtime
8046 @item --newer-mtime=@var{date}
8047 Acts like @option{--after-date}, but only looks at data modification times.
8050 These options limit @command{tar} to operate only on files which have
8051 been modified after the date specified. A file's status is considered to have
8052 changed if its contents have been modified, or if its owner,
8053 permissions, and so forth, have been changed. (For more information on
8054 how to specify a date, see @ref{Date input formats}; remember that the
8055 entire date argument must be quoted if it contains any spaces.)
8057 Gurus would say that @option{--after-date} tests both the data
8058 modification time (@code{mtime}, the time the contents of the file
8059 were last modified) and the status change time (@code{ctime}, the time
8060 the file's status was last changed: owner, permissions, etc.@:)
8061 fields, while @option{--newer-mtime} tests only the @code{mtime}
8064 To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
8065 @code{ctime} and processes the file if either one is more recent than
8066 @var{date}, while @option{--newer-mtime} only checks @code{mtime} and
8067 disregards @code{ctime}. Neither does it use @code{atime} (the last time the
8068 contents of the file were looked at).
8070 Date specifiers can have embedded spaces. Because of this, you may need
8071 to quote date arguments to keep the shell from parsing them as separate
8072 arguments. For example, the following command will add to the archive
8073 all the files modified less than two days ago:
8076 $ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'}
8079 When any of these options is used with the option @option{--verbose}
8080 (@pxref{verbose tutorial}) @GNUTAR{} will try to convert the specified
8081 date back to its textual representation and compare that with the
8082 one given with the option. If the two dates differ, @command{tar} will
8083 print a warning saying what date it will use. This is to help user
8084 ensure he is using the right date. For example:
8088 $ @kbd{tar -c -f archive.tar --after-date='10 days ago' .}
8089 tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
8095 @strong{Please Note:} @option{--after-date} and @option{--newer-mtime}
8096 should not be used for incremental backups. @xref{Incremental Dumps},
8097 for proper way of creating incremental backups.
8101 @section Descending into Directories
8103 @cindex Avoiding recursion in directories
8104 @cindex Descending directories, avoiding
8105 @cindex Directories, avoiding recursion
8106 @cindex Recursion in directories, avoiding
8108 @FIXME{arrggh! this is still somewhat confusing to me. :-< }
8110 Usually, @command{tar} will recursively explore all directories (either
8111 those given on the command line or through the @option{--files-from}
8112 option) for the various files they contain. However, you may not always
8113 want @command{tar} to act this way.
8115 @opindex no-recursion
8116 The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
8117 into specified directories. If you specify @option{--no-recursion}, you can
8118 use the @command{find} utility for hunting through levels of directories to
8119 construct a list of file names which you could then pass to @command{tar}.
8120 @command{find} allows you to be more selective when choosing which files to
8121 archive; see @ref{files}, for more information on using @command{find} with
8122 @command{tar}, or look.
8125 @item --no-recursion
8126 Prevents @command{tar} from recursively descending directories.
8130 Requires @command{tar} to recursively descend directories.
8131 This is the default.
8134 When you use @option{--no-recursion}, @GNUTAR{} grabs
8135 directory entries themselves, but does not descend on them
8136 recursively. Many people use @command{find} for locating files they
8137 want to back up, and since @command{tar} @emph{usually} recursively
8138 descends on directories, they have to use the @samp{@w{-not -type d}}
8139 test in their @command{find} invocation (@pxref{Type, Type, Type test,
8140 find, Finding Files}), as they usually do not want all the files in a
8141 directory. They then use the @option{--files-from} option to archive
8142 the files located via @command{find}.
8144 The problem when restoring files archived in this manner is that the
8145 directories themselves are not in the archive; so the
8146 @option{--same-permissions} (@option{--preserve-permissions},
8147 @option{-p}) option does not affect them---while users might really
8148 like it to. Specifying @option{--no-recursion} is a way to tell
8149 @command{tar} to grab only the directory entries given to it, adding
8150 no new files on its own. To summarize, if you use @command{find} to
8151 create a list of files to be stored in an archive, use it as follows:
8155 $ @kbd{find @var{dir} @var{tests} | \
8156 tar -cf @var{archive} -T - --no-recursion}
8160 The @option{--no-recursion} option also applies when extracting: it
8161 causes @command{tar} to extract only the matched directory entries, not
8162 the files under those directories.
8164 The @option{--no-recursion} option also affects how globbing patterns
8165 are interpreted (@pxref{controlling pattern-matching}).
8167 The @option{--no-recursion} and @option{--recursion} options apply to
8168 later options and operands, and can be overridden by later occurrences
8169 of @option{--no-recursion} and @option{--recursion}. For example:
8172 $ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
8176 creates an archive with one entry for @file{grape}, and the recursive
8177 contents of @file{grape/concord}, but no entries under @file{grape}
8178 other than @file{grape/concord}.
8181 @section Crossing File System Boundaries
8182 @cindex File system boundaries, not crossing
8185 @command{tar} will normally automatically cross file system boundaries in
8186 order to archive files which are part of a directory tree. You can
8187 change this behavior by running @command{tar} and specifying
8188 @option{--one-file-system}. This option only affects files that are
8189 archived because they are in a directory that is being archived;
8190 @command{tar} will still archive files explicitly named on the command line
8191 or through @option{--files-from}, regardless of where they reside.
8194 @opindex one-file-system
8195 @item --one-file-system
8196 Prevents @command{tar} from crossing file system boundaries when
8197 archiving. Use in conjunction with any write operation.
8200 The @option{--one-file-system} option causes @command{tar} to modify its
8201 normal behavior in archiving the contents of directories. If a file in
8202 a directory is not on the same file system as the directory itself, then
8203 @command{tar} will not archive that file. If the file is a directory
8204 itself, @command{tar} will not archive anything beneath it; in other words,
8205 @command{tar} will not cross mount points.
8207 This option is useful for making full or incremental archival backups of
8208 a file system. If this option is used in conjunction with
8209 @option{--verbose} (@option{-v}), files that are excluded are
8210 mentioned by name on the standard error.
8213 * directory:: Changing Directory
8214 * absolute:: Absolute File Names
8218 @subsection Changing the Working Directory
8220 @FIXME{need to read over this node now for continuity; i've switched
8221 things around some.}
8223 @cindex Changing directory mid-stream
8224 @cindex Directory, changing mid-stream
8225 @cindex Working directory, specifying
8226 To change the working directory in the middle of a list of file names,
8227 either on the command line or in a file specified using
8228 @option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
8229 This will change the working directory to the specified directory
8230 after that point in the list.
8234 @item --directory=@var{directory}
8235 @itemx -C @var{directory}
8236 Changes the working directory in the middle of a command line.
8242 $ @kbd{tar -c -f jams.tar grape prune -C food cherry}
8246 will place the files @file{grape} and @file{prune} from the current
8247 directory into the archive @file{jams.tar}, followed by the file
8248 @file{cherry} from the directory @file{food}. This option is especially
8249 useful when you have several widely separated files that you want to
8250 store in the same archive.
8252 Note that the file @file{cherry} is recorded in the archive under the
8253 precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the
8254 archive will contain three files that all appear to have come from the
8255 same directory; if the archive is extracted with plain @samp{tar
8256 --extract}, all three files will be written in the current directory.
8258 Contrast this with the command,
8261 $ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
8265 which records the third file in the archive under the name
8266 @file{red/cherry} so that, if the archive is extracted using
8267 @samp{tar --extract}, the third file will be written in a subdirectory
8268 named @file{orange-colored}.
8270 You can use the @option{--directory} option to make the archive
8271 independent of the original name of the directory holding the files.
8272 The following command places the files @file{/etc/passwd},
8273 @file{/etc/hosts}, and @file{/lib/libc.a} into the archive
8277 $ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
8281 However, the names of the archive members will be exactly what they were
8282 on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}.
8283 They will not appear to be related by file name to the original
8284 directories where those files were located.
8286 Note that @option{--directory} options are interpreted consecutively. If
8287 @option{--directory} specifies a relative file name, it is interpreted
8288 relative to the then current directory, which might not be the same as
8289 the original current working directory of @command{tar}, due to a previous
8290 @option{--directory} option.
8292 When using @option{--files-from} (@pxref{files}), you can put various
8293 @command{tar} options (including @option{-C}) in the file list. Notice,
8294 however, that in this case the option and its argument may not be
8295 separated by whitespace. If you use short option, its argument must
8296 either follow the option letter immediately, without any intervening
8297 whitespace, or occupy the next line. Otherwise, if you use long
8298 option, separate its argument by an equal sign.
8300 For instance, the file list for the above example will be:
8313 To use it, you would invoke @command{tar} as follows:
8316 $ @kbd{tar -c -f foo.tar --files-from list}
8319 The interpretation of @option{--directory} is disabled by
8320 @option{--null} option.
8323 @subsection Absolute File Names
8327 @opindex absolute-names
8328 @item --absolute-names
8330 Do not strip leading slashes from file names, and permit file names
8331 containing a @file{..} file name component.
8334 By default, @GNUTAR{} drops a leading @samp{/} on
8335 input or output, and complains about file names containing a @file{..}
8336 component. This option turns off this behavior.
8338 When @command{tar} extracts archive members from an archive, it strips any
8339 leading slashes (@samp{/}) from the member name. This causes absolute
8340 member names in the archive to be treated as relative file names. This
8341 allows you to have such members extracted wherever you want, instead of
8342 being restricted to extracting the member in the exact directory named
8343 in the archive. For example, if the archive member has the name
8344 @file{/etc/passwd}, @command{tar} will extract it as if the name were
8345 really @file{etc/passwd}.
8347 File names containing @file{..} can cause problems when extracting, so
8348 @command{tar} normally warns you about such files when creating an
8349 archive, and rejects attempts to extracts such files.
8351 Other @command{tar} programs do not do this. As a result, if you
8352 create an archive whose member names start with a slash, they will be
8353 difficult for other people with a non-@GNUTAR{}
8354 program to use. Therefore, @GNUTAR{} also strips
8355 leading slashes from member names when putting members into the
8356 archive. For example, if you ask @command{tar} to add the file
8357 @file{/bin/ls} to an archive, it will do so, but the member name will
8358 be @file{bin/ls}.@footnote{A side effect of this is that when
8359 @option{--create} is used with @option{--verbose} the resulting output
8360 is not, generally speaking, the same as the one you'd get running
8361 @kbd{tar --list} command. This may be important if you use some
8362 scripts for comparing both outputs. @xref{listing member and file names},
8363 for the information on how to handle this case.}
8365 If you use the @option{--absolute-names} (@option{-P}) option,
8366 @command{tar} will do none of these transformations.
8368 To archive or extract files relative to the root directory, specify
8369 the @option{--absolute-names} (@option{-P}) option.
8371 Normally, @command{tar} acts on files relative to the working
8372 directory---ignoring superior directory names when archiving, and
8373 ignoring leading slashes when extracting.
8375 When you specify @option{--absolute-names} (@option{-P}),
8376 @command{tar} stores file names including all superior directory
8377 names, and preserves leading slashes. If you only invoked
8378 @command{tar} from the root directory you would never need the
8379 @option{--absolute-names} option, but using this option
8380 may be more convenient than switching to root.
8382 @FIXME{Should be an example in the tutorial/wizardry section using this
8383 to transfer files between systems.}
8385 @FIXME{Is write access an issue?}
8388 @item --absolute-names
8389 Preserves full file names (including superior directory names) when
8390 archiving files. Preserves leading slash when extracting files.
8394 @FIXME{this is still horrible; need to talk with dan on monday.}
8396 @command{tar} prints out a message about removing the @samp{/} from
8397 file names. This message appears once per @GNUTAR{}
8398 invocation. It represents something which ought to be told; ignoring
8399 what it means can cause very serious surprises, later.
8401 Some people, nevertheless, do not want to see this message. Wanting to
8402 play really dangerously, one may of course redirect @command{tar} standard
8403 error to the sink. For example, under @command{sh}:
8406 $ @kbd{tar -c -f archive.tar /home 2> /dev/null}
8410 Another solution, both nicer and simpler, would be to change to
8411 the @file{/} directory first, and then avoid absolute notation.
8415 $ @kbd{tar -c -f archive.tar -C / home}
8418 @include getdate.texi
8421 @chapter Controlling the Archive Format
8423 @cindex Tar archive formats
8424 Due to historical reasons, there are several formats of tar archives.
8425 All of them are based on the same principles, but have some subtle
8426 differences that often make them incompatible with each other.
8428 GNU tar is able to create and handle archives in a variety of formats.
8429 The most frequently used formats are (in alphabetical order):
8433 Format used by @GNUTAR{} versions up to 1.13.25. This format derived
8434 from an early @acronym{POSIX} standard, adding some improvements such as
8435 sparse file handling and incremental archives. Unfortunately these
8436 features were implemented in a way incompatible with other archive
8439 Archives in @samp{gnu} format are able to hold file names of unlimited
8443 Format used by @GNUTAR{} of versions prior to 1.12.
8446 Archive format, compatible with the V7 implementation of tar. This
8447 format imposes a number of limitations. The most important of them
8451 @item The maximum length of a file name is limited to 99 characters.
8452 @item The maximum length of a symbolic link is limited to 99 characters.
8453 @item It is impossible to store special files (block and character
8454 devices, fifos etc.)
8455 @item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777
8457 @item V7 archives do not contain symbolic ownership information (user
8458 and group name of the file owner).
8461 This format has traditionally been used by Automake when producing
8462 Makefiles. This practice will change in the future, in the meantime,
8463 however this means that projects containing file names more than 99
8464 characters long will not be able to use @GNUTAR{} @value{VERSION} and
8465 Automake prior to 1.9.
8468 Archive format defined by @acronym{POSIX.1-1988} specification. It stores
8469 symbolic ownership information. It is also able to store
8470 special files. However, it imposes several restrictions as well:
8473 @item The maximum length of a file name is limited to 256 characters,
8474 provided that the file name can be split at a directory separator in
8475 two parts, first of them being at most 155 bytes long. So, in most
8476 cases the maximum file name length will be shorter than 256
8478 @item The maximum length of a symbolic link name is limited to
8480 @item Maximum size of a file the archive is able to accommodate
8482 @item Maximum value of UID/GID is 2097151.
8483 @item Maximum number of bits in device major and minor numbers is 21.
8487 Format used by J@"org Schilling @command{star}
8488 implementation. @GNUTAR{} is able to read @samp{star} archives but
8489 currently does not produce them.
8492 Archive format defined by @acronym{POSIX.1-2001} specification. This is the
8493 most flexible and feature-rich format. It does not impose any
8494 restrictions on file sizes or file name lengths. This format is quite
8495 recent, so not all tar implementations are able to handle it properly.
8496 However, this format is designed in such a way that any tar
8497 implementation able to read @samp{ustar} archives will be able to read
8498 most @samp{posix} archives as well, with the only exception that any
8499 additional information (such as long file names etc.) will in such
8500 case be extracted as plain text files along with the files it refers to.
8502 This archive format will be the default format for future versions
8507 The following table summarizes the limitations of each of these
8510 @multitable @columnfractions .10 .20 .20 .20 .20
8511 @headitem Format @tab UID @tab File Size @tab File Name @tab Devn
8512 @item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8513 @item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8514 @item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
8515 @item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
8516 @item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
8519 The default format for @GNUTAR{} is defined at compilation
8520 time. You may check it by running @command{tar --help}, and examining
8521 the last lines of its output. Usually, @GNUTAR{} is configured
8522 to create archives in @samp{gnu} format, however, future version will
8523 switch to @samp{posix}.
8526 * Compression:: Using Less Space through Compression
8527 * Attributes:: Handling File Attributes
8528 * Portability:: Making @command{tar} Archives More Portable
8529 * cpio:: Comparison of @command{tar} and @command{cpio}
8533 @section Using Less Space through Compression
8536 * gzip:: Creating and Reading Compressed Archives
8537 * sparse:: Archiving Sparse Files
8541 @subsection Creating and Reading Compressed Archives
8542 @cindex Compressed archives
8543 @cindex Storing archives in compressed format
8550 @GNUTAR{} is able to create and read compressed archives. It supports
8551 @command{gzip}, @command{bzip2}, @command{lzma} and @command{lzop} compression
8552 programs. For backward compatibility, it also supports
8553 @command{compress} command, although we strongly recommend against
8554 using it, because it is by far less effective than other compression
8555 programs@footnote{It also had patent problems in the past.}.
8557 Creating a compressed archive is simple: you just specify a
8558 @dfn{compression option} along with the usual archive creation
8559 commands. The compression option is @option{-z} (@option{--gzip}) to
8560 create a @command{gzip} compressed archive, @option{-j}
8561 (@option{--bzip2}) to create a @command{bzip2} compressed archive,
8562 @option{-J} (@option{--xz}) to create an @asis{XZ} archive,
8563 @option{--lzma} to create an @asis{LZMA} compressed
8564 archive, @option{--lzop} to create an @asis{LSOP} archive, and
8565 @option{-Z} (@option{--compress}) to use @command{compress} program.
8569 $ @kbd{tar cfz archive.tar.gz .}
8572 You can also let @GNUTAR{} select the compression program basing on
8573 the suffix of the archive file name. This is done using
8574 @option{--auto-compress} (@option{-a}) command line option. For
8575 example, the following invocation will use @command{bzip2} for
8579 $ @kbd{tar cfa archive.tar.bz2 .}
8583 whereas the following one will use @command{lzma}:
8586 $ @kbd{tar cfa archive.tar.lzma .}
8589 For a complete list of file name suffixes recognized by @GNUTAR{},
8590 @ref{auto-compress}.
8592 Reading compressed archive is even simpler: you don't need to specify
8593 any additional options as @GNUTAR{} recognizes its format
8594 automatically. Thus, the following commands will list and extract the
8595 archive created in previous example:
8598 # List the compressed archive
8599 $ @kbd{tar tf archive.tar.gz}
8600 # Extract the compressed archive
8601 $ @kbd{tar xf archive.tar.gz}
8604 The format recognition algorithm is based on @dfn{signatures}, a
8605 special byte sequences in the beginning of file, that are specific for
8606 certain compression formats. If this approach fails, @command{tar}
8607 falls back to using archive name suffix to determine its format
8608 (@xref{auto-compress}, for a list of recognized suffixes).
8610 The only case when you have to specify a decompression option while
8611 reading the archive is when reading from a pipe or from a tape drive
8612 that does not support random access. However, in this case @GNUTAR{}
8613 will indicate which option you should use. For example:
8616 $ @kbd{cat archive.tar.gz | tar tf -}
8617 tar: Archive is compressed. Use -z option
8618 tar: Error is not recoverable: exiting now
8621 If you see such diagnostics, just add the suggested option to the
8622 invocation of @GNUTAR{}:
8625 $ @kbd{cat archive.tar.gz | tar tfz -}
8628 Notice also, that there are several restrictions on operations on
8629 compressed archives. First of all, compressed archives cannot be
8630 modified, i.e., you cannot update (@option{--update} (@option{-u}))
8631 them or delete (@option{--delete}) members from them or
8632 add (@option{--append} (@option{-r})) members to them. Likewise, you
8633 cannot append another @command{tar} archive to a compressed archive using
8634 @option{--concatenate} (@option{-A})). Secondly, multi-volume
8635 archives cannot be compressed.
8637 The following table summarizes compression options used by @GNUTAR{}.
8640 @anchor{auto-compress}
8641 @opindex auto-compress
8642 @item --auto-compress
8644 Select a compression program to use by the archive file name
8645 suffix. The following suffixes are recognized:
8647 @multitable @columnfractions 0.3 0.6
8648 @headitem Suffix @tab Compression program
8649 @item @samp{.gz} @tab @command{gzip}
8650 @item @samp{.tgz} @tab @command{gzip}
8651 @item @samp{.taz} @tab @command{gzip}
8652 @item @samp{.Z} @tab @command{compress}
8653 @item @samp{.taZ} @tab @command{compress}
8654 @item @samp{.bz2} @tab @command{bzip2}
8655 @item @samp{.tz2} @tab @command{bzip2}
8656 @item @samp{.tbz2} @tab @command{bzip2}
8657 @item @samp{.tbz} @tab @command{bzip2}
8658 @item @samp{.lzma} @tab @command{lzma}
8659 @item @samp{.tlz} @tab @command{lzma}
8660 @item @samp{.lzo} @tab @command{lzop}
8661 @item @samp{.xz} @tab @command{xz}
8669 Filter the archive through @command{gzip}.
8671 You can use @option{--gzip} and @option{--gunzip} on physical devices
8672 (tape drives, etc.) and remote files as well as on normal files; data
8673 to or from such devices or remote files is reblocked by another copy
8674 of the @command{tar} program to enforce the specified (or default) record
8675 size. The default compression parameters are used; if you need to
8676 override them, set @env{GZIP} environment variable, e.g.:
8679 $ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
8683 Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
8684 @command{gzip} explicitly:
8687 $ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
8690 @cindex corrupted archives
8691 About corrupted compressed archives: @command{gzip}'ed files have no
8692 redundancy, for maximum compression. The adaptive nature of the
8693 compression scheme means that the compression tables are implicitly
8694 spread all over the archive. If you lose a few blocks, the dynamic
8695 construction of the compression tables becomes unsynchronized, and there
8696 is little chance that you could recover later in the archive.
8698 There are pending suggestions for having a per-volume or per-file
8699 compression in @GNUTAR{}. This would allow for viewing the
8700 contents without decompression, and for resynchronizing decompression at
8701 every volume or file, in case of corrupted archives. Doing so, we might
8702 lose some compressibility. But this would have make recovering easier.
8703 So, there are pros and cons. We'll see!
8708 Filter the archive through @code{xz}. Otherwise like
8713 Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
8717 Filter the archive through @command{lzma}. Otherwise like @option{--gzip}.
8721 Filter the archive through @command{lzop}. Otherwise like
8729 Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
8731 @opindex use-compress-program
8732 @item --use-compress-program=@var{prog}
8733 @itemx -I=@var{prog}
8734 Use external compression program @var{prog}. Use this option if you
8735 have a compression program that @GNUTAR{} does not support. There
8736 are two requirements to which @var{prog} should comply:
8738 First, when called without options, it should read data from standard
8739 input, compress it and output it on standard output.
8741 Secondly, if called with @option{-d} argument, it should do exactly
8742 the opposite, i.e., read the compressed data from the standard input
8743 and produce uncompressed data on the standard output.
8746 @cindex gpg, using with tar
8747 @cindex gnupg, using with tar
8748 @cindex Using encrypted archives
8749 The @option{--use-compress-program} option, in particular, lets you
8750 implement your own filters, not necessarily dealing with
8751 compression/decompression. For example, suppose you wish to implement
8752 PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
8753 gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard
8754 Manual}). The following script does that:
8760 -d) gpg --decrypt - | gzip -d -c;;
8761 '') gzip -c | gpg -s ;;
8762 *) echo "Unknown option $1">&2; exit 1;;
8767 Suppose you name it @file{gpgz} and save it somewhere in your
8768 @env{PATH}. Then the following command will create a compressed
8769 archive signed with your private key:
8772 $ @kbd{tar -cf foo.tar.gpgz -Igpgz .}
8776 Likewise, the command below will list its contents:
8779 $ @kbd{tar -tf foo.tar.gpgz -Igpgz .}
8783 The above is based on the following discussion:
8785 I have one question, or maybe it's a suggestion if there isn't a way
8786 to do it now. I would like to use @option{--gzip}, but I'd also like
8787 the output to be fed through a program like @acronym{GNU}
8788 @command{ecc} (actually, right now that's @samp{exactly} what I'd like
8789 to use :-)), basically adding ECC protection on top of compression.
8790 It seems as if this should be quite easy to do, but I can't work out
8791 exactly how to go about it. Of course, I can pipe the standard output
8792 of @command{tar} through @command{ecc}, but then I lose (though I
8793 haven't started using it yet, I confess) the ability to have
8794 @command{tar} use @command{rmt} for it's I/O (I think).
8796 I think the most straightforward thing would be to let me specify a
8797 general set of filters outboard of compression (preferably ordered,
8798 so the order can be automatically reversed on input operations, and
8799 with the options they require specifiable), but beggars shouldn't be
8800 choosers and anything you decide on would be fine with me.
8802 By the way, I like @command{ecc} but if (as the comments say) it can't
8803 deal with loss of block sync, I'm tempted to throw some time at adding
8804 that capability. Supposing I were to actually do such a thing and
8805 get it (apparently) working, do you accept contributed changes to
8806 utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
8808 Isn't that exactly the role of the
8809 @option{--use-compress-prog=@var{program}} option?
8810 I never tried it myself, but I suspect you may want to write a
8811 @var{prog} script or program able to filter stdin to stdout to
8812 way you want. It should recognize the @option{-d} option, for when
8813 extraction is needed rather than creation.
8815 It has been reported that if one writes compressed data (through the
8816 @option{--gzip} or @option{--compress} options) to a DLT and tries to use
8817 the DLT compression mode, the data will actually get bigger and one will
8818 end up with less space on the tape.
8822 @subsection Archiving Sparse Files
8823 @cindex Sparse Files
8825 Files in the file system occasionally have @dfn{holes}. A @dfn{hole}
8826 in a file is a section of the file's contents which was never written.
8827 The contents of a hole reads as all zeros. On many operating systems,
8828 actual disk storage is not allocated for holes, but they are counted
8829 in the length of the file. If you archive such a file, @command{tar}
8830 could create an archive longer than the original. To have @command{tar}
8831 attempt to recognize the holes in a file, use @option{--sparse}
8832 (@option{-S}). When you use this option, then, for any file using
8833 less disk space than would be expected from its length, @command{tar}
8834 searches the file for consecutive stretches of zeros. It then records
8835 in the archive for the file where the consecutive stretches of zeros
8836 are, and only archives the ``real contents'' of the file. On
8837 extraction (using @option{--sparse} is not needed on extraction) any
8838 such files have holes created wherever the continuous stretches of zeros
8839 were found. Thus, if you use @option{--sparse}, @command{tar} archives
8840 won't take more space than the original.
8846 This option instructs @command{tar} to test each file for sparseness
8847 before attempting to archive it. If the file is found to be sparse it
8848 is treated specially, thus allowing to decrease the amount of space
8849 used by its image in the archive.
8851 This option is meaningful only when creating or updating archives. It
8852 has no effect on extraction.
8855 Consider using @option{--sparse} when performing file system backups,
8856 to avoid archiving the expanded forms of files stored sparsely in the
8859 Even if your system has no sparse files currently, some may be
8860 created in the future. If you use @option{--sparse} while making file
8861 system backups as a matter of course, you can be assured the archive
8862 will never take more space on the media than the files take on disk
8863 (otherwise, archiving a disk filled with sparse files might take
8864 hundreds of tapes). @xref{Incremental Dumps}.
8866 However, be aware that @option{--sparse} option presents a serious
8867 drawback. Namely, in order to determine if the file is sparse
8868 @command{tar} has to read it before trying to archive it, so in total
8869 the file is read @strong{twice}. So, always bear in mind that the
8870 time needed to process all files with this option is roughly twice
8871 the time needed to archive them without it.
8872 @FIXME{A technical note:
8874 Programs like @command{dump} do not have to read the entire file; by
8875 examining the file system directly, they can determine in advance
8876 exactly where the holes are and thus avoid reading through them. The
8877 only data it need read are the actual allocated data blocks.
8878 @GNUTAR{} uses a more portable and straightforward
8879 archiving approach, it would be fairly difficult that it does
8880 otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, on
8884 What I did say is that you cannot tell the difference between a hole and an
8885 equivalent number of nulls without reading raw blocks. @code{st_blocks} at
8886 best tells you how many holes there are; it doesn't tell you @emph{where}.
8887 Just as programs may, conceivably, care what @code{st_blocks} is (care
8888 to name one that does?), they may also care where the holes are (I have
8889 no examples of this one either, but it's equally imaginable).
8891 I conclude from this that good archivers are not portable. One can
8892 arguably conclude that if you want a portable program, you can in good
8893 conscience restore files with as many holes as possible, since you can't
8898 @cindex sparse formats, defined
8899 When using @samp{POSIX} archive format, @GNUTAR{} is able to store
8900 sparse files using in three distinct ways, called @dfn{sparse
8901 formats}. A sparse format is identified by its @dfn{number},
8902 consisting, as usual of two decimal numbers, delimited by a dot. By
8903 default, format @samp{1.0} is used. If, for some reason, you wish to
8904 use an earlier format, you can select it using
8905 @option{--sparse-version} option.
8908 @opindex sparse-version
8909 @item --sparse-version=@var{version}
8911 Select the format to store sparse files in. Valid @var{version} values
8912 are: @samp{0.0}, @samp{0.1} and @samp{1.0}. @xref{Sparse Formats},
8913 for a detailed description of each format.
8916 Using @option{--sparse-format} option implies @option{--sparse}.
8919 @section Handling File Attributes
8922 When @command{tar} reads files, it updates their access times. To
8923 avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
8924 reset the access time retroactively or avoid changing it in the first
8927 Handling of file attributes
8930 @opindex atime-preserve
8931 @item --atime-preserve
8932 @itemx --atime-preserve=replace
8933 @itemx --atime-preserve=system
8934 Preserve the access times of files that are read. This works only for
8935 files that you own, unless you have superuser privileges.
8937 @option{--atime-preserve=replace} works on most systems, but it also
8938 restores the data modification time and updates the status change
8939 time. Hence it doesn't interact with incremental dumps nicely
8940 (@pxref{Incremental Dumps}), and it can set access or data modification times
8941 incorrectly if other programs access the file while @command{tar} is
8944 @option{--atime-preserve=system} avoids changing the access time in
8945 the first place, if the operating system supports this.
8946 Unfortunately, this may or may not work on any given operating system
8947 or file system. If @command{tar} knows for sure it won't work, it
8948 complains right away.
8950 Currently @option{--atime-preserve} with no operand defaults to
8951 @option{--atime-preserve=replace}, but this is intended to change to
8952 @option{--atime-preserve=system} when the latter is better-supported.
8957 Do not extract data modification time.
8959 When this option is used, @command{tar} leaves the data modification times
8960 of the files it extracts as the times when the files were extracted,
8961 instead of setting it to the times recorded in the archive.
8963 This option is meaningless with @option{--list} (@option{-t}).
8967 Create extracted files with the same ownership they have in the
8970 This is the default behavior for the superuser,
8971 so this option is meaningful only for non-root users, when @command{tar}
8972 is executed on those systems able to give files away. This is
8973 considered as a security flaw by many people, at least because it
8974 makes quite difficult to correctly account users for the disk space
8975 they occupy. Also, the @code{suid} or @code{sgid} attributes of
8976 files are easily and silently lost when files are given away.
8978 When writing an archive, @command{tar} writes the user @acronym{ID} and user name
8979 separately. If it can't find a user name (because the user @acronym{ID} is not
8980 in @file{/etc/passwd}), then it does not write one. When restoring,
8981 it tries to look the name (if one was written) up in
8982 @file{/etc/passwd}. If it fails, then it uses the user @acronym{ID} stored in
8983 the archive instead.
8985 @opindex no-same-owner
8986 @item --no-same-owner
8988 Do not attempt to restore ownership when extracting. This is the
8989 default behavior for ordinary users, so this option has an effect
8990 only for the superuser.
8992 @opindex numeric-owner
8993 @item --numeric-owner
8994 The @option{--numeric-owner} option allows (ANSI) archives to be written
8995 without user/group name information or such information to be ignored
8996 when extracting. It effectively disables the generation and/or use
8997 of user/group name information. This option forces extraction using
8998 the numeric ids from the archive, ignoring the names.
9000 This is useful in certain circumstances, when restoring a backup from
9001 an emergency floppy with different passwd/group files for example.
9002 It is otherwise impossible to extract files with the right ownerships
9003 if the password file in use during the extraction does not match the
9004 one belonging to the file system(s) being extracted. This occurs,
9005 for example, if you are restoring your files after a major crash and
9006 had booted from an emergency floppy with no password file or put your
9007 disk into another machine to do the restore.
9009 The numeric ids are @emph{always} saved into @command{tar} archives.
9010 The identifying names are added at create time when provided by the
9011 system, unless @option{--old-archive} (@option{-o}) is used. Numeric ids could be
9012 used when moving archives between a collection of machines using
9013 a centralized management for attribution of numeric ids to users
9014 and groups. This is often made through using the NIS capabilities.
9016 When making a @command{tar} file for distribution to other sites, it
9017 is sometimes cleaner to use a single owner for all files in the
9018 distribution, and nicer to specify the write permission bits of the
9019 files as stored in the archive independently of their actual value on
9020 the file system. The way to prepare a clean distribution is usually
9021 to have some Makefile rule creating a directory, copying all needed
9022 files in that directory, then setting ownership and permissions as
9023 wanted (there are a lot of possible schemes), and only then making a
9024 @command{tar} archive out of this directory, before cleaning
9025 everything out. Of course, we could add a lot of options to
9026 @GNUTAR{} for fine tuning permissions and ownership.
9027 This is not the good way, I think. @GNUTAR{} is
9028 already crowded with options and moreover, the approach just explained
9029 gives you a great deal of control already.
9031 @xopindex{same-permissions, short description}
9032 @xopindex{preserve-permissions, short description}
9034 @itemx --same-permissions
9035 @itemx --preserve-permissions
9036 Extract all protection information.
9038 This option causes @command{tar} to set the modes (access permissions) of
9039 extracted files exactly as recorded in the archive. If this option
9040 is not used, the current @code{umask} setting limits the permissions
9041 on extracted files. This option is by default enabled when
9042 @command{tar} is executed by a superuser.
9045 This option is meaningless with @option{--list} (@option{-t}).
9049 Same as both @option{--same-permissions} and @option{--same-order}.
9051 This option is deprecated, and will be removed in @GNUTAR{} version 1.23.
9056 @section Making @command{tar} Archives More Portable
9058 Creating a @command{tar} archive on a particular system that is meant to be
9059 useful later on many other machines and with other versions of @command{tar}
9060 is more challenging than you might think. @command{tar} archive formats
9061 have been evolving since the first versions of Unix. Many such formats
9062 are around, and are not always compatible with each other. This section
9063 discusses a few problems, and gives some advice about making @command{tar}
9064 archives more portable.
9066 One golden rule is simplicity. For example, limit your @command{tar}
9067 archives to contain only regular files and directories, avoiding
9068 other kind of special files. Do not attempt to save sparse files or
9069 contiguous files as such. Let's discuss a few more problems, in turn.
9071 @FIXME{Discuss GNU extensions (incremental backups, multi-volume
9072 archives and archive labels) in GNU and PAX formats.}
9075 * Portable Names:: Portable Names
9076 * dereference:: Symbolic Links
9077 * hard links:: Hard Links
9078 * old:: Old V7 Archives
9079 * ustar:: Ustar Archives
9080 * gnu:: GNU and old GNU format archives.
9081 * posix:: @acronym{POSIX} archives
9082 * Checksumming:: Checksumming Problems
9083 * Large or Negative Values:: Large files, negative time stamps, etc.
9084 * Other Tars:: How to Extract GNU-Specific Data Using
9085 Other @command{tar} Implementations
9088 @node Portable Names
9089 @subsection Portable Names
9091 Use portable file and member names. A name is portable if it contains
9092 only @acronym{ASCII} letters and digits, @samp{/}, @samp{.}, @samp{_}, and
9093 @samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
9094 contain @samp{/-}. Avoid deep directory nesting. For portability to
9095 old Unix hosts, limit your file name components to 14 characters or
9098 If you intend to have your @command{tar} archives to be read under
9099 MSDOS, you should not rely on case distinction for file names, and you
9100 might use the @acronym{GNU} @command{doschk} program for helping you
9101 further diagnosing illegal MSDOS names, which are even more limited
9105 @subsection Symbolic Links
9106 @cindex File names, using symbolic links
9107 @cindex Symbolic link as file name
9109 @opindex dereference
9110 Normally, when @command{tar} archives a symbolic link, it writes a
9111 block to the archive naming the target of the link. In that way, the
9112 @command{tar} archive is a faithful record of the file system contents.
9113 @option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
9114 @command{tar} to archive the files symbolic links point to, instead of
9115 the links themselves. When this option is used, when @command{tar}
9116 encounters a symbolic link, it will archive the linked-to file,
9117 instead of simply recording the presence of a symbolic link.
9119 The name under which the file is stored in the file system is not
9120 recorded in the archive. To record both the symbolic link name and
9121 the file name in the system, archive the file under both names. If
9122 all links were recorded automatically by @command{tar}, an extracted file
9123 might be linked to a file name that no longer exists in the file
9126 If a linked-to file is encountered again by @command{tar} while creating
9127 the same archive, an entire second copy of it will be stored. (This
9128 @emph{might} be considered a bug.)
9130 So, for portable archives, do not archive symbolic links as such,
9131 and use @option{--dereference} (@option{-h}): many systems do not support
9132 symbolic links, and moreover, your distribution might be unusable if
9133 it contains unresolved symbolic links.
9136 @subsection Hard Links
9138 @cindex File names, using hard links
9139 @cindex hard links, dereferencing
9140 @cindex dereferencing hard links
9142 Normally, when @command{tar} archives a hard link, it writes a
9143 block to the archive naming the target of the link (a @samp{1} type
9144 block). In that way, the actual file contents is stored in file only
9145 once. For example, consider the following two files:
9150 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 one
9151 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 jeden
9155 Here, @file{jeden} is a link to @file{one}. When archiving this
9156 directory with a verbose level 2, you will get an output similar to
9160 $ tar cfvv ../archive.tar .
9161 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9162 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9163 hrw-r--r-- gray/staff 0 2007-10-30 15:11 ./one link to ./jeden
9166 The last line shows that, instead of storing two copies of the file,
9167 @command{tar} stored it only once, under the name @file{jeden}, and
9168 stored file @file{one} as a hard link to this file.
9170 It may be important to know that all hard links to the given file are
9171 stored in the archive. For example, this may be necessary for exact
9172 reproduction of the file system. The following option does that:
9175 @xopindex{check-links, described}
9178 Check the number of links dumped for each processed file. If this
9179 number does not match the total number of hard links for the file, print
9183 For example, trying to archive only file @file{jeden} with this option
9184 produces the following diagnostics:
9187 $ tar -c -f ../archive.tar jeden
9188 tar: Missing links to `jeden'.
9191 Although creating special records for hard links helps keep a faithful
9192 record of the file system contents and makes archives more compact, it
9193 may present some difficulties when extracting individual members from
9194 the archive. For example, trying to extract file @file{one} from the
9195 archive created in previous examples produces, in the absense of file
9199 $ tar xf archive.tar ./one
9200 tar: ./one: Cannot hard link to `./jeden': No such file or directory
9201 tar: Error exit delayed from previous errors
9204 The reason for this behavior is that @command{tar} cannot seek back in
9205 the archive to the previous member (in this case, @file{one}), to
9206 extract it@footnote{There are plans to fix this in future releases.}.
9207 If you wish to avoid such problems at the cost of a bigger archive,
9208 use the following option:
9211 @xopindex{hard-dereference, described}
9212 @item --hard-dereference
9213 Dereference hard links and store the files they refer to.
9216 For example, trying this option on our two sample files, we get two
9217 copies in the archive, each of which can then be extracted
9218 independently of the other:
9222 $ tar -c -vv -f ../archive.tar --hard-dereference .
9223 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9224 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9225 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./one
9230 @subsection Old V7 Archives
9231 @cindex Format, old style
9232 @cindex Old style format
9233 @cindex Old style archives
9234 @cindex v7 archive format
9236 Certain old versions of @command{tar} cannot handle additional
9237 information recorded by newer @command{tar} programs. To create an
9238 archive in V7 format (not ANSI), which can be read by these old
9239 versions, specify the @option{--format=v7} option in
9240 conjunction with the @option{--create} (@option{-c}) (@command{tar} also
9241 accepts @option{--portability} or @option{--old-archive} for this
9242 option). When you specify it,
9243 @command{tar} leaves out information about directories, pipes, fifos,
9244 contiguous files, and device files, and specifies file ownership by
9245 group and user IDs instead of group and user names.
9247 When updating an archive, do not use @option{--format=v7}
9248 unless the archive was created using this option.
9250 In most cases, a @emph{new} format archive can be read by an @emph{old}
9251 @command{tar} program without serious trouble, so this option should
9252 seldom be needed. On the other hand, most modern @command{tar}s are
9253 able to read old format archives, so it might be safer for you to
9254 always use @option{--format=v7} for your distributions. Notice,
9255 however, that @samp{ustar} format is a better alternative, as it is
9256 free from many of @samp{v7}'s drawbacks.
9259 @subsection Ustar Archive Format
9261 @cindex ustar archive format
9262 Archive format defined by @acronym{POSIX}.1-1988 specification is called
9263 @code{ustar}. Although it is more flexible than the V7 format, it
9264 still has many restrictions (@xref{Formats,ustar}, for the detailed
9265 description of @code{ustar} format). Along with V7 format,
9266 @code{ustar} format is a good choice for archives intended to be read
9267 with other implementations of @command{tar}.
9269 To create archive in @code{ustar} format, use @option{--format=ustar}
9270 option in conjunction with the @option{--create} (@option{-c}).
9273 @subsection @acronym{GNU} and old @GNUTAR{} format
9275 @cindex GNU archive format
9276 @cindex Old GNU archive format
9277 @GNUTAR{} was based on an early draft of the
9278 @acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
9279 @command{tar}, such as the support for file names longer than 100
9280 characters, use portions of the @command{tar} header record which were
9281 specified in that @acronym{POSIX} draft as unused. Subsequent changes in
9282 @acronym{POSIX} have allocated the same parts of the header record for
9283 other purposes. As a result, @GNUTAR{} format is
9284 incompatible with the current @acronym{POSIX} specification, and with
9285 @command{tar} programs that follow it.
9287 In the majority of cases, @command{tar} will be configured to create
9288 this format by default. This will change in future releases, since
9289 we plan to make @samp{POSIX} format the default.
9291 To force creation a @GNUTAR{} archive, use option
9292 @option{--format=gnu}.
9295 @subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
9297 @cindex POSIX archive format
9298 @cindex PAX archive format
9299 Starting from version 1.14 @GNUTAR{} features full support for
9300 @acronym{POSIX.1-2001} archives.
9302 A @acronym{POSIX} conformant archive will be created if @command{tar}
9303 was given @option{--format=posix} (@option{--format=pax}) option. No
9304 special option is required to read and extract from a @acronym{POSIX}
9308 * PAX keywords:: Controlling Extended Header Keywords.
9312 @subsubsection Controlling Extended Header Keywords
9316 @item --pax-option=@var{keyword-list}
9317 Handle keywords in @acronym{PAX} extended headers. This option is
9318 equivalent to @option{-o} option of the @command{pax} utility.
9321 @var{Keyword-list} is a comma-separated
9322 list of keyword options, each keyword option taking one of
9323 the following forms:
9326 @item delete=@var{pattern}
9327 When used with one of archive-creation commands,
9328 this option instructs @command{tar} to omit from extended header records
9329 that it produces any keywords matching the string @var{pattern}.
9331 When used in extract or list mode, this option instructs tar
9332 to ignore any keywords matching the given @var{pattern} in the extended
9333 header records. In both cases, matching is performed using the pattern
9334 matching notation described in @acronym{POSIX 1003.2}, 3.13
9335 (@pxref{wildcards}). For example:
9338 --pax-option delete=security.*
9341 would suppress security-related information.
9343 @item exthdr.name=@var{string}
9345 This keyword allows user control over the name that is written into the
9346 ustar header blocks for the extended headers. The name is obtained
9347 from @var{string} after making the following substitutions:
9349 @multitable @columnfractions .25 .55
9350 @headitem Meta-character @tab Replaced By
9351 @item %d @tab The directory name of the file, equivalent to the
9352 result of the @command{dirname} utility on the translated file name.
9353 @item %f @tab The name of the file with the directory information
9354 stripped, equivalent to the result of the @command{basename} utility
9355 on the translated file name.
9356 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9357 @item %% @tab A @samp{%} character.
9360 Any other @samp{%} characters in @var{string} produce undefined
9363 If no option @samp{exthdr.name=string} is specified, @command{tar}
9364 will use the following default value:
9370 @item globexthdr.name=@var{string}
9371 This keyword allows user control over the name that is written into
9372 the ustar header blocks for global extended header records. The name
9373 is obtained from the contents of @var{string}, after making
9374 the following substitutions:
9376 @multitable @columnfractions .25 .55
9377 @headitem Meta-character @tab Replaced By
9378 @item %n @tab An integer that represents the
9379 sequence number of the global extended header record in the archive,
9381 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9382 @item %% @tab A @samp{%} character.
9385 Any other @samp{%} characters in @var{string} produce undefined results.
9387 If no option @samp{globexthdr.name=string} is specified, @command{tar}
9388 will use the following default value:
9391 $TMPDIR/GlobalHead.%p.%n
9395 where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
9396 environment variable. If @var{TMPDIR} is not set, @command{tar}
9399 @item @var{keyword}=@var{value}
9400 When used with one of archive-creation commands, these keyword/value pairs
9401 will be included at the beginning of the archive in a global extended
9402 header record. When used with one of archive-reading commands,
9403 @command{tar} will behave as if it has encountered these keyword/value
9404 pairs at the beginning of the archive in a global extended header
9407 @item @var{keyword}:=@var{value}
9408 When used with one of archive-creation commands, these keyword/value pairs
9409 will be included as records at the beginning of an extended header for
9410 each file. This is effectively equivalent to @var{keyword}=@var{value}
9411 form except that it creates no global extended header records.
9413 When used with one of archive-reading commands, @command{tar} will
9414 behave as if these keyword/value pairs were included as records at the
9415 end of each extended header; thus, they will override any global or
9416 file-specific extended header record keywords of the same names.
9417 For example, in the command:
9420 tar --format=posix --create \
9421 --file archive --pax-option gname:=user .
9424 the group name will be forced to a new value for all files
9425 stored in the archive.
9429 @subsection Checksumming Problems
9431 SunOS and HP-UX @command{tar} fail to accept archives created using
9432 @GNUTAR{} and containing non-@acronym{ASCII} file names, that
9433 is, file names having characters with the eight bit set, because they
9434 use signed checksums, while @GNUTAR{} uses unsigned
9435 checksums while creating archives, as per @acronym{POSIX} standards. On
9436 reading, @GNUTAR{} computes both checksums and
9437 accepts any. It is somewhat worrying that a lot of people may go
9438 around doing backup of their files using faulty (or at least
9439 non-standard) software, not learning about it until it's time to
9440 restore their missing files with an incompatible file extractor, or
9443 @GNUTAR{} compute checksums both ways, and accept
9444 any on read, so @acronym{GNU} tar can read Sun tapes even with their
9445 wrong checksums. @GNUTAR{} produces the standard
9446 checksum, however, raising incompatibilities with Sun. That is to
9447 say, @GNUTAR{} has not been modified to
9448 @emph{produce} incorrect archives to be read by buggy @command{tar}'s.
9449 I've been told that more recent Sun @command{tar} now read standard
9450 archives, so maybe Sun did a similar patch, after all?
9452 The story seems to be that when Sun first imported @command{tar}
9453 sources on their system, they recompiled it without realizing that
9454 the checksums were computed differently, because of a change in
9455 the default signing of @code{char}'s in their compiler. So they
9456 started computing checksums wrongly. When they later realized their
9457 mistake, they merely decided to stay compatible with it, and with
9458 themselves afterwards. Presumably, but I do not really know, HP-UX
9459 has chosen that their @command{tar} archives to be compatible with Sun's.
9460 The current standards do not favor Sun @command{tar} format. In any
9461 case, it now falls on the shoulders of SunOS and HP-UX users to get
9462 a @command{tar} able to read the good archives they receive.
9464 @node Large or Negative Values
9465 @subsection Large or Negative Values
9466 @cindex large values
9467 @cindex future time stamps
9468 @cindex negative time stamps
9471 The above sections suggest to use @samp{oldest possible} archive
9472 format if in doubt. However, sometimes it is not possible. If you
9473 attempt to archive a file whose metadata cannot be represented using
9474 required format, @GNUTAR{} will print error message and ignore such a
9475 file. You will than have to switch to a format that is able to
9476 handle such values. The format summary table (@pxref{Formats}) will
9479 In particular, when trying to archive files larger than 8GB or with
9480 timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
9481 12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
9482 @acronym{POSIX} archive formats. When considering which format to
9483 choose, bear in mind that the @acronym{GNU} format uses
9484 two's-complement base-256 notation to store values that do not fit
9485 into standard @acronym{ustar} range. Such archives can generally be
9486 read only by a @GNUTAR{} implementation. Moreover, they sometimes
9487 cannot be correctly restored on another hosts even by @GNUTAR{}. For
9488 example, using two's complement representation for negative time
9489 stamps that assumes a signed 32-bit @code{time_t} generates archives
9490 that are not portable to hosts with differing @code{time_t}
9493 On the other hand, @acronym{POSIX} archives, generally speaking, can
9494 be extracted by any tar implementation that understands older
9495 @acronym{ustar} format. The only exception are files larger than 8GB.
9497 @FIXME{Describe how @acronym{POSIX} archives are extracted by non
9501 @subsection How to Extract GNU-Specific Data Using Other @command{tar} Implementations
9503 In previous sections you became acquainted with various quirks
9504 necessary to make your archives portable. Sometimes you may need to
9505 extract archives containing GNU-specific members using some
9506 third-party @command{tar} implementation or an older version of
9507 @GNUTAR{}. Of course your best bet is to have @GNUTAR{} installed,
9508 but if it is for some reason impossible, this section will explain
9509 how to cope without it.
9511 When we speak about @dfn{GNU-specific} members we mean two classes of
9512 them: members split between the volumes of a multi-volume archive and
9513 sparse members. You will be able to always recover such members if
9514 the archive is in PAX format. In addition split members can be
9515 recovered from archives in old GNU format. The following subsections
9516 describe the required procedures in detail.
9519 * Split Recovery:: Members Split Between Volumes
9520 * Sparse Recovery:: Sparse Members
9523 @node Split Recovery
9524 @subsubsection Extracting Members Split Between Volumes
9526 @cindex Mutli-volume archives, extracting using non-GNU tars
9527 If a member is split between several volumes of an old GNU format archive
9528 most third party @command{tar} implementation will fail to extract
9529 it. To extract it, use @command{tarcat} program (@pxref{Tarcat}).
9530 This program is available from
9531 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tarcat.html, @GNUTAR{}
9532 home page}. It concatenates several archive volumes into a single
9533 valid archive. For example, if you have three volumes named from
9534 @file{vol-1.tar} to @file{vol-3.tar}, you can do the following to
9535 extract them using a third-party @command{tar}:
9538 $ @kbd{tarcat vol-1.tar vol-2.tar vol-3.tar | tar xf -}
9541 @cindex Mutli-volume archives in PAX format, extracting using non-GNU tars
9542 You could use this approach for most (although not all) PAX
9543 format archives as well. However, extracting split members from a PAX
9544 archive is a much easier task, because PAX volumes are constructed in
9545 such a way that each part of a split member is extracted to a
9546 different file by @command{tar} implementations that are not aware of
9547 GNU extensions. More specifically, the very first part retains its
9548 original name, and all subsequent parts are named using the pattern:
9551 %d/GNUFileParts.%p/%f.%n
9555 where symbols preceeded by @samp{%} are @dfn{macro characters} that
9556 have the following meaning:
9558 @multitable @columnfractions .25 .55
9559 @headitem Meta-character @tab Replaced By
9560 @item %d @tab The directory name of the file, equivalent to the
9561 result of the @command{dirname} utility on its full name.
9562 @item %f @tab The file name of the file, equivalent to the result
9563 of the @command{basename} utility on its full name.
9564 @item %p @tab The process @acronym{ID} of the @command{tar} process that
9565 created the archive.
9566 @item %n @tab Ordinal number of this particular part.
9569 For example, if the file @file{var/longfile} was split during archive
9570 creation between three volumes, and the creator @command{tar} process
9571 had process @acronym{ID} @samp{27962}, then the member names will be:
9575 var/GNUFileParts.27962/longfile.1
9576 var/GNUFileParts.27962/longfile.2
9579 When you extract your archive using a third-party @command{tar}, these
9580 files will be created on your disk, and the only thing you will need
9581 to do to restore your file in its original form is concatenate them in
9582 the proper order, for example:
9587 $ @kbd{cat GNUFileParts.27962/longfile.1 \
9588 GNUFileParts.27962/longfile.2 >> longfile}
9589 $ rm -f GNUFileParts.27962
9593 Notice, that if the @command{tar} implementation you use supports PAX
9594 format archives, it will probably emit warnings about unknown keywords
9595 during extraction. They will look like this:
9600 Unknown extended header keyword 'GNU.volume.filename' ignored.
9601 Unknown extended header keyword 'GNU.volume.size' ignored.
9602 Unknown extended header keyword 'GNU.volume.offset' ignored.
9607 You can safely ignore these warnings.
9609 If your @command{tar} implementation is not PAX-aware, you will get
9610 more warnings and more files generated on your disk, e.g.:
9614 $ @kbd{tar xf vol-1.tar}
9615 var/PaxHeaders.27962/longfile: Unknown file type 'x', extracted as
9617 Unexpected EOF in archive
9618 $ @kbd{tar xf vol-2.tar}
9619 tmp/GlobalHead.27962.1: Unknown file type 'g', extracted as normal file
9620 GNUFileParts.27962/PaxHeaders.27962/sparsefile.1: Unknown file type
9621 'x', extracted as normal file
9625 Ignore these warnings. The @file{PaxHeaders.*} directories created
9626 will contain files with @dfn{extended header keywords} describing the
9627 extracted files. You can delete them, unless they describe sparse
9628 members. Read further to learn more about them.
9630 @node Sparse Recovery
9631 @subsubsection Extracting Sparse Members
9633 @cindex sparse files, extracting with non-GNU tars
9634 Any @command{tar} implementation will be able to extract sparse members from a
9635 PAX archive. However, the extracted files will be @dfn{condensed},
9636 i.e., any zero blocks will be removed from them. When we restore such
9637 a condensed file to its original form, by adding zero blocks (or
9638 @dfn{holes}) back to their original locations, we call this process
9639 @dfn{expanding} a compressed sparse file.
9642 To expand a file, you will need a simple auxiliary program called
9643 @command{xsparse}. It is available in source form from
9644 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/xsparse.html, @GNUTAR{}
9647 @cindex sparse files v.1.0, extracting with non-GNU tars
9648 Let's begin with archive members in @dfn{sparse format
9649 version 1.0}@footnote{@xref{PAX 1}.}, which are the easiest to expand.
9650 The condensed file will contain both file map and file data, so no
9651 additional data will be needed to restore it. If the original file
9652 name was @file{@var{dir}/@var{name}}, then the condensed file will be
9653 named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
9654 @var{n} is a decimal number@footnote{technically speaking, @var{n} is a
9655 @dfn{process @acronym{ID}} of the @command{tar} process which created the
9656 archive (@pxref{PAX keywords}).}.
9658 To expand a version 1.0 file, run @command{xsparse} as follows:
9661 $ @kbd{xsparse @file{cond-file}}
9665 where @file{cond-file} is the name of the condensed file. The utility
9666 will deduce the name for the resulting expanded file using the
9667 following algorithm:
9670 @item If @file{cond-file} does not contain any directories,
9671 @file{../cond-file} will be used;
9673 @item If @file{cond-file} has the form
9674 @file{@var{dir}/@var{t}/@var{name}}, where both @var{t} and @var{name}
9675 are simple names, with no @samp{/} characters in them, the output file
9676 name will be @file{@var{dir}/@var{name}}.
9678 @item Otherwise, if @file{cond-file} has the form
9679 @file{@var{dir}/@var{name}}, the output file name will be
9683 In the unlikely case when this algorithm does not suit your needs,
9684 you can explicitly specify output file name as a second argument to
9688 $ @kbd{xsparse @file{cond-file} @file{out-file}}
9691 It is often a good idea to run @command{xsparse} in @dfn{dry run} mode
9692 first. In this mode, the command does not actually expand the file,
9693 but verbosely lists all actions it would be taking to do so. The dry
9694 run mode is enabled by @option{-n} command line argument:
9698 $ @kbd{xsparse -n /home/gray/GNUSparseFile.6058/sparsefile}
9699 Reading v.1.0 sparse map
9700 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9701 `/home/gray/sparsefile'
9706 To actually expand the file, you would run:
9709 $ @kbd{xsparse /home/gray/GNUSparseFile.6058/sparsefile}
9713 The program behaves the same way all UNIX utilities do: it will keep
9714 quiet unless it has simething important to tell you (e.g. an error
9715 condition or something). If you wish it to produce verbose output,
9716 similar to that from the dry run mode, use @option{-v} option:
9720 $ @kbd{xsparse -v /home/gray/GNUSparseFile.6058/sparsefile}
9721 Reading v.1.0 sparse map
9722 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9723 `/home/gray/sparsefile'
9728 Additionally, if your @command{tar} implementation has extracted the
9729 @dfn{extended headers} for this file, you can instruct @command{xstar}
9730 to use them in order to verify the integrity of the expanded file.
9731 The option @option{-x} sets the name of the extended header file to
9732 use. Continuing our example:
9736 $ @kbd{xsparse -v -x /home/gray/PaxHeaders.6058/sparsefile \
9737 /home/gray/GNUSparseFile.6058/sparsefile}
9738 Reading extended header file
9739 Found variable GNU.sparse.major = 1
9740 Found variable GNU.sparse.minor = 0
9741 Found variable GNU.sparse.name = sparsefile
9742 Found variable GNU.sparse.realsize = 217481216
9743 Reading v.1.0 sparse map
9744 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9745 `/home/gray/sparsefile'
9750 @anchor{extracting sparse v.0.x}
9751 @cindex sparse files v.0.1, extracting with non-GNU tars
9752 @cindex sparse files v.0.0, extracting with non-GNU tars
9753 An @dfn{extended header} is a special @command{tar} archive header
9754 that precedes an archive member and contains a set of
9755 @dfn{variables}, describing the member properties that cannot be
9756 stored in the standard @code{ustar} header. While optional for
9757 expanding sparse version 1.0 members, the use of extended headers is
9758 mandatory when expanding sparse members in older sparse formats: v.0.0
9759 and v.0.1 (The sparse formats are described in detail in @ref{Sparse
9760 Formats}.) So, for these formats, the question is: how to obtain
9761 extended headers from the archive?
9763 If you use a @command{tar} implementation that does not support PAX
9764 format, extended headers for each member will be extracted as a
9765 separate file. If we represent the member name as
9766 @file{@var{dir}/@var{name}}, then the extended header file will be
9767 named @file{@var{dir}/@/PaxHeaders.@var{n}/@/@var{name}}, where
9768 @var{n} is an integer number.
9770 Things become more difficult if your @command{tar} implementation
9771 does support PAX headers, because in this case you will have to
9772 manually extract the headers. We recommend the following algorithm:
9776 Consult the documentation of your @command{tar} implementation for an
9777 option that prints @dfn{block numbers} along with the archive
9778 listing (analogous to @GNUTAR{}'s @option{-R} option). For example,
9779 @command{star} has @option{-block-number}.
9782 Obtain verbose listing using the @samp{block number} option, and
9783 find block numbers of the sparse member in question and the member
9784 immediately following it. For example, running @command{star} on our
9789 $ @kbd{star -t -v -block-number -f arc.tar}
9791 star: Unknown extended header keyword 'GNU.sparse.size' ignored.
9792 star: Unknown extended header keyword 'GNU.sparse.numblocks' ignored.
9793 star: Unknown extended header keyword 'GNU.sparse.name' ignored.
9794 star: Unknown extended header keyword 'GNU.sparse.map' ignored.
9795 block 56: 425984 -rw-r--r-- gray/users Jun 25 14:46 2006 GNUSparseFile.28124/sparsefile
9796 block 897: 65391 -rw-r--r-- gray/users Jun 24 20:06 2006 README
9802 (as usual, ignore the warnings about unknown keywords.)
9805 Let @var{size} be the size of the sparse member, @var{Bs} be its block number
9806 and @var{Bn} be the block number of the next member.
9810 @var{N} = @var{Bs} - @var{Bn} - @var{size}/512 - 2
9814 This number gives the size of the extended header part in tar @dfn{blocks}.
9815 In our example, this formula gives: @code{897 - 56 - 425984 / 512 - 2
9819 Use @command{dd} to extract the headers:
9822 @kbd{dd if=@var{archive} of=@var{hname} bs=512 skip=@var{Bs} count=@var{N}}
9826 where @var{archive} is the archive name, @var{hname} is a name of the
9827 file to store the extended header in, @var{Bs} and @var{N} are
9828 computed in previous steps.
9830 In our example, this command will be
9833 $ @kbd{dd if=arc.tar of=xhdr bs=512 skip=56 count=7}
9837 Finally, you can expand the condensed file, using the obtained header:
9841 $ @kbd{xsparse -v -x xhdr GNUSparseFile.6058/sparsefile}
9842 Reading extended header file
9843 Found variable GNU.sparse.size = 217481216
9844 Found variable GNU.sparse.numblocks = 208
9845 Found variable GNU.sparse.name = sparsefile
9846 Found variable GNU.sparse.map = 0,2048,1050624,2048,@dots{}
9847 Expanding file `GNUSparseFile.28124/sparsefile' to `sparsefile'
9853 @section Comparison of @command{tar} and @command{cpio}
9856 @FIXME{Reorganize the following material}
9858 The @command{cpio} archive formats, like @command{tar}, do have maximum
9859 file name lengths. The binary and old @acronym{ASCII} formats have a maximum file
9860 length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max
9861 file length of 1024. @acronym{GNU} @command{cpio} can read and write archives
9862 with arbitrary file name lengths, but other @command{cpio} implementations
9863 may crash unexplainedly trying to read them.
9865 @command{tar} handles symbolic links in the form in which it comes in @acronym{BSD};
9866 @command{cpio} doesn't handle symbolic links in the form in which it comes
9867 in System V prior to SVR4, and some vendors may have added symlinks
9868 to their system without enhancing @command{cpio} to know about them.
9869 Others may have enhanced it in a way other than the way I did it
9870 at Sun, and which was adopted by AT&T (and which is, I think, also
9871 present in the @command{cpio} that Berkeley picked up from AT&T and put
9872 into a later @acronym{BSD} release---I think I gave them my changes).
9874 (SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
9875 can handle @command{tar} format input, and write it on output, and it
9876 probably handles symbolic links. They may not have bothered doing
9877 anything to enhance @command{tar} as a result.)
9879 @command{cpio} handles special files; traditional @command{tar} doesn't.
9881 @command{tar} comes with V7, System III, System V, and @acronym{BSD} source;
9882 @command{cpio} comes only with System III, System V, and later @acronym{BSD}
9883 (4.3-tahoe and later).
9885 @command{tar}'s way of handling multiple hard links to a file can handle
9886 file systems that support 32-bit inumbers (e.g., the @acronym{BSD} file system);
9887 @command{cpio}s way requires you to play some games (in its ``binary''
9888 format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
9889 they're 18 bits---it would have to play games with the "file system @acronym{ID}"
9890 field of the header to make sure that the file system @acronym{ID}/i-number pairs
9891 of different files were always different), and I don't know which
9892 @command{cpio}s, if any, play those games. Those that don't might get
9893 confused and think two files are the same file when they're not, and
9894 make hard links between them.
9896 @command{tar}s way of handling multiple hard links to a file places only
9897 one copy of the link on the tape, but the name attached to that copy
9898 is the @emph{only} one you can use to retrieve the file; @command{cpio}s
9899 way puts one copy for every link, but you can retrieve it using any
9903 What type of check sum (if any) is used, and how is this calculated.
9906 See the attached manual pages for @command{tar} and @command{cpio} format.
9907 @command{tar} uses a checksum which is the sum of all the bytes in the
9908 @command{tar} header for a file; @command{cpio} uses no checksum.
9911 If anyone knows why @command{cpio} was made when @command{tar} was present
9915 It wasn't. @command{cpio} first showed up in PWB/UNIX 1.0; no
9916 generally-available version of UNIX had @command{tar} at the time. I don't
9917 know whether any version that was generally available @emph{within AT&T}
9918 had @command{tar}, or, if so, whether the people within AT&T who did
9919 @command{cpio} knew about it.
9921 On restore, if there is a corruption on a tape @command{tar} will stop at
9922 that point, while @command{cpio} will skip over it and try to restore the
9925 The main difference is just in the command syntax and header format.
9927 @command{tar} is a little more tape-oriented in that everything is blocked
9928 to start on a record boundary.
9931 Is there any differences between the ability to recover crashed
9932 archives between the two of them. (Is there any chance of recovering
9933 crashed archives at all.)
9936 Theoretically it should be easier under @command{tar} since the blocking
9937 lets you find a header with some variation of @samp{dd skip=@var{nn}}.
9938 However, modern @command{cpio}'s and variations have an option to just
9939 search for the next file header after an error with a reasonable chance
9940 of resyncing. However, lots of tape driver software won't allow you to
9941 continue past a media error which should be the only reason for getting
9942 out of sync unless a file changed sizes while you were writing the
9946 If anyone knows why @command{cpio} was made when @command{tar} was present
9947 at the unix scene, please tell me about this too.
9950 Probably because it is more media efficient (by not blocking everything
9951 and using only the space needed for the headers where @command{tar}
9952 always uses 512 bytes per file header) and it knows how to archive
9955 You might want to look at the freely available alternatives. The
9956 major ones are @command{afio}, @GNUTAR{}, and
9957 @command{pax}, each of which have their own extensions with some
9958 backwards compatibility.
9960 Sparse files were @command{tar}red as sparse files (which you can
9961 easily test, because the resulting archive gets smaller, and
9962 @acronym{GNU} @command{cpio} can no longer read it).
9965 @chapter Tapes and Other Archive Media
9968 A few special cases about tape handling warrant more detailed
9969 description. These special cases are discussed below.
9971 Many complexities surround the use of @command{tar} on tape drives. Since
9972 the creation and manipulation of archives located on magnetic tape was
9973 the original purpose of @command{tar}, it contains many features making
9974 such manipulation easier.
9976 Archives are usually written on dismountable media---tape cartridges,
9977 mag tapes, or floppy disks.
9979 The amount of data a tape or disk holds depends not only on its size,
9980 but also on how it is formatted. A 2400 foot long reel of mag tape
9981 holds 40 megabytes of data when formatted at 1600 bits per inch. The
9982 physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
9984 Magnetic media are re-usable---once the archive on a tape is no longer
9985 needed, the archive can be erased and the tape or disk used over.
9986 Media quality does deteriorate with use, however. Most tapes or disks
9987 should be discarded when they begin to produce data errors. EXABYTE
9988 tape cartridges should be discarded when they generate an @dfn{error
9989 count} (number of non-usable bits) of more than 10k.
9991 Magnetic media are written and erased using magnetic fields, and
9992 should be protected from such fields to avoid damage to stored data.
9993 Sticking a floppy disk to a filing cabinet using a magnet is probably
9997 * Device:: Device selection and switching
9998 * Remote Tape Server::
9999 * Common Problems and Solutions::
10000 * Blocking:: Blocking
10001 * Many:: Many archives on one tape
10002 * Using Multiple Tapes:: Using Multiple Tapes
10003 * label:: Including a Label in the Archive
10005 * Write Protection::
10009 @section Device Selection and Switching
10013 @item -f [@var{hostname}:]@var{file}
10014 @itemx --file=[@var{hostname}:]@var{file}
10015 Use archive file or device @var{file} on @var{hostname}.
10018 This option is used to specify the file name of the archive @command{tar}
10021 If the file name is @samp{-}, @command{tar} reads the archive from standard
10022 input (when listing or extracting), or writes it to standard output
10023 (when creating). If the @samp{-} file name is given when updating an
10024 archive, @command{tar} will read the original archive from its standard
10025 input, and will write the entire new archive to its standard output.
10027 If the file name contains a @samp{:}, it is interpreted as
10028 @samp{hostname:file name}. If the @var{hostname} contains an @dfn{at}
10029 sign (@samp{@@}), it is treated as @samp{user@@hostname:file name}. In
10030 either case, @command{tar} will invoke the command @command{rsh} (or
10031 @command{remsh}) to start up an @command{/usr/libexec/rmt} on the remote
10032 machine. If you give an alternate login name, it will be given to the
10034 Naturally, the remote machine must have an executable
10035 @command{/usr/libexec/rmt}. This program is free software from the
10036 University of California, and a copy of the source code can be found
10037 with the sources for @command{tar}; it's compiled and installed by default.
10038 The exact path to this utility is determined when configuring the package.
10039 It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for
10040 your installation prefix. This location may also be overridden at
10041 runtime by using @option{rmt-command=@var{command}} option (@xref{Option Summary,
10042 ---rmt-command}, for detailed description of this option. @xref{Remote
10043 Tape Server}, for the description of @command{rmt} command).
10045 If this option is not given, but the environment variable @env{TAPE}
10046 is set, its value is used; otherwise, old versions of @command{tar}
10047 used a default archive name (which was picked when @command{tar} was
10048 compiled). The default is normally set up to be the @dfn{first} tape
10049 drive or other transportable I/O medium on the system.
10051 Starting with version 1.11.5, @GNUTAR{} uses
10052 standard input and standard output as the default device, and I will
10053 not try anymore supporting automatic device detection at installation
10054 time. This was failing really in too many cases, it was hopeless.
10055 This is now completely left to the installer to override standard
10056 input and standard output for default device, if this seems
10057 preferable. Further, I think @emph{most} actual usages of
10058 @command{tar} are done with pipes or disks, not really tapes,
10059 cartridges or diskettes.
10061 Some users think that using standard input and output is running
10062 after trouble. This could lead to a nasty surprise on your screen if
10063 you forget to specify an output file name---especially if you are going
10064 through a network or terminal server capable of buffering large amounts
10065 of output. We had so many bug reports in that area of configuring
10066 default tapes automatically, and so many contradicting requests, that
10067 we finally consider the problem to be portably intractable. We could
10068 of course use something like @samp{/dev/tape} as a default, but this
10069 is @emph{also} running after various kind of trouble, going from hung
10070 processes to accidental destruction of real tapes. After having seen
10071 all this mess, using standard input and output as a default really
10072 sounds like the only clean choice left, and a very useful one too.
10074 @GNUTAR{} reads and writes archive in records, I
10075 suspect this is the main reason why block devices are preferred over
10076 character devices. Most probably, block devices are more efficient
10077 too. The installer could also check for @samp{DEFTAPE} in
10078 @file{<sys/mtio.h>}.
10081 @xopindex{force-local, short description}
10082 @item --force-local
10083 Archive file is local even if it contains a colon.
10085 @opindex rsh-command
10086 @item --rsh-command=@var{command}
10087 Use remote @var{command} instead of @command{rsh}. This option exists
10088 so that people who use something other than the standard @command{rsh}
10089 (e.g., a Kerberized @command{rsh}) can access a remote device.
10091 When this command is not used, the shell command found when
10092 the @command{tar} program was installed is used instead. This is
10093 the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh},
10094 @file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}.
10095 The installer may have overridden this by defining the environment
10096 variable @env{RSH} @emph{at installation time}.
10099 Specify drive and density.
10101 @xopindex{multi-volume, short description}
10103 @itemx --multi-volume
10104 Create/list/extract multi-volume archive.
10106 This option causes @command{tar} to write a @dfn{multi-volume} archive---one
10107 that may be larger than will fit on the medium used to hold it.
10108 @xref{Multi-Volume Archives}.
10110 @xopindex{tape-length, short description}
10112 @itemx --tape-length=@var{num}
10113 Change tape after writing @var{num} x 1024 bytes.
10115 This option might be useful when your tape drivers do not properly
10116 detect end of physical tapes. By being slightly conservative on the
10117 maximum tape length, you might avoid the problem entirely.
10119 @xopindex{info-script, short description}
10120 @xopindex{new-volume-script, short description}
10121 @item -F @var{file}
10122 @itemx --info-script=@var{file}
10123 @itemx --new-volume-script=@var{file}
10124 Execute @file{file} at end of each tape. This implies
10125 @option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed
10126 description of this option.
10129 @node Remote Tape Server
10130 @section The Remote Tape Server
10132 @cindex remote tape drive
10134 In order to access the tape drive on a remote machine, @command{tar}
10135 uses the remote tape server written at the University of California at
10136 Berkeley. The remote tape server must be installed as
10137 @file{@var{prefix}/libexec/rmt} on any machine whose tape drive you
10138 want to use. @command{tar} calls @command{rmt} by running an
10139 @command{rsh} or @command{remsh} to the remote machine, optionally
10140 using a different login name if one is supplied.
10142 A copy of the source for the remote tape server is provided. It is
10143 Copyright @copyright{} 1983 by the Regents of the University of
10144 California, but can be freely distributed. It is compiled and
10145 installed by default.
10147 @cindex absolute file names
10148 Unless you use the @option{--absolute-names} (@option{-P}) option,
10149 @GNUTAR{} will not allow you to create an archive that contains
10150 absolute file names (a file name beginning with @samp{/}.) If you try,
10151 @command{tar} will automatically remove the leading @samp{/} from the
10152 file names it stores in the archive. It will also type a warning
10153 message telling you what it is doing.
10155 When reading an archive that was created with a different
10156 @command{tar} program, @GNUTAR{} automatically
10157 extracts entries in the archive which have absolute file names as if
10158 the file names were not absolute. This is an important feature. A
10159 visitor here once gave a @command{tar} tape to an operator to restore;
10160 the operator used Sun @command{tar} instead of @GNUTAR{},
10161 and the result was that it replaced large portions of
10162 our @file{/bin} and friends with versions from the tape; needless to
10163 say, we were unhappy about having to recover the file system from
10166 For example, if the archive contained a file @file{/usr/bin/computoy},
10167 @GNUTAR{} would extract the file to @file{usr/bin/computoy},
10168 relative to the current directory. If you want to extract the files in
10169 an archive to the same absolute names that they had when the archive
10170 was created, you should do a @samp{cd /} before extracting the files
10171 from the archive, or you should either use the @option{--absolute-names}
10172 option, or use the command @samp{tar -C / @dots{}}.
10174 @cindex Ultrix 3.1 and write failure
10175 Some versions of Unix (Ultrix 3.1 is known to have this problem),
10176 can claim that a short write near the end of a tape succeeded,
10177 when it actually failed. This will result in the -M option not
10178 working correctly. The best workaround at the moment is to use a
10179 significantly larger blocking factor than the default 20.
10181 In order to update an archive, @command{tar} must be able to backspace the
10182 archive in order to reread or rewrite a record that was just read (or
10183 written). This is currently possible only on two kinds of files: normal
10184 disk files (or any other file that can be backspaced with @samp{lseek}),
10185 and industry-standard 9-track magnetic tape (or any other kind of tape
10186 that can be backspaced with the @code{MTIOCTOP} @code{ioctl}.
10188 This means that the @option{--append}, @option{--concatenate}, and
10189 @option{--delete} commands will not work on any other kind of file.
10190 Some media simply cannot be backspaced, which means these commands and
10191 options will never be able to work on them. These non-backspacing
10192 media include pipes and cartridge tape drives.
10194 Some other media can be backspaced, and @command{tar} will work on them
10195 once @command{tar} is modified to do so.
10197 Archives created with the @option{--multi-volume}, @option{--label}, and
10198 @option{--incremental} (@option{-G}) options may not be readable by other version
10199 of @command{tar}. In particular, restoring a file that was split over
10200 a volume boundary will require some careful work with @command{dd}, if
10201 it can be done at all. Other versions of @command{tar} may also create
10202 an empty file whose name is that of the volume header. Some versions
10203 of @command{tar} may create normal files instead of directories archived
10204 with the @option{--incremental} (@option{-G}) option.
10206 @node Common Problems and Solutions
10207 @section Some Common Problems and their Solutions
10212 errors from system:
10214 no such file or directory
10217 errors from @command{tar}:
10218 directory checksum error
10219 header format error
10221 errors from media/system:
10232 @dfn{Block} and @dfn{record} terminology is rather confused, and it
10233 is also confusing to the expert reader. On the other hand, readers
10234 who are new to the field have a fresh mind, and they may safely skip
10235 the next two paragraphs, as the remainder of this manual uses those
10236 two terms in a quite consistent way.
10238 John Gilmore, the writer of the public domain @command{tar} from which
10239 @GNUTAR{} was originally derived, wrote (June 1995):
10242 The nomenclature of tape drives comes from IBM, where I believe
10243 they were invented for the IBM 650 or so. On IBM mainframes, what
10244 is recorded on tape are tape blocks. The logical organization of
10245 data is into records. There are various ways of putting records into
10246 blocks, including @code{F} (fixed sized records), @code{V} (variable
10247 sized records), @code{FB} (fixed blocked: fixed size records, @var{n}
10248 to a block), @code{VB} (variable size records, @var{n} to a block),
10249 @code{VSB} (variable spanned blocked: variable sized records that can
10250 occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=}
10251 parameter specified this to the operating system.
10253 The Unix man page on @command{tar} was totally confused about this.
10254 When I wrote @code{PD TAR}, I used the historically correct terminology
10255 (@command{tar} writes data records, which are grouped into blocks).
10256 It appears that the bogus terminology made it into @acronym{POSIX} (no surprise
10257 here), and now Fran@,{c}ois has migrated that terminology back
10258 into the source code too.
10261 The term @dfn{physical block} means the basic transfer chunk from or
10262 to a device, after which reading or writing may stop without anything
10263 being lost. In this manual, the term @dfn{block} usually refers to
10264 a disk physical block, @emph{assuming} that each disk block is 512
10265 bytes in length. It is true that some disk devices have different
10266 physical blocks, but @command{tar} ignore these differences in its own
10267 format, which is meant to be portable, so a @command{tar} block is always
10268 512 bytes in length, and @dfn{block} always mean a @command{tar} block.
10269 The term @dfn{logical block} often represents the basic chunk of
10270 allocation of many disk blocks as a single entity, which the operating
10271 system treats somewhat atomically; this concept is only barely used
10274 The term @dfn{physical record} is another way to speak of a physical
10275 block, those two terms are somewhat interchangeable. In this manual,
10276 the term @dfn{record} usually refers to a tape physical block,
10277 @emph{assuming} that the @command{tar} archive is kept on magnetic tape.
10278 It is true that archives may be put on disk or used with pipes,
10279 but nevertheless, @command{tar} tries to read and write the archive one
10280 @dfn{record} at a time, whatever the medium in use. One record is made
10281 up of an integral number of blocks, and this operation of putting many
10282 disk blocks into a single tape block is called @dfn{reblocking}, or
10283 more simply, @dfn{blocking}. The term @dfn{logical record} refers to
10284 the logical organization of many characters into something meaningful
10285 to the application. The term @dfn{unit record} describes a small set
10286 of characters which are transmitted whole to or by the application,
10287 and often refers to a line of text. Those two last terms are unrelated
10288 to what we call a @dfn{record} in @GNUTAR{}.
10290 When writing to tapes, @command{tar} writes the contents of the archive
10291 in chunks known as @dfn{records}. To change the default blocking
10292 factor, use the @option{--blocking-factor=@var{512-size}} (@option{-b
10293 @var{512-size}}) option. Each record will then be composed of
10294 @var{512-size} blocks. (Each @command{tar} block is 512 bytes.
10295 @xref{Standard}.) Each file written to the archive uses at least one
10296 full record. As a result, using a larger record size can result in
10297 more wasted space for small files. On the other hand, a larger record
10298 size can often be read and written much more efficiently.
10300 Further complicating the problem is that some tape drives ignore the
10301 blocking entirely. For these, a larger record size can still improve
10302 performance (because the software layers above the tape drive still
10303 honor the blocking), but not as dramatically as on tape drives that
10306 When reading an archive, @command{tar} can usually figure out the
10307 record size on itself. When this is the case, and a non-standard
10308 record size was used when the archive was created, @command{tar} will
10309 print a message about a non-standard blocking factor, and then operate
10310 normally. On some tape devices, however, @command{tar} cannot figure
10311 out the record size itself. On most of those, you can specify a
10312 blocking factor (with @option{--blocking-factor}) larger than the
10313 actual blocking factor, and then use the @option{--read-full-records}
10314 (@option{-B}) option. (If you specify a blocking factor with
10315 @option{--blocking-factor} and don't use the
10316 @option{--read-full-records} option, then @command{tar} will not
10317 attempt to figure out the recording size itself.) On some devices,
10318 you must always specify the record size exactly with
10319 @option{--blocking-factor} when reading, because @command{tar} cannot
10320 figure it out. In any case, use @option{--list} (@option{-t}) before
10321 doing any extractions to see whether @command{tar} is reading the archive
10324 @command{tar} blocks are all fixed size (512 bytes), and its scheme for
10325 putting them into records is to put a whole number of them (one or
10326 more) into each record. @command{tar} records are all the same size;
10327 at the end of the file there's a block containing all zeros, which
10328 is how you tell that the remainder of the last record(s) are garbage.
10330 In a standard @command{tar} file (no options), the block size is 512
10331 and the record size is 10240, for a blocking factor of 20. What the
10332 @option{--blocking-factor} option does is sets the blocking factor,
10333 changing the record size while leaving the block size at 512 bytes.
10334 20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives;
10335 most tape drives these days prefer much bigger records in order to
10336 stream and not waste tape. When writing tapes for myself, some tend
10337 to use a factor of the order of 2048, say, giving a record size of
10338 around one megabyte.
10340 If you use a blocking factor larger than 20, older @command{tar}
10341 programs might not be able to read the archive, so we recommend this
10342 as a limit to use in practice. @GNUTAR{}, however,
10343 will support arbitrarily large record sizes, limited only by the
10344 amount of virtual memory or the physical characteristics of the tape
10348 * Format Variations:: Format Variations
10349 * Blocking Factor:: The Blocking Factor of an Archive
10352 @node Format Variations
10353 @subsection Format Variations
10354 @cindex Format Parameters
10355 @cindex Format Options
10356 @cindex Options, archive format specifying
10357 @cindex Options, format specifying
10360 Format parameters specify how an archive is written on the archive
10361 media. The best choice of format parameters will vary depending on
10362 the type and number of files being archived, and on the media used to
10365 To specify format parameters when accessing or creating an archive,
10366 you can use the options described in the following sections.
10367 If you do not specify any format parameters, @command{tar} uses
10368 default parameters. You cannot modify a compressed archive.
10369 If you create an archive with the @option{--blocking-factor} option
10370 specified (@pxref{Blocking Factor}), you must specify that
10371 blocking-factor when operating on the archive. @xref{Formats}, for other
10372 examples of format parameter considerations.
10374 @node Blocking Factor
10375 @subsection The Blocking Factor of an Archive
10376 @cindex Blocking Factor
10377 @cindex Record Size
10378 @cindex Number of blocks per record
10379 @cindex Number of bytes per record
10380 @cindex Bytes per record
10381 @cindex Blocks per record
10384 @opindex blocking-factor
10385 The data in an archive is grouped into blocks, which are 512 bytes.
10386 Blocks are read and written in whole number multiples called
10387 @dfn{records}. The number of blocks in a record (i.e., the size of a
10388 record in units of 512 bytes) is called the @dfn{blocking factor}.
10389 The @option{--blocking-factor=@var{512-size}} (@option{-b
10390 @var{512-size}}) option specifies the blocking factor of an archive.
10391 The default blocking factor is typically 20 (i.e., 10240 bytes), but
10392 can be specified at installation. To find out the blocking factor of
10393 an existing archive, use @samp{tar --list --file=@var{archive-name}}.
10394 This may not work on some devices.
10396 Records are separated by gaps, which waste space on the archive media.
10397 If you are archiving on magnetic tape, using a larger blocking factor
10398 (and therefore larger records) provides faster throughput and allows you
10399 to fit more data on a tape (because there are fewer gaps). If you are
10400 archiving on cartridge, a very large blocking factor (say 126 or more)
10401 greatly increases performance. A smaller blocking factor, on the other
10402 hand, may be useful when archiving small files, to avoid archiving lots
10403 of nulls as @command{tar} fills out the archive to the end of the record.
10404 In general, the ideal record size depends on the size of the
10405 inter-record gaps on the tape you are using, and the average size of the
10406 files you are archiving. @xref{create}, for information on
10409 @FIXME{Need example of using a cartridge with blocking factor=126 or more.}
10411 Archives with blocking factors larger than 20 cannot be read
10412 by very old versions of @command{tar}, or by some newer versions
10413 of @command{tar} running on old machines with small address spaces.
10414 With @GNUTAR{}, the blocking factor of an archive is limited
10415 only by the maximum record size of the device containing the archive,
10416 or by the amount of available virtual memory.
10418 Also, on some systems, not using adequate blocking factors, as sometimes
10419 imposed by the device drivers, may yield unexpected diagnostics. For
10420 example, this has been reported:
10423 Cannot write to /dev/dlt: Invalid argument
10427 In such cases, it sometimes happen that the @command{tar} bundled by
10428 the system is aware of block size idiosyncrasies, while @GNUTAR{}
10429 requires an explicit specification for the block size,
10430 which it cannot guess. This yields some people to consider
10431 @GNUTAR{} is misbehaving, because by comparison,
10432 @cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}},
10433 for example, might resolve the problem.
10435 If you use a non-default blocking factor when you create an archive, you
10436 must specify the same blocking factor when you modify that archive. Some
10437 archive devices will also require you to specify the blocking factor when
10438 reading that archive, however this is not typically the case. Usually, you
10439 can use @option{--list} (@option{-t}) without specifying a blocking factor---@command{tar}
10440 reports a non-default record size and then lists the archive members as
10441 it would normally. To extract files from an archive with a non-standard
10442 blocking factor (particularly if you're not sure what the blocking factor
10443 is), you can usually use the @option{--read-full-records} (@option{-B}) option while
10444 specifying a blocking factor larger then the blocking factor of the archive
10445 (i.e., @samp{tar --extract --read-full-records --blocking-factor=300}.
10446 @xref{list}, for more information on the @option{--list} (@option{-t})
10447 operation. @xref{Reading}, for a more detailed explanation of that option.
10450 @item --blocking-factor=@var{number}
10451 @itemx -b @var{number}
10452 Specifies the blocking factor of an archive. Can be used with any
10453 operation, but is usually not necessary with @option{--list} (@option{-t}).
10459 @item -b @var{blocks}
10460 @itemx --blocking-factor=@var{blocks}
10461 Set record size to @math{@var{blocks} * 512} bytes.
10463 This option is used to specify a @dfn{blocking factor} for the archive.
10464 When reading or writing the archive, @command{tar}, will do reads and writes
10465 of the archive in records of @math{@var{block}*512} bytes. This is true
10466 even when the archive is compressed. Some devices requires that all
10467 write operations be a multiple of a certain size, and so, @command{tar}
10468 pads the archive out to the next record boundary.
10470 The default blocking factor is set when @command{tar} is compiled, and is
10471 typically 20. Blocking factors larger than 20 cannot be read by very
10472 old versions of @command{tar}, or by some newer versions of @command{tar}
10473 running on old machines with small address spaces.
10475 With a magnetic tape, larger records give faster throughput and fit
10476 more data on a tape (because there are fewer inter-record gaps).
10477 If the archive is in a disk file or a pipe, you may want to specify
10478 a smaller blocking factor, since a large one will result in a large
10479 number of null bytes at the end of the archive.
10481 When writing cartridge or other streaming tapes, a much larger
10482 blocking factor (say 126 or more) will greatly increase performance.
10483 However, you must specify the same blocking factor when reading or
10484 updating the archive.
10486 Apparently, Exabyte drives have a physical block size of 8K bytes.
10487 If we choose our blocksize as a multiple of 8k bytes, then the problem
10488 seems to disappear. Id est, we are using block size of 112 right
10489 now, and we haven't had the problem since we switched@dots{}
10491 With @GNUTAR{} the blocking factor is limited only
10492 by the maximum record size of the device containing the archive, or by
10493 the amount of available virtual memory.
10495 However, deblocking or reblocking is virtually avoided in a special
10496 case which often occurs in practice, but which requires all the
10497 following conditions to be simultaneously true:
10500 the archive is subject to a compression option,
10502 the archive is not handled through standard input or output, nor
10503 redirected nor piped,
10505 the archive is directly handled to a local disk, instead of any special
10508 @option{--blocking-factor} is not explicitly specified on the @command{tar}
10512 If the output goes directly to a local disk, and not through
10513 stdout, then the last write is not extended to a full record size.
10514 Otherwise, reblocking occurs. Here are a few other remarks on this
10520 @command{gzip} will complain about trailing garbage if asked to
10521 uncompress a compressed archive on tape, there is an option to turn
10522 the message off, but it breaks the regularity of simply having to use
10523 @samp{@var{prog} -d} for decompression. It would be nice if gzip was
10524 silently ignoring any number of trailing zeros. I'll ask Jean-loup
10525 Gailly, by sending a copy of this message to him.
10528 @command{compress} does not show this problem, but as Jean-loup pointed
10529 out to Michael, @samp{compress -d} silently adds garbage after
10530 the result of decompression, which tar ignores because it already
10531 recognized its end-of-file indicator. So this bug may be safely
10535 @samp{gzip -d -q} will be silent about the trailing zeros indeed,
10536 but will still return an exit status of 2 which tar reports in turn.
10537 @command{tar} might ignore the exit status returned, but I hate doing
10538 that, as it weakens the protection @command{tar} offers users against
10539 other possible problems at decompression time. If @command{gzip} was
10540 silently skipping trailing zeros @emph{and} also avoiding setting the
10541 exit status in this innocuous case, that would solve this situation.
10544 @command{tar} should become more solid at not stopping to read a pipe at
10545 the first null block encountered. This inelegantly breaks the pipe.
10546 @command{tar} should rather drain the pipe out before exiting itself.
10549 @xopindex{ignore-zeros, short description}
10551 @itemx --ignore-zeros
10552 Ignore blocks of zeros in archive (means EOF).
10554 The @option{--ignore-zeros} (@option{-i}) option causes @command{tar} to ignore blocks
10555 of zeros in the archive. Normally a block of zeros indicates the
10556 end of the archive, but when reading a damaged archive, or one which
10557 was created by concatenating several archives together, this option
10558 allows @command{tar} to read the entire archive. This option is not on
10559 by default because many versions of @command{tar} write garbage after
10562 Note that this option causes @command{tar} to read to the end of the
10563 archive file, which may sometimes avoid problems when multiple files
10564 are stored on a single physical tape.
10566 @xopindex{read-full-records, short description}
10568 @itemx --read-full-records
10569 Reblock as we read (for reading 4.2@acronym{BSD} pipes).
10571 If @option{--read-full-records} is used, @command{tar}
10572 will not panic if an attempt to read a record from the archive does
10573 not return a full record. Instead, @command{tar} will keep reading
10574 until it has obtained a full
10577 This option is turned on by default when @command{tar} is reading
10578 an archive from standard input, or from a remote machine. This is
10579 because on @acronym{BSD} Unix systems, a read of a pipe will return however
10580 much happens to be in the pipe, even if it is less than @command{tar}
10581 requested. If this option was not used, @command{tar} would fail as
10582 soon as it read an incomplete record from the pipe.
10584 This option is also useful with the commands for updating an archive.
10590 @FIXME{Appropriate options should be moved here from elsewhere.}
10592 @cindex blocking factor
10593 @cindex tape blocking
10595 When handling various tapes or cartridges, you have to take care of
10596 selecting a proper blocking, that is, the number of disk blocks you
10597 put together as a single tape block on the tape, without intervening
10598 tape gaps. A @dfn{tape gap} is a small landing area on the tape
10599 with no information on it, used for decelerating the tape to a
10600 full stop, and for later regaining the reading or writing speed.
10601 When the tape driver starts reading a record, the record has to
10602 be read whole without stopping, as a tape gap is needed to stop the
10603 tape motion without loosing information.
10605 @cindex Exabyte blocking
10606 @cindex DAT blocking
10607 Using higher blocking (putting more disk blocks per tape block) will use
10608 the tape more efficiently as there will be less tape gaps. But reading
10609 such tapes may be more difficult for the system, as more memory will be
10610 required to receive at once the whole record. Further, if there is a
10611 reading error on a huge record, this is less likely that the system will
10612 succeed in recovering the information. So, blocking should not be too
10613 low, nor it should be too high. @command{tar} uses by default a blocking of
10614 20 for historical reasons, and it does not really matter when reading or
10615 writing to disk. Current tape technology would easily accommodate higher
10616 blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs.
10617 We were told that for some DLT drives, the blocking should be a multiple
10618 of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance.
10619 Other manufacturers may use different recommendations for the same tapes.
10620 This might also depends of the buffering techniques used inside modern
10621 tape controllers. Some imposes a minimum blocking, or a maximum blocking.
10622 Others request blocking to be some exponent of two.
10624 So, there is no fixed rule for blocking. But blocking at read time
10625 should ideally be the same as blocking used at write time. At one place
10626 I know, with a wide variety of equipment, they found it best to use a
10627 blocking of 32 to guarantee that their tapes are fully interchangeable.
10629 I was also told that, for recycled tapes, prior erasure (by the same
10630 drive unit that will be used to create the archives) sometimes lowers
10631 the error rates observed at rewriting time.
10633 I might also use @option{--number-blocks} instead of
10634 @option{--block-number}, so @option{--block} will then expand to
10635 @option{--blocking-factor} unambiguously.
10638 @section Many Archives on One Tape
10640 @FIXME{Appropriate options should be moved here from elsewhere.}
10642 @findex ntape @r{device}
10643 Most tape devices have two entries in the @file{/dev} directory, or
10644 entries that come in pairs, which differ only in the minor number for
10645 this device. Let's take for example @file{/dev/tape}, which often
10646 points to the only or usual tape device of a given system. There might
10647 be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler
10648 name is the @emph{rewinding} version of the device, while the name
10649 having @samp{nr} in it is the @emph{no rewinding} version of the same
10652 A rewinding tape device will bring back the tape to its beginning point
10653 automatically when this device is opened or closed. Since @command{tar}
10654 opens the archive file before using it and closes it afterwards, this
10655 means that a simple:
10658 $ @kbd{tar cf /dev/tape @var{directory}}
10662 will reposition the tape to its beginning both prior and after saving
10663 @var{directory} contents to it, thus erasing prior tape contents and
10664 making it so that any subsequent write operation will destroy what has
10667 @cindex tape positioning
10668 So, a rewinding device is normally meant to hold one and only one file.
10669 If you want to put more than one @command{tar} archive on a given tape, you
10670 will need to avoid using the rewinding version of the tape device. You
10671 will also have to pay special attention to tape positioning. Errors in
10672 positioning may overwrite the valuable data already on your tape. Many
10673 people, burnt by past experiences, will only use rewinding devices and
10674 limit themselves to one file per tape, precisely to avoid the risk of
10675 such errors. Be fully aware that writing at the wrong position on a
10676 tape loses all information past this point and most probably until the
10677 end of the tape, and this destroyed information @emph{cannot} be
10680 To save @var{directory-1} as a first archive at the beginning of a
10681 tape, and leave that tape ready for a second archive, you should use:
10684 $ @kbd{mt -f /dev/nrtape rewind}
10685 $ @kbd{tar cf /dev/nrtape @var{directory-1}}
10689 @dfn{Tape marks} are special magnetic patterns written on the tape
10690 media, which are later recognizable by the reading hardware. These
10691 marks are used after each file, when there are many on a single tape.
10692 An empty file (that is to say, two tape marks in a row) signal the
10693 logical end of the tape, after which no file exist. Usually,
10694 non-rewinding tape device drivers will react to the close request issued
10695 by @command{tar} by first writing two tape marks after your archive, and by
10696 backspacing over one of these. So, if you remove the tape at that time
10697 from the tape drive, it is properly terminated. But if you write
10698 another file at the current position, the second tape mark will be
10699 erased by the new information, leaving only one tape mark between files.
10701 So, you may now save @var{directory-2} as a second archive after the
10702 first on the same tape by issuing the command:
10705 $ @kbd{tar cf /dev/nrtape @var{directory-2}}
10709 and so on for all the archives you want to put on the same tape.
10711 Another usual case is that you do not write all the archives the same
10712 day, and you need to remove and store the tape between two archive
10713 sessions. In general, you must remember how many files are already
10714 saved on your tape. Suppose your tape already has 16 files on it, and
10715 that you are ready to write the 17th. You have to take care of skipping
10716 the first 16 tape marks before saving @var{directory-17}, say, by using
10720 $ @kbd{mt -f /dev/nrtape rewind}
10721 $ @kbd{mt -f /dev/nrtape fsf 16}
10722 $ @kbd{tar cf /dev/nrtape @var{directory-17}}
10725 In all the previous examples, we put aside blocking considerations, but
10726 you should do the proper things for that as well. @xref{Blocking}.
10729 * Tape Positioning:: Tape Positions and Tape Marks
10730 * mt:: The @command{mt} Utility
10733 @node Tape Positioning
10734 @subsection Tape Positions and Tape Marks
10737 Just as archives can store more than one file from the file system,
10738 tapes can store more than one archive file. To keep track of where
10739 archive files (or any other type of file stored on tape) begin and
10740 end, tape archive devices write magnetic @dfn{tape marks} on the
10741 archive media. Tape drives write one tape mark between files,
10742 two at the end of all the file entries.
10744 If you think of data as a series of records "rrrr"'s, and tape marks as
10745 "*"'s, a tape might look like the following:
10748 rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
10751 Tape devices read and write tapes using a read/write @dfn{tape
10752 head}---a physical part of the device which can only access one
10753 point on the tape at a time. When you use @command{tar} to read or
10754 write archive data from a tape device, the device will begin reading
10755 or writing from wherever on the tape the tape head happens to be,
10756 regardless of which archive or what part of the archive the tape
10757 head is on. Before writing an archive, you should make sure that no
10758 data on the tape will be overwritten (unless it is no longer needed).
10759 Before reading an archive, you should make sure the tape head is at
10760 the beginning of the archive you want to read. You can do it manually
10761 via @code{mt} utility (@pxref{mt}). The @code{restore} script does
10762 that automatically (@pxref{Scripted Restoration}).
10764 If you want to add new archive file entries to a tape, you should
10765 advance the tape to the end of the existing file entries, backspace
10766 over the last tape mark, and write the new archive file. If you were
10767 to add two archives to the example above, the tape might look like the
10771 rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
10775 @subsection The @command{mt} Utility
10778 @FIXME{Is it true that this only works on non-block devices?
10779 should explain the difference, (fixed or variable).}
10780 @xref{Blocking Factor}.
10782 You can use the @command{mt} utility to advance or rewind a tape past a
10783 specified number of archive files on the tape. This will allow you
10784 to move to the beginning of an archive before extracting or reading
10785 it, or to the end of all the archives before writing a new one.
10786 @FIXME{Why isn't there an "advance 'til you find two tape marks
10789 The syntax of the @command{mt} command is:
10792 @kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
10795 where @var{tapename} is the name of the tape device, @var{number} is
10796 the number of times an operation is performed (with a default of one),
10797 and @var{operation} is one of the following:
10799 @FIXME{is there any use for record operations?}
10804 Writes @var{number} tape marks at the current position on the tape.
10807 Moves tape position forward @var{number} files.
10810 Moves tape position back @var{number} files.
10813 Rewinds the tape. (Ignores @var{number}).
10817 Rewinds the tape and takes the tape device off-line. (Ignores @var{number}).
10820 Prints status information about the tape unit.
10824 @FIXME{Is there a better way to frob the spacing on the list?}
10826 If you don't specify a @var{tapename}, @command{mt} uses the environment
10827 variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
10828 the default device specified in your @file{sys/mtio.h} file
10829 (@code{DEFTAPE} variable). If this is not defined, the program will
10830 display a descriptive error message and exit with code 1.
10832 @command{mt} returns a 0 exit status when the operation(s) were
10833 successful, 1 if the command was unrecognized, and 2 if an operation
10836 @node Using Multiple Tapes
10837 @section Using Multiple Tapes
10839 Often you might want to write a large archive, one larger than will fit
10840 on the actual tape you are using. In such a case, you can run multiple
10841 @command{tar} commands, but this can be inconvenient, particularly if you
10842 are using options like @option{--exclude=@var{pattern}} or dumping entire file systems.
10843 Therefore, @command{tar} provides a special mode for creating
10844 multi-volume archives.
10846 @dfn{Multi-volume} archive is a single @command{tar} archive, stored
10847 on several media volumes of fixed size. Although in this section we will
10848 often call @samp{volume} a @dfn{tape}, there is absolutely no
10849 requirement for multi-volume archives to be stored on tapes. Instead,
10850 they can use whatever media type the user finds convenient, they can
10851 even be located on files.
10853 When creating a multi-volume archive, @GNUTAR{} continues to fill
10854 current volume until it runs out of space, then it switches to
10855 next volume (usually the operator is queried to replace the tape on
10856 this point), and continues working on the new volume. This operation
10857 continues until all requested files are dumped. If @GNUTAR{} detects
10858 end of media while dumping a file, such a file is archived in split
10859 form. Some very big files can even be split across several volumes.
10861 Each volume is itself a valid @GNUTAR{} archive, so it can be read
10862 without any special options. Consequently any file member residing
10863 entirely on one volume can be extracted or otherwise operated upon
10864 without needing the other volume. Sure enough, to extract a split
10865 member you would need all volumes its parts reside on.
10867 Multi-volume archives suffer from several limitations. In particular,
10868 they cannot be compressed.
10870 @GNUTAR{} is able to create multi-volume archives of two formats
10871 (@pxref{Formats}): @samp{GNU} and @samp{POSIX}.
10874 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
10875 * Tape Files:: Tape Files
10876 * Tarcat:: Concatenate Volumes into a Single Archive
10880 @node Multi-Volume Archives
10881 @subsection Archives Longer than One Tape or Disk
10882 @cindex Multi-volume archives
10884 @opindex multi-volume
10885 To create an archive that is larger than will fit on a single unit of
10886 the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
10887 the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
10888 archive can be manipulated like any other archive (provided the
10889 @option{--multi-volume} option is specified), but is stored on more
10890 than one tape or disk.
10892 When you specify @option{--multi-volume}, @command{tar} does not report an
10893 error when it comes to the end of an archive volume (when reading), or
10894 the end of the media (when writing). Instead, it prompts you to load
10895 a new storage volume. If the archive is on a magnetic tape, you
10896 should change tapes when you see the prompt; if the archive is on a
10897 floppy disk, you should change disks; etc.
10900 @item --multi-volume
10902 Creates a multi-volume archive, when used in conjunction with
10903 @option{--create} (@option{-c}). To perform any other operation on a multi-volume
10904 archive, specify @option{--multi-volume} in conjunction with that
10909 $ @kbd{tar --create --multi-volume --file=/dev/tape @var{files}}
10913 The method @command{tar} uses to detect end of tape is not perfect, and
10914 fails on some operating systems or on some devices. If @command{tar}
10915 cannot detect the end of the tape itself, you can use
10916 @option{--tape-length} option to inform it about the capacity of the
10919 @anchor{tape-length}
10921 @opindex tape-length
10922 @item --tape-length=@var{size}
10923 @itemx -L @var{size}
10924 Set maximum length of a volume. The @var{size} argument should then
10925 be the usable size of the tape in units of 1024 bytes. This option
10926 selects @option{--multi-volume} automatically. For example:
10929 $ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}}
10933 @anchor{change volume prompt}
10934 When @GNUTAR{} comes to the end of a storage media, it asks you to
10935 change the volume. The built-in prompt for POSIX locale
10936 is@footnote{If you run @GNUTAR{} under a different locale, the
10937 translation to the locale's language will be used.}:
10940 Prepare volume #@var{n} for `@var{archive}' and hit return:
10944 where @var{n} is the ordinal number of the volume to be created and
10945 @var{archive} is archive file or device name.
10947 When prompting for a new tape, @command{tar} accepts any of the following
10952 Request @command{tar} to explain possible responses
10954 Request @command{tar} to exit immediately.
10955 @item n @var{file-name}
10956 Request @command{tar} to write the next volume on the file @var{file-name}.
10958 Request @command{tar} to run a subshell. This option can be disabled
10959 by giving @option{--restrict} command line option to
10960 @command{tar}@footnote{@xref{--restrict}, for more information about
10963 Request @command{tar} to begin writing the next volume.
10966 (You should only type @samp{y} after you have changed the tape;
10967 otherwise @command{tar} will write over the volume it just finished.)
10969 @cindex Volume number file
10971 @anchor{volno-file}
10972 @opindex volno-file
10973 The volume number used by @command{tar} in its tape-changing prompt
10974 can be changed; if you give the
10975 @option{--volno-file=@var{file-of-number}} option, then
10976 @var{file-of-number} should be an non-existing file to be created, or
10977 else, a file already containing a decimal number. That number will be
10978 used as the volume number of the first volume written. When
10979 @command{tar} is finished, it will rewrite the file with the
10980 now-current volume number. (This does not change the volume number
10981 written on a tape label, as per @ref{label}, it @emph{only} affects
10982 the number used in the prompt.)
10984 @cindex End-of-archive info script
10985 @cindex Info script
10986 @anchor{info-script}
10987 @opindex info-script
10988 @opindex new-volume-script
10989 If you want more elaborate behavior than this, you can write a special
10990 @dfn{new volume script}, that will be responsible for changing the
10991 volume, and instruct @command{tar} to use it instead of its normal
10992 prompting procedure:
10995 @item --info-script=@var{script-name}
10996 @itemx --new-volume-script=@var{script-name}
10997 @itemx -F @var{script-name}
10998 Specify the full name of the volume script to use. The script can be
10999 used to eject cassettes, or to broadcast messages such as
11000 @samp{Someone please come change my tape} when performing unattended
11004 The @var{script-name} is executed without any command line
11005 arguments. It inherits @command{tar}'s shell environment.
11006 Additional data is passed to it via the following
11007 environment variables:
11010 @vrindex TAR_VERSION, info script environment variable
11012 @GNUTAR{} version number.
11014 @vrindex TAR_ARCHIVE, info script environment variable
11016 The name of the archive @command{tar} is processing.
11018 @vrindex TAR_BLOCKING_FACTOR, info script environment variable
11019 @item TAR_BLOCKING_FACTOR
11020 Current blocking factor (@pxref{Blocking}.
11022 @vrindex TAR_VOLUME, info script environment variable
11024 Ordinal number of the volume @command{tar} is about to start.
11026 @vrindex TAR_SUBCOMMAND, info script environment variable
11027 @item TAR_SUBCOMMAND
11028 A short option describing the operation @command{tar} is executing
11029 @xref{Operations}, for a complete list of subcommand options.
11031 @vrindex TAR_FORMAT, info script environment variable
11033 Format of the archive being processed. @xref{Formats}, for a complete
11034 list of archive format names.
11036 @vrindex TAR_FD, info script environment variable
11038 File descriptor which can be used to communicate the new volume
11039 name to @command{tar}.
11042 The volume script can instruct @command{tar} to use new archive name,
11043 by writing in to file descriptor @env{$TAR_FD} (see below for an example).
11045 If the info script fails, @command{tar} exits; otherwise, it begins
11046 writing the next volume.
11048 If you want @command{tar} to cycle through a series of files or tape
11049 drives, there are three approaches to choose from. First of all, you
11050 can give @command{tar} multiple @option{--file} options. In this case
11051 the specified files will be used, in sequence, as the successive
11052 volumes of the archive. Only when the first one in the sequence needs
11053 to be used again will @command{tar} prompt for a tape change (or run
11054 the info script). For example, suppose someone has two tape drives on
11055 a system named @file{/dev/tape0} and @file{/dev/tape1}. For having
11056 @GNUTAR{} to switch to the second drive when it needs to write the
11057 second tape, and then back to the first tape, etc., just do either of:
11060 $ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
11061 $ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
11064 The second method is to use the @samp{n} response to the tape-change
11067 Finally, the most flexible approach is to use a volume script, that
11068 writes new archive name to the file descriptor @env{$TAR_FD}. For example, the
11069 following volume script will create a series of archive files, named
11070 @file{@var{archive}-@var{vol}}, where @var{archive} is the name of the
11071 archive being created (as given by @option{--file} option) and
11072 @var{vol} is the ordinal number of the archive being created:
11077 echo Preparing volume $TAR_VOLUME of $TAR_ARCHIVE.
11079 name=`expr $TAR_ARCHIVE : '\(.*\)-.*'`
11080 case $TAR_SUBCOMMAND in
11082 -d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
11087 echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&$TAR_FD
11091 The same script can be used while listing, comparing or extracting
11092 from the created archive. For example:
11096 # @r{Create a multi-volume archive:}
11097 $ @kbd{tar -c -L1024 -f archive.tar -F new-volume .}
11098 # @r{Extract from the created archive:}
11099 $ @kbd{tar -x -f archive.tar -F new-volume .}
11104 Notice, that the first command had to use @option{-L} option, since
11105 otherwise @GNUTAR{} will end up writing everything to file
11106 @file{archive.tar}.
11108 You can read each individual volume of a multi-volume archive as if it
11109 were an archive by itself. For example, to list the contents of one
11110 volume, use @option{--list}, without @option{--multi-volume} specified.
11111 To extract an archive member from one volume (assuming it is described
11112 that volume), use @option{--extract}, again without
11113 @option{--multi-volume}.
11115 If an archive member is split across volumes (i.e., its entry begins on
11116 one volume of the media and ends on another), you need to specify
11117 @option{--multi-volume} to extract it successfully. In this case, you
11118 should load the volume where the archive member starts, and use
11119 @samp{tar --extract --multi-volume}---@command{tar} will prompt for later
11120 volumes as it needs them. @xref{extracting archives}, for more
11121 information about extracting archives.
11123 Multi-volume archives can be modified like any other archive. To add
11124 files to a multi-volume archive, you need to only mount the last
11125 volume of the archive media (and new volumes, if needed). For all
11126 other operations, you need to use the entire archive.
11128 If a multi-volume archive was labeled using
11129 @option{--label=@var{archive-label}} (@pxref{label}) when it was
11130 created, @command{tar} will not automatically label volumes which are
11131 added later. To label subsequent volumes, specify
11132 @option{--label=@var{archive-label}} again in conjunction with the
11133 @option{--append}, @option{--update} or @option{--concatenate} operation.
11135 Notice that multi-volume support is a GNU extension and the archives
11136 created in this mode should be read only using @GNUTAR{}. If you
11137 absolutely have to process such archives using a third-party @command{tar}
11138 implementation, read @ref{Split Recovery}.
11141 @subsection Tape Files
11144 To give the archive a name which will be recorded in it, use the
11145 @option{--label=@var{volume-label}} (@option{-V @var{volume-label}})
11146 option. This will write a special block identifying
11147 @var{volume-label} as the name of the archive to the front of the
11148 archive which will be displayed when the archive is listed with
11149 @option{--list}. If you are creating a multi-volume archive with
11150 @option{--multi-volume} (@pxref{Using Multiple Tapes}), then the
11151 volume label will have @samp{Volume @var{nnn}} appended to the name
11152 you give, where @var{nnn} is the number of the volume of the archive.
11153 (If you use the @option{--label=@var{volume-label}}) option when
11154 reading an archive, it checks to make sure the label on the tape
11155 matches the one you give. @xref{label}.
11157 When @command{tar} writes an archive to tape, it creates a single
11158 tape file. If multiple archives are written to the same tape, one
11159 after the other, they each get written as separate tape files. When
11160 extracting, it is necessary to position the tape at the right place
11161 before running @command{tar}. To do this, use the @command{mt} command.
11162 For more information on the @command{mt} command and on the organization
11163 of tapes into a sequence of tape files, see @ref{mt}.
11165 People seem to often do:
11168 @kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
11171 or such, for pushing a common date in all volumes or an archive set.
11174 @subsection Concatenate Volumes into a Single Archive
11177 Sometimes it is necessary to convert existing @GNUTAR{} multi-volume
11178 archive to a single @command{tar} archive. Simply concatenating all
11179 volumes into one will not work, since each volume carries an additional
11180 information at the beginning. @GNUTAR{} is shipped with the shell
11181 script @command{tarcat} designed for this purpose.
11183 The script takes a list of files comprising a multi-volume archive
11184 and creates the resulting archive at the standard output. For example:
11187 @kbd{tarcat vol.1 vol.2 vol.3 | tar tf -}
11190 The script implements a simple heuristics to determine the format of
11191 the first volume file and to decide how to process the rest of the
11192 files. However, it makes no attempt to verify whether the files are
11193 given in order or even if they are valid @command{tar} archives.
11194 It uses @command{dd} and does not filter its standard error, so you
11195 will usually see lots of spurious messages.
11197 @FIXME{The script is not installed. Should we install it?}
11200 @section Including a Label in the Archive
11201 @cindex Labeling an archive
11202 @cindex Labels on the archive media
11203 @cindex Labeling multi-volume archives
11207 To avoid problems caused by misplaced paper labels on the archive
11208 media, you can include a @dfn{label} entry---an archive member which
11209 contains the name of the archive---in the archive itself. Use the
11210 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11211 option in conjunction with the @option{--create} operation to include
11212 a label entry in the archive as it is being created.
11215 @item --label=@var{archive-label}
11216 @itemx -V @var{archive-label}
11217 Includes an @dfn{archive-label} at the beginning of the archive when
11218 the archive is being created, when used in conjunction with the
11219 @option{--create} operation. Checks to make sure the archive label
11220 matches the one specified (when used in conjunction with any other
11224 If you create an archive using both
11225 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11226 and @option{--multi-volume} (@option{-M}), each volume of the archive
11227 will have an archive label of the form @samp{@var{archive-label}
11228 Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the
11229 next, and so on. @xref{Using Multiple Tapes}, for information on
11230 creating multiple volume archives.
11232 @cindex Volume label, listing
11233 @cindex Listing volume label
11234 The volume label will be displayed by @option{--list} along with
11235 the file contents. If verbose display is requested, it will also be
11236 explicitly marked as in the example below:
11240 $ @kbd{tar --verbose --list --file=iamanarchive}
11241 V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
11242 -rw-r--r-- ringo user 40 1990-05-21 13:30 iamafilename
11246 @opindex test-label
11247 @anchor{--test-label option}
11248 However, @option{--list} option will cause listing entire
11249 contents of the archive, which may be undesirable (for example, if the
11250 archive is stored on a tape). You can request checking only the volume
11251 by specifying @option{--test-label} option. This option reads only the
11252 first block of an archive, so it can be used with slow storage
11253 devices. For example:
11257 $ @kbd{tar --test-label --file=iamanarchive}
11262 If @option{--test-label} is used with a single command line
11263 argument, @command{tar} compares the volume label with the
11264 argument. It exits with code 0 if the two strings match, and with code
11265 2 otherwise. In this case no output is displayed. For example:
11269 $ @kbd{tar --test-label --file=iamanarchive 'iamalable'}
11271 $ @kbd{tar --test-label --file=iamanarchive 'iamalable' alabel}
11276 If you request any operation, other than @option{--create}, along
11277 with using @option{--label} option, @command{tar} will first check if
11278 the archive label matches the one specified and will refuse to proceed
11279 if it does not. Use this as a safety precaution to avoid accidentally
11280 overwriting existing archives. For example, if you wish to add files
11281 to @file{archive}, presumably labeled with string @samp{My volume},
11286 $ @kbd{tar -rf archive --label 'My volume' .}
11287 tar: Archive not labeled to match `My volume'
11292 in case its label does not match. This will work even if
11293 @file{archive} is not labeled at all.
11295 Similarly, @command{tar} will refuse to list or extract the
11296 archive if its label doesn't match the @var{archive-label}
11297 specified. In those cases, @var{archive-label} argument is interpreted
11298 as a globbing-style pattern which must match the actual magnetic
11299 volume label. @xref{exclude}, for a precise description of how match
11300 is attempted@footnote{Previous versions of @command{tar} used full
11301 regular expression matching, or before that, only exact string
11302 matching, instead of wildcard matchers. We decided for the sake of
11303 simplicity to use a uniform matching device through
11304 @command{tar}.}. If the switch @option{--multi-volume} (@option{-M}) is being used,
11305 the volume label matcher will also suffix @var{archive-label} by
11306 @w{@samp{ Volume [1-9]*}} if the initial match fails, before giving
11307 up. Since the volume numbering is automatically added in labels at
11308 creation time, it sounded logical to equally help the user taking care
11309 of it when the archive is being read.
11311 The @option{--label} was once called @option{--volume}, but is not
11312 available under that name anymore.
11314 You can also use @option{--label} to get a common information on
11315 all tapes of a series. For having this information different in each
11316 series created through a single script used on a regular basis, just
11317 manage to get some date string as part of the label. For example:
11321 $ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
11322 $ @kbd{tar --create --file=/dev/tape --multi-volume \
11323 --volume="Daily backup for `date +%Y-%m-%d`"}
11327 Also note that each label has its own date and time, which corresponds
11328 to when @GNUTAR{} initially attempted to write it,
11329 often soon after the operator launches @command{tar} or types the
11330 carriage return telling that the next tape is ready. Comparing date
11331 labels does give an idea of tape throughput only if the delays for
11332 rewinding tapes and the operator switching them were negligible, which
11333 is usually not the case.
11336 @section Verifying Data as It is Stored
11337 @cindex Verifying a write operation
11338 @cindex Double-checking a write operation
11343 @opindex verify, short description
11344 Attempt to verify the archive after writing.
11347 This option causes @command{tar} to verify the archive after writing it.
11348 Each volume is checked after it is written, and any discrepancies
11349 are recorded on the standard error output.
11351 Verification requires that the archive be on a back-space-able medium.
11352 This means pipes, some cartridge tape drives, and some other devices
11353 cannot be verified.
11355 You can insure the accuracy of an archive by comparing files in the
11356 system with archive members. @command{tar} can compare an archive to the
11357 file system as the archive is being written, to verify a write
11358 operation, or can compare a previously written archive, to insure that
11361 @xopindex{verify, using with @option{--create}}
11362 @xopindex{create, using with @option{--verify}}
11363 To check for discrepancies in an archive immediately after it is
11364 written, use the @option{--verify} (@option{-W}) option in conjunction with
11365 the @option{--create} operation. When this option is
11366 specified, @command{tar} checks archive members against their counterparts
11367 in the file system, and reports discrepancies on the standard error.
11369 To verify an archive, you must be able to read it from before the end
11370 of the last written entry. This option is useful for detecting data
11371 errors on some tapes. Archives written to pipes, some cartridge tape
11372 drives, and some other devices cannot be verified.
11374 One can explicitly compare an already made archive with the file
11375 system by using the @option{--compare} (@option{--diff}, @option{-d})
11376 option, instead of using the more automatic @option{--verify} option.
11379 Note that these two options have a slightly different intent. The
11380 @option{--compare} option checks how identical are the logical contents of some
11381 archive with what is on your disks, while the @option{--verify} option is
11382 really for checking if the physical contents agree and if the recording
11383 media itself is of dependable quality. So, for the @option{--verify}
11384 operation, @command{tar} tries to defeat all in-memory cache pertaining to
11385 the archive, while it lets the speed optimization undisturbed for the
11386 @option{--compare} option. If you nevertheless use @option{--compare} for
11387 media verification, you may have to defeat the in-memory cache yourself,
11388 maybe by opening and reclosing the door latch of your recording unit,
11389 forcing some doubt in your operating system about the fact this is really
11390 the same volume as the one just written or read.
11392 The @option{--verify} option would not be necessary if drivers were indeed
11393 able to detect dependably all write failures. This sometimes require many
11394 magnetic heads, some able to read after the writes occurred. One would
11395 not say that drivers unable to detect all cases are necessarily flawed,
11396 as long as programming is concerned.
11398 The @option{--verify} (@option{-W}) option will not work in
11399 conjunction with the @option{--multi-volume} (@option{-M}) option or
11400 the @option{--append} (@option{-r}), @option{--update} (@option{-u})
11401 and @option{--delete} operations. @xref{Operations}, for more
11402 information on these operations.
11404 Also, since @command{tar} normally strips leading @samp{/} from file
11405 names (@pxref{absolute}), a command like @samp{tar --verify -cf
11406 /tmp/foo.tar /etc} will work as desired only if the working directory is
11407 @file{/}, as @command{tar} uses the archive's relative member names
11408 (e.g., @file{etc/motd}) when verifying the archive.
11410 @node Write Protection
11411 @section Write Protection
11413 Almost all tapes and diskettes, and in a few rare cases, even disks can
11414 be @dfn{write protected}, to protect data on them from being changed.
11415 Once an archive is written, you should write protect the media to prevent
11416 the archive from being accidentally overwritten or deleted. (This will
11417 protect the archive from being changed with a tape or floppy drive---it
11418 will not protect it from magnet fields or other physical hazards).
11420 The write protection device itself is usually an integral part of the
11421 physical media, and can be a two position (write enabled/write
11422 disabled) switch, a notch which can be popped out or covered, a ring
11423 which can be removed from the center of a tape reel, or some other
11424 changeable feature.
11429 This appendix lists some important user-visible changes between
11430 version @GNUTAR{} @value{VERSION} and previous versions. An up-to-date
11431 version of this document is available at
11432 @uref{http://www.gnu.org/@/software/@/tar/manual/changes.html,the
11433 @GNUTAR{} documentation page}.
11436 @item Use of globbing patterns when listing and extracting.
11438 Previous versions of GNU tar assumed shell-style globbing when
11439 extracting from or listing an archive. For example:
11442 $ @kbd{tar xf foo.tar '*.c'}
11445 would extract all files whose names end in @samp{.c}. This behavior
11446 was not documented and was incompatible with traditional tar
11447 implementations. Therefore, starting from version 1.15.91, GNU tar
11448 no longer uses globbing by default. For example, the above invocation
11449 is now interpreted as a request to extract from the archive the file
11452 To facilitate transition to the new behavior for those users who got
11453 used to the previous incorrect one, @command{tar} will print a warning
11454 if it finds out that a requested member was not found in the archive
11455 and its name looks like a globbing pattern. For example:
11458 $ @kbd{tar xf foo.tar '*.c'}
11459 tar: Pattern matching characters used in file names. Please,
11460 tar: use --wildcards to enable pattern matching, or --no-wildcards to
11461 tar: suppress this warning.
11462 tar: *.c: Not found in archive
11463 tar: Error exit delayed from previous errors
11466 To treat member names as globbing patterns, use --wildcards option.
11467 If you want to tar to mimic the behavior of versions prior to 1.15.91,
11468 add this option to your @env{TAR_OPTIONS} variable.
11470 @xref{wildcards}, for the detailed discussion of the use of globbing
11471 patterns by @GNUTAR{}.
11473 @item Use of short option @option{-o}.
11475 Earlier versions of @GNUTAR{} understood @option{-o} command line
11476 option as a synonym for @option{--old-archive}.
11478 @GNUTAR{} starting from version 1.13.90 understands this option as
11479 a synonym for @option{--no-same-owner}. This is compatible with
11480 UNIX98 @command{tar} implementations.
11482 However, to facilitate transition, @option{-o} option retains its
11483 old semantics when it is used with one of archive-creation commands.
11484 Users are encouraged to use @option{--format=oldgnu} instead.
11486 It is especially important, since versions of @acronym{GNU} Automake
11487 up to and including 1.8.4 invoke tar with this option to produce
11488 distribution tarballs. @xref{Formats,v7}, for the detailed discussion
11489 of this issue and its implications.
11491 @FIXME{Change the first argument to tar-formats when the new Automake is
11492 out. The proposition to add @anchor{} to the appropriate place of its
11493 docs was accepted by Automake people --Sergey 2006-05-25}.
11494 @xref{Options, tar-v7, Changing Automake's Behavior,
11495 automake, GNU Automake}, for a description on how to use various
11496 archive formats with @command{automake}.
11498 Future versions of @GNUTAR{} will understand @option{-o} only as a
11499 synonym for @option{--no-same-owner}.
11501 @item Use of short option @option{-l}
11503 Earlier versions of @GNUTAR{} understood @option{-l} option as a
11504 synonym for @option{--one-file-system}. Since such usage contradicted
11505 to UNIX98 specification and harmed compatibility with other
11506 implementation, it was declared deprecated in version 1.14. However,
11507 to facilitate transition to its new semantics, it was supported by
11508 versions 1.15 and 1.15.90. The present use of @option{-l} as a short
11509 variant of @option{--check-links} was introduced in version 1.15.91.
11511 @item Use of options @option{--portability} and @option{--old-archive}
11513 These options are deprecated. Please use @option{--format=v7} instead.
11515 @item Use of option @option{--posix}
11517 This option is deprecated. Please use @option{--format=posix} instead.
11520 @node Configuring Help Summary
11521 @appendix Configuring Help Summary
11523 Running @kbd{tar --help} displays the short @command{tar} option
11524 summary (@pxref{help}). This summary is organized by @dfn{groups} of
11525 semantically close options. The options within each group are printed
11526 in the following order: a short option, eventually followed by a list
11527 of corresponding long option names, followed by a short description of
11528 the option. For example, here is an excerpt from the actual @kbd{tar
11532 Main operation mode:
11534 -A, --catenate, --concatenate append tar files to an archive
11535 -c, --create create a new archive
11536 -d, --diff, --compare find differences between archive and
11538 --delete delete from the archive
11541 @vrindex ARGP_HELP_FMT, environment variable
11542 The exact visual representation of the help output is configurable via
11543 @env{ARGP_HELP_FMT} environment variable. The value of this variable
11544 is a comma-separated list of @dfn{format variable} assignments. There
11545 are two kinds of format variables. An @dfn{offset variable} keeps the
11546 offset of some part of help output text from the leftmost column on
11547 the screen. A @dfn{boolean} variable is a flag that toggles some
11548 output feature on or off. Depending on the type of the corresponding
11549 variable, there are two kinds of assignments:
11552 @item Offset assignment
11554 The assignment to an offset variable has the following syntax:
11557 @var{variable}=@var{value}
11561 where @var{variable} is the variable name, and @var{value} is a
11562 numeric value to be assigned to the variable.
11564 @item Boolean assignment
11566 To assign @code{true} value to a variable, simply put this variable name. To
11567 assign @code{false} value, prefix the variable name with @samp{no-}. For
11572 # Assign @code{true} value:
11574 # Assign @code{false} value:
11580 Following variables are declared:
11582 @deftypevr {Help Output} boolean dup-args
11583 If true, arguments for an option are shown with both short and long
11584 options, even when a given option has both forms, for example:
11587 -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE
11590 If false, then if an option has both short and long forms, the
11591 argument is only shown with the long one, for example:
11594 -f, --file=ARCHIVE use archive file or device ARCHIVE
11598 and a message indicating that the argument is applicable to both
11599 forms is printed below the options. This message can be disabled
11600 using @code{dup-args-note} (see below).
11602 The default is false.
11605 @deftypevr {Help Output} boolean dup-args-note
11606 If this variable is true, which is the default, the following notice
11607 is displayed at the end of the help output:
11610 Mandatory or optional arguments to long options are also mandatory or
11611 optional for any corresponding short options.
11614 Setting @code{no-dup-args-note} inhibits this message. Normally, only one of
11615 variables @code{dup-args} or @code{dup-args-note} should be set.
11618 @deftypevr {Help Output} offset short-opt-col
11619 Column in which short options start. Default is 2.
11623 $ @kbd{tar --help|grep ARCHIVE}
11624 -f, --file=ARCHIVE use archive file or device ARCHIVE
11625 $ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE}
11626 -f, --file=ARCHIVE use archive file or device ARCHIVE
11631 @deftypevr {Help Output} offset long-opt-col
11632 Column in which long options start. Default is 6. For example:
11636 $ @kbd{tar --help|grep ARCHIVE}
11637 -f, --file=ARCHIVE use archive file or device ARCHIVE
11638 $ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE}
11639 -f, --file=ARCHIVE use archive file or device ARCHIVE
11644 @deftypevr {Help Output} offset doc-opt-col
11645 Column in which @dfn{doc options} start. A doc option isn't actually
11646 an option, but rather an arbitrary piece of documentation that is
11647 displayed in much the same manner as the options. For example, in
11648 the description of @option{--format} option:
11652 -H, --format=FORMAT create archive of the given format.
11654 FORMAT is one of the following:
11656 gnu GNU tar 1.13.x format
11657 oldgnu GNU format as per tar <= 1.12
11658 pax POSIX 1003.1-2001 (pax) format
11660 ustar POSIX 1003.1-1988 (ustar) format
11661 v7 old V7 tar format
11666 the format names are doc options. Thus, if you set
11667 @kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output
11668 will look as follows:
11672 -H, --format=FORMAT create archive of the given format.
11674 FORMAT is one of the following:
11676 gnu GNU tar 1.13.x format
11677 oldgnu GNU format as per tar <= 1.12
11678 pax POSIX 1003.1-2001 (pax) format
11680 ustar POSIX 1003.1-1988 (ustar) format
11681 v7 old V7 tar format
11686 @deftypevr {Help Output} offset opt-doc-col
11687 Column in which option description starts. Default is 29.
11691 $ @kbd{tar --help|grep ARCHIVE}
11692 -f, --file=ARCHIVE use archive file or device ARCHIVE
11693 $ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE}
11694 -f, --file=ARCHIVE use archive file or device ARCHIVE
11695 $ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE}
11697 use archive file or device ARCHIVE
11702 Notice, that the description starts on a separate line if
11703 @code{opt-doc-col} value is too small.
11706 @deftypevr {Help Output} offset header-col
11707 Column in which @dfn{group headers} are printed. A group header is a
11708 descriptive text preceding an option group. For example, in the
11712 Main operation mode:
11714 -A, --catenate, --concatenate append tar files to
11716 -c, --create create a new archive
11719 @samp{Main operation mode:} is the group header.
11721 The default value is 1.
11724 @deftypevr {Help Output} offset usage-indent
11725 Indentation of wrapped usage lines. Affects @option{--usage}
11726 output. Default is 12.
11729 @deftypevr {Help Output} offset rmargin
11730 Right margin of the text output. Used for wrapping.
11733 @node Fixing Snapshot Files
11734 @appendix Fixing Snapshot Files
11735 @include tar-snapshot-edit.texi
11737 @node Tar Internals
11738 @appendix Tar Internals
11739 @include intern.texi
11743 @include genfile.texi
11745 @node Free Software Needs Free Documentation
11746 @appendix Free Software Needs Free Documentation
11747 @include freemanuals.texi
11749 @node Copying This Manual
11750 @appendix Copying This Manual
11753 * GNU Free Documentation License:: License for copying this manual
11758 @node Index of Command Line Options
11759 @appendix Index of Command Line Options
11761 This appendix contains an index of all @GNUTAR{} long command line
11762 options. The options are listed without the preceding double-dash.
11763 For a cross-reference of short command line options, @ref{Short Option Summary}.
11776 @c Local variables:
11777 @c texinfo-column-for-description: 32
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