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
25 @c Put everything in one index (arbitrarily chosen to be the concept index).
33 This manual is for @acronym{GNU} @command{tar} (version
34 @value{VERSION}, @value{UPDATED}), which creates and extracts files
37 Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
38 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
41 Permission is granted to copy, distribute and/or modify this document
42 under the terms of the GNU Free Documentation License, Version 1.1 or
43 any later version published by the Free Software Foundation; with no
44 Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
45 and with the Back-Cover Texts as in (a) below. A copy of the license
46 is included in the section entitled "GNU Free Documentation License".
48 (a) The FSF's Back-Cover Text is: ``You have the freedom to
49 copy and modify this GNU manual. Buying copies from the FSF
50 supports it in developing GNU and promoting software freedom.''
54 @dircategory Archiving
56 * Tar: (tar). Making tape (or disk) archives.
59 @dircategory Individual utilities
61 * tar: (tar)tar invocation. Invoking @GNUTAR{}.
64 @shorttitlepage @acronym{GNU} @command{tar}
67 @title @acronym{GNU} tar: an archiver tool
68 @subtitle @value{RENDITION} @value{VERSION}, @value{UPDATED}
69 @author John Gilmore, Jay Fenlason et al.
72 @vskip 0pt plus 1filll
78 @top @acronym{GNU} tar: an archiver tool
83 @cindex archiving files
85 The first part of this master menu lists the major nodes in this Info
86 document. The rest of the menu lists all the lower level nodes.
89 @c The master menu goes here.
91 @c NOTE: To update it from within Emacs, make sure mastermenu.el is
92 @c loaded and run texinfo-master-menu.
93 @c To update it from the command line, run
104 * Date input formats::
111 * Configuring Help Summary::
112 * Fixing Snapshot Files::
115 * Free Software Needs Free Documentation::
116 * Copying This Manual::
117 * Index of Command Line Options::
121 --- The Detailed Node Listing ---
125 * Book Contents:: What this Book Contains
126 * Definitions:: Some Definitions
127 * What tar Does:: What @command{tar} Does
128 * Naming tar Archives:: How @command{tar} Archives are Named
129 * Authors:: @GNUTAR{} Authors
130 * Reports:: Reporting bugs or suggestions
132 Tutorial Introduction to @command{tar}
135 * stylistic conventions::
136 * basic tar options:: Basic @command{tar} Operations and Options
137 * frequent operations::
138 * Two Frequent Options::
139 * create:: How to Create Archives
140 * list:: How to List Archives
141 * extract:: How to Extract Members from an Archive
144 Two Frequently Used Options
150 How to Create Archives
152 * prepare for examples::
153 * Creating the archive::
162 How to Extract Members from an Archive
164 * extracting archives::
167 * extracting untrusted archives::
173 * using tar options::
182 The Three Option Styles
184 * Long Options:: Long Option Style
185 * Short Options:: Short Option Style
186 * Old Options:: Old Option Style
187 * Mixing:: Mixing Option Styles
189 All @command{tar} Options
191 * Operation Summary::
193 * Short Option Summary::
205 Advanced @GNUTAR{} Operations
214 How to Add Files to Existing Archives: @option{--append}
216 * appending files:: Appending Files to an Archive
223 Options Used by @option{--create}
225 * override:: Overriding File Metadata.
226 * Ignore Failed Read::
228 Options Used by @option{--extract}
230 * Reading:: Options to Help Read Archives
231 * Writing:: Changing How @command{tar} Writes Files
232 * Scarce:: Coping with Scarce Resources
234 Options to Help Read Archives
236 * read full records::
239 Changing How @command{tar} Writes Files
241 * Dealing with Old Files::
242 * Overwrite Old Files::
247 * Data Modification Times::
248 * Setting Access Permissions::
249 * Directory Modification Times and Permissions::
250 * Writing to Standard Output::
251 * Writing to an External Program::
254 Coping with Scarce Resources
259 Performing Backups and Restoring Files
261 * Full Dumps:: Using @command{tar} to Perform Full Dumps
262 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
263 * Backup Levels:: Levels of Backups
264 * Backup Parameters:: Setting Parameters for Backups and Restoration
265 * Scripted Backups:: Using the Backup Scripts
266 * Scripted Restoration:: Using the Restore Script
268 Setting Parameters for Backups and Restoration
270 * General-Purpose Variables::
271 * Magnetic Tape Control::
273 * backup-specs example:: An Example Text of @file{Backup-specs}
275 Choosing Files and Names for @command{tar}
277 * file:: Choosing the Archive's Name
278 * Selecting Archive Members::
279 * files:: Reading Names from a File
280 * exclude:: Excluding Some Files
281 * wildcards:: Wildcards Patterns and Matching
282 * quoting styles:: Ways of Quoting Special Characters in Names
283 * transform:: Modifying File and Member Names
284 * after:: Operating Only on New Files
285 * recurse:: Descending into Directories
286 * one:: Crossing File System Boundaries
288 Reading Names from a File
294 * problems with exclude::
296 Wildcards Patterns and Matching
298 * controlling pattern-matching::
300 Crossing File System Boundaries
302 * directory:: Changing Directory
303 * absolute:: Absolute File Names
307 * General date syntax:: Common rules.
308 * Calendar date items:: 19 Dec 1994.
309 * Time of day items:: 9:20pm.
310 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
311 * Day of week items:: Monday and others.
312 * Relative items in date strings:: next tuesday, 2 years ago.
313 * Pure numbers in date strings:: 19931219, 1440.
314 * Seconds since the Epoch:: @@1078100502.
315 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
316 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
318 Controlling the Archive Format
320 * Compression:: Using Less Space through Compression
321 * Attributes:: Handling File Attributes
322 * Portability:: Making @command{tar} Archives More Portable
323 * cpio:: Comparison of @command{tar} and @command{cpio}
325 Using Less Space through Compression
327 * gzip:: Creating and Reading Compressed Archives
328 * sparse:: Archiving Sparse Files
330 Making @command{tar} Archives More Portable
332 * Portable Names:: Portable Names
333 * dereference:: Symbolic Links
334 * hard links:: Hard Links
335 * old:: Old V7 Archives
336 * ustar:: Ustar Archives
337 * gnu:: GNU and old GNU format archives.
338 * posix:: @acronym{POSIX} archives
339 * Checksumming:: Checksumming Problems
340 * Large or Negative Values:: Large files, negative time stamps, etc.
341 * Other Tars:: How to Extract GNU-Specific Data Using
342 Other @command{tar} Implementations
344 @GNUTAR{} and @acronym{POSIX} @command{tar}
346 * PAX keywords:: Controlling Extended Header Keywords.
348 How to Extract GNU-Specific Data Using Other @command{tar} Implementations
350 * Split Recovery:: Members Split Between Volumes
351 * Sparse Recovery:: Sparse Members
353 Tapes and Other Archive Media
355 * Device:: Device selection and switching
356 * Remote Tape Server::
357 * Common Problems and Solutions::
358 * Blocking:: Blocking
359 * Many:: Many archives on one tape
360 * Using Multiple Tapes:: Using Multiple Tapes
361 * label:: Including a Label in the Archive
367 * Format Variations:: Format Variations
368 * Blocking Factor:: The Blocking Factor of an Archive
370 Many Archives on One Tape
372 * Tape Positioning:: Tape Positions and Tape Marks
373 * mt:: The @command{mt} Utility
377 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
378 * Tape Files:: Tape Files
379 * Tarcat:: Concatenate Volumes into a Single Archive
384 * Standard:: Basic Tar Format
385 * Extensions:: @acronym{GNU} Extensions to the Archive Format
386 * Sparse Formats:: Storing Sparse Files
393 * PAX 0:: PAX Format, Versions 0.0 and 0.1
394 * PAX 1:: PAX Format, Version 1.0
398 * Generate Mode:: File Generation Mode.
399 * Status Mode:: File Status Mode.
400 * Exec Mode:: Synchronous Execution mode.
404 * GNU Free Documentation License:: License for copying this manual
410 @chapter Introduction
413 and manipulates @dfn{archives} which are actually collections of
414 many other files; the program provides users with an organized and
415 systematic method for controlling a large amount of data.
416 The name ``tar'' originally came from the phrase ``Tape ARchive'', but
417 archives need not (and these days, typically do not) reside on tapes.
420 * Book Contents:: What this Book Contains
421 * Definitions:: Some Definitions
422 * What tar Does:: What @command{tar} Does
423 * Naming tar Archives:: How @command{tar} Archives are Named
424 * Authors:: @GNUTAR{} Authors
425 * Reports:: Reporting bugs or suggestions
429 @section What this Book Contains
431 The first part of this chapter introduces you to various terms that will
432 recur throughout the book. It also tells you who has worked on @GNUTAR{}
433 and its documentation, and where you should send bug reports
436 The second chapter is a tutorial (@pxref{Tutorial}) which provides a
437 gentle introduction for people who are new to using @command{tar}. It is
438 meant to be self contained, not requiring any reading from subsequent
439 chapters to make sense. It moves from topic to topic in a logical,
440 progressive order, building on information already explained.
442 Although the tutorial is paced and structured to allow beginners to
443 learn how to use @command{tar}, it is not intended solely for beginners.
444 The tutorial explains how to use the three most frequently used
445 operations (@samp{create}, @samp{list}, and @samp{extract}) as well as
446 two frequently used options (@samp{file} and @samp{verbose}). The other
447 chapters do not refer to the tutorial frequently; however, if a section
448 discusses something which is a complex variant of a basic concept, there
449 may be a cross reference to that basic concept. (The entire book,
450 including the tutorial, assumes that the reader understands some basic
451 concepts of using a Unix-type operating system; @pxref{Tutorial}.)
453 The third chapter presents the remaining five operations, and
454 information about using @command{tar} options and option syntax.
456 The other chapters are meant to be used as a reference. Each chapter
457 presents everything that needs to be said about a specific topic.
459 One of the chapters (@pxref{Date input formats}) exists in its
460 entirety in other @acronym{GNU} manuals, and is mostly self-contained.
461 In addition, one section of this manual (@pxref{Standard}) contains a
462 big quote which is taken directly from @command{tar} sources.
464 In general, we give both long and short (abbreviated) option names
465 at least once in each section where the relevant option is covered, so
466 that novice readers will become familiar with both styles. (A few
467 options have no short versions, and the relevant sections will
471 @section Some Definitions
475 The @command{tar} program is used to create and manipulate @command{tar}
476 archives. An @dfn{archive} is a single file which contains the contents
477 of many files, while still identifying the names of the files, their
478 owner(s), and so forth. (In addition, archives record access
479 permissions, user and group, size in bytes, and data modification time.
480 Some archives also record the file names in each archived directory, as
481 well as other file and directory information.) You can use @command{tar}
482 to @dfn{create} a new archive in a specified directory.
485 @cindex archive member
488 The files inside an archive are called @dfn{members}. Within this
489 manual, we use the term @dfn{file} to refer only to files accessible in
490 the normal ways (by @command{ls}, @command{cat}, and so forth), and the term
491 @dfn{member} to refer only to the members of an archive. Similarly, a
492 @dfn{file name} is the name of a file, as it resides in the file system,
493 and a @dfn{member name} is the name of an archive member within the
498 The term @dfn{extraction} refers to the process of copying an archive
499 member (or multiple members) into a file in the file system. Extracting
500 all the members of an archive is often called @dfn{extracting the
501 archive}. The term @dfn{unpack} can also be used to refer to the
502 extraction of many or all the members of an archive. Extracting an
503 archive does not destroy the archive's structure, just as creating an
504 archive does not destroy the copies of the files that exist outside of
505 the archive. You may also @dfn{list} the members in a given archive
506 (this is often thought of as ``printing'' them to the standard output,
507 or the command line), or @dfn{append} members to a pre-existing archive.
508 All of these operations can be performed using @command{tar}.
511 @section What @command{tar} Does
514 The @command{tar} program provides the ability to create @command{tar}
515 archives, as well as various other kinds of manipulation. For example,
516 you can use @command{tar} on previously created archives to extract files,
517 to store additional files, or to update or list files which were already
520 Initially, @command{tar} archives were used to store files conveniently on
521 magnetic tape. The name @command{tar} comes from this use; it stands for
522 @code{t}ape @code{ar}chiver. Despite the utility's name, @command{tar} can
523 direct its output to available devices, files, or other programs (using
524 pipes). @command{tar} may even access remote devices or files (as archives).
526 You can use @command{tar} archives in many ways. We want to stress a few
527 of them: storage, backup, and transportation.
529 @FIXME{the following table entries need a bit of work.}
532 Often, @command{tar} archives are used to store related files for
533 convenient file transfer over a network. For example, the
534 @acronym{GNU} Project distributes its software bundled into
535 @command{tar} archives, so that all the files relating to a particular
536 program (or set of related programs) can be transferred as a single
539 A magnetic tape can store several files in sequence. However, the tape
540 has no names for these files; it only knows their relative position on
541 the tape. One way to store several files on one tape and retain their
542 names is by creating a @command{tar} archive. Even when the basic transfer
543 mechanism can keep track of names, as FTP can, the nuisance of handling
544 multiple files, directories, and multiple links makes @command{tar}
547 Archive files are also used for long-term storage. You can think of
548 this as transportation from the present into the future. (It is a
549 science-fiction idiom that you can move through time as well as in
550 space; the idea here is that @command{tar} can be used to move archives in
551 all dimensions, even time!)
554 Because the archive created by @command{tar} is capable of preserving
555 file information and directory structure, @command{tar} is commonly
556 used for performing full and incremental backups of disks. A backup
557 puts a collection of files (possibly pertaining to many users and
558 projects) together on a disk or a tape. This guards against
559 accidental destruction of the information in those files.
560 @GNUTAR{} has special features that allow it to be
561 used to make incremental and full dumps of all the files in a
565 You can create an archive on one system, transfer it to another system,
566 and extract the contents there. This allows you to transport a group of
567 files from one system to another.
570 @node Naming tar Archives
571 @section How @command{tar} Archives are Named
573 Conventionally, @command{tar} archives are given names ending with
574 @samp{.tar}. This is not necessary for @command{tar} to operate properly,
575 but this manual follows that convention in order to accustom readers to
576 it and to make examples more clear.
581 Often, people refer to @command{tar} archives as ``@command{tar} files,'' and
582 archive members as ``files'' or ``entries''. For people familiar with
583 the operation of @command{tar}, this causes no difficulty. However, in
584 this manual, we consistently refer to ``archives'' and ``archive
585 members'' to make learning to use @command{tar} easier for novice users.
588 @section @GNUTAR{} Authors
590 @GNUTAR{} was originally written by John Gilmore,
591 and modified by many people. The @acronym{GNU} enhancements were
592 written by Jay Fenlason, then Joy Kendall, and the whole package has
593 been further maintained by Thomas Bushnell, n/BSG, Fran@,{c}ois
594 Pinard, Paul Eggert, and finally Sergey Poznyakoff with the help of
595 numerous and kind users.
597 We wish to stress that @command{tar} is a collective work, and owes much to
598 all those people who reported problems, offered solutions and other
599 insights, or shared their thoughts and suggestions. An impressive, yet
600 partial list of those contributors can be found in the @file{THANKS}
601 file from the @GNUTAR{} distribution.
603 @FIXME{i want all of these names mentioned, Absolutely. BUT, i'm not
604 sure i want to spell out the history in this detail, at least not for
605 the printed book. i'm just not sure it needs to be said this way.
606 i'll think about it.}
608 @FIXME{History is more important, and surely more interesting, than
609 actual names. Quoting names without history would be meaningless. FP}
611 Jay Fenlason put together a draft of a @GNUTAR{}
612 manual, borrowing notes from the original man page from John Gilmore.
613 This was withdrawn in version 1.11. Thomas Bushnell, n/BSG and Amy
614 Gorin worked on a tutorial and manual for @GNUTAR{}.
615 Fran@,{c}ois Pinard put version 1.11.8 of the manual together by
616 taking information from all these sources and merging them. Melissa
617 Weisshaus finally edited and redesigned the book to create version
618 1.12. The book for versions from 1.14 up to @value{VERSION} were edited
619 by the current maintainer, Sergey Poznyakoff.
621 For version 1.12, Daniel Hagerty contributed a great deal of technical
622 consulting. In particular, he is the primary author of @ref{Backups}.
624 In July, 2003 @GNUTAR{} was put on CVS at savannah.gnu.org
625 (see @url{http://savannah.gnu.org/projects/tar}), and
626 active development and maintenance work has started
627 again. Currently @GNUTAR{} is being maintained by Paul Eggert, Sergey
628 Poznyakoff and Jeff Bailey.
630 Support for @acronym{POSIX} archives was added by Sergey Poznyakoff.
633 @section Reporting bugs or suggestions
636 @cindex reporting bugs
637 If you find problems or have suggestions about this program or manual,
638 please report them to @file{bug-tar@@gnu.org}.
640 When reporting a bug, please be sure to include as much detail as
641 possible, in order to reproduce it. @FIXME{Be more specific, I'd
642 like to make this node as detailed as 'Bug reporting' node in Emacs
646 @chapter Tutorial Introduction to @command{tar}
648 This chapter guides you through some basic examples of three @command{tar}
649 operations: @option{--create}, @option{--list}, and @option{--extract}. If
650 you already know how to use some other version of @command{tar}, then you
651 may not need to read this chapter. This chapter omits most complicated
652 details about how @command{tar} works.
656 * stylistic conventions::
657 * basic tar options:: Basic @command{tar} Operations and Options
658 * frequent operations::
659 * Two Frequent Options::
660 * create:: How to Create Archives
661 * list:: How to List Archives
662 * extract:: How to Extract Members from an Archive
667 @section Assumptions this Tutorial Makes
669 This chapter is paced to allow beginners to learn about @command{tar}
670 slowly. At the same time, we will try to cover all the basic aspects of
671 these three operations. In order to accomplish both of these tasks, we
672 have made certain assumptions about your knowledge before reading this
673 manual, and the hardware you will be using:
677 Before you start to work through this tutorial, you should understand
678 what the terms ``archive'' and ``archive member'' mean
679 (@pxref{Definitions}). In addition, you should understand something
680 about how Unix-type operating systems work, and you should know how to
681 use some basic utilities. For example, you should know how to create,
682 list, copy, rename, edit, and delete files and directories; how to
683 change between directories; and how to figure out where you are in the
684 file system. You should have some basic understanding of directory
685 structure and how files are named according to which directory they are
686 in. You should understand concepts such as standard output and standard
687 input, what various definitions of the term @samp{argument} mean, and the
688 differences between relative and absolute file names. @FIXME{and what
692 This manual assumes that you are working from your own home directory
693 (unless we state otherwise). In this tutorial, you will create a
694 directory to practice @command{tar} commands in. When we show file names,
695 we will assume that those names are relative to your home directory.
696 For example, my home directory is @file{/home/fsf/melissa}. All of
697 my examples are in a subdirectory of the directory named by that file
698 name; the subdirectory is called @file{practice}.
701 In general, we show examples of archives which exist on (or can be
702 written to, or worked with from) a directory on a hard disk. In most
703 cases, you could write those archives to, or work with them on any other
704 device, such as a tape drive. However, some of the later examples in
705 the tutorial and next chapter will not work on tape drives.
706 Additionally, working with tapes is much more complicated than working
707 with hard disks. For these reasons, the tutorial does not cover working
708 with tape drives. @xref{Media}, for complete information on using
709 @command{tar} archives with tape drives.
711 @FIXME{this is a cop out. need to add some simple tape drive info.}
714 @node stylistic conventions
715 @section Stylistic Conventions
717 In the examples, @samp{$} represents a typical shell prompt. It
718 precedes lines you should type; to make this more clear, those lines are
719 shown in @kbd{this font}, as opposed to lines which represent the
720 computer's response; those lines are shown in @code{this font}, or
721 sometimes @samp{like this}.
723 @c When we have lines which are too long to be
724 @c displayed in any other way, we will show them like this:
726 @node basic tar options
727 @section Basic @command{tar} Operations and Options
729 @command{tar} can take a wide variety of arguments which specify and define
730 the actions it will have on the particular set of files or the archive.
731 The main types of arguments to @command{tar} fall into one of two classes:
732 operations, and options.
734 Some arguments fall into a class called @dfn{operations}; exactly one of
735 these is both allowed and required for any instance of using @command{tar};
736 you may @emph{not} specify more than one. People sometimes speak of
737 @dfn{operating modes}. You are in a particular operating mode when you
738 have specified the operation which specifies it; there are eight
739 operations in total, and thus there are eight operating modes.
741 The other arguments fall into the class known as @dfn{options}. You are
742 not required to specify any options, and you are allowed to specify more
743 than one at a time (depending on the way you are using @command{tar} at
744 that time). Some options are used so frequently, and are so useful for
745 helping you type commands more carefully that they are effectively
746 ``required''. We will discuss them in this chapter.
748 You can write most of the @command{tar} operations and options in any
749 of three forms: long (mnemonic) form, short form, and old style. Some
750 of the operations and options have no short or ``old'' forms; however,
751 the operations and options which we will cover in this tutorial have
752 corresponding abbreviations. We will indicate those abbreviations
753 appropriately to get you used to seeing them. (Note that the ``old
754 style'' option forms exist in @GNUTAR{} for compatibility with Unix
755 @command{tar}. In this book we present a full discussion of this way
756 of writing options and operations (@pxref{Old Options}), and we discuss
757 the other two styles of writing options (@xref{Long Options}, and
758 @pxref{Short Options}).
760 In the examples and in the text of this tutorial, we usually use the
761 long forms of operations and options; but the ``short'' forms produce
762 the same result and can make typing long @command{tar} commands easier.
763 For example, instead of typing
766 @kbd{tar --create --verbose --file=afiles.tar apple angst aspic}
772 @kbd{tar -c -v -f afiles.tar apple angst aspic}
778 @kbd{tar -cvf afiles.tar apple angst aspic}
782 For more information on option syntax, see @ref{Advanced tar}. In
783 discussions in the text, when we name an option by its long form, we
784 also give the corresponding short option in parentheses.
786 The term, ``option'', can be confusing at times, since ``operations''
787 are often lumped in with the actual, @emph{optional} ``options'' in certain
788 general class statements. For example, we just talked about ``short and
789 long forms of options and operations''. However, experienced @command{tar}
790 users often refer to these by shorthand terms such as, ``short and long
791 options''. This term assumes that the ``operations'' are included, also.
792 Context will help you determine which definition of ``options'' to use.
794 Similarly, the term ``command'' can be confusing, as it is often used in
795 two different ways. People sometimes refer to @command{tar} ``commands''.
796 A @command{tar} @dfn{command} is the entire command line of user input
797 which tells @command{tar} what to do --- including the operation, options,
798 and any arguments (file names, pipes, other commands, etc.). However,
799 you will also sometimes hear the term ``the @command{tar} command''. When
800 the word ``command'' is used specifically like this, a person is usually
801 referring to the @command{tar} @emph{operation}, not the whole line.
802 Again, use context to figure out which of the meanings the speaker
805 @node frequent operations
806 @section The Three Most Frequently Used Operations
808 Here are the three most frequently used operations (both short and long
809 forms), as well as a brief description of their meanings. The rest of
810 this chapter will cover how to use these operations in detail. We will
811 present the rest of the operations in the next chapter.
816 Create a new @command{tar} archive.
819 List the contents of an archive.
822 Extract one or more members from an archive.
825 @node Two Frequent Options
826 @section Two Frequently Used Options
828 To understand how to run @command{tar} in the three operating modes listed
829 previously, you also need to understand how to use two of the options to
830 @command{tar}: @option{--file} (which takes an archive file as an argument)
831 and @option{--verbose}. (You are usually not @emph{required} to specify
832 either of these options when you run @command{tar}, but they can be very
833 useful in making things more clear and helping you avoid errors.)
842 @unnumberedsubsec The @option{--file} Option
845 @xopindex{file, tutorial}
846 @item --file=@var{archive-name}
847 @itemx -f @var{archive-name}
848 Specify the name of an archive file.
851 You can specify an argument for the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option whenever you
852 use @command{tar}; this option determines the name of the archive file
853 that @command{tar} will work on.
856 If you don't specify this argument, then @command{tar} will examine
857 the environment variable @env{TAPE}. If it is set, its value will be
858 used as the archive name. Otherwise, @command{tar} will use the
859 default archive, determined at the compile time. Usually it is
860 standard output or some physical tape drive attached to your machine
861 (you can verify what the default is by running @kbd{tar
862 --show-defaults}, @pxref{defaults}). If there is no tape drive
863 attached, or the default is not meaningful, then @command{tar} will
864 print an error message. The error message might look roughly like one
868 tar: can't open /dev/rmt8 : No such device or address
869 tar: can't open /dev/rsmt0 : I/O error
873 To avoid confusion, we recommend that you always specify an archive file
874 name by using @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) when writing your @command{tar} commands.
875 For more information on using the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option, see
878 @node verbose tutorial
879 @unnumberedsubsec The @option{--verbose} Option
882 @xopindex{verbose, introduced}
885 Show the files being worked on as @command{tar} is running.
888 @option{--verbose} (@option{-v}) shows details about the results of running
889 @command{tar}. This can be especially useful when the results might not be
890 obvious. For example, if you want to see the progress of @command{tar} as
891 it writes files into the archive, you can use the @option{--verbose}
892 option. In the beginning, you may find it useful to use
893 @option{--verbose} at all times; when you are more accustomed to
894 @command{tar}, you will likely want to use it at certain times but not at
895 others. We will use @option{--verbose} at times to help make something
896 clear, and we will give many examples both using and not using
897 @option{--verbose} to show the differences.
899 Each instance of @option{--verbose} on the command line increases the
900 verbosity level by one, so if you need more details on the output,
903 When reading archives (@option{--list}, @option{--extract},
904 @option{--diff}), @command{tar} by default prints only the names of
905 the members being extracted. Using @option{--verbose} will show a full,
906 @command{ls} style member listing.
908 In contrast, when writing archives (@option{--create}, @option{--append},
909 @option{--update}), @command{tar} does not print file names by
910 default. So, a single @option{--verbose} option shows the file names
911 being added to the archive, while two @option{--verbose} options
912 enable the full listing.
914 For example, to create an archive in verbose mode:
917 $ @kbd{tar -cvf afiles.tar apple angst aspic}
924 Creating the same archive with the verbosity level 2 could give:
927 $ @kbd{tar -cvvf afiles.tar apple angst aspic}
928 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
929 -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst
930 -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
934 This works equally well using short or long forms of options. Using
935 long forms, you would simply write out the mnemonic form of the option
939 $ @kbd{tar --create --verbose --verbose @dots{}}
943 Note that you must double the hyphens properly each time.
945 Later in the tutorial, we will give examples using @w{@option{--verbose
948 @anchor{verbose member listing}
949 The full output consists of six fields:
952 @item File type and permissions in symbolic form.
953 These are displayed in the same format as the first column of
954 @command{ls -l} output (@pxref{What information is listed,
955 format=verbose, Verbose listing, fileutils, GNU file utilities}).
957 @item Owner name and group separated by a slash character.
958 If these data are not available (for example, when listing a @samp{v7} format
959 archive), numeric @acronym{ID} values are printed instead.
961 @item Size of the file, in bytes.
963 @item File modification date in ISO 8601 format.
965 @item File modification time.
968 If the name contains any special characters (white space, newlines,
969 etc.) these are displayed in an unambiguous form using so called
970 @dfn{quoting style}. For the detailed discussion of available styles
971 and on how to use them, see @ref{quoting styles}.
973 Depending on the file type, the name can be followed by some
974 additional information, described in the following table:
977 @item -> @var{link-name}
978 The file or archive member is a @dfn{symbolic link} and
979 @var{link-name} is the name of file it links to.
981 @item link to @var{link-name}
982 The file or archive member is a @dfn{hard link} and @var{link-name} is
983 the name of file it links to.
986 The archive member is an old GNU format long link. You will normally
990 The archive member is an old GNU format long name. You will normally
993 @item --Volume Header--
994 The archive member is a GNU @dfn{volume header} (@pxref{Tape Files}).
996 @item --Continued at byte @var{n}--
997 Encountered only at the beginning of a multi-volume archive
998 (@pxref{Using Multiple Tapes}). This archive member is a continuation
999 from the previous volume. The number @var{n} gives the offset where
1000 the original file was split.
1002 @item unknown file type @var{c}
1003 An archive member of unknown type. @var{c} is the type character from
1004 the archive header. If you encounter such a message, it means that
1005 either your archive contains proprietary member types @GNUTAR{} is not
1006 able to handle, or the archive is corrupted.
1011 For example, here is an archive listing containing most of the special
1012 suffixes explained above:
1016 V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header--
1017 -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at
1019 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
1020 lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple
1021 -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues
1022 hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
1030 @unnumberedsubsec Getting Help: Using the @option{--help} Option
1036 The @option{--help} option to @command{tar} prints out a very brief list of
1037 all operations and option available for the current version of
1038 @command{tar} available on your system.
1042 @section How to Create Archives
1045 @cindex Creation of the archive
1046 @cindex Archive, creation of
1047 One of the basic operations of @command{tar} is @option{--create} (@option{-c}), which
1048 you use to create a @command{tar} archive. We will explain
1049 @option{--create} first because, in order to learn about the other
1050 operations, you will find it useful to have an archive available to
1053 To make this easier, in this section you will first create a directory
1054 containing three files. Then, we will show you how to create an
1055 @emph{archive} (inside the new directory). Both the directory, and
1056 the archive are specifically for you to practice on. The rest of this
1057 chapter and the next chapter will show many examples using this
1058 directory and the files you will create: some of those files may be
1059 other directories and other archives.
1061 The three files you will archive in this example are called
1062 @file{blues}, @file{folk}, and @file{jazz}. The archive is called
1063 @file{collection.tar}.
1065 This section will proceed slowly, detailing how to use @option{--create}
1066 in @code{verbose} mode, and showing examples using both short and long
1067 forms. In the rest of the tutorial, and in the examples in the next
1068 chapter, we will proceed at a slightly quicker pace. This section
1069 moves more slowly to allow beginning users to understand how
1070 @command{tar} works.
1073 * prepare for examples::
1074 * Creating the archive::
1080 @node prepare for examples
1081 @subsection Preparing a Practice Directory for Examples
1083 To follow along with this and future examples, create a new directory
1084 called @file{practice} containing files called @file{blues}, @file{folk}
1085 and @file{jazz}. The files can contain any information you like:
1086 ideally, they should contain information which relates to their names,
1087 and be of different lengths. Our examples assume that @file{practice}
1088 is a subdirectory of your home directory.
1090 Now @command{cd} to the directory named @file{practice}; @file{practice}
1091 is now your @dfn{working directory}. (@emph{Please note}: Although
1092 the full file name of this directory is
1093 @file{/@var{homedir}/practice}, in our examples we will refer to
1094 this directory as @file{practice}; the @var{homedir} is presumed.
1096 In general, you should check that the files to be archived exist where
1097 you think they do (in the working directory) by running @command{ls}.
1098 Because you just created the directory and the files and have changed to
1099 that directory, you probably don't need to do that this time.
1101 It is very important to make sure there isn't already a file in the
1102 working directory with the archive name you intend to use (in this case,
1103 @samp{collection.tar}), or that you don't care about its contents.
1104 Whenever you use @samp{create}, @command{tar} will erase the current
1105 contents of the file named by @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) if it exists. @command{tar}
1106 will not tell you if you are about to overwrite an archive unless you
1107 specify an option which does this (@pxref{backup}, for the
1108 information on how to do so). To add files to an existing archive,
1109 you need to use a different option, such as @option{--append} (@option{-r}); see
1110 @ref{append} for information on how to do this.
1112 @node Creating the archive
1113 @subsection Creating the Archive
1115 @xopindex{create, introduced}
1116 To place the files @file{blues}, @file{folk}, and @file{jazz} into an
1117 archive named @file{collection.tar}, use the following command:
1120 $ @kbd{tar --create --file=collection.tar blues folk jazz}
1123 The order of the arguments is not very important, @emph{when using long
1124 option forms}. You could also say:
1127 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1131 However, you can see that this order is harder to understand; this is
1132 why we will list the arguments in the order that makes the commands
1133 easiest to understand (and we encourage you to do the same when you use
1134 @command{tar}, to avoid errors).
1136 Note that the sequence
1137 @option{--file=@-collection.tar} is considered to be @emph{one} argument.
1138 If you substituted any other string of characters for
1139 @kbd{collection.tar}, then that string would become the name of the
1140 archive file you create.
1142 The order of the options becomes more important when you begin to use
1143 short forms. With short forms, if you type commands in the wrong order
1144 (even if you type them correctly in all other ways), you may end up with
1145 results you don't expect. For this reason, it is a good idea to get
1146 into the habit of typing options in the order that makes inherent sense.
1147 @xref{short create}, for more information on this.
1149 In this example, you type the command as shown above: @option{--create}
1150 is the operation which creates the new archive
1151 (@file{collection.tar}), and @option{--file} is the option which lets
1152 you give it the name you chose. The files, @file{blues}, @file{folk},
1153 and @file{jazz}, are now members of the archive, @file{collection.tar}
1154 (they are @dfn{file name arguments} to the @option{--create} operation.
1155 @xref{Choosing}, for the detailed discussion on these.) Now that they are
1156 in the archive, they are called @emph{archive members}, not files.
1157 (@pxref{Definitions,members}).
1159 When you create an archive, you @emph{must} specify which files you
1160 want placed in the archive. If you do not specify any archive
1161 members, @GNUTAR{} will complain.
1163 If you now list the contents of the working directory (@command{ls}), you will
1164 find the archive file listed as well as the files you saw previously:
1167 blues folk jazz collection.tar
1171 Creating the archive @samp{collection.tar} did not destroy the copies of
1172 the files in the directory.
1174 Keep in mind that if you don't indicate an operation, @command{tar} will not
1175 run and will prompt you for one. If you don't name any files, @command{tar}
1176 will complain. You must have write access to the working directory,
1177 or else you will not be able to create an archive in that directory.
1179 @emph{Caution}: Do not attempt to use @option{--create} (@option{-c}) to add files to
1180 an existing archive; it will delete the archive and write a new one.
1181 Use @option{--append} (@option{-r}) instead. @xref{append}.
1183 @node create verbose
1184 @subsection Running @option{--create} with @option{--verbose}
1186 @xopindex{create, using with @option{--verbose}}
1187 @xopindex{verbose, using with @option{--create}}
1188 If you include the @option{--verbose} (@option{-v}) option on the command line,
1189 @command{tar} will list the files it is acting on as it is working. In
1190 verbose mode, the @code{create} example above would appear as:
1193 $ @kbd{tar --create --verbose --file=collection.tar blues folk jazz}
1199 This example is just like the example we showed which did not use
1200 @option{--verbose}, except that @command{tar} generated the remaining lines
1202 (note the different font styles).
1208 In the rest of the examples in this chapter, we will frequently use
1209 @code{verbose} mode so we can show actions or @command{tar} responses that
1210 you would otherwise not see, and which are important for you to
1214 @subsection Short Forms with @samp{create}
1216 As we said before, the @option{--create} (@option{-c}) operation is one of the most
1217 basic uses of @command{tar}, and you will use it countless times.
1218 Eventually, you will probably want to use abbreviated (or ``short'')
1219 forms of options. A full discussion of the three different forms that
1220 options can take appears in @ref{Styles}; for now, here is what the
1221 previous example (including the @option{--verbose} (@option{-v}) option) looks like
1222 using short option forms:
1225 $ @kbd{tar -cvf collection.tar blues folk jazz}
1232 As you can see, the system responds the same no matter whether you use
1233 long or short option forms.
1235 @FIXME{i don't like how this is worded:} One difference between using
1236 short and long option forms is that, although the exact placement of
1237 arguments following options is no more specific when using short forms,
1238 it is easier to become confused and make a mistake when using short
1239 forms. For example, suppose you attempted the above example in the
1243 $ @kbd{tar -cfv collection.tar blues folk jazz}
1247 In this case, @command{tar} will make an archive file called @file{v},
1248 containing the files @file{blues}, @file{folk}, and @file{jazz}, because
1249 the @samp{v} is the closest ``file name'' to the @option{-f} option, and
1250 is thus taken to be the chosen archive file name. @command{tar} will try
1251 to add a file called @file{collection.tar} to the @file{v} archive file;
1252 if the file @file{collection.tar} did not already exist, @command{tar} will
1253 report an error indicating that this file does not exist. If the file
1254 @file{collection.tar} does already exist (e.g., from a previous command
1255 you may have run), then @command{tar} will add this file to the archive.
1256 Because the @option{-v} option did not get registered, @command{tar} will not
1257 run under @samp{verbose} mode, and will not report its progress.
1259 The end result is that you may be quite confused about what happened,
1260 and possibly overwrite a file. To illustrate this further, we will show
1261 you how an example we showed previously would look using short forms.
1266 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1270 is confusing as it is. When shown using short forms, however, it
1271 becomes much more so:
1274 $ @kbd{tar blues -c folk -f collection.tar jazz}
1278 It would be very easy to put the wrong string of characters
1279 immediately following the @option{-f}, but doing that could sacrifice
1282 For this reason, we recommend that you pay very careful attention to
1283 the order of options and placement of file and archive names,
1284 especially when using short option forms. Not having the option name
1285 written out mnemonically can affect how well you remember which option
1286 does what, and therefore where different names have to be placed.
1289 @subsection Archiving Directories
1291 @cindex Archiving Directories
1292 @cindex Directories, Archiving
1293 You can archive a directory by specifying its directory name as a
1294 file name argument to @command{tar}. The files in the directory will be
1295 archived relative to the working directory, and the directory will be
1296 re-created along with its contents when the archive is extracted.
1298 To archive a directory, first move to its superior directory. If you
1299 have followed the previous instructions in this tutorial, you should
1308 This will put you into the directory which contains @file{practice},
1309 i.e., your home directory. Once in the superior directory, you can
1310 specify the subdirectory, @file{practice}, as a file name argument. To
1311 store @file{practice} in the new archive file @file{music.tar}, type:
1314 $ @kbd{tar --create --verbose --file=music.tar practice}
1318 @command{tar} should output:
1325 practice/collection.tar
1328 Note that the archive thus created is not in the subdirectory
1329 @file{practice}, but rather in the current working directory---the
1330 directory from which @command{tar} was invoked. Before trying to archive a
1331 directory from its superior directory, you should make sure you have
1332 write access to the superior directory itself, not only the directory
1333 you are trying archive with @command{tar}. For example, you will probably
1334 not be able to store your home directory in an archive by invoking
1335 @command{tar} from the root directory; @xref{absolute}. (Note
1336 also that @file{collection.tar}, the original archive file, has itself
1337 been archived. @command{tar} will accept any file as a file to be
1338 archived, regardless of its content. When @file{music.tar} is
1339 extracted, the archive file @file{collection.tar} will be re-written
1340 into the file system).
1342 If you give @command{tar} a command such as
1345 $ @kbd{tar --create --file=foo.tar .}
1349 @command{tar} will report @samp{tar: ./foo.tar is the archive; not
1350 dumped}. This happens because @command{tar} creates the archive
1351 @file{foo.tar} in the current directory before putting any files into
1352 it. Then, when @command{tar} attempts to add all the files in the
1353 directory @file{.} to the archive, it notices that the file
1354 @file{./foo.tar} is the same as the archive @file{foo.tar}, and skips
1355 it. (It makes no sense to put an archive into itself.) @GNUTAR{}
1356 will continue in this case, and create the archive
1357 normally, except for the exclusion of that one file. (@emph{Please
1358 note:} Other implementations of @command{tar} may not be so clever;
1359 they will enter an infinite loop when this happens, so you should not
1360 depend on this behavior unless you are certain you are running
1361 @GNUTAR{}. In general, it is wise to always place the archive outside
1362 of the directory being dumped.
1365 @section How to List Archives
1368 Frequently, you will find yourself wanting to determine exactly what a
1369 particular archive contains. You can use the @option{--list}
1370 (@option{-t}) operation to get the member names as they currently
1371 appear in the archive, as well as various attributes of the files at
1372 the time they were archived. For example, you can examine the archive
1373 @file{collection.tar} that you created in the last section with the
1377 $ @kbd{tar --list --file=collection.tar}
1381 The output of @command{tar} would then be:
1390 The archive @file{bfiles.tar} would list as follows:
1399 Be sure to use a @option{--file=@var{archive-name}} (@option{-f
1400 @var{archive-name}}) option just as with @option{--create}
1401 (@option{-c}) to specify the name of the archive.
1403 @xopindex{list, using with @option{--verbose}}
1404 @xopindex{verbose, using with @option{--list}}
1405 If you use the @option{--verbose} (@option{-v}) option with
1406 @option{--list}, then @command{tar} will print out a listing
1407 reminiscent of @w{@samp{ls -l}}, showing owner, file size, and so
1408 forth. This output is described in detail in @ref{verbose member listing}.
1410 If you had used @option{--verbose} (@option{-v}) mode, the example
1411 above would look like:
1414 $ @kbd{tar --list --verbose --file=collection.tar folk}
1415 -rw-r--r-- myself user 62 1990-05-23 10:55 folk
1418 @cindex listing member and file names
1419 @anchor{listing member and file names}
1420 It is important to notice that the output of @kbd{tar --list
1421 --verbose} does not necessarily match that produced by @kbd{tar
1422 --create --verbose} while creating the archive. It is because
1423 @GNUTAR{}, unless told explicitly not to do so, removes some directory
1424 prefixes from file names before storing them in the archive
1425 (@xref{absolute}, for more information). In other
1426 words, in verbose mode @GNUTAR{} shows @dfn{file names} when creating
1427 an archive and @dfn{member names} when listing it. Consider this
1432 $ @kbd{tar --create --verbose --file archive /etc/mail}
1433 tar: Removing leading `/' from member names
1435 /etc/mail/sendmail.cf
1437 $ @kbd{tar --test --file archive}
1439 etc/mail/sendmail.cf
1444 @opindex show-stored-names
1445 This default behavior can sometimes be inconvenient. You can force
1446 @GNUTAR{} show member names when creating archive by supplying
1447 @option{--show-stored-names} option.
1450 @item --show-stored-names
1451 Print member (as opposed to @emph{file}) names when creating the archive.
1454 @cindex File name arguments, using @option{--list} with
1455 @xopindex{list, using with file name arguments}
1456 You can specify one or more individual member names as arguments when
1457 using @samp{list}. In this case, @command{tar} will only list the
1458 names of members you identify. For example, @w{@kbd{tar --list
1459 --file=afiles.tar apple}} would only print @file{apple}.
1461 Because @command{tar} preserves file names, these must be specified as
1462 they appear in the archive (i.e., relative to the directory from which
1463 the archive was created). Therefore, it is essential when specifying
1464 member names to @command{tar} that you give the exact member names.
1465 For example, @w{@kbd{tar --list --file=bfiles.tar birds}} would produce an
1466 error message something like @samp{tar: birds: Not found in archive},
1467 because there is no member named @file{birds}, only one named
1468 @file{./birds}. While the names @file{birds} and @file{./birds} name
1469 the same file, @emph{member} names by default are compared verbatim.
1471 However, @w{@kbd{tar --list --file=bfiles.tar baboon}} would respond
1472 with @file{baboon}, because this exact member name is in the archive file
1473 @file{bfiles.tar}. If you are not sure of the exact file name,
1474 use @dfn{globbing patterns}, for example:
1477 $ @kbd{tar --list --file=bfiles.tar --wildcards '*b*'}
1481 will list all members whose name contains @samp{b}. @xref{wildcards},
1482 for a detailed discussion of globbing patterns and related
1483 @command{tar} command line options.
1490 @unnumberedsubsec Listing the Contents of a Stored Directory
1492 To get information about the contents of an archived directory,
1493 use the directory name as a file name argument in conjunction with
1494 @option{--list} (@option{-t}). To find out file attributes, include the
1495 @option{--verbose} (@option{-v}) option.
1497 For example, to find out about files in the directory @file{practice}, in
1498 the archive file @file{music.tar}, type:
1501 $ @kbd{tar --list --verbose --file=music.tar practice}
1504 @command{tar} responds:
1507 drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
1508 -rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues
1509 -rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk
1510 -rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz
1511 -rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar
1514 When you use a directory name as a file name argument, @command{tar} acts on
1515 all the files (including sub-directories) in that directory.
1518 @section How to Extract Members from an Archive
1521 @cindex Retrieving files from an archive
1522 @cindex Resurrecting files from an archive
1525 Creating an archive is only half the job---there is no point in storing
1526 files in an archive if you can't retrieve them. The act of retrieving
1527 members from an archive so they can be used and manipulated as
1528 unarchived files again is called @dfn{extraction}. To extract files
1529 from an archive, use the @option{--extract} (@option{--get} or
1530 @option{-x}) operation. As with @option{--create}, specify the name
1531 of the archive with @option{--file} (@option{-f}) option. Extracting
1532 an archive does not modify the archive in any way; you can extract it
1533 multiple times if you want or need to.
1535 Using @option{--extract}, you can extract an entire archive, or specific
1536 files. The files can be directories containing other files, or not. As
1537 with @option{--create} (@option{-c}) and @option{--list} (@option{-t}), you may use the short or the
1538 long form of the operation without affecting the performance.
1541 * extracting archives::
1542 * extracting files::
1544 * extracting untrusted archives::
1545 * failing commands::
1548 @node extracting archives
1549 @subsection Extracting an Entire Archive
1551 To extract an entire archive, specify the archive file name only, with
1552 no individual file names as arguments. For example,
1555 $ @kbd{tar -xvf collection.tar}
1562 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
1563 -rw-r--r-- me user 21 1996-09-23 16:44 blues
1564 -rw-r--r-- me user 20 1996-09-23 16:44 folk
1567 @node extracting files
1568 @subsection Extracting Specific Files
1570 To extract specific archive members, give their exact member names as
1571 arguments, as printed by @option{--list} (@option{-t}). If you had
1572 mistakenly deleted one of the files you had placed in the archive
1573 @file{collection.tar} earlier (say, @file{blues}), you can extract it
1574 from the archive without changing the archive's structure. Its
1575 contents will be identical to the original file @file{blues} that you
1578 First, make sure you are in the @file{practice} directory, and list the
1579 files in the directory. Now, delete the file, @samp{blues}, and list
1580 the files in the directory again.
1582 You can now extract the member @file{blues} from the archive file
1583 @file{collection.tar} like this:
1586 $ @kbd{tar --extract --file=collection.tar blues}
1590 If you list the files in the directory again, you will see that the file
1591 @file{blues} has been restored, with its original permissions, data
1592 modification times, and owner.@footnote{This is only accidentally
1593 true, but not in general. Whereas modification times are always
1594 restored, in most cases, one has to be root for restoring the owner,
1595 and use a special option for restoring permissions. Here, it just
1596 happens that the restoring user is also the owner of the archived
1597 members, and that the current @code{umask} is compatible with original
1598 permissions.} (These parameters will be identical to those which
1599 the file had when you originally placed it in the archive; any changes
1600 you may have made before deleting the file from the file system,
1601 however, will @emph{not} have been made to the archive member.) The
1602 archive file, @samp{collection.tar}, is the same as it was before you
1603 extracted @samp{blues}. You can confirm this by running @command{tar} with
1604 @option{--list} (@option{-t}).
1606 Remember that as with other operations, specifying the exact member
1607 name is important. @w{@kbd{tar --extract --file=bfiles.tar birds}}
1608 will fail, because there is no member named @file{birds}. To extract
1609 the member named @file{./birds}, you must specify @w{@kbd{tar
1610 --extract --file=bfiles.tar ./birds}}. If you don't remember the
1611 exact member names, use @option{--list} (@option{-t}) option
1612 (@pxref{list}). You can also extract those members that match a
1613 specific @dfn{globbing pattern}. For example, to extract from
1614 @file{bfiles.tar} all files that begin with @samp{b}, no matter their
1615 directory prefix, you could type:
1618 $ @kbd{tar -x -f bfiles.tar --wildcards --no-anchored 'b*'}
1622 Here, @option{--wildcards} instructs @command{tar} to treat
1623 command line arguments as globbing patterns and @option{--no-anchored}
1624 informs it that the patterns apply to member names after any @samp{/}
1625 delimiter. The use of globbing patterns is discussed in detail in
1628 You can extract a file to standard output by combining the above options
1629 with the @option{--to-stdout} (@option{-O}) option (@pxref{Writing to Standard
1632 If you give the @option{--verbose} option, then @option{--extract}
1633 will print the names of the archive members as it extracts them.
1636 @subsection Extracting Files that are Directories
1638 Extracting directories which are members of an archive is similar to
1639 extracting other files. The main difference to be aware of is that if
1640 the extracted directory has the same name as any directory already in
1641 the working directory, then files in the extracted directory will be
1642 placed into the directory of the same name. Likewise, if there are
1643 files in the pre-existing directory with the same names as the members
1644 which you extract, the files from the extracted archive will replace
1645 the files already in the working directory (and possible
1646 subdirectories). This will happen regardless of whether or not the
1647 files in the working directory were more recent than those extracted
1648 (there exist, however, special options that alter this behavior
1651 However, if a file was stored with a directory name as part of its file
1652 name, and that directory does not exist under the working directory when
1653 the file is extracted, @command{tar} will create the directory.
1655 We can demonstrate how to use @option{--extract} to extract a directory
1656 file with an example. Change to the @file{practice} directory if you
1657 weren't there, and remove the files @file{folk} and @file{jazz}. Then,
1658 go back to the parent directory and extract the archive
1659 @file{music.tar}. You may either extract the entire archive, or you may
1660 extract only the files you just deleted. To extract the entire archive,
1661 don't give any file names as arguments after the archive name
1662 @file{music.tar}. To extract only the files you deleted, use the
1666 $ @kbd{tar -xvf music.tar practice/folk practice/jazz}
1672 If you were to specify two @option{--verbose} (@option{-v}) options, @command{tar}
1673 would have displayed more detail about the extracted files, as shown
1674 in the example below:
1677 $ @kbd{tar -xvvf music.tar practice/folk practice/jazz}
1678 -rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz
1679 -rw-r--r-- me user 20 1996-09-23 16:44 practice/folk
1683 Because you created the directory with @file{practice} as part of the
1684 file names of each of the files by archiving the @file{practice}
1685 directory as @file{practice}, you must give @file{practice} as part
1686 of the file names when you extract those files from the archive.
1688 @node extracting untrusted archives
1689 @subsection Extracting Archives from Untrusted Sources
1691 Extracting files from archives can overwrite files that already exist.
1692 If you receive an archive from an untrusted source, you should make a
1693 new directory and extract into that directory, so that you don't have
1694 to worry about the extraction overwriting one of your existing files.
1695 For example, if @file{untrusted.tar} came from somewhere else on the
1696 Internet, and you don't necessarily trust its contents, you can
1697 extract it as follows:
1700 $ @kbd{mkdir newdir}
1702 $ @kbd{tar -xvf ../untrusted.tar}
1705 It is also a good practice to examine contents of the archive
1706 before extracting it, using @option{--list} (@option{-t}) option, possibly combined
1707 with @option{--verbose} (@option{-v}).
1709 @node failing commands
1710 @subsection Commands That Will Fail
1712 Here are some sample commands you might try which will not work, and why
1715 If you try to use this command,
1718 $ @kbd{tar -xvf music.tar folk jazz}
1722 you will get the following response:
1725 tar: folk: Not found in archive
1726 tar: jazz: Not found in archive
1731 This is because these files were not originally @emph{in} the parent
1732 directory @file{..}, where the archive is located; they were in the
1733 @file{practice} directory, and their file names reflect this:
1736 $ @kbd{tar -tvf music.tar}
1742 @FIXME{make sure the above works when going through the examples in
1746 Likewise, if you try to use this command,
1749 $ @kbd{tar -tvf music.tar folk jazz}
1753 you would get a similar response. Members with those names are not in the
1754 archive. You must use the correct member names, or wildcards, in order
1755 to extract the files from the archive.
1757 If you have forgotten the correct names of the files in the archive,
1758 use @w{@kbd{tar --list --verbose}} to list them correctly.
1760 @FIXME{more examples, here? hag thinks it's a good idea.}
1763 @section Going Further Ahead in this Manual
1766 @FIXME{need to write up a node here about the things that are going to
1767 be in the rest of the manual.}
1769 @node tar invocation
1770 @chapter Invoking @GNUTAR{}
1773 This chapter is about how one invokes the @GNUTAR{}
1774 command, from the command synopsis (@pxref{Synopsis}). There are
1775 numerous options, and many styles for writing them. One mandatory
1776 option specifies the operation @command{tar} should perform
1777 (@pxref{Operation Summary}), other options are meant to detail how
1778 this operation should be performed (@pxref{Option Summary}).
1779 Non-option arguments are not always interpreted the same way,
1780 depending on what the operation is.
1782 You will find in this chapter everything about option styles and rules for
1783 writing them (@pxref{Styles}). On the other hand, operations and options
1784 are fully described elsewhere, in other chapters. Here, you will find
1785 only synthetic descriptions for operations and options, together with
1786 pointers to other parts of the @command{tar} manual.
1788 Some options are so special they are fully described right in this
1789 chapter. They have the effect of inhibiting the normal operation of
1790 @command{tar} or else, they globally alter the amount of feedback the user
1791 receives about what is going on. These are the @option{--help} and
1792 @option{--version} (@pxref{help}), @option{--verbose} (@pxref{verbose})
1793 and @option{--interactive} options (@pxref{interactive}).
1797 * using tar options::
1808 @section General Synopsis of @command{tar}
1810 The @GNUTAR{} program is invoked as either one of:
1813 @kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
1814 @kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
1817 The second form is for when old options are being used.
1819 You can use @command{tar} to store files in an archive, to extract them from
1820 an archive, and to do other types of archive manipulation. The primary
1821 argument to @command{tar}, which is called the @dfn{operation}, specifies
1822 which action to take. The other arguments to @command{tar} are either
1823 @dfn{options}, which change the way @command{tar} performs an operation,
1824 or file names or archive members, which specify the files or members
1825 @command{tar} is to act on.
1827 You can actually type in arguments in any order, even if in this manual
1828 the options always precede the other arguments, to make examples easier
1829 to understand. Further, the option stating the main operation mode
1830 (the @command{tar} main command) is usually given first.
1832 Each @var{name} in the synopsis above is interpreted as an archive member
1833 name when the main command is one of @option{--compare}
1834 (@option{--diff}, @option{-d}), @option{--delete}, @option{--extract}
1835 (@option{--get}, @option{-x}), @option{--list} (@option{-t}) or
1836 @option{--update} (@option{-u}). When naming archive members, you
1837 must give the exact name of the member in the archive, as it is
1838 printed by @option{--list}. For @option{--append} (@option{-r}) and
1839 @option{--create} (@option{-c}), these @var{name} arguments specify
1840 the names of either files or directory hierarchies to place in the archive.
1841 These files or hierarchies should already exist in the file system,
1842 prior to the execution of the @command{tar} command.
1844 @command{tar} interprets relative file names as being relative to the
1845 working directory. @command{tar} will make all file names relative
1846 (by removing leading slashes when archiving or restoring files),
1847 unless you specify otherwise (using the @option{--absolute-names}
1848 option). @xref{absolute}, for more information about
1849 @option{--absolute-names}.
1851 If you give the name of a directory as either a file name or a member
1852 name, then @command{tar} acts recursively on all the files and directories
1853 beneath that directory. For example, the name @file{/} identifies all
1854 the files in the file system to @command{tar}.
1856 The distinction between file names and archive member names is especially
1857 important when shell globbing is used, and sometimes a source of confusion
1858 for newcomers. @xref{wildcards}, for more information about globbing.
1859 The problem is that shells may only glob using existing files in the
1860 file system. Only @command{tar} itself may glob on archive members, so when
1861 needed, you must ensure that wildcard characters reach @command{tar} without
1862 being interpreted by the shell first. Using a backslash before @samp{*}
1863 or @samp{?}, or putting the whole argument between quotes, is usually
1864 sufficient for this.
1866 Even if @var{name}s are often specified on the command line, they
1867 can also be read from a text file in the file system, using the
1868 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option.
1870 If you don't use any file name arguments, @option{--append} (@option{-r}),
1871 @option{--delete} and @option{--concatenate} (@option{--catenate},
1872 @option{-A}) will do nothing, while @option{--create} (@option{-c})
1873 will usually yield a diagnostic and inhibit @command{tar} execution.
1874 The other operations of @command{tar} (@option{--list},
1875 @option{--extract}, @option{--compare}, and @option{--update})
1876 will act on the entire contents of the archive.
1879 @cindex return status
1880 Besides successful exits, @GNUTAR{} may fail for
1881 many reasons. Some reasons correspond to bad usage, that is, when the
1882 @command{tar} command line is improperly written. Errors may be
1883 encountered later, while processing the archive or the files. Some
1884 errors are recoverable, in which case the failure is delayed until
1885 @command{tar} has completed all its work. Some errors are such that
1886 it would be not meaningful, or at least risky, to continue processing:
1887 @command{tar} then aborts processing immediately. All abnormal exits,
1888 whether immediate or delayed, should always be clearly diagnosed on
1889 @code{stderr}, after a line stating the nature of the error.
1891 Possible exit codes of @GNUTAR{} are summarized in the following
1896 @samp{Successful termination}.
1899 @samp{Some files differ}. If tar was invoked with @option{--compare}
1900 (@option{--diff}, @option{-d}) command line option, this means that
1901 some files in the archive differ from their disk counterparts
1902 (@pxref{compare}). If tar was given @option{--create},
1903 @option{--append} or @option{--update} option, this exit code means
1904 that some files were changed while being archived and so the resulting
1905 archive does not contain the exact copy of the file set.
1908 @samp{Fatal error}. This means that some fatal, unrecoverable error
1912 If @command{tar} has invoked a subprocess and that subprocess exited with a
1913 nonzero exit code, @command{tar} exits with that code as well.
1914 This can happen, for example, if @command{tar} was given some
1915 compression option (@pxref{gzip}) and the external compressor program
1916 failed. Another example is @command{rmt} failure during backup to the
1917 remote device (@pxref{Remote Tape Server}).
1919 @node using tar options
1920 @section Using @command{tar} Options
1922 @GNUTAR{} has a total of eight operating modes which
1923 allow you to perform a variety of tasks. You are required to choose
1924 one operating mode each time you employ the @command{tar} program by
1925 specifying one, and only one operation as an argument to the
1926 @command{tar} command (the corresponding options may be found
1927 at @ref{frequent operations} and @ref{Operations}). Depending on
1928 circumstances, you may also wish to customize how the chosen operating
1929 mode behaves. For example, you may wish to change the way the output
1930 looks, or the format of the files that you wish to archive may require
1931 you to do something special in order to make the archive look right.
1933 You can customize and control @command{tar}'s performance by running
1934 @command{tar} with one or more options (such as @option{--verbose}
1935 (@option{-v}), which we used in the tutorial). As we said in the
1936 tutorial, @dfn{options} are arguments to @command{tar} which are (as
1937 their name suggests) optional. Depending on the operating mode, you
1938 may specify one or more options. Different options will have different
1939 effects, but in general they all change details of the operation, such
1940 as archive format, archive name, or level of user interaction. Some
1941 options make sense with all operating modes, while others are
1942 meaningful only with particular modes. You will likely use some
1943 options frequently, while you will only use others infrequently, or
1944 not at all. (A full list of options is available in @pxref{All Options}.)
1946 @vrindex TAR_OPTIONS, environment variable
1947 @anchor{TAR_OPTIONS}
1948 The @env{TAR_OPTIONS} environment variable specifies default options to
1949 be placed in front of any explicit options. For example, if
1950 @code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as
1951 if the two options @option{-v} and @option{--unlink-first} had been
1952 specified before any explicit options. Option specifications are
1953 separated by whitespace. A backslash escapes the next character, so it
1954 can be used to specify an option containing whitespace or a backslash.
1956 Note that @command{tar} options are case sensitive. For example, the
1957 options @option{-T} and @option{-t} are different; the first requires an
1958 argument for stating the name of a file providing a list of @var{name}s,
1959 while the second does not require an argument and is another way to
1960 write @option{--list} (@option{-t}).
1962 In addition to the eight operations, there are many options to
1963 @command{tar}, and three different styles for writing both: long (mnemonic)
1964 form, short form, and old style. These styles are discussed below.
1965 Both the options and the operations can be written in any of these three
1968 @FIXME{menu at end of this node. need to think of an actual outline
1969 for this chapter; probably do that after stuff from chapter 4 is
1973 @section The Three Option Styles
1975 There are three styles for writing operations and options to the command
1976 line invoking @command{tar}. The different styles were developed at
1977 different times during the history of @command{tar}. These styles will be
1978 presented below, from the most recent to the oldest.
1980 Some options must take an argument. (For example, @option{--file}
1981 (@option{-f})) takes the name of an archive file as an argument. If
1982 you do not supply an archive file name, @command{tar} will use a
1983 default, but this can be confusing; thus, we recommend that you always
1984 supply a specific archive file name.) Where you @emph{place} the
1985 arguments generally depends on which style of options you choose. We
1986 will detail specific information relevant to each option style in the
1987 sections on the different option styles, below. The differences are
1988 subtle, yet can often be very important; incorrect option placement
1989 can cause you to overwrite a number of important files. We urge you
1990 to note these differences, and only use the option style(s) which
1991 makes the most sense to you until you feel comfortable with the others.
1993 Some options @emph{may} take an argument. Such options may have at
1994 most long and short forms, they do not have old style equivalent. The
1995 rules for specifying an argument for such options are stricter than
1996 those for specifying mandatory arguments. Please, pay special
2000 * Long Options:: Long Option Style
2001 * Short Options:: Short Option Style
2002 * Old Options:: Old Option Style
2003 * Mixing:: Mixing Option Styles
2007 @subsection Long Option Style
2009 Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
2010 dashes in a row, e.g., @option{--list}. The long names are more clear than
2011 their corresponding short or old names. It sometimes happens that a
2012 single long option has many different names which are
2013 synonymous, such as @option{--compare} and @option{--diff}. In addition,
2014 long option names can be given unique abbreviations. For example,
2015 @option{--cre} can be used in place of @option{--create} because there is no
2016 other long option which begins with @samp{cre}. (One way to find
2017 this out is by trying it and seeing what happens; if a particular
2018 abbreviation could represent more than one option, @command{tar} will tell
2019 you that that abbreviation is ambiguous and you'll know that that
2020 abbreviation won't work. You may also choose to run @samp{tar --help}
2021 to see a list of options. Be aware that if you run @command{tar} with a
2022 unique abbreviation for the long name of an option you didn't want to
2023 use, you are stuck; @command{tar} will perform the command as ordered.)
2025 Long options are meant to be obvious and easy to remember, and their
2026 meanings are generally easier to discern than those of their
2027 corresponding short options (see below). For example:
2030 $ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
2034 gives a fairly good set of hints about what the command does, even
2035 for those not fully acquainted with @command{tar}.
2037 Long options which require arguments take those arguments
2038 immediately following the option name. There are two ways of
2039 specifying a mandatory argument. It can be separated from the
2040 option name either by an equal sign, or by any amount of
2041 white space characters. For example, the @option{--file} option (which
2042 tells the name of the @command{tar} archive) is given a file such as
2043 @file{archive.tar} as argument by using any of the following notations:
2044 @option{--file=archive.tar} or @option{--file archive.tar}.
2046 In contrast, optional arguments must always be introduced using
2047 an equal sign. For example, the @option{--backup} option takes
2048 an optional argument specifying backup type. It must be used
2049 as @option{--backup=@var{backup-type}}.
2052 @subsection Short Option Style
2054 Most options also have a @dfn{short option} name. Short options start with
2055 a single dash, and are followed by a single character, e.g., @option{-t}
2056 (which is equivalent to @option{--list}). The forms are absolutely
2057 identical in function; they are interchangeable.
2059 The short option names are faster to type than long option names.
2061 Short options which require arguments take their arguments immediately
2062 following the option, usually separated by white space. It is also
2063 possible to stick the argument right after the short option name, using
2064 no intervening space. For example, you might write @w{@option{-f
2065 archive.tar}} or @option{-farchive.tar} instead of using
2066 @option{--file=archive.tar}. Both @option{--file=@var{archive-name}} and
2067 @w{@option{-f @var{archive-name}}} denote the option which indicates a
2068 specific archive, here named @file{archive.tar}.
2070 Short options which take optional arguments take their arguments
2071 immediately following the option letter, @emph{without any intervening
2072 white space characters}.
2074 Short options' letters may be clumped together, but you are not
2075 required to do this (as compared to old options; see below). When
2076 short options are clumped as a set, use one (single) dash for them
2077 all, e.g., @w{@samp{@command{tar} -cvf}}. Only the last option in
2078 such a set is allowed to have an argument@footnote{Clustering many
2079 options, the last of which has an argument, is a rather opaque way to
2080 write options. Some wonder if @acronym{GNU} @code{getopt} should not
2081 even be made helpful enough for considering such usages as invalid.}.
2083 When the options are separated, the argument for each option which requires
2084 an argument directly follows that option, as is usual for Unix programs.
2088 $ @kbd{tar -c -v -b 20 -f /dev/rmt0}
2091 If you reorder short options' locations, be sure to move any arguments
2092 that belong to them. If you do not move the arguments properly, you may
2093 end up overwriting files.
2096 @subsection Old Option Style
2099 Like short options, @dfn{old options} are single letters. However, old options
2100 must be written together as a single clumped set, without spaces separating
2101 them or dashes preceding them@footnote{Beware that if you precede options
2102 with a dash, you are announcing the short option style instead of the
2103 old option style; short options are decoded differently.}. This set
2104 of letters must be the first to appear on the command line, after the
2105 @command{tar} program name and some white space; old options cannot appear
2106 anywhere else. The letter of an old option is exactly the same letter as
2107 the corresponding short option. For example, the old option @samp{t} is
2108 the same as the short option @option{-t}, and consequently, the same as the
2109 long option @option{--list}. So for example, the command @w{@samp{tar
2110 cv}} specifies the option @option{-v} in addition to the operation @option{-c}.
2112 When options that need arguments are given together with the command,
2113 all the associated arguments follow, in the same order as the options.
2114 Thus, the example given previously could also be written in the old
2118 $ @kbd{tar cvbf 20 /dev/rmt0}
2122 Here, @samp{20} is the argument of @option{-b} and @samp{/dev/rmt0} is
2123 the argument of @option{-f}.
2125 On the other hand, this old style syntax makes it difficult to match
2126 option letters with their corresponding arguments, and is often
2127 confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example,
2128 @samp{20} is the argument for @option{-b}, @samp{/dev/rmt0} is the
2129 argument for @option{-f}, and @option{-v} does not have a corresponding
2130 argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f
2131 /dev/rmt0}} is clearer, putting all arguments next to the option they
2134 If you want to reorder the letters in the old option argument, be
2135 sure to reorder any corresponding argument appropriately.
2137 This old way of writing @command{tar} options can surprise even experienced
2138 users. For example, the two commands:
2141 @kbd{tar cfz archive.tar.gz file}
2142 @kbd{tar -cfz archive.tar.gz file}
2146 are quite different. The first example uses @file{archive.tar.gz} as
2147 the value for option @samp{f} and recognizes the option @samp{z}. The
2148 second example, however, uses @file{z} as the value for option
2149 @samp{f} --- probably not what was intended.
2151 Old options are kept for compatibility with old versions of @command{tar}.
2153 This second example could be corrected in many ways, among which the
2154 following are equivalent:
2157 @kbd{tar -czf archive.tar.gz file}
2158 @kbd{tar -cf archive.tar.gz -z file}
2159 @kbd{tar cf archive.tar.gz -z file}
2162 @cindex option syntax, traditional
2163 As far as we know, all @command{tar} programs, @acronym{GNU} and
2164 non-@acronym{GNU}, support old options. @GNUTAR{}
2165 supports them not only for historical reasons, but also because many
2166 people are used to them. For compatibility with Unix @command{tar},
2167 the first argument is always treated as containing command and option
2168 letters even if it doesn't start with @samp{-}. Thus, @samp{tar c} is
2169 equivalent to @w{@samp{tar -c}:} both of them specify the
2170 @option{--create} (@option{-c}) command to create an archive.
2173 @subsection Mixing Option Styles
2175 All three styles may be intermixed in a single @command{tar} command,
2176 so long as the rules for each style are fully
2177 respected@footnote{Before @GNUTAR{} version 1.11.6,
2178 a bug prevented intermixing old style options with long options in
2179 some cases.}. Old style options and either of the modern styles of
2180 options may be mixed within a single @command{tar} command. However,
2181 old style options must be introduced as the first arguments only,
2182 following the rule for old options (old options must appear directly
2183 after the @command{tar} command and some white space). Modern options
2184 may be given only after all arguments to the old options have been
2185 collected. If this rule is not respected, a modern option might be
2186 falsely interpreted as the value of the argument to one of the old
2189 For example, all the following commands are wholly equivalent, and
2190 illustrate the many combinations and orderings of option styles.
2193 @kbd{tar --create --file=archive.tar}
2194 @kbd{tar --create -f archive.tar}
2195 @kbd{tar --create -farchive.tar}
2196 @kbd{tar --file=archive.tar --create}
2197 @kbd{tar --file=archive.tar -c}
2198 @kbd{tar -c --file=archive.tar}
2199 @kbd{tar -c -f archive.tar}
2200 @kbd{tar -c -farchive.tar}
2201 @kbd{tar -cf archive.tar}
2202 @kbd{tar -cfarchive.tar}
2203 @kbd{tar -f archive.tar --create}
2204 @kbd{tar -f archive.tar -c}
2205 @kbd{tar -farchive.tar --create}
2206 @kbd{tar -farchive.tar -c}
2207 @kbd{tar c --file=archive.tar}
2208 @kbd{tar c -f archive.tar}
2209 @kbd{tar c -farchive.tar}
2210 @kbd{tar cf archive.tar}
2211 @kbd{tar f archive.tar --create}
2212 @kbd{tar f archive.tar -c}
2213 @kbd{tar fc archive.tar}
2216 On the other hand, the following commands are @emph{not} equivalent to
2220 @kbd{tar -f -c archive.tar}
2221 @kbd{tar -fc archive.tar}
2222 @kbd{tar -fcarchive.tar}
2223 @kbd{tar -farchive.tarc}
2224 @kbd{tar cfarchive.tar}
2228 These last examples mean something completely different from what the
2229 user intended (judging based on the example in the previous set which
2230 uses long options, whose intent is therefore very clear). The first
2231 four specify that the @command{tar} archive would be a file named
2232 @option{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc},
2233 respectively. The first two examples also specify a single non-option,
2234 @var{name} argument having the value @samp{archive.tar}. The last
2235 example contains only old style option letters (repeating option
2236 @samp{c} twice), not all of which are meaningful (eg., @samp{.},
2237 @samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked
2238 the first sentence of this paragraph..}
2241 @section All @command{tar} Options
2243 The coming manual sections contain an alphabetical listing of all
2244 @command{tar} operations and options, with brief descriptions and cross
2245 references to more in-depth explanations in the body of the manual.
2246 They also contain an alphabetically arranged table of the short option
2247 forms with their corresponding long option. You can use this table as
2248 a reference for deciphering @command{tar} commands in scripts.
2251 * Operation Summary::
2253 * Short Option Summary::
2256 @node Operation Summary
2257 @subsection Operations
2265 Appends files to the end of the archive. @xref{append}.
2267 @opsummary{catenate}
2271 Same as @option{--concatenate}. @xref{concatenate}.
2277 Compares archive members with their counterparts in the file
2278 system, and reports differences in file size, mode, owner,
2279 modification date and contents. @xref{compare}.
2281 @opsummary{concatenate}
2285 Appends other @command{tar} archives to the end of the archive.
2292 Creates a new @command{tar} archive. @xref{create}.
2297 Deletes members from the archive. Don't try this on a archive on a
2298 tape! @xref{delete}.
2304 Same @option{--compare}. @xref{compare}.
2310 Extracts members from the archive into the file system. @xref{extract}.
2316 Same as @option{--extract}. @xref{extract}.
2322 Lists the members in an archive. @xref{list}.
2328 Adds files to the end of the archive, but only if they are newer than
2329 their counterparts already in the archive, or if they do not already
2330 exist in the archive. @xref{update}.
2334 @node Option Summary
2335 @subsection @command{tar} Options
2339 @opsummary{absolute-names}
2340 @item --absolute-names
2343 Normally when creating an archive, @command{tar} strips an initial
2344 @samp{/} from member names. This option disables that behavior.
2347 @opsummary{after-date}
2350 (See @option{--newer}, @pxref{after})
2352 @opsummary{anchored}
2354 A pattern must match an initial subsequence of the name's components.
2355 @xref{controlling pattern-matching}.
2357 @opsummary{atime-preserve}
2358 @item --atime-preserve
2359 @itemx --atime-preserve=replace
2360 @itemx --atime-preserve=system
2362 Attempt to preserve the access time of files when reading them. This
2363 option currently is effective only on files that you own, unless you
2364 have superuser privileges.
2366 @option{--atime-preserve=replace} remembers the access time of a file
2367 before reading it, and then restores the access time afterwards. This
2368 may cause problems if other programs are reading the file at the same
2369 time, as the times of their accesses will be lost. On most platforms
2370 restoring the access time also requires @command{tar} to restore the
2371 data modification time too, so this option may also cause problems if
2372 other programs are writing the file at the same time. (Tar attempts
2373 to detect this situation, but cannot do so reliably due to race
2374 conditions.) Worse, on most platforms restoring the access time also
2375 updates the status change time, which means that this option is
2376 incompatible with incremental backups.
2378 @option{--atime-preserve=system} avoids changing time stamps on files,
2379 without interfering with time stamp updates
2380 caused by other programs, so it works better with incremental backups.
2381 However, it requires a special @code{O_NOATIME} option from the
2382 underlying operating and file system implementation, and it also requires
2383 that searching directories does not update their access times. As of
2384 this writing (November 2005) this works only with Linux, and only with
2385 Linux kernels 2.6.8 and later. Worse, there is currently no reliable
2386 way to know whether this feature actually works. Sometimes
2387 @command{tar} knows that it does not work, and if you use
2388 @option{--atime-preserve=system} then @command{tar} complains and
2389 exits right away. But other times @command{tar} might think that the
2390 option works when it actually does not.
2392 Currently @option{--atime-preserve} with no operand defaults to
2393 @option{--atime-preserve=replace}, but this may change in the future
2394 as support for @option{--atime-preserve=system} improves.
2396 If your operating system does not support
2397 @option{--atime-preserve=@-system}, you might be able to preserve access
2398 times reliably by by using the @command{mount} command. For example,
2399 you can mount the file system read-only, or access the file system via
2400 a read-only loopback mount, or use the @samp{noatime} mount option
2401 available on some systems. However, mounting typically requires
2402 superuser privileges and can be a pain to manage.
2404 @opsummary{auto-compress}
2405 @item --auto-compress
2408 During a @option{--create} operation, enables automatic compressed
2409 format recognition based on the archive suffix. The effect of this
2410 option is cancelled by @option{--no-auto-compress}. @xref{gzip}.
2413 @item --backup=@var{backup-type}
2415 Rather than deleting files from the file system, @command{tar} will
2416 back them up using simple or numbered backups, depending upon
2417 @var{backup-type}. @xref{backup}.
2419 @opsummary{block-number}
2420 @item --block-number
2423 With this option present, @command{tar} prints error messages for read errors
2424 with the block number in the archive file. @xref{block-number}.
2426 @opsummary{blocking-factor}
2427 @item --blocking-factor=@var{blocking}
2428 @itemx -b @var{blocking}
2430 Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
2431 record. @xref{Blocking Factor}.
2437 This option tells @command{tar} to read or write archives through
2438 @code{bzip2}. @xref{gzip}.
2440 @opsummary{check-device}
2441 @item --check-device
2442 Check device numbers when creating a list of modified files for
2443 incremental archiving. This is the default. @xref{device numbers},
2444 for a detailed description.
2446 @opsummary{checkpoint}
2447 @item --checkpoint[=@var{number}]
2449 This option directs @command{tar} to print periodic checkpoint
2450 messages as it reads through the archive. It is intended for when you
2451 want a visual indication that @command{tar} is still running, but
2452 don't want to see @option{--verbose} output. You can also instruct
2453 @command{tar} to execute a list of actions on each checkpoint, see
2454 @option{--checklist-action} below. For a detailed description, see
2457 @opsummary{checkpoint-action}
2458 @item --checkpoint-action=@var{action}
2459 Instruct @command{tar} to execute an action upon hitting a
2460 breakpoint. Here we give only a brief outline. @xref{checkpoints},
2461 for a complete description.
2463 The @var{action} argument can be one of the following:
2467 Produce an audible bell on the console.
2471 Print a single dot on the standard listing stream.
2474 Display a textual message on the standard error, with the status and
2475 number of the checkpoint. This is the default.
2477 @item echo=@var{string}
2478 Display @var{string} on the standard error. Before output, the string
2479 is subject to meta-character expansion.
2481 @item exec=@var{command}
2482 Execute the given @var{command}.
2484 @item sleep=@var{time}
2485 Wait for @var{time} seconds.
2487 @item ttyout=@var{string}
2488 Output @var{string} on the current console (@file{/dev/tty}).
2491 Several @option{--checkpoint-action} options can be specified. The
2492 supplied actions will be executed in order of their appearance in the
2495 Using @option{--checkpoint-action} without @option{--checkpoint}
2496 assumes default checkpoint frequency of one checkpoint per 10 records.
2498 @opsummary{check-links}
2501 If this option was given, @command{tar} will check the number of links
2502 dumped for each processed file. If this number does not match the
2503 total number of hard links for the file, a warning message will be
2504 output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2505 synonym for @option{--one-file-system}. The current semantics, which
2506 complies to UNIX98, was introduced with version
2507 1.15.91. @xref{Changes}, for more information.}.
2511 @opsummary{compress}
2512 @opsummary{uncompress}
2517 @command{tar} will use the @command{compress} program when reading or
2518 writing the archive. This allows you to directly act on archives
2519 while saving space. @xref{gzip}.
2521 @opsummary{confirmation}
2522 @item --confirmation
2524 (See @option{--interactive}.) @xref{interactive}.
2526 @opsummary{delay-directory-restore}
2527 @item --delay-directory-restore
2529 Delay setting modification times and permissions of extracted
2530 directories until the end of extraction. @xref{Directory Modification Times and Permissions}.
2532 @opsummary{dereference}
2536 When creating a @command{tar} archive, @command{tar} will archive the
2537 file that a symbolic link points to, rather than archiving the
2538 symlink. @xref{dereference}.
2540 @opsummary{directory}
2541 @item --directory=@var{dir}
2544 When this option is specified, @command{tar} will change its current directory
2545 to @var{dir} before performing any operations. When this option is used
2546 during archive creation, it is order sensitive. @xref{directory}.
2549 @item --exclude=@var{pattern}
2551 When performing operations, @command{tar} will skip files that match
2552 @var{pattern}. @xref{exclude}.
2554 @opsummary{exclude-from}
2555 @item --exclude-from=@var{file}
2556 @itemx -X @var{file}
2558 Similar to @option{--exclude}, except @command{tar} will use the list of
2559 patterns in the file @var{file}. @xref{exclude}.
2561 @opsummary{exclude-caches}
2562 @item --exclude-caches
2564 Exclude from dump any directory containing a valid cache directory
2565 tag file, but still dump the directory node and the tag file itself.
2569 @opsummary{exclude-caches-under}
2570 @item --exclude-caches-under
2572 Exclude from dump any directory containing a valid cache directory
2573 tag file, but still dump the directory node itself.
2577 @opsummary{exclude-caches-all}
2578 @item --exclude-caches-all
2580 Exclude from dump any directory containing a valid cache directory
2581 tag file. @xref{exclude}.
2583 @opsummary{exclude-tag}
2584 @item --exclude-tag=@var{file}
2586 Exclude from dump any directory containing file named @var{file}, but
2587 dump the directory node and @var{file} itself. @xref{exclude}.
2589 @opsummary{exclude-tag-under}
2590 @item --exclude-tag-under=@var{file}
2592 Exclude from dump the contents of any directory containing file
2593 named @var{file}, but dump the directory node itself. @xref{exclude}.
2595 @opsummary{exclude-tag-all}
2596 @item --exclude-tag-all=@var{file}
2598 Exclude from dump any directory containing file named @var{file}.
2601 @opsummary{exclude-vcs}
2604 Exclude from dump directories and files, that are internal for some
2605 widely used version control systems.
2610 @item --file=@var{archive}
2611 @itemx -f @var{archive}
2613 @command{tar} will use the file @var{archive} as the @command{tar} archive it
2614 performs operations on, rather than @command{tar}'s compilation dependent
2615 default. @xref{file tutorial}.
2617 @opsummary{files-from}
2618 @item --files-from=@var{file}
2619 @itemx -T @var{file}
2621 @command{tar} will use the contents of @var{file} as a list of archive members
2622 or files to operate on, in addition to those specified on the
2623 command-line. @xref{files}.
2625 @opsummary{force-local}
2628 Forces @command{tar} to interpret the file name given to @option{--file}
2629 as a local file, even if it looks like a remote tape drive name.
2630 @xref{local and remote archives}.
2633 @item --format=@var{format}
2634 @itemx -H @var{format}
2636 Selects output archive format. @var{Format} may be one of the
2641 Creates an archive that is compatible with Unix V7 @command{tar}.
2644 Creates an archive that is compatible with GNU @command{tar} version
2648 Creates archive in GNU tar 1.13 format. Basically it is the same as
2649 @samp{oldgnu} with the only difference in the way it handles long
2653 Creates a @acronym{POSIX.1-1988} compatible archive.
2656 Creates a @acronym{POSIX.1-2001 archive}.
2660 @xref{Formats}, for a detailed discussion of these formats.
2663 @item --group=@var{group}
2665 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
2666 rather than the group from the source file. @var{group} is first decoded
2667 as a group symbolic name, but if this interpretation fails, it has to be
2668 a decimal numeric group @acronym{ID}. @xref{override}.
2670 Also see the comments for the @option{--owner=@var{user}} option.
2680 This option tells @command{tar} to read or write archives through
2681 @command{gzip}, allowing @command{tar} to directly operate on several
2682 kinds of compressed archives transparently. @xref{gzip}.
2684 @opsummary{hard-dereference}
2685 @item --hard-dereference
2686 When creating an archive, dereference hard links and store the files
2687 they refer to, instead of creating usual hard link members.
2695 @command{tar} will print out a short message summarizing the operations and
2696 options to @command{tar} and exit. @xref{help}.
2698 @opsummary{ignore-case}
2700 Ignore case when matching member or file names with
2701 patterns. @xref{controlling pattern-matching}.
2703 @opsummary{ignore-command-error}
2704 @item --ignore-command-error
2705 Ignore exit codes of subprocesses. @xref{Writing to an External Program}.
2707 @opsummary{ignore-failed-read}
2708 @item --ignore-failed-read
2710 Do not exit unsuccessfully merely because an unreadable file was encountered.
2713 @opsummary{ignore-zeros}
2714 @item --ignore-zeros
2717 With this option, @command{tar} will ignore zeroed blocks in the
2718 archive, which normally signals EOF. @xref{Reading}.
2720 @opsummary{incremental}
2724 Informs @command{tar} that it is working with an old
2725 @acronym{GNU}-format incremental backup archive. It is intended
2726 primarily for backwards compatibility only. @xref{Incremental Dumps},
2727 for a detailed discussion of incremental archives.
2729 @opsummary{index-file}
2730 @item --index-file=@var{file}
2732 Send verbose output to @var{file} instead of to standard output.
2734 @opsummary{info-script}
2735 @opsummary{new-volume-script}
2736 @item --info-script=@var{script-file}
2737 @itemx --new-volume-script=@var{script-file}
2738 @itemx -F @var{script-file}
2740 When @command{tar} is performing multi-tape backups, @var{script-file} is run
2741 at the end of each tape. If @var{script-file} exits with nonzero status,
2742 @command{tar} fails immediately. @xref{info-script}, for a detailed
2743 discussion of @var{script-file}.
2745 @opsummary{interactive}
2747 @itemx --confirmation
2750 Specifies that @command{tar} should ask the user for confirmation before
2751 performing potentially destructive options, such as overwriting files.
2754 @opsummary{keep-newer-files}
2755 @item --keep-newer-files
2757 Do not replace existing files that are newer than their archive copies
2758 when extracting files from an archive.
2760 @opsummary{keep-old-files}
2761 @item --keep-old-files
2764 Do not overwrite existing files when extracting files from an archive.
2765 @xref{Keep Old Files}.
2768 @item --label=@var{name}
2769 @itemx -V @var{name}
2771 When creating an archive, instructs @command{tar} to write @var{name}
2772 as a name record in the archive. When extracting or listing archives,
2773 @command{tar} will only operate on archives that have a label matching
2774 the pattern specified in @var{name}. @xref{Tape Files}.
2776 @opsummary{listed-incremental}
2777 @item --listed-incremental=@var{snapshot-file}
2778 @itemx -g @var{snapshot-file}
2780 During a @option{--create} operation, specifies that the archive that
2781 @command{tar} creates is a new @acronym{GNU}-format incremental
2782 backup, using @var{snapshot-file} to determine which files to backup.
2783 With other operations, informs @command{tar} that the archive is in
2784 incremental format. @xref{Incremental Dumps}.
2789 This option tells @command{tar} to read or write archives through
2790 @command{lzma}. @xref{gzip}.
2794 This option tells @command{tar} to read or write archives through
2795 @command{lzop}. @xref{gzip}.
2798 @item --mode=@var{permissions}
2800 When adding files to an archive, @command{tar} will use
2801 @var{permissions} for the archive members, rather than the permissions
2802 from the files. @var{permissions} can be specified either as an octal
2803 number or as symbolic permissions, like with
2804 @command{chmod}. @xref{override}.
2807 @item --mtime=@var{date}
2809 When adding files to an archive, @command{tar} will use @var{date} as
2810 the modification time of members when creating archives, instead of
2811 their actual modification times. The value of @var{date} can be
2812 either a textual date representation (@pxref{Date input formats}) or a
2813 name of the existing file, starting with @samp{/} or @samp{.}. In the
2814 latter case, the modification time of that file is used. @xref{override}.
2816 @opsummary{multi-volume}
2817 @item --multi-volume
2820 Informs @command{tar} that it should create or otherwise operate on a
2821 multi-volume @command{tar} archive. @xref{Using Multiple Tapes}.
2823 @opsummary{new-volume-script}
2824 @item --new-volume-script
2829 @item --newer=@var{date}
2830 @itemx --after-date=@var{date}
2833 When creating an archive, @command{tar} will only add files that have changed
2834 since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it
2835 is taken to be the name of a file whose data modification time specifies
2836 the date. @xref{after}.
2838 @opsummary{newer-mtime}
2839 @item --newer-mtime=@var{date}
2841 Like @option{--newer}, but add only files whose
2842 contents have changed (as opposed to just @option{--newer}, which will
2843 also back up files for which any status information has
2844 changed). @xref{after}.
2846 @opsummary{no-anchored}
2848 An exclude pattern can match any subsequence of the name's components.
2849 @xref{controlling pattern-matching}.
2851 @opsummary{no-auto-compress}
2852 @item --no-auto-compress
2854 Disables automatic compressed format recognition based on the archive
2855 suffix. @xref{--auto-compress}. @xref{gzip}.
2857 @opsummary{no-check-device}
2858 @item --no-check-device
2859 Do not check device numbers when creating a list of modified files
2860 for incremental archiving. @xref{device numbers}, for
2861 a detailed description.
2863 @opsummary{no-delay-directory-restore}
2864 @item --no-delay-directory-restore
2866 Modification times and permissions of extracted
2867 directories are set when all files from this directory have been
2868 extracted. This is the default.
2869 @xref{Directory Modification Times and Permissions}.
2871 @opsummary{no-ignore-case}
2872 @item --no-ignore-case
2873 Use case-sensitive matching.
2874 @xref{controlling pattern-matching}.
2876 @opsummary{no-ignore-command-error}
2877 @item --no-ignore-command-error
2878 Print warnings about subprocesses that terminated with a nonzero exit
2879 code. @xref{Writing to an External Program}.
2884 If the @option{--null} option was given previously, this option
2885 cancels its effect, so that any following @option{--files-from}
2886 options will expect their file lists to be newline-terminated.
2888 @opsummary{no-overwrite-dir}
2889 @item --no-overwrite-dir
2891 Preserve metadata of existing directories when extracting files
2892 from an archive. @xref{Overwrite Old Files}.
2894 @opsummary{no-quote-chars}
2895 @item --no-quote-chars=@var{string}
2896 Remove characters listed in @var{string} from the list of quoted
2897 characters set by the previous @option{--quote-chars} option
2898 (@pxref{quoting styles}).
2900 @opsummary{no-recursion}
2901 @item --no-recursion
2903 With this option, @command{tar} will not recurse into directories.
2906 @opsummary{no-same-owner}
2907 @item --no-same-owner
2910 When extracting an archive, do not attempt to preserve the owner
2911 specified in the @command{tar} archive. This the default behavior
2914 @opsummary{no-same-permissions}
2915 @item --no-same-permissions
2917 When extracting an archive, subtract the user's umask from files from
2918 the permissions specified in the archive. This is the default behavior
2921 @opsummary{no-unquote}
2923 Treat all input file or member names literally, do not interpret
2924 escape sequences. @xref{input name quoting}.
2926 @opsummary{no-wildcards}
2927 @item --no-wildcards
2928 Do not use wildcards.
2929 @xref{controlling pattern-matching}.
2931 @opsummary{no-wildcards-match-slash}
2932 @item --no-wildcards-match-slash
2933 Wildcards do not match @samp{/}.
2934 @xref{controlling pattern-matching}.
2939 When @command{tar} is using the @option{--files-from} option, this option
2940 instructs @command{tar} to expect file names terminated with @acronym{NUL}, so
2941 @command{tar} can correctly work with file names that contain newlines.
2944 @opsummary{numeric-owner}
2945 @item --numeric-owner
2947 This option will notify @command{tar} that it should use numeric user
2948 and group IDs when creating a @command{tar} file, rather than names.
2952 The function of this option depends on the action @command{tar} is
2953 performing. When extracting files, @option{-o} is a synonym for
2954 @option{--no-same-owner}, i.e., it prevents @command{tar} from
2955 restoring ownership of files being extracted.
2957 When creating an archive, it is a synonym for
2958 @option{--old-archive}. This behavior is for compatibility
2959 with previous versions of @GNUTAR{}, and will be
2960 removed in future releases.
2962 @xref{Changes}, for more information.
2964 @opsummary{occurrence}
2965 @item --occurrence[=@var{number}]
2967 This option can be used in conjunction with one of the subcommands
2968 @option{--delete}, @option{--diff}, @option{--extract} or
2969 @option{--list} when a list of files is given either on the command
2970 line or via @option{-T} option.
2972 This option instructs @command{tar} to process only the @var{number}th
2973 occurrence of each named file. @var{Number} defaults to 1, so
2976 tar -x -f archive.tar --occurrence filename
2980 will extract the first occurrence of the member @file{filename} from @file{archive.tar}
2981 and will terminate without scanning to the end of the archive.
2983 @opsummary{old-archive}
2985 Synonym for @option{--format=v7}.
2987 @opsummary{one-file-system}
2988 @item --one-file-system
2989 Used when creating an archive. Prevents @command{tar} from recursing into
2990 directories that are on different file systems from the current
2993 @opsummary{overwrite}
2996 Overwrite existing files and directory metadata when extracting files
2997 from an archive. @xref{Overwrite Old Files}.
2999 @opsummary{overwrite-dir}
3000 @item --overwrite-dir
3002 Overwrite the metadata of existing directories when extracting files
3003 from an archive. @xref{Overwrite Old Files}.
3006 @item --owner=@var{user}
3008 Specifies that @command{tar} should use @var{user} as the owner of members
3009 when creating archives, instead of the user associated with the source
3010 file. @var{user} is first decoded as a user symbolic name, but if
3011 this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
3014 This option does not affect extraction from archives.
3016 @opsummary{pax-option}
3017 @item --pax-option=@var{keyword-list}
3018 This option is meaningful only with @acronym{POSIX.1-2001} archives
3019 (@pxref{posix}). It modifies the way @command{tar} handles the
3020 extended header keywords. @var{Keyword-list} is a comma-separated
3021 list of keyword options. @xref{PAX keywords}, for a detailed
3024 @opsummary{portability}
3026 @itemx --old-archive
3027 Synonym for @option{--format=v7}.
3031 Same as @option{--format=posix}.
3033 @opsummary{preserve}
3036 Synonymous with specifying both @option{--preserve-permissions} and
3037 @option{--same-order}. @xref{Setting Access Permissions}.
3039 @opsummary{preserve-order}
3040 @item --preserve-order
3042 (See @option{--same-order}; @pxref{Reading}.)
3044 @opsummary{preserve-permissions}
3045 @opsummary{same-permissions}
3046 @item --preserve-permissions
3047 @itemx --same-permissions
3050 When @command{tar} is extracting an archive, it normally subtracts the
3051 users' umask from the permissions specified in the archive and uses
3052 that number as the permissions to create the destination file.
3053 Specifying this option instructs @command{tar} that it should use the
3054 permissions directly from the archive. @xref{Setting Access Permissions}.
3056 @opsummary{quote-chars}
3057 @item --quote-chars=@var{string}
3058 Always quote characters from @var{string}, even if the selected
3059 quoting style would not quote them (@pxref{quoting styles}).
3061 @opsummary{quoting-style}
3062 @item --quoting-style=@var{style}
3063 Set quoting style to use when printing member and file names
3064 (@pxref{quoting styles}). Valid @var{style} values are:
3065 @code{literal}, @code{shell}, @code{shell-always}, @code{c},
3066 @code{escape}, @code{locale}, and @code{clocale}. Default quoting
3067 style is @code{escape}, unless overridden while configuring the
3070 @opsummary{read-full-records}
3071 @item --read-full-records
3074 Specifies that @command{tar} should reblock its input, for reading
3075 from pipes on systems with buggy implementations. @xref{Reading}.
3077 @opsummary{record-size}
3078 @item --record-size=@var{size}
3080 Instructs @command{tar} to use @var{size} bytes per record when accessing the
3081 archive. @xref{Blocking Factor}.
3083 @opsummary{recursion}
3086 With this option, @command{tar} recurses into directories (default).
3089 @opsummary{recursive-unlink}
3090 @item --recursive-unlink
3093 directory hierarchies before extracting directories of the same name
3094 from the archive. @xref{Recursive Unlink}.
3096 @opsummary{remove-files}
3097 @item --remove-files
3099 Directs @command{tar} to remove the source file from the file system after
3100 appending it to an archive. @xref{remove files}.
3102 @opsummary{restrict}
3105 Disable use of some potentially harmful @command{tar} options.
3106 Currently this option disables shell invocation from multi-volume menu
3107 (@pxref{Using Multiple Tapes}).
3109 @opsummary{rmt-command}
3110 @item --rmt-command=@var{cmd}
3112 Notifies @command{tar} that it should use @var{cmd} instead of
3113 the default @file{/usr/libexec/rmt} (@pxref{Remote Tape Server}).
3115 @opsummary{rsh-command}
3116 @item --rsh-command=@var{cmd}
3118 Notifies @command{tar} that is should use @var{cmd} to communicate with remote
3119 devices. @xref{Device}.
3121 @opsummary{same-order}
3123 @itemx --preserve-order
3126 This option is an optimization for @command{tar} when running on machines with
3127 small amounts of memory. It informs @command{tar} that the list of file
3128 arguments has already been sorted to match the order of files in the
3129 archive. @xref{Reading}.
3131 @opsummary{same-owner}
3134 When extracting an archive, @command{tar} will attempt to preserve the owner
3135 specified in the @command{tar} archive with this option present.
3136 This is the default behavior for the superuser; this option has an
3137 effect only for ordinary users. @xref{Attributes}.
3139 @opsummary{same-permissions}
3140 @item --same-permissions
3142 (See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
3148 Assume that the archive media supports seeks to arbitrary
3149 locations. Usually @command{tar} determines automatically whether
3150 the archive can be seeked or not. This option is intended for use
3151 in cases when such recognition fails.
3153 @opsummary{show-defaults}
3154 @item --show-defaults
3156 Displays the default options used by @command{tar} and exits
3157 successfully. This option is intended for use in shell scripts.
3158 Here is an example of what you can see using this option:
3161 $ tar --show-defaults
3162 --format=gnu -f- -b20 --quoting-style=escape \
3163 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
3166 @opsummary{show-omitted-dirs}
3167 @item --show-omitted-dirs
3169 Instructs @command{tar} to mention the directories it is skipping when
3170 operating on a @command{tar} archive. @xref{show-omitted-dirs}.
3172 @opsummary{show-transformed-names}
3173 @opsummary{show-stored-names}
3174 @item --show-transformed-names
3175 @itemx --show-stored-names
3177 Display file or member names after applying any transformations
3178 (@pxref{transform}). In particular, when used in conjunction with one of
3179 the archive creation operations it instructs @command{tar} to list the
3180 member names stored in the archive, as opposed to the actual file
3181 names. @xref{listing member and file names}.
3187 Invokes a @acronym{GNU} extension when adding files to an archive that handles
3188 sparse files efficiently. @xref{sparse}.
3190 @opsummary{sparse-version}
3191 @item --sparse-version=@var{version}
3193 Specifies the @dfn{format version} to use when archiving sparse
3194 files. Implies @option{--sparse}. @xref{sparse}. For the description
3195 of the supported sparse formats, @xref{Sparse Formats}.
3197 @opsummary{starting-file}
3198 @item --starting-file=@var{name}
3199 @itemx -K @var{name}
3201 This option affects extraction only; @command{tar} will skip extracting
3202 files in the archive until it finds one that matches @var{name}.
3205 @opsummary{strip-components}
3206 @item --strip-components=@var{number}
3207 Strip given @var{number} of leading components from file names before
3208 extraction. For example, if archive @file{archive.tar} contained
3209 @file{/some/file/name}, then running
3212 tar --extract --file archive.tar --strip-components=2
3216 would extract this file to file @file{name}.
3218 @opsummary{suffix}, summary
3219 @item --suffix=@var{suffix}
3221 Alters the suffix @command{tar} uses when backing up files from the default
3222 @samp{~}. @xref{backup}.
3224 @opsummary{tape-length}
3225 @item --tape-length=@var{num}
3228 Specifies the length of tapes that @command{tar} is writing as being
3229 @w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
3231 @opsummary{test-label}
3234 Reads the volume label. If an argument is specified, test whether it
3235 matches the volume label. @xref{--test-label option}.
3237 @opsummary{to-command}
3238 @item --to-command=@var{command}
3240 During extraction @command{tar} will pipe extracted files to the
3241 standard input of @var{command}. @xref{Writing to an External Program}.
3243 @opsummary{to-stdout}
3247 During extraction, @command{tar} will extract files to stdout rather
3248 than to the file system. @xref{Writing to Standard Output}.
3251 @item --totals[=@var{signo}]
3253 Displays the total number of bytes transferred when processing an
3254 archive. If an argument is given, these data are displayed on
3255 request, when signal @var{signo} is delivered to @command{tar}.
3262 Sets the data modification time of extracted files to the extraction time,
3263 rather than the data modification time stored in the archive.
3264 @xref{Data Modification Times}.
3266 @opsummary{transform}
3268 @item --transform=@var{sed-expr}
3269 @itemx --xform=@var{sed-expr}
3270 Transform file or member names using @command{sed} replacement expression
3271 @var{sed-expr}. For example,
3274 $ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
3278 will add to @file{archive} files from the current working directory,
3279 replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
3280 discussion, @xref{transform}.
3282 To see transformed member names in verbose listings, use
3283 @option{--show-transformed-names} option
3284 (@pxref{show-transformed-names}).
3286 @opsummary{uncompress}
3289 (See @option{--compress}. @pxref{gzip})
3294 (See @option{--gzip}. @pxref{gzip})
3296 @opsummary{unlink-first}
3297 @item --unlink-first
3300 Directs @command{tar} to remove the corresponding file from the file
3301 system before extracting it from the archive. @xref{Unlink First}.
3305 Enable unquoting input file or member names (default). @xref{input
3308 @opsummary{use-compress-program}
3309 @item --use-compress-program=@var{prog}
3310 @itemx -I=@var{prog}
3312 Instructs @command{tar} to access the archive through @var{prog}, which is
3313 presumed to be a compression program of some sort. @xref{gzip}.
3318 Display file modification dates in @acronym{UTC}. This option implies
3325 Specifies that @command{tar} should be more verbose about the
3326 operations it is performing. This option can be specified multiple
3327 times for some operations to increase the amount of information displayed.
3334 Verifies that the archive was correctly written when creating an
3335 archive. @xref{verify}.
3340 Print information about the program's name, version, origin and legal
3341 status, all on standard output, and then exit successfully.
3344 @opsummary{volno-file}
3345 @item --volno-file=@var{file}
3347 Used in conjunction with @option{--multi-volume}. @command{tar} will
3348 keep track of which volume of a multi-volume archive it is working in
3349 @var{file}. @xref{volno-file}.
3351 @opsummary{wildcards}
3353 Use wildcards when matching member names with patterns.
3354 @xref{controlling pattern-matching}.
3356 @opsummary{wildcards-match-slash}
3357 @item --wildcards-match-slash
3358 Wildcards match @samp{/}.
3359 @xref{controlling pattern-matching}.
3364 Use @command{xz} for compressing or decompressing the archives. @xref{gzip}.
3368 @node Short Option Summary
3369 @subsection Short Options Cross Reference
3371 Here is an alphabetized list of all of the short option forms, matching
3372 them with the equivalent long option.
3374 @multitable @columnfractions 0.20 0.80
3375 @headitem Short Option @tab Reference
3377 @item -A @tab @ref{--concatenate}.
3379 @item -B @tab @ref{--read-full-records}.
3381 @item -C @tab @ref{--directory}.
3383 @item -F @tab @ref{--info-script}.
3385 @item -G @tab @ref{--incremental}.
3387 @item -J @tab @ref{--xz}.
3389 @item -K @tab @ref{--starting-file}.
3391 @item -L @tab @ref{--tape-length}.
3393 @item -M @tab @ref{--multi-volume}.
3395 @item -N @tab @ref{--newer}.
3397 @item -O @tab @ref{--to-stdout}.
3399 @item -P @tab @ref{--absolute-names}.
3401 @item -R @tab @ref{--block-number}.
3403 @item -S @tab @ref{--sparse}.
3405 @item -T @tab @ref{--files-from}.
3407 @item -U @tab @ref{--unlink-first}.
3409 @item -V @tab @ref{--label}.
3411 @item -W @tab @ref{--verify}.
3413 @item -X @tab @ref{--exclude-from}.
3415 @item -Z @tab @ref{--compress}.
3417 @item -b @tab @ref{--blocking-factor}.
3419 @item -c @tab @ref{--create}.
3421 @item -d @tab @ref{--compare}.
3423 @item -f @tab @ref{--file}.
3425 @item -g @tab @ref{--listed-incremental}.
3427 @item -h @tab @ref{--dereference}.
3429 @item -i @tab @ref{--ignore-zeros}.
3431 @item -j @tab @ref{--bzip2}.
3433 @item -k @tab @ref{--keep-old-files}.
3435 @item -l @tab @ref{--check-links}.
3437 @item -m @tab @ref{--touch}.
3439 @item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
3440 @ref{--portability}.
3442 The latter usage is deprecated. It is retained for compatibility with
3443 the earlier versions of @GNUTAR{}. In future releases
3444 @option{-o} will be equivalent to @option{--no-same-owner} only.
3446 @item -p @tab @ref{--preserve-permissions}.
3448 @item -r @tab @ref{--append}.
3450 @item -s @tab @ref{--same-order}.
3452 @item -t @tab @ref{--list}.
3454 @item -u @tab @ref{--update}.
3456 @item -v @tab @ref{--verbose}.
3458 @item -w @tab @ref{--interactive}.
3460 @item -x @tab @ref{--extract}.
3462 @item -z @tab @ref{--gzip}.
3467 @section @GNUTAR{} documentation
3469 @cindex Getting program version number
3471 @cindex Version of the @command{tar} program
3472 Being careful, the first thing is really checking that you are using
3473 @GNUTAR{}, indeed. The @option{--version} option
3474 causes @command{tar} to print information about its name, version,
3475 origin and legal status, all on standard output, and then exit
3476 successfully. For example, @w{@samp{tar --version}} might print:
3479 tar (GNU tar) @value{VERSION}
3480 Copyright (C) 2008 Free Software Foundation, Inc.
3481 This is free software. You may redistribute copies of it under the terms
3482 of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
3483 There is NO WARRANTY, to the extent permitted by law.
3485 Written by John Gilmore and Jay Fenlason.
3489 The first occurrence of @samp{tar} in the result above is the program
3490 name in the package (for example, @command{rmt} is another program),
3491 while the second occurrence of @samp{tar} is the name of the package
3492 itself, containing possibly many programs. The package is currently
3493 named @samp{tar}, after the name of the main program it
3494 contains@footnote{There are plans to merge the @command{cpio} and
3495 @command{tar} packages into a single one which would be called
3496 @code{paxutils}. So, who knows if, one of this days, the
3497 @option{--version} would not output @w{@samp{tar (@acronym{GNU}
3500 @cindex Obtaining help
3501 @cindex Listing all @command{tar} options
3502 @xopindex{help, introduction}
3503 Another thing you might want to do is checking the spelling or meaning
3504 of some particular @command{tar} option, without resorting to this
3505 manual, for once you have carefully read it. @GNUTAR{}
3506 has a short help feature, triggerable through the
3507 @option{--help} option. By using this option, @command{tar} will
3508 print a usage message listing all available options on standard
3509 output, then exit successfully, without doing anything else and
3510 ignoring all other options. Even if this is only a brief summary, it
3511 may be several screens long. So, if you are not using some kind of
3512 scrollable window, you might prefer to use something like:
3515 $ @kbd{tar --help | less}
3519 presuming, here, that you like using @command{less} for a pager. Other
3520 popular pagers are @command{more} and @command{pg}. If you know about some
3521 @var{keyword} which interests you and do not want to read all the
3522 @option{--help} output, another common idiom is doing:
3525 tar --help | grep @var{keyword}
3529 for getting only the pertinent lines. Notice, however, that some
3530 @command{tar} options have long description lines and the above
3531 command will list only the first of them.
3533 The exact look of the option summary displayed by @kbd{tar --help} is
3534 configurable. @xref{Configuring Help Summary}, for a detailed description.
3537 If you only wish to check the spelling of an option, running @kbd{tar
3538 --usage} may be a better choice. This will display a terse list of
3539 @command{tar} option without accompanying explanations.
3541 The short help output is quite succinct, and you might have to get
3542 back to the full documentation for precise points. If you are reading
3543 this paragraph, you already have the @command{tar} manual in some
3544 form. This manual is available in a variety of forms from
3545 @url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{}
3546 distribution, provided you have @TeX{} already installed somewhere,
3547 and a laser printer around. Just configure the distribution, execute
3548 the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the
3549 usual way (contact your local guru to know how). If @GNUTAR{}
3550 has been conveniently installed at your place, this
3551 manual is also available in interactive, hypertextual form as an Info
3552 file. Just call @w{@samp{info tar}} or, if you do not have the
3553 @command{info} program handy, use the Info reader provided within
3554 @acronym{GNU} Emacs, calling @samp{tar} from the main Info menu.
3556 There is currently no @code{man} page for @GNUTAR{}.
3557 If you observe such a @code{man} page on the system you are running,
3558 either it does not belong to @GNUTAR{}, or it has not
3559 been produced by @acronym{GNU}. Some package maintainers convert
3560 @kbd{tar --help} output to a man page, using @command{help2man}. In
3561 any case, please bear in mind that the authoritative source of
3562 information about @GNUTAR{} is this Texinfo documentation.
3565 @section Obtaining @GNUTAR{} default values
3567 @opindex show-defaults
3568 @GNUTAR{} has some predefined defaults that are used when you do not
3569 explicitly specify another values. To obtain a list of such
3570 defaults, use @option{--show-defaults} option. This will output the
3571 values in the form of @command{tar} command line options:
3575 @kbd{tar --show-defaults}
3576 --format=gnu -f- -b20 --quoting-style=escape
3577 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3582 Notice, that this option outputs only one line. The example output above
3583 has been split to fit page boundaries.
3586 The above output shows that this version of @GNUTAR{} defaults to
3587 using @samp{gnu} archive format (@pxref{Formats}), it uses standard
3588 output as the archive, if no @option{--file} option has been given
3589 (@pxref{file tutorial}), the default blocking factor is 20
3590 (@pxref{Blocking Factor}). It also shows the default locations where
3591 @command{tar} will look for @command{rmt} and @command{rsh} binaries.
3594 @section Checking @command{tar} progress
3596 Typically, @command{tar} performs most operations without reporting any
3597 information to the user except error messages. When using @command{tar}
3598 with many options, particularly ones with complicated or
3599 difficult-to-predict behavior, it is possible to make serious mistakes.
3600 @command{tar} provides several options that make observing @command{tar}
3601 easier. These options cause @command{tar} to print information as it
3602 progresses in its job, and you might want to use them just for being
3603 more careful about what is going on, or merely for entertaining
3604 yourself. If you have encountered a problem when operating on an
3605 archive, however, you may need more information than just an error
3606 message in order to solve the problem. The following options can be
3607 helpful diagnostic tools.
3609 @cindex Verbose operation
3611 Normally, the @option{--list} (@option{-t}) command to list an archive
3612 prints just the file names (one per line) and the other commands are
3613 silent. When used with most operations, the @option{--verbose}
3614 (@option{-v}) option causes @command{tar} to print the name of each
3615 file or archive member as it is processed. This and the other options
3616 which make @command{tar} print status information can be useful in
3617 monitoring @command{tar}.
3619 With @option{--create} or @option{--extract}, @option{--verbose} used
3620 once just prints the names of the files or members as they are processed.
3621 Using it twice causes @command{tar} to print a longer listing
3622 (@xref{verbose member listing}, for the description) for each member.
3623 Since @option{--list} already prints the names of the members,
3624 @option{--verbose} used once with @option{--list} causes @command{tar}
3625 to print an @samp{ls -l} type listing of the files in the archive.
3626 The following examples both extract members with long list output:
3629 $ @kbd{tar --extract --file=archive.tar --verbose --verbose}
3630 $ @kbd{tar xvvf archive.tar}
3633 Verbose output appears on the standard output except when an archive is
3634 being written to the standard output, as with @samp{tar --create
3635 --file=- --verbose} (@samp{tar cfv -}, or even @samp{tar cv}---if the
3636 installer let standard output be the default archive). In that case
3637 @command{tar} writes verbose output to the standard error stream.
3639 If @option{--index-file=@var{file}} is specified, @command{tar} sends
3640 verbose output to @var{file} rather than to standard output or standard
3644 @cindex Obtaining total status information
3646 The @option{--totals} option causes @command{tar} to print on the
3647 standard error the total amount of bytes transferred when processing
3648 an archive. When creating or appending to an archive, this option
3649 prints the number of bytes written to the archive and the average
3650 speed at which they have been written, e.g.:
3654 $ @kbd{tar -c -f archive.tar --totals /home}
3655 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3659 When reading an archive, this option displays the number of bytes
3664 $ @kbd{tar -x -f archive.tar --totals}
3665 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3669 Finally, when deleting from an archive, the @option{--totals} option
3670 displays both numbers plus number of bytes removed from the archive:
3674 $ @kbd{tar --delete -f foo.tar --totals --wildcards '*~'}
3675 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3676 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3677 Total bytes deleted: 1474048
3681 You can also obtain this information on request. When
3682 @option{--totals} is used with an argument, this argument is
3683 interpreted as a symbolic name of a signal, upon delivery of which the
3684 statistics is to be printed:
3687 @item --totals=@var{signo}
3688 Print statistics upon delivery of signal @var{signo}. Valid arguments
3689 are: @code{SIGHUP}, @code{SIGQUIT}, @code{SIGINT}, @code{SIGUSR1} and
3690 @code{SIGUSR2}. Shortened names without @samp{SIG} prefix are also
3694 Both forms of @option{--totals} option can be used simultaneously.
3695 Thus, @kbd{tar -x --totals --totals=USR1} instructs @command{tar} to
3696 extract all members from its default archive and print statistics
3697 after finishing the extraction, as well as when receiving signal
3700 @anchor{Progress information}
3701 @cindex Progress information
3702 The @option{--checkpoint} option prints an occasional message
3703 as @command{tar} reads or writes the archive. It is designed for
3704 those who don't need the more detailed (and voluminous) output of
3705 @option{--block-number} (@option{-R}), but do want visual confirmation
3706 that @command{tar} is actually making forward progress. By default it
3707 prints a message each 10 records read or written. This can be changed
3708 by giving it a numeric argument after an equal sign:
3711 $ @kbd{tar -c --checkpoint=1000} /var
3712 tar: Write checkpoint 1000
3713 tar: Write checkpoint 2000
3714 tar: Write checkpoint 3000
3717 This example shows the default checkpoint message used by
3718 @command{tar}. If you place a dot immediately after the equal
3719 sign, it will print a @samp{.} at each checkpoint@footnote{This is
3720 actually a shortcut for @option{--checkpoint=@var{n}
3721 --checkpoint-action=dot}. @xref{checkpoints, dot}.}. For example:
3724 $ @kbd{tar -c --checkpoint=.1000} /var
3728 The @option{--checkpoint} option provides a flexible mechanism for
3729 executing arbitrary actions upon hitting checkpoints, see the next
3730 section (@pxref{checkpoints}), for more information on it.
3732 @opindex show-omitted-dirs
3733 @anchor{show-omitted-dirs}
3734 The @option{--show-omitted-dirs} option, when reading an archive---with
3735 @option{--list} or @option{--extract}, for example---causes a message
3736 to be printed for each directory in the archive which is skipped.
3737 This happens regardless of the reason for skipping: the directory might
3738 not have been named on the command line (implicitly or explicitly),
3739 it might be excluded by the use of the
3740 @option{--exclude=@var{pattern}} option, or some other reason.
3742 @opindex block-number
3743 @cindex Block number where error occurred
3744 @anchor{block-number}
3745 If @option{--block-number} (@option{-R}) is used, @command{tar} prints, along with
3746 every message it would normally produce, the block number within the
3747 archive where the message was triggered. Also, supplementary messages
3748 are triggered when reading blocks full of NULs, or when hitting end of
3749 file on the archive. As of now, if the archive is properly terminated
3750 with a NUL block, the reading of the file may stop before end of file
3751 is met, so the position of end of file will not usually show when
3752 @option{--block-number} (@option{-R}) is used. Note that @GNUTAR{}
3753 drains the archive before exiting when reading the
3754 archive from a pipe.
3756 @cindex Error message, block number of
3757 This option is especially useful when reading damaged archives, since
3758 it helps pinpoint the damaged sections. It can also be used with
3759 @option{--list} (@option{-t}) when listing a file-system backup tape, allowing you to
3760 choose among several backup tapes when retrieving a file later, in
3761 favor of the tape where the file appears earliest (closest to the
3762 front of the tape). @xref{backup}.
3765 @section Checkpoints
3766 @cindex checkpoints, defined
3768 @opindex checkpoint-action
3770 A @dfn{checkpoint} is a moment of time before writing @var{n}th record to
3771 the archive (a @dfn{write checkpoint}), or before reading @var{n}th record
3772 from the archive (a @dfn{read checkpoint}). Checkpoints allow to
3773 periodically execute arbitrary actions.
3775 The checkpoint facility is enabled using the following option:
3778 @xopindex{checkpoint, defined}
3779 @item --checkpoint[=@var{n}]
3780 Schedule checkpoints before writing or reading each @var{n}th record.
3781 The default value for @var{n} is 10.
3784 A list of arbitrary @dfn{actions} can be executed at each checkpoint.
3785 These actions include: pausing, displaying textual messages, and
3786 executing arbitrary external programs. Actions are defined using
3787 the @option{--checkpoint-action} option.
3790 @xopindex{checkpoint-action, defined}
3791 @item --checkpoint-action=@var{action}
3792 Execute an @var{action} at each checkpoint.
3795 @cindex @code{echo}, checkpoint action
3796 The simplest value of @var{action} is @samp{echo}. It instructs
3797 @command{tar} to display the default message on the standard error
3798 stream upon arriving at each checkpoint. The default message is (in
3799 @acronym{POSIX} locale) @samp{Write checkpoint @var{n}}, for write
3800 checkpoints, and @samp{Read checkpoint @var{n}}, for read checkpoints.
3801 Here, @var{n} represents ordinal number of the checkpoint.
3803 In another locales, translated versions of this message are used.
3805 This is the default action, so running:
3808 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=echo} /var
3815 $ @kbd{tar -c --checkpoint=1000} /var
3818 The @samp{echo} action also allows to supply a customized message.
3819 You do so by placing an equals sign and the message right after it,
3823 --checkpoint-action="echo=Hit %s checkpoint #%u"
3826 The @samp{%s} and @samp{%u} in the above example are
3827 @dfn{meta-characters}. The @samp{%s} meta-character is replaced with
3828 the @dfn{type} of the checkpoint: @samp{write} or
3829 @samp{read} (or a corresponding translated version in locales other
3830 than @acronym{POSIX}). The @samp{%u} meta-character is replaced with
3831 the ordinal number of the checkpoint. Thus, the above example could
3832 produce the following output when used with the @option{--create}
3836 tar: Hit write checkpoint #10
3837 tar: Hit write checkpoint #20
3838 tar: Hit write checkpoint #30
3841 Aside from meta-character expansion, the message string is subject to
3842 @dfn{unquoting}, during which the backslash @dfn{escape sequences} are
3843 replaced with their corresponding @acronym{ASCII} characters
3844 (@pxref{escape sequences}). E.g. the following action will produce an
3845 audible bell and the message described above at each checkpoint:
3848 --checkpoint-action='echo=\aHit %s checkpoint #%u'
3851 @cindex @code{bell}, checkpoint action
3852 There is also a special action which produces an audible signal:
3853 @samp{bell}. It is not equivalent to @samp{echo='\a'}, because
3854 @samp{bell} sends the bell directly to the console (@file{/dev/tty}),
3855 whereas @samp{echo='\a'} sends it to the standard error.
3857 @cindex @code{ttyout}, checkpoint action
3858 The @samp{ttyout=@var{string}} action outputs @var{string} to
3859 @file{/dev/tty}, so it can be used even if the standard output is
3860 redirected elsewhere. The @var{string} is subject to the same
3861 modifications as with @samp{echo} action. In contrast to the latter,
3862 @samp{ttyout} does not prepend @command{tar} executable name to the
3863 string, nor does it output a newline after it. For example, the
3864 following action will print the checkpoint message at the same screen
3865 line, overwriting any previous message:
3868 --checkpoint-action="ttyout=\rHit %s checkpoint #%u"
3871 @cindex @code{dot}, checkpoint action
3872 Another available checkpoint action is @samp{dot} (or @samp{.}). It
3873 instructs @command{tar} to print a single dot on the standard listing
3877 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=dot} /var
3881 For compatibility with previous @GNUTAR{} versions, this action can
3882 be abbreviated by placing a dot in front of the checkpoint frequency,
3883 as shown in the previous section.
3885 @cindex @code{sleep}, checkpoint action
3886 Yet another action, @samp{sleep}, pauses @command{tar} for a specified
3887 amount of seconds. The following example will stop for 30 seconds at each
3891 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=sleep=30}
3894 @cindex @code{exec}, checkpoint action
3895 Finally, the @code{exec} action executes a given external program.
3899 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint}
3902 This program is executed using @command{/bin/sh -c}, with no
3903 additional arguments. Its exit code is ignored. It gets a copy of
3904 @command{tar}'s environment plus the following variables:
3907 @vrindex TAR_VERSION, checkpoint script environment
3909 @GNUTAR{} version number.
3911 @vrindex TAR_ARCHIVE, checkpoint script environment
3913 The name of the archive @command{tar} is processing.
3915 @vrindex TAR_BLOCKING_FACTOR, checkpoint script environment
3916 @item TAR_BLOCKING_FACTOR
3917 Current blocking factor (@pxref{Blocking}).
3919 @vrindex TAR_CHECKPOINT, checkpoint script environment
3920 @item TAR_CHECKPOINT
3921 Number of the checkpoint.
3923 @vrindex TAR_SUBCOMMAND, checkpoint script environment
3924 @item TAR_SUBCOMMAND
3925 A short option describing the operation @command{tar} is executing.
3926 @xref{Operations}, for a complete list of subcommand options.
3928 @vrindex TAR_FORMAT, checkpoint script environment
3930 Format of the archive being processed. @xref{Formats}, for a complete
3931 list of archive format names.
3934 Any number of actions can be defined, by supplying several
3935 @option{--checkpoint-action} options in the command line. For
3936 example, the command below displays two messages, pauses
3937 execution for 30 seconds and executes the @file{/sbin/cpoint} script:
3941 $ @kbd{tar -c -f arc.tar \
3942 --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
3943 --checkpoint-action='echo=Sleeping for 30 seconds' \
3944 --checkpoint-action='sleep=30' \
3945 --checkpoint-action='exec=/sbin/cpoint'}
3949 This example also illustrates the fact that
3950 @option{--checkpoint-action} can be used without
3951 @option{--checkpoint}. In this case, the default checkpoint frequency
3952 (at each 10th record) is assumed.
3955 @section Asking for Confirmation During Operations
3956 @cindex Interactive operation
3958 Typically, @command{tar} carries out a command without stopping for
3959 further instructions. In some situations however, you may want to
3960 exclude some files and archive members from the operation (for instance
3961 if disk or storage space is tight). You can do this by excluding
3962 certain files automatically (@pxref{Choosing}), or by performing
3963 an operation interactively, using the @option{--interactive} (@option{-w}) option.
3964 @command{tar} also accepts @option{--confirmation} for this option.
3966 @opindex interactive
3967 When the @option{--interactive} (@option{-w}) option is specified, before
3968 reading, writing, or deleting files, @command{tar} first prints a message
3969 for each such file, telling what operation it intends to take, then asks
3970 for confirmation on the terminal. The actions which require
3971 confirmation include adding a file to the archive, extracting a file
3972 from the archive, deleting a file from the archive, and deleting a file
3973 from disk. To confirm the action, you must type a line of input
3974 beginning with @samp{y}. If your input line begins with anything other
3975 than @samp{y}, @command{tar} skips that file.
3977 If @command{tar} is reading the archive from the standard input,
3978 @command{tar} opens the file @file{/dev/tty} to support the interactive
3981 Verbose output is normally sent to standard output, separate from
3982 other error messages. However, if the archive is produced directly
3983 on standard output, then verbose output is mixed with errors on
3984 @code{stderr}. Producing the archive on standard output may be used
3985 as a way to avoid using disk space, when the archive is soon to be
3986 consumed by another process reading it, say. Some people felt the need
3987 of producing an archive on stdout, still willing to segregate between
3988 verbose output and error output. A possible approach would be using a
3989 named pipe to receive the archive, and having the consumer process to
3990 read from that named pipe. This has the advantage of letting standard
3991 output free to receive verbose output, all separate from errors.
3994 @chapter @GNUTAR{} Operations
4007 @section Basic @GNUTAR{} Operations
4009 The basic @command{tar} operations, @option{--create} (@option{-c}),
4010 @option{--list} (@option{-t}) and @option{--extract} (@option{--get},
4011 @option{-x}), are currently presented and described in the tutorial
4012 chapter of this manual. This section provides some complementary notes
4013 for these operations.
4016 @xopindex{create, complementary notes}
4020 Creating an empty archive would have some kind of elegance. One can
4021 initialize an empty archive and later use @option{--append}
4022 (@option{-r}) for adding all members. Some applications would not
4023 welcome making an exception in the way of adding the first archive
4024 member. On the other hand, many people reported that it is
4025 dangerously too easy for @command{tar} to destroy a magnetic tape with
4026 an empty archive@footnote{This is well described in @cite{Unix-haters
4027 Handbook}, by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG
4028 Books, ISBN 1-56884-203-1.}. The two most common errors are:
4032 Mistakingly using @code{create} instead of @code{extract}, when the
4033 intent was to extract the full contents of an archive. This error
4034 is likely: keys @kbd{c} and @kbd{x} are right next to each other on
4035 the QWERTY keyboard. Instead of being unpacked, the archive then
4036 gets wholly destroyed. When users speak about @dfn{exploding} an
4037 archive, they usually mean something else :-).
4040 Forgetting the argument to @code{file}, when the intent was to create
4041 an archive with a single file in it. This error is likely because a
4042 tired user can easily add the @kbd{f} key to the cluster of option
4043 letters, by the mere force of habit, without realizing the full
4044 consequence of doing so. The usual consequence is that the single
4045 file, which was meant to be saved, is rather destroyed.
4048 So, recognizing the likelihood and the catastrophic nature of these
4049 errors, @GNUTAR{} now takes some distance from elegance, and
4050 cowardly refuses to create an archive when @option{--create} option is
4051 given, there are no arguments besides options, and
4052 @option{--files-from} (@option{-T}) option is @emph{not} used. To get
4053 around the cautiousness of @GNUTAR{} and nevertheless create an
4054 archive with nothing in it, one may still use, as the value for the
4055 @option{--files-from} option, a file with no names in it, as shown in
4056 the following commands:
4059 @kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
4060 @kbd{tar cfT empty-archive.tar /dev/null}
4063 @xopindex{extract, complementary notes}
4068 A socket is stored, within a @GNUTAR{} archive, as a pipe.
4070 @item @option{--list} (@option{-t})
4072 @GNUTAR{} now shows dates as @samp{1996-08-30},
4073 while it used to show them as @samp{Aug 30 1996}. Preferably,
4074 people should get used to ISO 8601 dates. Local American dates should
4075 be made available again with full date localization support, once
4076 ready. In the meantime, programs not being localizable for dates
4077 should prefer international dates, that's really the way to go.
4079 Look up @url{http://www.cl.cam.ac.uk/@/~mgk25/@/iso-time.html} if you
4080 are curious, it contains a detailed explanation of the ISO 8601 standard.
4085 @section Advanced @GNUTAR{} Operations
4087 Now that you have learned the basics of using @GNUTAR{}, you may want
4088 to learn about further ways in which @command{tar} can help you.
4090 This chapter presents five, more advanced operations which you probably
4091 won't use on a daily basis, but which serve more specialized functions.
4092 We also explain the different styles of options and why you might want
4093 to use one or another, or a combination of them in your @command{tar}
4094 commands. Additionally, this chapter includes options which allow you to
4095 define the output from @command{tar} more carefully, and provide help and
4096 error correction in special circumstances.
4098 @FIXME{check this after the chapter is actually revised to make sure
4099 it still introduces the info in the chapter correctly : ).}
4111 @subsection The Five Advanced @command{tar} Operations
4114 In the last chapter, you learned about the first three operations to
4115 @command{tar}. This chapter presents the remaining five operations to
4116 @command{tar}: @option{--append}, @option{--update}, @option{--concatenate},
4117 @option{--delete}, and @option{--compare}.
4119 You are not likely to use these operations as frequently as those
4120 covered in the last chapter; however, since they perform specialized
4121 functions, they are quite useful when you do need to use them. We
4122 will give examples using the same directory and files that you created
4123 in the last chapter. As you may recall, the directory is called
4124 @file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk},
4125 @samp{rock}, and the two archive files you created are
4126 @samp{collection.tar} and @samp{music.tar}.
4128 We will also use the archive files @samp{afiles.tar} and
4129 @samp{bfiles.tar}. The archive @samp{afiles.tar} contains the members @samp{apple},
4130 @samp{angst}, and @samp{aspic}; @samp{bfiles.tar} contains the members
4131 @samp{./birds}, @samp{baboon}, and @samp{./box}.
4133 Unless we state otherwise, all practicing you do and examples you follow
4134 in this chapter will take place in the @file{practice} directory that
4135 you created in the previous chapter; see @ref{prepare for examples}.
4136 (Below in this section, we will remind you of the state of the examples
4137 where the last chapter left them.)
4139 The five operations that we will cover in this chapter are:
4144 Add new entries to an archive that already exists.
4147 Add more recent copies of archive members to the end of an archive, if
4152 Add one or more pre-existing archives to the end of another archive.
4154 Delete items from an archive (does not work on tapes).
4158 Compare archive members to their counterparts in the file system.
4162 @subsection How to Add Files to Existing Archives: @option{--append}
4166 If you want to add files to an existing archive, you don't need to
4167 create a new archive; you can use @option{--append} (@option{-r}).
4168 The archive must already exist in order to use @option{--append}. (A
4169 related operation is the @option{--update} operation; you can use this
4170 to add newer versions of archive members to an existing archive. To learn how to
4171 do this with @option{--update}, @pxref{update}.)
4173 If you use @option{--append} to add a file that has the same name as an
4174 archive member to an archive containing that archive member, then the
4175 old member is not deleted. What does happen, however, is somewhat
4176 complex. @command{tar} @emph{allows} you to have infinite number of files
4177 with the same name. Some operations treat these same-named members no
4178 differently than any other set of archive members: for example, if you
4179 view an archive with @option{--list} (@option{-t}), you will see all
4180 of those members listed, with their data modification times, owners, etc.
4182 Other operations don't deal with these members as perfectly as you might
4183 prefer; if you were to use @option{--extract} to extract the archive,
4184 only the most recently added copy of a member with the same name as four
4185 other members would end up in the working directory. This is because
4186 @option{--extract} extracts an archive in the order the members appeared
4187 in the archive; the most recently archived members will be extracted
4188 last. Additionally, an extracted member will @emph{replace} a file of
4189 the same name which existed in the directory already, and @command{tar}
4190 will not prompt you about this@footnote{Unless you give it
4191 @option{--keep-old-files} option, or the disk copy is newer than the
4192 the one in the archive and you invoke @command{tar} with
4193 @option{--keep-newer-files} option}. Thus, only the most recently archived
4194 member will end up being extracted, as it will replace the one
4195 extracted before it, and so on.
4197 There exists a special option that allows you to get around this
4198 behavior and extract (or list) only a particular copy of the file.
4199 This is @option{--occurrence} option. If you run @command{tar} with
4200 this option, it will extract only the first copy of the file. You
4201 may also give this option an argument specifying the number of
4202 copy to be extracted. Thus, for example if the archive
4203 @file{archive.tar} contained three copies of file @file{myfile}, then
4207 tar --extract --file archive.tar --occurrence=2 myfile
4211 would extract only the second copy. @xref{Option
4212 Summary,---occurrence}, for the description of @option{--occurrence}
4215 @FIXME{ hag -- you might want to incorporate some of the above into the
4216 MMwtSN node; not sure. i didn't know how to make it simpler...
4218 There are a few ways to get around this. (maybe xref Multiple Members
4219 with the Same Name.}
4221 @cindex Members, replacing with other members
4222 @cindex Replacing members with other members
4223 If you want to replace an archive member, use @option{--delete} to
4224 delete the member you want to remove from the archive, , and then use
4225 @option{--append} to add the member you want to be in the archive. Note
4226 that you can not change the order of the archive; the most recently
4227 added member will still appear last. In this sense, you cannot truly
4228 ``replace'' one member with another. (Replacing one member with another
4229 will not work on certain types of media, such as tapes; see @ref{delete}
4230 and @ref{Media}, for more information.)
4233 * appending files:: Appending Files to an Archive
4237 @node appending files
4238 @subsubsection Appending Files to an Archive
4240 @cindex Adding files to an Archive
4241 @cindex Appending files to an Archive
4242 @cindex Archives, Appending files to
4244 The simplest way to add a file to an already existing archive is the
4245 @option{--append} (@option{-r}) operation, which writes specified
4246 files into the archive whether or not they are already among the
4249 When you use @option{--append}, you @emph{must} specify file name
4250 arguments, as there is no default. If you specify a file that already
4251 exists in the archive, another copy of the file will be added to the
4252 end of the archive. As with other operations, the member names of the
4253 newly added files will be exactly the same as their names given on the
4254 command line. The @option{--verbose} (@option{-v}) option will print
4255 out the names of the files as they are written into the archive.
4257 @option{--append} cannot be performed on some tape drives, unfortunately,
4258 due to deficiencies in the formats those tape drives use. The archive
4259 must be a valid @command{tar} archive, or else the results of using this
4260 operation will be unpredictable. @xref{Media}.
4262 To demonstrate using @option{--append} to add a file to an archive,
4263 create a file called @file{rock} in the @file{practice} directory.
4264 Make sure you are in the @file{practice} directory. Then, run the
4265 following @command{tar} command to add @file{rock} to
4266 @file{collection.tar}:
4269 $ @kbd{tar --append --file=collection.tar rock}
4273 If you now use the @option{--list} (@option{-t}) operation, you will see that
4274 @file{rock} has been added to the archive:
4277 $ @kbd{tar --list --file=collection.tar}
4278 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4279 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4280 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4281 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4285 @subsubsection Multiple Members with the Same Name
4287 You can use @option{--append} (@option{-r}) to add copies of files
4288 which have been updated since the archive was created. (However, we
4289 do not recommend doing this since there is another @command{tar}
4290 option called @option{--update}; @xref{update}, for more information.
4291 We describe this use of @option{--append} here for the sake of
4292 completeness.) When you extract the archive, the older version will
4293 be effectively lost. This works because files are extracted from an
4294 archive in the order in which they were archived. Thus, when the
4295 archive is extracted, a file archived later in time will replace a
4296 file of the same name which was archived earlier, even though the
4297 older version of the file will remain in the archive unless you delete
4298 all versions of the file.
4300 Supposing you change the file @file{blues} and then append the changed
4301 version to @file{collection.tar}. As you saw above, the original
4302 @file{blues} is in the archive @file{collection.tar}. If you change the
4303 file and append the new version of the file to the archive, there will
4304 be two copies in the archive. When you extract the archive, the older
4305 version of the file will be extracted first, and then replaced by the
4306 newer version when it is extracted.
4308 You can append the new, changed copy of the file @file{blues} to the
4309 archive in this way:
4312 $ @kbd{tar --append --verbose --file=collection.tar blues}
4317 Because you specified the @option{--verbose} option, @command{tar} has
4318 printed the name of the file being appended as it was acted on. Now
4319 list the contents of the archive:
4322 $ @kbd{tar --list --verbose --file=collection.tar}
4323 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4324 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4325 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4326 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4327 -rw-r--r-- me user 58 1996-10-24 18:30 blues
4331 The newest version of @file{blues} is now at the end of the archive
4332 (note the different creation dates and file sizes). If you extract
4333 the archive, the older version of the file @file{blues} will be
4334 replaced by the newer version. You can confirm this by extracting
4335 the archive and running @samp{ls} on the directory.
4337 If you wish to extract the first occurrence of the file @file{blues}
4338 from the archive, use @option{--occurrence} option, as shown in
4339 the following example:
4342 $ @kbd{tar --extract -vv --occurrence --file=collection.tar blues}
4343 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4346 @xref{Writing}, for more information on @option{--extract} and
4347 @xref{Option Summary, --occurrence}, for the description of
4348 @option{--occurrence} option.
4351 @subsection Updating an Archive
4353 @cindex Updating an archive
4356 In the previous section, you learned how to use @option{--append} to
4357 add a file to an existing archive. A related operation is
4358 @option{--update} (@option{-u}). The @option{--update} operation
4359 updates a @command{tar} archive by comparing the date of the specified
4360 archive members against the date of the file with the same name. If
4361 the file has been modified more recently than the archive member, then
4362 the newer version of the file is added to the archive (as with
4365 Unfortunately, you cannot use @option{--update} with magnetic tape drives.
4366 The operation will fail.
4368 @FIXME{other examples of media on which --update will fail? need to ask
4369 charles and/or mib/thomas/dave shevett..}
4371 Both @option{--update} and @option{--append} work by adding to the end
4372 of the archive. When you extract a file from the archive, only the
4373 version stored last will wind up in the file system, unless you use
4374 the @option{--backup} option. @xref{multiple}, for a detailed discussion.
4381 @subsubsection How to Update an Archive Using @option{--update}
4383 You must use file name arguments with the @option{--update}
4384 (@option{-u}) operation. If you don't specify any files,
4385 @command{tar} won't act on any files and won't tell you that it didn't
4386 do anything (which may end up confusing you).
4388 @c note: the above parenthetical added because in fact, this
4389 @c behavior just confused the author. :-)
4391 To see the @option{--update} option at work, create a new file,
4392 @file{classical}, in your practice directory, and some extra text to the
4393 file @file{blues}, using any text editor. Then invoke @command{tar} with
4394 the @samp{update} operation and the @option{--verbose} (@option{-v})
4395 option specified, using the names of all the files in the practice
4396 directory as file name arguments:
4399 $ @kbd{tar --update -v -f collection.tar blues folk rock classical}
4406 Because we have specified verbose mode, @command{tar} prints out the names
4407 of the files it is working on, which in this case are the names of the
4408 files that needed to be updated. If you run @samp{tar --list} and look
4409 at the archive, you will see @file{blues} and @file{classical} at its
4410 end. There will be a total of two versions of the member @samp{blues};
4411 the one at the end will be newer and larger, since you added text before
4414 (The reason @command{tar} does not overwrite the older file when updating
4415 it is because writing to the middle of a section of tape is a difficult
4416 process. Tapes are not designed to go backward. @xref{Media}, for more
4417 information about tapes.
4419 @option{--update} (@option{-u}) is not suitable for performing backups for two
4420 reasons: it does not change directory content entries, and it
4421 lengthens the archive every time it is used. The @GNUTAR{}
4422 options intended specifically for backups are more
4423 efficient. If you need to run backups, please consult @ref{Backups}.
4426 @subsection Combining Archives with @option{--concatenate}
4428 @cindex Adding archives to an archive
4429 @cindex Concatenating Archives
4430 @opindex concatenate
4432 @c @cindex @option{-A} described
4433 Sometimes it may be convenient to add a second archive onto the end of
4434 an archive rather than adding individual files to the archive. To add
4435 one or more archives to the end of another archive, you should use the
4436 @option{--concatenate} (@option{--catenate}, @option{-A}) operation.
4438 To use @option{--concatenate}, give the first archive with
4439 @option{--file} option and name the rest of archives to be
4440 concatenated on the command line. The members, and their member
4441 names, will be copied verbatim from those archives to the first one.
4442 @footnote{This can cause multiple members to have the same name, for
4443 information on how this affects reading the archive, @ref{multiple}.}
4444 The new, concatenated archive will be called by the same name as the
4445 one given with the @option{--file} option. As usual, if you omit
4446 @option{--file}, @command{tar} will use the value of the environment
4447 variable @env{TAPE}, or, if this has not been set, the default archive name.
4449 @FIXME{There is no way to specify a new name...}
4451 To demonstrate how @option{--concatenate} works, create two small archives
4452 called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
4453 files from @file{practice}:
4456 $ @kbd{tar -cvf bluesrock.tar blues rock}
4459 $ @kbd{tar -cvf folkjazz.tar folk jazz}
4465 If you like, You can run @samp{tar --list} to make sure the archives
4466 contain what they are supposed to:
4469 $ @kbd{tar -tvf bluesrock.tar}
4470 -rw-r--r-- melissa user 105 1997-01-21 19:42 blues
4471 -rw-r--r-- melissa user 33 1997-01-20 15:34 rock
4472 $ @kbd{tar -tvf jazzfolk.tar}
4473 -rw-r--r-- melissa user 20 1996-09-23 16:44 folk
4474 -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
4477 We can concatenate these two archives with @command{tar}:
4481 $ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
4484 If you now list the contents of the @file{bluesrock.tar}, you will see
4485 that now it also contains the archive members of @file{jazzfolk.tar}:
4488 $ @kbd{tar --list --file=bluesrock.tar}
4495 When you use @option{--concatenate}, the source and target archives must
4496 already exist and must have been created using compatible format
4497 parameters. Notice, that @command{tar} does not check whether the
4498 archives it concatenates have compatible formats, it does not
4499 even check if the files are really tar archives.
4501 Like @option{--append} (@option{-r}), this operation cannot be performed on some
4502 tape drives, due to deficiencies in the formats those tape drives use.
4504 @cindex @code{concatenate} vs @command{cat}
4505 @cindex @command{cat} vs @code{concatenate}
4506 It may seem more intuitive to you to want or try to use @command{cat} to
4507 concatenate two archives instead of using the @option{--concatenate}
4508 operation; after all, @command{cat} is the utility for combining files.
4510 However, @command{tar} archives incorporate an end-of-file marker which
4511 must be removed if the concatenated archives are to be read properly as
4512 one archive. @option{--concatenate} removes the end-of-archive marker
4513 from the target archive before each new archive is appended. If you use
4514 @command{cat} to combine the archives, the result will not be a valid
4515 @command{tar} format archive. If you need to retrieve files from an
4516 archive that was added to using the @command{cat} utility, use the
4517 @option{--ignore-zeros} (@option{-i}) option. @xref{Ignore Zeros}, for further
4518 information on dealing with archives improperly combined using the
4519 @command{cat} shell utility.
4522 @subsection Removing Archive Members Using @option{--delete}
4524 @cindex Deleting files from an archive
4525 @cindex Removing files from an archive
4528 You can remove members from an archive by using the @option{--delete}
4529 option. Specify the name of the archive with @option{--file}
4530 (@option{-f}) and then specify the names of the members to be deleted;
4531 if you list no member names, nothing will be deleted. The
4532 @option{--verbose} option will cause @command{tar} to print the names
4533 of the members as they are deleted. As with @option{--extract}, you
4534 must give the exact member names when using @samp{tar --delete}.
4535 @option{--delete} will remove all versions of the named file from the
4536 archive. The @option{--delete} operation can run very slowly.
4538 Unlike other operations, @option{--delete} has no short form.
4540 @cindex Tapes, using @option{--delete} and
4541 @cindex Deleting from tape archives
4542 This operation will rewrite the archive. You can only use
4543 @option{--delete} on an archive if the archive device allows you to
4544 write to any point on the media, such as a disk; because of this, it
4545 does not work on magnetic tapes. Do not try to delete an archive member
4546 from a magnetic tape; the action will not succeed, and you will be
4547 likely to scramble the archive and damage your tape. There is no safe
4548 way (except by completely re-writing the archive) to delete files from
4549 most kinds of magnetic tape. @xref{Media}.
4551 To delete all versions of the file @file{blues} from the archive
4552 @file{collection.tar} in the @file{practice} directory, make sure you
4553 are in that directory, and then,
4556 $ @kbd{tar --list --file=collection.tar}
4561 $ @kbd{tar --delete --file=collection.tar blues}
4562 $ @kbd{tar --list --file=collection.tar}
4569 @FIXME{Check if the above listing is actually produced after running
4570 all the examples on collection.tar.}
4572 The @option{--delete} option has been reported to work properly when
4573 @command{tar} acts as a filter from @code{stdin} to @code{stdout}.
4576 @subsection Comparing Archive Members with the File System
4577 @cindex Verifying the currency of an archive
4581 The @option{--compare} (@option{-d}), or @option{--diff} operation compares
4582 specified archive members against files with the same names, and then
4583 reports differences in file size, mode, owner, modification date and
4584 contents. You should @emph{only} specify archive member names, not file
4585 names. If you do not name any members, then @command{tar} will compare the
4586 entire archive. If a file is represented in the archive but does not
4587 exist in the file system, @command{tar} reports a difference.
4589 You have to specify the record size of the archive when modifying an
4590 archive with a non-default record size.
4592 @command{tar} ignores files in the file system that do not have
4593 corresponding members in the archive.
4595 The following example compares the archive members @file{rock},
4596 @file{blues} and @file{funk} in the archive @file{bluesrock.tar} with
4597 files of the same name in the file system. (Note that there is no file,
4598 @file{funk}; @command{tar} will report an error message.)
4601 $ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
4604 tar: funk not found in archive
4607 The spirit behind the @option{--compare} (@option{--diff},
4608 @option{-d}) option is to check whether the archive represents the
4609 current state of files on disk, more than validating the integrity of
4610 the archive media. For this later goal, @xref{verify}.
4612 @node create options
4613 @section Options Used by @option{--create}
4615 @xopindex{create, additional options}
4616 The previous chapter described the basics of how to use
4617 @option{--create} (@option{-c}) to create an archive from a set of files.
4618 @xref{create}. This section described advanced options to be used with
4622 * override:: Overriding File Metadata.
4623 * Ignore Failed Read::
4627 @subsection Overriding File Metadata
4629 As described above, a @command{tar} archive keeps, for each member it contains,
4630 its @dfn{metadata}, such as modification time, mode and ownership of
4631 the file. @GNUTAR{} allows to replace these data with other values
4632 when adding files to the archive. The options described in this
4633 section affect creation of archives of any type. For POSIX archives,
4634 see also @ref{PAX keywords}, for additional ways of controlling
4635 metadata, stored in the archive.
4639 @item --mode=@var{permissions}
4641 When adding files to an archive, @command{tar} will use
4642 @var{permissions} for the archive members, rather than the permissions
4643 from the files. @var{permissions} can be specified either as an octal
4644 number or as symbolic permissions, like with
4645 @command{chmod} (@xref{File permissions, Permissions, File
4646 permissions, fileutils, @acronym{GNU} file utilities}. This reference
4647 also has useful information for those not being overly familiar with
4648 the UNIX permission system). Using latter syntax allows for
4649 more flexibility. For example, the value @samp{a+rw} adds read and write
4650 permissions for everybody, while retaining executable bits on directories
4651 or on any other file already marked as executable:
4654 $ @kbd{tar -c -f archive.tar --mode='a+rw' .}
4657 @item --mtime=@var{date}
4660 When adding files to an archive, @command{tar} will use @var{date} as
4661 the modification time of members when creating archives, instead of
4662 their actual modification times. The argument @var{date} can be
4663 either a textual date representation in almost arbitrary format
4664 (@pxref{Date input formats}) or a name of the existing file, starting
4665 with @samp{/} or @samp{.}. In the latter case, the modification time
4666 of that file will be used.
4668 The following example will set the modification date to 00:00:00 UTC,
4672 $ @kbd{tar -c -f archive.tar --mtime='1970-01-01' .}
4676 When used with @option{--verbose} (@pxref{verbose tutorial}) @GNUTAR{}
4677 will try to convert the specified date back to its textual
4678 representation and compare it with the one given with
4679 @option{--mtime} options. If the two dates differ, @command{tar} will
4680 print a warning saying what date it will use. This is to help user
4681 ensure he is using the right date.
4686 $ @kbd{tar -c -f archive.tar -v --mtime=yesterday .}
4687 tar: Option --mtime: Treating date `yesterday' as 2006-06-20
4692 @item --owner=@var{user}
4695 Specifies that @command{tar} should use @var{user} as the owner of members
4696 when creating archives, instead of the user associated with the source
4697 file. The argument @var{user} can be either an existing user symbolic
4698 name, or a decimal numeric user @acronym{ID}.
4700 There is no value indicating a missing number, and @samp{0} usually means
4701 @code{root}. Some people like to force @samp{0} as the value to offer in
4702 their distributions for the owner of files, because the @code{root} user is
4703 anonymous anyway, so that might as well be the owner of anonymous
4704 archives. For example:
4708 $ @kbd{tar -c -f archive.tar --owner=0 .}
4710 $ @kbd{tar -c -f archive.tar --owner=root .}
4714 @item --group=@var{group}
4717 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
4718 rather than the group from the source file. The argument @var{group}
4719 can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
4722 @node Ignore Failed Read
4723 @subsection Ignore Fail Read
4726 @item --ignore-failed-read
4727 @opindex ignore-failed-read
4728 Do not exit with nonzero on unreadable files or directories.
4731 @node extract options
4732 @section Options Used by @option{--extract}
4735 @xopindex{extract, additional options}
4736 The previous chapter showed how to use @option{--extract} to extract
4737 an archive into the file system. Various options cause @command{tar} to
4738 extract more information than just file contents, such as the owner,
4739 the permissions, the modification date, and so forth. This section
4740 presents options to be used with @option{--extract} when certain special
4741 considerations arise. You may review the information presented in
4742 @ref{extract} for more basic information about the
4743 @option{--extract} operation.
4746 * Reading:: Options to Help Read Archives
4747 * Writing:: Changing How @command{tar} Writes Files
4748 * Scarce:: Coping with Scarce Resources
4752 @subsection Options to Help Read Archives
4753 @cindex Options when reading archives
4756 @cindex Reading incomplete records
4757 @cindex Records, incomplete
4758 @opindex read-full-records
4759 Normally, @command{tar} will request data in full record increments from
4760 an archive storage device. If the device cannot return a full record,
4761 @command{tar} will report an error. However, some devices do not always
4762 return full records, or do not require the last record of an archive to
4763 be padded out to the next record boundary. To keep reading until you
4764 obtain a full record, or to accept an incomplete record if it contains
4765 an end-of-archive marker, specify the @option{--read-full-records} (@option{-B}) option
4766 in conjunction with the @option{--extract} or @option{--list} operations.
4769 The @option{--read-full-records} (@option{-B}) option is turned on by default when
4770 @command{tar} reads an archive from standard input, or from a remote
4771 machine. This is because on @acronym{BSD} Unix systems, attempting to read a
4772 pipe returns however much happens to be in the pipe, even if it is
4773 less than was requested. If this option were not enabled, @command{tar}
4774 would fail as soon as it read an incomplete record from the pipe.
4776 If you're not sure of the blocking factor of an archive, you can
4777 read the archive by specifying @option{--read-full-records} (@option{-B}) and
4778 @option{--blocking-factor=@var{512-size}} (@option{-b
4779 @var{512-size}}), using a blocking factor larger than what the archive
4780 uses. This lets you avoid having to determine the blocking factor
4781 of an archive. @xref{Blocking Factor}.
4784 * read full records::
4788 @node read full records
4789 @unnumberedsubsubsec Reading Full Records
4791 @FIXME{need sentence or so of intro here}
4794 @opindex read-full-records
4795 @item --read-full-records
4797 Use in conjunction with @option{--extract} (@option{--get},
4798 @option{-x}) to read an archive which contains incomplete records, or
4799 one which has a blocking factor less than the one specified.
4803 @unnumberedsubsubsec Ignoring Blocks of Zeros
4805 @cindex End-of-archive blocks, ignoring
4806 @cindex Ignoring end-of-archive blocks
4807 @opindex ignore-zeros
4808 Normally, @command{tar} stops reading when it encounters a block of zeros
4809 between file entries (which usually indicates the end of the archive).
4810 @option{--ignore-zeros} (@option{-i}) allows @command{tar} to
4811 completely read an archive which contains a block of zeros before the
4812 end (i.e., a damaged archive, or one that was created by concatenating
4813 several archives together).
4815 The @option{--ignore-zeros} (@option{-i}) option is turned off by default because many
4816 versions of @command{tar} write garbage after the end-of-archive entry,
4817 since that part of the media is never supposed to be read. @GNUTAR{}
4818 does not write after the end of an archive, but seeks to
4819 maintain compatibility among archiving utilities.
4822 @item --ignore-zeros
4824 To ignore blocks of zeros (i.e., end-of-archive entries) which may be
4825 encountered while reading an archive. Use in conjunction with
4826 @option{--extract} or @option{--list}.
4830 @subsection Changing How @command{tar} Writes Files
4833 @FIXME{Introductory paragraph}
4836 * Dealing with Old Files::
4837 * Overwrite Old Files::
4839 * Keep Newer Files::
4841 * Recursive Unlink::
4842 * Data Modification Times::
4843 * Setting Access Permissions::
4844 * Directory Modification Times and Permissions::
4845 * Writing to Standard Output::
4846 * Writing to an External Program::
4850 @node Dealing with Old Files
4851 @unnumberedsubsubsec Options Controlling the Overwriting of Existing Files
4853 @xopindex{overwrite-dir, introduced}
4854 When extracting files, if @command{tar} discovers that the extracted
4855 file already exists, it normally replaces the file by removing it before
4856 extracting it, to prevent confusion in the presence of hard or symbolic
4857 links. (If the existing file is a symbolic link, it is removed, not
4858 followed.) However, if a directory cannot be removed because it is
4859 nonempty, @command{tar} normally overwrites its metadata (ownership,
4860 permission, etc.). The @option{--overwrite-dir} option enables this
4861 default behavior. To be more cautious and preserve the metadata of
4862 such a directory, use the @option{--no-overwrite-dir} option.
4864 @cindex Overwriting old files, prevention
4865 @xopindex{keep-old-files, introduced}
4866 To be even more cautious and prevent existing files from being replaced, use
4867 the @option{--keep-old-files} (@option{-k}) option. It causes @command{tar} to refuse
4868 to replace or update a file that already exists, i.e., a file with the
4869 same name as an archive member prevents extraction of that archive
4870 member. Instead, it reports an error.
4872 @xopindex{overwrite, introduced}
4873 To be more aggressive about altering existing files, use the
4874 @option{--overwrite} option. It causes @command{tar} to overwrite
4875 existing files and to follow existing symbolic links when extracting.
4877 @cindex Protecting old files
4878 Some people argue that @GNUTAR{} should not hesitate
4879 to overwrite files with other files when extracting. When extracting
4880 a @command{tar} archive, they expect to see a faithful copy of the
4881 state of the file system when the archive was created. It is debatable
4882 that this would always be a proper behavior. For example, suppose one
4883 has an archive in which @file{usr/local} is a link to
4884 @file{usr/local2}. Since then, maybe the site removed the link and
4885 renamed the whole hierarchy from @file{/usr/local2} to
4886 @file{/usr/local}. Such things happen all the time. I guess it would
4887 not be welcome at all that @GNUTAR{} removes the
4888 whole hierarchy just to make room for the link to be reinstated
4889 (unless it @emph{also} simultaneously restores the full
4890 @file{/usr/local2}, of course!) @GNUTAR{} is indeed
4891 able to remove a whole hierarchy to reestablish a symbolic link, for
4892 example, but @emph{only if} @option{--recursive-unlink} is specified
4893 to allow this behavior. In any case, single files are silently
4896 @xopindex{unlink-first, introduced}
4897 Finally, the @option{--unlink-first} (@option{-U}) option can improve performance in
4898 some cases by causing @command{tar} to remove files unconditionally
4899 before extracting them.
4901 @node Overwrite Old Files
4902 @unnumberedsubsubsec Overwrite Old Files
4907 Overwrite existing files and directory metadata when extracting files
4910 This causes @command{tar} to write extracted files into the file system without
4911 regard to the files already on the system; i.e., files with the same
4912 names as archive members are overwritten when the archive is extracted.
4913 It also causes @command{tar} to extract the ownership, permissions,
4914 and time stamps onto any preexisting files or directories.
4915 If the name of a corresponding file name is a symbolic link, the file
4916 pointed to by the symbolic link will be overwritten instead of the
4917 symbolic link itself (if this is possible). Moreover, special devices,
4918 empty directories and even symbolic links are automatically removed if
4919 they are in the way of extraction.
4921 Be careful when using the @option{--overwrite} option, particularly when
4922 combined with the @option{--absolute-names} (@option{-P}) option, as this combination
4923 can change the contents, ownership or permissions of any file on your
4924 system. Also, many systems do not take kindly to overwriting files that
4925 are currently being executed.
4927 @opindex overwrite-dir
4928 @item --overwrite-dir
4929 Overwrite the metadata of directories when extracting files from an
4930 archive, but remove other files before extracting.
4933 @node Keep Old Files
4934 @unnumberedsubsubsec Keep Old Files
4937 @opindex keep-old-files
4938 @item --keep-old-files
4940 Do not replace existing files from archive. The
4941 @option{--keep-old-files} (@option{-k}) option prevents @command{tar}
4942 from replacing existing files with files with the same name from the
4943 archive. The @option{--keep-old-files} option is meaningless with
4944 @option{--list} (@option{-t}). Prevents @command{tar} from replacing
4945 files in the file system during extraction.
4948 @node Keep Newer Files
4949 @unnumberedsubsubsec Keep Newer Files
4952 @opindex keep-newer-files
4953 @item --keep-newer-files
4954 Do not replace existing files that are newer than their archive
4955 copies. This option is meaningless with @option{--list} (@option{-t}).
4959 @unnumberedsubsubsec Unlink First
4962 @opindex unlink-first
4963 @item --unlink-first
4965 Remove files before extracting over them.
4966 This can make @command{tar} run a bit faster if you know in advance
4967 that the extracted files all need to be removed. Normally this option
4968 slows @command{tar} down slightly, so it is disabled by default.
4971 @node Recursive Unlink
4972 @unnumberedsubsubsec Recursive Unlink
4975 @opindex recursive-unlink
4976 @item --recursive-unlink
4977 When this option is specified, try removing files and directory hierarchies
4978 before extracting over them. @emph{This is a dangerous option!}
4981 If you specify the @option{--recursive-unlink} option,
4982 @command{tar} removes @emph{anything} that keeps you from extracting a file
4983 as far as current permissions will allow it. This could include removal
4984 of the contents of a full directory hierarchy.
4986 @node Data Modification Times
4987 @unnumberedsubsubsec Setting Data Modification Times
4989 @cindex Data modification times of extracted files
4990 @cindex Modification times of extracted files
4991 Normally, @command{tar} sets the data modification times of extracted
4992 files to the corresponding times recorded for the files in the archive, but
4993 limits the permissions of extracted files by the current @code{umask}
4996 To set the data modification times of extracted files to the time when
4997 the files were extracted, use the @option{--touch} (@option{-m}) option in
4998 conjunction with @option{--extract} (@option{--get}, @option{-x}).
5004 Sets the data modification time of extracted archive members to the time
5005 they were extracted, not the time recorded for them in the archive.
5006 Use in conjunction with @option{--extract} (@option{--get}, @option{-x}).
5009 @node Setting Access Permissions
5010 @unnumberedsubsubsec Setting Access Permissions
5012 @cindex Permissions of extracted files
5013 @cindex Modes of extracted files
5014 To set the modes (access permissions) of extracted files to those
5015 recorded for those files in the archive, use @option{--same-permissions}
5016 in conjunction with the @option{--extract} (@option{--get},
5017 @option{-x}) operation.
5020 @opindex preserve-permissions
5021 @opindex same-permissions
5022 @item --preserve-permissions
5023 @itemx --same-permissions
5024 @c @itemx --ignore-umask
5026 Set modes of extracted archive members to those recorded in the
5027 archive, instead of current umask settings. Use in conjunction with
5028 @option{--extract} (@option{--get}, @option{-x}).
5031 @node Directory Modification Times and Permissions
5032 @unnumberedsubsubsec Directory Modification Times and Permissions
5034 After successfully extracting a file member, @GNUTAR{} normally
5035 restores its permissions and modification times, as described in the
5036 previous sections. This cannot be done for directories, because
5037 after extracting a directory @command{tar} will almost certainly
5038 extract files into that directory and this will cause the directory
5039 modification time to be updated. Moreover, restoring that directory
5040 permissions may not permit file creation within it. Thus, restoring
5041 directory permissions and modification times must be delayed at least
5042 until all files have been extracted into that directory. @GNUTAR{}
5043 restores directories using the following approach.
5045 The extracted directories are created with the mode specified in the
5046 archive, as modified by the umask of the user, which gives sufficient
5047 permissions to allow file creation. The meta-information about the
5048 directory is recorded in the temporary list of directories. When
5049 preparing to extract next archive member, @GNUTAR{} checks if the
5050 directory prefix of this file contains the remembered directory. If
5051 it does not, the program assumes that all files have been extracted
5052 into that directory, restores its modification time and permissions
5053 and removes its entry from the internal list. This approach allows
5054 to correctly restore directory meta-information in the majority of
5055 cases, while keeping memory requirements sufficiently small. It is
5056 based on the fact, that most @command{tar} archives use the predefined
5057 order of members: first the directory, then all the files and
5058 subdirectories in that directory.
5060 However, this is not always true. The most important exception are
5061 incremental archives (@pxref{Incremental Dumps}). The member order in
5062 an incremental archive is reversed: first all directory members are
5063 stored, followed by other (non-directory) members. So, when extracting
5064 from incremental archives, @GNUTAR{} alters the above procedure. It
5065 remembers all restored directories, and restores their meta-data
5066 only after the entire archive has been processed. Notice, that you do
5067 not need to specify any special options for that, as @GNUTAR{}
5068 automatically detects archives in incremental format.
5070 There may be cases, when such processing is required for normal archives
5071 too. Consider the following example:
5075 $ @kbd{tar --no-recursion -cvf archive \
5076 foo foo/file1 bar bar/file foo/file2}
5085 During the normal operation, after encountering @file{bar}
5086 @GNUTAR{} will assume that all files from the directory @file{foo}
5087 were already extracted and will therefore restore its timestamp and
5088 permission bits. However, after extracting @file{foo/file2} the
5089 directory timestamp will be offset again.
5091 To correctly restore directory meta-information in such cases, use
5092 @option{delay-directory-restore} command line option:
5095 @opindex delay-directory-restore
5096 @item --delay-directory-restore
5097 Delays restoring of the modification times and permissions of extracted
5098 directories until the end of extraction. This way, correct
5099 meta-information is restored even if the archive has unusual member
5102 @opindex no-delay-directory-restore
5103 @item --no-delay-directory-restore
5104 Cancel the effect of the previous @option{--delay-directory-restore}.
5105 Use this option if you have used @option{--delay-directory-restore} in
5106 @env{TAR_OPTIONS} variable (@pxref{TAR_OPTIONS}) and wish to
5107 temporarily disable it.
5110 @node Writing to Standard Output
5111 @unnumberedsubsubsec Writing to Standard Output
5113 @cindex Writing extracted files to standard output
5114 @cindex Standard output, writing extracted files to
5115 To write the extracted files to the standard output, instead of
5116 creating the files on the file system, use @option{--to-stdout} (@option{-O}) in
5117 conjunction with @option{--extract} (@option{--get}, @option{-x}). This option is useful if you are
5118 extracting files to send them through a pipe, and do not need to
5119 preserve them in the file system. If you extract multiple members,
5120 they appear on standard output concatenated, in the order they are
5121 found in the archive.
5127 Writes files to the standard output. Use only in conjunction with
5128 @option{--extract} (@option{--get}, @option{-x}). When this option is
5129 used, instead of creating the files specified, @command{tar} writes
5130 the contents of the files extracted to its standard output. This may
5131 be useful if you are only extracting the files in order to send them
5132 through a pipe. This option is meaningless with @option{--list}
5136 This can be useful, for example, if you have a tar archive containing
5137 a big file and don't want to store the file on disk before processing
5138 it. You can use a command like this:
5141 tar -xOzf foo.tgz bigfile | process
5144 or even like this if you want to process the concatenation of the files:
5147 tar -xOzf foo.tgz bigfile1 bigfile2 | process
5150 However, @option{--to-command} may be more convenient for use with
5151 multiple files. See the next section.
5153 @node Writing to an External Program
5154 @unnumberedsubsubsec Writing to an External Program
5156 You can instruct @command{tar} to send the contents of each extracted
5157 file to the standard input of an external program:
5161 @item --to-command=@var{command}
5162 Extract files and pipe their contents to the standard input of
5163 @var{command}. When this option is used, instead of creating the
5164 files specified, @command{tar} invokes @var{command} and pipes the
5165 contents of the files to its standard output. @var{Command} may
5166 contain command line arguments. The program is executed via
5167 @code{sh -c}. Notice, that @var{command} is executed once for each regular file
5168 extracted. Non-regular files (directories, etc.) are ignored when this
5172 The command can obtain the information about the file it processes
5173 from the following environment variables:
5176 @vrindex TAR_FILETYPE, to-command environment
5178 Type of the file. It is a single letter with the following meaning:
5180 @multitable @columnfractions 0.10 0.90
5181 @item f @tab Regular file
5182 @item d @tab Directory
5183 @item l @tab Symbolic link
5184 @item h @tab Hard link
5185 @item b @tab Block device
5186 @item c @tab Character device
5189 Currently only regular files are supported.
5191 @vrindex TAR_MODE, to-command environment
5193 File mode, an octal number.
5195 @vrindex TAR_FILENAME, to-command environment
5197 The name of the file.
5199 @vrindex TAR_REALNAME, to-command environment
5201 Name of the file as stored in the archive.
5203 @vrindex TAR_UNAME, to-command environment
5205 Name of the file owner.
5207 @vrindex TAR_GNAME, to-command environment
5209 Name of the file owner group.
5211 @vrindex TAR_ATIME, to-command environment
5213 Time of last access. It is a decimal number, representing seconds
5214 since the epoch. If the archive provides times with nanosecond
5215 precision, the nanoseconds are appended to the timestamp after a
5218 @vrindex TAR_MTIME, to-command environment
5220 Time of last modification.
5222 @vrindex TAR_CTIME, to-command environment
5224 Time of last status change.
5226 @vrindex TAR_SIZE, to-command environment
5230 @vrindex TAR_UID, to-command environment
5232 UID of the file owner.
5234 @vrindex TAR_GID, to-command environment
5236 GID of the file owner.
5239 In addition to these variables, @env{TAR_VERSION} contains the
5240 @GNUTAR{} version number.
5242 If @var{command} exits with a non-0 status, @command{tar} will print
5243 an error message similar to the following:
5246 tar: 2345: Child returned status 1
5249 Here, @samp{2345} is the PID of the finished process.
5251 If this behavior is not wanted, use @option{--ignore-command-error}:
5254 @opindex ignore-command-error
5255 @item --ignore-command-error
5256 Ignore exit codes of subprocesses. Notice that if the program
5257 exits on signal or otherwise terminates abnormally, the error message
5258 will be printed even if this option is used.
5260 @opindex no-ignore-command-error
5261 @item --no-ignore-command-error
5262 Cancel the effect of any previous @option{--ignore-command-error}
5263 option. This option is useful if you have set
5264 @option{--ignore-command-error} in @env{TAR_OPTIONS}
5265 (@pxref{TAR_OPTIONS}) and wish to temporarily cancel it.
5269 @unnumberedsubsubsec Removing Files
5271 @FIXME{The section is too terse. Something more to add? An example,
5275 @opindex remove-files
5276 @item --remove-files
5277 Remove files after adding them to the archive.
5281 @subsection Coping with Scarce Resources
5284 @cindex Small memory
5285 @cindex Running out of space
5293 @unnumberedsubsubsec Starting File
5296 @opindex starting-file
5297 @item --starting-file=@var{name}
5298 @itemx -K @var{name}
5299 Starts an operation in the middle of an archive. Use in conjunction
5300 with @option{--extract} (@option{--get}, @option{-x}) or @option{--list} (@option{-t}).
5303 @cindex Middle of the archive, starting in the
5304 If a previous attempt to extract files failed due to lack of disk
5305 space, you can use @option{--starting-file=@var{name}} (@option{-K
5306 @var{name}}) to start extracting only after member @var{name} of the
5307 archive. This assumes, of course, that there is now free space, or
5308 that you are now extracting into a different file system. (You could
5309 also choose to suspend @command{tar}, remove unnecessary files from
5310 the file system, and then restart the same @command{tar} operation.
5311 In this case, @option{--starting-file} is not necessary.
5312 @xref{Incremental Dumps}, @xref{interactive}, and @ref{exclude}.)
5315 @unnumberedsubsubsec Same Order
5318 @cindex Large lists of file names on small machines
5320 @opindex preserve-order
5322 @itemx --preserve-order
5324 To process large lists of file names on machines with small amounts of
5325 memory. Use in conjunction with @option{--compare} (@option{--diff},
5326 @option{-d}), @option{--list} (@option{-t}) or @option{--extract}
5327 (@option{--get}, @option{-x}).
5330 The @option{--same-order} (@option{--preserve-order}, @option{-s}) option tells @command{tar} that the list of file
5331 names to be listed or extracted is sorted in the same order as the
5332 files in the archive. This allows a large list of names to be used,
5333 even on a small machine that would not otherwise be able to hold all
5334 the names in memory at the same time. Such a sorted list can easily be
5335 created by running @samp{tar -t} on the archive and editing its output.
5337 This option is probably never needed on modern computer systems.
5340 @section Backup options
5342 @cindex backup options
5344 @GNUTAR{} offers options for making backups of files
5345 before writing new versions. These options control the details of
5346 these backups. They may apply to the archive itself before it is
5347 created or rewritten, as well as individual extracted members. Other
5348 @acronym{GNU} programs (@command{cp}, @command{install}, @command{ln},
5349 and @command{mv}, for example) offer similar options.
5351 Backup options may prove unexpectedly useful when extracting archives
5352 containing many members having identical name, or when extracting archives
5353 on systems having file name limitations, making different members appear
5354 as having similar names through the side-effect of name truncation.
5355 @FIXME{This is true only if we have a good scheme for truncated backup names,
5356 which I'm not sure at all: I suspect work is needed in this area.}
5357 When any existing file is backed up before being overwritten by extraction,
5358 then clashing files are automatically be renamed to be unique, and the
5359 true name is kept for only the last file of a series of clashing files.
5360 By using verbose mode, users may track exactly what happens.
5362 At the detail level, some decisions are still experimental, and may
5363 change in the future, we are waiting comments from our users. So, please
5364 do not learn to depend blindly on the details of the backup features.
5365 For example, currently, directories themselves are never renamed through
5366 using these options, so, extracting a file over a directory still has
5367 good chances to fail. Also, backup options apply to created archives,
5368 not only to extracted members. For created archives, backups will not
5369 be attempted when the archive is a block or character device, or when it
5370 refers to a remote file.
5372 For the sake of simplicity and efficiency, backups are made by renaming old
5373 files prior to creation or extraction, and not by copying. The original
5374 name is restored if the file creation fails. If a failure occurs after a
5375 partial extraction of a file, both the backup and the partially extracted
5379 @item --backup[=@var{method}]
5381 @vindex VERSION_CONTROL
5383 Back up files that are about to be overwritten or removed.
5384 Without this option, the original versions are destroyed.
5386 Use @var{method} to determine the type of backups made.
5387 If @var{method} is not specified, use the value of the @env{VERSION_CONTROL}
5388 environment variable. And if @env{VERSION_CONTROL} is not set,
5389 use the @samp{existing} method.
5391 @vindex version-control @r{Emacs variable}
5392 This option corresponds to the Emacs variable @samp{version-control};
5393 the same values for @var{method} are accepted as in Emacs. This option
5394 also allows more descriptive names. The valid @var{method}s are:
5399 @cindex numbered @r{backup method}
5400 Always make numbered backups.
5404 @cindex existing @r{backup method}
5405 Make numbered backups of files that already have them, simple backups
5410 @cindex simple @r{backup method}
5411 Always make simple backups.
5415 @item --suffix=@var{suffix}
5417 @cindex backup suffix
5418 @vindex SIMPLE_BACKUP_SUFFIX
5419 Append @var{suffix} to each backup file made with @option{--backup}. If this
5420 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
5421 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
5422 set, the default is @samp{~}, just as in Emacs.
5427 @section Notable @command{tar} Usages
5430 @FIXME{Using Unix file linking capability to recreate directory
5431 structures---linking files into one subdirectory and then
5432 @command{tar}ring that directory.}
5434 @FIXME{Nice hairy example using absolute-names, newer, etc.}
5437 You can easily use archive files to transport a group of files from
5438 one system to another: put all relevant files into an archive on one
5439 computer system, transfer the archive to another system, and extract
5440 the contents there. The basic transfer medium might be magnetic tape,
5441 Internet FTP, or even electronic mail (though you must encode the
5442 archive with @command{uuencode} in order to transport it properly by
5443 mail). Both machines do not have to use the same operating system, as
5444 long as they both support the @command{tar} program.
5446 For example, here is how you might copy a directory's contents from
5447 one disk to another, while preserving the dates, modes, owners and
5448 link-structure of all the files therein. In this case, the transfer
5449 medium is a @dfn{pipe}, which is one a Unix redirection mechanism:
5452 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
5456 You can avoid subshells by using @option{-C} option:
5459 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xf -}
5463 The command also works using short option forms:
5466 $ @kbd{(cd sourcedir; tar --create --file=- . ) \
5467 | (cd targetdir; tar --extract --file=-)}
5469 $ @kbd{tar --directory sourcedir --create --file=- . ) \
5470 | tar --directory targetdir --extract --file=-}
5474 This is one of the easiest methods to transfer a @command{tar} archive.
5477 @section Looking Ahead: The Rest of this Manual
5479 You have now seen how to use all eight of the operations available to
5480 @command{tar}, and a number of the possible options. The next chapter
5481 explains how to choose and change file and archive names, how to use
5482 files to store names of other files which you can then call as
5483 arguments to @command{tar} (this can help you save time if you expect to
5484 archive the same list of files a number of times), and so forth.
5485 @FIXME{in case it's not obvious, i'm making this up in some sense
5486 based on my limited memory of what the next chapter *really* does. i
5487 just wanted to flesh out this final section a little bit so i'd
5488 remember to stick it in here. :-)}
5490 If there are too many files to conveniently list on the command line,
5491 you can list the names in a file, and @command{tar} will read that file.
5494 There are various ways of causing @command{tar} to skip over some files,
5495 and not archive them. @xref{Choosing}.
5498 @chapter Performing Backups and Restoring Files
5501 @GNUTAR{} is distributed along with the scripts
5502 which the Free Software Foundation uses for performing backups. There
5503 is no corresponding scripts available yet for doing restoration of
5504 files. Even if there is a good chance those scripts may be satisfying
5505 to you, they are not the only scripts or methods available for doing
5506 backups and restore. You may well create your own, or use more
5507 sophisticated packages dedicated to that purpose.
5509 Some users are enthusiastic about @code{Amanda} (The Advanced Maryland
5510 Automatic Network Disk Archiver), a backup system developed by James
5511 da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
5512 This is free software, and it is available at these places:
5515 http://www.cs.umd.edu/projects/amanda/amanda.html
5516 ftp://ftp.cs.umd.edu/pub/amanda
5521 Here is a possible plan for a future documentation about the backuping
5522 scripts which are provided within the @GNUTAR{}
5528 @item what are dumps
5529 @item different levels of dumps
5531 @item full dump = dump everything
5532 @item level 1, level 2 dumps etc
5533 A level @var{n} dump dumps everything changed since the last level
5536 @item how to use scripts for dumps (ie, the concept)
5538 @item scripts to run after editing backup specs (details)
5540 @item Backup Specs, what is it.
5542 @item how to customize
5543 @item actual text of script [/sp/dump/backup-specs]
5547 @item rsh doesn't work
5548 @item rtape isn't installed
5551 @item the @option{--incremental} option of tar
5554 @item write protection
5555 @item types of media, different sizes and types, useful for different things
5556 @item files and tape marks
5557 one tape mark between files, two at end.
5558 @item positioning the tape
5559 MT writes two at end of write,
5560 backspaces over one when writing again.
5566 This chapter documents both the provided shell scripts and @command{tar}
5567 options which are more specific to usage as a backup tool.
5569 To @dfn{back up} a file system means to create archives that contain
5570 all the files in that file system. Those archives can then be used to
5571 restore any or all of those files (for instance if a disk crashes or a
5572 file is accidentally deleted). File system @dfn{backups} are also
5576 * Full Dumps:: Using @command{tar} to Perform Full Dumps
5577 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
5578 * Backup Levels:: Levels of Backups
5579 * Backup Parameters:: Setting Parameters for Backups and Restoration
5580 * Scripted Backups:: Using the Backup Scripts
5581 * Scripted Restoration:: Using the Restore Script
5585 @section Using @command{tar} to Perform Full Dumps
5591 @cindex corrupted archives
5592 Full dumps should only be made when no other people or programs
5593 are modifying files in the file system. If files are modified while
5594 @command{tar} is making the backup, they may not be stored properly in
5595 the archive, in which case you won't be able to restore them if you
5596 have to. (Files not being modified are written with no trouble, and do
5597 not corrupt the entire archive.)
5599 You will want to use the @option{--label=@var{archive-label}}
5600 (@option{-V @var{archive-label}}) option to give the archive a
5601 volume label, so you can tell what this archive is even if the label
5602 falls off the tape, or anything like that.
5604 Unless the file system you are dumping is guaranteed to fit on
5605 one volume, you will need to use the @option{--multi-volume} (@option{-M}) option.
5606 Make sure you have enough tapes on hand to complete the backup.
5608 If you want to dump each file system separately you will need to use
5609 the @option{--one-file-system} option to prevent
5610 @command{tar} from crossing file system boundaries when storing
5613 The @option{--incremental} (@option{-G}) (@pxref{Incremental Dumps})
5614 option is not needed, since this is a complete copy of everything in
5615 the file system, and a full restore from this backup would only be
5616 done onto a completely
5619 Unless you are in a hurry, and trust the @command{tar} program (and your
5620 tapes), it is a good idea to use the @option{--verify} (@option{-W})
5621 option, to make sure your files really made it onto the dump properly.
5622 This will also detect cases where the file was modified while (or just
5623 after) it was being archived. Not all media (notably cartridge tapes)
5624 are capable of being verified, unfortunately.
5626 @node Incremental Dumps
5627 @section Using @command{tar} to Perform Incremental Dumps
5629 @dfn{Incremental backup} is a special form of @GNUTAR{} archive that
5630 stores additional metadata so that exact state of the file system
5631 can be restored when extracting the archive.
5633 @GNUTAR{} currently offers two options for handling incremental
5634 backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
5635 @var{snapshot-file}}) and @option{--incremental} (@option{-G}).
5637 @opindex listed-incremental
5638 The option @option{--listed-incremental} instructs tar to operate on
5639 an incremental archive with additional metadata stored in a standalone
5640 file, called a @dfn{snapshot file}. The purpose of this file is to help
5641 determine which files have been changed, added or deleted since the
5642 last backup, so that the next incremental backup will contain only
5643 modified files. The name of the snapshot file is given as an argument
5647 @item --listed-incremental=@var{file}
5648 @itemx -g @var{file}
5649 Handle incremental backups with snapshot data in @var{file}.
5652 To create an incremental backup, you would use
5653 @option{--listed-incremental} together with @option{--create}
5654 (@pxref{create}). For example:
5657 $ @kbd{tar --create \
5658 --file=archive.1.tar \
5659 --listed-incremental=/var/log/usr.snar \
5663 This will create in @file{archive.1.tar} an incremental backup of
5664 the @file{/usr} file system, storing additional metadata in the file
5665 @file{/var/log/usr.snar}. If this file does not exist, it will be
5666 created. The created archive will then be a @dfn{level 0 backup};
5667 please see the next section for more on backup levels.
5669 Otherwise, if the file @file{/var/log/usr.snar} exists, it
5670 determines which files are modified. In this case only these files will be
5671 stored in the archive. Suppose, for example, that after running the
5672 above command, you delete file @file{/usr/doc/old} and create
5673 directory @file{/usr/local/db} with the following contents:
5676 $ @kbd{ls /usr/local/db}
5681 Some time later you create another incremental backup. You will
5685 $ @kbd{tar --create \
5686 --file=archive.2.tar \
5687 --listed-incremental=/var/log/usr.snar \
5689 tar: usr/local/db: Directory is new
5696 The created archive @file{archive.2.tar} will contain only these
5697 three members. This archive is called a @dfn{level 1 backup}. Notice
5698 that @file{/var/log/usr.snar} will be updated with the new data, so if
5699 you plan to create more @samp{level 1} backups, it is necessary to
5700 create a working copy of the snapshot file before running
5701 @command{tar}. The above example will then be modified as follows:
5704 $ @kbd{cp /var/log/usr.snar /var/log/usr.snar-1}
5705 $ @kbd{tar --create \
5706 --file=archive.2.tar \
5707 --listed-incremental=/var/log/usr.snar-1 \
5711 Incremental dumps depend crucially on time stamps, so the results are
5712 unreliable if you modify a file's time stamps during dumping (e.g.,
5713 with the @option{--atime-preserve=replace} option), or if you set the clock
5716 @anchor{device numbers}
5717 @cindex Device numbers, using in incremental backups
5718 Metadata stored in snapshot files include device numbers, which,
5719 obviously are supposed to be a non-volatile values. However, it turns
5720 out that @acronym{NFS} devices have undependable values when an automounter
5721 gets in the picture. This can lead to a great deal of spurious
5722 redumping in incremental dumps, so it is somewhat useless to compare
5723 two @acronym{NFS} devices numbers over time. The solution implemented
5724 currently is to considers all @acronym{NFS} devices as being equal
5725 when it comes to comparing directories; this is fairly gross, but
5726 there does not seem to be a better way to go.
5728 Apart from using @acronym{NFS}, there are a number of cases where
5729 relying on device numbers can cause spurious redumping of unmodified
5730 files. For example, this occurs when archiving @acronym{LVM} snapshot
5731 volumes. To avoid this, use @option{--no-check-device} option:
5734 @xopindex{no-check-device, described}
5735 @item --no-check-device
5736 Do not rely on device numbers when preparing a list of changed files
5737 for an incremental dump.
5739 @xopindex{check-device, described}
5740 @item --check-device
5741 Use device numbers when preparing a list of changed files
5742 for an incremental dump. This is the default behavior. The purpose
5743 of this option is to undo the effect of the @option{--no-check-device}
5744 if it was given in @env{TAR_OPTIONS} environment variable
5745 (@pxref{TAR_OPTIONS}).
5748 There is also another way to cope with changing device numbers. It is
5749 described in detail in @ref{Fixing Snapshot Files}.
5751 Note that incremental archives use @command{tar} extensions and may
5752 not be readable by non-@acronym{GNU} versions of the @command{tar} program.
5754 @xopindex{listed-incremental, using with @option{--extract}}
5755 @xopindex{extract, using with @option{--listed-incremental}}
5756 To extract from the incremental dumps, use
5757 @option{--listed-incremental} together with @option{--extract}
5758 option (@pxref{extracting files}). In this case, @command{tar} does
5759 not need to access snapshot file, since all the data necessary for
5760 extraction are stored in the archive itself. So, when extracting, you
5761 can give whatever argument to @option{--listed-incremental}, the usual
5762 practice is to use @option{--listed-incremental=/dev/null}.
5763 Alternatively, you can use @option{--incremental}, which needs no
5764 arguments. In general, @option{--incremental} (@option{-G}) can be
5765 used as a shortcut for @option{--listed-incremental} when listing or
5766 extracting incremental backups (for more information, regarding this
5767 option, @pxref{incremental-op}).
5769 When extracting from the incremental backup @GNUTAR{} attempts to
5770 restore the exact state the file system had when the archive was
5771 created. In particular, it will @emph{delete} those files in the file
5772 system that did not exist in their directories when the archive was
5773 created. If you have created several levels of incremental files,
5774 then in order to restore the exact contents the file system had when
5775 the last level was created, you will need to restore from all backups
5776 in turn. Continuing our example, to restore the state of @file{/usr}
5777 file system, one would do@footnote{Notice, that since both archives
5778 were created without @option{-P} option (@pxref{absolute}), these
5779 commands should be run from the root file system.}:
5782 $ @kbd{tar --extract \
5783 --listed-incremental=/dev/null \
5784 --file archive.1.tar}
5785 $ @kbd{tar --extract \
5786 --listed-incremental=/dev/null \
5787 --file archive.2.tar}
5790 To list the contents of an incremental archive, use @option{--list}
5791 (@pxref{list}), as usual. To obtain more information about the
5792 archive, use @option{--listed-incremental} or @option{--incremental}
5793 combined with two @option{--verbose} options@footnote{Two
5794 @option{--verbose} options were selected to avoid breaking usual
5795 verbose listing output (@option{--list --verbose}) when using in
5798 @xopindex{incremental, using with @option{--list}}
5799 @xopindex{listed-incremental, using with @option{--list}}
5800 @xopindex{list, using with @option{--incremental}}
5801 @xopindex{list, using with @option{--listed-incremental}}
5802 Versions of @GNUTAR{} up to 1.15.1 used to dump verbatim binary
5803 contents of the DUMPDIR header (with terminating nulls) when
5804 @option{--incremental} or @option{--listed-incremental} option was
5805 given, no matter what the verbosity level. This behavior, and,
5806 especially, the binary output it produced were considered inconvenient
5807 and were changed in version 1.16}:
5810 @kbd{tar --list --incremental --verbose --verbose archive.tar}
5813 This command will print, for each directory in the archive, the list
5814 of files in that directory at the time the archive was created. This
5815 information is put out in a format which is both human-readable and
5816 unambiguous for a program: each file name is printed as
5823 where @var{x} is a letter describing the status of the file: @samp{Y}
5824 if the file is present in the archive, @samp{N} if the file is not
5825 included in the archive, or a @samp{D} if the file is a directory (and
5826 is included in the archive). @xref{Dumpdir}, for the detailed
5827 description of dumpdirs and status codes. Each such
5828 line is terminated by a newline character. The last line is followed
5829 by an additional newline to indicate the end of the data.
5831 @anchor{incremental-op}The option @option{--incremental} (@option{-G})
5832 gives the same behavior as @option{--listed-incremental} when used
5833 with @option{--list} and @option{--extract} options. When used with
5834 @option{--create} option, it creates an incremental archive without
5835 creating snapshot file. Thus, it is impossible to create several
5836 levels of incremental backups with @option{--incremental} option.
5839 @section Levels of Backups
5841 An archive containing all the files in the file system is called a
5842 @dfn{full backup} or @dfn{full dump}. You could insure your data by
5843 creating a full dump every day. This strategy, however, would waste a
5844 substantial amount of archive media and user time, as unchanged files
5845 are daily re-archived.
5847 It is more efficient to do a full dump only occasionally. To back up
5848 files between full dumps, you can use @dfn{incremental dumps}. A @dfn{level
5849 one} dump archives all the files that have changed since the last full
5852 A typical dump strategy would be to perform a full dump once a week,
5853 and a level one dump once a day. This means some versions of files
5854 will in fact be archived more than once, but this dump strategy makes
5855 it possible to restore a file system to within one day of accuracy by
5856 only extracting two archives---the last weekly (full) dump and the
5857 last daily (level one) dump. The only information lost would be in
5858 files changed or created since the last daily backup. (Doing dumps
5859 more than once a day is usually not worth the trouble).
5861 @GNUTAR{} comes with scripts you can use to do full
5862 and level-one (actually, even level-two and so on) dumps. Using
5863 scripts (shell programs) to perform backups and restoration is a
5864 convenient and reliable alternative to typing out file name lists
5865 and @command{tar} commands by hand.
5867 Before you use these scripts, you need to edit the file
5868 @file{backup-specs}, which specifies parameters used by the backup
5869 scripts and by the restore script. This file is usually located
5870 in @file{/etc/backup} directory. @xref{Backup Parameters}, for its
5871 detailed description. Once the backup parameters are set, you can
5872 perform backups or restoration by running the appropriate script.
5874 The name of the backup script is @code{backup}. The name of the
5875 restore script is @code{restore}. The following sections describe
5876 their use in detail.
5878 @emph{Please Note:} The backup and restoration scripts are
5879 designed to be used together. While it is possible to restore files by
5880 hand from an archive which was created using a backup script, and to create
5881 an archive by hand which could then be extracted using the restore script,
5882 it is easier to use the scripts. @xref{Incremental Dumps}, before
5883 making such an attempt.
5885 @node Backup Parameters
5886 @section Setting Parameters for Backups and Restoration
5888 The file @file{backup-specs} specifies backup parameters for the
5889 backup and restoration scripts provided with @command{tar}. You must
5890 edit @file{backup-specs} to fit your system configuration and schedule
5891 before using these scripts.
5893 Syntactically, @file{backup-specs} is a shell script, containing
5894 mainly variable assignments. However, any valid shell construct
5895 is allowed in this file. Particularly, you may wish to define
5896 functions within that script (e.g., see @code{RESTORE_BEGIN} below).
5897 For more information about shell script syntax, please refer to
5898 @url{http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
5899 g_02, the definition of the Shell Command Language}. See also
5900 @ref{Top,,Bash Features,bashref,Bash Reference Manual}.
5902 The shell variables controlling behavior of @code{backup} and
5903 @code{restore} are described in the following subsections.
5906 * General-Purpose Variables::
5907 * Magnetic Tape Control::
5909 * backup-specs example:: An Example Text of @file{Backup-specs}
5912 @node General-Purpose Variables
5913 @subsection General-Purpose Variables
5915 @defvr {Backup variable} ADMINISTRATOR
5916 The user name of the backup administrator. @code{Backup} scripts
5917 sends a backup report to this address.
5920 @defvr {Backup variable} BACKUP_HOUR
5921 The hour at which the backups are done. This can be a number from 0
5922 to 23, or the time specification in form @var{hours}:@var{minutes},
5923 or the string @samp{now}.
5925 This variable is used by @code{backup}. Its value may be overridden
5926 using @option{--time} option (@pxref{Scripted Backups}).
5929 @defvr {Backup variable} TAPE_FILE
5931 The device @command{tar} writes the archive to. If @var{TAPE_FILE}
5932 is a remote archive (@pxref{remote-dev}), backup script will suppose
5933 that your @command{mt} is able to access remote devices. If @var{RSH}
5934 (@pxref{RSH}) is set, @option{--rsh-command} option will be added to
5935 invocations of @command{mt}.
5938 @defvr {Backup variable} BLOCKING
5940 The blocking factor @command{tar} will use when writing the dump archive.
5941 @xref{Blocking Factor}.
5944 @defvr {Backup variable} BACKUP_DIRS
5946 A list of file systems to be dumped (for @code{backup}), or restored
5947 (for @code{restore}). You can include any directory
5948 name in the list --- subdirectories on that file system will be
5949 included, regardless of how they may look to other networked machines.
5950 Subdirectories on other file systems will be ignored.
5952 The host name specifies which host to run @command{tar} on, and should
5953 normally be the host that actually contains the file system. However,
5954 the host machine must have @GNUTAR{} installed, and
5955 must be able to access the directory containing the backup scripts and
5956 their support files using the same file name that is used on the
5957 machine where the scripts are run (i.e., what @command{pwd} will print
5958 when in that directory on that machine). If the host that contains
5959 the file system does not have this capability, you can specify another
5960 host as long as it can access the file system through @acronym{NFS}.
5962 If the list of file systems is very long you may wish to put it
5963 in a separate file. This file is usually named
5964 @file{/etc/backup/dirs}, but this name may be overridden in
5965 @file{backup-specs} using @code{DIRLIST} variable.
5968 @defvr {Backup variable} DIRLIST
5970 The name of the file that contains a list of file systems to backup
5971 or restore. By default it is @file{/etc/backup/dirs}.
5974 @defvr {Backup variable} BACKUP_FILES
5976 A list of individual files to be dumped (for @code{backup}), or restored
5977 (for @code{restore}). These should be accessible from the machine on
5978 which the backup script is run.
5980 If the list of file systems is very long you may wish to store it
5981 in a separate file. This file is usually named
5982 @file{/etc/backup/files}, but this name may be overridden in
5983 @file{backup-specs} using @code{FILELIST} variable.
5986 @defvr {Backup variable} FILELIST
5988 The name of the file that contains a list of individual files to backup
5989 or restore. By default it is @file{/etc/backup/files}.
5992 @defvr {Backup variable} MT
5994 Full file name of @command{mt} binary.
5997 @defvr {Backup variable} RSH
5999 Full file name of @command{rsh} binary or its equivalent. You may wish to
6000 set it to @code{ssh}, to improve security. In this case you will have
6001 to use public key authentication.
6004 @defvr {Backup variable} RSH_COMMAND
6006 Full file name of @command{rsh} binary on remote machines. This will
6007 be passed via @option{--rsh-command} option to the remote invocation
6011 @defvr {Backup variable} VOLNO_FILE
6013 Name of temporary file to hold volume numbers. This needs to be accessible
6014 by all the machines which have file systems to be dumped.
6017 @defvr {Backup variable} XLIST
6019 Name of @dfn{exclude file list}. An @dfn{exclude file list} is a file
6020 located on the remote machine and containing the list of files to
6021 be excluded from the backup. Exclude file lists are searched in
6022 /etc/tar-backup directory. A common use for exclude file lists
6023 is to exclude files containing security-sensitive information
6024 (e.g., @file{/etc/shadow} from backups).
6026 This variable affects only @code{backup}.
6029 @defvr {Backup variable} SLEEP_TIME
6031 Time to sleep between dumps of any two successive file systems
6033 This variable affects only @code{backup}.
6036 @defvr {Backup variable} DUMP_REMIND_SCRIPT
6038 Script to be run when it's time to insert a new tape in for the next
6039 volume. Administrators may want to tailor this script for their site.
6040 If this variable isn't set, @GNUTAR{} will display its built-in
6041 prompt, and will expect confirmation from the console. For the
6042 description of the default prompt, see @ref{change volume prompt}.
6046 @defvr {Backup variable} SLEEP_MESSAGE
6048 Message to display on the terminal while waiting for dump time. Usually
6049 this will just be some literal text.
6052 @defvr {Backup variable} TAR
6054 Full file name of the @GNUTAR{} executable. If this is not set, backup
6055 scripts will search @command{tar} in the current shell path.
6058 @node Magnetic Tape Control
6059 @subsection Magnetic Tape Control
6061 Backup scripts access tape device using special @dfn{hook functions}.
6062 These functions take a single argument -- the name of the tape
6063 device. Their names are kept in the following variables:
6065 @defvr {Backup variable} MT_BEGIN
6066 The name of @dfn{begin} function. This function is called before
6067 accessing the drive. By default it retensions the tape:
6073 mt -f "$1" retension
6078 @defvr {Backup variable} MT_REWIND
6079 The name of @dfn{rewind} function. The default definition is as
6092 @defvr {Backup variable} MT_OFFLINE
6093 The name of the function switching the tape off line. By default
6094 it is defined as follows:
6097 MT_OFFLINE=mt_offline
6105 @defvr {Backup variable} MT_STATUS
6106 The name of the function used to obtain the status of the archive device,
6107 including error count. Default definition:
6119 @subsection User Hooks
6121 @dfn{User hooks} are shell functions executed before and after
6122 each @command{tar} invocation. Thus, there are @dfn{backup
6123 hooks}, which are executed before and after dumping each file
6124 system, and @dfn{restore hooks}, executed before and
6125 after restoring a file system. Each user hook is a shell function
6126 taking four arguments:
6128 @deffn {User Hook Function} hook @var{level} @var{host} @var{fs} @var{fsname}
6133 Current backup or restore level.
6136 Name or IP address of the host machine being dumped or restored.
6139 Full file name of the file system being dumped or restored.
6142 File system name with directory separators replaced with colons. This
6143 is useful, e.g., for creating unique files.
6147 Following variables keep the names of user hook functions
6149 @defvr {Backup variable} DUMP_BEGIN
6150 Dump begin function. It is executed before dumping the file system.
6153 @defvr {Backup variable} DUMP_END
6154 Executed after dumping the file system.
6157 @defvr {Backup variable} RESTORE_BEGIN
6158 Executed before restoring the file system.
6161 @defvr {Backup variable} RESTORE_END
6162 Executed after restoring the file system.
6165 @node backup-specs example
6166 @subsection An Example Text of @file{Backup-specs}
6168 The following is an example of @file{backup-specs}:
6171 # site-specific parameters for file system backup.
6173 ADMINISTRATOR=friedman
6175 TAPE_FILE=/dev/nrsmt0
6177 # Use @code{ssh} instead of the less secure @code{rsh}
6179 RSH_COMMAND=/usr/bin/ssh
6181 # Override MT_STATUS function:
6187 # Disable MT_OFFLINE function
6204 apple-gunkies:/com/mailer/gnu
6205 apple-gunkies:/com/archive/gnu"
6207 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
6211 @node Scripted Backups
6212 @section Using the Backup Scripts
6214 The syntax for running a backup script is:
6217 backup --level=@var{level} --time=@var{time}
6220 The @option{level} option requests the dump level. Thus, to produce
6221 a full dump, specify @code{--level=0} (this is the default, so
6222 @option{--level} may be omitted if its value is @code{0}).
6223 @footnote{For backward compatibility, the @code{backup} will also
6224 try to deduce the requested dump level from the name of the
6225 script itself. If the name consists of a string @samp{level-}
6226 followed by a single decimal digit, that digit is taken as
6227 the dump level number. Thus, you may create a link from @code{backup}
6228 to @code{level-1} and then run @code{level-1} whenever you need to
6229 create a level one dump.}
6231 The @option{--time} option determines when should the backup be
6232 run. @var{Time} may take three forms:
6235 @item @var{hh}:@var{mm}
6237 The dump must be run at @var{hh} hours @var{mm} minutes.
6241 The dump must be run at @var{hh} hours
6245 The dump must be run immediately.
6248 You should start a script with a tape or disk mounted. Once you
6249 start a script, it prompts you for new tapes or disks as it
6250 needs them. Media volumes don't have to correspond to archive
6251 files --- a multi-volume archive can be started in the middle of a
6252 tape that already contains the end of another multi-volume archive.
6253 The @code{restore} script prompts for media by its archive volume,
6254 so to avoid an error message you should keep track of which tape
6255 (or disk) contains which volume of the archive (@pxref{Scripted
6258 The backup scripts write two files on the file system. The first is a
6259 record file in @file{/etc/tar-backup/}, which is used by the scripts
6260 to store and retrieve information about which files were dumped. This
6261 file is not meant to be read by humans, and should not be deleted by
6262 them. @xref{Snapshot Files}, for a more detailed explanation of this
6265 The second file is a log file containing the names of the file systems
6266 and files dumped, what time the backup was made, and any error
6267 messages that were generated, as well as how much space was left in
6268 the media volume after the last volume of the archive was written.
6269 You should check this log file after every backup. The file name is
6270 @file{log-@var{mm-dd-yyyy}-level-@var{n}}, where @var{mm-dd-yyyy}
6271 represents current date, and @var{n} represents current dump level number.
6273 The script also prints the name of each system being dumped to the
6276 Following is the full list of options accepted by @code{backup}
6280 @item -l @var{level}
6281 @itemx --level=@var{level}
6282 Do backup level @var{level} (default 0).
6286 Force backup even if today's log file already exists.
6288 @item -v[@var{level}]
6289 @itemx --verbose[=@var{level}]
6290 Set verbosity level. The higher the level is, the more debugging
6291 information will be output during execution. Default @var{level}
6292 is 100, which means the highest debugging level.
6294 @item -t @var{start-time}
6295 @itemx --time=@var{start-time}
6296 Wait till @var{time}, then do backup.
6300 Display short help message and exit.
6304 Display information about the program's name, version, origin and legal
6305 status, all on standard output, and then exit successfully.
6309 @node Scripted Restoration
6310 @section Using the Restore Script
6312 To restore files that were archived using a scripted backup, use the
6313 @code{restore} script. Its usage is quite straightforward. In the
6314 simplest form, invoke @code{restore --all}, it will
6315 then restore all the file systems and files specified in
6316 @file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
6318 You may select the file systems (and/or files) to restore by
6319 giving @code{restore} list of @dfn{patterns} in its command
6320 line. For example, running
6327 will restore all file systems on the machine @samp{albert}. A more
6328 complicated example:
6331 restore 'albert:*' '*:/var'
6335 This command will restore all file systems on the machine @samp{albert}
6336 as well as @file{/var} file system on all machines.
6338 By default @code{restore} will start restoring files from the lowest
6339 available dump level (usually zero) and will continue through
6340 all available dump levels. There may be situations where such a
6341 thorough restore is not necessary. For example, you may wish to
6342 restore only files from the recent level one backup. To do so,
6343 use @option{--level} option, as shown in the example below:
6349 The full list of options accepted by @code{restore} follows:
6354 Restore all file systems and files specified in @file{backup-specs}
6356 @item -l @var{level}
6357 @itemx --level=@var{level}
6358 Start restoring from the given backup level, instead of the default 0.
6360 @item -v[@var{level}]
6361 @itemx --verbose[=@var{level}]
6362 Set verbosity level. The higher the level is, the more debugging
6363 information will be output during execution. Default @var{level}
6364 is 100, which means the highest debugging level.
6368 Display short help message and exit.
6372 Display information about the program's name, version, origin and legal
6373 status, all on standard output, and then exit successfully.
6376 You should start the restore script with the media containing the
6377 first volume of the archive mounted. The script will prompt for other
6378 volumes as they are needed. If the archive is on tape, you don't need
6379 to rewind the tape to to its beginning---if the tape head is
6380 positioned past the beginning of the archive, the script will rewind
6381 the tape as needed. @xref{Tape Positioning}, for a discussion of tape
6385 @strong{Warning:} The script will delete files from the active file
6386 system if they were not in the file system when the archive was made.
6389 @xref{Incremental Dumps}, for an explanation of how the script makes
6393 @chapter Choosing Files and Names for @command{tar}
6396 Certain options to @command{tar} enable you to specify a name for your
6397 archive. Other options let you decide which files to include or exclude
6398 from the archive, based on when or whether files were modified, whether
6399 the file names do or don't match specified patterns, or whether files
6400 are in specified directories.
6402 This chapter discusses these options in detail.
6405 * file:: Choosing the Archive's Name
6406 * Selecting Archive Members::
6407 * files:: Reading Names from a File
6408 * exclude:: Excluding Some Files
6409 * wildcards:: Wildcards Patterns and Matching
6410 * quoting styles:: Ways of Quoting Special Characters in Names
6411 * transform:: Modifying File and Member Names
6412 * after:: Operating Only on New Files
6413 * recurse:: Descending into Directories
6414 * one:: Crossing File System Boundaries
6418 @section Choosing and Naming Archive Files
6421 @cindex Naming an archive
6422 @cindex Archive Name
6423 @cindex Choosing an archive file
6424 @cindex Where is the archive?
6425 By default, @command{tar} uses an archive file name that was compiled when
6426 it was built on the system; usually this name refers to some physical
6427 tape drive on the machine. However, the person who installed @command{tar}
6428 on the system may not have set the default to a meaningful value as far as
6429 most users are concerned. As a result, you will usually want to tell
6430 @command{tar} where to find (or create) the archive. The
6431 @option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
6432 option allows you to either specify or name a file to use as the archive
6433 instead of the default archive file location.
6436 @xopindex{file, short description}
6437 @item --file=@var{archive-name}
6438 @itemx -f @var{archive-name}
6439 Name the archive to create or operate on. Use in conjunction with
6443 For example, in this @command{tar} command,
6446 $ @kbd{tar -cvf collection.tar blues folk jazz}
6450 @file{collection.tar} is the name of the archive. It must directly
6451 follow the @option{-f} option, since whatever directly follows @option{-f}
6452 @emph{will} end up naming the archive. If you neglect to specify an
6453 archive name, you may end up overwriting a file in the working directory
6454 with the archive you create since @command{tar} will use this file's name
6455 for the archive name.
6457 An archive can be saved as a file in the file system, sent through a
6458 pipe or over a network, or written to an I/O device such as a tape,
6459 floppy disk, or CD write drive.
6461 @cindex Writing new archives
6462 @cindex Archive creation
6463 If you do not name the archive, @command{tar} uses the value of the
6464 environment variable @env{TAPE} as the file name for the archive. If
6465 that is not available, @command{tar} uses a default, compiled-in archive
6466 name, usually that for tape unit zero (i.e., @file{/dev/tu00}).
6468 @cindex Standard input and output
6469 @cindex tar to standard input and output
6470 If you use @file{-} as an @var{archive-name}, @command{tar} reads the
6471 archive from standard input (when listing or extracting files), or
6472 writes it to standard output (when creating an archive). If you use
6473 @file{-} as an @var{archive-name} when modifying an archive,
6474 @command{tar} reads the original archive from its standard input and
6475 writes the entire new archive to its standard output.
6477 The following example is a convenient way of copying directory
6478 hierarchy from @file{sourcedir} to @file{targetdir}.
6481 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)}
6484 The @option{-C} option allows to avoid using subshells:
6487 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xpf -}
6490 In both examples above, the leftmost @command{tar} invocation archives
6491 the contents of @file{sourcedir} to the standard output, while the
6492 rightmost one reads this archive from its standard input and
6493 extracts it. The @option{-p} option tells it to restore permissions
6494 of the extracted files.
6496 @cindex Remote devices
6497 @cindex tar to a remote device
6499 To specify an archive file on a device attached to a remote machine,
6503 @kbd{--file=@var{hostname}:/@var{dev}/@var{file-name}}
6507 @command{tar} will complete the remote connection, if possible, and
6508 prompt you for a username and password. If you use
6509 @option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
6510 will complete the remote connection, if possible, using your username
6511 as the username on the remote machine.
6513 @cindex Local and remote archives
6514 @anchor{local and remote archives}
6515 If the archive file name includes a colon (@samp{:}), then it is assumed
6516 to be a file on another machine. If the archive file is
6517 @samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the
6518 host @var{host}. The remote host is accessed using the @command{rsh}
6519 program, with a username of @var{user}. If the username is omitted
6520 (along with the @samp{@@} sign), then your user name will be used.
6521 (This is the normal @command{rsh} behavior.) It is necessary for the
6522 remote machine, in addition to permitting your @command{rsh} access, to
6523 have the @file{rmt} program installed (This command is included in
6524 the @GNUTAR{} distribution and by default is installed under
6525 @file{@var{prefix}/libexec/rmt}, were @var{prefix} means your
6526 installation prefix). If you need to use a file whose name includes a
6527 colon, then the remote tape drive behavior
6528 can be inhibited by using the @option{--force-local} option.
6530 When the archive is being created to @file{/dev/null}, @GNUTAR{}
6531 tries to minimize input and output operations. The Amanda backup
6532 system, when used with @GNUTAR{}, has an initial sizing pass which
6535 @node Selecting Archive Members
6536 @section Selecting Archive Members
6537 @cindex Specifying files to act on
6538 @cindex Specifying archive members
6540 @dfn{File Name arguments} specify which files in the file system
6541 @command{tar} operates on, when creating or adding to an archive, or which
6542 archive members @command{tar} operates on, when reading or deleting from
6543 an archive. @xref{Operations}.
6545 To specify file names, you can include them as the last arguments on
6546 the command line, as follows:
6548 @kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
6551 If a file name begins with dash (@samp{-}), precede it with
6552 @option{--add-file} option to prevent it from being treated as an
6555 @anchor{input name quoting}
6556 By default @GNUTAR{} attempts to @dfn{unquote} each file or member
6557 name, replacing @dfn{escape sequences} according to the following
6560 @multitable @columnfractions 0.20 0.60
6561 @headitem Escape @tab Replaced with
6562 @item \a @tab Audible bell (@acronym{ASCII} 7)
6563 @item \b @tab Backspace (@acronym{ASCII} 8)
6564 @item \f @tab Form feed (@acronym{ASCII} 12)
6565 @item \n @tab New line (@acronym{ASCII} 10)
6566 @item \r @tab Carriage return (@acronym{ASCII} 13)
6567 @item \t @tab Horizontal tabulation (@acronym{ASCII} 9)
6568 @item \v @tab Vertical tabulation (@acronym{ASCII} 11)
6569 @item \? @tab @acronym{ASCII} 127
6570 @item \@var{n} @tab @acronym{ASCII} @var{n} (@var{n} should be an octal number
6574 A backslash followed by any other symbol is retained.
6576 This default behavior is controlled by the following command line
6582 Enable unquoting input file or member names (default).
6586 Disable unquoting input file or member names.
6589 If you specify a directory name as a file name argument, all the files
6590 in that directory are operated on by @command{tar}.
6592 If you do not specify files, @command{tar} behavior differs depending
6593 on the operation mode as described below:
6595 When @command{tar} is invoked with @option{--create} (@option{-c}),
6596 @command{tar} will stop immediately, reporting the following:
6600 $ @kbd{tar cf a.tar}
6601 tar: Cowardly refusing to create an empty archive
6602 Try `tar --help' or `tar --usage' for more information.
6606 If you specify either @option{--list} (@option{-t}) or
6607 @option{--extract} (@option{--get}, @option{-x}), @command{tar}
6608 operates on all the archive members in the archive.
6610 If run with @option{--diff} option, tar will compare the archive with
6611 the contents of the current working directory.
6613 If you specify any other operation, @command{tar} does nothing.
6615 By default, @command{tar} takes file names from the command line. However,
6616 there are other ways to specify file or member names, or to modify the
6617 manner in which @command{tar} selects the files or members upon which to
6618 operate. In general, these methods work both for specifying the names
6619 of files and archive members.
6622 @section Reading Names from a File
6624 @cindex Reading file names from a file
6625 @cindex Lists of file names
6626 @cindex File Name arguments, alternatives
6627 Instead of giving the names of files or archive members on the command
6628 line, you can put the names into a file, and then use the
6629 @option{--files-from=@var{file-of-names}} (@option{-T
6630 @var{file-of-names}}) option to @command{tar}. Give the name of the
6631 file which contains the list of files to include as the argument to
6632 @option{--files-from}. In the list, the file names should be separated by
6633 newlines. You will frequently use this option when you have generated
6634 the list of files to archive with the @command{find} utility.
6638 @item --files-from=@var{file-name}
6639 @itemx -T @var{file-name}
6640 Get names to extract or create from file @var{file-name}.
6643 If you give a single dash as a file name for @option{--files-from}, (i.e.,
6644 you specify either @code{--files-from=-} or @code{-T -}), then the file
6645 names are read from standard input.
6647 Unless you are running @command{tar} with @option{--create}, you can not use
6648 both @code{--files-from=-} and @code{--file=-} (@code{-f -}) in the same
6651 Any number of @option{-T} options can be given in the command line.
6653 The following example shows how to use @command{find} to generate a list of
6654 files smaller than 400K in length and put that list into a file
6655 called @file{small-files}. You can then use the @option{-T} option to
6656 @command{tar} to specify the files from that file, @file{small-files}, to
6657 create the archive @file{little.tgz}. (The @option{-z} option to
6658 @command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for
6662 $ @kbd{find . -size -400 -print > small-files}
6663 $ @kbd{tar -c -v -z -T small-files -f little.tgz}
6667 In the file list given by @option{-T} option, any file name beginning
6668 with @samp{-} character is considered a @command{tar} option and is
6669 processed accordingly.@footnote{Versions of @GNUTAR{} up to 1.15.1
6670 recognized only @option{-C} option in file lists, and only if the
6671 option and its argument occupied two consecutive lines.} For example,
6672 the common use of this feature is to change to another directory by
6673 specifying @option{-C} option:
6683 $ @kbd{tar -c -f foo.tar --files-from list}
6688 In this example, @command{tar} will first switch to @file{/etc}
6689 directory and add files @file{passwd} and @file{hosts} to the
6690 archive. Then it will change to @file{/lib} directory and will archive
6691 the file @file{libc.a}. Thus, the resulting archive @file{foo.tar} will
6696 $ @kbd{tar tf foo.tar}
6704 @xopindex{directory, using in @option{--files-from} argument}
6705 Notice that the option parsing algorithm used with @option{-T} is
6706 stricter than the one used by shell. Namely, when specifying option
6707 arguments, you should observe the following rules:
6711 When using short (single-letter) option form, its argument must
6712 immediately follow the option letter, without any intervening
6713 whitespace. For example: @code{-Cdir}.
6716 When using long option form, the option argument must be separated
6717 from the option by a single equal sign. No whitespace is allowed on
6718 any side of the equal sign. For example: @code{--directory=dir}.
6721 For both short and long option forms, the option argument can be given
6722 on the next line after the option name, e.g.:
6743 If you happen to have a file whose name starts with @samp{-},
6744 precede it with @option{--add-file} option to prevent it from
6745 being recognized as an option. For example: @code{--add-file=--my-file}.
6752 @subsection @code{NUL} Terminated File Names
6754 @cindex File names, terminated by @code{NUL}
6755 @cindex @code{NUL} terminated file names
6756 The @option{--null} option causes
6757 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
6758 to read file names terminated by a @code{NUL} instead of a newline, so
6759 files whose names contain newlines can be archived using
6760 @option{--files-from}.
6763 @xopindex{null, described}
6765 Only consider @code{NUL} terminated file names, instead of files that
6766 terminate in a newline.
6768 @xopindex{no-null, described}
6770 Undo the effect of any previous @option{--null} option.
6773 The @option{--null} option is just like the one in @acronym{GNU}
6774 @command{xargs} and @command{cpio}, and is useful with the
6775 @option{-print0} predicate of @acronym{GNU} @command{find}. In
6776 @command{tar}, @option{--null} also disables special handling for
6777 file names that begin with dash.
6779 This example shows how to use @command{find} to generate a list of files
6780 larger than 800K in length and put that list into a file called
6781 @file{long-files}. The @option{-print0} option to @command{find} is just
6782 like @option{-print}, except that it separates files with a @code{NUL}
6783 rather than with a newline. You can then run @command{tar} with both the
6784 @option{--null} and @option{-T} options to specify that @command{tar} get the
6785 files from that file, @file{long-files}, to create the archive
6786 @file{big.tgz}. The @option{--null} option to @command{tar} will cause
6787 @command{tar} to recognize the @code{NUL} separator between files.
6790 $ @kbd{find . -size +800 -print0 > long-files}
6791 $ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
6794 The @option{--no-null} option can be used if you need to read both
6795 zero-terminated and newline-terminated files on the same command line.
6796 For example, if @file{flist} is a newline-terminated file, then the
6797 following command can be used to combine it with the above command:
6801 $ @kbd{find . -size +800 -print0 |
6802 tar -c -f big.tar --null -T - --no-null -T flist}
6806 This example uses short options for typographic reasons, to avoid
6809 @GNUTAR is able to automatically detect null-terminated file lists, so
6810 it is safe to use them even without the @option{--null} option. In
6811 this case @command{tar} will print a warning and continue reading such
6812 a file as if @option{--null} were actually given:
6816 $ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
6817 tar: -: file name read contains nul character
6821 The null terminator, however, remains in effect only for this
6822 particular file, any following @option{-T} options will assume
6823 newline termination. Of course, the null autodetection applies
6824 to these eventual surplus @option{-T} options as well.
6827 @section Excluding Some Files
6830 @cindex File names, excluding files by
6831 @cindex Excluding files by name and pattern
6832 @cindex Excluding files by file system
6833 To avoid operating on files whose names match a particular pattern,
6834 use the @option{--exclude} or @option{--exclude-from} options.
6838 @item --exclude=@var{pattern}
6839 Causes @command{tar} to ignore files that match the @var{pattern}.
6843 The @option{--exclude=@var{pattern}} option prevents any file or
6844 member whose name matches the shell wildcard (@var{pattern}) from
6846 For example, to create an archive with all the contents of the directory
6847 @file{src} except for files whose names end in @file{.o}, use the
6848 command @samp{tar -cf src.tar --exclude='*.o' src}.
6850 You may give multiple @option{--exclude} options.
6853 @opindex exclude-from
6854 @item --exclude-from=@var{file}
6855 @itemx -X @var{file}
6856 Causes @command{tar} to ignore files that match the patterns listed in
6860 @findex exclude-from
6861 Use the @option{--exclude-from} option to read a
6862 list of patterns, one per line, from @var{file}; @command{tar} will
6863 ignore files matching those patterns. Thus if @command{tar} is
6864 called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a
6865 single line @file{*.o}, no files whose names end in @file{.o} will be
6866 added to the archive.
6868 Notice, that lines from @var{file} are read verbatim. One of the
6869 frequent errors is leaving some extra whitespace after a file name,
6870 which is difficult to catch using text editors.
6872 However, empty lines are OK.
6874 @cindex version control system, excluding files
6875 @cindex VCS, excluding files
6876 @cindex SCCS, excluding files
6877 @cindex RCS, excluding files
6878 @cindex CVS, excluding files
6879 @cindex SVN, excluding files
6880 @cindex git, excluding files
6881 @cindex Bazaar, excluding files
6882 @cindex Arch, excluding files
6883 @cindex Mercurial, excluding files
6884 @cindex Darcs, excluding files
6886 @opindex exclude-vcs
6888 Exclude files and directories used by following version control
6889 systems: @samp{CVS}, @samp{RCS}, @samp{SCCS}, @samp{SVN}, @samp{Arch},
6890 @samp{Bazaar}, @samp{Mercurial}, and @samp{Darcs}.
6893 As of version @value{VERSION}, the following files are excluded:
6896 @item @file{CVS/}, and everything under it
6897 @item @file{RCS/}, and everything under it
6898 @item @file{SCCS/}, and everything under it
6899 @item @file{.git/}, and everything under it
6900 @item @file{.gitignore}
6901 @item @file{.cvsignore}
6902 @item @file{.svn/}, and everything under it
6903 @item @file{.arch-ids/}, and everything under it
6904 @item @file{@{arch@}/}, and everything under it
6905 @item @file{=RELEASE-ID}
6906 @item @file{=meta-update}
6907 @item @file{=update}
6909 @item @file{.bzrignore}
6910 @item @file{.bzrtags}
6912 @item @file{.hgignore}
6913 @item @file{.hgrags}
6917 @findex exclude-caches
6918 When creating an archive, the @option{--exclude-caches} option family
6919 causes @command{tar} to exclude all directories that contain a @dfn{cache
6920 directory tag}. A cache directory tag is a short file with the
6921 well-known name @file{CACHEDIR.TAG} and having a standard header
6922 specified in @url{http://www.brynosaurus.com/cachedir/spec.html}.
6923 Various applications write cache directory tags into directories they
6924 use to hold regenerable, non-precious data, so that such data can be
6925 more easily excluded from backups.
6927 There are three @samp{exclude-caches} options, each providing a different
6928 exclusion semantics:
6931 @opindex exclude-caches
6932 @item --exclude-caches
6933 Do not archive the contents of the directory, but archive the
6934 directory itself and the @file{CACHEDIR.TAG} file.
6936 @opindex exclude-caches-under
6937 @item --exclude-caches-under
6938 Do not archive the contents of the directory, nor the
6939 @file{CACHEDIR.TAG} file, archive only the directory itself.
6941 @opindex exclude-caches-all
6942 @item --exclude-caches-all
6943 Omit directories containing @file{CACHEDIR.TAG} file entirely.
6947 Another option family, @option{--exclude-tag}, provides a generalization of
6948 this concept. It takes a single argument, a file name to look for.
6949 Any directory that contains this file will be excluded from the dump.
6950 Similarly to @samp{exclude-caches}, there are three options in this
6954 @opindex exclude-tag
6955 @item --exclude-tag=@var{file}
6956 Do not dump the contents of the directory, but dump the
6957 directory itself and the @var{file}.
6959 @opindex exclude-tag-under
6960 @item --exclude-tag-under=@var{file}
6961 Do not dump the contents of the directory, nor the
6962 @var{file}, archive only the directory itself.
6964 @opindex exclude-tag-all
6965 @item --exclude-tag-all=@var{file}
6966 Omit directories containing @var{file} file entirely.
6969 Multiple @option{--exclude-tag*} options can be given.
6971 For example, given this directory:
6986 The @option{--exclude-tag} will produce the following:
6989 $ @kbd{tar -cf archive.tar --exclude-tag=tagfile -v dir}
6994 tar: dir/folk/: contains a cache directory tag tagfile;
6999 Both the @file{dir/folk} directory and its tagfile are preserved in
7000 the archive, however the rest of files in this directory are not.
7002 Now, using the @option{--exclude-tag-under} option will exclude
7003 @file{tagfile} from the dump, while still preserving the directory
7004 itself, as shown in this example:
7007 $ @kbd{tar -cf archive.tar --exclude-tag-under=tagfile -v dir}
7012 ./tar: dir/folk/: contains a cache directory tag tagfile;
7016 Finally, using @option{--exclude-tag-all} omits the @file{dir/folk}
7020 $ @kbd{tar -cf archive.tar --exclude-tag-all=tagfile -v dir}
7024 ./tar: dir/folk/: contains a cache directory tag tagfile;
7025 directory not dumped
7029 * problems with exclude::
7032 @node problems with exclude
7033 @unnumberedsubsec Problems with Using the @code{exclude} Options
7035 @xopindex{exclude, potential problems with}
7036 Some users find @samp{exclude} options confusing. Here are some common
7041 The main operating mode of @command{tar} does not act on a file name
7042 explicitly listed on the command line, if one of its file name
7043 components is excluded. In the example above, if
7044 you create an archive and exclude files that end with @samp{*.o}, but
7045 explicitly name the file @samp{dir.o/foo} after all the options have been
7046 listed, @samp{dir.o/foo} will be excluded from the archive.
7049 You can sometimes confuse the meanings of @option{--exclude} and
7050 @option{--exclude-from}. Be careful: use @option{--exclude} when files
7051 to be excluded are given as a pattern on the command line. Use
7052 @option{--exclude-from} to introduce the name of a file which contains
7053 a list of patterns, one per line; each of these patterns can exclude
7054 zero, one, or many files.
7057 When you use @option{--exclude=@var{pattern}}, be sure to quote the
7058 @var{pattern} parameter, so @GNUTAR{} sees wildcard characters
7059 like @samp{*}. If you do not do this, the shell might expand the
7060 @samp{*} itself using files at hand, so @command{tar} might receive a
7061 list of files instead of one pattern, or none at all, making the
7062 command somewhat illegal. This might not correspond to what you want.
7067 $ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}}
7075 $ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
7079 You must use use shell syntax, or globbing, rather than @code{regexp}
7080 syntax, when using exclude options in @command{tar}. If you try to use
7081 @code{regexp} syntax to describe files to be excluded, your command
7085 @FIXME{The change in semantics must have occurred before 1.11,
7086 so I doubt if it is worth mentioning at all. Anyway, should at
7087 least specify in which version the semantics changed.}
7088 In earlier versions of @command{tar}, what is now the
7089 @option{--exclude-from} option was called @option{--exclude} instead.
7090 Now, @option{--exclude} applies to patterns listed on the command
7091 line and @option{--exclude-from} applies to patterns listed in a
7097 @section Wildcards Patterns and Matching
7099 @dfn{Globbing} is the operation by which @dfn{wildcard} characters,
7100 @samp{*} or @samp{?} for example, are replaced and expanded into all
7101 existing files matching the given pattern. @GNUTAR{} can use wildcard
7102 patterns for matching (or globbing) archive members when extracting
7103 from or listing an archive. Wildcard patterns are also used for
7104 verifying volume labels of @command{tar} archives. This section has the
7105 purpose of explaining wildcard syntax for @command{tar}.
7107 @FIXME{the next few paragraphs need work.}
7109 A @var{pattern} should be written according to shell syntax, using wildcard
7110 characters to effect globbing. Most characters in the pattern stand
7111 for themselves in the matched string, and case is significant: @samp{a}
7112 will match only @samp{a}, and not @samp{A}. The character @samp{?} in the
7113 pattern matches any single character in the matched string. The character
7114 @samp{*} in the pattern matches zero, one, or more single characters in
7115 the matched string. The character @samp{\} says to take the following
7116 character of the pattern @emph{literally}; it is useful when one needs to
7117 match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves.
7119 The character @samp{[}, up to the matching @samp{]}, introduces a character
7120 class. A @dfn{character class} is a list of acceptable characters
7121 for the next single character of the matched string. For example,
7122 @samp{[abcde]} would match any of the first five letters of the alphabet.
7123 Note that within a character class, all of the ``special characters''
7124 listed above other than @samp{\} lose their special meaning; for example,
7125 @samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\},
7126 @samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints,
7127 the characters @samp{-} and @samp{]} must either come @emph{first} or
7128 @emph{last} in a character class.)
7130 @cindex Excluding characters from a character class
7131 @cindex Character class, excluding characters from
7132 If the first character of the class after the opening @samp{[}
7133 is @samp{!} or @samp{^}, then the meaning of the class is reversed.
7134 Rather than listing character to match, it lists those characters which
7135 are @emph{forbidden} as the next single character of the matched string.
7137 Other characters of the class stand for themselves. The special
7138 construction @samp{[@var{a}-@var{e}]}, using an hyphen between two
7139 letters, is meant to represent all characters between @var{a} and
7142 @FIXME{need to add a sentence or so here to make this clear for those
7143 who don't have dan around.}
7145 Periods (@samp{.}) or forward slashes (@samp{/}) are not considered
7146 special for wildcard matches. However, if a pattern completely matches
7147 a directory prefix of a matched string, then it matches the full matched
7148 string: thus, excluding a directory also excludes all the files beneath it.
7151 * controlling pattern-matching::
7154 @node controlling pattern-matching
7155 @unnumberedsubsec Controlling Pattern-Matching
7157 For the purposes of this section, we call @dfn{exclusion members} all
7158 member names obtained while processing @option{--exclude} and
7159 @option{--exclude-from} options, and @dfn{inclusion members} those
7160 member names that were given in the command line or read from the file
7161 specified with @option{--files-from} option.
7163 These two pairs of member lists are used in the following operations:
7164 @option{--diff}, @option{--extract}, @option{--list},
7167 There are no inclusion members in create mode (@option{--create} and
7168 @option{--append}), since in this mode the names obtained from the
7169 command line refer to @emph{files}, not archive members.
7171 By default, inclusion members are compared with archive members
7172 literally @footnote{Notice that earlier @GNUTAR{} versions used
7173 globbing for inclusion members, which contradicted to UNIX98
7174 specification and was not documented. @xref{Changes}, for more
7175 information on this and other changes.} and exclusion members are
7176 treated as globbing patterns. For example:
7180 $ @kbd{tar tf foo.tar}
7185 # @i{Member names are used verbatim:}
7186 $ @kbd{tar -xf foo.tar -v '[remarks]'}
7188 # @i{Exclude member names are globbed:}
7189 $ @kbd{tar -xf foo.tar -v --exclude '*.c'}
7195 This behavior can be altered by using the following options:
7200 Treat all member names as wildcards.
7202 @opindex no-wildcards
7203 @item --no-wildcards
7204 Treat all member names as literal strings.
7207 Thus, to extract files whose names end in @samp{.c}, you can use:
7210 $ @kbd{tar -xf foo.tar -v --wildcards '*.c'}
7216 Notice quoting of the pattern to prevent the shell from interpreting
7219 The effect of @option{--wildcards} option is canceled by
7220 @option{--no-wildcards}. This can be used to pass part of
7221 the command line arguments verbatim and other part as globbing
7222 patterns. For example, the following invocation:
7225 $ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'}
7229 instructs @command{tar} to extract from @file{foo.tar} all files whose
7230 names end in @samp{.txt} and the file named @file{[remarks]}.
7232 Normally, a pattern matches a name if an initial subsequence of the
7233 name's components matches the pattern, where @samp{*}, @samp{?}, and
7234 @samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
7235 and wildcards can match @samp{/}.
7237 Other than optionally stripping leading @samp{/} from names
7238 (@pxref{absolute}), patterns and names are used as-is. For
7239 example, trailing @samp{/} is not trimmed from a user-specified name
7240 before deciding whether to exclude it.
7242 However, this matching procedure can be altered by the options listed
7243 below. These options accumulate. For example:
7246 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
7250 ignores case when excluding @samp{makefile}, but not when excluding
7255 @opindex no-anchored
7257 @itemx --no-anchored
7258 If anchored, a pattern must match an initial subsequence
7259 of the name's components. Otherwise, the pattern can match any
7260 subsequence. Default is @option{--no-anchored} for exclusion members
7261 and @option{--anchored} inclusion members.
7263 @opindex ignore-case
7264 @opindex no-ignore-case
7266 @itemx --no-ignore-case
7267 When ignoring case, upper-case patterns match lower-case names and vice versa.
7268 When not ignoring case (the default), matching is case-sensitive.
7270 @opindex wildcards-match-slash
7271 @opindex no-wildcards-match-slash
7272 @item --wildcards-match-slash
7273 @itemx --no-wildcards-match-slash
7274 When wildcards match slash (the default for exclusion members), a
7275 wildcard like @samp{*} in the pattern can match a @samp{/} in the
7276 name. Otherwise, @samp{/} is matched only by @samp{/}.
7280 The @option{--recursion} and @option{--no-recursion} options
7281 (@pxref{recurse}) also affect how member patterns are interpreted. If
7282 recursion is in effect, a pattern matches a name if it matches any of
7283 the name's parent directories.
7285 The following table summarizes pattern-matching default values:
7287 @multitable @columnfractions .3 .7
7288 @headitem Members @tab Default settings
7289 @item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash}
7290 @item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash}
7293 @node quoting styles
7294 @section Quoting Member Names
7296 When displaying member names, @command{tar} takes care to avoid
7297 ambiguities caused by certain characters. This is called @dfn{name
7298 quoting}. The characters in question are:
7301 @item Non-printable control characters:
7302 @anchor{escape sequences}
7303 @multitable @columnfractions 0.20 0.10 0.60
7304 @headitem Character @tab @acronym{ASCII} @tab Character name
7305 @item \a @tab 7 @tab Audible bell
7306 @item \b @tab 8 @tab Backspace
7307 @item \f @tab 12 @tab Form feed
7308 @item \n @tab 10 @tab New line
7309 @item \r @tab 13 @tab Carriage return
7310 @item \t @tab 9 @tab Horizontal tabulation
7311 @item \v @tab 11 @tab Vertical tabulation
7314 @item Space (@acronym{ASCII} 32)
7316 @item Single and double quotes (@samp{'} and @samp{"})
7318 @item Backslash (@samp{\})
7321 The exact way @command{tar} uses to quote these characters depends on
7322 the @dfn{quoting style}. The default quoting style, called
7323 @dfn{escape} (see below), uses backslash notation to represent control
7324 characters, space and backslash. Using this quoting style, control
7325 characters are represented as listed in column @samp{Character} in the
7326 above table, a space is printed as @samp{\ } and a backslash as @samp{\\}.
7328 @GNUTAR{} offers seven distinct quoting styles, which can be selected
7329 using @option{--quoting-style} option:
7332 @item --quoting-style=@var{style}
7333 @opindex quoting-style
7335 Sets quoting style. Valid values for @var{style} argument are:
7336 literal, shell, shell-always, c, escape, locale, clocale.
7339 These styles are described in detail below. To illustrate their
7340 effect, we will use an imaginary tar archive @file{arch.tar}
7341 containing the following members:
7345 # 1. Contains horizontal tabulation character.
7347 # 2. Contains newline character
7350 # 3. Contains a space
7352 # 4. Contains double quotes
7354 # 5. Contains single quotes
7356 # 6. Contains a backslash character:
7361 Here is how usual @command{ls} command would have listed them, if they
7362 had existed in the current working directory:
7380 No quoting, display each character as is:
7384 $ @kbd{tar tf arch.tar --quoting-style=literal}
7397 Display characters the same way Bourne shell does:
7398 control characters, except @samp{\t} and @samp{\n}, are printed using
7399 backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a
7400 single quote is printed as @samp{\'}. If a name contains any quoted
7401 characters, it is enclosed in single quotes. In particular, if a name
7402 contains single quotes, it is printed as several single-quoted strings:
7406 $ @kbd{tar tf arch.tar --quoting-style=shell}
7409 './a'\''single'\''quote'
7419 Same as @samp{shell}, but the names are always enclosed in single
7424 $ @kbd{tar tf arch.tar --quoting-style=shell-always}
7427 './a'\''single'\''quote'
7437 Use the notation of the C programming language. All names are
7438 enclosed in double quotes. Control characters are quoted using
7439 backslash notations, double quotes are represented as @samp{\"},
7440 backslash characters are represented as @samp{\\}. Single quotes and
7441 spaces are not quoted:
7445 $ @kbd{tar tf arch.tar --quoting-style=c}
7449 "./a\"double\"quote"
7457 Control characters are printed using backslash notation, a space is
7458 printed as @samp{\ } and a backslash as @samp{\\}. This is the
7459 default quoting style, unless it was changed when configured the
7464 $ @kbd{tar tf arch.tar --quoting-style=escape}
7476 Control characters, single quote and backslash are printed using
7477 backslash notation. All names are quoted using left and right
7478 quotation marks, appropriate to the current locale. If it does not
7479 define quotation marks, use @samp{`} as left and @samp{'} as right
7480 quotation marks. Any occurrences of the right quotation mark in a
7481 name are escaped with @samp{\}, for example:
7487 $ @kbd{tar tf arch.tar --quoting-style=locale}
7490 `./a\'single\'quote'
7499 Same as @samp{locale}, but @samp{"} is used for both left and right
7500 quotation marks, if not provided by the currently selected locale:
7504 $ @kbd{tar tf arch.tar --quoting-style=clocale}
7508 "./a\"double\"quote"
7516 You can specify which characters should be quoted in addition to those
7517 implied by the current quoting style:
7520 @item --quote-chars=@var{string}
7521 Always quote characters from @var{string}, even if the selected
7522 quoting style would not quote them.
7525 For example, using @samp{escape} quoting (compare with the usual
7526 escape listing above):
7530 $ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'}
7541 To disable quoting of such additional characters, use the following
7545 @item --no-quote-chars=@var{string}
7546 Remove characters listed in @var{string} from the list of quoted
7547 characters set by the previous @option{--quote-chars} option.
7550 This option is particularly useful if you have added
7551 @option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS})
7552 and wish to disable it for the current invocation.
7554 Note, that @option{--no-quote-chars} does @emph{not} disable those
7555 characters that are quoted by default in the selected quoting style.
7558 @section Modifying File and Member Names
7560 @command{Tar} archives contain detailed information about files stored
7561 in them and full file names are part of that information. When
7562 storing file to an archive, its file name is recorded in it,
7563 along with the actual file contents. When restoring from an archive,
7564 a file is created on disk with exactly the same name as that stored
7565 in the archive. In the majority of cases this is the desired behavior
7566 of a file archiver. However, there are some cases when it is not.
7568 First of all, it is often unsafe to extract archive members with
7569 absolute file names or those that begin with a @file{../}. @GNUTAR{}
7570 takes special precautions when extracting such names and provides a
7571 special option for handling them, which is described in
7574 Secondly, you may wish to extract file names without some leading
7575 directory components, or with otherwise modified names. In other
7576 cases it is desirable to store files under differing names in the
7579 @GNUTAR{} provides several options for these needs.
7582 @opindex strip-components
7583 @item --strip-components=@var{number}
7584 Strip given @var{number} of leading components from file names before
7588 For example, suppose you have archived whole @file{/usr} hierarchy to
7589 a tar archive named @file{usr.tar}. Among other files, this archive
7590 contains @file{usr/include/stdlib.h}, which you wish to extract to
7591 the current working directory. To do so, you type:
7594 $ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h}
7597 The option @option{--strip=2} instructs @command{tar} to strip the
7598 two leading components (@file{usr/} and @file{include/}) off the file
7601 If you add the @option{--verbose} (@option{-v}) option to the invocation
7602 above, you will note that the verbose listing still contains the
7603 full file name, with the two removed components still in place. This
7604 can be inconvenient, so @command{tar} provides a special option for
7605 altering this behavior:
7607 @anchor{show-transformed-names}
7609 @opindex show-transformed-names
7610 @item --show-transformed-names
7611 Display file or member names with all requested transformations
7620 $ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h}
7621 usr/include/stdlib.h
7622 $ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h}
7627 Notice that in both cases the file @file{stdlib.h} is extracted to the
7628 current working directory, @option{--show-transformed-names} affects
7629 only the way its name is displayed.
7631 This option is especially useful for verifying whether the invocation
7632 will have the desired effect. Thus, before running
7635 $ @kbd{tar -x --strip=@var{n}}
7639 it is often advisable to run
7642 $ @kbd{tar -t -v --show-transformed --strip=@var{n}}
7646 to make sure the command will produce the intended results.
7648 In case you need to apply more complex modifications to the file name,
7649 @GNUTAR{} provides a general-purpose transformation option:
7654 @item --transform=@var{expression}
7655 @itemx --xform=@var{expression}
7656 Modify file names using supplied @var{expression}.
7660 The @var{expression} is a @command{sed}-like replace expression of the
7664 s/@var{regexp}/@var{replace}/[@var{flags}]
7668 where @var{regexp} is a @dfn{regular expression}, @var{replace} is a
7669 replacement for each file name part that matches @var{regexp}. Both
7670 @var{regexp} and @var{replace} are described in detail in
7671 @ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
7673 Any delimiter can be used in lieue of @samp{/}, the only requirement being
7674 that it be used consistently throughout the expression. For example,
7675 the following two expressions are equivalent:
7684 Changing delimiters is often useful when the @var{regex} contains
7685 slashes. For example, it is more convenient to write @code{s,/,-,} than
7688 As in @command{sed}, you can give several replace expressions,
7689 separated by a semicolon.
7691 Supported @var{flags} are:
7695 Apply the replacement to @emph{all} matches to the @var{regexp}, not
7699 Use case-insensitive matching
7702 @var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
7703 regexps, Extended regular expressions, Extended regular expressions,
7707 Only replace the @var{number}th match of the @var{regexp}.
7709 Note: the @acronym{POSIX} standard does not specify what should happen
7710 when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
7711 follows the GNU @command{sed} implementation in this regard, so
7712 the interaction is defined to be: ignore matches before the
7713 @var{number}th, and then match and replace all matches from the
7718 In addition, several @dfn{transformation scope} flags are supported,
7719 that control to what files transformations apply. These are:
7723 Apply transformation to regular archive members.
7726 Do not apply transformation to regular archive members.
7729 Apply transformation to symbolic link targets.
7732 Do not apply transformation to symbolic link targets.
7735 Apply transformation to hard link targets.
7738 Do not apply transformation to hard link targets.
7741 Default is @samp{rsh}, which means to apply tranformations to both archive
7742 members and targets of symbolic and hard links.
7744 Default scope flags can also be changed using @samp{flags=} statement
7745 in the transform expression. The flags set this way remain in force
7746 until next @samp{flags=} statement or end of expression, whichever
7747 occurs first. For example:
7750 --transform 'flags=S;s|^|/usr/local/|'
7753 Here are several examples of @option{--transform} usage:
7756 @item Extract @file{usr/} hierarchy into @file{usr/local/}:
7759 $ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar}
7762 @item Strip two leading directory components (equivalent to
7763 @option{--strip-components=2}):
7766 $ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
7769 @item Convert each file name to lower case:
7772 $ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
7775 @item Prepend @file{/prefix/} to each file name:
7778 $ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
7781 @item Archive the @file{/lib} directory, prepending @samp{/usr/local}
7782 to each archive member:
7785 $ @kbd{tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib}
7789 Notice the use of flags in the last example. The @file{/lib}
7790 directory often contains many symbolic links to files within it.
7791 It may look, for example, like this:
7795 drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
7796 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
7797 lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
7801 Using the expression @samp{s,^,/usr/local/,} would mean adding
7802 @samp{/usr/local} to both regular archive members and to link
7803 targets. In this case, @file{/lib/libc.so.6} would become:
7806 /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
7809 This is definitely not desired. To avoid this, the @samp{S} flag
7810 are used, which excludes symbolic link targets from filename
7811 transformations. The result is:
7814 $ @kbd{tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
7815 --show-transformed /lib}
7816 drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
7817 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
7818 lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 ->
7822 Unlike @option{--strip-components}, @option{--transform} can be used
7823 in any @GNUTAR{} operation mode. For example, the following command
7824 adds files to the archive while replacing the leading @file{usr/}
7825 component with @file{var/}:
7828 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /}
7831 To test @option{--transform} effect we suggest using
7832 @option{--show-transformed-names} option:
7835 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \
7836 --verbose --show-transformed-names /}
7839 If both @option{--strip-components} and @option{--transform} are used
7840 together, then @option{--transform} is applied first, and the required
7841 number of components is then stripped from its result.
7843 You can use as many @option{--transform} options in a single command
7844 line as you want. The specified expressions will then be applied in
7845 order of their appearance. For example, the following two invocations
7849 $ @kbd{tar -cf arch.tar --transform='s,/usr/var,/var/' \
7850 --transform='s,/usr/local,/usr/,'}
7851 $ @kbd{tar -cf arch.tar \
7852 --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'}
7856 @section Operating Only on New Files
7859 @cindex Excluding file by age
7860 @cindex Data Modification time, excluding files by
7861 @cindex Modification time, excluding files by
7862 @cindex Age, excluding files by
7863 The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
7864 @option{-N @var{date}}) option causes @command{tar} to only work on
7865 files whose data modification or status change times are newer than
7866 the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
7867 it is taken to be a file name; the data modification time of that file
7868 is used as the date. If you use this option when creating or appending
7869 to an archive, the archive will only include new files. If you use
7870 @option{--after-date} when extracting an archive, @command{tar} will
7871 only extract files newer than the @var{date} you specify.
7873 If you only want @command{tar} to make the date comparison based on
7874 modification of the file's data (rather than status
7875 changes), then use the @option{--newer-mtime=@var{date}} option.
7877 You may use these options with any operation. Note that these options
7878 differ from the @option{--update} (@option{-u}) operation in that they
7879 allow you to specify a particular date against which @command{tar} can
7880 compare when deciding whether or not to archive the files.
7885 @item --after-date=@var{date}
7886 @itemx --newer=@var{date}
7887 @itemx -N @var{date}
7888 Only store files newer than @var{date}.
7890 Acts on files only if their data modification or status change times are
7891 later than @var{date}. Use in conjunction with any operation.
7893 If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
7894 name; the data modification time of that file is used as the date.
7896 @opindex newer-mtime
7897 @item --newer-mtime=@var{date}
7898 Acts like @option{--after-date}, but only looks at data modification times.
7901 These options limit @command{tar} to operate only on files which have
7902 been modified after the date specified. A file's status is considered to have
7903 changed if its contents have been modified, or if its owner,
7904 permissions, and so forth, have been changed. (For more information on
7905 how to specify a date, see @ref{Date input formats}; remember that the
7906 entire date argument must be quoted if it contains any spaces.)
7908 Gurus would say that @option{--after-date} tests both the data
7909 modification time (@code{mtime}, the time the contents of the file
7910 were last modified) and the status change time (@code{ctime}, the time
7911 the file's status was last changed: owner, permissions, etc.@:)
7912 fields, while @option{--newer-mtime} tests only the @code{mtime}
7915 To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
7916 @code{ctime} and processes the file if either one is more recent than
7917 @var{date}, while @option{--newer-mtime} only checks @code{mtime} and
7918 disregards @code{ctime}. Neither does it use @code{atime} (the last time the
7919 contents of the file were looked at).
7921 Date specifiers can have embedded spaces. Because of this, you may need
7922 to quote date arguments to keep the shell from parsing them as separate
7923 arguments. For example, the following command will add to the archive
7924 all the files modified less than two days ago:
7927 $ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'}
7930 When any of these options is used with the option @option{--verbose}
7931 (@pxref{verbose tutorial}) @GNUTAR{} will try to convert the specified
7932 date back to its textual representation and compare that with the
7933 one given with the option. If the two dates differ, @command{tar} will
7934 print a warning saying what date it will use. This is to help user
7935 ensure he is using the right date. For example:
7939 $ @kbd{tar -c -f archive.tar --after-date='10 days ago' .}
7940 tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
7946 @strong{Please Note:} @option{--after-date} and @option{--newer-mtime}
7947 should not be used for incremental backups. @xref{Incremental Dumps},
7948 for proper way of creating incremental backups.
7952 @section Descending into Directories
7954 @cindex Avoiding recursion in directories
7955 @cindex Descending directories, avoiding
7956 @cindex Directories, avoiding recursion
7957 @cindex Recursion in directories, avoiding
7959 @FIXME{arrggh! this is still somewhat confusing to me. :-< }
7961 Usually, @command{tar} will recursively explore all directories (either
7962 those given on the command line or through the @option{--files-from}
7963 option) for the various files they contain. However, you may not always
7964 want @command{tar} to act this way.
7966 @opindex no-recursion
7967 The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
7968 into specified directories. If you specify @option{--no-recursion}, you can
7969 use the @command{find} utility for hunting through levels of directories to
7970 construct a list of file names which you could then pass to @command{tar}.
7971 @command{find} allows you to be more selective when choosing which files to
7972 archive; see @ref{files}, for more information on using @command{find} with
7973 @command{tar}, or look.
7976 @item --no-recursion
7977 Prevents @command{tar} from recursively descending directories.
7981 Requires @command{tar} to recursively descend directories.
7982 This is the default.
7985 When you use @option{--no-recursion}, @GNUTAR{} grabs
7986 directory entries themselves, but does not descend on them
7987 recursively. Many people use @command{find} for locating files they
7988 want to back up, and since @command{tar} @emph{usually} recursively
7989 descends on directories, they have to use the @samp{@w{-not -type d}}
7990 test in their @command{find} invocation (@pxref{Type, Type, Type test,
7991 find, Finding Files}), as they usually do not want all the files in a
7992 directory. They then use the @option{--files-from} option to archive
7993 the files located via @command{find}.
7995 The problem when restoring files archived in this manner is that the
7996 directories themselves are not in the archive; so the
7997 @option{--same-permissions} (@option{--preserve-permissions},
7998 @option{-p}) option does not affect them---while users might really
7999 like it to. Specifying @option{--no-recursion} is a way to tell
8000 @command{tar} to grab only the directory entries given to it, adding
8001 no new files on its own. To summarize, if you use @command{find} to
8002 create a list of files to be stored in an archive, use it as follows:
8006 $ @kbd{find @var{dir} @var{tests} | \
8007 tar -cf @var{archive} -T - --no-recursion}
8011 The @option{--no-recursion} option also applies when extracting: it
8012 causes @command{tar} to extract only the matched directory entries, not
8013 the files under those directories.
8015 The @option{--no-recursion} option also affects how globbing patterns
8016 are interpreted (@pxref{controlling pattern-matching}).
8018 The @option{--no-recursion} and @option{--recursion} options apply to
8019 later options and operands, and can be overridden by later occurrences
8020 of @option{--no-recursion} and @option{--recursion}. For example:
8023 $ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
8027 creates an archive with one entry for @file{grape}, and the recursive
8028 contents of @file{grape/concord}, but no entries under @file{grape}
8029 other than @file{grape/concord}.
8032 @section Crossing File System Boundaries
8033 @cindex File system boundaries, not crossing
8036 @command{tar} will normally automatically cross file system boundaries in
8037 order to archive files which are part of a directory tree. You can
8038 change this behavior by running @command{tar} and specifying
8039 @option{--one-file-system}. This option only affects files that are
8040 archived because they are in a directory that is being archived;
8041 @command{tar} will still archive files explicitly named on the command line
8042 or through @option{--files-from}, regardless of where they reside.
8045 @opindex one-file-system
8046 @item --one-file-system
8047 Prevents @command{tar} from crossing file system boundaries when
8048 archiving. Use in conjunction with any write operation.
8051 The @option{--one-file-system} option causes @command{tar} to modify its
8052 normal behavior in archiving the contents of directories. If a file in
8053 a directory is not on the same file system as the directory itself, then
8054 @command{tar} will not archive that file. If the file is a directory
8055 itself, @command{tar} will not archive anything beneath it; in other words,
8056 @command{tar} will not cross mount points.
8058 This option is useful for making full or incremental archival backups of
8059 a file system. If this option is used in conjunction with
8060 @option{--verbose} (@option{-v}), files that are excluded are
8061 mentioned by name on the standard error.
8064 * directory:: Changing Directory
8065 * absolute:: Absolute File Names
8069 @subsection Changing the Working Directory
8071 @FIXME{need to read over this node now for continuity; i've switched
8072 things around some.}
8074 @cindex Changing directory mid-stream
8075 @cindex Directory, changing mid-stream
8076 @cindex Working directory, specifying
8077 To change the working directory in the middle of a list of file names,
8078 either on the command line or in a file specified using
8079 @option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
8080 This will change the working directory to the specified directory
8081 after that point in the list.
8085 @item --directory=@var{directory}
8086 @itemx -C @var{directory}
8087 Changes the working directory in the middle of a command line.
8093 $ @kbd{tar -c -f jams.tar grape prune -C food cherry}
8097 will place the files @file{grape} and @file{prune} from the current
8098 directory into the archive @file{jams.tar}, followed by the file
8099 @file{cherry} from the directory @file{food}. This option is especially
8100 useful when you have several widely separated files that you want to
8101 store in the same archive.
8103 Note that the file @file{cherry} is recorded in the archive under the
8104 precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the
8105 archive will contain three files that all appear to have come from the
8106 same directory; if the archive is extracted with plain @samp{tar
8107 --extract}, all three files will be written in the current directory.
8109 Contrast this with the command,
8112 $ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
8116 which records the third file in the archive under the name
8117 @file{red/cherry} so that, if the archive is extracted using
8118 @samp{tar --extract}, the third file will be written in a subdirectory
8119 named @file{orange-colored}.
8121 You can use the @option{--directory} option to make the archive
8122 independent of the original name of the directory holding the files.
8123 The following command places the files @file{/etc/passwd},
8124 @file{/etc/hosts}, and @file{/lib/libc.a} into the archive
8128 $ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
8132 However, the names of the archive members will be exactly what they were
8133 on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}.
8134 They will not appear to be related by file name to the original
8135 directories where those files were located.
8137 Note that @option{--directory} options are interpreted consecutively. If
8138 @option{--directory} specifies a relative file name, it is interpreted
8139 relative to the then current directory, which might not be the same as
8140 the original current working directory of @command{tar}, due to a previous
8141 @option{--directory} option.
8143 When using @option{--files-from} (@pxref{files}), you can put various
8144 @command{tar} options (including @option{-C}) in the file list. Notice,
8145 however, that in this case the option and its argument may not be
8146 separated by whitespace. If you use short option, its argument must
8147 either follow the option letter immediately, without any intervening
8148 whitespace, or occupy the next line. Otherwise, if you use long
8149 option, separate its argument by an equal sign.
8151 For instance, the file list for the above example will be:
8164 To use it, you would invoke @command{tar} as follows:
8167 $ @kbd{tar -c -f foo.tar --files-from list}
8170 The interpretation of @option{--directory} is disabled by
8171 @option{--null} option.
8174 @subsection Absolute File Names
8178 @opindex absolute-names
8179 @item --absolute-names
8181 Do not strip leading slashes from file names, and permit file names
8182 containing a @file{..} file name component.
8185 By default, @GNUTAR{} drops a leading @samp{/} on
8186 input or output, and complains about file names containing a @file{..}
8187 component. This option turns off this behavior.
8189 When @command{tar} extracts archive members from an archive, it strips any
8190 leading slashes (@samp{/}) from the member name. This causes absolute
8191 member names in the archive to be treated as relative file names. This
8192 allows you to have such members extracted wherever you want, instead of
8193 being restricted to extracting the member in the exact directory named
8194 in the archive. For example, if the archive member has the name
8195 @file{/etc/passwd}, @command{tar} will extract it as if the name were
8196 really @file{etc/passwd}.
8198 File names containing @file{..} can cause problems when extracting, so
8199 @command{tar} normally warns you about such files when creating an
8200 archive, and rejects attempts to extracts such files.
8202 Other @command{tar} programs do not do this. As a result, if you
8203 create an archive whose member names start with a slash, they will be
8204 difficult for other people with a non-@GNUTAR{}
8205 program to use. Therefore, @GNUTAR{} also strips
8206 leading slashes from member names when putting members into the
8207 archive. For example, if you ask @command{tar} to add the file
8208 @file{/bin/ls} to an archive, it will do so, but the member name will
8209 be @file{bin/ls}.@footnote{A side effect of this is that when
8210 @option{--create} is used with @option{--verbose} the resulting output
8211 is not, generally speaking, the same as the one you'd get running
8212 @kbd{tar --list} command. This may be important if you use some
8213 scripts for comparing both outputs. @xref{listing member and file names},
8214 for the information on how to handle this case.}
8216 If you use the @option{--absolute-names} (@option{-P}) option,
8217 @command{tar} will do none of these transformations.
8219 To archive or extract files relative to the root directory, specify
8220 the @option{--absolute-names} (@option{-P}) option.
8222 Normally, @command{tar} acts on files relative to the working
8223 directory---ignoring superior directory names when archiving, and
8224 ignoring leading slashes when extracting.
8226 When you specify @option{--absolute-names} (@option{-P}),
8227 @command{tar} stores file names including all superior directory
8228 names, and preserves leading slashes. If you only invoked
8229 @command{tar} from the root directory you would never need the
8230 @option{--absolute-names} option, but using this option
8231 may be more convenient than switching to root.
8233 @FIXME{Should be an example in the tutorial/wizardry section using this
8234 to transfer files between systems.}
8236 @FIXME{Is write access an issue?}
8239 @item --absolute-names
8240 Preserves full file names (including superior directory names) when
8241 archiving files. Preserves leading slash when extracting files.
8245 @FIXME{this is still horrible; need to talk with dan on monday.}
8247 @command{tar} prints out a message about removing the @samp{/} from
8248 file names. This message appears once per @GNUTAR{}
8249 invocation. It represents something which ought to be told; ignoring
8250 what it means can cause very serious surprises, later.
8252 Some people, nevertheless, do not want to see this message. Wanting to
8253 play really dangerously, one may of course redirect @command{tar} standard
8254 error to the sink. For example, under @command{sh}:
8257 $ @kbd{tar -c -f archive.tar /home 2> /dev/null}
8261 Another solution, both nicer and simpler, would be to change to
8262 the @file{/} directory first, and then avoid absolute notation.
8266 $ @kbd{tar -c -f archive.tar -C / home}
8269 @include getdate.texi
8272 @chapter Controlling the Archive Format
8274 @cindex Tar archive formats
8275 Due to historical reasons, there are several formats of tar archives.
8276 All of them are based on the same principles, but have some subtle
8277 differences that often make them incompatible with each other.
8279 GNU tar is able to create and handle archives in a variety of formats.
8280 The most frequently used formats are (in alphabetical order):
8284 Format used by @GNUTAR{} versions up to 1.13.25. This format derived
8285 from an early @acronym{POSIX} standard, adding some improvements such as
8286 sparse file handling and incremental archives. Unfortunately these
8287 features were implemented in a way incompatible with other archive
8290 Archives in @samp{gnu} format are able to hold file names of unlimited
8294 Format used by @GNUTAR{} of versions prior to 1.12.
8297 Archive format, compatible with the V7 implementation of tar. This
8298 format imposes a number of limitations. The most important of them
8302 @item The maximum length of a file name is limited to 99 characters.
8303 @item The maximum length of a symbolic link is limited to 99 characters.
8304 @item It is impossible to store special files (block and character
8305 devices, fifos etc.)
8306 @item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777
8308 @item V7 archives do not contain symbolic ownership information (user
8309 and group name of the file owner).
8312 This format has traditionally been used by Automake when producing
8313 Makefiles. This practice will change in the future, in the meantime,
8314 however this means that projects containing file names more than 99
8315 characters long will not be able to use @GNUTAR{} @value{VERSION} and
8316 Automake prior to 1.9.
8319 Archive format defined by @acronym{POSIX.1-1988} specification. It stores
8320 symbolic ownership information. It is also able to store
8321 special files. However, it imposes several restrictions as well:
8324 @item The maximum length of a file name is limited to 256 characters,
8325 provided that the file name can be split at a directory separator in
8326 two parts, first of them being at most 155 bytes long. So, in most
8327 cases the maximum file name length will be shorter than 256
8329 @item The maximum length of a symbolic link name is limited to
8331 @item Maximum size of a file the archive is able to accommodate
8333 @item Maximum value of UID/GID is 2097151.
8334 @item Maximum number of bits in device major and minor numbers is 21.
8338 Format used by J@"org Schilling @command{star}
8339 implementation. @GNUTAR{} is able to read @samp{star} archives but
8340 currently does not produce them.
8343 Archive format defined by @acronym{POSIX.1-2001} specification. This is the
8344 most flexible and feature-rich format. It does not impose any
8345 restrictions on file sizes or file name lengths. This format is quite
8346 recent, so not all tar implementations are able to handle it properly.
8347 However, this format is designed in such a way that any tar
8348 implementation able to read @samp{ustar} archives will be able to read
8349 most @samp{posix} archives as well, with the only exception that any
8350 additional information (such as long file names etc.) will in such
8351 case be extracted as plain text files along with the files it refers to.
8353 This archive format will be the default format for future versions
8358 The following table summarizes the limitations of each of these
8361 @multitable @columnfractions .10 .20 .20 .20 .20
8362 @headitem Format @tab UID @tab File Size @tab File Name @tab Devn
8363 @item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8364 @item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8365 @item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
8366 @item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
8367 @item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
8370 The default format for @GNUTAR{} is defined at compilation
8371 time. You may check it by running @command{tar --help}, and examining
8372 the last lines of its output. Usually, @GNUTAR{} is configured
8373 to create archives in @samp{gnu} format, however, future version will
8374 switch to @samp{posix}.
8377 * Compression:: Using Less Space through Compression
8378 * Attributes:: Handling File Attributes
8379 * Portability:: Making @command{tar} Archives More Portable
8380 * cpio:: Comparison of @command{tar} and @command{cpio}
8384 @section Using Less Space through Compression
8387 * gzip:: Creating and Reading Compressed Archives
8388 * sparse:: Archiving Sparse Files
8392 @subsection Creating and Reading Compressed Archives
8393 @cindex Compressed archives
8394 @cindex Storing archives in compressed format
8401 @GNUTAR{} is able to create and read compressed archives. It supports
8402 @command{gzip}, @command{bzip2}, @command{lzma} and @command{lzop} compression
8403 programs. For backward compatibility, it also supports
8404 @command{compress} command, although we strongly recommend against
8405 using it, because it is by far less effective than other compression
8406 programs@footnote{It also had patent problems in the past.}.
8408 Creating a compressed archive is simple: you just specify a
8409 @dfn{compression option} along with the usual archive creation
8410 commands. The compression option is @option{-z} (@option{--gzip}) to
8411 create a @command{gzip} compressed archive, @option{-j}
8412 (@option{--bzip2}) to create a @command{bzip2} compressed archive,
8413 @option{-J} (@option{--xz}) to create an @asis{XZ} archive,
8414 @option{--lzma} to create an @asis{LZMA} compressed
8415 archive, @option{--lzop} to create an @asis{LSOP} archive, and
8416 @option{-Z} (@option{--compress}) to use @command{compress} program.
8420 $ @kbd{tar cfz archive.tar.gz .}
8423 You can also let @GNUTAR{} select the compression program basing on
8424 the suffix of the archive file name. This is done using
8425 @option{--auto-compress} (@option{-a}) command line option. For
8426 example, the following invocation will use @command{bzip2} for
8430 $ @kbd{tar cfa archive.tar.bz2 .}
8434 whereas the following one will use @command{lzma}:
8437 $ @kbd{tar cfa archive.tar.lzma .}
8440 For a complete list of file name suffixes recognized by @GNUTAR{},
8441 @ref{auto-compress}.
8443 Reading compressed archive is even simpler: you don't need to specify
8444 any additional options as @GNUTAR{} recognizes its format
8445 automatically. Thus, the following commands will list and extract the
8446 archive created in previous example:
8449 # List the compressed archive
8450 $ @kbd{tar tf archive.tar.gz}
8451 # Extract the compressed archive
8452 $ @kbd{tar xf archive.tar.gz}
8455 The format recognition algorithm is based on @dfn{signatures}, a
8456 special byte sequences in the beginning of file, that are specific for
8457 certain compression formats. If this approach fails, @command{tar}
8458 falls back to using archive name suffix to determine its format
8459 (@xref{auto-compress}, for a list of recognized suffixes).
8461 The only case when you have to specify a decompression option while
8462 reading the archive is when reading from a pipe or from a tape drive
8463 that does not support random access. However, in this case @GNUTAR{}
8464 will indicate which option you should use. For example:
8467 $ @kbd{cat archive.tar.gz | tar tf -}
8468 tar: Archive is compressed. Use -z option
8469 tar: Error is not recoverable: exiting now
8472 If you see such diagnostics, just add the suggested option to the
8473 invocation of @GNUTAR{}:
8476 $ @kbd{cat archive.tar.gz | tar tfz -}
8479 Notice also, that there are several restrictions on operations on
8480 compressed archives. First of all, compressed archives cannot be
8481 modified, i.e., you cannot update (@option{--update} (@option{-u}))
8482 them or delete (@option{--delete}) members from them or
8483 add (@option{--append} (@option{-r})) members to them. Likewise, you
8484 cannot append another @command{tar} archive to a compressed archive using
8485 @option{--concatenate} (@option{-A})). Secondly, multi-volume
8486 archives cannot be compressed.
8488 The following table summarizes compression options used by @GNUTAR{}.
8491 @anchor{auto-compress}
8492 @opindex auto-compress
8493 @item --auto-compress
8495 Select a compression program to use by the archive file name
8496 suffix. The following suffixes are recognized:
8498 @multitable @columnfractions 0.3 0.6
8499 @headitem Suffix @tab Compression program
8500 @item @samp{.gz} @tab @command{gzip}
8501 @item @samp{.tgz} @tab @command{gzip}
8502 @item @samp{.taz} @tab @command{gzip}
8503 @item @samp{.Z} @tab @command{compress}
8504 @item @samp{.taZ} @tab @command{compress}
8505 @item @samp{.bz2} @tab @command{bzip2}
8506 @item @samp{.tz2} @tab @command{bzip2}
8507 @item @samp{.tbz2} @tab @command{bzip2}
8508 @item @samp{.tbz} @tab @command{bzip2}
8509 @item @samp{.lzma} @tab @command{lzma}
8510 @item @samp{.tlz} @tab @command{lzma}
8511 @item @samp{.lzo} @tab @command{lzop}
8512 @item @samp{.xz} @tab @command{xz}
8520 Filter the archive through @command{gzip}.
8522 You can use @option{--gzip} and @option{--gunzip} on physical devices
8523 (tape drives, etc.) and remote files as well as on normal files; data
8524 to or from such devices or remote files is reblocked by another copy
8525 of the @command{tar} program to enforce the specified (or default) record
8526 size. The default compression parameters are used; if you need to
8527 override them, set @env{GZIP} environment variable, e.g.:
8530 $ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
8534 Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
8535 @command{gzip} explicitly:
8538 $ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
8541 @cindex corrupted archives
8542 About corrupted compressed archives: @command{gzip}'ed files have no
8543 redundancy, for maximum compression. The adaptive nature of the
8544 compression scheme means that the compression tables are implicitly
8545 spread all over the archive. If you lose a few blocks, the dynamic
8546 construction of the compression tables becomes unsynchronized, and there
8547 is little chance that you could recover later in the archive.
8549 There are pending suggestions for having a per-volume or per-file
8550 compression in @GNUTAR{}. This would allow for viewing the
8551 contents without decompression, and for resynchronizing decompression at
8552 every volume or file, in case of corrupted archives. Doing so, we might
8553 lose some compressibility. But this would have make recovering easier.
8554 So, there are pros and cons. We'll see!
8559 Filter the archive through @code{xz}. Otherwise like
8564 Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
8568 Filter the archive through @command{lzma}. Otherwise like @option{--gzip}.
8572 Filter the archive through @command{lzop}. Otherwise like
8580 Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
8582 @opindex use-compress-program
8583 @item --use-compress-program=@var{prog}
8584 @itemx -I=@var{prog}
8585 Use external compression program @var{prog}. Use this option if you
8586 have a compression program that @GNUTAR{} does not support. There
8587 are two requirements to which @var{prog} should comply:
8589 First, when called without options, it should read data from standard
8590 input, compress it and output it on standard output.
8592 Secondly, if called with @option{-d} argument, it should do exactly
8593 the opposite, i.e., read the compressed data from the standard input
8594 and produce uncompressed data on the standard output.
8597 @cindex gpg, using with tar
8598 @cindex gnupg, using with tar
8599 @cindex Using encrypted archives
8600 The @option{--use-compress-program} option, in particular, lets you
8601 implement your own filters, not necessarily dealing with
8602 compression/decompression. For example, suppose you wish to implement
8603 PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
8604 gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard
8605 Manual}). The following script does that:
8611 -d) gpg --decrypt - | gzip -d -c;;
8612 '') gzip -c | gpg -s ;;
8613 *) echo "Unknown option $1">&2; exit 1;;
8618 Suppose you name it @file{gpgz} and save it somewhere in your
8619 @env{PATH}. Then the following command will create a compressed
8620 archive signed with your private key:
8623 $ @kbd{tar -cf foo.tar.gpgz -Igpgz .}
8627 Likewise, the command below will list its contents:
8630 $ @kbd{tar -tf foo.tar.gpgz -Igpgz .}
8634 The above is based on the following discussion:
8636 I have one question, or maybe it's a suggestion if there isn't a way
8637 to do it now. I would like to use @option{--gzip}, but I'd also like
8638 the output to be fed through a program like @acronym{GNU}
8639 @command{ecc} (actually, right now that's @samp{exactly} what I'd like
8640 to use :-)), basically adding ECC protection on top of compression.
8641 It seems as if this should be quite easy to do, but I can't work out
8642 exactly how to go about it. Of course, I can pipe the standard output
8643 of @command{tar} through @command{ecc}, but then I lose (though I
8644 haven't started using it yet, I confess) the ability to have
8645 @command{tar} use @command{rmt} for it's I/O (I think).
8647 I think the most straightforward thing would be to let me specify a
8648 general set of filters outboard of compression (preferably ordered,
8649 so the order can be automatically reversed on input operations, and
8650 with the options they require specifiable), but beggars shouldn't be
8651 choosers and anything you decide on would be fine with me.
8653 By the way, I like @command{ecc} but if (as the comments say) it can't
8654 deal with loss of block sync, I'm tempted to throw some time at adding
8655 that capability. Supposing I were to actually do such a thing and
8656 get it (apparently) working, do you accept contributed changes to
8657 utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
8659 Isn't that exactly the role of the
8660 @option{--use-compress-prog=@var{program}} option?
8661 I never tried it myself, but I suspect you may want to write a
8662 @var{prog} script or program able to filter stdin to stdout to
8663 way you want. It should recognize the @option{-d} option, for when
8664 extraction is needed rather than creation.
8666 It has been reported that if one writes compressed data (through the
8667 @option{--gzip} or @option{--compress} options) to a DLT and tries to use
8668 the DLT compression mode, the data will actually get bigger and one will
8669 end up with less space on the tape.
8673 @subsection Archiving Sparse Files
8674 @cindex Sparse Files
8676 Files in the file system occasionally have @dfn{holes}. A @dfn{hole}
8677 in a file is a section of the file's contents which was never written.
8678 The contents of a hole reads as all zeros. On many operating systems,
8679 actual disk storage is not allocated for holes, but they are counted
8680 in the length of the file. If you archive such a file, @command{tar}
8681 could create an archive longer than the original. To have @command{tar}
8682 attempt to recognize the holes in a file, use @option{--sparse}
8683 (@option{-S}). When you use this option, then, for any file using
8684 less disk space than would be expected from its length, @command{tar}
8685 searches the file for consecutive stretches of zeros. It then records
8686 in the archive for the file where the consecutive stretches of zeros
8687 are, and only archives the ``real contents'' of the file. On
8688 extraction (using @option{--sparse} is not needed on extraction) any
8689 such files have holes created wherever the continuous stretches of zeros
8690 were found. Thus, if you use @option{--sparse}, @command{tar} archives
8691 won't take more space than the original.
8697 This option instructs @command{tar} to test each file for sparseness
8698 before attempting to archive it. If the file is found to be sparse it
8699 is treated specially, thus allowing to decrease the amount of space
8700 used by its image in the archive.
8702 This option is meaningful only when creating or updating archives. It
8703 has no effect on extraction.
8706 Consider using @option{--sparse} when performing file system backups,
8707 to avoid archiving the expanded forms of files stored sparsely in the
8710 Even if your system has no sparse files currently, some may be
8711 created in the future. If you use @option{--sparse} while making file
8712 system backups as a matter of course, you can be assured the archive
8713 will never take more space on the media than the files take on disk
8714 (otherwise, archiving a disk filled with sparse files might take
8715 hundreds of tapes). @xref{Incremental Dumps}.
8717 However, be aware that @option{--sparse} option presents a serious
8718 drawback. Namely, in order to determine if the file is sparse
8719 @command{tar} has to read it before trying to archive it, so in total
8720 the file is read @strong{twice}. So, always bear in mind that the
8721 time needed to process all files with this option is roughly twice
8722 the time needed to archive them without it.
8723 @FIXME{A technical note:
8725 Programs like @command{dump} do not have to read the entire file; by
8726 examining the file system directly, they can determine in advance
8727 exactly where the holes are and thus avoid reading through them. The
8728 only data it need read are the actual allocated data blocks.
8729 @GNUTAR{} uses a more portable and straightforward
8730 archiving approach, it would be fairly difficult that it does
8731 otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, on
8735 What I did say is that you cannot tell the difference between a hole and an
8736 equivalent number of nulls without reading raw blocks. @code{st_blocks} at
8737 best tells you how many holes there are; it doesn't tell you @emph{where}.
8738 Just as programs may, conceivably, care what @code{st_blocks} is (care
8739 to name one that does?), they may also care where the holes are (I have
8740 no examples of this one either, but it's equally imaginable).
8742 I conclude from this that good archivers are not portable. One can
8743 arguably conclude that if you want a portable program, you can in good
8744 conscience restore files with as many holes as possible, since you can't
8749 @cindex sparse formats, defined
8750 When using @samp{POSIX} archive format, @GNUTAR{} is able to store
8751 sparse files using in three distinct ways, called @dfn{sparse
8752 formats}. A sparse format is identified by its @dfn{number},
8753 consisting, as usual of two decimal numbers, delimited by a dot. By
8754 default, format @samp{1.0} is used. If, for some reason, you wish to
8755 use an earlier format, you can select it using
8756 @option{--sparse-version} option.
8759 @opindex sparse-version
8760 @item --sparse-version=@var{version}
8762 Select the format to store sparse files in. Valid @var{version} values
8763 are: @samp{0.0}, @samp{0.1} and @samp{1.0}. @xref{Sparse Formats},
8764 for a detailed description of each format.
8767 Using @option{--sparse-format} option implies @option{--sparse}.
8770 @section Handling File Attributes
8773 When @command{tar} reads files, it updates their access times. To
8774 avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
8775 reset the access time retroactively or avoid changing it in the first
8778 Handling of file attributes
8781 @opindex atime-preserve
8782 @item --atime-preserve
8783 @itemx --atime-preserve=replace
8784 @itemx --atime-preserve=system
8785 Preserve the access times of files that are read. This works only for
8786 files that you own, unless you have superuser privileges.
8788 @option{--atime-preserve=replace} works on most systems, but it also
8789 restores the data modification time and updates the status change
8790 time. Hence it doesn't interact with incremental dumps nicely
8791 (@pxref{Incremental Dumps}), and it can set access or data modification times
8792 incorrectly if other programs access the file while @command{tar} is
8795 @option{--atime-preserve=system} avoids changing the access time in
8796 the first place, if the operating system supports this.
8797 Unfortunately, this may or may not work on any given operating system
8798 or file system. If @command{tar} knows for sure it won't work, it
8799 complains right away.
8801 Currently @option{--atime-preserve} with no operand defaults to
8802 @option{--atime-preserve=replace}, but this is intended to change to
8803 @option{--atime-preserve=system} when the latter is better-supported.
8808 Do not extract data modification time.
8810 When this option is used, @command{tar} leaves the data modification times
8811 of the files it extracts as the times when the files were extracted,
8812 instead of setting it to the times recorded in the archive.
8814 This option is meaningless with @option{--list} (@option{-t}).
8818 Create extracted files with the same ownership they have in the
8821 This is the default behavior for the superuser,
8822 so this option is meaningful only for non-root users, when @command{tar}
8823 is executed on those systems able to give files away. This is
8824 considered as a security flaw by many people, at least because it
8825 makes quite difficult to correctly account users for the disk space
8826 they occupy. Also, the @code{suid} or @code{sgid} attributes of
8827 files are easily and silently lost when files are given away.
8829 When writing an archive, @command{tar} writes the user @acronym{ID} and user name
8830 separately. If it can't find a user name (because the user @acronym{ID} is not
8831 in @file{/etc/passwd}), then it does not write one. When restoring,
8832 it tries to look the name (if one was written) up in
8833 @file{/etc/passwd}. If it fails, then it uses the user @acronym{ID} stored in
8834 the archive instead.
8836 @opindex no-same-owner
8837 @item --no-same-owner
8839 Do not attempt to restore ownership when extracting. This is the
8840 default behavior for ordinary users, so this option has an effect
8841 only for the superuser.
8843 @opindex numeric-owner
8844 @item --numeric-owner
8845 The @option{--numeric-owner} option allows (ANSI) archives to be written
8846 without user/group name information or such information to be ignored
8847 when extracting. It effectively disables the generation and/or use
8848 of user/group name information. This option forces extraction using
8849 the numeric ids from the archive, ignoring the names.
8851 This is useful in certain circumstances, when restoring a backup from
8852 an emergency floppy with different passwd/group files for example.
8853 It is otherwise impossible to extract files with the right ownerships
8854 if the password file in use during the extraction does not match the
8855 one belonging to the file system(s) being extracted. This occurs,
8856 for example, if you are restoring your files after a major crash and
8857 had booted from an emergency floppy with no password file or put your
8858 disk into another machine to do the restore.
8860 The numeric ids are @emph{always} saved into @command{tar} archives.
8861 The identifying names are added at create time when provided by the
8862 system, unless @option{--old-archive} (@option{-o}) is used. Numeric ids could be
8863 used when moving archives between a collection of machines using
8864 a centralized management for attribution of numeric ids to users
8865 and groups. This is often made through using the NIS capabilities.
8867 When making a @command{tar} file for distribution to other sites, it
8868 is sometimes cleaner to use a single owner for all files in the
8869 distribution, and nicer to specify the write permission bits of the
8870 files as stored in the archive independently of their actual value on
8871 the file system. The way to prepare a clean distribution is usually
8872 to have some Makefile rule creating a directory, copying all needed
8873 files in that directory, then setting ownership and permissions as
8874 wanted (there are a lot of possible schemes), and only then making a
8875 @command{tar} archive out of this directory, before cleaning
8876 everything out. Of course, we could add a lot of options to
8877 @GNUTAR{} for fine tuning permissions and ownership.
8878 This is not the good way, I think. @GNUTAR{} is
8879 already crowded with options and moreover, the approach just explained
8880 gives you a great deal of control already.
8882 @xopindex{same-permissions, short description}
8883 @xopindex{preserve-permissions, short description}
8885 @itemx --same-permissions
8886 @itemx --preserve-permissions
8887 Extract all protection information.
8889 This option causes @command{tar} to set the modes (access permissions) of
8890 extracted files exactly as recorded in the archive. If this option
8891 is not used, the current @code{umask} setting limits the permissions
8892 on extracted files. This option is by default enabled when
8893 @command{tar} is executed by a superuser.
8896 This option is meaningless with @option{--list} (@option{-t}).
8900 Same as both @option{--same-permissions} and @option{--same-order}.
8902 This option is deprecated, and will be removed in @GNUTAR{} version 1.23.
8907 @section Making @command{tar} Archives More Portable
8909 Creating a @command{tar} archive on a particular system that is meant to be
8910 useful later on many other machines and with other versions of @command{tar}
8911 is more challenging than you might think. @command{tar} archive formats
8912 have been evolving since the first versions of Unix. Many such formats
8913 are around, and are not always compatible with each other. This section
8914 discusses a few problems, and gives some advice about making @command{tar}
8915 archives more portable.
8917 One golden rule is simplicity. For example, limit your @command{tar}
8918 archives to contain only regular files and directories, avoiding
8919 other kind of special files. Do not attempt to save sparse files or
8920 contiguous files as such. Let's discuss a few more problems, in turn.
8922 @FIXME{Discuss GNU extensions (incremental backups, multi-volume
8923 archives and archive labels) in GNU and PAX formats.}
8926 * Portable Names:: Portable Names
8927 * dereference:: Symbolic Links
8928 * hard links:: Hard Links
8929 * old:: Old V7 Archives
8930 * ustar:: Ustar Archives
8931 * gnu:: GNU and old GNU format archives.
8932 * posix:: @acronym{POSIX} archives
8933 * Checksumming:: Checksumming Problems
8934 * Large or Negative Values:: Large files, negative time stamps, etc.
8935 * Other Tars:: How to Extract GNU-Specific Data Using
8936 Other @command{tar} Implementations
8939 @node Portable Names
8940 @subsection Portable Names
8942 Use portable file and member names. A name is portable if it contains
8943 only @acronym{ASCII} letters and digits, @samp{/}, @samp{.}, @samp{_}, and
8944 @samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
8945 contain @samp{/-}. Avoid deep directory nesting. For portability to
8946 old Unix hosts, limit your file name components to 14 characters or
8949 If you intend to have your @command{tar} archives to be read under
8950 MSDOS, you should not rely on case distinction for file names, and you
8951 might use the @acronym{GNU} @command{doschk} program for helping you
8952 further diagnosing illegal MSDOS names, which are even more limited
8956 @subsection Symbolic Links
8957 @cindex File names, using symbolic links
8958 @cindex Symbolic link as file name
8960 @opindex dereference
8961 Normally, when @command{tar} archives a symbolic link, it writes a
8962 block to the archive naming the target of the link. In that way, the
8963 @command{tar} archive is a faithful record of the file system contents.
8964 @option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
8965 @command{tar} to archive the files symbolic links point to, instead of
8966 the links themselves. When this option is used, when @command{tar}
8967 encounters a symbolic link, it will archive the linked-to file,
8968 instead of simply recording the presence of a symbolic link.
8970 The name under which the file is stored in the file system is not
8971 recorded in the archive. To record both the symbolic link name and
8972 the file name in the system, archive the file under both names. If
8973 all links were recorded automatically by @command{tar}, an extracted file
8974 might be linked to a file name that no longer exists in the file
8977 If a linked-to file is encountered again by @command{tar} while creating
8978 the same archive, an entire second copy of it will be stored. (This
8979 @emph{might} be considered a bug.)
8981 So, for portable archives, do not archive symbolic links as such,
8982 and use @option{--dereference} (@option{-h}): many systems do not support
8983 symbolic links, and moreover, your distribution might be unusable if
8984 it contains unresolved symbolic links.
8987 @subsection Hard Links
8989 @cindex File names, using hard links
8990 @cindex hard links, dereferencing
8991 @cindex dereferencing hard links
8993 Normally, when @command{tar} archives a hard link, it writes a
8994 block to the archive naming the target of the link (a @samp{1} type
8995 block). In that way, the actual file contents is stored in file only
8996 once. For example, consider the following two files:
9001 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 one
9002 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 jeden
9006 Here, @file{jeden} is a link to @file{one}. When archiving this
9007 directory with a verbose level 2, you will get an output similar to
9011 $ tar cfvv ../archive.tar .
9012 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9013 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9014 hrw-r--r-- gray/staff 0 2007-10-30 15:11 ./one link to ./jeden
9017 The last line shows that, instead of storing two copies of the file,
9018 @command{tar} stored it only once, under the name @file{jeden}, and
9019 stored file @file{one} as a hard link to this file.
9021 It may be important to know that all hard links to the given file are
9022 stored in the archive. For example, this may be necessary for exact
9023 reproduction of the file system. The following option does that:
9026 @xopindex{check-links, described}
9029 Check the number of links dumped for each processed file. If this
9030 number does not match the total number of hard links for the file, print
9034 For example, trying to archive only file @file{jeden} with this option
9035 produces the following diagnostics:
9038 $ tar -c -f ../archive.tar jeden
9039 tar: Missing links to `jeden'.
9042 Although creating special records for hard links helps keep a faithful
9043 record of the file system contents and makes archives more compact, it
9044 may present some difficulties when extracting individual members from
9045 the archive. For example, trying to extract file @file{one} from the
9046 archive created in previous examples produces, in the absense of file
9050 $ tar xf archive.tar ./one
9051 tar: ./one: Cannot hard link to `./jeden': No such file or directory
9052 tar: Error exit delayed from previous errors
9055 The reason for this behavior is that @command{tar} cannot seek back in
9056 the archive to the previous member (in this case, @file{one}), to
9057 extract it@footnote{There are plans to fix this in future releases.}.
9058 If you wish to avoid such problems at the cost of a bigger archive,
9059 use the following option:
9062 @xopindex{hard-dereference, described}
9063 @item --hard-dereference
9064 Dereference hard links and store the files they refer to.
9067 For example, trying this option on our two sample files, we get two
9068 copies in the archive, each of which can then be extracted
9069 independently of the other:
9073 $ tar -c -vv -f ../archive.tar --hard-dereference .
9074 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9075 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9076 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./one
9081 @subsection Old V7 Archives
9082 @cindex Format, old style
9083 @cindex Old style format
9084 @cindex Old style archives
9085 @cindex v7 archive format
9087 Certain old versions of @command{tar} cannot handle additional
9088 information recorded by newer @command{tar} programs. To create an
9089 archive in V7 format (not ANSI), which can be read by these old
9090 versions, specify the @option{--format=v7} option in
9091 conjunction with the @option{--create} (@option{-c}) (@command{tar} also
9092 accepts @option{--portability} or @option{--old-archive} for this
9093 option). When you specify it,
9094 @command{tar} leaves out information about directories, pipes, fifos,
9095 contiguous files, and device files, and specifies file ownership by
9096 group and user IDs instead of group and user names.
9098 When updating an archive, do not use @option{--format=v7}
9099 unless the archive was created using this option.
9101 In most cases, a @emph{new} format archive can be read by an @emph{old}
9102 @command{tar} program without serious trouble, so this option should
9103 seldom be needed. On the other hand, most modern @command{tar}s are
9104 able to read old format archives, so it might be safer for you to
9105 always use @option{--format=v7} for your distributions. Notice,
9106 however, that @samp{ustar} format is a better alternative, as it is
9107 free from many of @samp{v7}'s drawbacks.
9110 @subsection Ustar Archive Format
9112 @cindex ustar archive format
9113 Archive format defined by @acronym{POSIX}.1-1988 specification is called
9114 @code{ustar}. Although it is more flexible than the V7 format, it
9115 still has many restrictions (@xref{Formats,ustar}, for the detailed
9116 description of @code{ustar} format). Along with V7 format,
9117 @code{ustar} format is a good choice for archives intended to be read
9118 with other implementations of @command{tar}.
9120 To create archive in @code{ustar} format, use @option{--format=ustar}
9121 option in conjunction with the @option{--create} (@option{-c}).
9124 @subsection @acronym{GNU} and old @GNUTAR{} format
9126 @cindex GNU archive format
9127 @cindex Old GNU archive format
9128 @GNUTAR{} was based on an early draft of the
9129 @acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
9130 @command{tar}, such as the support for file names longer than 100
9131 characters, use portions of the @command{tar} header record which were
9132 specified in that @acronym{POSIX} draft as unused. Subsequent changes in
9133 @acronym{POSIX} have allocated the same parts of the header record for
9134 other purposes. As a result, @GNUTAR{} format is
9135 incompatible with the current @acronym{POSIX} specification, and with
9136 @command{tar} programs that follow it.
9138 In the majority of cases, @command{tar} will be configured to create
9139 this format by default. This will change in future releases, since
9140 we plan to make @samp{POSIX} format the default.
9142 To force creation a @GNUTAR{} archive, use option
9143 @option{--format=gnu}.
9146 @subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
9148 @cindex POSIX archive format
9149 @cindex PAX archive format
9150 Starting from version 1.14 @GNUTAR{} features full support for
9151 @acronym{POSIX.1-2001} archives.
9153 A @acronym{POSIX} conformant archive will be created if @command{tar}
9154 was given @option{--format=posix} (@option{--format=pax}) option. No
9155 special option is required to read and extract from a @acronym{POSIX}
9159 * PAX keywords:: Controlling Extended Header Keywords.
9163 @subsubsection Controlling Extended Header Keywords
9167 @item --pax-option=@var{keyword-list}
9168 Handle keywords in @acronym{PAX} extended headers. This option is
9169 equivalent to @option{-o} option of the @command{pax} utility.
9172 @var{Keyword-list} is a comma-separated
9173 list of keyword options, each keyword option taking one of
9174 the following forms:
9177 @item delete=@var{pattern}
9178 When used with one of archive-creation commands,
9179 this option instructs @command{tar} to omit from extended header records
9180 that it produces any keywords matching the string @var{pattern}.
9182 When used in extract or list mode, this option instructs tar
9183 to ignore any keywords matching the given @var{pattern} in the extended
9184 header records. In both cases, matching is performed using the pattern
9185 matching notation described in @acronym{POSIX 1003.2}, 3.13
9186 (@pxref{wildcards}). For example:
9189 --pax-option delete=security.*
9192 would suppress security-related information.
9194 @item exthdr.name=@var{string}
9196 This keyword allows user control over the name that is written into the
9197 ustar header blocks for the extended headers. The name is obtained
9198 from @var{string} after making the following substitutions:
9200 @multitable @columnfractions .25 .55
9201 @headitem Meta-character @tab Replaced By
9202 @item %d @tab The directory name of the file, equivalent to the
9203 result of the @command{dirname} utility on the translated file name.
9204 @item %f @tab The name of the file with the directory information
9205 stripped, equivalent to the result of the @command{basename} utility
9206 on the translated file name.
9207 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9208 @item %% @tab A @samp{%} character.
9211 Any other @samp{%} characters in @var{string} produce undefined
9214 If no option @samp{exthdr.name=string} is specified, @command{tar}
9215 will use the following default value:
9221 @item globexthdr.name=@var{string}
9222 This keyword allows user control over the name that is written into
9223 the ustar header blocks for global extended header records. The name
9224 is obtained from the contents of @var{string}, after making
9225 the following substitutions:
9227 @multitable @columnfractions .25 .55
9228 @headitem Meta-character @tab Replaced By
9229 @item %n @tab An integer that represents the
9230 sequence number of the global extended header record in the archive,
9232 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9233 @item %% @tab A @samp{%} character.
9236 Any other @samp{%} characters in @var{string} produce undefined results.
9238 If no option @samp{globexthdr.name=string} is specified, @command{tar}
9239 will use the following default value:
9242 $TMPDIR/GlobalHead.%p.%n
9246 where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
9247 environment variable. If @var{TMPDIR} is not set, @command{tar}
9250 @item @var{keyword}=@var{value}
9251 When used with one of archive-creation commands, these keyword/value pairs
9252 will be included at the beginning of the archive in a global extended
9253 header record. When used with one of archive-reading commands,
9254 @command{tar} will behave as if it has encountered these keyword/value
9255 pairs at the beginning of the archive in a global extended header
9258 @item @var{keyword}:=@var{value}
9259 When used with one of archive-creation commands, these keyword/value pairs
9260 will be included as records at the beginning of an extended header for
9261 each file. This is effectively equivalent to @var{keyword}=@var{value}
9262 form except that it creates no global extended header records.
9264 When used with one of archive-reading commands, @command{tar} will
9265 behave as if these keyword/value pairs were included as records at the
9266 end of each extended header; thus, they will override any global or
9267 file-specific extended header record keywords of the same names.
9268 For example, in the command:
9271 tar --format=posix --create \
9272 --file archive --pax-option gname:=user .
9275 the group name will be forced to a new value for all files
9276 stored in the archive.
9280 @subsection Checksumming Problems
9282 SunOS and HP-UX @command{tar} fail to accept archives created using
9283 @GNUTAR{} and containing non-@acronym{ASCII} file names, that
9284 is, file names having characters with the eight bit set, because they
9285 use signed checksums, while @GNUTAR{} uses unsigned
9286 checksums while creating archives, as per @acronym{POSIX} standards. On
9287 reading, @GNUTAR{} computes both checksums and
9288 accepts any. It is somewhat worrying that a lot of people may go
9289 around doing backup of their files using faulty (or at least
9290 non-standard) software, not learning about it until it's time to
9291 restore their missing files with an incompatible file extractor, or
9294 @GNUTAR{} compute checksums both ways, and accept
9295 any on read, so @acronym{GNU} tar can read Sun tapes even with their
9296 wrong checksums. @GNUTAR{} produces the standard
9297 checksum, however, raising incompatibilities with Sun. That is to
9298 say, @GNUTAR{} has not been modified to
9299 @emph{produce} incorrect archives to be read by buggy @command{tar}'s.
9300 I've been told that more recent Sun @command{tar} now read standard
9301 archives, so maybe Sun did a similar patch, after all?
9303 The story seems to be that when Sun first imported @command{tar}
9304 sources on their system, they recompiled it without realizing that
9305 the checksums were computed differently, because of a change in
9306 the default signing of @code{char}'s in their compiler. So they
9307 started computing checksums wrongly. When they later realized their
9308 mistake, they merely decided to stay compatible with it, and with
9309 themselves afterwards. Presumably, but I do not really know, HP-UX
9310 has chosen that their @command{tar} archives to be compatible with Sun's.
9311 The current standards do not favor Sun @command{tar} format. In any
9312 case, it now falls on the shoulders of SunOS and HP-UX users to get
9313 a @command{tar} able to read the good archives they receive.
9315 @node Large or Negative Values
9316 @subsection Large or Negative Values
9317 @cindex large values
9318 @cindex future time stamps
9319 @cindex negative time stamps
9322 The above sections suggest to use @samp{oldest possible} archive
9323 format if in doubt. However, sometimes it is not possible. If you
9324 attempt to archive a file whose metadata cannot be represented using
9325 required format, @GNUTAR{} will print error message and ignore such a
9326 file. You will than have to switch to a format that is able to
9327 handle such values. The format summary table (@pxref{Formats}) will
9330 In particular, when trying to archive files larger than 8GB or with
9331 timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
9332 12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
9333 @acronym{POSIX} archive formats. When considering which format to
9334 choose, bear in mind that the @acronym{GNU} format uses
9335 two's-complement base-256 notation to store values that do not fit
9336 into standard @acronym{ustar} range. Such archives can generally be
9337 read only by a @GNUTAR{} implementation. Moreover, they sometimes
9338 cannot be correctly restored on another hosts even by @GNUTAR{}. For
9339 example, using two's complement representation for negative time
9340 stamps that assumes a signed 32-bit @code{time_t} generates archives
9341 that are not portable to hosts with differing @code{time_t}
9344 On the other hand, @acronym{POSIX} archives, generally speaking, can
9345 be extracted by any tar implementation that understands older
9346 @acronym{ustar} format. The only exception are files larger than 8GB.
9348 @FIXME{Describe how @acronym{POSIX} archives are extracted by non
9352 @subsection How to Extract GNU-Specific Data Using Other @command{tar} Implementations
9354 In previous sections you became acquainted with various quirks
9355 necessary to make your archives portable. Sometimes you may need to
9356 extract archives containing GNU-specific members using some
9357 third-party @command{tar} implementation or an older version of
9358 @GNUTAR{}. Of course your best bet is to have @GNUTAR{} installed,
9359 but if it is for some reason impossible, this section will explain
9360 how to cope without it.
9362 When we speak about @dfn{GNU-specific} members we mean two classes of
9363 them: members split between the volumes of a multi-volume archive and
9364 sparse members. You will be able to always recover such members if
9365 the archive is in PAX format. In addition split members can be
9366 recovered from archives in old GNU format. The following subsections
9367 describe the required procedures in detail.
9370 * Split Recovery:: Members Split Between Volumes
9371 * Sparse Recovery:: Sparse Members
9374 @node Split Recovery
9375 @subsubsection Extracting Members Split Between Volumes
9377 @cindex Mutli-volume archives, extracting using non-GNU tars
9378 If a member is split between several volumes of an old GNU format archive
9379 most third party @command{tar} implementation will fail to extract
9380 it. To extract it, use @command{tarcat} program (@pxref{Tarcat}).
9381 This program is available from
9382 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tarcat.html, @GNUTAR{}
9383 home page}. It concatenates several archive volumes into a single
9384 valid archive. For example, if you have three volumes named from
9385 @file{vol-1.tar} to @file{vol-3.tar}, you can do the following to
9386 extract them using a third-party @command{tar}:
9389 $ @kbd{tarcat vol-1.tar vol-2.tar vol-3.tar | tar xf -}
9392 @cindex Mutli-volume archives in PAX format, extracting using non-GNU tars
9393 You could use this approach for most (although not all) PAX
9394 format archives as well. However, extracting split members from a PAX
9395 archive is a much easier task, because PAX volumes are constructed in
9396 such a way that each part of a split member is extracted to a
9397 different file by @command{tar} implementations that are not aware of
9398 GNU extensions. More specifically, the very first part retains its
9399 original name, and all subsequent parts are named using the pattern:
9402 %d/GNUFileParts.%p/%f.%n
9406 where symbols preceeded by @samp{%} are @dfn{macro characters} that
9407 have the following meaning:
9409 @multitable @columnfractions .25 .55
9410 @headitem Meta-character @tab Replaced By
9411 @item %d @tab The directory name of the file, equivalent to the
9412 result of the @command{dirname} utility on its full name.
9413 @item %f @tab The file name of the file, equivalent to the result
9414 of the @command{basename} utility on its full name.
9415 @item %p @tab The process @acronym{ID} of the @command{tar} process that
9416 created the archive.
9417 @item %n @tab Ordinal number of this particular part.
9420 For example, if the file @file{var/longfile} was split during archive
9421 creation between three volumes, and the creator @command{tar} process
9422 had process @acronym{ID} @samp{27962}, then the member names will be:
9426 var/GNUFileParts.27962/longfile.1
9427 var/GNUFileParts.27962/longfile.2
9430 When you extract your archive using a third-party @command{tar}, these
9431 files will be created on your disk, and the only thing you will need
9432 to do to restore your file in its original form is concatenate them in
9433 the proper order, for example:
9438 $ @kbd{cat GNUFileParts.27962/longfile.1 \
9439 GNUFileParts.27962/longfile.2 >> longfile}
9440 $ rm -f GNUFileParts.27962
9444 Notice, that if the @command{tar} implementation you use supports PAX
9445 format archives, it will probably emit warnings about unknown keywords
9446 during extraction. They will look like this:
9451 Unknown extended header keyword 'GNU.volume.filename' ignored.
9452 Unknown extended header keyword 'GNU.volume.size' ignored.
9453 Unknown extended header keyword 'GNU.volume.offset' ignored.
9458 You can safely ignore these warnings.
9460 If your @command{tar} implementation is not PAX-aware, you will get
9461 more warnings and more files generated on your disk, e.g.:
9465 $ @kbd{tar xf vol-1.tar}
9466 var/PaxHeaders.27962/longfile: Unknown file type 'x', extracted as
9468 Unexpected EOF in archive
9469 $ @kbd{tar xf vol-2.tar}
9470 tmp/GlobalHead.27962.1: Unknown file type 'g', extracted as normal file
9471 GNUFileParts.27962/PaxHeaders.27962/sparsefile.1: Unknown file type
9472 'x', extracted as normal file
9476 Ignore these warnings. The @file{PaxHeaders.*} directories created
9477 will contain files with @dfn{extended header keywords} describing the
9478 extracted files. You can delete them, unless they describe sparse
9479 members. Read further to learn more about them.
9481 @node Sparse Recovery
9482 @subsubsection Extracting Sparse Members
9484 @cindex sparse files, extracting with non-GNU tars
9485 Any @command{tar} implementation will be able to extract sparse members from a
9486 PAX archive. However, the extracted files will be @dfn{condensed},
9487 i.e., any zero blocks will be removed from them. When we restore such
9488 a condensed file to its original form, by adding zero blocks (or
9489 @dfn{holes}) back to their original locations, we call this process
9490 @dfn{expanding} a compressed sparse file.
9493 To expand a file, you will need a simple auxiliary program called
9494 @command{xsparse}. It is available in source form from
9495 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/xsparse.html, @GNUTAR{}
9498 @cindex sparse files v.1.0, extracting with non-GNU tars
9499 Let's begin with archive members in @dfn{sparse format
9500 version 1.0}@footnote{@xref{PAX 1}.}, which are the easiest to expand.
9501 The condensed file will contain both file map and file data, so no
9502 additional data will be needed to restore it. If the original file
9503 name was @file{@var{dir}/@var{name}}, then the condensed file will be
9504 named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
9505 @var{n} is a decimal number@footnote{technically speaking, @var{n} is a
9506 @dfn{process @acronym{ID}} of the @command{tar} process which created the
9507 archive (@pxref{PAX keywords}).}.
9509 To expand a version 1.0 file, run @command{xsparse} as follows:
9512 $ @kbd{xsparse @file{cond-file}}
9516 where @file{cond-file} is the name of the condensed file. The utility
9517 will deduce the name for the resulting expanded file using the
9518 following algorithm:
9521 @item If @file{cond-file} does not contain any directories,
9522 @file{../cond-file} will be used;
9524 @item If @file{cond-file} has the form
9525 @file{@var{dir}/@var{t}/@var{name}}, where both @var{t} and @var{name}
9526 are simple names, with no @samp{/} characters in them, the output file
9527 name will be @file{@var{dir}/@var{name}}.
9529 @item Otherwise, if @file{cond-file} has the form
9530 @file{@var{dir}/@var{name}}, the output file name will be
9534 In the unlikely case when this algorithm does not suit your needs,
9535 you can explicitly specify output file name as a second argument to
9539 $ @kbd{xsparse @file{cond-file} @file{out-file}}
9542 It is often a good idea to run @command{xsparse} in @dfn{dry run} mode
9543 first. In this mode, the command does not actually expand the file,
9544 but verbosely lists all actions it would be taking to do so. The dry
9545 run mode is enabled by @option{-n} command line argument:
9549 $ @kbd{xsparse -n /home/gray/GNUSparseFile.6058/sparsefile}
9550 Reading v.1.0 sparse map
9551 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9552 `/home/gray/sparsefile'
9557 To actually expand the file, you would run:
9560 $ @kbd{xsparse /home/gray/GNUSparseFile.6058/sparsefile}
9564 The program behaves the same way all UNIX utilities do: it will keep
9565 quiet unless it has simething important to tell you (e.g. an error
9566 condition or something). If you wish it to produce verbose output,
9567 similar to that from the dry run mode, use @option{-v} option:
9571 $ @kbd{xsparse -v /home/gray/GNUSparseFile.6058/sparsefile}
9572 Reading v.1.0 sparse map
9573 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9574 `/home/gray/sparsefile'
9579 Additionally, if your @command{tar} implementation has extracted the
9580 @dfn{extended headers} for this file, you can instruct @command{xstar}
9581 to use them in order to verify the integrity of the expanded file.
9582 The option @option{-x} sets the name of the extended header file to
9583 use. Continuing our example:
9587 $ @kbd{xsparse -v -x /home/gray/PaxHeaders.6058/sparsefile \
9588 /home/gray/GNUSparseFile.6058/sparsefile}
9589 Reading extended header file
9590 Found variable GNU.sparse.major = 1
9591 Found variable GNU.sparse.minor = 0
9592 Found variable GNU.sparse.name = sparsefile
9593 Found variable GNU.sparse.realsize = 217481216
9594 Reading v.1.0 sparse map
9595 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9596 `/home/gray/sparsefile'
9601 @anchor{extracting sparse v.0.x}
9602 @cindex sparse files v.0.1, extracting with non-GNU tars
9603 @cindex sparse files v.0.0, extracting with non-GNU tars
9604 An @dfn{extended header} is a special @command{tar} archive header
9605 that precedes an archive member and contains a set of
9606 @dfn{variables}, describing the member properties that cannot be
9607 stored in the standard @code{ustar} header. While optional for
9608 expanding sparse version 1.0 members, the use of extended headers is
9609 mandatory when expanding sparse members in older sparse formats: v.0.0
9610 and v.0.1 (The sparse formats are described in detail in @ref{Sparse
9611 Formats}.) So, for these formats, the question is: how to obtain
9612 extended headers from the archive?
9614 If you use a @command{tar} implementation that does not support PAX
9615 format, extended headers for each member will be extracted as a
9616 separate file. If we represent the member name as
9617 @file{@var{dir}/@var{name}}, then the extended header file will be
9618 named @file{@var{dir}/@/PaxHeaders.@var{n}/@/@var{name}}, where
9619 @var{n} is an integer number.
9621 Things become more difficult if your @command{tar} implementation
9622 does support PAX headers, because in this case you will have to
9623 manually extract the headers. We recommend the following algorithm:
9627 Consult the documentation of your @command{tar} implementation for an
9628 option that prints @dfn{block numbers} along with the archive
9629 listing (analogous to @GNUTAR{}'s @option{-R} option). For example,
9630 @command{star} has @option{-block-number}.
9633 Obtain verbose listing using the @samp{block number} option, and
9634 find block numbers of the sparse member in question and the member
9635 immediately following it. For example, running @command{star} on our
9640 $ @kbd{star -t -v -block-number -f arc.tar}
9642 star: Unknown extended header keyword 'GNU.sparse.size' ignored.
9643 star: Unknown extended header keyword 'GNU.sparse.numblocks' ignored.
9644 star: Unknown extended header keyword 'GNU.sparse.name' ignored.
9645 star: Unknown extended header keyword 'GNU.sparse.map' ignored.
9646 block 56: 425984 -rw-r--r-- gray/users Jun 25 14:46 2006 GNUSparseFile.28124/sparsefile
9647 block 897: 65391 -rw-r--r-- gray/users Jun 24 20:06 2006 README
9653 (as usual, ignore the warnings about unknown keywords.)
9656 Let @var{size} be the size of the sparse member, @var{Bs} be its block number
9657 and @var{Bn} be the block number of the next member.
9661 @var{N} = @var{Bs} - @var{Bn} - @var{size}/512 - 2
9665 This number gives the size of the extended header part in tar @dfn{blocks}.
9666 In our example, this formula gives: @code{897 - 56 - 425984 / 512 - 2
9670 Use @command{dd} to extract the headers:
9673 @kbd{dd if=@var{archive} of=@var{hname} bs=512 skip=@var{Bs} count=@var{N}}
9677 where @var{archive} is the archive name, @var{hname} is a name of the
9678 file to store the extended header in, @var{Bs} and @var{N} are
9679 computed in previous steps.
9681 In our example, this command will be
9684 $ @kbd{dd if=arc.tar of=xhdr bs=512 skip=56 count=7}
9688 Finally, you can expand the condensed file, using the obtained header:
9692 $ @kbd{xsparse -v -x xhdr GNUSparseFile.6058/sparsefile}
9693 Reading extended header file
9694 Found variable GNU.sparse.size = 217481216
9695 Found variable GNU.sparse.numblocks = 208
9696 Found variable GNU.sparse.name = sparsefile
9697 Found variable GNU.sparse.map = 0,2048,1050624,2048,@dots{}
9698 Expanding file `GNUSparseFile.28124/sparsefile' to `sparsefile'
9704 @section Comparison of @command{tar} and @command{cpio}
9707 @FIXME{Reorganize the following material}
9709 The @command{cpio} archive formats, like @command{tar}, do have maximum
9710 file name lengths. The binary and old @acronym{ASCII} formats have a maximum file
9711 length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max
9712 file length of 1024. @acronym{GNU} @command{cpio} can read and write archives
9713 with arbitrary file name lengths, but other @command{cpio} implementations
9714 may crash unexplainedly trying to read them.
9716 @command{tar} handles symbolic links in the form in which it comes in @acronym{BSD};
9717 @command{cpio} doesn't handle symbolic links in the form in which it comes
9718 in System V prior to SVR4, and some vendors may have added symlinks
9719 to their system without enhancing @command{cpio} to know about them.
9720 Others may have enhanced it in a way other than the way I did it
9721 at Sun, and which was adopted by AT&T (and which is, I think, also
9722 present in the @command{cpio} that Berkeley picked up from AT&T and put
9723 into a later @acronym{BSD} release---I think I gave them my changes).
9725 (SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
9726 can handle @command{tar} format input, and write it on output, and it
9727 probably handles symbolic links. They may not have bothered doing
9728 anything to enhance @command{tar} as a result.)
9730 @command{cpio} handles special files; traditional @command{tar} doesn't.
9732 @command{tar} comes with V7, System III, System V, and @acronym{BSD} source;
9733 @command{cpio} comes only with System III, System V, and later @acronym{BSD}
9734 (4.3-tahoe and later).
9736 @command{tar}'s way of handling multiple hard links to a file can handle
9737 file systems that support 32-bit inumbers (e.g., the @acronym{BSD} file system);
9738 @command{cpio}s way requires you to play some games (in its ``binary''
9739 format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
9740 they're 18 bits---it would have to play games with the "file system @acronym{ID}"
9741 field of the header to make sure that the file system @acronym{ID}/i-number pairs
9742 of different files were always different), and I don't know which
9743 @command{cpio}s, if any, play those games. Those that don't might get
9744 confused and think two files are the same file when they're not, and
9745 make hard links between them.
9747 @command{tar}s way of handling multiple hard links to a file places only
9748 one copy of the link on the tape, but the name attached to that copy
9749 is the @emph{only} one you can use to retrieve the file; @command{cpio}s
9750 way puts one copy for every link, but you can retrieve it using any
9754 What type of check sum (if any) is used, and how is this calculated.
9757 See the attached manual pages for @command{tar} and @command{cpio} format.
9758 @command{tar} uses a checksum which is the sum of all the bytes in the
9759 @command{tar} header for a file; @command{cpio} uses no checksum.
9762 If anyone knows why @command{cpio} was made when @command{tar} was present
9766 It wasn't. @command{cpio} first showed up in PWB/UNIX 1.0; no
9767 generally-available version of UNIX had @command{tar} at the time. I don't
9768 know whether any version that was generally available @emph{within AT&T}
9769 had @command{tar}, or, if so, whether the people within AT&T who did
9770 @command{cpio} knew about it.
9772 On restore, if there is a corruption on a tape @command{tar} will stop at
9773 that point, while @command{cpio} will skip over it and try to restore the
9776 The main difference is just in the command syntax and header format.
9778 @command{tar} is a little more tape-oriented in that everything is blocked
9779 to start on a record boundary.
9782 Is there any differences between the ability to recover crashed
9783 archives between the two of them. (Is there any chance of recovering
9784 crashed archives at all.)
9787 Theoretically it should be easier under @command{tar} since the blocking
9788 lets you find a header with some variation of @samp{dd skip=@var{nn}}.
9789 However, modern @command{cpio}'s and variations have an option to just
9790 search for the next file header after an error with a reasonable chance
9791 of resyncing. However, lots of tape driver software won't allow you to
9792 continue past a media error which should be the only reason for getting
9793 out of sync unless a file changed sizes while you were writing the
9797 If anyone knows why @command{cpio} was made when @command{tar} was present
9798 at the unix scene, please tell me about this too.
9801 Probably because it is more media efficient (by not blocking everything
9802 and using only the space needed for the headers where @command{tar}
9803 always uses 512 bytes per file header) and it knows how to archive
9806 You might want to look at the freely available alternatives. The
9807 major ones are @command{afio}, @GNUTAR{}, and
9808 @command{pax}, each of which have their own extensions with some
9809 backwards compatibility.
9811 Sparse files were @command{tar}red as sparse files (which you can
9812 easily test, because the resulting archive gets smaller, and
9813 @acronym{GNU} @command{cpio} can no longer read it).
9816 @chapter Tapes and Other Archive Media
9819 A few special cases about tape handling warrant more detailed
9820 description. These special cases are discussed below.
9822 Many complexities surround the use of @command{tar} on tape drives. Since
9823 the creation and manipulation of archives located on magnetic tape was
9824 the original purpose of @command{tar}, it contains many features making
9825 such manipulation easier.
9827 Archives are usually written on dismountable media---tape cartridges,
9828 mag tapes, or floppy disks.
9830 The amount of data a tape or disk holds depends not only on its size,
9831 but also on how it is formatted. A 2400 foot long reel of mag tape
9832 holds 40 megabytes of data when formatted at 1600 bits per inch. The
9833 physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
9835 Magnetic media are re-usable---once the archive on a tape is no longer
9836 needed, the archive can be erased and the tape or disk used over.
9837 Media quality does deteriorate with use, however. Most tapes or disks
9838 should be discarded when they begin to produce data errors. EXABYTE
9839 tape cartridges should be discarded when they generate an @dfn{error
9840 count} (number of non-usable bits) of more than 10k.
9842 Magnetic media are written and erased using magnetic fields, and
9843 should be protected from such fields to avoid damage to stored data.
9844 Sticking a floppy disk to a filing cabinet using a magnet is probably
9848 * Device:: Device selection and switching
9849 * Remote Tape Server::
9850 * Common Problems and Solutions::
9851 * Blocking:: Blocking
9852 * Many:: Many archives on one tape
9853 * Using Multiple Tapes:: Using Multiple Tapes
9854 * label:: Including a Label in the Archive
9856 * Write Protection::
9860 @section Device Selection and Switching
9864 @item -f [@var{hostname}:]@var{file}
9865 @itemx --file=[@var{hostname}:]@var{file}
9866 Use archive file or device @var{file} on @var{hostname}.
9869 This option is used to specify the file name of the archive @command{tar}
9872 If the file name is @samp{-}, @command{tar} reads the archive from standard
9873 input (when listing or extracting), or writes it to standard output
9874 (when creating). If the @samp{-} file name is given when updating an
9875 archive, @command{tar} will read the original archive from its standard
9876 input, and will write the entire new archive to its standard output.
9878 If the file name contains a @samp{:}, it is interpreted as
9879 @samp{hostname:file name}. If the @var{hostname} contains an @dfn{at}
9880 sign (@samp{@@}), it is treated as @samp{user@@hostname:file name}. In
9881 either case, @command{tar} will invoke the command @command{rsh} (or
9882 @command{remsh}) to start up an @command{/usr/libexec/rmt} on the remote
9883 machine. If you give an alternate login name, it will be given to the
9885 Naturally, the remote machine must have an executable
9886 @command{/usr/libexec/rmt}. This program is free software from the
9887 University of California, and a copy of the source code can be found
9888 with the sources for @command{tar}; it's compiled and installed by default.
9889 The exact path to this utility is determined when configuring the package.
9890 It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for
9891 your installation prefix. This location may also be overridden at
9892 runtime by using @option{rmt-command=@var{command}} option (@xref{Option Summary,
9893 ---rmt-command}, for detailed description of this option. @xref{Remote
9894 Tape Server}, for the description of @command{rmt} command).
9896 If this option is not given, but the environment variable @env{TAPE}
9897 is set, its value is used; otherwise, old versions of @command{tar}
9898 used a default archive name (which was picked when @command{tar} was
9899 compiled). The default is normally set up to be the @dfn{first} tape
9900 drive or other transportable I/O medium on the system.
9902 Starting with version 1.11.5, @GNUTAR{} uses
9903 standard input and standard output as the default device, and I will
9904 not try anymore supporting automatic device detection at installation
9905 time. This was failing really in too many cases, it was hopeless.
9906 This is now completely left to the installer to override standard
9907 input and standard output for default device, if this seems
9908 preferable. Further, I think @emph{most} actual usages of
9909 @command{tar} are done with pipes or disks, not really tapes,
9910 cartridges or diskettes.
9912 Some users think that using standard input and output is running
9913 after trouble. This could lead to a nasty surprise on your screen if
9914 you forget to specify an output file name---especially if you are going
9915 through a network or terminal server capable of buffering large amounts
9916 of output. We had so many bug reports in that area of configuring
9917 default tapes automatically, and so many contradicting requests, that
9918 we finally consider the problem to be portably intractable. We could
9919 of course use something like @samp{/dev/tape} as a default, but this
9920 is @emph{also} running after various kind of trouble, going from hung
9921 processes to accidental destruction of real tapes. After having seen
9922 all this mess, using standard input and output as a default really
9923 sounds like the only clean choice left, and a very useful one too.
9925 @GNUTAR{} reads and writes archive in records, I
9926 suspect this is the main reason why block devices are preferred over
9927 character devices. Most probably, block devices are more efficient
9928 too. The installer could also check for @samp{DEFTAPE} in
9929 @file{<sys/mtio.h>}.
9932 @xopindex{force-local, short description}
9934 Archive file is local even if it contains a colon.
9936 @opindex rsh-command
9937 @item --rsh-command=@var{command}
9938 Use remote @var{command} instead of @command{rsh}. This option exists
9939 so that people who use something other than the standard @command{rsh}
9940 (e.g., a Kerberized @command{rsh}) can access a remote device.
9942 When this command is not used, the shell command found when
9943 the @command{tar} program was installed is used instead. This is
9944 the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh},
9945 @file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}.
9946 The installer may have overridden this by defining the environment
9947 variable @env{RSH} @emph{at installation time}.
9950 Specify drive and density.
9952 @xopindex{multi-volume, short description}
9954 @itemx --multi-volume
9955 Create/list/extract multi-volume archive.
9957 This option causes @command{tar} to write a @dfn{multi-volume} archive---one
9958 that may be larger than will fit on the medium used to hold it.
9959 @xref{Multi-Volume Archives}.
9961 @xopindex{tape-length, short description}
9963 @itemx --tape-length=@var{num}
9964 Change tape after writing @var{num} x 1024 bytes.
9966 This option might be useful when your tape drivers do not properly
9967 detect end of physical tapes. By being slightly conservative on the
9968 maximum tape length, you might avoid the problem entirely.
9970 @xopindex{info-script, short description}
9971 @xopindex{new-volume-script, short description}
9973 @itemx --info-script=@var{file}
9974 @itemx --new-volume-script=@var{file}
9975 Execute @file{file} at end of each tape. This implies
9976 @option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed
9977 description of this option.
9980 @node Remote Tape Server
9981 @section The Remote Tape Server
9983 @cindex remote tape drive
9985 In order to access the tape drive on a remote machine, @command{tar}
9986 uses the remote tape server written at the University of California at
9987 Berkeley. The remote tape server must be installed as
9988 @file{@var{prefix}/libexec/rmt} on any machine whose tape drive you
9989 want to use. @command{tar} calls @command{rmt} by running an
9990 @command{rsh} or @command{remsh} to the remote machine, optionally
9991 using a different login name if one is supplied.
9993 A copy of the source for the remote tape server is provided. It is
9994 Copyright @copyright{} 1983 by the Regents of the University of
9995 California, but can be freely distributed. It is compiled and
9996 installed by default.
9998 @cindex absolute file names
9999 Unless you use the @option{--absolute-names} (@option{-P}) option,
10000 @GNUTAR{} will not allow you to create an archive that contains
10001 absolute file names (a file name beginning with @samp{/}.) If you try,
10002 @command{tar} will automatically remove the leading @samp{/} from the
10003 file names it stores in the archive. It will also type a warning
10004 message telling you what it is doing.
10006 When reading an archive that was created with a different
10007 @command{tar} program, @GNUTAR{} automatically
10008 extracts entries in the archive which have absolute file names as if
10009 the file names were not absolute. This is an important feature. A
10010 visitor here once gave a @command{tar} tape to an operator to restore;
10011 the operator used Sun @command{tar} instead of @GNUTAR{},
10012 and the result was that it replaced large portions of
10013 our @file{/bin} and friends with versions from the tape; needless to
10014 say, we were unhappy about having to recover the file system from
10017 For example, if the archive contained a file @file{/usr/bin/computoy},
10018 @GNUTAR{} would extract the file to @file{usr/bin/computoy},
10019 relative to the current directory. If you want to extract the files in
10020 an archive to the same absolute names that they had when the archive
10021 was created, you should do a @samp{cd /} before extracting the files
10022 from the archive, or you should either use the @option{--absolute-names}
10023 option, or use the command @samp{tar -C / @dots{}}.
10025 @cindex Ultrix 3.1 and write failure
10026 Some versions of Unix (Ultrix 3.1 is known to have this problem),
10027 can claim that a short write near the end of a tape succeeded,
10028 when it actually failed. This will result in the -M option not
10029 working correctly. The best workaround at the moment is to use a
10030 significantly larger blocking factor than the default 20.
10032 In order to update an archive, @command{tar} must be able to backspace the
10033 archive in order to reread or rewrite a record that was just read (or
10034 written). This is currently possible only on two kinds of files: normal
10035 disk files (or any other file that can be backspaced with @samp{lseek}),
10036 and industry-standard 9-track magnetic tape (or any other kind of tape
10037 that can be backspaced with the @code{MTIOCTOP} @code{ioctl}.
10039 This means that the @option{--append}, @option{--concatenate}, and
10040 @option{--delete} commands will not work on any other kind of file.
10041 Some media simply cannot be backspaced, which means these commands and
10042 options will never be able to work on them. These non-backspacing
10043 media include pipes and cartridge tape drives.
10045 Some other media can be backspaced, and @command{tar} will work on them
10046 once @command{tar} is modified to do so.
10048 Archives created with the @option{--multi-volume}, @option{--label}, and
10049 @option{--incremental} (@option{-G}) options may not be readable by other version
10050 of @command{tar}. In particular, restoring a file that was split over
10051 a volume boundary will require some careful work with @command{dd}, if
10052 it can be done at all. Other versions of @command{tar} may also create
10053 an empty file whose name is that of the volume header. Some versions
10054 of @command{tar} may create normal files instead of directories archived
10055 with the @option{--incremental} (@option{-G}) option.
10057 @node Common Problems and Solutions
10058 @section Some Common Problems and their Solutions
10063 errors from system:
10065 no such file or directory
10068 errors from @command{tar}:
10069 directory checksum error
10070 header format error
10072 errors from media/system:
10083 @dfn{Block} and @dfn{record} terminology is rather confused, and it
10084 is also confusing to the expert reader. On the other hand, readers
10085 who are new to the field have a fresh mind, and they may safely skip
10086 the next two paragraphs, as the remainder of this manual uses those
10087 two terms in a quite consistent way.
10089 John Gilmore, the writer of the public domain @command{tar} from which
10090 @GNUTAR{} was originally derived, wrote (June 1995):
10093 The nomenclature of tape drives comes from IBM, where I believe
10094 they were invented for the IBM 650 or so. On IBM mainframes, what
10095 is recorded on tape are tape blocks. The logical organization of
10096 data is into records. There are various ways of putting records into
10097 blocks, including @code{F} (fixed sized records), @code{V} (variable
10098 sized records), @code{FB} (fixed blocked: fixed size records, @var{n}
10099 to a block), @code{VB} (variable size records, @var{n} to a block),
10100 @code{VSB} (variable spanned blocked: variable sized records that can
10101 occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=}
10102 parameter specified this to the operating system.
10104 The Unix man page on @command{tar} was totally confused about this.
10105 When I wrote @code{PD TAR}, I used the historically correct terminology
10106 (@command{tar} writes data records, which are grouped into blocks).
10107 It appears that the bogus terminology made it into @acronym{POSIX} (no surprise
10108 here), and now Fran@,{c}ois has migrated that terminology back
10109 into the source code too.
10112 The term @dfn{physical block} means the basic transfer chunk from or
10113 to a device, after which reading or writing may stop without anything
10114 being lost. In this manual, the term @dfn{block} usually refers to
10115 a disk physical block, @emph{assuming} that each disk block is 512
10116 bytes in length. It is true that some disk devices have different
10117 physical blocks, but @command{tar} ignore these differences in its own
10118 format, which is meant to be portable, so a @command{tar} block is always
10119 512 bytes in length, and @dfn{block} always mean a @command{tar} block.
10120 The term @dfn{logical block} often represents the basic chunk of
10121 allocation of many disk blocks as a single entity, which the operating
10122 system treats somewhat atomically; this concept is only barely used
10125 The term @dfn{physical record} is another way to speak of a physical
10126 block, those two terms are somewhat interchangeable. In this manual,
10127 the term @dfn{record} usually refers to a tape physical block,
10128 @emph{assuming} that the @command{tar} archive is kept on magnetic tape.
10129 It is true that archives may be put on disk or used with pipes,
10130 but nevertheless, @command{tar} tries to read and write the archive one
10131 @dfn{record} at a time, whatever the medium in use. One record is made
10132 up of an integral number of blocks, and this operation of putting many
10133 disk blocks into a single tape block is called @dfn{reblocking}, or
10134 more simply, @dfn{blocking}. The term @dfn{logical record} refers to
10135 the logical organization of many characters into something meaningful
10136 to the application. The term @dfn{unit record} describes a small set
10137 of characters which are transmitted whole to or by the application,
10138 and often refers to a line of text. Those two last terms are unrelated
10139 to what we call a @dfn{record} in @GNUTAR{}.
10141 When writing to tapes, @command{tar} writes the contents of the archive
10142 in chunks known as @dfn{records}. To change the default blocking
10143 factor, use the @option{--blocking-factor=@var{512-size}} (@option{-b
10144 @var{512-size}}) option. Each record will then be composed of
10145 @var{512-size} blocks. (Each @command{tar} block is 512 bytes.
10146 @xref{Standard}.) Each file written to the archive uses at least one
10147 full record. As a result, using a larger record size can result in
10148 more wasted space for small files. On the other hand, a larger record
10149 size can often be read and written much more efficiently.
10151 Further complicating the problem is that some tape drives ignore the
10152 blocking entirely. For these, a larger record size can still improve
10153 performance (because the software layers above the tape drive still
10154 honor the blocking), but not as dramatically as on tape drives that
10157 When reading an archive, @command{tar} can usually figure out the
10158 record size on itself. When this is the case, and a non-standard
10159 record size was used when the archive was created, @command{tar} will
10160 print a message about a non-standard blocking factor, and then operate
10161 normally. On some tape devices, however, @command{tar} cannot figure
10162 out the record size itself. On most of those, you can specify a
10163 blocking factor (with @option{--blocking-factor}) larger than the
10164 actual blocking factor, and then use the @option{--read-full-records}
10165 (@option{-B}) option. (If you specify a blocking factor with
10166 @option{--blocking-factor} and don't use the
10167 @option{--read-full-records} option, then @command{tar} will not
10168 attempt to figure out the recording size itself.) On some devices,
10169 you must always specify the record size exactly with
10170 @option{--blocking-factor} when reading, because @command{tar} cannot
10171 figure it out. In any case, use @option{--list} (@option{-t}) before
10172 doing any extractions to see whether @command{tar} is reading the archive
10175 @command{tar} blocks are all fixed size (512 bytes), and its scheme for
10176 putting them into records is to put a whole number of them (one or
10177 more) into each record. @command{tar} records are all the same size;
10178 at the end of the file there's a block containing all zeros, which
10179 is how you tell that the remainder of the last record(s) are garbage.
10181 In a standard @command{tar} file (no options), the block size is 512
10182 and the record size is 10240, for a blocking factor of 20. What the
10183 @option{--blocking-factor} option does is sets the blocking factor,
10184 changing the record size while leaving the block size at 512 bytes.
10185 20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives;
10186 most tape drives these days prefer much bigger records in order to
10187 stream and not waste tape. When writing tapes for myself, some tend
10188 to use a factor of the order of 2048, say, giving a record size of
10189 around one megabyte.
10191 If you use a blocking factor larger than 20, older @command{tar}
10192 programs might not be able to read the archive, so we recommend this
10193 as a limit to use in practice. @GNUTAR{}, however,
10194 will support arbitrarily large record sizes, limited only by the
10195 amount of virtual memory or the physical characteristics of the tape
10199 * Format Variations:: Format Variations
10200 * Blocking Factor:: The Blocking Factor of an Archive
10203 @node Format Variations
10204 @subsection Format Variations
10205 @cindex Format Parameters
10206 @cindex Format Options
10207 @cindex Options, archive format specifying
10208 @cindex Options, format specifying
10211 Format parameters specify how an archive is written on the archive
10212 media. The best choice of format parameters will vary depending on
10213 the type and number of files being archived, and on the media used to
10216 To specify format parameters when accessing or creating an archive,
10217 you can use the options described in the following sections.
10218 If you do not specify any format parameters, @command{tar} uses
10219 default parameters. You cannot modify a compressed archive.
10220 If you create an archive with the @option{--blocking-factor} option
10221 specified (@pxref{Blocking Factor}), you must specify that
10222 blocking-factor when operating on the archive. @xref{Formats}, for other
10223 examples of format parameter considerations.
10225 @node Blocking Factor
10226 @subsection The Blocking Factor of an Archive
10227 @cindex Blocking Factor
10228 @cindex Record Size
10229 @cindex Number of blocks per record
10230 @cindex Number of bytes per record
10231 @cindex Bytes per record
10232 @cindex Blocks per record
10235 @opindex blocking-factor
10236 The data in an archive is grouped into blocks, which are 512 bytes.
10237 Blocks are read and written in whole number multiples called
10238 @dfn{records}. The number of blocks in a record (i.e., the size of a
10239 record in units of 512 bytes) is called the @dfn{blocking factor}.
10240 The @option{--blocking-factor=@var{512-size}} (@option{-b
10241 @var{512-size}}) option specifies the blocking factor of an archive.
10242 The default blocking factor is typically 20 (i.e., 10240 bytes), but
10243 can be specified at installation. To find out the blocking factor of
10244 an existing archive, use @samp{tar --list --file=@var{archive-name}}.
10245 This may not work on some devices.
10247 Records are separated by gaps, which waste space on the archive media.
10248 If you are archiving on magnetic tape, using a larger blocking factor
10249 (and therefore larger records) provides faster throughput and allows you
10250 to fit more data on a tape (because there are fewer gaps). If you are
10251 archiving on cartridge, a very large blocking factor (say 126 or more)
10252 greatly increases performance. A smaller blocking factor, on the other
10253 hand, may be useful when archiving small files, to avoid archiving lots
10254 of nulls as @command{tar} fills out the archive to the end of the record.
10255 In general, the ideal record size depends on the size of the
10256 inter-record gaps on the tape you are using, and the average size of the
10257 files you are archiving. @xref{create}, for information on
10260 @FIXME{Need example of using a cartridge with blocking factor=126 or more.}
10262 Archives with blocking factors larger than 20 cannot be read
10263 by very old versions of @command{tar}, or by some newer versions
10264 of @command{tar} running on old machines with small address spaces.
10265 With @GNUTAR{}, the blocking factor of an archive is limited
10266 only by the maximum record size of the device containing the archive,
10267 or by the amount of available virtual memory.
10269 Also, on some systems, not using adequate blocking factors, as sometimes
10270 imposed by the device drivers, may yield unexpected diagnostics. For
10271 example, this has been reported:
10274 Cannot write to /dev/dlt: Invalid argument
10278 In such cases, it sometimes happen that the @command{tar} bundled by
10279 the system is aware of block size idiosyncrasies, while @GNUTAR{}
10280 requires an explicit specification for the block size,
10281 which it cannot guess. This yields some people to consider
10282 @GNUTAR{} is misbehaving, because by comparison,
10283 @cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}},
10284 for example, might resolve the problem.
10286 If you use a non-default blocking factor when you create an archive, you
10287 must specify the same blocking factor when you modify that archive. Some
10288 archive devices will also require you to specify the blocking factor when
10289 reading that archive, however this is not typically the case. Usually, you
10290 can use @option{--list} (@option{-t}) without specifying a blocking factor---@command{tar}
10291 reports a non-default record size and then lists the archive members as
10292 it would normally. To extract files from an archive with a non-standard
10293 blocking factor (particularly if you're not sure what the blocking factor
10294 is), you can usually use the @option{--read-full-records} (@option{-B}) option while
10295 specifying a blocking factor larger then the blocking factor of the archive
10296 (i.e., @samp{tar --extract --read-full-records --blocking-factor=300}.
10297 @xref{list}, for more information on the @option{--list} (@option{-t})
10298 operation. @xref{Reading}, for a more detailed explanation of that option.
10301 @item --blocking-factor=@var{number}
10302 @itemx -b @var{number}
10303 Specifies the blocking factor of an archive. Can be used with any
10304 operation, but is usually not necessary with @option{--list} (@option{-t}).
10310 @item -b @var{blocks}
10311 @itemx --blocking-factor=@var{blocks}
10312 Set record size to @math{@var{blocks} * 512} bytes.
10314 This option is used to specify a @dfn{blocking factor} for the archive.
10315 When reading or writing the archive, @command{tar}, will do reads and writes
10316 of the archive in records of @math{@var{block}*512} bytes. This is true
10317 even when the archive is compressed. Some devices requires that all
10318 write operations be a multiple of a certain size, and so, @command{tar}
10319 pads the archive out to the next record boundary.
10321 The default blocking factor is set when @command{tar} is compiled, and is
10322 typically 20. Blocking factors larger than 20 cannot be read by very
10323 old versions of @command{tar}, or by some newer versions of @command{tar}
10324 running on old machines with small address spaces.
10326 With a magnetic tape, larger records give faster throughput and fit
10327 more data on a tape (because there are fewer inter-record gaps).
10328 If the archive is in a disk file or a pipe, you may want to specify
10329 a smaller blocking factor, since a large one will result in a large
10330 number of null bytes at the end of the archive.
10332 When writing cartridge or other streaming tapes, a much larger
10333 blocking factor (say 126 or more) will greatly increase performance.
10334 However, you must specify the same blocking factor when reading or
10335 updating the archive.
10337 Apparently, Exabyte drives have a physical block size of 8K bytes.
10338 If we choose our blocksize as a multiple of 8k bytes, then the problem
10339 seems to disappear. Id est, we are using block size of 112 right
10340 now, and we haven't had the problem since we switched@dots{}
10342 With @GNUTAR{} the blocking factor is limited only
10343 by the maximum record size of the device containing the archive, or by
10344 the amount of available virtual memory.
10346 However, deblocking or reblocking is virtually avoided in a special
10347 case which often occurs in practice, but which requires all the
10348 following conditions to be simultaneously true:
10351 the archive is subject to a compression option,
10353 the archive is not handled through standard input or output, nor
10354 redirected nor piped,
10356 the archive is directly handled to a local disk, instead of any special
10359 @option{--blocking-factor} is not explicitly specified on the @command{tar}
10363 If the output goes directly to a local disk, and not through
10364 stdout, then the last write is not extended to a full record size.
10365 Otherwise, reblocking occurs. Here are a few other remarks on this
10371 @command{gzip} will complain about trailing garbage if asked to
10372 uncompress a compressed archive on tape, there is an option to turn
10373 the message off, but it breaks the regularity of simply having to use
10374 @samp{@var{prog} -d} for decompression. It would be nice if gzip was
10375 silently ignoring any number of trailing zeros. I'll ask Jean-loup
10376 Gailly, by sending a copy of this message to him.
10379 @command{compress} does not show this problem, but as Jean-loup pointed
10380 out to Michael, @samp{compress -d} silently adds garbage after
10381 the result of decompression, which tar ignores because it already
10382 recognized its end-of-file indicator. So this bug may be safely
10386 @samp{gzip -d -q} will be silent about the trailing zeros indeed,
10387 but will still return an exit status of 2 which tar reports in turn.
10388 @command{tar} might ignore the exit status returned, but I hate doing
10389 that, as it weakens the protection @command{tar} offers users against
10390 other possible problems at decompression time. If @command{gzip} was
10391 silently skipping trailing zeros @emph{and} also avoiding setting the
10392 exit status in this innocuous case, that would solve this situation.
10395 @command{tar} should become more solid at not stopping to read a pipe at
10396 the first null block encountered. This inelegantly breaks the pipe.
10397 @command{tar} should rather drain the pipe out before exiting itself.
10400 @xopindex{ignore-zeros, short description}
10402 @itemx --ignore-zeros
10403 Ignore blocks of zeros in archive (means EOF).
10405 The @option{--ignore-zeros} (@option{-i}) option causes @command{tar} to ignore blocks
10406 of zeros in the archive. Normally a block of zeros indicates the
10407 end of the archive, but when reading a damaged archive, or one which
10408 was created by concatenating several archives together, this option
10409 allows @command{tar} to read the entire archive. This option is not on
10410 by default because many versions of @command{tar} write garbage after
10413 Note that this option causes @command{tar} to read to the end of the
10414 archive file, which may sometimes avoid problems when multiple files
10415 are stored on a single physical tape.
10417 @xopindex{read-full-records, short description}
10419 @itemx --read-full-records
10420 Reblock as we read (for reading 4.2@acronym{BSD} pipes).
10422 If @option{--read-full-records} is used, @command{tar}
10423 will not panic if an attempt to read a record from the archive does
10424 not return a full record. Instead, @command{tar} will keep reading
10425 until it has obtained a full
10428 This option is turned on by default when @command{tar} is reading
10429 an archive from standard input, or from a remote machine. This is
10430 because on @acronym{BSD} Unix systems, a read of a pipe will return however
10431 much happens to be in the pipe, even if it is less than @command{tar}
10432 requested. If this option was not used, @command{tar} would fail as
10433 soon as it read an incomplete record from the pipe.
10435 This option is also useful with the commands for updating an archive.
10441 @FIXME{Appropriate options should be moved here from elsewhere.}
10443 @cindex blocking factor
10444 @cindex tape blocking
10446 When handling various tapes or cartridges, you have to take care of
10447 selecting a proper blocking, that is, the number of disk blocks you
10448 put together as a single tape block on the tape, without intervening
10449 tape gaps. A @dfn{tape gap} is a small landing area on the tape
10450 with no information on it, used for decelerating the tape to a
10451 full stop, and for later regaining the reading or writing speed.
10452 When the tape driver starts reading a record, the record has to
10453 be read whole without stopping, as a tape gap is needed to stop the
10454 tape motion without loosing information.
10456 @cindex Exabyte blocking
10457 @cindex DAT blocking
10458 Using higher blocking (putting more disk blocks per tape block) will use
10459 the tape more efficiently as there will be less tape gaps. But reading
10460 such tapes may be more difficult for the system, as more memory will be
10461 required to receive at once the whole record. Further, if there is a
10462 reading error on a huge record, this is less likely that the system will
10463 succeed in recovering the information. So, blocking should not be too
10464 low, nor it should be too high. @command{tar} uses by default a blocking of
10465 20 for historical reasons, and it does not really matter when reading or
10466 writing to disk. Current tape technology would easily accommodate higher
10467 blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs.
10468 We were told that for some DLT drives, the blocking should be a multiple
10469 of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance.
10470 Other manufacturers may use different recommendations for the same tapes.
10471 This might also depends of the buffering techniques used inside modern
10472 tape controllers. Some imposes a minimum blocking, or a maximum blocking.
10473 Others request blocking to be some exponent of two.
10475 So, there is no fixed rule for blocking. But blocking at read time
10476 should ideally be the same as blocking used at write time. At one place
10477 I know, with a wide variety of equipment, they found it best to use a
10478 blocking of 32 to guarantee that their tapes are fully interchangeable.
10480 I was also told that, for recycled tapes, prior erasure (by the same
10481 drive unit that will be used to create the archives) sometimes lowers
10482 the error rates observed at rewriting time.
10484 I might also use @option{--number-blocks} instead of
10485 @option{--block-number}, so @option{--block} will then expand to
10486 @option{--blocking-factor} unambiguously.
10489 @section Many Archives on One Tape
10491 @FIXME{Appropriate options should be moved here from elsewhere.}
10493 @findex ntape @r{device}
10494 Most tape devices have two entries in the @file{/dev} directory, or
10495 entries that come in pairs, which differ only in the minor number for
10496 this device. Let's take for example @file{/dev/tape}, which often
10497 points to the only or usual tape device of a given system. There might
10498 be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler
10499 name is the @emph{rewinding} version of the device, while the name
10500 having @samp{nr} in it is the @emph{no rewinding} version of the same
10503 A rewinding tape device will bring back the tape to its beginning point
10504 automatically when this device is opened or closed. Since @command{tar}
10505 opens the archive file before using it and closes it afterwards, this
10506 means that a simple:
10509 $ @kbd{tar cf /dev/tape @var{directory}}
10513 will reposition the tape to its beginning both prior and after saving
10514 @var{directory} contents to it, thus erasing prior tape contents and
10515 making it so that any subsequent write operation will destroy what has
10518 @cindex tape positioning
10519 So, a rewinding device is normally meant to hold one and only one file.
10520 If you want to put more than one @command{tar} archive on a given tape, you
10521 will need to avoid using the rewinding version of the tape device. You
10522 will also have to pay special attention to tape positioning. Errors in
10523 positioning may overwrite the valuable data already on your tape. Many
10524 people, burnt by past experiences, will only use rewinding devices and
10525 limit themselves to one file per tape, precisely to avoid the risk of
10526 such errors. Be fully aware that writing at the wrong position on a
10527 tape loses all information past this point and most probably until the
10528 end of the tape, and this destroyed information @emph{cannot} be
10531 To save @var{directory-1} as a first archive at the beginning of a
10532 tape, and leave that tape ready for a second archive, you should use:
10535 $ @kbd{mt -f /dev/nrtape rewind}
10536 $ @kbd{tar cf /dev/nrtape @var{directory-1}}
10540 @dfn{Tape marks} are special magnetic patterns written on the tape
10541 media, which are later recognizable by the reading hardware. These
10542 marks are used after each file, when there are many on a single tape.
10543 An empty file (that is to say, two tape marks in a row) signal the
10544 logical end of the tape, after which no file exist. Usually,
10545 non-rewinding tape device drivers will react to the close request issued
10546 by @command{tar} by first writing two tape marks after your archive, and by
10547 backspacing over one of these. So, if you remove the tape at that time
10548 from the tape drive, it is properly terminated. But if you write
10549 another file at the current position, the second tape mark will be
10550 erased by the new information, leaving only one tape mark between files.
10552 So, you may now save @var{directory-2} as a second archive after the
10553 first on the same tape by issuing the command:
10556 $ @kbd{tar cf /dev/nrtape @var{directory-2}}
10560 and so on for all the archives you want to put on the same tape.
10562 Another usual case is that you do not write all the archives the same
10563 day, and you need to remove and store the tape between two archive
10564 sessions. In general, you must remember how many files are already
10565 saved on your tape. Suppose your tape already has 16 files on it, and
10566 that you are ready to write the 17th. You have to take care of skipping
10567 the first 16 tape marks before saving @var{directory-17}, say, by using
10571 $ @kbd{mt -f /dev/nrtape rewind}
10572 $ @kbd{mt -f /dev/nrtape fsf 16}
10573 $ @kbd{tar cf /dev/nrtape @var{directory-17}}
10576 In all the previous examples, we put aside blocking considerations, but
10577 you should do the proper things for that as well. @xref{Blocking}.
10580 * Tape Positioning:: Tape Positions and Tape Marks
10581 * mt:: The @command{mt} Utility
10584 @node Tape Positioning
10585 @subsection Tape Positions and Tape Marks
10588 Just as archives can store more than one file from the file system,
10589 tapes can store more than one archive file. To keep track of where
10590 archive files (or any other type of file stored on tape) begin and
10591 end, tape archive devices write magnetic @dfn{tape marks} on the
10592 archive media. Tape drives write one tape mark between files,
10593 two at the end of all the file entries.
10595 If you think of data as a series of records "rrrr"'s, and tape marks as
10596 "*"'s, a tape might look like the following:
10599 rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
10602 Tape devices read and write tapes using a read/write @dfn{tape
10603 head}---a physical part of the device which can only access one
10604 point on the tape at a time. When you use @command{tar} to read or
10605 write archive data from a tape device, the device will begin reading
10606 or writing from wherever on the tape the tape head happens to be,
10607 regardless of which archive or what part of the archive the tape
10608 head is on. Before writing an archive, you should make sure that no
10609 data on the tape will be overwritten (unless it is no longer needed).
10610 Before reading an archive, you should make sure the tape head is at
10611 the beginning of the archive you want to read. You can do it manually
10612 via @code{mt} utility (@pxref{mt}). The @code{restore} script does
10613 that automatically (@pxref{Scripted Restoration}).
10615 If you want to add new archive file entries to a tape, you should
10616 advance the tape to the end of the existing file entries, backspace
10617 over the last tape mark, and write the new archive file. If you were
10618 to add two archives to the example above, the tape might look like the
10622 rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
10626 @subsection The @command{mt} Utility
10629 @FIXME{Is it true that this only works on non-block devices?
10630 should explain the difference, (fixed or variable).}
10631 @xref{Blocking Factor}.
10633 You can use the @command{mt} utility to advance or rewind a tape past a
10634 specified number of archive files on the tape. This will allow you
10635 to move to the beginning of an archive before extracting or reading
10636 it, or to the end of all the archives before writing a new one.
10637 @FIXME{Why isn't there an "advance 'til you find two tape marks
10640 The syntax of the @command{mt} command is:
10643 @kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
10646 where @var{tapename} is the name of the tape device, @var{number} is
10647 the number of times an operation is performed (with a default of one),
10648 and @var{operation} is one of the following:
10650 @FIXME{is there any use for record operations?}
10655 Writes @var{number} tape marks at the current position on the tape.
10658 Moves tape position forward @var{number} files.
10661 Moves tape position back @var{number} files.
10664 Rewinds the tape. (Ignores @var{number}).
10668 Rewinds the tape and takes the tape device off-line. (Ignores @var{number}).
10671 Prints status information about the tape unit.
10675 @FIXME{Is there a better way to frob the spacing on the list?}
10677 If you don't specify a @var{tapename}, @command{mt} uses the environment
10678 variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
10679 the default device specified in your @file{sys/mtio.h} file
10680 (@code{DEFTAPE} variable). If this is not defined, the program will
10681 display a descriptive error message and exit with code 1.
10683 @command{mt} returns a 0 exit status when the operation(s) were
10684 successful, 1 if the command was unrecognized, and 2 if an operation
10687 @node Using Multiple Tapes
10688 @section Using Multiple Tapes
10690 Often you might want to write a large archive, one larger than will fit
10691 on the actual tape you are using. In such a case, you can run multiple
10692 @command{tar} commands, but this can be inconvenient, particularly if you
10693 are using options like @option{--exclude=@var{pattern}} or dumping entire file systems.
10694 Therefore, @command{tar} provides a special mode for creating
10695 multi-volume archives.
10697 @dfn{Multi-volume} archive is a single @command{tar} archive, stored
10698 on several media volumes of fixed size. Although in this section we will
10699 often call @samp{volume} a @dfn{tape}, there is absolutely no
10700 requirement for multi-volume archives to be stored on tapes. Instead,
10701 they can use whatever media type the user finds convenient, they can
10702 even be located on files.
10704 When creating a multi-volume archive, @GNUTAR{} continues to fill
10705 current volume until it runs out of space, then it switches to
10706 next volume (usually the operator is queried to replace the tape on
10707 this point), and continues working on the new volume. This operation
10708 continues until all requested files are dumped. If @GNUTAR{} detects
10709 end of media while dumping a file, such a file is archived in split
10710 form. Some very big files can even be split across several volumes.
10712 Each volume is itself a valid @GNUTAR{} archive, so it can be read
10713 without any special options. Consequently any file member residing
10714 entirely on one volume can be extracted or otherwise operated upon
10715 without needing the other volume. Sure enough, to extract a split
10716 member you would need all volumes its parts reside on.
10718 Multi-volume archives suffer from several limitations. In particular,
10719 they cannot be compressed.
10721 @GNUTAR{} is able to create multi-volume archives of two formats
10722 (@pxref{Formats}): @samp{GNU} and @samp{POSIX}.
10725 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
10726 * Tape Files:: Tape Files
10727 * Tarcat:: Concatenate Volumes into a Single Archive
10731 @node Multi-Volume Archives
10732 @subsection Archives Longer than One Tape or Disk
10733 @cindex Multi-volume archives
10735 @opindex multi-volume
10736 To create an archive that is larger than will fit on a single unit of
10737 the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
10738 the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
10739 archive can be manipulated like any other archive (provided the
10740 @option{--multi-volume} option is specified), but is stored on more
10741 than one tape or disk.
10743 When you specify @option{--multi-volume}, @command{tar} does not report an
10744 error when it comes to the end of an archive volume (when reading), or
10745 the end of the media (when writing). Instead, it prompts you to load
10746 a new storage volume. If the archive is on a magnetic tape, you
10747 should change tapes when you see the prompt; if the archive is on a
10748 floppy disk, you should change disks; etc.
10751 @item --multi-volume
10753 Creates a multi-volume archive, when used in conjunction with
10754 @option{--create} (@option{-c}). To perform any other operation on a multi-volume
10755 archive, specify @option{--multi-volume} in conjunction with that
10760 $ @kbd{tar --create --multi-volume --file=/dev/tape @var{files}}
10764 The method @command{tar} uses to detect end of tape is not perfect, and
10765 fails on some operating systems or on some devices. If @command{tar}
10766 cannot detect the end of the tape itself, you can use
10767 @option{--tape-length} option to inform it about the capacity of the
10770 @anchor{tape-length}
10772 @opindex tape-length
10773 @item --tape-length=@var{size}
10774 @itemx -L @var{size}
10775 Set maximum length of a volume. The @var{size} argument should then
10776 be the usable size of the tape in units of 1024 bytes. This option
10777 selects @option{--multi-volume} automatically. For example:
10780 $ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}}
10784 @anchor{change volume prompt}
10785 When @GNUTAR{} comes to the end of a storage media, it asks you to
10786 change the volume. The built-in prompt for POSIX locale
10787 is@footnote{If you run @GNUTAR{} under a different locale, the
10788 translation to the locale's language will be used.}:
10791 Prepare volume #@var{n} for `@var{archive}' and hit return:
10795 where @var{n} is the ordinal number of the volume to be created and
10796 @var{archive} is archive file or device name.
10798 When prompting for a new tape, @command{tar} accepts any of the following
10803 Request @command{tar} to explain possible responses
10805 Request @command{tar} to exit immediately.
10806 @item n @var{file-name}
10807 Request @command{tar} to write the next volume on the file @var{file-name}.
10809 Request @command{tar} to run a subshell. This option can be disabled
10810 by giving @option{--restrict} command line option to
10811 @command{tar}@footnote{@xref{--restrict}, for more information about
10814 Request @command{tar} to begin writing the next volume.
10817 (You should only type @samp{y} after you have changed the tape;
10818 otherwise @command{tar} will write over the volume it just finished.)
10820 @cindex Volume number file
10822 @anchor{volno-file}
10823 @opindex volno-file
10824 The volume number used by @command{tar} in its tape-changing prompt
10825 can be changed; if you give the
10826 @option{--volno-file=@var{file-of-number}} option, then
10827 @var{file-of-number} should be an non-existing file to be created, or
10828 else, a file already containing a decimal number. That number will be
10829 used as the volume number of the first volume written. When
10830 @command{tar} is finished, it will rewrite the file with the
10831 now-current volume number. (This does not change the volume number
10832 written on a tape label, as per @ref{label}, it @emph{only} affects
10833 the number used in the prompt.)
10835 @cindex End-of-archive info script
10836 @cindex Info script
10837 @anchor{info-script}
10838 @opindex info-script
10839 @opindex new-volume-script
10840 If you want more elaborate behavior than this, you can write a special
10841 @dfn{new volume script}, that will be responsible for changing the
10842 volume, and instruct @command{tar} to use it instead of its normal
10843 prompting procedure:
10846 @item --info-script=@var{script-name}
10847 @itemx --new-volume-script=@var{script-name}
10848 @itemx -F @var{script-name}
10849 Specify the full name of the volume script to use. The script can be
10850 used to eject cassettes, or to broadcast messages such as
10851 @samp{Someone please come change my tape} when performing unattended
10855 The @var{script-name} is executed without any command line
10856 arguments. It inherits @command{tar}'s shell environment.
10857 Additional data is passed to it via the following
10858 environment variables:
10861 @vrindex TAR_VERSION, info script environment variable
10863 @GNUTAR{} version number.
10865 @vrindex TAR_ARCHIVE, info script environment variable
10867 The name of the archive @command{tar} is processing.
10869 @vrindex TAR_BLOCKING_FACTOR, info script environment variable
10870 @item TAR_BLOCKING_FACTOR
10871 Current blocking factor (@pxref{Blocking}.
10873 @vrindex TAR_VOLUME, info script environment variable
10875 Ordinal number of the volume @command{tar} is about to start.
10877 @vrindex TAR_SUBCOMMAND, info script environment variable
10878 @item TAR_SUBCOMMAND
10879 A short option describing the operation @command{tar} is executing
10880 @xref{Operations}, for a complete list of subcommand options.
10882 @vrindex TAR_FORMAT, info script environment variable
10884 Format of the archive being processed. @xref{Formats}, for a complete
10885 list of archive format names.
10887 @vrindex TAR_FD, info script environment variable
10889 File descriptor which can be used to communicate the new volume
10890 name to @command{tar}.
10893 The volume script can instruct @command{tar} to use new archive name,
10894 by writing in to file descriptor @env{$TAR_FD} (see below for an example).
10896 If the info script fails, @command{tar} exits; otherwise, it begins
10897 writing the next volume.
10899 If you want @command{tar} to cycle through a series of files or tape
10900 drives, there are three approaches to choose from. First of all, you
10901 can give @command{tar} multiple @option{--file} options. In this case
10902 the specified files will be used, in sequence, as the successive
10903 volumes of the archive. Only when the first one in the sequence needs
10904 to be used again will @command{tar} prompt for a tape change (or run
10905 the info script). For example, suppose someone has two tape drives on
10906 a system named @file{/dev/tape0} and @file{/dev/tape1}. For having
10907 @GNUTAR{} to switch to the second drive when it needs to write the
10908 second tape, and then back to the first tape, etc., just do either of:
10911 $ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
10912 $ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
10915 The second method is to use the @samp{n} response to the tape-change
10918 Finally, the most flexible approach is to use a volume script, that
10919 writes new archive name to the file descriptor @env{$TAR_FD}. For example, the
10920 following volume script will create a series of archive files, named
10921 @file{@var{archive}-@var{vol}}, where @var{archive} is the name of the
10922 archive being created (as given by @option{--file} option) and
10923 @var{vol} is the ordinal number of the archive being created:
10928 echo Preparing volume $TAR_VOLUME of $TAR_ARCHIVE.
10930 name=`expr $TAR_ARCHIVE : '\(.*\)-.*'`
10931 case $TAR_SUBCOMMAND in
10933 -d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
10938 echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&$TAR_FD
10942 The same script can be used while listing, comparing or extracting
10943 from the created archive. For example:
10947 # @r{Create a multi-volume archive:}
10948 $ @kbd{tar -c -L1024 -f archive.tar -F new-volume .}
10949 # @r{Extract from the created archive:}
10950 $ @kbd{tar -x -f archive.tar -F new-volume .}
10955 Notice, that the first command had to use @option{-L} option, since
10956 otherwise @GNUTAR{} will end up writing everything to file
10957 @file{archive.tar}.
10959 You can read each individual volume of a multi-volume archive as if it
10960 were an archive by itself. For example, to list the contents of one
10961 volume, use @option{--list}, without @option{--multi-volume} specified.
10962 To extract an archive member from one volume (assuming it is described
10963 that volume), use @option{--extract}, again without
10964 @option{--multi-volume}.
10966 If an archive member is split across volumes (i.e., its entry begins on
10967 one volume of the media and ends on another), you need to specify
10968 @option{--multi-volume} to extract it successfully. In this case, you
10969 should load the volume where the archive member starts, and use
10970 @samp{tar --extract --multi-volume}---@command{tar} will prompt for later
10971 volumes as it needs them. @xref{extracting archives}, for more
10972 information about extracting archives.
10974 Multi-volume archives can be modified like any other archive. To add
10975 files to a multi-volume archive, you need to only mount the last
10976 volume of the archive media (and new volumes, if needed). For all
10977 other operations, you need to use the entire archive.
10979 If a multi-volume archive was labeled using
10980 @option{--label=@var{archive-label}} (@pxref{label}) when it was
10981 created, @command{tar} will not automatically label volumes which are
10982 added later. To label subsequent volumes, specify
10983 @option{--label=@var{archive-label}} again in conjunction with the
10984 @option{--append}, @option{--update} or @option{--concatenate} operation.
10986 Notice that multi-volume support is a GNU extension and the archives
10987 created in this mode should be read only using @GNUTAR{}. If you
10988 absolutely have to process such archives using a third-party @command{tar}
10989 implementation, read @ref{Split Recovery}.
10992 @subsection Tape Files
10995 To give the archive a name which will be recorded in it, use the
10996 @option{--label=@var{volume-label}} (@option{-V @var{volume-label}})
10997 option. This will write a special block identifying
10998 @var{volume-label} as the name of the archive to the front of the
10999 archive which will be displayed when the archive is listed with
11000 @option{--list}. If you are creating a multi-volume archive with
11001 @option{--multi-volume} (@pxref{Using Multiple Tapes}), then the
11002 volume label will have @samp{Volume @var{nnn}} appended to the name
11003 you give, where @var{nnn} is the number of the volume of the archive.
11004 (If you use the @option{--label=@var{volume-label}}) option when
11005 reading an archive, it checks to make sure the label on the tape
11006 matches the one you give. @xref{label}.
11008 When @command{tar} writes an archive to tape, it creates a single
11009 tape file. If multiple archives are written to the same tape, one
11010 after the other, they each get written as separate tape files. When
11011 extracting, it is necessary to position the tape at the right place
11012 before running @command{tar}. To do this, use the @command{mt} command.
11013 For more information on the @command{mt} command and on the organization
11014 of tapes into a sequence of tape files, see @ref{mt}.
11016 People seem to often do:
11019 @kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
11022 or such, for pushing a common date in all volumes or an archive set.
11025 @subsection Concatenate Volumes into a Single Archive
11028 Sometimes it is necessary to convert existing @GNUTAR{} multi-volume
11029 archive to a single @command{tar} archive. Simply concatenating all
11030 volumes into one will not work, since each volume carries an additional
11031 information at the beginning. @GNUTAR{} is shipped with the shell
11032 script @command{tarcat} designed for this purpose.
11034 The script takes a list of files comprising a multi-volume archive
11035 and creates the resulting archive at the standard output. For example:
11038 @kbd{tarcat vol.1 vol.2 vol.3 | tar tf -}
11041 The script implements a simple heuristics to determine the format of
11042 the first volume file and to decide how to process the rest of the
11043 files. However, it makes no attempt to verify whether the files are
11044 given in order or even if they are valid @command{tar} archives.
11045 It uses @command{dd} and does not filter its standard error, so you
11046 will usually see lots of spurious messages.
11048 @FIXME{The script is not installed. Should we install it?}
11051 @section Including a Label in the Archive
11052 @cindex Labeling an archive
11053 @cindex Labels on the archive media
11054 @cindex Labeling multi-volume archives
11058 To avoid problems caused by misplaced paper labels on the archive
11059 media, you can include a @dfn{label} entry---an archive member which
11060 contains the name of the archive---in the archive itself. Use the
11061 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11062 option in conjunction with the @option{--create} operation to include
11063 a label entry in the archive as it is being created.
11066 @item --label=@var{archive-label}
11067 @itemx -V @var{archive-label}
11068 Includes an @dfn{archive-label} at the beginning of the archive when
11069 the archive is being created, when used in conjunction with the
11070 @option{--create} operation. Checks to make sure the archive label
11071 matches the one specified (when used in conjunction with any other
11075 If you create an archive using both
11076 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11077 and @option{--multi-volume} (@option{-M}), each volume of the archive
11078 will have an archive label of the form @samp{@var{archive-label}
11079 Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the
11080 next, and so on. @xref{Using Multiple Tapes}, for information on
11081 creating multiple volume archives.
11083 @cindex Volume label, listing
11084 @cindex Listing volume label
11085 The volume label will be displayed by @option{--list} along with
11086 the file contents. If verbose display is requested, it will also be
11087 explicitly marked as in the example below:
11091 $ @kbd{tar --verbose --list --file=iamanarchive}
11092 V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
11093 -rw-r--r-- ringo user 40 1990-05-21 13:30 iamafilename
11097 @opindex test-label
11098 @anchor{--test-label option}
11099 However, @option{--list} option will cause listing entire
11100 contents of the archive, which may be undesirable (for example, if the
11101 archive is stored on a tape). You can request checking only the volume
11102 by specifying @option{--test-label} option. This option reads only the
11103 first block of an archive, so it can be used with slow storage
11104 devices. For example:
11108 $ @kbd{tar --test-label --file=iamanarchive}
11113 If @option{--test-label} is used with a single command line
11114 argument, @command{tar} compares the volume label with the
11115 argument. It exits with code 0 if the two strings match, and with code
11116 2 otherwise. In this case no output is displayed. For example:
11120 $ @kbd{tar --test-label --file=iamanarchive 'iamalable'}
11122 $ @kbd{tar --test-label --file=iamanarchive 'iamalable' alabel}
11127 If you request any operation, other than @option{--create}, along
11128 with using @option{--label} option, @command{tar} will first check if
11129 the archive label matches the one specified and will refuse to proceed
11130 if it does not. Use this as a safety precaution to avoid accidentally
11131 overwriting existing archives. For example, if you wish to add files
11132 to @file{archive}, presumably labeled with string @samp{My volume},
11137 $ @kbd{tar -rf archive --label 'My volume' .}
11138 tar: Archive not labeled to match `My volume'
11143 in case its label does not match. This will work even if
11144 @file{archive} is not labeled at all.
11146 Similarly, @command{tar} will refuse to list or extract the
11147 archive if its label doesn't match the @var{archive-label}
11148 specified. In those cases, @var{archive-label} argument is interpreted
11149 as a globbing-style pattern which must match the actual magnetic
11150 volume label. @xref{exclude}, for a precise description of how match
11151 is attempted@footnote{Previous versions of @command{tar} used full
11152 regular expression matching, or before that, only exact string
11153 matching, instead of wildcard matchers. We decided for the sake of
11154 simplicity to use a uniform matching device through
11155 @command{tar}.}. If the switch @option{--multi-volume} (@option{-M}) is being used,
11156 the volume label matcher will also suffix @var{archive-label} by
11157 @w{@samp{ Volume [1-9]*}} if the initial match fails, before giving
11158 up. Since the volume numbering is automatically added in labels at
11159 creation time, it sounded logical to equally help the user taking care
11160 of it when the archive is being read.
11162 The @option{--label} was once called @option{--volume}, but is not
11163 available under that name anymore.
11165 You can also use @option{--label} to get a common information on
11166 all tapes of a series. For having this information different in each
11167 series created through a single script used on a regular basis, just
11168 manage to get some date string as part of the label. For example:
11172 $ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
11173 $ @kbd{tar --create --file=/dev/tape --multi-volume \
11174 --volume="Daily backup for `date +%Y-%m-%d`"}
11178 Also note that each label has its own date and time, which corresponds
11179 to when @GNUTAR{} initially attempted to write it,
11180 often soon after the operator launches @command{tar} or types the
11181 carriage return telling that the next tape is ready. Comparing date
11182 labels does give an idea of tape throughput only if the delays for
11183 rewinding tapes and the operator switching them were negligible, which
11184 is usually not the case.
11187 @section Verifying Data as It is Stored
11188 @cindex Verifying a write operation
11189 @cindex Double-checking a write operation
11194 @opindex verify, short description
11195 Attempt to verify the archive after writing.
11198 This option causes @command{tar} to verify the archive after writing it.
11199 Each volume is checked after it is written, and any discrepancies
11200 are recorded on the standard error output.
11202 Verification requires that the archive be on a back-space-able medium.
11203 This means pipes, some cartridge tape drives, and some other devices
11204 cannot be verified.
11206 You can insure the accuracy of an archive by comparing files in the
11207 system with archive members. @command{tar} can compare an archive to the
11208 file system as the archive is being written, to verify a write
11209 operation, or can compare a previously written archive, to insure that
11212 @xopindex{verify, using with @option{--create}}
11213 @xopindex{create, using with @option{--verify}}
11214 To check for discrepancies in an archive immediately after it is
11215 written, use the @option{--verify} (@option{-W}) option in conjunction with
11216 the @option{--create} operation. When this option is
11217 specified, @command{tar} checks archive members against their counterparts
11218 in the file system, and reports discrepancies on the standard error.
11220 To verify an archive, you must be able to read it from before the end
11221 of the last written entry. This option is useful for detecting data
11222 errors on some tapes. Archives written to pipes, some cartridge tape
11223 drives, and some other devices cannot be verified.
11225 One can explicitly compare an already made archive with the file
11226 system by using the @option{--compare} (@option{--diff}, @option{-d})
11227 option, instead of using the more automatic @option{--verify} option.
11230 Note that these two options have a slightly different intent. The
11231 @option{--compare} option checks how identical are the logical contents of some
11232 archive with what is on your disks, while the @option{--verify} option is
11233 really for checking if the physical contents agree and if the recording
11234 media itself is of dependable quality. So, for the @option{--verify}
11235 operation, @command{tar} tries to defeat all in-memory cache pertaining to
11236 the archive, while it lets the speed optimization undisturbed for the
11237 @option{--compare} option. If you nevertheless use @option{--compare} for
11238 media verification, you may have to defeat the in-memory cache yourself,
11239 maybe by opening and reclosing the door latch of your recording unit,
11240 forcing some doubt in your operating system about the fact this is really
11241 the same volume as the one just written or read.
11243 The @option{--verify} option would not be necessary if drivers were indeed
11244 able to detect dependably all write failures. This sometimes require many
11245 magnetic heads, some able to read after the writes occurred. One would
11246 not say that drivers unable to detect all cases are necessarily flawed,
11247 as long as programming is concerned.
11249 The @option{--verify} (@option{-W}) option will not work in
11250 conjunction with the @option{--multi-volume} (@option{-M}) option or
11251 the @option{--append} (@option{-r}), @option{--update} (@option{-u})
11252 and @option{--delete} operations. @xref{Operations}, for more
11253 information on these operations.
11255 Also, since @command{tar} normally strips leading @samp{/} from file
11256 names (@pxref{absolute}), a command like @samp{tar --verify -cf
11257 /tmp/foo.tar /etc} will work as desired only if the working directory is
11258 @file{/}, as @command{tar} uses the archive's relative member names
11259 (e.g., @file{etc/motd}) when verifying the archive.
11261 @node Write Protection
11262 @section Write Protection
11264 Almost all tapes and diskettes, and in a few rare cases, even disks can
11265 be @dfn{write protected}, to protect data on them from being changed.
11266 Once an archive is written, you should write protect the media to prevent
11267 the archive from being accidentally overwritten or deleted. (This will
11268 protect the archive from being changed with a tape or floppy drive---it
11269 will not protect it from magnet fields or other physical hazards).
11271 The write protection device itself is usually an integral part of the
11272 physical media, and can be a two position (write enabled/write
11273 disabled) switch, a notch which can be popped out or covered, a ring
11274 which can be removed from the center of a tape reel, or some other
11275 changeable feature.
11280 This appendix lists some important user-visible changes between
11281 version @GNUTAR{} @value{VERSION} and previous versions. An up-to-date
11282 version of this document is available at
11283 @uref{http://www.gnu.org/@/software/@/tar/manual/changes.html,the
11284 @GNUTAR{} documentation page}.
11287 @item Use of globbing patterns when listing and extracting.
11289 Previous versions of GNU tar assumed shell-style globbing when
11290 extracting from or listing an archive. For example:
11293 $ @kbd{tar xf foo.tar '*.c'}
11296 would extract all files whose names end in @samp{.c}. This behavior
11297 was not documented and was incompatible with traditional tar
11298 implementations. Therefore, starting from version 1.15.91, GNU tar
11299 no longer uses globbing by default. For example, the above invocation
11300 is now interpreted as a request to extract from the archive the file
11303 To facilitate transition to the new behavior for those users who got
11304 used to the previous incorrect one, @command{tar} will print a warning
11305 if it finds out that a requested member was not found in the archive
11306 and its name looks like a globbing pattern. For example:
11309 $ @kbd{tar xf foo.tar '*.c'}
11310 tar: Pattern matching characters used in file names. Please,
11311 tar: use --wildcards to enable pattern matching, or --no-wildcards to
11312 tar: suppress this warning.
11313 tar: *.c: Not found in archive
11314 tar: Error exit delayed from previous errors
11317 To treat member names as globbing patterns, use --wildcards option.
11318 If you want to tar to mimic the behavior of versions prior to 1.15.91,
11319 add this option to your @env{TAR_OPTIONS} variable.
11321 @xref{wildcards}, for the detailed discussion of the use of globbing
11322 patterns by @GNUTAR{}.
11324 @item Use of short option @option{-o}.
11326 Earlier versions of @GNUTAR{} understood @option{-o} command line
11327 option as a synonym for @option{--old-archive}.
11329 @GNUTAR{} starting from version 1.13.90 understands this option as
11330 a synonym for @option{--no-same-owner}. This is compatible with
11331 UNIX98 @command{tar} implementations.
11333 However, to facilitate transition, @option{-o} option retains its
11334 old semantics when it is used with one of archive-creation commands.
11335 Users are encouraged to use @option{--format=oldgnu} instead.
11337 It is especially important, since versions of @acronym{GNU} Automake
11338 up to and including 1.8.4 invoke tar with this option to produce
11339 distribution tarballs. @xref{Formats,v7}, for the detailed discussion
11340 of this issue and its implications.
11342 @FIXME{Change the first argument to tar-formats when the new Automake is
11343 out. The proposition to add @anchor{} to the appropriate place of its
11344 docs was accepted by Automake people --Sergey 2006-05-25}.
11345 @xref{Options, tar-v7, Changing Automake's Behavior,
11346 automake, GNU Automake}, for a description on how to use various
11347 archive formats with @command{automake}.
11349 Future versions of @GNUTAR{} will understand @option{-o} only as a
11350 synonym for @option{--no-same-owner}.
11352 @item Use of short option @option{-l}
11354 Earlier versions of @GNUTAR{} understood @option{-l} option as a
11355 synonym for @option{--one-file-system}. Since such usage contradicted
11356 to UNIX98 specification and harmed compatibility with other
11357 implementation, it was declared deprecated in version 1.14. However,
11358 to facilitate transition to its new semantics, it was supported by
11359 versions 1.15 and 1.15.90. The present use of @option{-l} as a short
11360 variant of @option{--check-links} was introduced in version 1.15.91.
11362 @item Use of options @option{--portability} and @option{--old-archive}
11364 These options are deprecated. Please use @option{--format=v7} instead.
11366 @item Use of option @option{--posix}
11368 This option is deprecated. Please use @option{--format=posix} instead.
11371 @node Configuring Help Summary
11372 @appendix Configuring Help Summary
11374 Running @kbd{tar --help} displays the short @command{tar} option
11375 summary (@pxref{help}). This summary is organized by @dfn{groups} of
11376 semantically close options. The options within each group are printed
11377 in the following order: a short option, eventually followed by a list
11378 of corresponding long option names, followed by a short description of
11379 the option. For example, here is an excerpt from the actual @kbd{tar
11383 Main operation mode:
11385 -A, --catenate, --concatenate append tar files to an archive
11386 -c, --create create a new archive
11387 -d, --diff, --compare find differences between archive and
11389 --delete delete from the archive
11392 @vrindex ARGP_HELP_FMT, environment variable
11393 The exact visual representation of the help output is configurable via
11394 @env{ARGP_HELP_FMT} environment variable. The value of this variable
11395 is a comma-separated list of @dfn{format variable} assignments. There
11396 are two kinds of format variables. An @dfn{offset variable} keeps the
11397 offset of some part of help output text from the leftmost column on
11398 the screen. A @dfn{boolean} variable is a flag that toggles some
11399 output feature on or off. Depending on the type of the corresponding
11400 variable, there are two kinds of assignments:
11403 @item Offset assignment
11405 The assignment to an offset variable has the following syntax:
11408 @var{variable}=@var{value}
11412 where @var{variable} is the variable name, and @var{value} is a
11413 numeric value to be assigned to the variable.
11415 @item Boolean assignment
11417 To assign @code{true} value to a variable, simply put this variable name. To
11418 assign @code{false} value, prefix the variable name with @samp{no-}. For
11423 # Assign @code{true} value:
11425 # Assign @code{false} value:
11431 Following variables are declared:
11433 @deftypevr {Help Output} boolean dup-args
11434 If true, arguments for an option are shown with both short and long
11435 options, even when a given option has both forms, for example:
11438 -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE
11441 If false, then if an option has both short and long forms, the
11442 argument is only shown with the long one, for example:
11445 -f, --file=ARCHIVE use archive file or device ARCHIVE
11449 and a message indicating that the argument is applicable to both
11450 forms is printed below the options. This message can be disabled
11451 using @code{dup-args-note} (see below).
11453 The default is false.
11456 @deftypevr {Help Output} boolean dup-args-note
11457 If this variable is true, which is the default, the following notice
11458 is displayed at the end of the help output:
11461 Mandatory or optional arguments to long options are also mandatory or
11462 optional for any corresponding short options.
11465 Setting @code{no-dup-args-note} inhibits this message. Normally, only one of
11466 variables @code{dup-args} or @code{dup-args-note} should be set.
11469 @deftypevr {Help Output} offset short-opt-col
11470 Column in which short options start. Default is 2.
11474 $ @kbd{tar --help|grep ARCHIVE}
11475 -f, --file=ARCHIVE use archive file or device ARCHIVE
11476 $ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE}
11477 -f, --file=ARCHIVE use archive file or device ARCHIVE
11482 @deftypevr {Help Output} offset long-opt-col
11483 Column in which long options start. Default is 6. For example:
11487 $ @kbd{tar --help|grep ARCHIVE}
11488 -f, --file=ARCHIVE use archive file or device ARCHIVE
11489 $ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE}
11490 -f, --file=ARCHIVE use archive file or device ARCHIVE
11495 @deftypevr {Help Output} offset doc-opt-col
11496 Column in which @dfn{doc options} start. A doc option isn't actually
11497 an option, but rather an arbitrary piece of documentation that is
11498 displayed in much the same manner as the options. For example, in
11499 the description of @option{--format} option:
11503 -H, --format=FORMAT create archive of the given format.
11505 FORMAT is one of the following:
11507 gnu GNU tar 1.13.x format
11508 oldgnu GNU format as per tar <= 1.12
11509 pax POSIX 1003.1-2001 (pax) format
11511 ustar POSIX 1003.1-1988 (ustar) format
11512 v7 old V7 tar format
11517 the format names are doc options. Thus, if you set
11518 @kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output
11519 will look as follows:
11523 -H, --format=FORMAT create archive of the given format.
11525 FORMAT is one of the following:
11527 gnu GNU tar 1.13.x format
11528 oldgnu GNU format as per tar <= 1.12
11529 pax POSIX 1003.1-2001 (pax) format
11531 ustar POSIX 1003.1-1988 (ustar) format
11532 v7 old V7 tar format
11537 @deftypevr {Help Output} offset opt-doc-col
11538 Column in which option description starts. Default is 29.
11542 $ @kbd{tar --help|grep ARCHIVE}
11543 -f, --file=ARCHIVE use archive file or device ARCHIVE
11544 $ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE}
11545 -f, --file=ARCHIVE use archive file or device ARCHIVE
11546 $ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE}
11548 use archive file or device ARCHIVE
11553 Notice, that the description starts on a separate line if
11554 @code{opt-doc-col} value is too small.
11557 @deftypevr {Help Output} offset header-col
11558 Column in which @dfn{group headers} are printed. A group header is a
11559 descriptive text preceding an option group. For example, in the
11563 Main operation mode:
11565 -A, --catenate, --concatenate append tar files to
11567 -c, --create create a new archive
11570 @samp{Main operation mode:} is the group header.
11572 The default value is 1.
11575 @deftypevr {Help Output} offset usage-indent
11576 Indentation of wrapped usage lines. Affects @option{--usage}
11577 output. Default is 12.
11580 @deftypevr {Help Output} offset rmargin
11581 Right margin of the text output. Used for wrapping.
11584 @node Fixing Snapshot Files
11585 @appendix Fixing Snapshot Files
11586 @include tar-snapshot-edit.texi
11588 @node Tar Internals
11589 @appendix Tar Internals
11590 @include intern.texi
11594 @include genfile.texi
11596 @node Free Software Needs Free Documentation
11597 @appendix Free Software Needs Free Documentation
11598 @include freemanuals.texi
11600 @node Copying This Manual
11601 @appendix Copying This Manual
11604 * GNU Free Documentation License:: License for copying this manual
11609 @node Index of Command Line Options
11610 @appendix Index of Command Line Options
11612 This appendix contains an index of all @GNUTAR{} long command line
11613 options. The options are listed without the preceding double-dash.
11614 For a cross-reference of short command line options, @ref{Short Option Summary}.
11627 @c Local variables:
11628 @c texinfo-column-for-description: 32
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