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 1.1. Run `make check-options' to make sure all options are properly
18 @c 2.1. 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 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 are free to copy and modify
49 this GNU Manual. Buying copies from GNU Press supports the FSF in
50 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::
114 * Free Software Needs Free Documentation::
115 * Copying This Manual::
116 * Index of Command Line Options::
120 --- The Detailed Node Listing ---
124 * Book Contents:: What this Book Contains
125 * Definitions:: Some Definitions
126 * What tar Does:: What @command{tar} Does
127 * Naming tar Archives:: How @command{tar} Archives are Named
128 * Authors:: @GNUTAR{} Authors
129 * Reports:: Reporting bugs or suggestions
131 Tutorial Introduction to @command{tar}
134 * stylistic conventions::
135 * basic tar options:: Basic @command{tar} Operations and Options
136 * frequent operations::
137 * Two Frequent Options::
138 * create:: How to Create Archives
139 * list:: How to List Archives
140 * extract:: How to Extract Members from an Archive
143 Two Frequently Used Options
149 How to Create Archives
151 * prepare for examples::
152 * Creating the archive::
161 How to Extract Members from an Archive
163 * extracting archives::
166 * extracting untrusted archives::
172 * using tar options::
180 The Three Option Styles
182 * Long Options:: Long Option Style
183 * Short Options:: Short Option Style
184 * Old Options:: Old Option Style
185 * Mixing:: Mixing Option Styles
187 All @command{tar} Options
189 * Operation Summary::
191 * Short Option Summary::
203 Advanced @GNUTAR{} Operations
212 How to Add Files to Existing Archives: @option{--append}
214 * appending files:: Appending Files to an Archive
221 Options Used by @option{--create}
223 * Ignore Failed Read::
225 Options Used by @option{--extract}
227 * Reading:: Options to Help Read Archives
228 * Writing:: Changing How @command{tar} Writes Files
229 * Scarce:: Coping with Scarce Resources
231 Options to Help Read Archives
233 * read full records::
236 Changing How @command{tar} Writes Files
238 * Dealing with Old Files::
239 * Overwrite Old Files::
244 * Data Modification Times::
245 * Setting Access Permissions::
246 * Directory Modification Times and Permissions::
247 * Writing to Standard Output::
248 * Writing to an External Program::
251 Coping with Scarce Resources
256 Performing Backups and Restoring Files
258 * Full Dumps:: Using @command{tar} to Perform Full Dumps
259 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
260 * Backup Levels:: Levels of Backups
261 * Backup Parameters:: Setting Parameters for Backups and Restoration
262 * Scripted Backups:: Using the Backup Scripts
263 * Scripted Restoration:: Using the Restore Script
265 Setting Parameters for Backups and Restoration
267 * General-Purpose Variables::
268 * Magnetic Tape Control::
270 * backup-specs example:: An Example Text of @file{Backup-specs}
272 Choosing Files and Names for @command{tar}
274 * file:: Choosing the Archive's Name
275 * Selecting Archive Members::
276 * files:: Reading Names from a File
277 * exclude:: Excluding Some Files
278 * wildcards:: Wildcards Patterns and Matching
279 * quoting styles:: Ways of Quoting Special Characters in Names
280 * transform:: Modifying File and Member Names
281 * after:: Operating Only on New Files
282 * recurse:: Descending into Directories
283 * one:: Crossing File System Boundaries
285 Reading Names from a File
291 * problems with exclude::
293 Wildcards Patterns and Matching
295 * controlling pattern-matching::
297 Crossing File System Boundaries
299 * directory:: Changing Directory
300 * absolute:: Absolute File Names
304 * General date syntax:: Common rules.
305 * Calendar date items:: 19 Dec 1994.
306 * Time of day items:: 9:20pm.
307 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
308 * Day of week items:: Monday and others.
309 * Relative items in date strings:: next tuesday, 2 years ago.
310 * Pure numbers in date strings:: 19931219, 1440.
311 * Seconds since the Epoch:: @@1078100502.
312 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
313 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
315 Controlling the Archive Format
317 * Portability:: Making @command{tar} Archives More Portable
318 * Compression:: Using Less Space through Compression
319 * Attributes:: Handling File Attributes
320 * cpio:: Comparison of @command{tar} and @command{cpio}
322 Making @command{tar} Archives More Portable
324 * Portable Names:: Portable Names
325 * dereference:: Symbolic Links
326 * old:: Old V7 Archives
327 * ustar:: Ustar Archives
328 * gnu:: GNU and old GNU format archives.
329 * posix:: @acronym{POSIX} archives
330 * Checksumming:: Checksumming Problems
331 * Large or Negative Values:: Large files, negative time stamps, etc.
333 @GNUTAR{} and @acronym{POSIX} @command{tar}
335 * PAX keywords:: Controlling Extended Header Keywords.
337 Using Less Space through Compression
339 * gzip:: Creating and Reading Compressed Archives
340 * sparse:: Archiving Sparse Files
342 Tapes and Other Archive Media
344 * Device:: Device selection and switching
345 * Remote Tape Server::
346 * Common Problems and Solutions::
347 * Blocking:: Blocking
348 * Many:: Many archives on one tape
349 * Using Multiple Tapes:: Using Multiple Tapes
350 * label:: Including a Label in the Archive
356 * Format Variations:: Format Variations
357 * Blocking Factor:: The Blocking Factor of an Archive
359 Many Archives on One Tape
361 * Tape Positioning:: Tape Positions and Tape Marks
362 * mt:: The @command{mt} Utility
366 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
367 * Tape Files:: Tape Files
368 * Tarcat:: Concatenate Volumes into a Single Archive
373 * Generate Mode:: File Generation Mode.
374 * Status Mode:: File Status Mode.
375 * Exec Mode:: Synchronous Execution mode.
379 * Standard:: Basic Tar Format
380 * Extensions:: @acronym{GNU} Extensions to the Archive Format
386 * GNU Free Documentation License:: License for copying this manual
392 @chapter Introduction
395 and manipulates @dfn{archives} which are actually collections of
396 many other files; the program provides users with an organized and
397 systematic method for controlling a large amount of data.
398 The name ``tar'' originally came from the phrase ``Tape ARchive'', but
399 archives need not (and these days, typically do not) reside on tapes.
402 * Book Contents:: What this Book Contains
403 * Definitions:: Some Definitions
404 * What tar Does:: What @command{tar} Does
405 * Naming tar Archives:: How @command{tar} Archives are Named
406 * Authors:: @GNUTAR{} Authors
407 * Reports:: Reporting bugs or suggestions
411 @section What this Book Contains
413 The first part of this chapter introduces you to various terms that will
414 recur throughout the book. It also tells you who has worked on @GNUTAR{}
415 and its documentation, and where you should send bug reports
418 The second chapter is a tutorial (@pxref{Tutorial}) which provides a
419 gentle introduction for people who are new to using @command{tar}. It is
420 meant to be self contained, not requiring any reading from subsequent
421 chapters to make sense. It moves from topic to topic in a logical,
422 progressive order, building on information already explained.
424 Although the tutorial is paced and structured to allow beginners to
425 learn how to use @command{tar}, it is not intended solely for beginners.
426 The tutorial explains how to use the three most frequently used
427 operations (@samp{create}, @samp{list}, and @samp{extract}) as well as
428 two frequently used options (@samp{file} and @samp{verbose}). The other
429 chapters do not refer to the tutorial frequently; however, if a section
430 discusses something which is a complex variant of a basic concept, there
431 may be a cross reference to that basic concept. (The entire book,
432 including the tutorial, assumes that the reader understands some basic
433 concepts of using a Unix-type operating system; @pxref{Tutorial}.)
435 The third chapter presents the remaining five operations, and
436 information about using @command{tar} options and option syntax.
438 @FIXME{this sounds more like a @acronym{GNU} Project Manuals Concept [tm] more
439 than the reality. should think about whether this makes sense to say
440 here, or not.} The other chapters are meant to be used as a
441 reference. Each chapter presents everything that needs to be said
442 about a specific topic.
444 One of the chapters (@pxref{Date input formats}) exists in its
445 entirety in other @acronym{GNU} manuals, and is mostly self-contained.
446 In addition, one section of this manual (@pxref{Standard}) contains a
447 big quote which is taken directly from @command{tar} sources.
449 In general, we give both long and short (abbreviated) option names
450 at least once in each section where the relevant option is covered, so
451 that novice readers will become familiar with both styles. (A few
452 options have no short versions, and the relevant sections will
456 @section Some Definitions
460 The @command{tar} program is used to create and manipulate @command{tar}
461 archives. An @dfn{archive} is a single file which contains the contents
462 of many files, while still identifying the names of the files, their
463 owner(s), and so forth. (In addition, archives record access
464 permissions, user and group, size in bytes, and data modification time.
465 Some archives also record the file names in each archived directory, as
466 well as other file and directory information.) You can use @command{tar}
467 to @dfn{create} a new archive in a specified directory.
470 @cindex archive member
473 The files inside an archive are called @dfn{members}. Within this
474 manual, we use the term @dfn{file} to refer only to files accessible in
475 the normal ways (by @command{ls}, @command{cat}, and so forth), and the term
476 @dfn{member} to refer only to the members of an archive. Similarly, a
477 @dfn{file name} is the name of a file, as it resides in the file system,
478 and a @dfn{member name} is the name of an archive member within the
483 The term @dfn{extraction} refers to the process of copying an archive
484 member (or multiple members) into a file in the file system. Extracting
485 all the members of an archive is often called @dfn{extracting the
486 archive}. The term @dfn{unpack} can also be used to refer to the
487 extraction of many or all the members of an archive. Extracting an
488 archive does not destroy the archive's structure, just as creating an
489 archive does not destroy the copies of the files that exist outside of
490 the archive. You may also @dfn{list} the members in a given archive
491 (this is often thought of as ``printing'' them to the standard output,
492 or the command line), or @dfn{append} members to a pre-existing archive.
493 All of these operations can be performed using @command{tar}.
496 @section What @command{tar} Does
499 The @command{tar} program provides the ability to create @command{tar}
500 archives, as well as various other kinds of manipulation. For example,
501 you can use @command{tar} on previously created archives to extract files,
502 to store additional files, or to update or list files which were already
505 Initially, @command{tar} archives were used to store files conveniently on
506 magnetic tape. The name @command{tar} comes from this use; it stands for
507 @code{t}ape @code{ar}chiver. Despite the utility's name, @command{tar} can
508 direct its output to available devices, files, or other programs (using
509 pipes). @command{tar} may even access remote devices or files (as archives).
511 You can use @command{tar} archives in many ways. We want to stress a few
512 of them: storage, backup, and transportation.
514 @FIXME{the following table entries need a bit of work..}
517 Often, @command{tar} archives are used to store related files for
518 convenient file transfer over a network. For example, the
519 @acronym{GNU} Project distributes its software bundled into
520 @command{tar} archives, so that all the files relating to a particular
521 program (or set of related programs) can be transferred as a single
524 A magnetic tape can store several files in sequence. However, the tape
525 has no names for these files; it only knows their relative position on
526 the tape. One way to store several files on one tape and retain their
527 names is by creating a @command{tar} archive. Even when the basic transfer
528 mechanism can keep track of names, as FTP can, the nuisance of handling
529 multiple files, directories, and multiple links makes @command{tar}
532 Archive files are also used for long-term storage. You can think of
533 this as transportation from the present into the future. (It is a
534 science-fiction idiom that you can move through time as well as in
535 space; the idea here is that @command{tar} can be used to move archives in
536 all dimensions, even time!)
539 Because the archive created by @command{tar} is capable of preserving
540 file information and directory structure, @command{tar} is commonly
541 used for performing full and incremental backups of disks. A backup
542 puts a collection of files (possibly pertaining to many users and
543 projects) together on a disk or a tape. This guards against
544 accidental destruction of the information in those files.
545 @GNUTAR{} has special features that allow it to be
546 used to make incremental and full dumps of all the files in a
550 You can create an archive on one system, transfer it to another system,
551 and extract the contents there. This allows you to transport a group of
552 files from one system to another.
555 @node Naming tar Archives
556 @section How @command{tar} Archives are Named
558 Conventionally, @command{tar} archives are given names ending with
559 @samp{.tar}. This is not necessary for @command{tar} to operate properly,
560 but this manual follows that convention in order to accustom readers to
561 it and to make examples more clear.
566 Often, people refer to @command{tar} archives as ``@command{tar} files,'' and
567 archive members as ``files'' or ``entries''. For people familiar with
568 the operation of @command{tar}, this causes no difficulty. However, in
569 this manual, we consistently refer to ``archives'' and ``archive
570 members'' to make learning to use @command{tar} easier for novice users.
573 @section @GNUTAR{} Authors
575 @GNUTAR{} was originally written by John Gilmore,
576 and modified by many people. The @acronym{GNU} enhancements were
577 written by Jay Fenlason, then Joy Kendall, and the whole package has
578 been further maintained by Thomas Bushnell, n/BSG, Fran@,{c}ois
579 Pinard, Paul Eggert, and finally Sergey Poznyakoff with the help of
580 numerous and kind users.
582 We wish to stress that @command{tar} is a collective work, and owes much to
583 all those people who reported problems, offered solutions and other
584 insights, or shared their thoughts and suggestions. An impressive, yet
585 partial list of those contributors can be found in the @file{THANKS}
586 file from the @GNUTAR{} distribution.
588 @FIXME{i want all of these names mentioned, Absolutely. BUT, i'm not
589 sure i want to spell out the history in this detail, at least not for
590 the printed book. i'm just not sure it needs to be said this way.
591 i'll think about it.}
593 @FIXME{History is more important, and surely more interesting, than
594 actual names. Quoting names without history would be meaningless. FP}
596 Jay Fenlason put together a draft of a @GNUTAR{}
597 manual, borrowing notes from the original man page from John Gilmore.
598 This was withdrawn in version 1.11. Thomas Bushnell, n/BSG and Amy
599 Gorin worked on a tutorial and manual for @GNUTAR{}.
600 Fran@,{c}ois Pinard put version 1.11.8 of the manual together by
601 taking information from all these sources and merging them. Melissa
602 Weisshaus finally edited and redesigned the book to create version
603 1.12. The book for versions from 1.14 up to @value{VERSION} were edited
604 by the current maintainer, Sergey Poznyakoff.
606 For version 1.12, Daniel Hagerty contributed a great deal of technical
607 consulting. In particular, he is the primary author of @ref{Backups}.
609 In July, 2003 @GNUTAR{} was put on CVS at savannah.gnu.org
610 (see @url{http://savannah.gnu.org/projects/tar}), and
611 active development and maintenance work has started
612 again. Currently @GNUTAR{} is being maintained by Paul Eggert, Sergey
613 Poznyakoff and Jeff Bailey.
615 Support for @acronym{POSIX} archives was added by Sergey Poznyakoff.
618 @section Reporting bugs or suggestions
621 @cindex reporting bugs
622 If you find problems or have suggestions about this program or manual,
623 please report them to @file{bug-tar@@gnu.org}.
625 When reporting a bug, please be sure to include as much detail as
626 possible, in order to reproduce it. @FIXME{Be more specific, I'd
627 like to make this node as detailed as 'Bug reporting' node in Emacs
631 @chapter Tutorial Introduction to @command{tar}
633 This chapter guides you through some basic examples of three @command{tar}
634 operations: @option{--create}, @option{--list}, and @option{--extract}. If
635 you already know how to use some other version of @command{tar}, then you
636 may not need to read this chapter. This chapter omits most complicated
637 details about how @command{tar} works.
641 * stylistic conventions::
642 * basic tar options:: Basic @command{tar} Operations and Options
643 * frequent operations::
644 * Two Frequent Options::
645 * create:: How to Create Archives
646 * list:: How to List Archives
647 * extract:: How to Extract Members from an Archive
652 @section Assumptions this Tutorial Makes
654 This chapter is paced to allow beginners to learn about @command{tar}
655 slowly. At the same time, we will try to cover all the basic aspects of
656 these three operations. In order to accomplish both of these tasks, we
657 have made certain assumptions about your knowledge before reading this
658 manual, and the hardware you will be using:
662 Before you start to work through this tutorial, you should understand
663 what the terms ``archive'' and ``archive member'' mean
664 (@pxref{Definitions}). In addition, you should understand something
665 about how Unix-type operating systems work, and you should know how to
666 use some basic utilities. For example, you should know how to create,
667 list, copy, rename, edit, and delete files and directories; how to
668 change between directories; and how to figure out where you are in the
669 file system. You should have some basic understanding of directory
670 structure and how files are named according to which directory they are
671 in. You should understand concepts such as standard output and standard
672 input, what various definitions of the term ``argument'' mean, and the
673 differences between relative and absolute path names. @FIXME{and what
677 This manual assumes that you are working from your own home directory
678 (unless we state otherwise). In this tutorial, you will create a
679 directory to practice @command{tar} commands in. When we show path names,
680 we will assume that those paths are relative to your home directory.
681 For example, my home directory path is @file{/home/fsf/melissa}. All of
682 my examples are in a subdirectory of the directory named by that path
683 name; the subdirectory is called @file{practice}.
686 In general, we show examples of archives which exist on (or can be
687 written to, or worked with from) a directory on a hard disk. In most
688 cases, you could write those archives to, or work with them on any other
689 device, such as a tape drive. However, some of the later examples in
690 the tutorial and next chapter will not work on tape drives.
691 Additionally, working with tapes is much more complicated than working
692 with hard disks. For these reasons, the tutorial does not cover working
693 with tape drives. @xref{Media}, for complete information on using
694 @command{tar} archives with tape drives.
696 @FIXME{this is a cop out. need to add some simple tape drive info.}
699 @node stylistic conventions
700 @section Stylistic Conventions
702 In the examples, @samp{$} represents a typical shell prompt. It
703 precedes lines you should type; to make this more clear, those lines are
704 shown in @kbd{this font}, as opposed to lines which represent the
705 computer's response; those lines are shown in @code{this font}, or
706 sometimes @samp{like this}.
708 @c When we have lines which are too long to be
709 @c displayed in any other way, we will show them like this:
711 @node basic tar options
712 @section Basic @command{tar} Operations and Options
714 @command{tar} can take a wide variety of arguments which specify and define
715 the actions it will have on the particular set of files or the archive.
716 The main types of arguments to @command{tar} fall into one of two classes:
717 operations, and options.
719 Some arguments fall into a class called @dfn{operations}; exactly one of
720 these is both allowed and required for any instance of using @command{tar};
721 you may @emph{not} specify more than one. People sometimes speak of
722 @dfn{operating modes}. You are in a particular operating mode when you
723 have specified the operation which specifies it; there are eight
724 operations in total, and thus there are eight operating modes.
726 The other arguments fall into the class known as @dfn{options}. You are
727 not required to specify any options, and you are allowed to specify more
728 than one at a time (depending on the way you are using @command{tar} at
729 that time). Some options are used so frequently, and are so useful for
730 helping you type commands more carefully that they are effectively
731 ``required''. We will discuss them in this chapter.
733 You can write most of the @command{tar} operations and options in any
734 of three forms: long (mnemonic) form, short form, and old style. Some
735 of the operations and options have no short or ``old'' forms; however,
736 the operations and options which we will cover in this tutorial have
737 corresponding abbreviations. @FIXME{make sure this is still the case,
738 at the end}We will indicate those abbreviations appropriately to get
739 you used to seeing them. (Note that the ``old style'' option forms
740 exist in @GNUTAR{} for compatibility with Unix
741 @command{tar}. In this book we present a full discussion of this way
742 of writing options and operations (@pxref{Old Options}), and we discuss
743 the other two styles of writing options (@xref{Long Options}, and
744 @pxref{Short Options}).
746 In the examples and in the text of this tutorial, we usually use the
747 long forms of operations and options; but the ``short'' forms produce
748 the same result and can make typing long @command{tar} commands easier.
749 For example, instead of typing
752 @kbd{tar --create --verbose --file=afiles.tar apple angst aspic}
758 @kbd{tar -c -v -f afiles.tar apple angst aspic}
764 @kbd{tar -cvf afiles.tar apple angst aspic}
768 For more information on option syntax, see @ref{Advanced tar}. In
769 discussions in the text, when we name an option by its long form, we
770 also give the corresponding short option in parentheses.
772 The term, ``option'', can be confusing at times, since ``operations''
773 are often lumped in with the actual, @emph{optional} ``options'' in certain
774 general class statements. For example, we just talked about ``short and
775 long forms of options and operations''. However, experienced @command{tar}
776 users often refer to these by shorthand terms such as, ``short and long
777 options''. This term assumes that the ``operations'' are included, also.
778 Context will help you determine which definition of ``options'' to use.
780 Similarly, the term ``command'' can be confusing, as it is often used in
781 two different ways. People sometimes refer to @command{tar} ``commands''.
782 A @command{tar} @dfn{command} is the entire command line of user input
783 which tells @command{tar} what to do --- including the operation, options,
784 and any arguments (file names, pipes, other commands, etc). However,
785 you will also sometimes hear the term ``the @command{tar} command''. When
786 the word ``command'' is used specifically like this, a person is usually
787 referring to the @command{tar} @emph{operation}, not the whole line.
788 Again, use context to figure out which of the meanings the speaker
791 @node frequent operations
792 @section The Three Most Frequently Used Operations
794 Here are the three most frequently used operations (both short and long
795 forms), as well as a brief description of their meanings. The rest of
796 this chapter will cover how to use these operations in detail. We will
797 present the rest of the operations in the next chapter.
802 Create a new @command{tar} archive.
805 List the contents of an archive.
808 Extract one or more members from an archive.
811 @node Two Frequent Options
812 @section Two Frequently Used Options
814 To understand how to run @command{tar} in the three operating modes listed
815 previously, you also need to understand how to use two of the options to
816 @command{tar}: @option{--file} (which takes an archive file as an argument)
817 and @option{--verbose}. (You are usually not @emph{required} to specify
818 either of these options when you run @command{tar}, but they can be very
819 useful in making things more clear and helping you avoid errors.)
828 @unnumberedsubsec The @option{--file} Option
831 @xopindex{file, tutorial}
832 @item --file=@var{archive-name}
833 @itemx -f @var{archive-name}
834 Specify the name of an archive file.
837 You can specify an argument for the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option whenever you
838 use @command{tar}; this option determines the name of the archive file
839 that @command{tar} will work on.
842 If you don't specify this argument, then @command{tar} will examine
843 the environment variable @env{TAPE}. If it is set, its value will be
844 used as the archive name. Otherwise, @command{tar} will use the
845 default archive, determined at the compile time. Usually it is
846 standard output or some physical tape drive attached to your machine
847 (you can verify what the default is by running @kbd{tar
848 --show-defaults}, @pxref{defaults}). If there is no tape drive
849 attached, or the default is not meaningful, then @command{tar} will
850 print an error message. The error message might look roughly like one
854 tar: can't open /dev/rmt8 : No such device or address
855 tar: can't open /dev/rsmt0 : I/O error
859 To avoid confusion, we recommend that you always specify an archive file
860 name by using @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) when writing your @command{tar} commands.
861 For more information on using the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option, see
864 @node verbose tutorial
865 @unnumberedsubsec The @option{--verbose} Option
868 @xopindex{verbose, introduced}
871 Show the files being worked on as @command{tar} is running.
874 @option{--verbose} (@option{-v}) shows details about the results of running
875 @command{tar}. This can be especially useful when the results might not be
876 obvious. For example, if you want to see the progress of @command{tar} as
877 it writes files into the archive, you can use the @option{--verbose}
878 option. In the beginning, you may find it useful to use
879 @option{--verbose} at all times; when you are more accustomed to
880 @command{tar}, you will likely want to use it at certain times but not at
881 others. We will use @option{--verbose} at times to help make something
882 clear, and we will give many examples both using and not using
883 @option{--verbose} to show the differences.
885 Each instance of @option{--verbose} on the command line increases the
886 verbosity level by one, so if you need more details on the output,
889 When reading archives (@option{--list}, @option{--extract},
890 @option{--diff}), @command{tar} by default prints only the names of
891 the members being extracted. Using @option{--verbose} will show a full,
892 @command{ls} style member listing.
894 In contrast, when writing archives (@option{--create}, @option{--append},
895 @option{--update}), @command{tar} does not print file names by
896 default. So, a single @option{--verbose} option shows the file names
897 being added to the archive, while two @option{--verbose} options
898 enable the full listing.
900 For example, to create an archive in verbose mode:
903 $ @kbd{tar -cvf afiles.tar apple angst aspic}
910 Creating the same archive with the verbosity level 2 could give:
913 $ @kbd{tar -cvvf afiles.tar apple angst aspic}
914 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
915 -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst
916 -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
920 This works equally well using short or long forms of options. Using
921 long forms, you would simply write out the mnemonic form of the option
925 $ @kbd{tar --create --verbose --verbose @dots{}}
929 Note that you must double the hyphens properly each time.
931 Later in the tutorial, we will give examples using @w{@option{--verbose
934 @anchor{verbose member listing}
935 The full output consists of six fields:
938 @item File type and permissions in symbolic form.
939 These are displayed in the same format as the first column of
940 @command{ls -l} output (@pxref{What information is listed,
941 format=verbose, Verbose listing, fileutils, GNU file utilities}).
943 @item Owner name and group separated by a slash character.
944 If these data are not available (for example, when listing a @samp{v7} format
945 archive), numeric ID values are printed instead.
947 @item Size of the file, in bytes.
949 @item File modification date in ISO 8601 format.
951 @item File modification time.
954 If the name contains any special characters (white space, newlines,
955 etc.) these are displayed in an unambiguous form using so called
956 @dfn{quoting style}. For the detailed discussion of available styles
957 and on how to use them, see @ref{quoting styles}.
959 Depending on the file type, the name can be followed by some
960 additional information, described in the following table:
963 @item -> @var{link-name}
964 The file or archive member is a @dfn{symbolic link} and
965 @var{link-name} is the name of file it links to.
967 @item link to @var{link-name}
968 The file or archive member is a @dfn{hard link} and @var{link-name} is
969 the name of file it links to.
972 The archive member is an old GNU format long link. You will normally
976 The archive member is an old GNU format long name. You will normally
979 @item --Volume Header--
980 The archive member is a GNU @dfn{volume header} (@pxref{Tape Files}).
982 @item --Continued at byte @var{n}--
983 Encountered only at the beginning of a multy-volume archive
984 (@pxref{Using Multiple Tapes}). This archive member is a continuation
985 from the previous volume. The number @var{n} gives the offset where
986 the original file was split.
988 @item --Mangled file names--
989 This archive member contains @dfn{mangled file names} declarations,
990 a special member type that was used by early versions of @GNUTAR{}.
991 You probably will never encounter this, unless you are reading a very
994 @item unknown file type @var{c}
995 An archive member of unknown type. @var{c} is the type character from
996 the archive header. If you encounter such a message, it means that
997 either your archive contains proprietary member types @GNUTAR{} is not
998 able to handle, or the archive is corrupted.
1003 For example, here is an archive listing containing most of the special
1004 suffixes explained above:
1008 V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header--
1009 -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at
1011 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
1012 lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple
1013 -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues
1014 hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
1022 @unnumberedsubsec Getting Help: Using the @option{--help} Option
1028 The @option{--help} option to @command{tar} prints out a very brief list of
1029 all operations and option available for the current version of
1030 @command{tar} available on your system.
1034 @section How to Create Archives
1037 @cindex Creation of the archive
1038 @cindex Archive, creation of
1039 One of the basic operations of @command{tar} is @option{--create} (@option{-c}), which
1040 you use to create a @command{tar} archive. We will explain
1041 @option{--create} first because, in order to learn about the other
1042 operations, you will find it useful to have an archive available to
1045 To make this easier, in this section you will first create a directory
1046 containing three files. Then, we will show you how to create an
1047 @emph{archive} (inside the new directory). Both the directory, and
1048 the archive are specifically for you to practice on. The rest of this
1049 chapter and the next chapter will show many examples using this
1050 directory and the files you will create: some of those files may be
1051 other directories and other archives.
1053 The three files you will archive in this example are called
1054 @file{blues}, @file{folk}, and @file{jazz}. The archive is called
1055 @file{collection.tar}.
1057 This section will proceed slowly, detailing how to use @option{--create}
1058 in @code{verbose} mode, and showing examples using both short and long
1059 forms. In the rest of the tutorial, and in the examples in the next
1060 chapter, we will proceed at a slightly quicker pace. This section
1061 moves more slowly to allow beginning users to understand how
1062 @command{tar} works.
1065 * prepare for examples::
1066 * Creating the archive::
1072 @node prepare for examples
1073 @subsection Preparing a Practice Directory for Examples
1075 To follow along with this and future examples, create a new directory
1076 called @file{practice} containing files called @file{blues}, @file{folk}
1077 and @file{jazz}. The files can contain any information you like:
1078 ideally, they should contain information which relates to their names,
1079 and be of different lengths. Our examples assume that @file{practice}
1080 is a subdirectory of your home directory.
1082 Now @command{cd} to the directory named @file{practice}; @file{practice}
1083 is now your @dfn{working directory}. (@emph{Please note}: Although
1084 the full path name of this directory is
1085 @file{/@var{homedir}/practice}, in our examples we will refer to
1086 this directory as @file{practice}; the @var{homedir} is presumed.
1088 In general, you should check that the files to be archived exist where
1089 you think they do (in the working directory) by running @command{ls}.
1090 Because you just created the directory and the files and have changed to
1091 that directory, you probably don't need to do that this time.
1093 It is very important to make sure there isn't already a file in the
1094 working directory with the archive name you intend to use (in this case,
1095 @samp{collection.tar}), or that you don't care about its contents.
1096 Whenever you use @samp{create}, @command{tar} will erase the current
1097 contents of the file named by @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) if it exists. @command{tar}
1098 will not tell you if you are about to overwrite an archive unless you
1099 specify an option which does this (@pxref{backup}, for the
1100 information on how to do so). To add files to an existing archive,
1101 you need to use a different option, such as @option{--append} (@option{-r}); see
1102 @ref{append} for information on how to do this.
1104 @node Creating the archive
1105 @subsection Creating the Archive
1107 @xopindex{create, introduced}
1108 To place the files @file{blues}, @file{folk}, and @file{jazz} into an
1109 archive named @file{collection.tar}, use the following command:
1112 $ @kbd{tar --create --file=collection.tar blues folk jazz}
1115 The order of the arguments is not very important, @emph{when using long
1116 option forms}. You could also say:
1119 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1123 However, you can see that this order is harder to understand; this is
1124 why we will list the arguments in the order that makes the commands
1125 easiest to understand (and we encourage you to do the same when you use
1126 @command{tar}, to avoid errors).
1128 Note that the part of the command which says,
1129 @option{--file=@-collection.tar} is considered to be @emph{one} argument.
1130 If you substituted any other string of characters for
1131 @kbd{collection.tar}, then that string would become the name of the
1132 archive file you create.
1134 The order of the options becomes more important when you begin to use
1135 short forms. With short forms, if you type commands in the wrong order
1136 (even if you type them correctly in all other ways), you may end up with
1137 results you don't expect. For this reason, it is a good idea to get
1138 into the habit of typing options in the order that makes inherent sense.
1139 @xref{short create}, for more information on this.
1141 In this example, you type the command as shown above: @option{--create}
1142 is the operation which creates the new archive
1143 (@file{collection.tar}), and @option{--file} is the option which lets
1144 you give it the name you chose. The files, @file{blues}, @file{folk},
1145 and @file{jazz}, are now members of the archive, @file{collection.tar}
1146 (they are @dfn{file name arguments} to the @option{--create} operation.
1147 @xref{Choosing}, for the detailed discussion on these.) Now that they are
1148 in the archive, they are called @emph{archive members}, not files.
1149 (@pxref{Definitions,members}).
1151 When you create an archive, you @emph{must} specify which files you
1152 want placed in the archive. If you do not specify any archive
1153 members, @GNUTAR{} will complain.
1155 If you now list the contents of the working directory (@command{ls}), you will
1156 find the archive file listed as well as the files you saw previously:
1159 blues folk jazz collection.tar
1163 Creating the archive @samp{collection.tar} did not destroy the copies of
1164 the files in the directory.
1166 Keep in mind that if you don't indicate an operation, @command{tar} will not
1167 run and will prompt you for one. If you don't name any files, @command{tar}
1168 will complain. You must have write access to the working directory,
1169 or else you will not be able to create an archive in that directory.
1171 @emph{Caution}: Do not attempt to use @option{--create} (@option{-c}) to add files to
1172 an existing archive; it will delete the archive and write a new one.
1173 Use @option{--append} (@option{-r}) instead. @xref{append}.
1175 @node create verbose
1176 @subsection Running @option{--create} with @option{--verbose}
1178 @xopindex{create, using with @option{--verbose}}
1179 @xopindex{verbose, using with @option{--create}}
1180 If you include the @option{--verbose} (@option{-v}) option on the command line,
1181 @command{tar} will list the files it is acting on as it is working. In
1182 verbose mode, the @code{create} example above would appear as:
1185 $ @kbd{tar --create --verbose --file=collection.tar blues folk jazz}
1191 This example is just like the example we showed which did not use
1192 @option{--verbose}, except that @command{tar} generated the remaining lines
1194 (note the different font styles).
1200 In the rest of the examples in this chapter, we will frequently use
1201 @code{verbose} mode so we can show actions or @command{tar} responses that
1202 you would otherwise not see, and which are important for you to
1206 @subsection Short Forms with @samp{create}
1208 As we said before, the @option{--create} (@option{-c}) operation is one of the most
1209 basic uses of @command{tar}, and you will use it countless times.
1210 Eventually, you will probably want to use abbreviated (or ``short'')
1211 forms of options. A full discussion of the three different forms that
1212 options can take appears in @ref{Styles}; for now, here is what the
1213 previous example (including the @option{--verbose} (@option{-v}) option) looks like
1214 using short option forms:
1217 $ @kbd{tar -cvf collection.tar blues folk jazz}
1224 As you can see, the system responds the same no matter whether you use
1225 long or short option forms.
1227 @FIXME{i don't like how this is worded:} One difference between using
1228 short and long option forms is that, although the exact placement of
1229 arguments following options is no more specific when using short forms,
1230 it is easier to become confused and make a mistake when using short
1231 forms. For example, suppose you attempted the above example in the
1235 $ @kbd{tar -cfv collection.tar blues folk jazz}
1239 In this case, @command{tar} will make an archive file called @file{v},
1240 containing the files @file{blues}, @file{folk}, and @file{jazz}, because
1241 the @samp{v} is the closest ``file name'' to the @option{-f} option, and
1242 is thus taken to be the chosen archive file name. @command{tar} will try
1243 to add a file called @file{collection.tar} to the @file{v} archive file;
1244 if the file @file{collection.tar} did not already exist, @command{tar} will
1245 report an error indicating that this file does not exist. If the file
1246 @file{collection.tar} does already exist (e.g., from a previous command
1247 you may have run), then @command{tar} will add this file to the archive.
1248 Because the @option{-v} option did not get registered, @command{tar} will not
1249 run under @samp{verbose} mode, and will not report its progress.
1251 The end result is that you may be quite confused about what happened,
1252 and possibly overwrite a file. To illustrate this further, we will show
1253 you how an example we showed previously would look using short forms.
1258 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1262 is confusing as it is. When shown using short forms, however, it
1263 becomes much more so:
1266 $ @kbd{tar blues -c folk -f collection.tar jazz}
1270 It would be very easy to put the wrong string of characters
1271 immediately following the @option{-f}, but doing that could sacrifice
1274 For this reason, we recommend that you pay very careful attention to
1275 the order of options and placement of file and archive names,
1276 especially when using short option forms. Not having the option name
1277 written out mnemonically can affect how well you remember which option
1278 does what, and therefore where different names have to be placed.
1281 @subsection Archiving Directories
1283 @cindex Archiving Directories
1284 @cindex Directories, Archiving
1285 You can archive a directory by specifying its directory name as a
1286 file name argument to @command{tar}. The files in the directory will be
1287 archived relative to the working directory, and the directory will be
1288 re-created along with its contents when the archive is extracted.
1290 To archive a directory, first move to its superior directory. If you
1291 have followed the previous instructions in this tutorial, you should
1300 This will put you into the directory which contains @file{practice},
1301 i.e., your home directory. Once in the superior directory, you can
1302 specify the subdirectory, @file{practice}, as a file name argument. To
1303 store @file{practice} in the new archive file @file{music.tar}, type:
1306 $ @kbd{tar --create --verbose --file=music.tar practice}
1310 @command{tar} should output:
1317 practice/collection.tar
1320 Note that the archive thus created is not in the subdirectory
1321 @file{practice}, but rather in the current working directory---the
1322 directory from which @command{tar} was invoked. Before trying to archive a
1323 directory from its superior directory, you should make sure you have
1324 write access to the superior directory itself, not only the directory
1325 you are trying archive with @command{tar}. For example, you will probably
1326 not be able to store your home directory in an archive by invoking
1327 @command{tar} from the root directory; @xref{absolute}. (Note
1328 also that @file{collection.tar}, the original archive file, has itself
1329 been archived. @command{tar} will accept any file as a file to be
1330 archived, regardless of its content. When @file{music.tar} is
1331 extracted, the archive file @file{collection.tar} will be re-written
1332 into the file system).
1334 If you give @command{tar} a command such as
1337 $ @kbd{tar --create --file=foo.tar .}
1341 @command{tar} will report @samp{tar: ./foo.tar is the archive; not
1342 dumped}. This happens because @command{tar} creates the archive
1343 @file{foo.tar} in the current directory before putting any files into
1344 it. Then, when @command{tar} attempts to add all the files in the
1345 directory @file{.} to the archive, it notices that the file
1346 @file{./foo.tar} is the same as the archive @file{foo.tar}, and skips
1347 it. (It makes no sense to put an archive into itself.) @GNUTAR{}
1348 will continue in this case, and create the archive
1349 normally, except for the exclusion of that one file. (@emph{Please
1350 note:} Other implementations of @command{tar} may not be so clever;
1351 they will enter an infinite loop when this happens, so you should not
1352 depend on this behavior unless you are certain you are running
1353 @GNUTAR{}. In general, it is wise to always place the archive outside
1354 of the directory being dumped.
1357 @section How to List Archives
1360 Frequently, you will find yourself wanting to determine exactly what a
1361 particular archive contains. You can use the @option{--list}
1362 (@option{-t}) operation to get the member names as they currently
1363 appear in the archive, as well as various attributes of the files at
1364 the time they were archived. For example, you can examine the archive
1365 @file{collection.tar} that you created in the last section with the
1369 $ @kbd{tar --list --file=collection.tar}
1373 The output of @command{tar} would then be:
1382 The archive @file{bfiles.tar} would list as follows:
1391 Be sure to use a @option{--file=@var{archive-name}} (@option{-f
1392 @var{archive-name}}) option just as with @option{--create}
1393 (@option{-c}) to specify the name of the archive.
1395 @xopindex{list, using with @option{--verbose}}
1396 @xopindex{verbose, using with @option{--list}}
1397 If you use the @option{--verbose} (@option{-v}) option with
1398 @option{--list}, then @command{tar} will print out a listing
1399 reminiscent of @w{@samp{ls -l}}, showing owner, file size, and so
1400 forth. This output is described in detail in @ref{verbose member listing}.
1402 If you had used @option{--verbose} (@option{-v}) mode, the example
1403 above would look like:
1406 $ @kbd{tar --list --verbose --file=collection.tar folk}
1407 -rw-r--r-- myself user 62 1990-05-23 10:55 folk
1410 @cindex listing member and file names
1411 @anchor{listing member and file names}
1412 It is important to notice that the output of @kbd{tar --list
1413 --verbose} does not necessarily match that produced by @kbd{tar
1414 --create --verbose} while creating the archive. It is because
1415 @GNUTAR{}, unless told explicitly not to do so, removes some directory
1416 prefixes from file names before storing them in the archive
1417 (@xref{absolute}, for more information). In other
1418 words, in verbose mode @GNUTAR{} shows @dfn{file names} when creating
1419 an archive and @dfn{member names} when listing it. Consider this
1424 $ @kbd{tar cfv archive /etc/mail}
1425 tar: Removing leading `/' from member names
1427 /etc/mail/sendmail.cf
1429 $ @kbd{tar tf archive}
1431 etc/mail/sendmail.cf
1436 @opindex show-stored-names
1437 This default behavior can sometimes be inconvenient. You can force
1438 @GNUTAR{} show member names when creating archive by supplying
1439 @option{--show-stored-names} option.
1442 @item --show-stored-names
1443 Print member (as opposed to @emph{file}) names when creating the archive.
1446 @cindex File name arguments, using @option{--list} with
1447 @xopindex{list, using with file name arguments}
1448 You can specify one or more individual member names as arguments when
1449 using @samp{list}. In this case, @command{tar} will only list the
1450 names of members you identify. For example, @w{@kbd{tar --list
1451 --file=afiles.tar apple}} would only print @file{apple}.
1453 Because @command{tar} preserves paths, file names must be specified as
1454 they appear in the archive (i.e., relative to the directory from which
1455 the archive was created). Therefore, it is essential when specifying
1456 member names to @command{tar} that you give the exact member names.
1457 For example, @w{@kbd{tar --list --file=bfiles.tar birds}} would produce an
1458 error message something like @samp{tar: birds: Not found in archive},
1459 because there is no member named @file{birds}, only one named
1460 @file{./birds}. While the names @file{birds} and @file{./birds} name
1461 the same file, @emph{member} names by default are compared verbatim.
1463 However, @w{@kbd{tar --list --file=bfiles.tar baboon}} would respond
1464 with @file{baboon}, because this exact member name is in the archive file
1465 @file{bfiles.tar}. If you are not sure of the exact file name,
1466 use @dfn{globbing patterns}, for example:
1469 $ @kbd{tar --list --file=bfiles.tar --wildcards '*b*'}
1473 will list all members whose name contains @samp{b}. @xref{wildcards},
1474 for a detailed discussion of globbing patterns and related
1475 @command{tar} command line options.
1482 @unnumberedsubsec Listing the Contents of a Stored Directory
1484 To get information about the contents of an archived directory,
1485 use the directory name as a file name argument in conjunction with
1486 @option{--list} (@option{-t}). To find out file attributes, include the
1487 @option{--verbose} (@option{-v}) option.
1489 For example, to find out about files in the directory @file{practice}, in
1490 the archive file @file{music.tar}, type:
1493 $ @kbd{tar --list --verbose --file=music.tar practice}
1496 @command{tar} responds:
1499 drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
1500 -rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues
1501 -rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk
1502 -rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz
1503 -rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar
1506 When you use a directory name as a file name argument, @command{tar} acts on
1507 all the files (including sub-directories) in that directory.
1510 @section How to Extract Members from an Archive
1513 @cindex Retrieving files from an archive
1514 @cindex Resurrecting files from an archive
1517 Creating an archive is only half the job---there is no point in storing
1518 files in an archive if you can't retrieve them. The act of retrieving
1519 members from an archive so they can be used and manipulated as
1520 unarchived files again is called @dfn{extraction}. To extract files
1521 from an archive, use the @option{--extract} (@option{--get} or
1522 @option{-x}) operation. As with @option{--create}, specify the name
1523 of the archive with @option{--file} (@option{-f}) option. Extracting
1524 an archive does not modify the archive in any way; you can extract it
1525 multiple times if you want or need to.
1527 Using @option{--extract}, you can extract an entire archive, or specific
1528 files. The files can be directories containing other files, or not. As
1529 with @option{--create} (@option{-c}) and @option{--list} (@option{-t}), you may use the short or the
1530 long form of the operation without affecting the performance.
1533 * extracting archives::
1534 * extracting files::
1536 * extracting untrusted archives::
1537 * failing commands::
1540 @node extracting archives
1541 @subsection Extracting an Entire Archive
1543 To extract an entire archive, specify the archive file name only, with
1544 no individual file names as arguments. For example,
1547 $ @kbd{tar -xvf collection.tar}
1554 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
1555 -rw-r--r-- me user 21 1996-09-23 16:44 blues
1556 -rw-r--r-- me user 20 1996-09-23 16:44 folk
1559 @node extracting files
1560 @subsection Extracting Specific Files
1562 To extract specific archive members, give their exact member names as
1563 arguments, as printed by @option{--list} (@option{-t}). If you had
1564 mistakenly deleted one of the files you had placed in the archive
1565 @file{collection.tar} earlier (say, @file{blues}), you can extract it
1566 from the archive without changing the archive's structure. Its
1567 contents will be identical to the original file @file{blues} that you
1570 First, make sure you are in the @file{practice} directory, and list the
1571 files in the directory. Now, delete the file, @samp{blues}, and list
1572 the files in the directory again.
1574 You can now extract the member @file{blues} from the archive file
1575 @file{collection.tar} like this:
1578 $ @kbd{tar --extract --file=collection.tar blues}
1582 If you list the files in the directory again, you will see that the file
1583 @file{blues} has been restored, with its original permissions, data
1584 modification times, and owner.@footnote{This is only accidentally
1585 true, but not in general. Whereas modification times are always
1586 restored, in most cases, one has to be root for restoring the owner,
1587 and use a special option for restoring permissions. Here, it just
1588 happens that the restoring user is also the owner of the archived
1589 members, and that the current @code{umask} is compatible with original
1590 permissions.} (These parameters will be identical to those which
1591 the file had when you originally placed it in the archive; any changes
1592 you may have made before deleting the file from the file system,
1593 however, will @emph{not} have been made to the archive member.) The
1594 archive file, @samp{collection.tar}, is the same as it was before you
1595 extracted @samp{blues}. You can confirm this by running @command{tar} with
1596 @option{--list} (@option{-t}).
1598 Remember that as with other operations, specifying the exact member
1599 name is important. @w{@kbd{tar --extract --file=bfiles.tar birds}}
1600 will fail, because there is no member named @file{birds}. To extract
1601 the member named @file{./birds}, you must specify @w{@kbd{tar
1602 --extract --file=bfiles.tar ./birds}}. If you don't remember the
1603 exact member names, use @option{--list} (@option{-t}) option
1604 (@pxref{list}). You can also extract those members that match a
1605 specific @dfn{globbing pattern}. For example, to extract from
1606 @file{bfiles.tar} all files that begin with @samp{b}, no matter their
1607 directory prefix, you could type:
1610 $ @kbd{tar -x -f bfiles.tar --wildcards --no-anchored 'b*'}
1614 Here, @option{--wildcards} instructs @command{tar} to treat
1615 command line arguments as globbing patterns and @option{--no-anchored}
1616 informs it that the patterns apply to member names after any @samp{/}
1617 delimiter. The use of globbing patterns is discussed in detail in
1620 You can extract a file to standard output by combining the above options
1621 with the @option{--to-stdout} (@option{-O}) option (@pxref{Writing to Standard
1624 If you give the @option{--verbose} option, then @option{--extract}
1625 will print the names of the archive members as it extracts them.
1628 @subsection Extracting Files that are Directories
1630 Extracting directories which are members of an archive is similar to
1631 extracting other files. The main difference to be aware of is that if
1632 the extracted directory has the same name as any directory already in
1633 the working directory, then files in the extracted directory will be
1634 placed into the directory of the same name. Likewise, if there are
1635 files in the pre-existing directory with the same names as the members
1636 which you extract, the files from the extracted archive will replace
1637 the files already in the working directory (and possible
1638 subdirectories). This will happen regardless of whether or not the
1639 files in the working directory were more recent than those extracted
1640 (there exist, however, special options that alter this behavior
1643 However, if a file was stored with a directory name as part of its file
1644 name, and that directory does not exist under the working directory when
1645 the file is extracted, @command{tar} will create the directory.
1647 We can demonstrate how to use @option{--extract} to extract a directory
1648 file with an example. Change to the @file{practice} directory if you
1649 weren't there, and remove the files @file{folk} and @file{jazz}. Then,
1650 go back to the parent directory and extract the archive
1651 @file{music.tar}. You may either extract the entire archive, or you may
1652 extract only the files you just deleted. To extract the entire archive,
1653 don't give any file names as arguments after the archive name
1654 @file{music.tar}. To extract only the files you deleted, use the
1658 $ @kbd{tar -xvf music.tar practice/folk practice/jazz}
1664 If you were to specify two @option{--verbose} (@option{-v}) options, @command{tar}
1665 would have displayed more detail about the extracted files, as shown
1666 in the example below:
1669 $ @kbd{tar -xvvf music.tar practice/folk practice/jazz}
1670 -rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz
1671 -rw-r--r-- me user 20 1996-09-23 16:44 practice/folk
1675 Because you created the directory with @file{practice} as part of the
1676 file names of each of the files by archiving the @file{practice}
1677 directory as @file{practice}, you must give @file{practice} as part
1678 of the file names when you extract those files from the archive.
1680 @node extracting untrusted archives
1681 @subsection Extracting Archives from Untrusted Sources
1683 Extracting files from archives can overwrite files that already exist.
1684 If you receive an archive from an untrusted source, you should make a
1685 new directory and extract into that directory, so that you don't have
1686 to worry about the extraction overwriting one of your existing files.
1687 For example, if @file{untrusted.tar} came from somewhere else on the
1688 Internet, and you don't necessarily trust its contents, you can
1689 extract it as follows:
1692 $ @kbd{mkdir newdir}
1694 $ @kbd{tar -xvf ../untrusted.tar}
1697 It is also a good practice to examine contents of the archive
1698 before extracting it, using @option{--list} (@option{-t}) option, possibly combined
1699 with @option{--verbose} (@option{-v}).
1701 @node failing commands
1702 @subsection Commands That Will Fail
1704 Here are some sample commands you might try which will not work, and why
1707 If you try to use this command,
1710 $ @kbd{tar -xvf music.tar folk jazz}
1714 you will get the following response:
1717 tar: folk: Not found in archive
1718 tar: jazz: Not found in archive
1723 This is because these files were not originally @emph{in} the parent
1724 directory @file{..}, where the archive is located; they were in the
1725 @file{practice} directory, and their file names reflect this:
1728 $ @kbd{tar -tvf music.tar}
1734 @FIXME{make sure the above works when going through the examples in
1738 Likewise, if you try to use this command,
1741 $ @kbd{tar -tvf music.tar folk jazz}
1745 you would get a similar response. Members with those names are not in the
1746 archive. You must use the correct member names, or wildcards, in order
1747 to extract the files from the archive.
1749 If you have forgotten the correct names of the files in the archive,
1750 use @w{@kbd{tar --list --verbose}} to list them correctly.
1752 @FIXME{more examples, here? hag thinks it's a good idea.}
1755 @section Going Further Ahead in this Manual
1757 @FIXME{need to write up a node here about the things that are going to
1758 be in the rest of the manual.}
1760 @node tar invocation
1761 @chapter Invoking @GNUTAR{}
1764 This chapter is about how one invokes the @GNUTAR{}
1765 command, from the command synopsis (@pxref{Synopsis}). There are
1766 numerous options, and many styles for writing them. One mandatory
1767 option specifies the operation @command{tar} should perform
1768 (@pxref{Operation Summary}), other options are meant to detail how
1769 this operation should be performed (@pxref{Option Summary}).
1770 Non-option arguments are not always interpreted the same way,
1771 depending on what the operation is.
1773 You will find in this chapter everything about option styles and rules for
1774 writing them (@pxref{Styles}). On the other hand, operations and options
1775 are fully described elsewhere, in other chapters. Here, you will find
1776 only synthetic descriptions for operations and options, together with
1777 pointers to other parts of the @command{tar} manual.
1779 Some options are so special they are fully described right in this
1780 chapter. They have the effect of inhibiting the normal operation of
1781 @command{tar} or else, they globally alter the amount of feedback the user
1782 receives about what is going on. These are the @option{--help} and
1783 @option{--version} (@pxref{help}), @option{--verbose} (@pxref{verbose})
1784 and @option{--interactive} options (@pxref{interactive}).
1788 * using tar options::
1798 @section General Synopsis of @command{tar}
1800 The @GNUTAR{} program is invoked as either one of:
1803 @kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
1804 @kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
1807 The second form is for when old options are being used.
1809 You can use @command{tar} to store files in an archive, to extract them from
1810 an archive, and to do other types of archive manipulation. The primary
1811 argument to @command{tar}, which is called the @dfn{operation}, specifies
1812 which action to take. The other arguments to @command{tar} are either
1813 @dfn{options}, which change the way @command{tar} performs an operation,
1814 or file names or archive members, which specify the files or members
1815 @command{tar} is to act on.
1817 You can actually type in arguments in any order, even if in this manual
1818 the options always precede the other arguments, to make examples easier
1819 to understand. Further, the option stating the main operation mode
1820 (the @command{tar} main command) is usually given first.
1822 Each @var{name} in the synopsis above is interpreted as an archive member
1823 name when the main command is one of @option{--compare}
1824 (@option{--diff}, @option{-d}), @option{--delete}, @option{--extract}
1825 (@option{--get}, @option{-x}), @option{--list} (@option{-t}) or
1826 @option{--update} (@option{-u}). When naming archive members, you
1827 must give the exact name of the member in the archive, as it is
1828 printed by @option{--list}. For @option{--append} (@option{-r}) and
1829 @option{--create} (@option{-c}), these @var{name} arguments specify
1830 the names of either files or directory hierarchies to place in the archive.
1831 These files or hierarchies should already exist in the file system,
1832 prior to the execution of the @command{tar} command.
1834 @command{tar} interprets relative file names as being relative to the
1835 working directory. @command{tar} will make all file names relative
1836 (by removing leading slashes when archiving or restoring files),
1837 unless you specify otherwise (using the @option{--absolute-names}
1838 option). @xref{absolute}, for more information about
1839 @option{--absolute-names}.
1841 If you give the name of a directory as either a file name or a member
1842 name, then @command{tar} acts recursively on all the files and directories
1843 beneath that directory. For example, the name @file{/} identifies all
1844 the files in the file system to @command{tar}.
1846 The distinction between file names and archive member names is especially
1847 important when shell globbing is used, and sometimes a source of confusion
1848 for newcomers. @xref{wildcards}, for more information about globbing.
1849 The problem is that shells may only glob using existing files in the
1850 file system. Only @command{tar} itself may glob on archive members, so when
1851 needed, you must ensure that wildcard characters reach @command{tar} without
1852 being interpreted by the shell first. Using a backslash before @samp{*}
1853 or @samp{?}, or putting the whole argument between quotes, is usually
1854 sufficient for this.
1856 Even if @var{name}s are often specified on the command line, they
1857 can also be read from a text file in the file system, using the
1858 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option.
1860 If you don't use any file name arguments, @option{--append} (@option{-r}),
1861 @option{--delete} and @option{--concatenate} (@option{--catenate},
1862 @option{-A}) will do nothing, while @option{--create} (@option{-c})
1863 will usually yield a diagnostic and inhibit @command{tar} execution.
1864 The other operations of @command{tar} (@option{--list},
1865 @option{--extract}, @option{--compare}, and @option{--update})
1866 will act on the entire contents of the archive.
1869 @cindex return status
1870 Besides successful exits, @GNUTAR{} may fail for
1871 many reasons. Some reasons correspond to bad usage, that is, when the
1872 @command{tar} command is improperly written. Errors may be
1873 encountered later, while encountering an error processing the archive
1874 or the files. Some errors are recoverable, in which case the failure
1875 is delayed until @command{tar} has completed all its work. Some
1876 errors are such that it would not meaningful, or at least risky, to
1877 continue processing: @command{tar} then aborts processing immediately.
1878 All abnormal exits, whether immediate or delayed, should always be
1879 clearly diagnosed on @code{stderr}, after a line stating the nature of
1882 @GNUTAR{} returns only a few exit statuses. I'm really
1883 aiming simplicity in that area, for now. If you are not using the
1884 @option{--compare} @option{--diff}, @option{-d}) option, zero means
1885 that everything went well, besides maybe innocuous warnings. Nonzero
1886 means that something went wrong. Right now, as of today, ``nonzero''
1887 is almost always 2, except for remote operations, where it may be
1890 @node using tar options
1891 @section Using @command{tar} Options
1893 @GNUTAR{} has a total of eight operating modes which
1894 allow you to perform a variety of tasks. You are required to choose
1895 one operating mode each time you employ the @command{tar} program by
1896 specifying one, and only one operation as an argument to the
1897 @command{tar} command (two lists of four operations each may be found
1898 at @ref{frequent operations} and @ref{Operations}). Depending on
1899 circumstances, you may also wish to customize how the chosen operating
1900 mode behaves. For example, you may wish to change the way the output
1901 looks, or the format of the files that you wish to archive may require
1902 you to do something special in order to make the archive look right.
1904 You can customize and control @command{tar}'s performance by running
1905 @command{tar} with one or more options (such as @option{--verbose}
1906 (@option{-v}), which we used in the tutorial). As we said in the
1907 tutorial, @dfn{options} are arguments to @command{tar} which are (as
1908 their name suggests) optional. Depending on the operating mode, you
1909 may specify one or more options. Different options will have different
1910 effects, but in general they all change details of the operation, such
1911 as archive format, archive name, or level of user interaction. Some
1912 options make sense with all operating modes, while others are
1913 meaningful only with particular modes. You will likely use some
1914 options frequently, while you will only use others infrequently, or
1915 not at all. (A full list of options is available in @pxref{All Options}.)
1917 @vrindex TAR_OPTIONS, environment variable
1918 @anchor{TAR_OPTIONS}
1919 The @env{TAR_OPTIONS} environment variable specifies default options to
1920 be placed in front of any explicit options. For example, if
1921 @code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as
1922 if the two options @option{-v} and @option{--unlink-first} had been
1923 specified before any explicit options. Option specifications are
1924 separated by whitespace. A backslash escapes the next character, so it
1925 can be used to specify an option containing whitespace or a backslash.
1927 Note that @command{tar} options are case sensitive. For example, the
1928 options @option{-T} and @option{-t} are different; the first requires an
1929 argument for stating the name of a file providing a list of @var{name}s,
1930 while the second does not require an argument and is another way to
1931 write @option{--list} (@option{-t}).
1933 In addition to the eight operations, there are many options to
1934 @command{tar}, and three different styles for writing both: long (mnemonic)
1935 form, short form, and old style. These styles are discussed below.
1936 Both the options and the operations can be written in any of these three
1939 @FIXME{menu at end of this node. need to think of an actual outline
1940 for this chapter; probably do that after stuff from chapter 4 is
1944 @section The Three Option Styles
1946 There are three styles for writing operations and options to the command
1947 line invoking @command{tar}. The different styles were developed at
1948 different times during the history of @command{tar}. These styles will be
1949 presented below, from the most recent to the oldest.
1951 Some options must take an argument. (For example, @option{--file}
1952 (@option{-f})) takes the name of an archive file as an argument. If
1953 you do not supply an archive file name, @command{tar} will use a
1954 default, but this can be confusing; thus, we recommend that you always
1955 supply a specific archive file name.) Where you @emph{place} the
1956 arguments generally depends on which style of options you choose. We
1957 will detail specific information relevant to each option style in the
1958 sections on the different option styles, below. The differences are
1959 subtle, yet can often be very important; incorrect option placement
1960 can cause you to overwrite a number of important files. We urge you
1961 to note these differences, and only use the option style(s) which
1962 makes the most sense to you until you feel comfortable with the others.
1964 Some options @emph{may} take an argument (currently, there are
1965 two such options: @option{--backup} and @option{--occurrence}). Such
1966 options may have at most long and short forms, they do not have old style
1967 equivalent. The rules for specifying an argument for such options
1968 are stricter than those for specifying mandatory arguments. Please,
1969 pay special attention to them.
1972 * Long Options:: Long Option Style
1973 * Short Options:: Short Option Style
1974 * Old Options:: Old Option Style
1975 * Mixing:: Mixing Option Styles
1979 @subsection Long Option Style
1981 Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
1982 dashes in a row, e.g., @option{--list}. The long names are more clear than
1983 their corresponding short or old names. It sometimes happens that a
1984 single long option has many different different names which are
1985 synonymous, such as @option{--compare} and @option{--diff}. In addition,
1986 long option names can be given unique abbreviations. For example,
1987 @option{--cre} can be used in place of @option{--create} because there is no
1988 other long option which begins with @samp{cre}. (One way to find
1989 this out is by trying it and seeing what happens; if a particular
1990 abbreviation could represent more than one option, @command{tar} will tell
1991 you that that abbreviation is ambiguous and you'll know that that
1992 abbreviation won't work. You may also choose to run @samp{tar --help}
1993 to see a list of options. Be aware that if you run @command{tar} with a
1994 unique abbreviation for the long name of an option you didn't want to
1995 use, you are stuck; @command{tar} will perform the command as ordered.)
1997 Long options are meant to be obvious and easy to remember, and their
1998 meanings are generally easier to discern than those of their
1999 corresponding short options (see below). For example:
2002 $ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
2006 gives a fairly good set of hints about what the command does, even
2007 for those not fully acquainted with @command{tar}.
2009 Long options which require arguments take those arguments
2010 immediately following the option name. There are two ways of
2011 specifying a mandatory argument. It can be separated from the
2012 option name either by an equal sign, or by any amount of
2013 white space characters. For example, the @option{--file} option (which
2014 tells the name of the @command{tar} archive) is given a file such as
2015 @file{archive.tar} as argument by using any of the following notations:
2016 @option{--file=archive.tar} or @option{--file archive.tar}.
2018 In contrast, optional arguments must always be introduced using
2019 an equal sign. For example, the @option{--backup} option takes
2020 an optional argument specifying backup type. It must be used
2021 as @option{--backup=@var{backup-type}}.
2024 @subsection Short Option Style
2026 Most options also have a @dfn{short option} name. Short options start with
2027 a single dash, and are followed by a single character, e.g., @option{-t}
2028 (which is equivalent to @option{--list}). The forms are absolutely
2029 identical in function; they are interchangeable.
2031 The short option names are faster to type than long option names.
2033 Short options which require arguments take their arguments immediately
2034 following the option, usually separated by white space. It is also
2035 possible to stick the argument right after the short option name, using
2036 no intervening space. For example, you might write @w{@option{-f
2037 archive.tar}} or @option{-farchive.tar} instead of using
2038 @option{--file=archive.tar}. Both @option{--file=@var{archive-name}} and
2039 @w{@option{-f @var{archive-name}}} denote the option which indicates a
2040 specific archive, here named @file{archive.tar}.
2042 Short options which take optional arguments take their arguments
2043 immediately following the option letter, @emph{without any intervening
2044 white space characters}.
2046 Short options' letters may be clumped together, but you are not
2047 required to do this (as compared to old options; see below). When
2048 short options are clumped as a set, use one (single) dash for them
2049 all, e.g., @w{@samp{@command{tar} -cvf}}. Only the last option in
2050 such a set is allowed to have an argument@footnote{Clustering many
2051 options, the last of which has an argument, is a rather opaque way to
2052 write options. Some wonder if @acronym{GNU} @code{getopt} should not
2053 even be made helpful enough for considering such usages as invalid.}.
2055 When the options are separated, the argument for each option which requires
2056 an argument directly follows that option, as is usual for Unix programs.
2060 $ @kbd{tar -c -v -b 20 -f /dev/rmt0}
2063 If you reorder short options' locations, be sure to move any arguments
2064 that belong to them. If you do not move the arguments properly, you may
2065 end up overwriting files.
2068 @subsection Old Option Style
2071 Like short options, @dfn{old options} are single letters. However, old options
2072 must be written together as a single clumped set, without spaces separating
2073 them or dashes preceding them@footnote{Beware that if you precede options
2074 with a dash, you are announcing the short option style instead of the
2075 old option style; short options are decoded differently.}. This set
2076 of letters must be the first to appear on the command line, after the
2077 @command{tar} program name and some white space; old options cannot appear
2078 anywhere else. The letter of an old option is exactly the same letter as
2079 the corresponding short option. For example, the old option @samp{t} is
2080 the same as the short option @option{-t}, and consequently, the same as the
2081 long option @option{--list}. So for example, the command @w{@samp{tar
2082 cv}} specifies the option @option{-v} in addition to the operation @option{-c}.
2084 When options that need arguments are given together with the command,
2085 all the associated arguments follow, in the same order as the options.
2086 Thus, the example given previously could also be written in the old
2090 $ @kbd{tar cvbf 20 /dev/rmt0}
2094 Here, @samp{20} is the argument of @option{-b} and @samp{/dev/rmt0} is
2095 the argument of @option{-f}.
2097 On the other hand, this old style syntax makes it difficult to match
2098 option letters with their corresponding arguments, and is often
2099 confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example,
2100 @samp{20} is the argument for @option{-b}, @samp{/dev/rmt0} is the
2101 argument for @option{-f}, and @option{-v} does not have a corresponding
2102 argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f
2103 /dev/rmt0}} is clearer, putting all arguments next to the option they
2106 If you want to reorder the letters in the old option argument, be
2107 sure to reorder any corresponding argument appropriately.
2109 This old way of writing @command{tar} options can surprise even experienced
2110 users. For example, the two commands:
2113 @kbd{tar cfz archive.tar.gz file}
2114 @kbd{tar -cfz archive.tar.gz file}
2118 are quite different. The first example uses @file{archive.tar.gz} as
2119 the value for option @samp{f} and recognizes the option @samp{z}. The
2120 second example, however, uses @file{z} as the value for option
2121 @samp{f} --- probably not what was intended.
2123 Old options are kept for compatibility with old versions of @command{tar}.
2125 This second example could be corrected in many ways, among which the
2126 following are equivalent:
2129 @kbd{tar -czf archive.tar.gz file}
2130 @kbd{tar -cf archive.tar.gz -z file}
2131 @kbd{tar cf archive.tar.gz -z file}
2134 @cindex option syntax, traditional
2135 As far as we know, all @command{tar} programs, @acronym{GNU} and
2136 non-@acronym{GNU}, support old options. @GNUTAR{}
2137 supports them not only for historical reasons, but also because many
2138 people are used to them. For compatibility with Unix @command{tar},
2139 the first argument is always treated as containing command and option
2140 letters even if it doesn't start with @samp{-}. Thus, @samp{tar c} is
2141 equivalent to @w{@samp{tar -c}:} both of them specify the
2142 @option{--create} (@option{-c}) command to create an archive.
2145 @subsection Mixing Option Styles
2147 All three styles may be intermixed in a single @command{tar} command,
2148 so long as the rules for each style are fully
2149 respected@footnote{Before @GNUTAR{} version 1.11.6,
2150 a bug prevented intermixing old style options with long options in
2151 some cases.}. Old style options and either of the modern styles of
2152 options may be mixed within a single @command{tar} command. However,
2153 old style options must be introduced as the first arguments only,
2154 following the rule for old options (old options must appear directly
2155 after the @command{tar} command and some white space). Modern options
2156 may be given only after all arguments to the old options have been
2157 collected. If this rule is not respected, a modern option might be
2158 falsely interpreted as the value of the argument to one of the old
2161 For example, all the following commands are wholly equivalent, and
2162 illustrate the many combinations and orderings of option styles.
2165 @kbd{tar --create --file=archive.tar}
2166 @kbd{tar --create -f archive.tar}
2167 @kbd{tar --create -farchive.tar}
2168 @kbd{tar --file=archive.tar --create}
2169 @kbd{tar --file=archive.tar -c}
2170 @kbd{tar -c --file=archive.tar}
2171 @kbd{tar -c -f archive.tar}
2172 @kbd{tar -c -farchive.tar}
2173 @kbd{tar -cf archive.tar}
2174 @kbd{tar -cfarchive.tar}
2175 @kbd{tar -f archive.tar --create}
2176 @kbd{tar -f archive.tar -c}
2177 @kbd{tar -farchive.tar --create}
2178 @kbd{tar -farchive.tar -c}
2179 @kbd{tar c --file=archive.tar}
2180 @kbd{tar c -f archive.tar}
2181 @kbd{tar c -farchive.tar}
2182 @kbd{tar cf archive.tar}
2183 @kbd{tar f archive.tar --create}
2184 @kbd{tar f archive.tar -c}
2185 @kbd{tar fc archive.tar}
2188 On the other hand, the following commands are @emph{not} equivalent to
2192 @kbd{tar -f -c archive.tar}
2193 @kbd{tar -fc archive.tar}
2194 @kbd{tar -fcarchive.tar}
2195 @kbd{tar -farchive.tarc}
2196 @kbd{tar cfarchive.tar}
2200 These last examples mean something completely different from what the
2201 user intended (judging based on the example in the previous set which
2202 uses long options, whose intent is therefore very clear). The first
2203 four specify that the @command{tar} archive would be a file named
2204 @option{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc},
2205 respectively. The first two examples also specify a single non-option,
2206 @var{name} argument having the value @samp{archive.tar}. The last
2207 example contains only old style option letters (repeating option
2208 @samp{c} twice), not all of which are meaningful (eg., @samp{.},
2209 @samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked
2210 the first sentence of this paragraph..}
2213 @section All @command{tar} Options
2215 The coming manual sections contain an alphabetical listing of all
2216 @command{tar} operations and options, with brief descriptions and cross
2217 references to more in-depth explanations in the body of the manual.
2218 They also contain an alphabetically arranged table of the short option
2219 forms with their corresponding long option. You can use this table as
2220 a reference for deciphering @command{tar} commands in scripts.
2223 * Operation Summary::
2225 * Short Option Summary::
2228 @node Operation Summary
2229 @subsection Operations
2237 Appends files to the end of the archive. @xref{append}.
2239 @opsummary{catenate}
2243 Same as @option{--concatenate}. @xref{concatenate}.
2249 Compares archive members with their counterparts in the file
2250 system, and reports differences in file size, mode, owner,
2251 modification date and contents. @xref{compare}.
2253 @opsummary{concatenate}
2257 Appends other @command{tar} archives to the end of the archive.
2264 Creates a new @command{tar} archive. @xref{create}.
2269 Deletes members from the archive. Don't try this on a archive on a
2270 tape! @xref{delete}.
2276 Same @option{--compare}. @xref{compare}.
2282 Extracts members from the archive into the file system. @xref{extract}.
2288 Same as @option{--extract}. @xref{extract}.
2294 Lists the members in an archive. @xref{list}.
2300 Adds files to the end of the archive, but only if they are newer than
2301 their counterparts already in the archive, or if they do not already
2302 exist in the archive. @xref{update}.
2306 @node Option Summary
2307 @subsection @command{tar} Options
2311 @opsummary{absolute-names}
2312 @item --absolute-names
2315 Normally when creating an archive, @command{tar} strips an initial
2316 @samp{/} from member names. This option disables that behavior.
2319 @opsummary{after-date}
2322 (See @option{--newer}, @pxref{after})
2324 @opsummary{anchored}
2326 A pattern must match an initial subsequence of the name's components.
2327 @xref{controlling pattern-matching}.
2329 @opsummary{atime-preserve}
2330 @item --atime-preserve
2331 @itemx --atime-preserve=replace
2332 @itemx --atime-preserve=system
2334 Attempt to preserve the access time of files when reading them. This
2335 option currently is effective only on files that you own, unless you
2336 have superuser privileges.
2338 @option{--atime-preserve=replace} remembers the access time of a file
2339 before reading it, and then restores the access time afterwards. This
2340 may cause problems if other programs are reading the file at the same
2341 time, as the times of their accesses will be lost. On most platforms
2342 restoring the access time also requires @command{tar} to restore the
2343 data modification time too, so this option may also cause problems if
2344 other programs are writing the file at the same time. (Tar attempts
2345 to detect this situation, but cannot do so reliably due to race
2346 conditions.) Worse, on most platforms restoring the access time also
2347 updates the status change time, which means that this option is
2348 incompatible with incremental backups.
2350 @option{--atime-preserve=system} avoids changing time stamps on files,
2351 without interfering with time stamp updates
2352 caused by other programs, so it works better with incremental backups.
2353 However, it requires a special @code{O_NOATIME} option from the
2354 underlying operating and file system implementation, and it also requires
2355 that searching directories does not update their access times. As of
2356 this writing (November 2005) this works only with Linux, and only with
2357 Linux kernels 2.6.8 and later. Worse, there is currently no reliable
2358 way to know whether this feature actually works. Sometimes
2359 @command{tar} knows that it does not work, and if you use
2360 @option{--atime-preserve=system} then @command{tar} complains and
2361 exits right away. But other times @command{tar} might think that the
2362 option works when it actually does not.
2364 Currently @option{--atime-preserve} with no operand defaults to
2365 @option{--atime-preserve=replace}, but this may change in the future
2366 as support for @option{--atime-preserve=system} improves.
2368 If your operating system does not support
2369 @option{--atime-preserve=@-system}, you might be able to preserve access
2370 times reliably by by using the @command{mount} command. For example,
2371 you can mount the file system read-only, or access the file system via
2372 a read-only loopback mount, or use the @samp{noatime} mount option
2373 available on some systems. However, mounting typically requires
2374 superuser privileges and can be a pain to manage.
2377 @item --backup=@var{backup-type}
2379 Rather than deleting files from the file system, @command{tar} will
2380 back them up using simple or numbered backups, depending upon
2381 @var{backup-type}. @xref{backup}.
2383 @opsummary{block-number}
2384 @item --block-number
2387 With this option present, @command{tar} prints error messages for read errors
2388 with the block number in the archive file. @xref{block-number}.
2390 @opsummary{blocking-factor}
2391 @item --blocking-factor=@var{blocking}
2392 @itemx -b @var{blocking}
2394 Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
2395 record. @xref{Blocking Factor}.
2401 This option tells @command{tar} to read or write archives through
2402 @code{bzip2}. @xref{gzip}.
2404 @opsummary{checkpoint}
2405 @item --checkpoint[=@var{number}]
2407 This option directs @command{tar} to print periodic checkpoint
2408 messages as it reads through the archive. It is intended for when you
2409 want a visual indication that @command{tar} is still running, but
2410 don't want to see @option{--verbose} output. For a detailed
2411 description, see @ref{Progress information}.
2413 @opsummary{check-links}
2416 If this option was given, @command{tar} will check the number of links
2417 dumped for each processed file. If this number does not match the
2418 total number of hard links for the file, a warning message will be
2419 output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2420 synonym for @option{--one-file-system}. The current semantics, which
2421 complies to UNIX98, was introduced with version
2422 1.15.91. @xref{Changes}, for more information.}.
2424 @opsummary{compress}
2425 @opsummary{uncompress}
2430 @command{tar} will use the @command{compress} program when reading or
2431 writing the archive. This allows you to directly act on archives
2432 while saving space. @xref{gzip}.
2434 @opsummary{confirmation}
2435 @item --confirmation
2437 (See @option{--interactive}.) @xref{interactive}.
2439 @opsummary{delay-directory-restore}
2440 @item --delay-directory-restore
2442 Delay setting modification times and permissions of extracted
2443 directories until the end of extraction. @xref{Directory Modification Times and Permissions}.
2445 @opsummary{dereference}
2449 When creating a @command{tar} archive, @command{tar} will archive the
2450 file that a symbolic link points to, rather than archiving the
2451 symlink. @xref{dereference}.
2453 @opsummary{directory}
2454 @item --directory=@var{dir}
2457 When this option is specified, @command{tar} will change its current directory
2458 to @var{dir} before performing any operations. When this option is used
2459 during archive creation, it is order sensitive. @xref{directory}.
2462 @item --exclude=@var{pattern}
2464 When performing operations, @command{tar} will skip files that match
2465 @var{pattern}. @xref{exclude}.
2467 @opsummary{exclude-from}
2468 @item --exclude-from=@var{file}
2469 @itemx -X @var{file}
2471 Similar to @option{--exclude}, except @command{tar} will use the list of
2472 patterns in the file @var{file}. @xref{exclude}.
2474 @opsummary{exclude-caches}
2475 @item --exclude-caches
2477 Automatically excludes all directories
2478 containing a cache directory tag. @xref{exclude}.
2481 @item --file=@var{archive}
2482 @itemx -f @var{archive}
2484 @command{tar} will use the file @var{archive} as the @command{tar} archive it
2485 performs operations on, rather than @command{tar}'s compilation dependent
2486 default. @xref{file tutorial}.
2488 @opsummary{files-from}
2489 @item --files-from=@var{file}
2490 @itemx -T @var{file}
2492 @command{tar} will use the contents of @var{file} as a list of archive members
2493 or files to operate on, in addition to those specified on the
2494 command-line. @xref{files}.
2496 @opsummary{force-local}
2499 Forces @command{tar} to interpret the filename given to @option{--file}
2500 as a local file, even if it looks like a remote tape drive name.
2501 @xref{local and remote archives}.
2504 @item --format=@var{format}
2505 @itemx -H @var{format}
2507 Selects output archive format. @var{Format} may be one of the
2512 Creates an archive that is compatible with Unix V7 @command{tar}.
2515 Creates an archive that is compatible with GNU @command{tar} version
2519 Creates archive in GNU tar 1.13 format. Basically it is the same as
2520 @samp{oldgnu} with the only difference in the way it handles long
2524 Creates a @acronym{POSIX.1-1988} compatible archive.
2527 Creates a @acronym{POSIX.1-2001 archive}.
2531 @xref{Formats}, for a detailed discussion of these formats.
2534 @item --group=@var{group}
2536 Files added to the @command{tar} archive will have a group id of @var{group},
2537 rather than the group from the source file. @var{group} is first decoded
2538 as a group symbolic name, but if this interpretation fails, it has to be
2539 a decimal numeric group ID. @FIXME-xref{}
2541 Also see the comments for the @option{--owner=@var{user}} option.
2551 This option tells @command{tar} to read or write archives through
2552 @command{gzip}, allowing @command{tar} to directly operate on several
2553 kinds of compressed archives transparently. @xref{gzip}.
2559 @command{tar} will print out a short message summarizing the operations and
2560 options to @command{tar} and exit. @xref{help}.
2562 @opsummary{ignore-case}
2564 Ignore case when matching member or file names with
2565 patterns. @xref{controlling pattern-matching}.
2567 @opsummary{ignore-command-error}
2568 @item --ignore-command-error
2569 Ignore exit codes of subprocesses. @xref{Writing to an External Program}.
2571 @opsummary{ignore-failed-read}
2572 @item --ignore-failed-read
2574 Do not exit unsuccessfully merely because an unreadable file was encountered.
2577 @opsummary{ignore-zeros}
2578 @item --ignore-zeros
2581 With this option, @command{tar} will ignore zeroed blocks in the
2582 archive, which normally signals EOF. @xref{Reading}.
2584 @opsummary{incremental}
2588 Used to inform @command{tar} that it is working with an old
2589 @acronym{GNU}-format incremental backup archive. It is intended
2590 primarily for backwards compatibility only. @xref{Incremental Dumps},
2591 for a detailed discussion of incremental archives.
2593 @opsummary{index-file}
2594 @item --index-file=@var{file}
2596 Send verbose output to @var{file} instead of to standard output.
2598 @opsummary{info-script}
2599 @opsummary{new-volume-script}
2600 @item --info-script=@var{script-file}
2601 @itemx --new-volume-script=@var{script-file}
2602 @itemx -F @var{script-file}
2604 When @command{tar} is performing multi-tape backups, @var{script-file} is run
2605 at the end of each tape. If @var{script-file} exits with nonzero status,
2606 @command{tar} fails immediately. @xref{info-script}, for a detailed
2607 discussion of @var{script-file}.
2609 @opsummary{interactive}
2611 @itemx --confirmation
2614 Specifies that @command{tar} should ask the user for confirmation before
2615 performing potentially destructive options, such as overwriting files.
2618 @opsummary{keep-newer-files}
2619 @item --keep-newer-files
2621 Do not replace existing files that are newer than their archive copies
2622 when extracting files from an archive.
2624 @opsummary{keep-old-files}
2625 @item --keep-old-files
2628 Do not overwrite existing files when extracting files from an archive.
2629 @xref{Keep Old Files}.
2632 @item --label=@var{name}
2633 @itemx -V @var{name}
2635 When creating an archive, instructs @command{tar} to write @var{name}
2636 as a name record in the archive. When extracting or listing archives,
2637 @command{tar} will only operate on archives that have a label matching
2638 the pattern specified in @var{name}. @xref{Tape Files}.
2640 @opsummary{listed-incremental}
2641 @item --listed-incremental=@var{snapshot-file}
2642 @itemx -g @var{snapshot-file}
2644 During a @option{--create} operation, specifies that the archive that
2645 @command{tar} creates is a new @acronym{GNU}-format incremental
2646 backup, using @var{snapshot-file} to determine which files to backup.
2647 With other operations, informs @command{tar} that the archive is in
2648 incremental format. @xref{Incremental Dumps}.
2651 @item --mode=@var{permissions}
2653 When adding files to an archive, @command{tar} will use
2654 @var{permissions} for the archive members, rather than the permissions
2655 from the files. The program @command{chmod} and this @command{tar}
2656 option share the same syntax for what @var{permissions} might be.
2657 @xref{File permissions, Permissions, File permissions, fileutils,
2658 @acronym{GNU} file utilities}. This reference also has useful
2659 information for those not being overly familiar with the Unix
2662 Of course, @var{permissions} might be plainly specified as an octal number.
2663 However, by using generic symbolic modifications to mode bits, this allows
2664 more flexibility. For example, the value @samp{a+rw} adds read and write
2665 permissions for everybody, while retaining executable bits on directories
2666 or on any other file already marked as executable.
2668 @opsummary{multi-volume}
2669 @item --multi-volume
2672 Informs @command{tar} that it should create or otherwise operate on a
2673 multi-volume @command{tar} archive. @xref{Using Multiple Tapes}.
2675 @opsummary{new-volume-script}
2676 @item --new-volume-script
2684 Assume that the archive media supports seeks to arbitrary
2685 locations. Usually @command{tar} determines automatically whether
2686 the archive can be seeked or not. This option is intended for use
2687 in cases when such recognition fails.
2690 @item --newer=@var{date}
2691 @itemx --after-date=@var{date}
2694 When creating an archive, @command{tar} will only add files that have changed
2695 since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it
2696 is taken to be the name of a file whose data modification time specifies
2697 the date. @xref{after}.
2699 @opsummary{newer-mtime}
2700 @item --newer-mtime=@var{date}
2702 Like @option{--newer}, but add only files whose
2703 contents have changed (as opposed to just @option{--newer}, which will
2704 also back up files for which any status information has changed).
2706 @opsummary{no-anchored}
2708 An exclude pattern can match any subsequence of the name's components.
2709 @xref{controlling pattern-matching}.
2711 @opsummary{no-delay-directory-restore}
2712 @item --no-delay-directory-restore
2714 Setting modification times and permissions of extracted
2715 directories when all files from this directory has been
2716 extracted. This is the default. @xref{Directory Modification Times and Permissions}.
2718 @opsummary{no-ignore-case}
2719 @item --no-ignore-case
2720 Use case-sensitive matching.
2721 @xref{controlling pattern-matching}.
2723 @opsummary{no-ignore-command-error}
2724 @item --no-ignore-command-error
2725 Print warnings about subprocesses terminated with a non-zero exit
2726 code. @xref{Writing to an External Program}.
2728 @opsummary{no-overwrite-dir}
2729 @item --no-overwrite-dir
2731 Preserve metadata of existing directories when extracting files
2732 from an archive. @xref{Overwrite Old Files}.
2734 @opsummary{no-quote-chars}
2735 @item --no-quote-chars=@var{string}
2736 Remove characters listed in @var{string} from the list of quoted
2737 characters set by the previous @option{--quote-chars} option
2738 (@pxref{quoting styles}).
2740 @opsummary{no-recursion}
2741 @item --no-recursion
2743 With this option, @command{tar} will not recurse into directories.
2746 @opsummary{no-same-owner}
2747 @item --no-same-owner
2750 When extracting an archive, do not attempt to preserve the owner
2751 specified in the @command{tar} archive. This the default behavior
2754 @opsummary{no-same-permissions}
2755 @item --no-same-permissions
2757 When extracting an archive, subtract the user's umask from files from
2758 the permissions specified in the archive. This is the default behavior
2761 @opsummary{no-unquote}
2763 Treat all input file or member names literally, do not interpret
2764 escape sequences. @xref{input name quoting}.
2766 @opsummary{no-wildcards}
2767 @item --no-wildcards
2768 Do not use wildcards.
2769 @xref{controlling pattern-matching}.
2771 @opsummary{no-wildcards-match-slash}
2772 @item --no-wildcards-match-slash
2773 Wildcards do not match @samp{/}.
2774 @xref{controlling pattern-matching}.
2779 When @command{tar} is using the @option{--files-from} option, this option
2780 instructs @command{tar} to expect filenames terminated with @option{NUL}, so
2781 @command{tar} can correctly work with file names that contain newlines.
2784 @opsummary{numeric-owner}
2785 @item --numeric-owner
2787 This option will notify @command{tar} that it should use numeric user
2788 and group IDs when creating a @command{tar} file, rather than names.
2792 When extracting files, this option is a synonym for
2793 @option{--no-same-owner}, i.e. it prevents @command{tar} from
2794 restoring ownership of files being extracted.
2796 When creating an archive, @option{-o} is a synonym for
2797 @option{--old-archive}. This behavior is for compatibility
2798 with previous versions of @GNUTAR{}, and will be
2799 removed in the future releases.
2801 @xref{Changes}, for more information.
2803 @opsummary{occurrence}
2804 @item --occurrence[=@var{number}]
2806 This option can be used in conjunction with one of the subcommands
2807 @option{--delete}, @option{--diff}, @option{--extract} or
2808 @option{--list} when a list of files is given either on the command
2809 line or via @option{-T} option.
2811 This option instructs @command{tar} to process only the @var{number}th
2812 occurrence of each named file. @var{Number} defaults to 1, so
2815 tar -x -f archive.tar --occurrence filename
2819 will extract the first occurrence of @file{filename} from @file{archive.tar}
2820 and will terminate without scanning to the end of the archive.
2822 @opsummary{old-archive}
2824 Synonym for @option{--format=v7}.
2826 @opsummary{one-file-system}
2827 @item --one-file-system
2828 Used when creating an archive. Prevents @command{tar} from recursing into
2829 directories that are on different file systems from the current
2830 directory @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2831 synonym for @option{--one-file-system}. This has changed in version
2832 1.15.91. @xref{Changes}, for more information.}.
2834 @opsummary{overwrite}
2837 Overwrite existing files and directory metadata when extracting files
2838 from an archive. @xref{Overwrite Old Files}.
2840 @opsummary{overwrite-dir}
2841 @item --overwrite-dir
2843 Overwrite the metadata of existing directories when extracting files
2844 from an archive. @xref{Overwrite Old Files}.
2847 @item --owner=@var{user}
2849 Specifies that @command{tar} should use @var{user} as the owner of members
2850 when creating archives, instead of the user associated with the source
2851 file. @var{user} is first decoded as a user symbolic name, but if
2852 this interpretation fails, it has to be a decimal numeric user ID.
2855 There is no value indicating a missing number, and @samp{0} usually means
2856 @code{root}. Some people like to force @samp{0} as the value to offer in
2857 their distributions for the owner of files, because the @code{root} user is
2858 anonymous anyway, so that might as well be the owner of anonymous archives.
2860 This option does not affect extraction from archives.
2862 @opsummary{transform}
2863 @item --transform=@var{sed-expr}
2865 Transform file or member names using @command{sed} replacement expression
2866 @var{sed-expr}. For example,
2869 $ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
2873 will add to @file{archive} files from the current working directory,
2874 replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
2875 discussion, @xref{transform}.
2877 To see transformed member names in verbose listings, use
2878 @option{--show-transformed-names} option
2879 (@pxref{show-transformed-names}).
2881 @opsummary{quote-chars}
2882 @item --quote-chars=@var{string}
2883 Always quote characters from @var{string}, even if the selected
2884 quoting style would not quote them (@pxref{quoting styles}).
2886 @opsummary{quoting-style}
2887 @item --quoting-style=@var{style}
2888 Set quoting style to use when printing member and file names
2889 (@pxref{quoting styles}). Valid @var{style} values are:
2890 @code{literal}, @code{shell}, @code{shell-always}, @code{c},
2891 @code{escape}, @code{locale}, and @code{clocale}. Default quoting
2892 style is @code{escape}, unless overridden while configuring the
2895 @opsummary{pax-option}
2896 @item --pax-option=@var{keyword-list}
2897 This option is meaningful only with @acronym{POSIX.1-2001} archives
2898 (@pxref{posix}). It modifies the way @command{tar} handles the
2899 extended header keywords. @var{Keyword-list} is a comma-separated
2900 list of keyword options. @xref{PAX keywords}, for a detailed
2903 @opsummary{portability}
2905 @itemx --old-archive
2906 Synonym for @option{--format=v7}.
2910 Same as @option{--format=posix}.
2912 @opsummary{preserve}
2915 Synonymous with specifying both @option{--preserve-permissions} and
2916 @option{--same-order}. @xref{Setting Access Permissions}.
2918 @opsummary{preserve-order}
2919 @item --preserve-order
2921 (See @option{--same-order}; @pxref{Reading}.)
2923 @opsummary{preserve-permissions}
2924 @opsummary{same-permissions}
2925 @item --preserve-permissions
2926 @itemx --same-permissions
2929 When @command{tar} is extracting an archive, it normally subtracts the
2930 users' umask from the permissions specified in the archive and uses
2931 that number as the permissions to create the destination file.
2932 Specifying this option instructs @command{tar} that it should use the
2933 permissions directly from the archive. @xref{Setting Access Permissions}.
2935 @opsummary{read-full-records}
2936 @item --read-full-records
2939 Specifies that @command{tar} should reblock its input, for reading
2940 from pipes on systems with buggy implementations. @xref{Reading}.
2942 @opsummary{record-size}
2943 @item --record-size=@var{size}
2945 Instructs @command{tar} to use @var{size} bytes per record when accessing the
2946 archive. @xref{Blocking Factor}.
2948 @opsummary{recursion}
2951 With this option, @command{tar} recurses into directories.
2954 @opsummary{recursive-unlink}
2955 @item --recursive-unlink
2958 directory hierarchies before extracting directories of the same name
2959 from the archive. @xref{Recursive Unlink}.
2961 @opsummary{remove-files}
2962 @item --remove-files
2964 Directs @command{tar} to remove the source file from the file system after
2965 appending it to an archive. @xref{remove files}.
2967 @opsummary{restrict}
2970 Disable use of some potentially harmful @command{tar} options.
2971 Currently this option disables shell invocaton from multi-volume menu
2972 (@pxref{Using Multiple Tapes}).
2974 @opsummary{rmt-command}
2975 @item --rmt-command=@var{cmd}
2977 Notifies @command{tar} that it should use @var{cmd} instead of
2978 the default @file{/usr/libexec/rmt} (@pxref{Remote Tape Server}).
2980 @opsummary{rsh-command}
2981 @item --rsh-command=@var{cmd}
2983 Notifies @command{tar} that is should use @var{cmd} to communicate with remote
2984 devices. @xref{Device}.
2986 @opsummary{same-order}
2988 @itemx --preserve-order
2991 This option is an optimization for @command{tar} when running on machines with
2992 small amounts of memory. It informs @command{tar} that the list of file
2993 arguments has already been sorted to match the order of files in the
2994 archive. @xref{Reading}.
2996 @opsummary{same-owner}
2999 When extracting an archive, @command{tar} will attempt to preserve the owner
3000 specified in the @command{tar} archive with this option present.
3001 This is the default behavior for the superuser; this option has an
3002 effect only for ordinary users. @xref{Attributes}.
3004 @opsummary{same-permissions}
3005 @item --same-permissions
3007 (See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
3009 @opsummary{show-defaults}
3010 @item --show-defaults
3012 Displays the default options used by @command{tar} and exits
3013 successfully. This option is intended for use in shell scripts.
3014 Here is an example of what you can see using this option:
3017 $ tar --show-defaults
3018 --format=gnu -f- -b20 --quoting-style=escape \
3019 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
3022 @opsummary{show-omitted-dirs}
3023 @item --show-omitted-dirs
3025 Instructs @command{tar} to mention directories its skipping over when
3026 operating on a @command{tar} archive. @xref{show-omitted-dirs}.
3028 @opsummary{show-transformed-names}
3029 @opsummary{show-stored-names}
3030 @item --show-transformed-names
3031 @itemx --show-stored-names
3033 Display file or member names after applying any transformations
3034 (@pxref{transform}). In particular, when used in conjunction with one of
3035 archive creation operations it instructs tar to list the member names
3036 stored in the archive, as opposed to the actual file
3037 names. @xref{listing member and file names}.
3043 Invokes a @acronym{GNU} extension when adding files to an archive that handles
3044 sparse files efficiently. @xref{sparse}.
3046 @opsummary{starting-file}
3047 @item --starting-file=@var{name}
3048 @itemx -K @var{name}
3050 This option affects extraction only; @command{tar} will skip extracting
3051 files in the archive until it finds one that matches @var{name}.
3054 @opsummary{strip-components}
3055 @item --strip-components=@var{number}
3056 Strip given @var{number} of leading components from file names before
3057 extraction.@footnote{This option was called @option{--strip-path} in
3058 version 1.14.} For example, if archive @file{archive.tar} contained
3059 @file{/some/file/name}, then running
3062 tar --extract --file archive.tar --strip-components=2
3066 would extract this file to file @file{name}.
3068 @opsummary{suffix}, summary
3069 @item --suffix=@var{suffix}
3071 Alters the suffix @command{tar} uses when backing up files from the default
3072 @samp{~}. @xref{backup}.
3074 @opsummary{tape-length}
3075 @item --tape-length=@var{num}
3078 Specifies the length of tapes that @command{tar} is writing as being
3079 @w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
3081 @opsummary{test-label}
3084 Reads the volume label. If an argument is specified, test whether it
3085 matches the volume label. @xref{--test-label option}.
3087 @opsummary{to-command}
3088 @item --to-command=@var{command}
3090 During extraction @command{tar} will pipe extracted files to the
3091 standard input of @var{command}. @xref{Writing to an External Program}.
3093 @opsummary{to-stdout}
3097 During extraction, @command{tar} will extract files to stdout rather
3098 than to the file system. @xref{Writing to Standard Output}.
3101 @item --totals[=@var{signo}]
3103 Displays the total number of bytes transferred when processing an
3104 archive. If an argument is given, these data are displayed on
3105 request, when signal @var{signo} is delivered to @command{tar}.
3112 Sets the data modification time of extracted files to the extraction time,
3113 rather than the data modification time stored in the archive.
3114 @xref{Data Modification Times}.
3116 @opsummary{uncompress}
3119 (See @option{--compress}. @pxref{gzip})
3124 (See @option{--gzip}. @pxref{gzip})
3126 @opsummary{unlink-first}
3127 @item --unlink-first
3130 Directs @command{tar} to remove the corresponding file from the file
3131 system before extracting it from the archive. @xref{Unlink First}.
3135 Enable unquoting input file or member names (default). @xref{input
3138 @opsummary{use-compress-program}
3139 @item --use-compress-program=@var{prog}
3141 Instructs @command{tar} to access the archive through @var{prog}, which is
3142 presumed to be a compression program of some sort. @xref{gzip}.
3147 Display file modification dates in @acronym{UTC}. This option implies
3154 Specifies that @command{tar} should be more verbose about the operations its
3155 performing. This option can be specified multiple times for some
3156 operations to increase the amount of information displayed.
3163 Verifies that the archive was correctly written when creating an
3164 archive. @xref{verify}.
3169 Print information about the program's name, version, origin and legal
3170 status, all on standard output, and then exit successfully.
3173 @opsummary{volno-file}
3174 @item --volno-file=@var{file}
3176 Used in conjunction with @option{--multi-volume}. @command{tar} will
3177 keep track of which volume of a multi-volume archive its working in
3178 @var{file}. @xref{volno-file}.
3180 @opsummary{wildcards}
3182 Use wildcards when matching member names with patterns.
3183 @xref{controlling pattern-matching}.
3185 @opsummary{wildcards-match-slash}
3186 @item --wildcards-match-slash
3187 Wildcards match @samp{/}.
3188 @xref{controlling pattern-matching}.
3191 @node Short Option Summary
3192 @subsection Short Options Cross Reference
3194 Here is an alphabetized list of all of the short option forms, matching
3195 them with the equivalent long option.
3197 @multitable @columnfractions 0.20 0.80
3198 @headitem Short Option @tab Reference
3200 @item -A @tab @ref{--concatenate}.
3202 @item -B @tab @ref{--read-full-records}.
3204 @item -C @tab @ref{--directory}.
3206 @item -F @tab @ref{--info-script}.
3208 @item -G @tab @ref{--incremental}.
3210 @item -K @tab @ref{--starting-file}.
3212 @item -L @tab @ref{--tape-length}.
3214 @item -M @tab @ref{--multi-volume}.
3216 @item -N @tab @ref{--newer}.
3218 @item -O @tab @ref{--to-stdout}.
3220 @item -P @tab @ref{--absolute-names}.
3222 @item -R @tab @ref{--block-number}.
3224 @item -S @tab @ref{--sparse}.
3226 @item -T @tab @ref{--files-from}.
3228 @item -U @tab @ref{--unlink-first}.
3230 @item -V @tab @ref{--label}.
3232 @item -W @tab @ref{--verify}.
3234 @item -X @tab @ref{--exclude-from}.
3236 @item -Z @tab @ref{--compress}.
3238 @item -b @tab @ref{--blocking-factor}.
3240 @item -c @tab @ref{--create}.
3242 @item -d @tab @ref{--compare}.
3244 @item -f @tab @ref{--file}.
3246 @item -g @tab @ref{--listed-incremental}.
3248 @item -h @tab @ref{--dereference}.
3250 @item -i @tab @ref{--ignore-zeros}.
3252 @item -j @tab @ref{--bzip2}.
3254 @item -k @tab @ref{--keep-old-files}.
3256 @item -l @tab @ref{--check-links}.
3258 @item -m @tab @ref{--touch}.
3260 @item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
3261 @ref{--portability}.
3263 The later usage is deprecated. It is retained for compatibility with
3264 the earlier versions of @GNUTAR{}. In the future releases
3265 @option{-o} will be equivalent to @option{--no-same-owner} only.
3267 @item -p @tab @ref{--preserve-permissions}.
3269 @item -r @tab @ref{--append}.
3271 @item -s @tab @ref{--same-order}.
3273 @item -t @tab @ref{--list}.
3275 @item -u @tab @ref{--update}.
3277 @item -v @tab @ref{--verbose}.
3279 @item -w @tab @ref{--interactive}.
3281 @item -x @tab @ref{--extract}.
3283 @item -z @tab @ref{--gzip}.
3288 @section @GNUTAR{} documentation
3290 @cindex Getting program version number
3292 @cindex Version of the @command{tar} program
3293 Being careful, the first thing is really checking that you are using
3294 @GNUTAR{}, indeed. The @option{--version} option
3295 causes @command{tar} to print information about its name, version,
3296 origin and legal status, all on standard output, and then exit
3297 successfully. For example, @w{@samp{tar --version}} might print:
3300 tar (GNU tar) @value{VERSION}
3301 Copyright (C) 2006 Free Software Foundation, Inc.
3302 This is free software. You may redistribute copies of it under the terms of
3303 the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
3304 There is NO WARRANTY, to the extent permitted by law.
3306 Written by John Gilmore and Jay Fenlason.
3310 The first occurrence of @samp{tar} in the result above is the program
3311 name in the package (for example, @command{rmt} is another program),
3312 while the second occurrence of @samp{tar} is the name of the package
3313 itself, containing possibly many programs. The package is currently
3314 named @samp{tar}, after the name of the main program it
3315 contains@footnote{There are plans to merge the @command{cpio} and
3316 @command{tar} packages into a single one which would be called
3317 @code{paxutils}. So, who knows if, one of this days, the
3318 @option{--version} would not output @w{@samp{tar (@acronym{GNU}
3321 @cindex Obtaining help
3322 @cindex Listing all @command{tar} options
3323 @xopindex{help, introduction}
3324 Another thing you might want to do is checking the spelling or meaning
3325 of some particular @command{tar} option, without resorting to this
3326 manual, for once you have carefully read it. @GNUTAR{}
3327 has a short help feature, triggerable through the
3328 @option{--help} option. By using this option, @command{tar} will
3329 print a usage message listing all available options on standard
3330 output, then exit successfully, without doing anything else and
3331 ignoring all other options. Even if this is only a brief summary, it
3332 may be several screens long. So, if you are not using some kind of
3333 scrollable window, you might prefer to use something like:
3336 $ @kbd{tar --help | less}
3340 presuming, here, that you like using @command{less} for a pager. Other
3341 popular pagers are @command{more} and @command{pg}. If you know about some
3342 @var{keyword} which interests you and do not want to read all the
3343 @option{--help} output, another common idiom is doing:
3346 tar --help | grep @var{keyword}
3350 for getting only the pertinent lines. Notice, however, that some
3351 @command{tar} options have long description lines and the above
3352 command will list only the first of them.
3354 The exact look of the option summary displayed by @kbd{tar --help} is
3355 configurable. @xref{Configuring Help Summary}, for a detailed description.
3358 If you only wish to check the spelling of an option, running @kbd{tar
3359 --usage} may be a better choice. This will display a terse list of
3360 @command{tar} option without accompanying explanations.
3362 The short help output is quite succinct, and you might have to get
3363 back to the full documentation for precise points. If you are reading
3364 this paragraph, you already have the @command{tar} manual in some
3365 form. This manual is available in a variety of forms from
3366 @url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{}
3367 distribution, provided you have @TeX{} already installed somewhere,
3368 and a laser printer around. Just configure the distribution, execute
3369 the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the
3370 usual way (contact your local guru to know how). If @GNUTAR{}
3371 has been conveniently installed at your place, this
3372 manual is also available in interactive, hypertextual form as an Info
3373 file. Just call @w{@samp{info tar}} or, if you do not have the
3374 @command{info} program handy, use the Info reader provided within
3375 @acronym{GNU} Emacs, calling @samp{tar} from the main Info menu.
3377 There is currently no @code{man} page for @GNUTAR{}.
3378 If you observe such a @code{man} page on the system you are running,
3379 either it does not belong to @GNUTAR{}, or it has not
3380 been produced by @acronym{GNU}. Some package maintainers convert
3381 @kbd{tar --help} output to a man page, using @command{help2man}. In
3382 any case, please bear in mind that the authoritative source of
3383 information about @GNUTAR{} is this Texinfo documentation.
3386 @section Obtaining @GNUTAR{} default values
3388 @opindex show-defaults
3389 @GNUTAR{} has some predefined defaults that are used when you do not
3390 explicitely specify another values. To obtain a list of such
3391 defaults, use @option{--show-defaults} option. This will output the
3392 values in the form of @command{tar} command line options:
3396 @kbd{tar --show-defaults}
3397 --format=gnu -f- -b20 --quoting-style=escape
3398 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3403 Notice, that this option outputs only one line. The example output above
3404 has been split to fit page boundaries.
3407 The above output shows that this version of @GNUTAR{} defaults to
3408 using @samp{gnu} archive format (@pxref{Formats}), it uses standard
3409 output as the archive, if no @option{--file} option has been given
3410 (@pxref{file tutorial}), the default blocking factor is 20
3411 (@pxref{Blocking Factor}). It also shows the default locations where
3412 @command{tar} will look for @command{rmt} and @command{rsh} binaries.
3415 @section Checking @command{tar} progress
3417 Typically, @command{tar} performs most operations without reporting any
3418 information to the user except error messages. When using @command{tar}
3419 with many options, particularly ones with complicated or
3420 difficult-to-predict behavior, it is possible to make serious mistakes.
3421 @command{tar} provides several options that make observing @command{tar}
3422 easier. These options cause @command{tar} to print information as it
3423 progresses in its job, and you might want to use them just for being
3424 more careful about what is going on, or merely for entertaining
3425 yourself. If you have encountered a problem when operating on an
3426 archive, however, you may need more information than just an error
3427 message in order to solve the problem. The following options can be
3428 helpful diagnostic tools.
3430 @cindex Verbose operation
3432 Normally, the @option{--list} (@option{-t}) command to list an archive
3433 prints just the file names (one per line) and the other commands are
3434 silent. When used with most operations, the @option{--verbose}
3435 (@option{-v}) option causes @command{tar} to print the name of each
3436 file or archive member as it is processed. This and the other options
3437 which make @command{tar} print status information can be useful in
3438 monitoring @command{tar}.
3440 With @option{--create} or @option{--extract}, @option{--verbose} used
3441 once just prints the names of the files or members as they are processed.
3442 Using it twice causes @command{tar} to print a longer listing
3443 (@xref{verbose member listing}, for the description) for each member.
3444 Since @option{--list} already prints the names of the members,
3445 @option{--verbose} used once with @option{--list} causes @command{tar}
3446 to print an @samp{ls -l} type listing of the files in the archive.
3447 The following examples both extract members with long list output:
3450 $ @kbd{tar --extract --file=archive.tar --verbose --verbose}
3451 $ @kbd{tar xvvf archive.tar}
3454 Verbose output appears on the standard output except when an archive is
3455 being written to the standard output, as with @samp{tar --create
3456 --file=- --verbose} (@samp{tar cfv -}, or even @samp{tar cv}---if the
3457 installer let standard output be the default archive). In that case
3458 @command{tar} writes verbose output to the standard error stream.
3460 If @option{--index-file=@var{file}} is specified, @command{tar} sends
3461 verbose output to @var{file} rather than to standard output or standard
3465 @cindex Obtaining total status information
3467 The @option{--totals} option causes @command{tar} to print on the
3468 standard error the total amount of bytes transferred when processing
3469 an archive. When creating or appending to an archive, this option
3470 prints the number of bytes written to the archive and the average
3471 speed at which they have been written, e.g.:
3475 $ @kbd{tar -c -f archive.tar --totals /home}
3476 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3480 When reading an archive, this option displays the number of bytes
3485 $ @kbd{tar -x -f archive.tar --totals}
3486 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3490 Finally, when deleting from an archive, the @option{--totals} option
3491 displays both numbers plus number of bytes removed from the archive:
3495 $ @kbd{tar --delete -f foo.tar --totals --wildcards '*~'}
3496 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3497 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3498 Total bytes deleted: 1474048
3502 You can also obtain this information on request. When
3503 @option{--totals} is used with an argument, this argument is
3504 interpreted as a symbolic name of a signal, upon delivery of which the
3505 statistics is to be printed:
3508 @item --totals=@var{signo}
3509 Print statistics upon delivery of signal @var{signo}. Valid arguments
3510 are: @code{SIGHUP}, @code{SIGQUIT}, @code{SIGINT}, @code{SIGUSR1} and
3511 @code{SIGUSR2}. Shortened names without @samp{SIG} prefix are also
3515 Both forms of @option{--totals} option can be used simultaneously.
3516 Thus, @kbd{tar -x --totals --totals=USR1} instructs @command{tar} to
3517 extract all members from its default archive and print statistics
3518 after finishing the extraction, as well as when receiving signal
3521 @anchor{Progress information}
3522 @cindex Progress information
3524 The @option{--checkpoint} option prints an occasional message
3525 as @command{tar} reads or writes the archive. It is designed for
3526 those who don't need the more detailed (and voluminous) output of
3527 @option{--block-number} (@option{-R}), but do want visual confirmation
3528 that @command{tar} is actually making forward progress. By default it
3529 prints a message each 10 records read or written. This can be changed
3530 by giving it a numeric argument after an equal sign:
3533 $ @kbd{tar -c --checkpoint=1000} /var
3534 tar: Write checkpoint 1000
3535 tar: Write checkpoint 2000
3536 tar: Write checkpoint 3000
3539 This example shows the default checkpoint message used by
3540 @command{tar}. If you place a dot immediately after the equal
3541 sign, it will print a @samp{.} at each checkpoint. For example:
3544 $ @kbd{tar -c --checkpoint=.1000} /var
3548 @opindex show-omitted-dirs
3549 @anchor{show-omitted-dirs}
3550 The @option{--show-omitted-dirs} option, when reading an archive---with
3551 @option{--list} or @option{--extract}, for example---causes a message
3552 to be printed for each directory in the archive which is skipped.
3553 This happens regardless of the reason for skipping: the directory might
3554 not have been named on the command line (implicitly or explicitly),
3555 it might be excluded by the use of the
3556 @option{--exclude=@var{pattern}} option, or some other reason.
3558 @opindex block-number
3559 @cindex Block number where error occurred
3560 @anchor{block-number}
3561 If @option{--block-number} (@option{-R}) is used, @command{tar} prints, along with
3562 every message it would normally produce, the block number within the
3563 archive where the message was triggered. Also, supplementary messages
3564 are triggered when reading blocks full of NULs, or when hitting end of
3565 file on the archive. As of now, if the archive if properly terminated
3566 with a NUL block, the reading of the file may stop before end of file
3567 is met, so the position of end of file will not usually show when
3568 @option{--block-number} (@option{-R}) is used. Note that @GNUTAR{}
3569 drains the archive before exiting when reading the
3570 archive from a pipe.
3572 @cindex Error message, block number of
3573 This option is especially useful when reading damaged archives, since
3574 it helps pinpoint the damaged sections. It can also be used with
3575 @option{--list} (@option{-t}) when listing a file-system backup tape, allowing you to
3576 choose among several backup tapes when retrieving a file later, in
3577 favor of the tape where the file appears earliest (closest to the
3578 front of the tape). @xref{backup}.
3581 @section Asking for Confirmation During Operations
3582 @cindex Interactive operation
3584 Typically, @command{tar} carries out a command without stopping for
3585 further instructions. In some situations however, you may want to
3586 exclude some files and archive members from the operation (for instance
3587 if disk or storage space is tight). You can do this by excluding
3588 certain files automatically (@pxref{Choosing}), or by performing
3589 an operation interactively, using the @option{--interactive} (@option{-w}) option.
3590 @command{tar} also accepts @option{--confirmation} for this option.
3592 @opindex interactive
3593 When the @option{--interactive} (@option{-w}) option is specified, before
3594 reading, writing, or deleting files, @command{tar} first prints a message
3595 for each such file, telling what operation it intends to take, then asks
3596 for confirmation on the terminal. The actions which require
3597 confirmation include adding a file to the archive, extracting a file
3598 from the archive, deleting a file from the archive, and deleting a file
3599 from disk. To confirm the action, you must type a line of input
3600 beginning with @samp{y}. If your input line begins with anything other
3601 than @samp{y}, @command{tar} skips that file.
3603 If @command{tar} is reading the archive from the standard input,
3604 @command{tar} opens the file @file{/dev/tty} to support the interactive
3607 Verbose output is normally sent to standard output, separate from
3608 other error messages. However, if the archive is produced directly
3609 on standard output, then verbose output is mixed with errors on
3610 @code{stderr}. Producing the archive on standard output may be used
3611 as a way to avoid using disk space, when the archive is soon to be
3612 consumed by another process reading it, say. Some people felt the need
3613 of producing an archive on stdout, still willing to segregate between
3614 verbose output and error output. A possible approach would be using a
3615 named pipe to receive the archive, and having the consumer process to
3616 read from that named pipe. This has the advantage of letting standard
3617 output free to receive verbose output, all separate from errors.
3620 @chapter @GNUTAR{} Operations
3633 @section Basic @GNUTAR{} Operations
3635 The basic @command{tar} operations, @option{--create} (@option{-c}),
3636 @option{--list} (@option{-t}) and @option{--extract} (@option{--get},
3637 @option{-x}), are currently presented and described in the tutorial
3638 chapter of this manual. This section provides some complementary notes
3639 for these operations.
3642 @xopindex{create, complementary notes}
3646 Creating an empty archive would have some kind of elegance. One can
3647 initialize an empty archive and later use @option{--append}
3648 (@option{-r}) for adding all members. Some applications would not
3649 welcome making an exception in the way of adding the first archive
3650 member. On the other hand, many people reported that it is
3651 dangerously too easy for @command{tar} to destroy a magnetic tape with
3652 an empty archive@footnote{This is well described in @cite{Unix-haters
3653 Handbook}, by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG
3654 Books, ISBN 1-56884-203-1.}. The two most common errors are:
3658 Mistakingly using @code{create} instead of @code{extract}, when the
3659 intent was to extract the full contents of an archive. This error
3660 is likely: keys @kbd{c} and @kbd{x} are right next to each other on
3661 the QWERTY keyboard. Instead of being unpacked, the archive then
3662 gets wholly destroyed. When users speak about @dfn{exploding} an
3663 archive, they usually mean something else :-).
3666 Forgetting the argument to @code{file}, when the intent was to create
3667 an archive with a single file in it. This error is likely because a
3668 tired user can easily add the @kbd{f} key to the cluster of option
3669 letters, by the mere force of habit, without realizing the full
3670 consequence of doing so. The usual consequence is that the single
3671 file, which was meant to be saved, is rather destroyed.
3674 So, recognizing the likelihood and the catastrophical nature of these
3675 errors, @GNUTAR{} now takes some distance from elegance, and
3676 cowardly refuses to create an archive when @option{--create} option is
3677 given, there are no arguments besides options, and
3678 @option{--files-from} (@option{-T}) option is @emph{not} used. To get
3679 around the cautiousness of @GNUTAR{} and nevertheless create an
3680 archive with nothing in it, one may still use, as the value for the
3681 @option{--files-from} option, a file with no names in it, as shown in
3682 the following commands:
3685 @kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
3686 @kbd{tar cfT empty-archive.tar /dev/null}
3689 @xopindex{extract, complementary notes}
3694 A socket is stored, within a @GNUTAR{} archive, as a pipe.
3696 @item @option{--list} (@option{-t})
3698 @GNUTAR{} now shows dates as @samp{1996-08-30},
3699 while it used to show them as @samp{Aug 30 1996}. Preferably,
3700 people should get used to ISO 8601 dates. Local American dates should
3701 be made available again with full date localization support, once
3702 ready. In the meantime, programs not being localizable for dates
3703 should prefer international dates, that's really the way to go.
3705 Look up @url{http://www.ft.uni-erlangen.de/@/~mskuhn/@/iso-time.html} if you
3706 are curious, it contains a detailed explanation of the ISO 8601 standard.
3711 @section Advanced @GNUTAR{} Operations
3713 Now that you have learned the basics of using @GNUTAR{}, you may want
3714 to learn about further ways in which @command{tar} can help you.
3716 This chapter presents five, more advanced operations which you probably
3717 won't use on a daily basis, but which serve more specialized functions.
3718 We also explain the different styles of options and why you might want
3719 to use one or another, or a combination of them in your @command{tar}
3720 commands. Additionally, this chapter includes options which allow you to
3721 define the output from @command{tar} more carefully, and provide help and
3722 error correction in special circumstances.
3724 @FIXME{check this after the chapter is actually revised to make sure
3725 it still introduces the info in the chapter correctly : ).}
3737 @subsection The Five Advanced @command{tar} Operations
3740 In the last chapter, you learned about the first three operations to
3741 @command{tar}. This chapter presents the remaining five operations to
3742 @command{tar}: @option{--append}, @option{--update}, @option{--concatenate},
3743 @option{--delete}, and @option{--compare}.
3745 You are not likely to use these operations as frequently as those
3746 covered in the last chapter; however, since they perform specialized
3747 functions, they are quite useful when you do need to use them. We
3748 will give examples using the same directory and files that you created
3749 in the last chapter. As you may recall, the directory is called
3750 @file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk},
3751 @samp{rock}, and the two archive files you created are
3752 @samp{collection.tar} and @samp{music.tar}.
3754 We will also use the archive files @samp{afiles.tar} and
3755 @samp{bfiles.tar}. @samp{afiles.tar} contains the members @samp{apple},
3756 @samp{angst}, and @samp{aspic}. @samp{bfiles.tar} contains the members
3757 @samp{./birds}, @samp{baboon}, and @samp{./box}.
3759 Unless we state otherwise, all practicing you do and examples you follow
3760 in this chapter will take place in the @file{practice} directory that
3761 you created in the previous chapter; see @ref{prepare for examples}.
3762 (Below in this section, we will remind you of the state of the examples
3763 where the last chapter left them.)
3765 The five operations that we will cover in this chapter are:
3770 Add new entries to an archive that already exists.
3773 Add more recent copies of archive members to the end of an archive, if
3778 Add one or more pre-existing archives to the end of another archive.
3780 Delete items from an archive (does not work on tapes).
3784 Compare archive members to their counterparts in the file system.
3788 @subsection How to Add Files to Existing Archives: @option{--append}
3792 If you want to add files to an existing archive, you don't need to
3793 create a new archive; you can use @option{--append} (@option{-r}).
3794 The archive must already exist in order to use @option{--append}. (A
3795 related operation is the @option{--update} operation; you can use this
3796 to add newer versions of archive members to an existing archive. To learn how to
3797 do this with @option{--update}, @pxref{update}.)
3799 If you use @option{--append} to add a file that has the same name as an
3800 archive member to an archive containing that archive member, then the
3801 old member is not deleted. What does happen, however, is somewhat
3802 complex. @command{tar} @emph{allows} you to have infinite number of files
3803 with the same name. Some operations treat these same-named members no
3804 differently than any other set of archive members: for example, if you
3805 view an archive with @option{--list} (@option{-t}), you will see all
3806 of those members listed, with their data modification times, owners, etc.
3808 Other operations don't deal with these members as perfectly as you might
3809 prefer; if you were to use @option{--extract} to extract the archive,
3810 only the most recently added copy of a member with the same name as four
3811 other members would end up in the working directory. This is because
3812 @option{--extract} extracts an archive in the order the members appeared
3813 in the archive; the most recently archived members will be extracted
3814 last. Additionally, an extracted member will @emph{replace} a file of
3815 the same name which existed in the directory already, and @command{tar}
3816 will not prompt you about this@footnote{Unless you give it
3817 @option{--keep-old-files} option, or the disk copy is newer than the
3818 the one in the archive and you invoke @command{tar} with
3819 @option{--keep-newer-files} option}. Thus, only the most recently archived
3820 member will end up being extracted, as it will replace the one
3821 extracted before it, and so on.
3823 There exists a special option that allows you to get around this
3824 behavior and extract (or list) only a particular copy of the file.
3825 This is @option{--occurrence} option. If you run @command{tar} with
3826 this option, it will extract only the first copy of the file. You
3827 may also give this option an argument specifying the number of
3828 copy to be extracted. Thus, for example if the archive
3829 @file{archive.tar} contained three copies of file @file{myfile}, then
3833 tar --extract --file archive.tar --occurrence=2 myfile
3837 would extract only the second copy. @xref{Option
3838 Summary,---occurrence}, for the description of @option{--occurrence}
3841 @FIXME{ hag -- you might want to incorporate some of the above into the
3842 MMwtSN node; not sure. i didn't know how to make it simpler...
3844 There are a few ways to get around this. (maybe xref Multiple Members
3845 with the Same Name.}
3847 @cindex Members, replacing with other members
3848 @cindex Replacing members with other members
3849 If you want to replace an archive member, use @option{--delete} to
3850 delete the member you want to remove from the archive, , and then use
3851 @option{--append} to add the member you want to be in the archive. Note
3852 that you can not change the order of the archive; the most recently
3853 added member will still appear last. In this sense, you cannot truly
3854 ``replace'' one member with another. (Replacing one member with another
3855 will not work on certain types of media, such as tapes; see @ref{delete}
3856 and @ref{Media}, for more information.)
3859 * appending files:: Appending Files to an Archive
3863 @node appending files
3864 @subsubsection Appending Files to an Archive
3866 @cindex Adding files to an Archive
3867 @cindex Appending files to an Archive
3868 @cindex Archives, Appending files to
3870 The simplest way to add a file to an already existing archive is the
3871 @option{--append} (@option{-r}) operation, which writes specified
3872 files into the archive whether or not they are already among the
3875 When you use @option{--append}, you @emph{must} specify file name
3876 arguments, as there is no default. If you specify a file that already
3877 exists in the archive, another copy of the file will be added to the
3878 end of the archive. As with other operations, the member names of the
3879 newly added files will be exactly the same as their names given on the
3880 command line. The @option{--verbose} (@option{-v}) option will print
3881 out the names of the files as they are written into the archive.
3883 @option{--append} cannot be performed on some tape drives, unfortunately,
3884 due to deficiencies in the formats those tape drives use. The archive
3885 must be a valid @command{tar} archive, or else the results of using this
3886 operation will be unpredictable. @xref{Media}.
3888 To demonstrate using @option{--append} to add a file to an archive,
3889 create a file called @file{rock} in the @file{practice} directory.
3890 Make sure you are in the @file{practice} directory. Then, run the
3891 following @command{tar} command to add @file{rock} to
3892 @file{collection.tar}:
3895 $ @kbd{tar --append --file=collection.tar rock}
3899 If you now use the @option{--list} (@option{-t}) operation, you will see that
3900 @file{rock} has been added to the archive:
3903 $ @kbd{tar --list --file=collection.tar}
3904 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
3905 -rw-r--r-- me user 21 1996-09-23 16:44 blues
3906 -rw-r--r-- me user 20 1996-09-23 16:44 folk
3907 -rw-r--r-- me user 20 1996-09-23 16:44 rock
3911 @subsubsection Multiple Members with the Same Name
3913 You can use @option{--append} (@option{-r}) to add copies of files
3914 which have been updated since the archive was created. (However, we
3915 do not recommend doing this since there is another @command{tar}
3916 option called @option{--update}; @xref{update}, for more information.
3917 We describe this use of @option{--append} here for the sake of
3918 completeness.) When you extract the archive, the older version will
3919 be effectively lost. This works because files are extracted from an
3920 archive in the order in which they were archived. Thus, when the
3921 archive is extracted, a file archived later in time will replace a
3922 file of the same name which was archived earlier, even though the
3923 older version of the file will remain in the archive unless you delete
3924 all versions of the file.
3926 Supposing you change the file @file{blues} and then append the changed
3927 version to @file{collection.tar}. As you saw above, the original
3928 @file{blues} is in the archive @file{collection.tar}. If you change the
3929 file and append the new version of the file to the archive, there will
3930 be two copies in the archive. When you extract the archive, the older
3931 version of the file will be extracted first, and then replaced by the
3932 newer version when it is extracted.
3934 You can append the new, changed copy of the file @file{blues} to the
3935 archive in this way:
3938 $ @kbd{tar --append --verbose --file=collection.tar blues}
3943 Because you specified the @option{--verbose} option, @command{tar} has
3944 printed the name of the file being appended as it was acted on. Now
3945 list the contents of the archive:
3948 $ @kbd{tar --list --verbose --file=collection.tar}
3949 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
3950 -rw-r--r-- me user 21 1996-09-23 16:44 blues
3951 -rw-r--r-- me user 20 1996-09-23 16:44 folk
3952 -rw-r--r-- me user 20 1996-09-23 16:44 rock
3953 -rw-r--r-- me user 58 1996-10-24 18:30 blues
3957 The newest version of @file{blues} is now at the end of the archive
3958 (note the different creation dates and file sizes). If you extract
3959 the archive, the older version of the file @file{blues} will be
3960 replaced by the newer version. You can confirm this by extracting
3961 the archive and running @samp{ls} on the directory.
3963 If you wish to extract the first occurrence of the file @file{blues}
3964 from the archive, use @option{--occurrence} option, as shown in
3965 the following example:
3968 $ @kbd{tar --extract -vv --occurrence --file=collection.tar blues}
3969 -rw-r--r-- me user 21 1996-09-23 16:44 blues
3972 @xref{Writing}, for more information on @option{--extract} and
3973 @xref{Option Summary, --occurrence}, for the description of
3974 @option{--occurrence} option.
3977 @subsection Updating an Archive
3979 @cindex Updating an archive
3982 In the previous section, you learned how to use @option{--append} to
3983 add a file to an existing archive. A related operation is
3984 @option{--update} (@option{-u}). The @option{--update} operation
3985 updates a @command{tar} archive by comparing the date of the specified
3986 archive members against the date of the file with the same name. If
3987 the file has been modified more recently than the archive member, then
3988 the newer version of the file is added to the archive (as with
3991 Unfortunately, you cannot use @option{--update} with magnetic tape drives.
3992 The operation will fail.
3994 @FIXME{other examples of media on which --update will fail? need to ask
3995 charles and/or mib/thomas/dave shevett..}
3997 Both @option{--update} and @option{--append} work by adding to the end
3998 of the archive. When you extract a file from the archive, only the
3999 version stored last will wind up in the file system, unless you use
4000 the @option{--backup} option. @xref{multiple}, for a detailed discussion.
4007 @subsubsection How to Update an Archive Using @option{--update}
4009 You must use file name arguments with the @option{--update}
4010 (@option{-u}) operation. If you don't specify any files,
4011 @command{tar} won't act on any files and won't tell you that it didn't
4012 do anything (which may end up confusing you).
4014 @c note: the above parenthetical added because in fact, this
4015 @c behavior just confused the author. :-)
4017 To see the @option{--update} option at work, create a new file,
4018 @file{classical}, in your practice directory, and some extra text to the
4019 file @file{blues}, using any text editor. Then invoke @command{tar} with
4020 the @samp{update} operation and the @option{--verbose} (@option{-v})
4021 option specified, using the names of all the files in the practice
4022 directory as file name arguments:
4025 $ @kbd{tar --update -v -f collection.tar blues folk rock classical}
4032 Because we have specified verbose mode, @command{tar} prints out the names
4033 of the files it is working on, which in this case are the names of the
4034 files that needed to be updated. If you run @samp{tar --list} and look
4035 at the archive, you will see @file{blues} and @file{classical} at its
4036 end. There will be a total of two versions of the member @samp{blues};
4037 the one at the end will be newer and larger, since you added text before
4040 (The reason @command{tar} does not overwrite the older file when updating
4041 it is because writing to the middle of a section of tape is a difficult
4042 process. Tapes are not designed to go backward. @xref{Media}, for more
4043 information about tapes.
4045 @option{--update} (@option{-u}) is not suitable for performing backups for two
4046 reasons: it does not change directory content entries, and it
4047 lengthens the archive every time it is used. The @GNUTAR{}
4048 options intended specifically for backups are more
4049 efficient. If you need to run backups, please consult @ref{Backups}.
4052 @subsection Combining Archives with @option{--concatenate}
4054 @cindex Adding archives to an archive
4055 @cindex Concatenating Archives
4056 @opindex concatenate
4058 @c @cindex @option{-A} described
4059 Sometimes it may be convenient to add a second archive onto the end of
4060 an archive rather than adding individual files to the archive. To add
4061 one or more archives to the end of another archive, you should use the
4062 @option{--concatenate} (@option{--catenate}, @option{-A}) operation.
4064 To use @option{--concatenate}, give the first archive with
4065 @option{--file} option and name the rest of archives to be
4066 concatenated on the command line. The members, and their member
4067 names, will be copied verbatim from those archives to the first one.
4068 @footnote{This can cause multiple members to have the same name, for
4069 information on how this affects reading the archive, @ref{multiple}.}
4070 The new, concatenated archive will be called by the same name as the
4071 one given with the @option{--file} option. As usual, if you omit
4072 @option{--file}, @command{tar} will use the value of the environment
4073 variable @env{TAPE}, or, if this has not been set, the default archive name.
4075 @FIXME{There is no way to specify a new name...}
4077 To demonstrate how @option{--concatenate} works, create two small archives
4078 called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
4079 files from @file{practice}:
4082 $ @kbd{tar -cvf bluesrock.tar blues rock}
4085 $ @kbd{tar -cvf folkjazz.tar folk jazz}
4091 If you like, You can run @samp{tar --list} to make sure the archives
4092 contain what they are supposed to:
4095 $ @kbd{tar -tvf bluesrock.tar}
4096 -rw-r--r-- melissa user 105 1997-01-21 19:42 blues
4097 -rw-r--r-- melissa user 33 1997-01-20 15:34 rock
4098 $ @kbd{tar -tvf jazzfolk.tar}
4099 -rw-r--r-- melissa user 20 1996-09-23 16:44 folk
4100 -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
4103 We can concatenate these two archives with @command{tar}:
4107 $ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
4110 If you now list the contents of the @file{bluesrock.tar}, you will see
4111 that now it also contains the archive members of @file{jazzfolk.tar}:
4114 $ @kbd{tar --list --file=bluesrock.tar}
4121 When you use @option{--concatenate}, the source and target archives must
4122 already exist and must have been created using compatible format
4123 parameters. Notice, that @command{tar} does not check whether the
4124 archives it concatenates have compatible formats, it does not
4125 even check if the files are really tar archives.
4127 Like @option{--append} (@option{-r}), this operation cannot be performed on some
4128 tape drives, due to deficiencies in the formats those tape drives use.
4130 @cindex @code{concatenate} vs @command{cat}
4131 @cindex @command{cat} vs @code{concatenate}
4132 It may seem more intuitive to you to want or try to use @command{cat} to
4133 concatenate two archives instead of using the @option{--concatenate}
4134 operation; after all, @command{cat} is the utility for combining files.
4136 However, @command{tar} archives incorporate an end-of-file marker which
4137 must be removed if the concatenated archives are to be read properly as
4138 one archive. @option{--concatenate} removes the end-of-archive marker
4139 from the target archive before each new archive is appended. If you use
4140 @command{cat} to combine the archives, the result will not be a valid
4141 @command{tar} format archive. If you need to retrieve files from an
4142 archive that was added to using the @command{cat} utility, use the
4143 @option{--ignore-zeros} (@option{-i}) option. @xref{Ignore Zeros}, for further
4144 information on dealing with archives improperly combined using the
4145 @command{cat} shell utility.
4148 @subsection Removing Archive Members Using @option{--delete}
4150 @cindex Deleting files from an archive
4151 @cindex Removing files from an archive
4154 You can remove members from an archive by using the @option{--delete}
4155 option. Specify the name of the archive with @option{--file}
4156 (@option{-f}) and then specify the names of the members to be deleted;
4157 if you list no member names, nothing will be deleted. The
4158 @option{--verbose} option will cause @command{tar} to print the names
4159 of the members as they are deleted. As with @option{--extract}, you
4160 must give the exact member names when using @samp{tar --delete}.
4161 @option{--delete} will remove all versions of the named file from the
4162 archive. The @option{--delete} operation can run very slowly.
4164 Unlike other operations, @option{--delete} has no short form.
4166 @cindex Tapes, using @option{--delete} and
4167 @cindex Deleting from tape archives
4168 This operation will rewrite the archive. You can only use
4169 @option{--delete} on an archive if the archive device allows you to
4170 write to any point on the media, such as a disk; because of this, it
4171 does not work on magnetic tapes. Do not try to delete an archive member
4172 from a magnetic tape; the action will not succeed, and you will be
4173 likely to scramble the archive and damage your tape. There is no safe
4174 way (except by completely re-writing the archive) to delete files from
4175 most kinds of magnetic tape. @xref{Media}.
4177 To delete all versions of the file @file{blues} from the archive
4178 @file{collection.tar} in the @file{practice} directory, make sure you
4179 are in that directory, and then,
4182 $ @kbd{tar --list --file=collection.tar}
4187 $ @kbd{tar --delete --file=collection.tar blues}
4188 $ @kbd{tar --list --file=collection.tar}
4195 @FIXME{Check if the above listing is actually produced after running
4196 all the examples on collection.tar.}
4198 The @option{--delete} option has been reported to work properly when
4199 @command{tar} acts as a filter from @code{stdin} to @code{stdout}.
4202 @subsection Comparing Archive Members with the File System
4203 @cindex Verifying the currency of an archive
4207 The @option{--compare} (@option{-d}), or @option{--diff} operation compares
4208 specified archive members against files with the same names, and then
4209 reports differences in file size, mode, owner, modification date and
4210 contents. You should @emph{only} specify archive member names, not file
4211 names. If you do not name any members, then @command{tar} will compare the
4212 entire archive. If a file is represented in the archive but does not
4213 exist in the file system, @command{tar} reports a difference.
4215 You have to specify the record size of the archive when modifying an
4216 archive with a non-default record size.
4218 @command{tar} ignores files in the file system that do not have
4219 corresponding members in the archive.
4221 The following example compares the archive members @file{rock},
4222 @file{blues} and @file{funk} in the archive @file{bluesrock.tar} with
4223 files of the same name in the file system. (Note that there is no file,
4224 @file{funk}; @command{tar} will report an error message.)
4227 $ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
4230 tar: funk not found in archive
4233 The spirit behind the @option{--compare} (@option{--diff},
4234 @option{-d}) option is to check whether the archive represents the
4235 current state of files on disk, more than validating the integrity of
4236 the archive media. For this later goal, @xref{verify}.
4238 @node create options
4239 @section Options Used by @option{--create}
4241 @xopindex{create, additional options}
4242 The previous chapter described the basics of how to use
4243 @option{--create} (@option{-c}) to create an archive from a set of files.
4244 @xref{create}. This section described advanced options to be used with
4248 * Ignore Failed Read::
4251 @node Ignore Failed Read
4252 @subsection Ignore Fail Read
4255 @item --ignore-failed-read
4256 Do not exit with nonzero on unreadable files or directories.
4259 @node extract options
4260 @section Options Used by @option{--extract}
4263 @xopindex{extract, additional options}
4264 The previous chapter showed how to use @option{--extract} to extract
4265 an archive into the file system. Various options cause @command{tar} to
4266 extract more information than just file contents, such as the owner,
4267 the permissions, the modification date, and so forth. This section
4268 presents options to be used with @option{--extract} when certain special
4269 considerations arise. You may review the information presented in
4270 @ref{extract} for more basic information about the
4271 @option{--extract} operation.
4274 * Reading:: Options to Help Read Archives
4275 * Writing:: Changing How @command{tar} Writes Files
4276 * Scarce:: Coping with Scarce Resources
4280 @subsection Options to Help Read Archives
4281 @cindex Options when reading archives
4284 @cindex Reading incomplete records
4285 @cindex Records, incomplete
4286 @opindex read-full-records
4287 Normally, @command{tar} will request data in full record increments from
4288 an archive storage device. If the device cannot return a full record,
4289 @command{tar} will report an error. However, some devices do not always
4290 return full records, or do not require the last record of an archive to
4291 be padded out to the next record boundary. To keep reading until you
4292 obtain a full record, or to accept an incomplete record if it contains
4293 an end-of-archive marker, specify the @option{--read-full-records} (@option{-B}) option
4294 in conjunction with the @option{--extract} or @option{--list} operations.
4297 The @option{--read-full-records} (@option{-B}) option is turned on by default when
4298 @command{tar} reads an archive from standard input, or from a remote
4299 machine. This is because on BSD Unix systems, attempting to read a
4300 pipe returns however much happens to be in the pipe, even if it is
4301 less than was requested. If this option were not enabled, @command{tar}
4302 would fail as soon as it read an incomplete record from the pipe.
4304 If you're not sure of the blocking factor of an archive, you can
4305 read the archive by specifying @option{--read-full-records} (@option{-B}) and
4306 @option{--blocking-factor=@var{512-size}} (@option{-b
4307 @var{512-size}}), using a blocking factor larger than what the archive
4308 uses. This lets you avoid having to determine the blocking factor
4309 of an archive. @xref{Blocking Factor}.
4312 * read full records::
4316 @node read full records
4317 @unnumberedsubsubsec Reading Full Records
4319 @FIXME{need sentence or so of intro here}
4322 @opindex read-full-records
4323 @item --read-full-records
4325 Use in conjunction with @option{--extract} (@option{--get},
4326 @option{-x}) to read an archive which contains incomplete records, or
4327 one which has a blocking factor less than the one specified.
4331 @unnumberedsubsubsec Ignoring Blocks of Zeros
4333 @cindex End-of-archive blocks, ignoring
4334 @cindex Ignoring end-of-archive blocks
4335 @opindex ignore-zeros
4336 Normally, @command{tar} stops reading when it encounters a block of zeros
4337 between file entries (which usually indicates the end of the archive).
4338 @option{--ignore-zeros} (@option{-i}) allows @command{tar} to
4339 completely read an archive which contains a block of zeros before the
4340 end (i.e., a damaged archive, or one that was created by concatenating
4341 several archives together).
4343 The @option{--ignore-zeros} (@option{-i}) option is turned off by default because many
4344 versions of @command{tar} write garbage after the end-of-archive entry,
4345 since that part of the media is never supposed to be read. @GNUTAR{}
4346 does not write after the end of an archive, but seeks to
4347 maintain compatiblity among archiving utilities.
4350 @item --ignore-zeros
4352 To ignore blocks of zeros (i.e., end-of-archive entries) which may be
4353 encountered while reading an archive. Use in conjunction with
4354 @option{--extract} or @option{--list}.
4358 @subsection Changing How @command{tar} Writes Files
4361 @FIXME{Introductory paragraph}
4364 * Dealing with Old Files::
4365 * Overwrite Old Files::
4367 * Keep Newer Files::
4369 * Recursive Unlink::
4370 * Data Modification Times::
4371 * Setting Access Permissions::
4372 * Directory Modification Times and Permissions::
4373 * Writing to Standard Output::
4374 * Writing to an External Program::
4378 @node Dealing with Old Files
4379 @unnumberedsubsubsec Options Controlling the Overwriting of Existing Files
4381 @xopindex{overwrite-dir, introduced}
4382 When extracting files, if @command{tar} discovers that the extracted
4383 file already exists, it normally replaces the file by removing it before
4384 extracting it, to prevent confusion in the presence of hard or symbolic
4385 links. (If the existing file is a symbolic link, it is removed, not
4386 followed.) However, if a directory cannot be removed because it is
4387 nonempty, @command{tar} normally overwrites its metadata (ownership,
4388 permission, etc.). The @option{--overwrite-dir} option enables this
4389 default behavior. To be more cautious and preserve the metadata of
4390 such a directory, use the @option{--no-overwrite-dir} option.
4392 @cindex Overwriting old files, prevention
4393 @xopindex{keep-old-files, introduced}
4394 To be even more cautious and prevent existing files from being replaced, use
4395 the @option{--keep-old-files} (@option{-k}) option. It causes @command{tar} to refuse
4396 to replace or update a file that already exists, i.e., a file with the
4397 same name as an archive member prevents extraction of that archive
4398 member. Instead, it reports an error.
4400 @xopindex{overwrite, introduced}
4401 To be more aggressive about altering existing files, use the
4402 @option{--overwrite} option. It causes @command{tar} to overwrite
4403 existing files and to follow existing symbolic links when extracting.
4405 @cindex Protecting old files
4406 Some people argue that @GNUTAR{} should not hesitate
4407 to overwrite files with other files when extracting. When extracting
4408 a @command{tar} archive, they expect to see a faithful copy of the
4409 state of the file system when the archive was created. It is debatable
4410 that this would always be a proper behavior. For example, suppose one
4411 has an archive in which @file{usr/local} is a link to
4412 @file{usr/local2}. Since then, maybe the site removed the link and
4413 renamed the whole hierarchy from @file{/usr/local2} to
4414 @file{/usr/local}. Such things happen all the time. I guess it would
4415 not be welcome at all that @GNUTAR{} removes the
4416 whole hierarchy just to make room for the link to be reinstated
4417 (unless it @emph{also} simultaneously restores the full
4418 @file{/usr/local2}, of course!) @GNUTAR{} is indeed
4419 able to remove a whole hierarchy to reestablish a symbolic link, for
4420 example, but @emph{only if} @option{--recursive-unlink} is specified
4421 to allow this behavior. In any case, single files are silently
4424 @xopindex{unlink-first, introduced}
4425 Finally, the @option{--unlink-first} (@option{-U}) option can improve performance in
4426 some cases by causing @command{tar} to remove files unconditionally
4427 before extracting them.
4429 @node Overwrite Old Files
4430 @unnumberedsubsubsec Overwrite Old Files
4435 Overwrite existing files and directory metadata when extracting files
4438 This causes @command{tar} to write extracted files into the file system without
4439 regard to the files already on the system; i.e., files with the same
4440 names as archive members are overwritten when the archive is extracted.
4441 It also causes @command{tar} to extract the ownership, permissions,
4442 and time stamps onto any preexisting files or directories.
4443 If the name of a corresponding file name is a symbolic link, the file
4444 pointed to by the symbolic link will be overwritten instead of the
4445 symbolic link itself (if this is possible). Moreover, special devices,
4446 empty directories and even symbolic links are automatically removed if
4447 they are in the way of extraction.
4449 Be careful when using the @option{--overwrite} option, particularly when
4450 combined with the @option{--absolute-names} (@option{-P}) option, as this combination
4451 can change the contents, ownership or permissions of any file on your
4452 system. Also, many systems do not take kindly to overwriting files that
4453 are currently being executed.
4455 @opindex overwrite-dir
4456 @item --overwrite-dir
4457 Overwrite the metadata of directories when extracting files from an
4458 archive, but remove other files before extracting.
4461 @node Keep Old Files
4462 @unnumberedsubsubsec Keep Old Files
4465 @opindex keep-old-files
4466 @item --keep-old-files
4468 Do not replace existing files from archive. The
4469 @option{--keep-old-files} (@option{-k}) option prevents @command{tar}
4470 from replacing existing files with files with the same name from the
4471 archive. The @option{--keep-old-files} option is meaningless with
4472 @option{--list} (@option{-t}). Prevents @command{tar} from replacing
4473 files in the file system during extraction.
4476 @node Keep Newer Files
4477 @unnumberedsubsubsec Keep Newer Files
4480 @opindex keep-newer-files
4481 @item --keep-newer-files
4482 Do not replace existing files that are newer than their archive
4483 copies. This option is meaningless with @option{--list} (@option{-t}).
4487 @unnumberedsubsubsec Unlink First
4490 @opindex unlink-first
4491 @item --unlink-first
4493 Remove files before extracting over them.
4494 This can make @command{tar} run a bit faster if you know in advance
4495 that the extracted files all need to be removed. Normally this option
4496 slows @command{tar} down slightly, so it is disabled by default.
4499 @node Recursive Unlink
4500 @unnumberedsubsubsec Recursive Unlink
4503 @opindex recursive-unlink
4504 @item --recursive-unlink
4505 When this option is specified, try removing files and directory hierarchies
4506 before extracting over them. @emph{This is a dangerous option!}
4509 If you specify the @option{--recursive-unlink} option,
4510 @command{tar} removes @emph{anything} that keeps you from extracting a file
4511 as far as current permissions will allow it. This could include removal
4512 of the contents of a full directory hierarchy.
4514 @node Data Modification Times
4515 @unnumberedsubsubsec Setting Data Modification Times
4517 @cindex Data modification times of extracted files
4518 @cindex Modification times of extracted files
4519 Normally, @command{tar} sets the data modification times of extracted
4520 files to the corresponding times recorded for the files in the archive, but
4521 limits the permissions of extracted files by the current @code{umask}
4524 To set the data modification times of extracted files to the time when
4525 the files were extracted, use the @option{--touch} (@option{-m}) option in
4526 conjunction with @option{--extract} (@option{--get}, @option{-x}).
4532 Sets the data modification time of extracted archive members to the time
4533 they were extracted, not the time recorded for them in the archive.
4534 Use in conjunction with @option{--extract} (@option{--get}, @option{-x}).
4537 @node Setting Access Permissions
4538 @unnumberedsubsubsec Setting Access Permissions
4540 @cindex Permissions of extracted files
4541 @cindex Modes of extracted files
4542 To set the modes (access permissions) of extracted files to those
4543 recorded for those files in the archive, use @option{--same-permissions}
4544 in conjunction with the @option{--extract} (@option{--get},
4545 @option{-x}) operation.
4548 @opindex preserve-permissions
4549 @opindex same-permissions
4550 @item --preserve-permissions
4551 @itemx --same-permissions
4552 @c @itemx --ignore-umask
4554 Set modes of extracted archive members to those recorded in the
4555 archive, instead of current umask settings. Use in conjunction with
4556 @option{--extract} (@option{--get}, @option{-x}).
4559 @node Directory Modification Times and Permissions
4560 @unnumberedsubsubsec Directory Modification Times and Permissions
4562 After sucessfully extracting a file member, @GNUTAR{} normally
4563 restores its permissions and modification times, as described in the
4564 previous sections. This cannot be done for directories, because
4565 after extracting a directory @command{tar} will almost certainly
4566 extract files into that directory and this will cause the directory
4567 modification time to be updated. Moreover, restoring that directory
4568 permissions may not permit file creation within it. Thus, restoring
4569 directory permissions and modification times must be delayed at least
4570 until all files have been extracted into that directory. @GNUTAR{}
4571 restores directories using the following approach.
4573 The extracted directories are created with the mode specified in the
4574 archive, as modified by the umask of the user, which gives sufficient
4575 permissions to allow file creation. The meta-information about the
4576 directory is recorded in the temporary list of directories. When
4577 preparing to extract next archive member, @GNUTAR{} checks if the
4578 directory prefix of this file contains the remembered directory. If
4579 it does not, the program assumes that all files have been extracted
4580 into that directory, restores its modification time and permissions
4581 and removes its entry from the internal list. This approach allows
4582 to correctly restore directory meta-information in the majority of
4583 cases, while keeping memory requirements sufficiently small. It is
4584 based on the fact, that most @command{tar} archives use the predefined
4585 order of members: first the directory, then all the files and
4586 subdirectories in that directory.
4588 However, this is not always true. The most important exception are
4589 incremental archives (@pxref{Incremental Dumps}). The member order in
4590 an incremental archive is reversed: first all directory members are
4591 stored, followed by other (non-directory) members. So, when extracting
4592 from incremental archives, @GNUTAR{} alters the above procedure. It
4593 remebers all restored directories, and restores their meta-data
4594 only after the entire archive has been processed. Notice, that you do
4595 not need to specity any special options for that, as @GNUTAR{}
4596 automatically detects archives in incremental format.
4598 There may be cases, when such processing is required for normal archives
4599 too. Consider the following example:
4603 $ @kbd{tar --no-recursion -cvf archive \
4604 foo foo/file1 bar bar/file foo/file2}
4613 During the normal operation, after encountering @file{bar}
4614 @GNUTAR{} will assume that all files from the directory @file{foo}
4615 were already extracted and will therefore restore its timestamp and
4616 permission bits. However, after extracting @file{foo/file2} the
4617 directory timestamp will be offset again.
4619 To correctly restore directory meta-information in such cases, use
4620 @option{delay-directory-restore} command line option:
4623 @opindex delay-directory-restore
4624 @item --delay-directory-restore
4625 Delays restoring of the modification times and permissions of extracted
4626 directories until the end of extraction. This way, correct
4627 meta-information is restored even if the archive has unusual member
4630 @opindex no-delay-directory-restore
4631 @item --no-delay-directory-restore
4632 Cancel the effect of the previous @option{--delay-directory-restore}.
4633 Use this option if you have used @option{--delay-directory-restore} in
4634 @env{TAR_OPTIONS} variable (@pxref{TAR_OPTIONS}) and wish to
4635 temporarily disable it.
4638 @node Writing to Standard Output
4639 @unnumberedsubsubsec Writing to Standard Output
4641 @cindex Writing extracted files to standard output
4642 @cindex Standard output, writing extracted files to
4643 To write the extracted files to the standard output, instead of
4644 creating the files on the file system, use @option{--to-stdout} (@option{-O}) in
4645 conjunction with @option{--extract} (@option{--get}, @option{-x}). This option is useful if you are
4646 extracting files to send them through a pipe, and do not need to
4647 preserve them in the file system. If you extract multiple members,
4648 they appear on standard output concatenated, in the order they are
4649 found in the archive.
4655 Writes files to the standard output. Use only in conjunction with
4656 @option{--extract} (@option{--get}, @option{-x}). When this option is
4657 used, instead of creating the files specified, @command{tar} writes
4658 the contents of the files extracted to its standard output. This may
4659 be useful if you are only extracting the files in order to send them
4660 through a pipe. This option is meaningless with @option{--list}
4664 This can be useful, for example, if you have a tar archive containing
4665 a big file and don't want to store the file on disk before processing
4666 it. You can use a command like this:
4669 tar -xOzf foo.tgz bigfile | process
4672 or even like this if you want to process the concatenation of the files:
4675 tar -xOzf foo.tgz bigfile1 bigfile2 | process
4678 Hovewer, @option{--to-command} may be more convenient for use with
4679 multiple files. See the next section.
4681 @node Writing to an External Program
4682 @unnumberedsubsubsec Writing to an External Program
4684 You can instruct @command{tar} to send the contents of each extracted
4685 file to the standard input of an external program:
4689 @item --to-command=@var{command}
4690 Extract files and pipe their contents to the standard input of
4691 @var{command}. When this option is used, instead of creating the
4692 files specified, @command{tar} invokes @var{command} and pipes the
4693 contents of the files to its standard output. @var{Command} may
4694 contain command line arguments. The program is executed via
4695 @code{sh -c}. Notice, that @var{command} is executed once for each regular file
4696 extracted. Non-regular files (directories, etc.) are ignored when this
4700 The command can obtain the information about the file it processes
4701 from the following environment variables:
4704 @vrindex TAR_FILETYPE, to-command environment
4706 Type of the file. It is a single letter with the following meaning:
4708 @multitable @columnfractions 0.10 0.90
4709 @item f @tab Regular file
4710 @item d @tab Directory
4711 @item l @tab Symbolic link
4712 @item h @tab Hard link
4713 @item b @tab Block device
4714 @item c @tab Character device
4717 Currently only regular files are supported.
4719 @vrindex TAR_MODE, to-command environment
4721 File mode, an octal number.
4723 @vrindex TAR_FILENAME, to-command environment
4725 The name of the file.
4727 @vrindex TAR_REALNAME, to-command environment
4729 Name of the file as stored in the archive.
4731 @vrindex TAR_UNAME, to-command environment
4733 Name of the file owner.
4735 @vrindex TAR_GNAME, to-command environment
4737 Name of the file owner group.
4739 @vrindex TAR_ATIME, to-command environment
4741 Time of last access. It is a decimal number, representing seconds
4742 since the epoch. If the archive provides times with nanosecond
4743 precision, the nanoseconds are appended to the timestamp after a
4746 @vrindex TAR_MTIME, to-command environment
4748 Time of last modification.
4750 @vrindex TAR_CTIME, to-command environment
4752 Time of last status change.
4754 @vrindex TAR_SIZE, to-command environment
4758 @vrindex TAR_UID, to-command environment
4760 UID of the file owner.
4762 @vrindex TAR_GID, to-command environment
4764 GID of the file owner.
4767 In addition to these variables, @env{TAR_VERSION} contains the
4768 @GNUTAR{} version number.
4770 If @var{command} exits with a non-0 status, @command{tar} will print
4771 an error message similar to the following:
4774 tar: 2345: Child returned status 1
4777 Here, @samp{2345} is the PID of the finished process.
4779 If this behavior is not wanted, use @option{--ignore-command-error}:
4782 @opindex ignore-command-error
4783 @item --ignore-command-error
4784 Ignore exit codes of subprocesses. Notice that if the program
4785 exits on signal or otherwise terminates abnormally, the error message
4786 will be printed even if this option is used.
4788 @opindex no-ignore-command-error
4789 @item --no-ignore-command-error
4790 Cancel the effect of any previous @option{--ignore-command-error}
4791 option. This option is useful if you have set
4792 @option{--ignore-command-error} in @env{TAR_OPTIONS}
4793 (@pxref{TAR_OPTIONS}) and wish to temporarily cancel it.
4797 @unnumberedsubsubsec Removing Files
4799 @FIXME{The section is too terse. Something more to add? An example,
4803 @opindex remove-files
4804 @item --remove-files
4805 Remove files after adding them to the archive.
4809 @subsection Coping with Scarce Resources
4812 @cindex Small memory
4813 @cindex Running out of space
4821 @unnumberedsubsubsec Starting File
4824 @opindex starting-file
4825 @item --starting-file=@var{name}
4826 @itemx -K @var{name}
4827 Starts an operation in the middle of an archive. Use in conjunction
4828 with @option{--extract} (@option{--get}, @option{-x}) or @option{--list} (@option{-t}).
4831 @cindex Middle of the archive, starting in the
4832 If a previous attempt to extract files failed due to lack of disk
4833 space, you can use @option{--starting-file=@var{name}} (@option{-K
4834 @var{name}}) to start extracting only after member @var{name} of the
4835 archive. This assumes, of course, that there is now free space, or
4836 that you are now extracting into a different file system. (You could
4837 also choose to suspend @command{tar}, remove unnecessary files from
4838 the file system, and then restart the same @command{tar} operation.
4839 In this case, @option{--starting-file} is not necessary.
4840 @xref{Incremental Dumps}, @xref{interactive}, and @ref{exclude}.)
4843 @unnumberedsubsubsec Same Order
4846 @cindex Large lists of file names on small machines
4848 @opindex preserve-order
4850 @itemx --preserve-order
4852 To process large lists of file names on machines with small amounts of
4853 memory. Use in conjunction with @option{--compare} (@option{--diff},
4854 @option{-d}), @option{--list} (@option{-t}) or @option{--extract}
4855 (@option{--get}, @option{-x}).
4858 The @option{--same-order} (@option{--preserve-order}, @option{-s}) option tells @command{tar} that the list of file
4859 names to be listed or extracted is sorted in the same order as the
4860 files in the archive. This allows a large list of names to be used,
4861 even on a small machine that would not otherwise be able to hold all
4862 the names in memory at the same time. Such a sorted list can easily be
4863 created by running @samp{tar -t} on the archive and editing its output.
4865 This option is probably never needed on modern computer systems.
4868 @section Backup options
4870 @cindex backup options
4872 @GNUTAR{} offers options for making backups of files
4873 before writing new versions. These options control the details of
4874 these backups. They may apply to the archive itself before it is
4875 created or rewritten, as well as individual extracted members. Other
4876 @acronym{GNU} programs (@command{cp}, @command{install}, @command{ln},
4877 and @command{mv}, for example) offer similar options.
4879 Backup options may prove unexpectedly useful when extracting archives
4880 containing many members having identical name, or when extracting archives
4881 on systems having file name limitations, making different members appear
4882 has having similar names through the side-effect of name truncation.
4883 (This is true only if we have a good scheme for truncated backup names,
4884 which I'm not sure at all: I suspect work is needed in this area.)
4885 When any existing file is backed up before being overwritten by extraction,
4886 then clashing files are automatically be renamed to be unique, and the
4887 true name is kept for only the last file of a series of clashing files.
4888 By using verbose mode, users may track exactly what happens.
4890 At the detail level, some decisions are still experimental, and may
4891 change in the future, we are waiting comments from our users. So, please
4892 do not learn to depend blindly on the details of the backup features.
4893 For example, currently, directories themselves are never renamed through
4894 using these options, so, extracting a file over a directory still has
4895 good chances to fail. Also, backup options apply to created archives,
4896 not only to extracted members. For created archives, backups will not
4897 be attempted when the archive is a block or character device, or when it
4898 refers to a remote file.
4900 For the sake of simplicity and efficiency, backups are made by renaming old
4901 files prior to creation or extraction, and not by copying. The original
4902 name is restored if the file creation fails. If a failure occurs after a
4903 partial extraction of a file, both the backup and the partially extracted
4907 @item --backup[=@var{method}]
4909 @vindex VERSION_CONTROL
4911 Back up files that are about to be overwritten or removed.
4912 Without this option, the original versions are destroyed.
4914 Use @var{method} to determine the type of backups made.
4915 If @var{method} is not specified, use the value of the @env{VERSION_CONTROL}
4916 environment variable. And if @env{VERSION_CONTROL} is not set,
4917 use the @samp{existing} method.
4919 @vindex version-control @r{Emacs variable}
4920 This option corresponds to the Emacs variable @samp{version-control};
4921 the same values for @var{method} are accepted as in Emacs. This option
4922 also allows more descriptive names. The valid @var{method}s are:
4927 @cindex numbered @r{backup method}
4928 Always make numbered backups.
4932 @cindex existing @r{backup method}
4933 Make numbered backups of files that already have them, simple backups
4938 @cindex simple @r{backup method}
4939 Always make simple backups.
4943 @item --suffix=@var{suffix}
4945 @cindex backup suffix
4946 @vindex SIMPLE_BACKUP_SUFFIX
4947 Append @var{suffix} to each backup file made with @option{--backup}. If this
4948 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
4949 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
4950 set, the default is @samp{~}, just as in Emacs.
4955 @section Notable @command{tar} Usages
4958 @FIXME{Using Unix file linking capability to recreate directory
4959 structures---linking files into one subdirectory and then
4960 @command{tar}ring that directory.}
4962 @FIXME{Nice hairy example using absolute-names, newer, etc.}
4965 You can easily use archive files to transport a group of files from
4966 one system to another: put all relevant files into an archive on one
4967 computer system, transfer the archive to another system, and extract
4968 the contents there. The basic transfer medium might be magnetic tape,
4969 Internet FTP, or even electronic mail (though you must encode the
4970 archive with @command{uuencode} in order to transport it properly by
4971 mail). Both machines do not have to use the same operating system, as
4972 long as they both support the @command{tar} program.
4974 For example, here is how you might copy a directory's contents from
4975 one disk to another, while preserving the dates, modes, owners and
4976 link-structure of all the files therein. In this case, the transfer
4977 medium is a @dfn{pipe}, which is one a Unix redirection mechanism:
4980 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
4984 You can avoid subshells by using @option{-C} option:
4987 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xf -}
4991 The command also works using short option forms:
4994 $ @kbd{(cd sourcedir; tar --create --file=- . ) \
4995 | (cd targetdir; tar --extract --file=-)}
4997 $ @kbd{tar --directory sourcedir --create --file=- . ) \
4998 | tar --directory targetdir --extract --file=-}
5002 This is one of the easiest methods to transfer a @command{tar} archive.
5005 @section Looking Ahead: The Rest of this Manual
5007 You have now seen how to use all eight of the operations available to
5008 @command{tar}, and a number of the possible options. The next chapter
5009 explains how to choose and change file and archive names, how to use
5010 files to store names of other files which you can then call as
5011 arguments to @command{tar} (this can help you save time if you expect to
5012 archive the same list of files a number of times), and so forth.
5013 @FIXME{in case it's not obvious, i'm making this up in some sense
5014 based on my limited memory of what the next chapter *really* does. i
5015 just wanted to flesh out this final section a little bit so i'd
5016 remember to stick it in here. :-)}
5018 If there are too many files to conveniently list on the command line,
5019 you can list the names in a file, and @command{tar} will read that file.
5022 There are various ways of causing @command{tar} to skip over some files,
5023 and not archive them. @xref{Choosing}.
5026 @chapter Performing Backups and Restoring Files
5029 @GNUTAR{} is distributed along with the scripts
5030 which the Free Software Foundation uses for performing backups. There
5031 is no corresponding scripts available yet for doing restoration of
5032 files. Even if there is a good chance those scripts may be satisfying
5033 to you, they are not the only scripts or methods available for doing
5034 backups and restore. You may well create your own, or use more
5035 sophisticated packages dedicated to that purpose.
5037 Some users are enthusiastic about @code{Amanda} (The Advanced Maryland
5038 Automatic Network Disk Archiver), a backup system developed by James
5039 da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
5040 This is free software, and it is available at these places:
5043 http://www.cs.umd.edu/projects/amanda/amanda.html
5044 ftp://ftp.cs.umd.edu/pub/amanda
5049 Here is a possible plan for a future documentation about the backuping
5050 scripts which are provided within the @GNUTAR{}
5056 @item what are dumps
5057 @item different levels of dumps
5059 @item full dump = dump everything
5060 @item level 1, level 2 dumps etc
5061 A level @var{n} dump dumps everything changed since the last level
5064 @item how to use scripts for dumps (ie, the concept)
5066 @item scripts to run after editing backup specs (details)
5068 @item Backup Specs, what is it.
5070 @item how to customize
5071 @item actual text of script [/sp/dump/backup-specs]
5075 @item rsh doesn't work
5076 @item rtape isn't installed
5079 @item the @option{--incremental} option of tar
5082 @item write protection
5083 @item types of media, different sizes and types, useful for different things
5084 @item files and tape marks
5085 one tape mark between files, two at end.
5086 @item positioning the tape
5087 MT writes two at end of write,
5088 backspaces over one when writing again.
5094 This chapter documents both the provided shell scripts and @command{tar}
5095 options which are more specific to usage as a backup tool.
5097 To @dfn{back up} a file system means to create archives that contain
5098 all the files in that file system. Those archives can then be used to
5099 restore any or all of those files (for instance if a disk crashes or a
5100 file is accidentally deleted). File system @dfn{backups} are also
5104 * Full Dumps:: Using @command{tar} to Perform Full Dumps
5105 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
5106 * Backup Levels:: Levels of Backups
5107 * Backup Parameters:: Setting Parameters for Backups and Restoration
5108 * Scripted Backups:: Using the Backup Scripts
5109 * Scripted Restoration:: Using the Restore Script
5113 @section Using @command{tar} to Perform Full Dumps
5119 @cindex corrupted archives
5120 Full dumps should only be made when no other people or programs
5121 are modifying files in the file system. If files are modified while
5122 @command{tar} is making the backup, they may not be stored properly in
5123 the archive, in which case you won't be able to restore them if you
5124 have to. (Files not being modified are written with no trouble, and do
5125 not corrupt the entire archive.)
5127 You will want to use the @option{--label=@var{archive-label}}
5128 (@option{-V @var{archive-label}}) option to give the archive a
5129 volume label, so you can tell what this archive is even if the label
5130 falls off the tape, or anything like that.
5132 Unless the file system you are dumping is guaranteed to fit on
5133 one volume, you will need to use the @option{--multi-volume} (@option{-M}) option.
5134 Make sure you have enough tapes on hand to complete the backup.
5136 If you want to dump each file system separately you will need to use
5137 the @option{--one-file-system} option to prevent
5138 @command{tar} from crossing file system boundaries when storing
5141 The @option{--incremental} (@option{-G}) (@pxref{Incremental Dumps})
5142 option is not needed, since this is a complete copy of everything in
5143 the file system, and a full restore from this backup would only be
5144 done onto a completely
5147 Unless you are in a hurry, and trust the @command{tar} program (and your
5148 tapes), it is a good idea to use the @option{--verify} (@option{-W})
5149 option, to make sure your files really made it onto the dump properly.
5150 This will also detect cases where the file was modified while (or just
5151 after) it was being archived. Not all media (notably cartridge tapes)
5152 are capable of being verified, unfortunately.
5154 @node Incremental Dumps
5155 @section Using @command{tar} to Perform Incremental Dumps
5157 @dfn{Incremental backup} is a special form of @GNUTAR{} archive that
5158 stores additional metadata so that exact state of the file system
5159 can be restored when extracting the archive.
5161 @GNUTAR{} currently offers two options for handling incremental
5162 backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
5163 @var{snapshot-file}}) and @option{--incremental} (@option{-G}).
5165 @opindex listed-incremental
5166 The option @option{--listed-incremental} instructs tar to operate on
5167 an incremental archive with additional metadata stored in a standalone
5168 file, called a @dfn{snapshot file}. The purpose of this file is to help
5169 determine which files have been changed, added or deleted since the
5170 last backup, so that the next incremental backup will contain only
5171 modified files. The name of the snapshot file is given as an argument
5175 @item --listed-incremental=@var{file}
5176 @itemx -g @var{file}
5177 Handle incremental backups with snapshot data in @var{file}.
5180 To create an incremental backup, you would use
5181 @option{--listed-incremental} together with @option{--create}
5182 (@pxref{create}). For example:
5185 $ @kbd{tar --create \
5186 --file=archive.1.tar \
5187 --listed-incremental=/var/log/usr.snar \
5191 This will create in @file{archive.1.tar} an incremental backup of
5192 the @file{/usr} file system, storing additional metadata in the file
5193 @file{/var/log/usr.snar}. If this file does not exist, it will be
5194 created. The created archive will then be a @dfn{level 0 backup};
5195 please see the next section for more on backup levels.
5197 Otherwise, if the file @file{/var/log/usr.snar} exists, it
5198 determines which files are modified. In this case only these files will be
5199 stored in the archive. Suppose, for example, that after running the
5200 above command, you delete file @file{/usr/doc/old} and create
5201 directory @file{/usr/local/db} with the following contents:
5204 $ @kbd{ls /usr/local/db}
5209 Some time later you create another incremental backup. You will
5213 $ @kbd{tar --create \
5214 --file=archive.2.tar \
5215 --listed-incremental=/var/log/usr.snar \
5217 tar: usr/local/db: Directory is new
5224 The created archive @file{archive.2.tar} will contain only these
5225 three members. This archive is called a @dfn{level 1 backup}. Notice
5226 that @file{/var/log/usr.snar} will be updated with the new data, so if
5227 you plan to create more @samp{level 1} backups, it is necessary to
5228 create a working copy of the snapshot file before running
5229 @command{tar}. The above example will then be modified as follows:
5232 $ @kbd{cp /var/log/usr.snar /var/log/usr.snar-1}
5233 $ @kbd{tar --create \
5234 --file=archive.2.tar \
5235 --listed-incremental=/var/log/usr.snar-1 \
5239 Incremental dumps depend crucially on time stamps, so the results are
5240 unreliable if you modify a file's time stamps during dumping (e.g.,
5241 with the @option{--atime-preserve=replace} option), or if you set the clock
5244 Metadata stored in snapshot files include device numbers, which,
5245 obviously is supposed to be a non-volatile value. However, it turns
5246 out that NFS devices have undependable values when an automounter
5247 gets in the picture. This can lead to a great deal of spurious
5248 redumping in incremental dumps, so it is somewhat useless to compare
5249 two NFS devices numbers over time. The solution implemented currently
5250 is to considers all NFS devices as being equal when it comes to
5251 comparing directories; this is fairly gross, but there does not seem
5252 to be a better way to go.
5254 Note that incremental archives use @command{tar} extensions and may
5255 not be readable by non-@acronym{GNU} versions of the @command{tar} program.
5257 @xopindex{listed-incremental, using with @option{--extract}}
5258 @xopindex{extract, using with @option{--listed-incremental}}
5259 To extract from the incremental dumps, use
5260 @option{--listed-incremental} together with @option{--extract}
5261 option (@pxref{extracting files}). In this case, @command{tar} does
5262 not need to access snapshot file, since all the data necessary for
5263 extraction are stored in the archive itself. So, when extracting, you
5264 can give whatever argument to @option{--listed-incremental}, the usual
5265 practice is to use @option{--listed-incremental=/dev/null}.
5266 Alternatively, you can use @option{--incremental}, which needs no
5267 arguments. In general, @option{--incremental} (@option{-G}) can be
5268 used as a shortcut for @option{--listed-incremental} when listing or
5269 extracting incremental backups (for more information, regarding this
5270 option, @pxref{incremental-op}).
5272 When extracting from the incremental backup @GNUTAR{} attempts to
5273 restore the exact state the file system had when the archive was
5274 created. In particular, it will @emph{delete} those files in the file
5275 system that did not exist in their directories when the archive was
5276 created. If you have created several levels of incremental files,
5277 then in order to restore the exact contents the file system had when
5278 the last level was created, you will need to restore from all backups
5279 in turn. Continuing our example, to restore the state of @file{/usr}
5280 file system, one would do@footnote{Notice, that since both archives
5281 were created withouth @option{-P} option (@pxref{absolute}), these
5282 commands should be run from the root file system.}:
5285 $ @kbd{tar --extract \
5286 --listed-incremental=/dev/null \
5287 --file archive.1.tar}
5288 $ @kbd{tar --extract \
5289 --listed-incremental=/dev/null \
5290 --file archive.2.tar}
5293 To list the contents of an incremental archive, use @option{--list}
5294 (@pxref{list}), as usual. To obtain more information about the
5295 archive, use @option{--listed-incremental} or @option{--incremental}
5296 combined with two @option{--verbose} options@footnote{Two
5297 @option{--verbose} options were selected to avoid breaking usual
5298 verbose listing output (@option{--list --verbose}) when using in
5301 @xopindex{incremental, using with @option{--list}}
5302 @xopindex{listed-incremental, using with @option{--list}}
5303 @xopindex{list, using with @option{--incremental}}
5304 @xopindex{list, using with @option{--listed-incremental}}
5305 Versions of @GNUTAR{} up to 1.15.1 used to dump verbatim binary
5306 contents of the DUMPDIR header (with terminating nulls) when
5307 @option{--incremental} or @option{--listed-incremental} option was
5308 given, no matter what the verbosity level. This behavior, and,
5309 especially, the binary output it produced were considered incovenient
5310 and were changed in version 1.16}:
5313 @kbd{tar --list --incremental --verbose --verbose archive.tar}
5316 This command will print, for each directory in the archive, the list
5317 of files in that directory at the time the archive was created. This
5318 information is put out in a format which is both human-readable and
5319 unambiguous for a program: each file name is printed as
5326 where @var{x} is a letter describing the status of the file: @samp{Y}
5327 if the file is present in the archive, @samp{N} if the file is not
5328 included in the archive, or a @samp{D} if the file is a directory (and
5329 is included in the archive). @xref{Dumpdir}, for the detailed
5330 description of dumpdirs and status codes. Each such
5331 line is terminated by a newline character. The last line is followed
5332 by an additional newline to indicate the end of the data.
5334 @anchor{incremental-op}The option @option{--incremental} (@option{-G})
5335 gives the same behavior as @option{--listed-incremental} when used
5336 with @option{--list} and @option{--extract} options. When used with
5337 @option{--create} option, it creates an incremental archive without
5338 creating snapshot file. Thus, it is impossible to create several
5339 levels of incremental backups with @option{--incremental} option.
5342 @section Levels of Backups
5344 An archive containing all the files in the file system is called a
5345 @dfn{full backup} or @dfn{full dump}. You could insure your data by
5346 creating a full dump every day. This strategy, however, would waste a
5347 substantial amount of archive media and user time, as unchanged files
5348 are daily re-archived.
5350 It is more efficient to do a full dump only occasionally. To back up
5351 files between full dumps, you can use @dfn{incremental dumps}. A @dfn{level
5352 one} dump archives all the files that have changed since the last full
5355 A typical dump strategy would be to perform a full dump once a week,
5356 and a level one dump once a day. This means some versions of files
5357 will in fact be archived more than once, but this dump strategy makes
5358 it possible to restore a file system to within one day of accuracy by
5359 only extracting two archives---the last weekly (full) dump and the
5360 last daily (level one) dump. The only information lost would be in
5361 files changed or created since the last daily backup. (Doing dumps
5362 more than once a day is usually not worth the trouble).
5364 @GNUTAR{} comes with scripts you can use to do full
5365 and level-one (actually, even level-two and so on) dumps. Using
5366 scripts (shell programs) to perform backups and restoration is a
5367 convenient and reliable alternative to typing out file name lists
5368 and @command{tar} commands by hand.
5370 Before you use these scripts, you need to edit the file
5371 @file{backup-specs}, which specifies parameters used by the backup
5372 scripts and by the restore script. This file is usually located
5373 in @file{/etc/backup} directory. @xref{Backup Parameters}, for its
5374 detailed description. Once the backup parameters are set, you can
5375 perform backups or restoration by running the appropriate script.
5377 The name of the backup script is @code{backup}. The name of the
5378 restore script is @code{restore}. The following sections describe
5379 their use in detail.
5381 @emph{Please Note:} The backup and restoration scripts are
5382 designed to be used together. While it is possible to restore files by
5383 hand from an archive which was created using a backup script, and to create
5384 an archive by hand which could then be extracted using the restore script,
5385 it is easier to use the scripts. @xref{Incremental Dumps}, before
5386 making such an attempt.
5388 @node Backup Parameters
5389 @section Setting Parameters for Backups and Restoration
5391 The file @file{backup-specs} specifies backup parameters for the
5392 backup and restoration scripts provided with @command{tar}. You must
5393 edit @file{backup-specs} to fit your system configuration and schedule
5394 before using these scripts.
5396 Syntactically, @file{backup-specs} is a shell script, containing
5397 mainly variable assignments. However, any valid shell construct
5398 is allowed in this file. Particularly, you may wish to define
5399 functions within that script (e.g., see @code{RESTORE_BEGIN} below).
5400 For more information about shell script syntax, please refer to
5401 @url{http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
5402 g_02, the definition of the Shell Command Language}. See also
5403 @ref{Top,,Bash Features,bashref,Bash Reference Manual}.
5405 The shell variables controlling behavior of @code{backup} and
5406 @code{restore} are described in the following subsections.
5409 * General-Purpose Variables::
5410 * Magnetic Tape Control::
5412 * backup-specs example:: An Example Text of @file{Backup-specs}
5415 @node General-Purpose Variables
5416 @subsection General-Purpose Variables
5418 @defvr {Backup variable} ADMINISTRATOR
5419 The user name of the backup administrator. @code{Backup} scripts
5420 sends a backup report to this address.
5423 @defvr {Backup variable} BACKUP_HOUR
5424 The hour at which the backups are done. This can be a number from 0
5425 to 23, or the time specification in form @var{hours}:@var{minutes},
5426 or the string @samp{now}.
5428 This variable is used by @code{backup}. Its value may be overridden
5429 using @option{--time} option (@pxref{Scripted Backups}).
5432 @defvr {Backup variable} TAPE_FILE
5434 The device @command{tar} writes the archive to. If @var{TAPE_FILE}
5435 is a remote archive (@pxref{remote-dev}), backup script will suppose
5436 that your @command{mt} is able to access remote devices. If @var{RSH}
5437 (@pxref{RSH}) is set, @option{--rsh-command} option will be added to
5438 invocations of @command{mt}.
5441 @defvr {Backup variable} BLOCKING
5443 The blocking factor @command{tar} will use when writing the dump archive.
5444 @xref{Blocking Factor}.
5447 @defvr {Backup variable} BACKUP_DIRS
5449 A list of file systems to be dumped (for @code{backup}), or restored
5450 (for @code{restore}). You can include any directory
5451 name in the list --- subdirectories on that file system will be
5452 included, regardless of how they may look to other networked machines.
5453 Subdirectories on other file systems will be ignored.
5455 The host name specifies which host to run @command{tar} on, and should
5456 normally be the host that actually contains the file system. However,
5457 the host machine must have @GNUTAR{} installed, and
5458 must be able to access the directory containing the backup scripts and
5459 their support files using the same file name that is used on the
5460 machine where the scripts are run (i.e. what @command{pwd} will print
5461 when in that directory on that machine). If the host that contains
5462 the file system does not have this capability, you can specify another
5463 host as long as it can access the file system through NFS.
5465 If the list of file systems is very long you may wish to put it
5466 in a separate file. This file is usually named
5467 @file{/etc/backup/dirs}, but this name may be overridden in
5468 @file{backup-specs} using @code{DIRLIST} variable.
5471 @defvr {Backup variable} DIRLIST
5473 A path to the file containing the list of the file systems to backup
5474 or restore. By default it is @file{/etc/backup/dirs}.
5477 @defvr {Backup variable} BACKUP_FILES
5479 A list of individual files to be dumped (for @code{backup}), or restored
5480 (for @code{restore}). These should be accessible from the machine on
5481 which the backup script is run.
5483 If the list of file systems is very long you may wish to store it
5484 in a separate file. This file is usually named
5485 @file{/etc/backup/files}, but this name may be overridden in
5486 @file{backup-specs} using @code{FILELIST} variable.
5489 @defvr {Backup variable} FILELIST
5491 A path to the file containing the list of the individual files to backup
5492 or restore. By default it is @file{/etc/backup/files}.
5495 @defvr {Backup variable} MT
5497 Full file name of @command{mt} binary.
5500 @defvr {Backup variable} RSH
5502 Full file name of @command{rsh} binary or its equivalent. You may wish to
5503 set it to @code{ssh}, to improve security. In this case you will have
5504 to use public key authentication.
5507 @defvr {Backup variable} RSH_COMMAND
5509 Full file name of @command{rsh} binary on remote mashines. This will
5510 be passed via @option{--rsh-command} option to the remote invocation
5514 @defvr {Backup variable} VOLNO_FILE
5516 Name of temporary file to hold volume numbers. This needs to be accessible
5517 by all the machines which have file systems to be dumped.
5520 @defvr {Backup variable} XLIST
5522 Name of @dfn{exclude file list}. An @dfn{exclude file list} is a file
5523 located on the remote machine and containing the list of files to
5524 be excluded from the backup. Exclude file lists are searched in
5525 /etc/tar-backup directory. A common use for exclude file lists
5526 is to exclude files containing security-sensitive information
5527 (e.g., @file{/etc/shadow} from backups).
5529 This variable affects only @code{backup}.
5532 @defvr {Backup variable} SLEEP_TIME
5534 Time to sleep between dumps of any two successive file systems
5536 This variable affects only @code{backup}.
5539 @defvr {Backup variable} DUMP_REMIND_SCRIPT
5541 Script to be run when it's time to insert a new tape in for the next
5542 volume. Administrators may want to tailor this script for their site.
5543 If this variable isn't set, @GNUTAR{} will display its built-in
5544 prompt, and will expect confirmation from the console.
5546 The built-in prompt for POSIX locale is:
5549 Prepare volume #@var{n} for `@var{archive}' and hit return:
5553 where @var{n} is the ordinal number of the volume to be created and
5554 @var{archive} is archive file or device name.
5556 If you run @GNUTAR{} under a different locale, the translation of
5557 the above prompt to the locale's language will be used.
5561 @defvr {Backup variable} SLEEP_MESSAGE
5563 Message to display on the terminal while waiting for dump time. Usually
5564 this will just be some literal text.
5567 @defvr {Backup variable} TAR
5569 Full file name of the @GNUTAR{} executable. If this is not set, backup
5570 scripts will search @command{tar} in the current shell path.
5573 @node Magnetic Tape Control
5574 @subsection Magnetic Tape Control
5576 Backup scripts access tape device using special @dfn{hook functions}.
5577 These functions take a single argument -- the name of the tape
5578 device. Their names are kept in the following variables:
5580 @defvr {Backup variable} MT_BEGIN
5581 The name of @dfn{begin} function. This function is called before
5582 accessing the drive. By default it retensions the tape:
5588 mt -f "$1" retension
5593 @defvr {Backup variable} MT_REWIND
5594 The name of @dfn{rewind} function. The default definition is as
5607 @defvr {Backup variable} MT_OFFLINE
5608 The name of the function switching the tape off line. By default
5609 it is defined as follows:
5612 MT_OFFLINE=mt_offline
5620 @defvr {Backup variable} MT_STATUS
5621 The name of the function used to obtain the status of the archive device,
5622 including error count. Default definition:
5634 @subsection User Hooks
5636 @dfn{User hooks} are shell functions executed before and after
5637 each @command{tar} invocation. Thus, there are @dfn{backup
5638 hooks}, which are executed before and after dumping each file
5639 system, and @dfn{restore hooks}, executed before and
5640 after restoring a file system. Each user hook is a shell function
5641 taking four arguments:
5643 @deffn {User Hook Function} hook @var{level} @var{host} @var{fs} @var{fsname}
5648 Current backup or restore level.
5651 Name or IP address of the host machine being dumped or restored.
5654 Full path name to the file system being dumped or restored.
5657 File system name with directory separators replaced with colons. This
5658 is useful, e.g., for creating unique files.
5662 Following variables keep the names of user hook functions
5664 @defvr {Backup variable} DUMP_BEGIN
5665 Dump begin function. It is executed before dumping the file system.
5668 @defvr {Backup variable} DUMP_END
5669 Executed after dumping the file system.
5672 @defvr {Backup variable} RESTORE_BEGIN
5673 Executed before restoring the file system.
5676 @defvr {Backup variable} RESTORE_END
5677 Executed after restoring the file system.
5680 @node backup-specs example
5681 @subsection An Example Text of @file{Backup-specs}
5683 The following is an example of @file{backup-specs}:
5686 # site-specific parameters for file system backup.
5688 ADMINISTRATOR=friedman
5690 TAPE_FILE=/dev/nrsmt0
5692 # Use @code{ssh} instead of the less secure @code{rsh}
5694 RSH_COMMAND=/usr/bin/ssh
5696 # Override MT_STATUS function:
5702 # Disable MT_OFFLINE function
5719 apple-gunkies:/com/mailer/gnu
5720 apple-gunkies:/com/archive/gnu"
5722 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
5726 @node Scripted Backups
5727 @section Using the Backup Scripts
5729 The syntax for running a backup script is:
5732 backup --level=@var{level} --time=@var{time}
5735 The @option{level} option requests the dump level. Thus, to produce
5736 a full dump, specify @code{--level=0} (this is the default, so
5737 @option{--level} may be omitted if its value is @code{0}).
5738 @footnote{For backward compatibility, the @code{backup} will also
5739 try to deduce the requested dump level from the name of the
5740 script itself. If the name consists of a string @samp{level-}
5741 followed by a single decimal digit, that digit is taken as
5742 the dump level number. Thus, you may create a link from @code{backup}
5743 to @code{level-1} and then run @code{level-1} whenever you need to
5744 create a level one dump.}
5746 The @option{--time} option determines when should the backup be
5747 run. @var{Time} may take three forms:
5750 @item @var{hh}:@var{mm}
5752 The dump must be run at @var{hh} hours @var{mm} minutes.
5756 The dump must be run at @var{hh} hours
5760 The dump must be run immediately.
5763 You should start a script with a tape or disk mounted. Once you
5764 start a script, it prompts you for new tapes or disks as it
5765 needs them. Media volumes don't have to correspond to archive
5766 files --- a multi-volume archive can be started in the middle of a
5767 tape that already contains the end of another multi-volume archive.
5768 The @code{restore} script prompts for media by its archive volume,
5769 so to avoid an error message you should keep track of which tape
5770 (or disk) contains which volume of the archive (@pxref{Scripted
5773 The backup scripts write two files on the file system. The first is a
5774 record file in @file{/etc/tar-backup/}, which is used by the scripts
5775 to store and retrieve information about which files were dumped. This
5776 file is not meant to be read by humans, and should not be deleted by
5777 them. @xref{Snapshot Files}, for a more detailed explanation of this
5780 The second file is a log file containing the names of the file systems
5781 and files dumped, what time the backup was made, and any error
5782 messages that were generated, as well as how much space was left in
5783 the media volume after the last volume of the archive was written.
5784 You should check this log file after every backup. The file name is
5785 @file{log-@var{mm-dd-yyyy}-level-@var{n}}, where @var{mm-dd-yyyy}
5786 represents current date, and @var{n} represents current dump level number.
5788 The script also prints the name of each system being dumped to the
5791 Following is the full list of options accepted by @code{backup}
5795 @item -l @var{level}
5796 @itemx --level=@var{level}
5797 Do backup level @var{level} (default 0).
5801 Force backup even if today's log file already exists.
5803 @item -v[@var{level}]
5804 @itemx --verbose[=@var{level}]
5805 Set verbosity level. The higher the level is, the more debugging
5806 information will be output during execution. Devault @var{level}
5807 is 100, which means the highest debugging level.
5809 @item -t @var{start-time}
5810 @itemx --time=@var{start-time}
5811 Wait till @var{time}, then do backup.
5815 Display short help message and exit.
5819 Display information about the program's name, version, origin and legal
5820 status, all on standard output, and then exit successfully.
5824 @node Scripted Restoration
5825 @section Using the Restore Script
5827 To restore files that were archived using a scripted backup, use the
5828 @code{restore} script. Its usage is quite straightforward. In the
5829 simplest form, invoke @code{restore --all}, it will
5830 then restore all the file systems and files specified in
5831 @file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
5833 You may select the file systems (and/or files) to restore by
5834 giving @code{restore} list of @dfn{patterns} in its command
5835 line. For example, running
5842 will restore all file systems on the machine @samp{albert}. A more
5843 complicated example:
5846 restore 'albert:*' '*:/var'
5850 This command will restore all file systems on the machine @samp{albert}
5851 as well as @file{/var} file system on all machines.
5853 By default @code{restore} will start restoring files from the lowest
5854 available dump level (usually zero) and will continue through
5855 all available dump levels. There may be situations where such a
5856 thorough restore is not necessary. For example, you may wish to
5857 restore only files from the recent level one backup. To do so,
5858 use @option{--level} option, as shown in the example below:
5864 The full list of options accepted by @code{restore} follows:
5869 Restore all file systems and files specified in @file{backup-specs}
5871 @item -l @var{level}
5872 @itemx --level=@var{level}
5873 Start restoring from the given backup level, instead of the default 0.
5875 @item -v[@var{level}]
5876 @itemx --verbose[=@var{level}]
5877 Set verbosity level. The higher the level is, the more debugging
5878 information will be output during execution. Devault @var{level}
5879 is 100, which means the highest debugging level.
5883 Display short help message and exit.
5887 Display information about the program's name, version, origin and legal
5888 status, all on standard output, and then exit successfully.
5891 You should start the restore script with the media containing the
5892 first volume of the archive mounted. The script will prompt for other
5893 volumes as they are needed. If the archive is on tape, you don't need
5894 to rewind the tape to to its beginning---if the tape head is
5895 positioned past the beginning of the archive, the script will rewind
5896 the tape as needed. @xref{Tape Positioning}, for a discussion of tape
5900 @strong{Warning:} The script will delete files from the active file
5901 system if they were not in the file system when the archive was made.
5904 @xref{Incremental Dumps}, for an explanation of how the script makes
5908 @chapter Choosing Files and Names for @command{tar}
5911 Certain options to @command{tar} enable you to specify a name for your
5912 archive. Other options let you decide which files to include or exclude
5913 from the archive, based on when or whether files were modified, whether
5914 the file names do or don't match specified patterns, or whether files
5915 are in specified directories.
5917 This chapter discusses these options in detail.
5920 * file:: Choosing the Archive's Name
5921 * Selecting Archive Members::
5922 * files:: Reading Names from a File
5923 * exclude:: Excluding Some Files
5924 * wildcards:: Wildcards Patterns and Matching
5925 * quoting styles:: Ways of Quoting Special Characters in Names
5926 * transform:: Modifying File and Member Names
5927 * after:: Operating Only on New Files
5928 * recurse:: Descending into Directories
5929 * one:: Crossing File System Boundaries
5933 @section Choosing and Naming Archive Files
5936 @cindex Naming an archive
5937 @cindex Archive Name
5938 @cindex Choosing an archive file
5939 @cindex Where is the archive?
5940 By default, @command{tar} uses an archive file name that was compiled when
5941 it was built on the system; usually this name refers to some physical
5942 tape drive on the machine. However, the person who installed @command{tar}
5943 on the system may not have set the default to a meaningful value as far as
5944 most users are concerned. As a result, you will usually want to tell
5945 @command{tar} where to find (or create) the archive. The
5946 @option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
5947 option allows you to either specify or name a file to use as the archive
5948 instead of the default archive file location.
5951 @xopindex{file, short description}
5952 @item --file=@var{archive-name}
5953 @itemx -f @var{archive-name}
5954 Name the archive to create or operate on. Use in conjunction with
5958 For example, in this @command{tar} command,
5961 $ @kbd{tar -cvf collection.tar blues folk jazz}
5965 @file{collection.tar} is the name of the archive. It must directly
5966 follow the @option{-f} option, since whatever directly follows @option{-f}
5967 @emph{will} end up naming the archive. If you neglect to specify an
5968 archive name, you may end up overwriting a file in the working directory
5969 with the archive you create since @command{tar} will use this file's name
5970 for the archive name.
5972 An archive can be saved as a file in the file system, sent through a
5973 pipe or over a network, or written to an I/O device such as a tape,
5974 floppy disk, or CD write drive.
5976 @cindex Writing new archives
5977 @cindex Archive creation
5978 If you do not name the archive, @command{tar} uses the value of the
5979 environment variable @env{TAPE} as the file name for the archive. If
5980 that is not available, @command{tar} uses a default, compiled-in archive
5981 name, usually that for tape unit zero (i.e. @file{/dev/tu00}).
5983 @cindex Standard input and output
5984 @cindex tar to standard input and output
5985 If you use @file{-} as an @var{archive-name}, @command{tar} reads the
5986 archive from standard input (when listing or extracting files), or
5987 writes it to standard output (when creating an archive). If you use
5988 @file{-} as an @var{archive-name} when modifying an archive,
5989 @command{tar} reads the original archive from its standard input and
5990 writes the entire new archive to its standard output.
5992 The following example is a convenient way of copying directory
5993 hierarchy from @file{sourcedir} to @file{targetdir}.
5996 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)}
5999 The @option{-C} option allows to avoid using subshells:
6002 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xpf -}
6005 In both examples above, the leftmost @command{tar} invocation archives
6006 the contents of @file{sourcedir} to the standard output, while the
6007 rightmost one reads this archive from its standard input and
6008 extracts it. The @option{-p} option tells it to restore permissions
6009 of the extracted files.
6011 @cindex Remote devices
6012 @cindex tar to a remote device
6014 To specify an archive file on a device attached to a remote machine,
6018 @kbd{--file=@var{hostname}:/@var{dev}/@var{file-name}}
6022 @command{tar} will complete the remote connection, if possible, and
6023 prompt you for a username and password. If you use
6024 @option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
6025 will complete the remote connection, if possible, using your username
6026 as the username on the remote machine.
6028 @cindex Local and remote archives
6029 @anchor{local and remote archives}
6030 If the archive file name includes a colon (@samp{:}), then it is assumed
6031 to be a file on another machine. If the archive file is
6032 @samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the
6033 host @var{host}. The remote host is accessed using the @command{rsh}
6034 program, with a username of @var{user}. If the username is omitted
6035 (along with the @samp{@@} sign), then your user name will be used.
6036 (This is the normal @command{rsh} behavior.) It is necessary for the
6037 remote machine, in addition to permitting your @command{rsh} access, to
6038 have the @file{rmt} program installed (This command is included in
6039 the @GNUTAR{} distribution and by default is installed under
6040 @file{@var{prefix}/libexec/rmt}, were @var{prefix} means your
6041 installation prefix). If you need to use a file whose name includes a
6042 colon, then the remote tape drive behavior
6043 can be inhibited by using the @option{--force-local} option.
6045 When the archive is being created to @file{/dev/null}, @GNUTAR{}
6046 tries to minimize input and output operations. The Amanda backup
6047 system, when used with @GNUTAR{}, has an initial sizing pass which
6050 @node Selecting Archive Members
6051 @section Selecting Archive Members
6052 @cindex Specifying files to act on
6053 @cindex Specifying archive members
6055 @dfn{File Name arguments} specify which files in the file system
6056 @command{tar} operates on, when creating or adding to an archive, or which
6057 archive members @command{tar} operates on, when reading or deleting from
6058 an archive. @xref{Operations}.
6060 To specify file names, you can include them as the last arguments on
6061 the command line, as follows:
6063 @kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
6066 If a file name begins with dash (@samp{-}), precede it with
6067 @option{--add-file} option to prevent it from being treated as an
6070 @anchor{input name quoting}
6071 By default @GNUTAR{} attempts to @dfn{unquote} each file or member
6072 name, replacing @dfn{escape sequences} according to the following
6075 @multitable @columnfractions 0.20 0.60
6076 @headitem Escape @tab Replaced with
6077 @item \a @tab Audible bell (ASCII 7)
6078 @item \b @tab Backspace (ASCII 8)
6079 @item \f @tab Form feed (ASCII 12)
6080 @item \n @tab New line (ASCII 10)
6081 @item \r @tab Carriage return (ASCII 13)
6082 @item \t @tab Horizontal tabulation (ASCII 9)
6083 @item \v @tab Vertical tabulation (ASCII 11)
6084 @item \? @tab ASCII 127
6085 @item \@var{n} @tab ASCII @var{n} (@var{n} should be an octal number
6089 A backslash followed by any other symbol is retained.
6091 This default behavior is controlled by the following command line
6097 Enable unquoting input file or member names (default).
6101 Disable unquoting input file or member names.
6104 If you specify a directory name as a file name argument, all the files
6105 in that directory are operated on by @command{tar}.
6107 If you do not specify files, @command{tar} behavior differs depending
6108 on the operation mode as described below:
6110 When @command{tar} is invoked with @option{--create} (@option{-c}),
6111 @command{tar} will stop immediately, reporting the following:
6115 $ @kbd{tar cf a.tar}
6116 tar: Cowardly refusing to create an empty archive
6117 Try `tar --help' or `tar --usage' for more information.
6121 If you specify either @option{--list} (@option{-t}) or
6122 @option{--extract} (@option{--get}, @option{-x}), @command{tar}
6123 operates on all the archive members in the archive.
6125 If run with @option{--diff} option, tar will compare the archive with
6126 the contents of the current working directory.
6128 If you specify any other operation, @command{tar} does nothing.
6130 By default, @command{tar} takes file names from the command line. However,
6131 there are other ways to specify file or member names, or to modify the
6132 manner in which @command{tar} selects the files or members upon which to
6133 operate. In general, these methods work both for specifying the names
6134 of files and archive members.
6137 @section Reading Names from a File
6139 @cindex Reading file names from a file
6140 @cindex Lists of file names
6141 @cindex File Name arguments, alternatives
6142 Instead of giving the names of files or archive members on the command
6143 line, you can put the names into a file, and then use the
6144 @option{--files-from=@var{file-of-names}} (@option{-T
6145 @var{file-of-names}}) option to @command{tar}. Give the name of the
6146 file which contains the list of files to include as the argument to
6147 @option{--files-from}. In the list, the file names should be separated by
6148 newlines. You will frequently use this option when you have generated
6149 the list of files to archive with the @command{find} utility.
6153 @item --files-from=@var{file-name}
6154 @itemx -T @var{file-name}
6155 Get names to extract or create from file @var{file-name}.
6158 If you give a single dash as a file name for @option{--files-from}, (i.e.,
6159 you specify either @code{--files-from=-} or @code{-T -}), then the file
6160 names are read from standard input.
6162 Unless you are running @command{tar} with @option{--create}, you can not use
6163 both @code{--files-from=-} and @code{--file=-} (@code{-f -}) in the same
6166 Any number of @option{-T} options can be given in the command line.
6168 The following example shows how to use @command{find} to generate a list of
6169 files smaller than 400K in length and put that list into a file
6170 called @file{small-files}. You can then use the @option{-T} option to
6171 @command{tar} to specify the files from that file, @file{small-files}, to
6172 create the archive @file{little.tgz}. (The @option{-z} option to
6173 @command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for
6177 $ @kbd{find . -size -400 -print > small-files}
6178 $ @kbd{tar -c -v -z -T small-files -f little.tgz}
6182 In the file list given by @option{-T} option, any file name beginning
6183 with @samp{-} character is considered a @command{tar} option and is
6184 processed accordingly.@footnote{Versions of @GNUTAR{} up to 1.15.1
6185 recognized only @option{-C} option in file lists, and only if the
6186 option and its argument occupied two consecutive lines.} For example,
6187 the common use of this feature is to change to another directory by
6188 specifying @option{-C} option:
6198 $ @kbd{tar -c -f foo.tar --files-from list}
6203 In this example, @command{tar} will first switch to @file{/etc}
6204 directory and add files @file{passwd} and @file{hosts} to the
6205 archive. Then it will change to @file{/lib} directory and will archive
6206 the file @file{libc.a}. Thus, the resulting archive @file{foo.tar} will
6211 $ @kbd{tar tf foo.tar}
6219 @xopindex{directory, using in @option{--files-from} argument}
6220 Notice that the option parsing algorithm used with @option{-T} is
6221 stricter than the one used by shell. Namely, when specifying option
6222 arguments, you should observe the following rules:
6226 When using short (single-letter) option form, its argument must
6227 immediately follow the option letter, without any intervening
6228 whitespace. For example: @code{-Cdir}.
6231 When using long option form, the option argument must be separated
6232 from the option by a single equal sign. No whitespace is allowed on
6233 any side of the equal sign. For example: @code{--directory=dir}.
6236 For both short and long option forms, the option argument can be given
6237 on the next line after the option name, e.g.:
6258 If you happen to have a file whose name starts with @samp{-},
6259 precede it with @option{--add-file} option to prevent it from
6260 being recognized as an option. For example: @code{--add-file=--my-file}.
6267 @subsection @code{NUL} Terminated File Names
6269 @cindex File names, terminated by @code{NUL}
6270 @cindex @code{NUL} terminated file names
6271 The @option{--null} option causes
6272 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
6273 to read file names terminated by a @code{NUL} instead of a newline, so
6274 files whose names contain newlines can be archived using
6275 @option{--files-from}.
6280 Only consider @code{NUL} terminated file names, instead of files that
6281 terminate in a newline.
6284 The @option{--null} option is just like the one in @acronym{GNU}
6285 @command{xargs} and @command{cpio}, and is useful with the
6286 @option{-print0} predicate of @acronym{GNU} @command{find}. In
6287 @command{tar}, @option{--null} also disables special handling for
6288 file names that begin with dash.
6290 This example shows how to use @command{find} to generate a list of files
6291 larger than 800K in length and put that list into a file called
6292 @file{long-files}. The @option{-print0} option to @command{find} is just
6293 like @option{-print}, except that it separates files with a @code{NUL}
6294 rather than with a newline. You can then run @command{tar} with both the
6295 @option{--null} and @option{-T} options to specify that @command{tar} get the
6296 files from that file, @file{long-files}, to create the archive
6297 @file{big.tgz}. The @option{--null} option to @command{tar} will cause
6298 @command{tar} to recognize the @code{NUL} separator between files.
6301 $ @kbd{find . -size +800 -print0 > long-files}
6302 $ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
6305 @FIXME{say anything else here to conclude the section?}
6308 @section Excluding Some Files
6311 @cindex File names, excluding files by
6312 @cindex Excluding files by name and pattern
6313 @cindex Excluding files by file system
6314 To avoid operating on files whose names match a particular pattern,
6315 use the @option{--exclude} or @option{--exclude-from} options.
6319 @item --exclude=@var{pattern}
6320 Causes @command{tar} to ignore files that match the @var{pattern}.
6324 The @option{--exclude=@var{pattern}} option prevents any file or
6325 member whose name matches the shell wildcard (@var{pattern}) from
6327 For example, to create an archive with all the contents of the directory
6328 @file{src} except for files whose names end in @file{.o}, use the
6329 command @samp{tar -cf src.tar --exclude='*.o' src}.
6331 You may give multiple @option{--exclude} options.
6334 @opindex exclude-from
6335 @item --exclude-from=@var{file}
6336 @itemx -X @var{file}
6337 Causes @command{tar} to ignore files that match the patterns listed in
6341 @findex exclude-from
6342 Use the @option{--exclude-from} option to read a
6343 list of patterns, one per line, from @var{file}; @command{tar} will
6344 ignore files matching those patterns. Thus if @command{tar} is
6345 called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a
6346 single line @file{*.o}, no files whose names end in @file{.o} will be
6347 added to the archive.
6350 @opindex exclude-caches
6351 @item --exclude-caches
6352 Causes @command{tar} to ignore directories containing a cache directory tag.
6355 @findex exclude-caches
6356 When creating an archive, the @option{--exclude-caches} option causes
6357 @command{tar} to exclude all directories that contain a @dfn{cache
6358 directory tag}. A cache directory tag is a short file with the
6359 well-known name @file{CACHEDIR.TAG} and having a standard header
6360 specified in @url{http://www.brynosaurus.com/cachedir/spec.html}.
6361 Various applications write cache directory tags into directories they
6362 use to hold regenerable, non-precious data, so that such data can be
6363 more easily excluded from backups.
6366 * problems with exclude::
6369 @node problems with exclude
6370 @unnumberedsubsec Problems with Using the @code{exclude} Options
6372 @xopindex{exclude, potential problems with}
6373 Some users find @samp{exclude} options confusing. Here are some common
6378 The main operating mode of @command{tar} does not act on a path name
6379 explicitly listed on the command line if one of its file name
6380 components is excluded. In the example above, if
6381 you create an archive and exclude files that end with @samp{*.o}, but
6382 explicitly name the file @samp{dir.o/foo} after all the options have been
6383 listed, @samp{dir.o/foo} will be excluded from the archive.
6386 You can sometimes confuse the meanings of @option{--exclude} and
6387 @option{--exclude-from}. Be careful: use @option{--exclude} when files
6388 to be excluded are given as a pattern on the command line. Use
6389 @option{--exclude-from} to introduce the name of a file which contains
6390 a list of patterns, one per line; each of these patterns can exclude
6391 zero, one, or many files.
6394 When you use @option{--exclude=@var{pattern}}, be sure to quote the
6395 @var{pattern} parameter, so @GNUTAR{} sees wildcard characters
6396 like @samp{*}. If you do not do this, the shell might expand the
6397 @samp{*} itself using files at hand, so @command{tar} might receive a
6398 list of files instead of one pattern, or none at all, making the
6399 command somewhat illegal. This might not correspond to what you want.
6404 $ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}}
6412 $ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
6416 You must use use shell syntax, or globbing, rather than @code{regexp}
6417 syntax, when using exclude options in @command{tar}. If you try to use
6418 @code{regexp} syntax to describe files to be excluded, your command
6422 @FIXME{The change in semantics must have occurred before 1.11,
6423 so I doubt if it is worth mentioning at all. Anyway, should at
6424 least specify in which version the semantics changed.}
6425 In earlier versions of @command{tar}, what is now the
6426 @option{--exclude-from} option was called @option{--exclude} instead.
6427 Now, @option{--exclude} applies to patterns listed on the command
6428 line and @option{--exclude-from} applies to patterns listed in a
6434 @section Wildcards Patterns and Matching
6436 @dfn{Globbing} is the operation by which @dfn{wildcard} characters,
6437 @samp{*} or @samp{?} for example, are replaced and expanded into all
6438 existing files matching the given pattern. @GNUTAR{} can use wildcard
6439 patterns for matching (or globbing) archive members when extracting
6440 from or listing an archive. Wildcard patterns are also used for
6441 verifying volume labels of @command{tar} archives. This section has the
6442 purpose of explaining wildcard syntax for @command{tar}.
6444 @FIXME{the next few paragraphs need work.}
6446 A @var{pattern} should be written according to shell syntax, using wildcard
6447 characters to effect globbing. Most characters in the pattern stand
6448 for themselves in the matched string, and case is significant: @samp{a}
6449 will match only @samp{a}, and not @samp{A}. The character @samp{?} in the
6450 pattern matches any single character in the matched string. The character
6451 @samp{*} in the pattern matches zero, one, or more single characters in
6452 the matched string. The character @samp{\} says to take the following
6453 character of the pattern @emph{literally}; it is useful when one needs to
6454 match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves.
6456 The character @samp{[}, up to the matching @samp{]}, introduces a character
6457 class. A @dfn{character class} is a list of acceptable characters
6458 for the next single character of the matched string. For example,
6459 @samp{[abcde]} would match any of the first five letters of the alphabet.
6460 Note that within a character class, all of the ``special characters''
6461 listed above other than @samp{\} lose their special meaning; for example,
6462 @samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\},
6463 @samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints,
6464 the characters @samp{-} and @samp{]} must either come @emph{first} or
6465 @emph{last} in a character class.)
6467 @cindex Excluding characters from a character class
6468 @cindex Character class, excluding characters from
6469 If the first character of the class after the opening @samp{[}
6470 is @samp{!} or @samp{^}, then the meaning of the class is reversed.
6471 Rather than listing character to match, it lists those characters which
6472 are @emph{forbidden} as the next single character of the matched string.
6474 Other characters of the class stand for themselves. The special
6475 construction @samp{[@var{a}-@var{e}]}, using an hyphen between two
6476 letters, is meant to represent all characters between @var{a} and
6479 @FIXME{need to add a sentence or so here to make this clear for those
6480 who don't have dan around.}
6482 Periods (@samp{.}) or forward slashes (@samp{/}) are not considered
6483 special for wildcard matches. However, if a pattern completely matches
6484 a directory prefix of a matched string, then it matches the full matched
6485 string: thus, excluding a directory also excludes all the files beneath it.
6488 * controlling pattern-matching::
6491 @node controlling pattern-matching
6492 @unnumberedsubsec Controlling Pattern-Matching
6494 For the purposes of this section, we call @dfn{exclusion members} all
6495 member names obtained while processing @option{--exclude} and
6496 @option{--exclude-from} options, and @dfn{inclusion members} those
6497 member names that were given in the command line or read from the file
6498 specified with @option{--files-from} option.
6500 These two pairs of member lists are used in the following operations:
6501 @option{--diff}, @option{--extract}, @option{--list},
6504 There are no inclusion members in create mode (@option{--create} and
6505 @option{--append}), since in this mode the names obtained from the
6506 command line refer to @emph{files}, not archive members.
6508 By default, inclusion members are compared with archive members
6509 literally @footnote{Notice that earlier @GNUTAR{} versions used
6510 globbing for inclusion members, which contradicted to UNIX98
6511 specification and was not documented. @xref{Changes}, for more
6512 information on this and other changes.} and exclusion members are
6513 treated as globbing patterns. For example:
6517 $ @kbd{tar tf foo.tar}
6522 # @i{Member names are used verbatim:}
6523 $ @kbd{tar -xf foo.tar -v '[remarks]'}
6525 # @i{Exclude member names are globbed:}
6526 $ @kbd{tar -xf foo.tar -v --exclude '*.c'}
6532 This behavior can be altered by using the following options:
6537 Treat all member names as wildcards.
6539 @opindex no-wildcards
6540 @item --no-wildcards
6541 Treat all member names as literal strings.
6544 Thus, to extract files whose names end in @samp{.c}, you can use:
6547 $ @kbd{tar -xf foo.tar -v --wildcards '*.c'}
6553 Notice quoting of the pattern to prevent the shell from interpreting
6556 The effect of @option{--wildcards} option is cancelled by
6557 @option{--no-wildcards}. This can be used to pass part of
6558 the command line arguments verbatim and other part as globbing
6559 patterns. For example, the following invocation:
6562 $ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'}
6566 instructs @command{tar} to extract from @file{foo.tar} all files whose
6567 names end in @samp{.txt} and the file named @file{[remarks]}.
6569 Normally, a pattern matches a name if an initial subsequence of the
6570 name's components matches the pattern, where @samp{*}, @samp{?}, and
6571 @samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
6572 and wildcards can match @samp{/}.
6574 Other than optionally stripping leading @samp{/} from names
6575 (@pxref{absolute}), patterns and names are used as-is. For
6576 example, trailing @samp{/} is not trimmed from a user-specified name
6577 before deciding whether to exclude it.
6579 However, this matching procedure can be altered by the options listed
6580 below. These options accumulate. For example:
6583 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
6587 ignores case when excluding @samp{makefile}, but not when excluding
6592 @opindex no-anchored
6594 @itemx --no-anchored
6595 If anchored, a pattern must match an initial subsequence
6596 of the name's components. Otherwise, the pattern can match any
6597 subsequence. Default is @option{--no-anchored} for exclusion members
6598 and @option{--anchored} inclusion members.
6600 @opindex ignore-case
6601 @opindex no-ignore-case
6603 @itemx --no-ignore-case
6604 When ignoring case, upper-case patterns match lower-case names and vice versa.
6605 When not ignoring case (the default), matching is case-sensitive.
6607 @opindex wildcards-match-slash
6608 @opindex no-wildcards-match-slash
6609 @item --wildcards-match-slash
6610 @itemx --no-wildcards-match-slash
6611 When wildcards match slash (the default for exclusion members), a
6612 wildcard like @samp{*} in the pattern can match a @samp{/} in the
6613 name. Otherwise, @samp{/} is matched only by @samp{/}.
6617 The @option{--recursion} and @option{--no-recursion} options
6618 (@pxref{recurse}) also affect how member patterns are interpreted. If
6619 recursion is in effect, a pattern matches a name if it matches any of
6620 the name's parent directories.
6622 The following table summarizes pattern-matching default values:
6624 @multitable @columnfractions .3 .7
6625 @headitem Members @tab Default settings
6626 @item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash}
6627 @item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash}
6630 @node quoting styles
6631 @section Quoting Member Names
6633 When displaying member names, @command{tar} takes care to avoid
6634 ambiguities caused by certain characters. This is called @dfn{name
6635 quoting}. The characters in question are:
6638 @item Non-printable control characters:
6640 @multitable @columnfractions 0.20 0.10 0.60
6641 @headitem Character @tab ASCII @tab Character name
6642 @item \a @tab 7 @tab Audible bell
6643 @item \b @tab 8 @tab Backspace
6644 @item \f @tab 12 @tab Form feed
6645 @item \n @tab 10 @tab New line
6646 @item \r @tab 13 @tab Carriage return
6647 @item \t @tab 9 @tab Horizontal tabulation
6648 @item \v @tab 11 @tab Vertical tabulation
6651 @item Space (ASCII 32)
6653 @item Single and double quotes (@samp{'} and @samp{"})
6655 @item Backslash (@samp{\})
6658 The exact way @command{tar} uses to quote these characters depends on
6659 the @dfn{quoting style}. The default quoting style, called
6660 @dfn{escape} (see below), uses backslash notation to represent control
6661 characters, space and backslash. Using this quoting style, control
6662 characters are represented as listed in column @samp{Character} in the
6663 above table, a space is printed as @samp{\ } and a backslash as @samp{\\}.
6665 @GNUTAR{} offers seven distinct quoting styles, which can be selected
6666 using @option{--quoting-style} option:
6669 @item --quoting-style=@var{style}
6670 @opindex quoting-style
6672 Sets quoting style. Valid values for @var{style} argument are:
6673 literal, shell, shell-always, c, escape, locale, clocale.
6676 These styles are described in detail below. To illustrate their
6677 effect, we will use an imaginary tar archive @file{arch.tar}
6678 containing the following members:
6682 # 1. Contains horizontal tabulation character.
6684 # 2. Contains newline character
6687 # 3. Contains a space
6689 # 4. Contains double quotes
6691 # 5. Contains single quotes
6693 # 6. Contains a backslash character:
6698 Here is how usual @command{ls} command would have listed them, if they
6699 had existed in the current working directory:
6717 No quoting, display each character as is:
6721 $ @kbd{tar tf arch.tar --quoting-style=literal}
6734 Display characters the same way Bourne shell does:
6735 control characters, except @samp{\t} and @samp{\n}, are printed using
6736 backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a
6737 single quote is printed as @samp{\'}. If a name contains any quoted
6738 characters, it is enclosed in single quotes. In particular, if a name
6739 contains single quotes, it is printed as several single-quoted strings:
6743 $ @kbd{tar tf arch.tar --quoting-style=shell}
6746 './a'\''single'\''quote'
6756 Same as @samp{shell}, but the names are always enclosed in single
6761 $ @kbd{tar tf arch.tar --quoting-style=shell-always}
6764 './a'\''single'\''quote'
6774 Use the notation of the C programming language. All names are
6775 enclosed in double quotes. Control characters are quoted using
6776 backslash notations, double quotes are represented as @samp{\"},
6777 backslash characters are represented as @samp{\\}. Single quotes and
6778 spaces are not quoted:
6782 $ @kbd{tar tf arch.tar --quoting-style=c}
6786 "./a\"double\"quote"
6794 Control characters are printed using backslash notation, a space is
6795 printed as @samp{\ } and a backslash as @samp{\\}. This is the
6796 default quoting style, unless it was changed when configured the
6801 $ @kbd{tar tf arch.tar --quoting-style=escape}
6813 Control characters, single quote and backslash are printed using
6814 backslash notation. All names are quoted using left and right
6815 quotation marks, appropriate to the current locale. If it does not
6816 define quotation marks, use @samp{`} as left and @samp{'} as right
6817 quotation marks. Any occurrences of the right quotation mark in a
6818 name are escaped with @samp{\}, for example:
6824 $ @kbd{tar tf arch.tar --quoting-style=locale}
6827 `./a\'single\'quote'
6836 Same as @samp{locale}, but @samp{"} is used for both left and right
6837 quotation marks, if not provided by the currently selected locale:
6841 $ @kbd{tar tf arch.tar --quoting-style=clocale}
6845 "./a\"double\"quote"
6853 You can specify which characters should be quoted in addition to those
6854 implied by the current quoting style:
6857 @item --quote-chars=@var{string}
6858 Always quote characters from @var{string}, even if the selected
6859 quoting style would not quote them.
6862 For example, using @samp{escape} quoting (compare with the usual
6863 escape listing above):
6867 $ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'}
6878 To disable quoting of such additional characters, use the following
6882 @item --no-quote-chars=@var{string}
6883 Remove characters listed in @var{string} from the list of quoted
6884 characters set by the previous @option{--quote-chars} option.
6887 This option is particularly useful if you have added
6888 @option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS})
6889 and wish to disable it for the current invocation.
6891 Note, that @option{--no-quote-chars} does @emph{not} disable those
6892 characters that are quoted by default in the selected quoting style.
6895 @section Modifying File and Member Names
6897 @command{Tar} archives contain detailed information about files stored
6898 in them and full file names are part of that information. When
6899 storing file to an archive, its file name is recorded in the archive
6900 along with the actual file contents. When restoring from an archive,
6901 a file is created on disk with exactly the same name as that stored
6902 in the archive. In the majority of cases this is the desired behavior
6903 of a file archiver. However, there are some cases when it is not.
6905 First of all, it is often unsafe to extract archive members with
6906 absolute file names or those that begin with a @file{../}. @GNUTAR{}
6907 takes special precautions when extracting such names and provides a
6908 special option for handling them, which is described in
6911 Secondly, you may wish to extract file names without some leading
6912 directory components, or with otherwise modified names. In other
6913 cases it is desirable to store files under differing names in the
6916 @GNUTAR{} provides two options for these needs.
6919 @opindex strip-components
6920 @item --strip-components=@var{number}
6921 Strip given @var{number} of leading components from file names before
6925 For example, suppose you have archived whole @file{/usr} hierarchy to
6926 a tar archive named @file{usr.tar}. Among other files, this archive
6927 contains @file{usr/include/stdlib.h}, which you wish to extract to
6928 the current working directory. To do so, you type:
6931 $ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h}
6934 The option @option{--strip=2} instructs @command{tar} to strip the
6935 two leading components (@file{usr/} and @file{include/}) off the file
6938 If you add to the above invocation @option{--verbose} (@option{-v})
6939 option, you will note that the verbose listing still contains the
6940 full file name, with the two removed components still in place. This
6941 can be inconvenient, so @command{tar} provides a special option for
6942 altering this behavior:
6944 @anchor{show-transformed-names}
6946 @opindex show-transformed-names
6947 @item --show-transformed-names
6948 Display file or member names with all requested transformations
6957 $ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h}
6958 usr/include/stdlib.h
6959 $ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h}
6964 Notice that in both cases the file is @file{stdlib.h} extracted to the
6965 current working directory, @option{--show-transformed-names} affects
6966 only the way its name is displayed.
6968 This option is especially useful for verifying whether the invocation
6969 will have the desired effect. Thus, before running
6972 $ @kbd{tar -x --strip=@var{n}}
6976 it is often advisable to run
6979 $ @kbd{tar -t -v --show-transformed --strip=@var{n}}
6983 to make sure the command will produce the intended results.
6985 In case you need to apply more complex modifications to the file name,
6986 @GNUTAR{} provides a general-purpose transformation option:
6990 @item --transform=@var{expression}
6991 Modify file names using supplied @var{expression}.
6995 The @var{expression} is a @command{sed}-like replace expression of the
6999 s/@var{regexp}/@var{replace}/[@var{flags}]
7003 where @var{regexp} is a @dfn{regular expression}, @var{replace} is a
7004 replacement for each file name part that matches @var{regexp}. Both
7005 @var{regexp} and @var{replace} are described in detail in
7006 @ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
7008 Supported @var{flags} are:
7012 Apply the replacement to @emph{all} matches to the @var{regexp}, not
7016 Use case-insensitive matching
7019 @var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
7020 regexps, Extended regular expressions, Extended regular expressions,
7024 Only replace the @var{number}th match of the @var{regexp}.
7026 Note: the @var{posix} standard does not specify what should happen
7027 when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
7028 follows the GNU @command{sed} implementation in this regard, so
7029 the the interaction is defined to be: ignore matches before the
7030 @var{number}th, and then match and replace all matches from the
7035 Any delimiter can be used in lieue of @samp{/}, the only requirement being
7036 that it be used consistently throughout the expression. For example,
7037 the following two expressions are equivalent:
7046 Changing delimiters is often useful when the @var{regex} contains
7047 slashes. For example, it is more convenient to write @code{s,/,-,} than
7050 Here are several examples of @option{--transform} usage:
7053 @item Extract @file{usr/} hierarchy into @file{usr/local/}:
7056 $ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar}
7059 @item Strip two leading directory components (equivalent to
7060 @option{--strip-components=2}):
7063 $ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
7066 @item Prepend @file{/prefix/} to each file name:
7069 $ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
7072 @item Convert each file name to lower case:
7075 $ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
7080 Unlike @option{--strip-components}, @option{--transform} can be used
7081 in any @GNUTAR{} operation mode. For example, the following command
7082 adds files to the archive while replacing the leading @file{usr/}
7083 component with @file{var/}:
7086 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /}
7089 To test @option{--transform} effect we suggest using
7090 @option{--show-transformed-names} option:
7093 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \
7094 --verbose --show-transformed-names /}
7097 If both @option{--strip-components} and @option{--transform} are used
7098 together, then @option{--transform} is applied first, and the required
7099 number of components is then stripped from its result.
7102 @section Operating Only on New Files
7105 @cindex Excluding file by age
7106 @cindex Data Modification time, excluding files by
7107 @cindex Modification time, excluding files by
7108 @cindex Age, excluding files by
7109 The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
7110 @option{-N @var{date}}) option causes @command{tar} to only work on
7111 files whose data modification or status change times are newer than
7112 the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
7113 it is taken to be a file name; the data modification time of that file
7114 is used as the date. If you use this option when creating or appending
7115 to an archive, the archive will only include new files. If you use
7116 @option{--after-date} when extracting an archive, @command{tar} will
7117 only extract files newer than the @var{date} you specify.
7119 If you only want @command{tar} to make the date comparison based on
7120 modification of the file's data (rather than status
7121 changes), then use the @option{--newer-mtime=@var{date}} option.
7123 You may use these options with any operation. Note that these options
7124 differ from the @option{--update} (@option{-u}) operation in that they
7125 allow you to specify a particular date against which @command{tar} can
7126 compare when deciding whether or not to archive the files.
7131 @item --after-date=@var{date}
7132 @itemx --newer=@var{date}
7133 @itemx -N @var{date}
7134 Only store files newer than @var{date}.
7136 Acts on files only if their data modification or status change times are
7137 later than @var{date}. Use in conjunction with any operation.
7139 If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
7140 name; the data modification time of that file is used as the date.
7142 @opindex newer-mtime
7143 @item --newer-mtime=@var{date}
7144 Acts like @option{--after-date}, but only looks at data modification times.
7147 These options limit @command{tar} to operate only on files which have
7148 been modified after the date specified. A file's status is considered to have
7149 changed if its contents have been modified, or if its owner,
7150 permissions, and so forth, have been changed. (For more information on
7151 how to specify a date, see @ref{Date input formats}; remember that the
7152 entire date argument must be quoted if it contains any spaces.)
7154 Gurus would say that @option{--after-date} tests both the data
7155 modification time (@code{mtime}, the time the contents of the file
7156 were last modified) and the status change time (@code{ctime}, the time
7157 the file's status was last changed: owner, permissions, etc.@:)
7158 fields, while @option{--newer-mtime} tests only the @code{mtime}
7161 To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
7162 @code{ctime} and processes the file if either one is more recent than
7163 @var{date}, while @option{--newer-mtime} only checks @code{mtime} and
7164 disregards @code{ctime}. Neither does it use @code{atime} (the last time the
7165 contents of the file were looked at).
7167 Date specifiers can have embedded spaces. Because of this, you may need
7168 to quote date arguments to keep the shell from parsing them as separate
7169 arguments. For example, the following command will add to the archive
7170 all the files modified less than two days ago:
7173 $ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'}
7177 @strong{Please Note:} @option{--after-date} and @option{--newer-mtime}
7178 should not be used for incremental backups. @xref{Incremental Dumps},
7179 for proper way of creating incremental backups.
7183 @section Descending into Directories
7185 @cindex Avoiding recursion in directories
7186 @cindex Descending directories, avoiding
7187 @cindex Directories, avoiding recursion
7188 @cindex Recursion in directories, avoiding
7190 @FIXME{arrggh! this is still somewhat confusing to me. :-< }
7192 Usually, @command{tar} will recursively explore all directories (either
7193 those given on the command line or through the @option{--files-from}
7194 option) for the various files they contain. However, you may not always
7195 want @command{tar} to act this way.
7197 @opindex no-recursion
7198 The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
7199 into specified directories. If you specify @option{--no-recursion}, you can
7200 use the @command{find} utility for hunting through levels of directories to
7201 construct a list of file names which you could then pass to @command{tar}.
7202 @command{find} allows you to be more selective when choosing which files to
7203 archive; see @ref{files}, for more information on using @command{find} with
7204 @command{tar}, or look.
7207 @item --no-recursion
7208 Prevents @command{tar} from recursively descending directories.
7212 Requires @command{tar} to recursively descend directories.
7213 This is the default.
7216 When you use @option{--no-recursion}, @GNUTAR{} grabs
7217 directory entries themselves, but does not descend on them
7218 recursively. Many people use @command{find} for locating files they
7219 want to back up, and since @command{tar} @emph{usually} recursively
7220 descends on directories, they have to use the @samp{@w{-not -type d}}
7221 test in their @command{find} invocation (@pxref{Type, Type, Type test,
7222 find, Finding Files}), as they usually do not want all the files in a
7223 directory. They then use the @option{--files-from} option to archive
7224 the files located via @command{find}.
7226 The problem when restoring files archived in this manner is that the
7227 directories themselves are not in the archive; so the
7228 @option{--same-permissions} (@option{--preserve-permissions},
7229 @option{-p}) option does not affect them---while users might really
7230 like it to. Specifying @option{--no-recursion} is a way to tell
7231 @command{tar} to grab only the directory entries given to it, adding
7232 no new files on its own. To summarize, if you use @command{find} to
7233 create a list of files to be stored in an archive, use it as follows:
7237 $ @kbd{find @var{dir} @var{tests} | \
7238 tar -cf @var{archive} -T - --no-recursion}
7242 The @option{--no-recursion} option also applies when extracting: it
7243 causes @command{tar} to extract only the matched directory entries, not
7244 the files under those directories.
7246 The @option{--no-recursion} option also affects how globbing patterns
7247 are interpreted (@pxref{controlling pattern-matching}).
7249 The @option{--no-recursion} and @option{--recursion} options apply to
7250 later options and operands, and can be overridden by later occurrences
7251 of @option{--no-recursion} and @option{--recursion}. For example:
7254 $ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
7258 creates an archive with one entry for @file{grape}, and the recursive
7259 contents of @file{grape/concord}, but no entries under @file{grape}
7260 other than @file{grape/concord}.
7263 @section Crossing File System Boundaries
7264 @cindex File system boundaries, not crossing
7267 @command{tar} will normally automatically cross file system boundaries in
7268 order to archive files which are part of a directory tree. You can
7269 change this behavior by running @command{tar} and specifying
7270 @option{--one-file-system}. This option only affects files that are
7271 archived because they are in a directory that is being archived;
7272 @command{tar} will still archive files explicitly named on the command line
7273 or through @option{--files-from}, regardless of where they reside.
7276 @opindex one-file-system
7277 @item --one-file-system
7278 Prevents @command{tar} from crossing file system boundaries when
7279 archiving. Use in conjunction with any write operation.
7282 The @option{--one-file-system} option causes @command{tar} to modify its
7283 normal behavior in archiving the contents of directories. If a file in
7284 a directory is not on the same file system as the directory itself, then
7285 @command{tar} will not archive that file. If the file is a directory
7286 itself, @command{tar} will not archive anything beneath it; in other words,
7287 @command{tar} will not cross mount points.
7289 This option is useful for making full or incremental archival backups of
7290 a file system. If this option is used in conjunction with
7291 @option{--verbose} (@option{-v}), files that are excluded are
7292 mentioned by name on the standard error.
7295 * directory:: Changing Directory
7296 * absolute:: Absolute File Names
7300 @subsection Changing the Working Directory
7303 @FIXME{need to read over this node now for continuity; i've switched
7304 things around some.}
7306 @cindex Changing directory mid-stream
7307 @cindex Directory, changing mid-stream
7308 @cindex Working directory, specifying
7309 To change the working directory in the middle of a list of file names,
7310 either on the command line or in a file specified using
7311 @option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
7312 This will change the working directory to the specified directory
7313 after that point in the list.
7317 @item --directory=@var{directory}
7318 @itemx -C @var{directory}
7319 Changes the working directory in the middle of a command line.
7325 $ @kbd{tar -c -f jams.tar grape prune -C food cherry}
7329 will place the files @file{grape} and @file{prune} from the current
7330 directory into the archive @file{jams.tar}, followed by the file
7331 @file{cherry} from the directory @file{food}. This option is especially
7332 useful when you have several widely separated files that you want to
7333 store in the same archive.
7335 Note that the file @file{cherry} is recorded in the archive under the
7336 precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the
7337 archive will contain three files that all appear to have come from the
7338 same directory; if the archive is extracted with plain @samp{tar
7339 --extract}, all three files will be written in the current directory.
7341 Contrast this with the command,
7344 $ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
7348 which records the third file in the archive under the name
7349 @file{red/cherry} so that, if the archive is extracted using
7350 @samp{tar --extract}, the third file will be written in a subdirectory
7351 named @file{orange-colored}.
7353 You can use the @option{--directory} option to make the archive
7354 independent of the original name of the directory holding the files.
7355 The following command places the files @file{/etc/passwd},
7356 @file{/etc/hosts}, and @file{/lib/libc.a} into the archive
7360 $ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
7364 However, the names of the archive members will be exactly what they were
7365 on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}.
7366 They will not appear to be related by file name to the original
7367 directories where those files were located.
7369 Note that @option{--directory} options are interpreted consecutively. If
7370 @option{--directory} specifies a relative file name, it is interpreted
7371 relative to the then current directory, which might not be the same as
7372 the original current working directory of @command{tar}, due to a previous
7373 @option{--directory} option.
7375 When using @option{--files-from} (@pxref{files}), you can put various
7376 @command{tar} options (including @option{-C}) in the file list. Notice,
7377 however, that in this case the option and its argument may not be
7378 separated by whitespace. If you use short option, its argument must
7379 either follow the option letter immediately, without any intervening
7380 whitespace, or occupy the next line. Otherwise, if you use long
7381 option, separate its argument by an equal sign.
7383 For instance, the file list for the above example will be:
7398 To use it, you would invoke @command{tar} as follows:
7401 $ @kbd{tar -c -f foo.tar --files-from list}
7404 Notice also that you can only use the short option variant in the file
7405 list, i.e., always use @option{-C}, not @option{--directory}.
7407 The interpretation of @option{--directory} is disabled by
7408 @option{--null} option.
7411 @subsection Absolute File Names
7415 @opindex absolute-names
7416 @item --absolute-names
7418 Do not strip leading slashes from file names, and permit file names
7419 containing a @file{..} file name component.
7422 By default, @GNUTAR{} drops a leading @samp{/} on
7423 input or output, and complains about file names containing a @file{..}
7424 component. This option turns off this behavior.
7426 When @command{tar} extracts archive members from an archive, it strips any
7427 leading slashes (@samp{/}) from the member name. This causes absolute
7428 member names in the archive to be treated as relative file names. This
7429 allows you to have such members extracted wherever you want, instead of
7430 being restricted to extracting the member in the exact directory named
7431 in the archive. For example, if the archive member has the name
7432 @file{/etc/passwd}, @command{tar} will extract it as if the name were
7433 really @file{etc/passwd}.
7435 File names containing @file{..} can cause problems when extracting, so
7436 @command{tar} normally warns you about such files when creating an
7437 archive, and rejects attempts to extracts such files.
7439 Other @command{tar} programs do not do this. As a result, if you
7440 create an archive whose member names start with a slash, they will be
7441 difficult for other people with a non-@GNUTAR{}
7442 program to use. Therefore, @GNUTAR{} also strips
7443 leading slashes from member names when putting members into the
7444 archive. For example, if you ask @command{tar} to add the file
7445 @file{/bin/ls} to an archive, it will do so, but the member name will
7446 be @file{bin/ls}.@footnote{A side effect of this is that when
7447 @option{--create} is used with @option{--verbose} the resulting output
7448 is not, generally speaking, the same as the one you'd get running
7449 @kbd{tar --list} command. This may be important if you use some
7450 scripts for comparing both outputs. @xref{listing member and file names},
7451 for the information on how to handle this case.}
7453 If you use the @option{--absolute-names} (@option{-P}) option,
7454 @command{tar} will do none of these transformations.
7456 To archive or extract files relative to the root directory, specify
7457 the @option{--absolute-names} (@option{-P}) option.
7459 Normally, @command{tar} acts on files relative to the working
7460 directory---ignoring superior directory names when archiving, and
7461 ignoring leading slashes when extracting.
7463 When you specify @option{--absolute-names} (@option{-P}),
7464 @command{tar} stores file names including all superior directory
7465 names, and preserves leading slashes. If you only invoked
7466 @command{tar} from the root directory you would never need the
7467 @option{--absolute-names} option, but using this option
7468 may be more convenient than switching to root.
7470 @FIXME{Should be an example in the tutorial/wizardry section using this
7471 to transfer files between systems.}
7473 @FIXME{Is write access an issue?}
7476 @item --absolute-names
7477 Preserves full file names (including superior directory names) when
7478 archiving files. Preserves leading slash when extracting files.
7482 @FIXME{this is still horrible; need to talk with dan on monday.}
7484 @command{tar} prints out a message about removing the @samp{/} from
7485 file names. This message appears once per @GNUTAR{}
7486 invocation. It represents something which ought to be told; ignoring
7487 what it means can cause very serious surprises, later.
7489 Some people, nevertheless, do not want to see this message. Wanting to
7490 play really dangerously, one may of course redirect @command{tar} standard
7491 error to the sink. For example, under @command{sh}:
7494 $ @kbd{tar -c -f archive.tar /home 2> /dev/null}
7498 Another solution, both nicer and simpler, would be to change to
7499 the @file{/} directory first, and then avoid absolute notation.
7503 $ @kbd{(cd / && tar -c -f archive.tar home)}
7505 $ @kbd{tar -c -f archive.tar -C / home}
7508 @include getdate.texi
7511 @chapter Controlling the Archive Format
7513 @cindex Tar archive formats
7514 Due to historical reasons, there are several formats of tar archives.
7515 All of them are based on the same principles, but have some subtle
7516 differences that often make them incompatible with each other.
7518 GNU tar is able to create and handle archives in a variety of formats.
7519 The most frequently used formats are (in alphabetical order):
7523 Format used by @GNUTAR{} versions up to 1.13.25. This format derived
7524 from an early @acronym{POSIX} standard, adding some improvements such as
7525 sparse file handling and incremental archives. Unfortunately these
7526 features were implemented in a way incompatible with other archive
7529 Archives in @samp{gnu} format are able to hold pathnames of unlimited
7533 Format used by @GNUTAR{} of versions prior to 1.12.
7536 Archive format, compatible with the V7 implementation of tar. This
7537 format imposes a number of limitations. The most important of them
7541 @item The maximum length of a file name is limited to 99 characters.
7542 @item The maximum length of a symbolic link is limited to 99 characters.
7543 @item It is impossible to store special files (block and character
7544 devices, fifos etc.)
7545 @item Maximum value of user or group ID is limited to 2097151 (7777777
7547 @item V7 archives do not contain symbolic ownership information (user
7548 and group name of the file owner).
7551 This format has traditionally been used by Automake when producing
7552 Makefiles. This practice will change in the future, in the meantime,
7553 however this means that projects containing filenames more than 99
7554 characters long will not be able to use @GNUTAR{} @value{VERSION} and
7555 Automake prior to 1.9.
7558 Archive format defined by @acronym{POSIX.1-1988} specification. It stores
7559 symbolic ownership information. It is also able to store
7560 special files. However, it imposes several restrictions as well:
7563 @item The maximum length of a file name is limited to 256 characters,
7564 provided that the filename can be split at directory separator in
7565 two parts, first of them being at most 155 bytes long. So, in most
7566 cases the maximum file name length will be shorter than 256
7568 @item The maximum length of a symbolic link name is limited to
7570 @item Maximum size of a file the archive is able to accomodate
7572 @item Maximum value of UID/GID is 2097151.
7573 @item Maximum number of bits in device major and minor numbers is 21.
7577 Format used by J@"org Schilling @command{star}
7578 implementation. @GNUTAR{} is able to read @samp{star} archives but
7579 currently does not produce them.
7582 Archive format defined by @acronym{POSIX.1-2001} specification. This is the
7583 most flexible and feature-rich format. It does not impose any
7584 restrictions on file sizes or filename lengths. This format is quite
7585 recent, so not all tar implementations are able to handle it properly.
7586 However, this format is designed in such a way that any tar
7587 implementation able to read @samp{ustar} archives will be able to read
7588 most @samp{posix} archives as well, with the only exception that any
7589 additional information (such as long file names etc.) will in such
7590 case be extracted as plain text files along with the files it refers to.
7592 This archive format will be the default format for future versions
7597 The following table summarizes the limitations of each of these
7600 @multitable @columnfractions .10 .20 .20 .20 .20
7601 @headitem Format @tab UID @tab File Size @tab Path Name @tab Devn
7602 @item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
7603 @item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
7604 @item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
7605 @item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
7606 @item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
7609 The default format for @GNUTAR{} is defined at compilation
7610 time. You may check it by running @command{tar --help}, and examining
7611 the last lines of its output. Usually, @GNUTAR{} is configured
7612 to create archives in @samp{gnu} format, however, future version will
7613 switch to @samp{posix}.
7616 * Portability:: Making @command{tar} Archives More Portable
7617 * Compression:: Using Less Space through Compression
7618 * Attributes:: Handling File Attributes
7619 * cpio:: Comparison of @command{tar} and @command{cpio}
7623 @section Making @command{tar} Archives More Portable
7625 Creating a @command{tar} archive on a particular system that is meant to be
7626 useful later on many other machines and with other versions of @command{tar}
7627 is more challenging than you might think. @command{tar} archive formats
7628 have been evolving since the first versions of Unix. Many such formats
7629 are around, and are not always compatible with each other. This section
7630 discusses a few problems, and gives some advice about making @command{tar}
7631 archives more portable.
7633 One golden rule is simplicity. For example, limit your @command{tar}
7634 archives to contain only regular files and directories, avoiding
7635 other kind of special files. Do not attempt to save sparse files or
7636 contiguous files as such. Let's discuss a few more problems, in turn.
7638 @FIXME{Discuss GNU extensions (incremental backups, multi-volume
7639 archives and archive labels) in GNU and PAX formats.}
7642 * Portable Names:: Portable Names
7643 * dereference:: Symbolic Links
7644 * old:: Old V7 Archives
7645 * ustar:: Ustar Archives
7646 * gnu:: GNU and old GNU format archives.
7647 * posix:: @acronym{POSIX} archives
7648 * Checksumming:: Checksumming Problems
7649 * Large or Negative Values:: Large files, negative time stamps, etc.
7652 @node Portable Names
7653 @subsection Portable Names
7655 Use portable file and member names. A name is portable if it contains
7656 only ASCII letters and digits, @samp{/}, @samp{.}, @samp{_}, and
7657 @samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
7658 contain @samp{/-}. Avoid deep directory nesting. For portability to
7659 old Unix hosts, limit your file name components to 14 characters or
7662 If you intend to have your @command{tar} archives to be read under
7663 MSDOS, you should not rely on case distinction for file names, and you
7664 might use the @acronym{GNU} @command{doschk} program for helping you
7665 further diagnosing illegal MSDOS names, which are even more limited
7669 @subsection Symbolic Links
7670 @cindex File names, using symbolic links
7671 @cindex Symbolic link as file name
7673 @opindex dereference
7674 Normally, when @command{tar} archives a symbolic link, it writes a
7675 block to the archive naming the target of the link. In that way, the
7676 @command{tar} archive is a faithful record of the file system contents.
7677 @option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
7678 @command{tar} to archive the files symbolic links point to, instead of
7679 the links themselves. When this option is used, when @command{tar}
7680 encounters a symbolic link, it will archive the linked-to file,
7681 instead of simply recording the presence of a symbolic link.
7683 The name under which the file is stored in the file system is not
7684 recorded in the archive. To record both the symbolic link name and
7685 the file name in the system, archive the file under both names. If
7686 all links were recorded automatically by @command{tar}, an extracted file
7687 might be linked to a file name that no longer exists in the file
7690 If a linked-to file is encountered again by @command{tar} while creating
7691 the same archive, an entire second copy of it will be stored. (This
7692 @emph{might} be considered a bug.)
7694 So, for portable archives, do not archive symbolic links as such,
7695 and use @option{--dereference} (@option{-h}): many systems do not support
7696 symbolic links, and moreover, your distribution might be unusable if
7697 it contains unresolved symbolic links.
7700 @subsection Old V7 Archives
7701 @cindex Format, old style
7702 @cindex Old style format
7703 @cindex Old style archives
7704 @cindex v7 archive format
7706 Certain old versions of @command{tar} cannot handle additional
7707 information recorded by newer @command{tar} programs. To create an
7708 archive in V7 format (not ANSI), which can be read by these old
7709 versions, specify the @option{--format=v7} option in
7710 conjunction with the @option{--create} (@option{-c}) (@command{tar} also
7711 accepts @option{--portability} or @samp{op-old-archive} for this
7712 option). When you specify it,
7713 @command{tar} leaves out information about directories, pipes, fifos,
7714 contiguous files, and device files, and specifies file ownership by
7715 group and user IDs instead of group and user names.
7717 When updating an archive, do not use @option{--format=v7}
7718 unless the archive was created using this option.
7720 In most cases, a @emph{new} format archive can be read by an @emph{old}
7721 @command{tar} program without serious trouble, so this option should
7722 seldom be needed. On the other hand, most modern @command{tar}s are
7723 able to read old format archives, so it might be safer for you to
7724 always use @option{--format=v7} for your distributions.
7727 @subsection Ustar Archive Format
7729 @cindex ustar archive format
7730 Archive format defined by @acronym{POSIX}.1-1988 specification is called
7731 @code{ustar}. Although it is more flexible than the V7 format, it
7732 still has many restrictions (@xref{Formats,ustar}, for the detailed
7733 description of @code{ustar} format). Along with V7 format,
7734 @code{ustar} format is a good choice for archives intended to be read
7735 with other implementations of @command{tar}.
7737 To create archive in @code{ustar} format, use @option{--format=ustar}
7738 option in conjunction with the @option{--create} (@option{-c}).
7741 @subsection @acronym{GNU} and old @GNUTAR{} format
7743 @cindex GNU archive format
7744 @cindex Old GNU archive format
7745 @GNUTAR{} was based on an early draft of the
7746 @acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
7747 @command{tar}, such as the support for file names longer than 100
7748 characters, use portions of the @command{tar} header record which were
7749 specified in that @acronym{POSIX} draft as unused. Subsequent changes in
7750 @acronym{POSIX} have allocated the same parts of the header record for
7751 other purposes. As a result, @GNUTAR{} format is
7752 incompatible with the current @acronym{POSIX} specification, and with
7753 @command{tar} programs that follow it.
7755 In the majority of cases, @command{tar} will be configured to create
7756 this format by default. This will change in the future releases, since
7757 we plan to make @samp{posix} format the default.
7759 To force creation a @GNUTAR{} archive, use option
7760 @option{--format=gnu}.
7763 @subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
7765 @cindex POSIX archive format
7766 @cindex PAX archive format
7767 Starting from version 1.14 @GNUTAR{} features full support for
7768 @acronym{POSIX.1-2001} archives.
7770 A @acronym{POSIX} conformant archive will be created if @command{tar}
7771 was given @option{--format=posix} (@option{--format=pax}) option. No
7772 special option is required to read and extract from a @acronym{POSIX}
7776 * PAX keywords:: Controlling Extended Header Keywords.
7780 @subsubsection Controlling Extended Header Keywords
7784 @item --pax-option=@var{keyword-list}
7785 Handle keywords in @acronym{PAX} extended headers. This option is
7786 equivalent to @option{-o} option of the @command{pax} utility.
7789 @var{Keyword-list} is a comma-separated
7790 list of keyword options, each keyword option taking one of
7791 the following forms:
7794 @item delete=@var{pattern}
7795 When used with one of archive-creation commands,
7796 this option instructs @command{tar} to omit from extended header records
7797 that it produces any keywords matching the string @var{pattern}.
7799 When used in extract or list mode, this option instructs tar
7800 to ignore any keywords matching the given @var{pattern} in the extended
7801 header records. In both cases, matching is performed using the pattern
7802 matching notation described in @acronym{POSIX 1003.2}, 3.13
7803 (@pxref{wildcards}). For example:
7806 --pax-option delete=security.*
7809 would suppress security-related information.
7811 @item exthdr.name=@var{string}
7813 This keyword allows user control over the name that is written into the
7814 ustar header blocks for the extended headers. The name is obtained
7815 from @var{string} after making the following substitutions:
7817 @multitable @columnfractions .25 .55
7818 @headitem Meta-character @tab Replaced By
7819 @item %d @tab The directory name of the file, equivalent to the
7820 result of the @command{dirname} utility on the translated pathname.
7821 @item %f @tab The filename of the file, equivalent to the result
7822 of the @command{basename} utility on the translated pathname.
7823 @item %p @tab The process ID of the @command{tar} process.
7824 @item %% @tab A @samp{%} character.
7827 Any other @samp{%} characters in @var{string} produce undefined
7830 If no option @samp{exthdr.name=string} is specified, @command{tar}
7831 will use the following default value:
7837 @item globexthdr.name=@var{string}
7838 This keyword allows user control over the name that is written into
7839 the ustar header blocks for global extended header records. The name
7840 is obtained from the contents of @var{string}, after making
7841 the following substitutions:
7843 @multitable @columnfractions .25 .55
7844 @headitem Meta-character @tab Replaced By
7845 @item %n @tab An integer that represents the
7846 sequence number of the global extended header record in the archive,
7848 @item %p @tab The process ID of the @command{tar} process.
7849 @item %% @tab A @samp{%} character.
7852 Any other @samp{%} characters in @var{string} produce undefined results.
7854 If no option @samp{globexthdr.name=string} is specified, @command{tar}
7855 will use the following default value:
7858 $TMPDIR/GlobalHead.%p.%n
7862 where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
7863 environment variable. If @var{TMPDIR} is not set, @command{tar}
7866 @item @var{keyword}=@var{value}
7867 When used with one of archive-creation commands, these keyword/value pairs
7868 will be included at the beginning of the archive in a global extended
7869 header record. When used with one of archive-reading commands,
7870 @command{tar} will behave as if it has encountered these keyword/value
7871 pairs at the beginning of the archive in a global extended header
7874 @item @var{keyword}:=@var{value}
7875 When used with one of archive-creation commands, these keyword/value pairs
7876 will be included as records at the beginning of an extended header for
7877 each file. This is effectively equivalent to @var{keyword}=@var{value}
7878 form except that it creates no global extended header records.
7880 When used with one of archive-reading commands, @command{tar} will
7881 behave as if these keyword/value pairs were included as records at the
7882 end of each extended header; thus, they will override any global or
7883 file-specific extended header record keywords of the same names.
7884 For example, in the command:
7887 tar --format=posix --create \
7888 --file archive --pax-option gname:=user .
7891 the group name will be forced to a new value for all files
7892 stored in the archive.
7896 @subsection Checksumming Problems
7898 SunOS and HP-UX @command{tar} fail to accept archives created using
7899 @GNUTAR{} and containing non-ASCII file names, that
7900 is, file names having characters with the eight bit set, because they
7901 use signed checksums, while @GNUTAR{} uses unsigned
7902 checksums while creating archives, as per @acronym{POSIX} standards. On
7903 reading, @GNUTAR{} computes both checksums and
7904 accept any. It is somewhat worrying that a lot of people may go
7905 around doing backup of their files using faulty (or at least
7906 non-standard) software, not learning about it until it's time to
7907 restore their missing files with an incompatible file extractor, or
7910 @GNUTAR{} compute checksums both ways, and accept
7911 any on read, so @acronym{GNU} tar can read Sun tapes even with their
7912 wrong checksums. @GNUTAR{} produces the standard
7913 checksum, however, raising incompatibilities with Sun. That is to
7914 say, @GNUTAR{} has not been modified to
7915 @emph{produce} incorrect archives to be read by buggy @command{tar}'s.
7916 I've been told that more recent Sun @command{tar} now read standard
7917 archives, so maybe Sun did a similar patch, after all?
7919 The story seems to be that when Sun first imported @command{tar}
7920 sources on their system, they recompiled it without realizing that
7921 the checksums were computed differently, because of a change in
7922 the default signing of @code{char}'s in their compiler. So they
7923 started computing checksums wrongly. When they later realized their
7924 mistake, they merely decided to stay compatible with it, and with
7925 themselves afterwards. Presumably, but I do not really know, HP-UX
7926 has chosen that their @command{tar} archives to be compatible with Sun's.
7927 The current standards do not favor Sun @command{tar} format. In any
7928 case, it now falls on the shoulders of SunOS and HP-UX users to get
7929 a @command{tar} able to read the good archives they receive.
7931 @node Large or Negative Values
7932 @subsection Large or Negative Values
7933 @cindex large values
7934 @cindex future time stamps
7935 @cindex negative time stamps
7938 The above sections suggest to use @samp{oldest possible} archive
7939 format if in doubt. However, sometimes it is not possible. If you
7940 attempt to archive a file whose metadata cannot be represented using
7941 required format, @GNUTAR{} will print error message and ignore such a
7942 file. You will than have to switch to a format that is able to
7943 handle such values. The format summary table (@pxref{Formats}) will
7946 In particular, when trying to archive files larger than 8GB or with
7947 timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
7948 12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
7949 @acronym{POSIX} archive formats. When considering which format to
7950 choose, bear in mind that the @acronym{GNU} format uses
7951 two's-complement base-256 notation to store values that do not fit
7952 into standard @acronym{ustar} range. Such archives can generally be
7953 read only by a @GNUTAR{} implementation. Moreover, they sometimes
7954 cannot be correctly restored on another hosts even by @GNUTAR{}. For
7955 example, using two's complement representation for negative time
7956 stamps that assumes a signed 32-bit @code{time_t} generates archives
7957 that are not portable to hosts with differing @code{time_t}
7960 On the other hand, @acronym{POSIX} archives, generally speaking, can
7961 be extracted by any tar implementation that understands older
7962 @acronym{ustar} format. The only exception are files larger than 8GB.
7964 @FIXME{Describe how @acronym{POSIX} archives are extracted by non
7968 @section Using Less Space through Compression
7971 * gzip:: Creating and Reading Compressed Archives
7972 * sparse:: Archiving Sparse Files
7976 @subsection Creating and Reading Compressed Archives
7977 @cindex Compressed archives
7978 @cindex Storing archives in compressed format
7980 @GNUTAR{} is able to create and read compressed archives. It supports
7981 @command{gzip} and @command{bzip2} compression programs. For backward
7982 compatibilty, it also supports @command{compress} command, although
7983 we strongly recommend against using it, since there is a patent
7984 covering the algorithm it uses and you could be sued for patent
7985 infringement merely by running @command{compress}! Besides, it is less
7986 effective than @command{gzip} and @command{bzip2}.
7988 Creating a compressed archive is simple: you just specify a
7989 @dfn{compression option} along with the usual archive creation
7990 commands. The compression option is @option{-z} (@option{--gzip}) to
7991 create a @command{gzip} compressed archive, @option{-j}
7992 (@option{--bzip2}) to create a @command{bzip2} compressed archive, and
7993 @option{-Z} (@option{--compress}) to use @command{compress} program.
7997 $ @kbd{tar cfz archive.tar.gz .}
8000 Reading compressed archive is even simpler: you don't need to specify
8001 any additional options as @GNUTAR{} recognizes its format
8002 automatically. Thus, the following commands will list and extract the
8003 archive created in previous example:
8006 # List the compressed archive
8007 $ @kbd{tar tf archive.tar.gz}
8008 # Extract the compressed archive
8009 $ @kbd{tar xf archive.tar.gz}
8012 The only case when you have to specify a decompression option while
8013 reading the archive is when reading from a pipe or from a tape drive
8014 that does not support random access. However, in this case @GNUTAR{}
8015 will indicate which option you should use. For example:
8018 $ @kbd{cat archive.tar.gz | tar tf -}
8019 tar: Archive is compressed. Use -z option
8020 tar: Error is not recoverable: exiting now
8023 If you see such diagnostics, just add the suggested option to the
8024 invocation of @GNUTAR{}:
8027 $ @kbd{cat archive.tar.gz | tar tfz -}
8030 Notice also, that there are several restrictions on operations on
8031 compressed archives. First of all, compressed archives cannot be
8032 modified, i.e., you cannot update (@option{--update} (@option{-u})) them or delete
8033 (@option{--delete}) members from them. Likewise, you cannot append
8034 another @command{tar} archive to a compressed archive using
8035 @option{--append} (@option{-r})). Secondly, multi-volume archives cannot be
8038 The following table summarizes compression options used by @GNUTAR{}.
8046 Filter the archive through @command{gzip}.
8048 You can use @option{--gzip} and @option{--gunzip} on physical devices
8049 (tape drives, etc.) and remote files as well as on normal files; data
8050 to or from such devices or remote files is reblocked by another copy
8051 of the @command{tar} program to enforce the specified (or default) record
8052 size. The default compression parameters are used; if you need to
8053 override them, set @env{GZIP} environment variable, e.g.:
8056 $ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
8060 Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
8061 @command{gzip} explicitly:
8064 $ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
8067 @cindex corrupted archives
8068 About corrupted compressed archives: @command{gzip}'ed files have no
8069 redundancy, for maximum compression. The adaptive nature of the
8070 compression scheme means that the compression tables are implicitly
8071 spread all over the archive. If you lose a few blocks, the dynamic
8072 construction of the compression tables becomes unsynchronized, and there
8073 is little chance that you could recover later in the archive.
8075 There are pending suggestions for having a per-volume or per-file
8076 compression in @GNUTAR{}. This would allow for viewing the
8077 contents without decompression, and for resynchronizing decompression at
8078 every volume or file, in case of corrupted archives. Doing so, we might
8079 lose some compressibility. But this would have make recovering easier.
8080 So, there are pros and cons. We'll see!
8085 Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
8092 Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
8094 The @acronym{GNU} Project recommends you not use
8095 @command{compress}, because there is a patent covering the algorithm it
8096 uses. You could be sued for patent infringement merely by running
8099 @opindex use-compress-program
8100 @item --use-compress-program=@var{prog}
8101 Use external compression program @var{prog}. Use this option if you
8102 have a compression program that @GNUTAR{} does not support. There
8103 are two requirements to which @var{prog} should comply:
8105 First, when called without options, it should read data from standard
8106 input, compress it and output it on standard output.
8108 Secondly, if called with @option{-d} argument, it should do exactly
8109 the opposite, i.e., read the compressed data from the standard input
8110 and produce uncompressed data on the standard output.
8113 @cindex gpg, using with tar
8114 @cindex gnupg, using with tar
8115 @cindex Using encrypted archives
8116 The @option{--use-compress-program} option, in particular, lets you
8117 implement your own filters, not necessarily dealing with
8118 compression/decomression. For example, suppose you wish to implement
8119 PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
8120 gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard
8121 Manual}). The following script does that:
8127 -d) gpg --decrypt - | gzip -d -c;;
8128 '') gzip -c | gpg -s ;;
8129 *) echo "Unknown option $1">&2; exit 1;;
8134 Suppose you name it @file{gpgz} and save it somewhere in your
8135 @env{PATH}. Then the following command will create a commpressed
8136 archive signed with your private key:
8139 $ @kbd{tar -cf foo.tar.gpgz --use-compress=gpgz .}
8143 Likewise, the following command will list its contents:
8146 $ @kbd{tar -tf foo.tar.gpgz --use-compress=gpgz .}
8150 The above is based on the following discussion:
8152 I have one question, or maybe it's a suggestion if there isn't a way
8153 to do it now. I would like to use @option{--gzip}, but I'd also like
8154 the output to be fed through a program like @acronym{GNU}
8155 @command{ecc} (actually, right now that's @samp{exactly} what I'd like
8156 to use :-)), basically adding ECC protection on top of compression.
8157 It seems as if this should be quite easy to do, but I can't work out
8158 exactly how to go about it. Of course, I can pipe the standard output
8159 of @command{tar} through @command{ecc}, but then I lose (though I
8160 haven't started using it yet, I confess) the ability to have
8161 @command{tar} use @command{rmt} for it's I/O (I think).
8163 I think the most straightforward thing would be to let me specify a
8164 general set of filters outboard of compression (preferably ordered,
8165 so the order can be automatically reversed on input operations, and
8166 with the options they require specifiable), but beggars shouldn't be
8167 choosers and anything you decide on would be fine with me.
8169 By the way, I like @command{ecc} but if (as the comments say) it can't
8170 deal with loss of block sync, I'm tempted to throw some time at adding
8171 that capability. Supposing I were to actually do such a thing and
8172 get it (apparently) working, do you accept contributed changes to
8173 utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
8175 Isn't that exactly the role of the
8176 @option{--use-compress-prog=@var{program}} option?
8177 I never tried it myself, but I suspect you may want to write a
8178 @var{prog} script or program able to filter stdin to stdout to
8179 way you want. It should recognize the @option{-d} option, for when
8180 extraction is needed rather than creation.
8182 It has been reported that if one writes compressed data (through the
8183 @option{--gzip} or @option{--compress} options) to a DLT and tries to use
8184 the DLT compression mode, the data will actually get bigger and one will
8185 end up with less space on the tape.
8189 @subsection Archiving Sparse Files
8190 @cindex Sparse Files
8197 Handle sparse files efficiently.
8200 This option causes all files to be put in the archive to be tested for
8201 sparseness, and handled specially if they are. The @option{--sparse}
8202 (@option{-S}) option is useful when many @code{dbm} files, for example, are being
8203 backed up. Using this option dramatically decreases the amount of
8204 space needed to store such a file.
8206 In later versions, this option may be removed, and the testing and
8207 treatment of sparse files may be done automatically with any special
8208 @acronym{GNU} options. For now, it is an option needing to be specified on
8209 the command line with the creation or updating of an archive.
8211 Files in the file system occasionally have ``holes.'' A hole in a file
8212 is a section of the file's contents which was never written. The
8213 contents of a hole read as all zeros. On many operating systems,
8214 actual disk storage is not allocated for holes, but they are counted
8215 in the length of the file. If you archive such a file, @command{tar}
8216 could create an archive longer than the original. To have @command{tar}
8217 attempt to recognize the holes in a file, use @option{--sparse} (@option{-S}). When
8218 you use this option, then, for any file using less disk space than
8219 would be expected from its length, @command{tar} searches the file for
8220 consecutive stretches of zeros. It then records in the archive for
8221 the file where the consecutive stretches of zeros are, and only
8222 archives the ``real contents'' of the file. On extraction (using
8223 @option{--sparse} is not needed on extraction) any such
8224 files have holes created wherever the continuous stretches of zeros
8225 were found. Thus, if you use @option{--sparse}, @command{tar} archives
8226 won't take more space than the original.
8228 A file is sparse if it contains blocks of zeros whose existence is
8229 recorded, but that have no space allocated on disk. When you specify
8230 the @option{--sparse} option in conjunction with the @option{--create}
8231 (@option{-c}) operation, @command{tar} tests all files for sparseness
8232 while archiving. If @command{tar} finds a file to be sparse, it uses a
8233 sparse representation of the file in the archive. @xref{create}, for
8234 more information about creating archives.
8236 @option{--sparse} is useful when archiving files, such as dbm files,
8237 likely to contain many nulls. This option dramatically
8238 decreases the amount of space needed to store such an archive.
8241 @strong{Please Note:} Always use @option{--sparse} when performing file
8242 system backups, to avoid archiving the expanded forms of files stored
8243 sparsely in the system.
8245 Even if your system has no sparse files currently, some may be
8246 created in the future. If you use @option{--sparse} while making file
8247 system backups as a matter of course, you can be assured the archive
8248 will never take more space on the media than the files take on disk
8249 (otherwise, archiving a disk filled with sparse files might take
8250 hundreds of tapes). @xref{Incremental Dumps}.
8253 @command{tar} ignores the @option{--sparse} option when reading an archive.
8258 Files stored sparsely in the file system are represented sparsely in
8259 the archive. Use in conjunction with write operations.
8262 However, users should be well aware that at archive creation time,
8263 @GNUTAR{} still has to read whole disk file to
8264 locate the @dfn{holes}, and so, even if sparse files use little space
8265 on disk and in the archive, they may sometimes require inordinate
8266 amount of time for reading and examining all-zero blocks of a file.
8267 Although it works, it's painfully slow for a large (sparse) file, even
8268 though the resulting tar archive may be small. (One user reports that
8269 dumping a @file{core} file of over 400 megabytes, but with only about
8270 3 megabytes of actual data, took about 9 minutes on a Sun Sparcstation
8271 ELC, with full CPU utilization.)
8273 This reading is required in all cases and is not related to the fact
8274 the @option{--sparse} option is used or not, so by merely @emph{not}
8275 using the option, you are not saving time@footnote{Well! We should say
8276 the whole truth, here. When @option{--sparse} is selected while creating
8277 an archive, the current @command{tar} algorithm requires sparse files to be
8278 read twice, not once. We hope to develop a new archive format for saving
8279 sparse files in which one pass will be sufficient.}.
8281 Programs like @command{dump} do not have to read the entire file; by
8282 examining the file system directly, they can determine in advance
8283 exactly where the holes are and thus avoid reading through them. The
8284 only data it need read are the actual allocated data blocks.
8285 @GNUTAR{} uses a more portable and straightforward
8286 archiving approach, it would be fairly difficult that it does
8287 otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, on
8291 What I did say is that you cannot tell the difference between a hole and an
8292 equivalent number of nulls without reading raw blocks. @code{st_blocks} at
8293 best tells you how many holes there are; it doesn't tell you @emph{where}.
8294 Just as programs may, conceivably, care what @code{st_blocks} is (care
8295 to name one that does?), they may also care where the holes are (I have
8296 no examples of this one either, but it's equally imaginable).
8298 I conclude from this that good archivers are not portable. One can
8299 arguably conclude that if you want a portable program, you can in good
8300 conscience restore files with as many holes as possible, since you can't
8305 @section Handling File Attributes
8308 When @command{tar} reads files, it updates their access times. To
8309 avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
8310 reset the access time retroactively or avoid changing it in the first
8313 Handling of file attributes
8316 @opindex atime-preserve
8317 @item --atime-preserve
8318 @itemx --atime-preserve=replace
8319 @itemx --atime-preserve=system
8320 Preserve the access times of files that are read. This works only for
8321 files that you own, unless you have superuser privileges.
8323 @option{--atime-preserve=replace} works on most systems, but it also
8324 restores the data modification time and updates the status change
8325 time. Hence it doesn't interact with incremental dumps nicely
8326 (@pxref{Backups}), and it can set access or data modification times
8327 incorrectly if other programs access the file while @command{tar} is
8330 @option{--atime-preserve=system} avoids changing the access time in
8331 the first place, if the operating system supports this.
8332 Unfortunately, this may or may not work on any given operating system
8333 or file system. If @command{tar} knows for sure it won't work, it
8334 complains right away.
8336 Currently @option{--atime-preserve} with no operand defaults to
8337 @option{--atime-preserve=replace}, but this is intended to change to
8338 @option{--atime-preserve=system} when the latter is better-supported.
8343 Do not extract data modification time.
8345 When this option is used, @command{tar} leaves the data modification times
8346 of the files it extracts as the times when the files were extracted,
8347 instead of setting it to the times recorded in the archive.
8349 This option is meaningless with @option{--list} (@option{-t}).
8353 Create extracted files with the same ownership they have in the
8356 This is the default behavior for the superuser,
8357 so this option is meaningful only for non-root users, when @command{tar}
8358 is executed on those systems able to give files away. This is
8359 considered as a security flaw by many people, at least because it
8360 makes quite difficult to correctly account users for the disk space
8361 they occupy. Also, the @code{suid} or @code{sgid} attributes of
8362 files are easily and silently lost when files are given away.
8364 When writing an archive, @command{tar} writes the user id and user name
8365 separately. If it can't find a user name (because the user id is not
8366 in @file{/etc/passwd}), then it does not write one. When restoring,
8367 it tries to look the name (if one was written) up in
8368 @file{/etc/passwd}. If it fails, then it uses the user id stored in
8369 the archive instead.
8371 @opindex no-same-owner
8372 @item --no-same-owner
8374 Do not attempt to restore ownership when extracting. This is the
8375 default behavior for ordinary users, so this option has an effect
8376 only for the superuser.
8378 @opindex numeric-owner
8379 @item --numeric-owner
8380 The @option{--numeric-owner} option allows (ANSI) archives to be written
8381 without user/group name information or such information to be ignored
8382 when extracting. It effectively disables the generation and/or use
8383 of user/group name information. This option forces extraction using
8384 the numeric ids from the archive, ignoring the names.
8386 This is useful in certain circumstances, when restoring a backup from
8387 an emergency floppy with different passwd/group files for example.
8388 It is otherwise impossible to extract files with the right ownerships
8389 if the password file in use during the extraction does not match the
8390 one belonging to the file system(s) being extracted. This occurs,
8391 for example, if you are restoring your files after a major crash and
8392 had booted from an emergency floppy with no password file or put your
8393 disk into another machine to do the restore.
8395 The numeric ids are @emph{always} saved into @command{tar} archives.
8396 The identifying names are added at create time when provided by the
8397 system, unless @option{--old-archive} (@option{-o}) is used. Numeric ids could be
8398 used when moving archives between a collection of machines using
8399 a centralized management for attribution of numeric ids to users
8400 and groups. This is often made through using the NIS capabilities.
8402 When making a @command{tar} file for distribution to other sites, it
8403 is sometimes cleaner to use a single owner for all files in the
8404 distribution, and nicer to specify the write permission bits of the
8405 files as stored in the archive independently of their actual value on
8406 the file system. The way to prepare a clean distribution is usually
8407 to have some Makefile rule creating a directory, copying all needed
8408 files in that directory, then setting ownership and permissions as
8409 wanted (there are a lot of possible schemes), and only then making a
8410 @command{tar} archive out of this directory, before cleaning
8411 everything out. Of course, we could add a lot of options to
8412 @GNUTAR{} for fine tuning permissions and ownership.
8413 This is not the good way, I think. @GNUTAR{} is
8414 already crowded with options and moreover, the approach just explained
8415 gives you a great deal of control already.
8417 @xopindex{same-permissions, short description}
8418 @xopindex{preserve-permissions, short description}
8420 @itemx --same-permissions
8421 @itemx --preserve-permissions
8422 Extract all protection information.
8424 This option causes @command{tar} to set the modes (access permissions) of
8425 extracted files exactly as recorded in the archive. If this option
8426 is not used, the current @code{umask} setting limits the permissions
8427 on extracted files. This option is by default enabled when
8428 @command{tar} is executed by a superuser.
8431 This option is meaningless with @option{--list} (@option{-t}).
8435 Same as both @option{--same-permissions} and @option{--same-order}.
8437 The @option{--preserve} option has no equivalent short option name.
8438 It is equivalent to @option{--same-permissions} plus @option{--same-order}.
8440 @FIXME{I do not see the purpose of such an option. (Neither I. FP.)
8441 Neither do I. --Sergey}
8446 @section Comparison of @command{tar} and @command{cpio}
8449 @FIXME{Reorganize the following material}
8451 The @command{cpio} archive formats, like @command{tar}, do have maximum
8452 pathname lengths. The binary and old ASCII formats have a max path
8453 length of 256, and the new ASCII and CRC ASCII formats have a max
8454 path length of 1024. @acronym{GNU} @command{cpio} can read and write archives
8455 with arbitrary pathname lengths, but other @command{cpio} implementations
8456 may crash unexplainedly trying to read them.
8458 @command{tar} handles symbolic links in the form in which it comes in BSD;
8459 @command{cpio} doesn't handle symbolic links in the form in which it comes
8460 in System V prior to SVR4, and some vendors may have added symlinks
8461 to their system without enhancing @command{cpio} to know about them.
8462 Others may have enhanced it in a way other than the way I did it
8463 at Sun, and which was adopted by AT&T (and which is, I think, also
8464 present in the @command{cpio} that Berkeley picked up from AT&T and put
8465 into a later BSD release---I think I gave them my changes).
8467 (SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
8468 can handle @command{tar} format input, and write it on output, and it
8469 probably handles symbolic links. They may not have bothered doing
8470 anything to enhance @command{tar} as a result.)
8472 @command{cpio} handles special files; traditional @command{tar} doesn't.
8474 @command{tar} comes with V7, System III, System V, and BSD source;
8475 @command{cpio} comes only with System III, System V, and later BSD
8476 (4.3-tahoe and later).
8478 @command{tar}'s way of handling multiple hard links to a file can handle
8479 file systems that support 32-bit inumbers (e.g., the BSD file system);
8480 @command{cpio}s way requires you to play some games (in its "binary"
8481 format, i-numbers are only 16 bits, and in its "portable ASCII" format,
8482 they're 18 bits---it would have to play games with the "file system ID"
8483 field of the header to make sure that the file system ID/i-number pairs
8484 of different files were always different), and I don't know which
8485 @command{cpio}s, if any, play those games. Those that don't might get
8486 confused and think two files are the same file when they're not, and
8487 make hard links between them.
8489 @command{tar}s way of handling multiple hard links to a file places only
8490 one copy of the link on the tape, but the name attached to that copy
8491 is the @emph{only} one you can use to retrieve the file; @command{cpio}s
8492 way puts one copy for every link, but you can retrieve it using any
8496 What type of check sum (if any) is used, and how is this calculated.
8499 See the attached manual pages for @command{tar} and @command{cpio} format.
8500 @command{tar} uses a checksum which is the sum of all the bytes in the
8501 @command{tar} header for a file; @command{cpio} uses no checksum.
8504 If anyone knows why @command{cpio} was made when @command{tar} was present
8508 It wasn't. @command{cpio} first showed up in PWB/UNIX 1.0; no
8509 generally-available version of UNIX had @command{tar} at the time. I don't
8510 know whether any version that was generally available @emph{within AT&T}
8511 had @command{tar}, or, if so, whether the people within AT&T who did
8512 @command{cpio} knew about it.
8514 On restore, if there is a corruption on a tape @command{tar} will stop at
8515 that point, while @command{cpio} will skip over it and try to restore the
8518 The main difference is just in the command syntax and header format.
8520 @command{tar} is a little more tape-oriented in that everything is blocked
8521 to start on a record boundary.
8524 Is there any differences between the ability to recover crashed
8525 archives between the two of them. (Is there any chance of recovering
8526 crashed archives at all.)
8529 Theoretically it should be easier under @command{tar} since the blocking
8530 lets you find a header with some variation of @samp{dd skip=@var{nn}}.
8531 However, modern @command{cpio}'s and variations have an option to just
8532 search for the next file header after an error with a reasonable chance
8533 of resyncing. However, lots of tape driver software won't allow you to
8534 continue past a media error which should be the only reason for getting
8535 out of sync unless a file changed sizes while you were writing the
8539 If anyone knows why @command{cpio} was made when @command{tar} was present
8540 at the unix scene, please tell me about this too.
8543 Probably because it is more media efficient (by not blocking everything
8544 and using only the space needed for the headers where @command{tar}
8545 always uses 512 bytes per file header) and it knows how to archive
8548 You might want to look at the freely available alternatives. The
8549 major ones are @command{afio}, @GNUTAR{}, and
8550 @command{pax}, each of which have their own extensions with some
8551 backwards compatibility.
8553 Sparse files were @command{tar}red as sparse files (which you can
8554 easily test, because the resulting archive gets smaller, and
8555 @acronym{GNU} @command{cpio} can no longer read it).
8558 @chapter Tapes and Other Archive Media
8561 A few special cases about tape handling warrant more detailed
8562 description. These special cases are discussed below.
8564 Many complexities surround the use of @command{tar} on tape drives. Since
8565 the creation and manipulation of archives located on magnetic tape was
8566 the original purpose of @command{tar}, it contains many features making
8567 such manipulation easier.
8569 Archives are usually written on dismountable media---tape cartridges,
8570 mag tapes, or floppy disks.
8572 The amount of data a tape or disk holds depends not only on its size,
8573 but also on how it is formatted. A 2400 foot long reel of mag tape
8574 holds 40 megabytes of data when formatted at 1600 bits per inch. The
8575 physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
8577 Magnetic media are re-usable---once the archive on a tape is no longer
8578 needed, the archive can be erased and the tape or disk used over.
8579 Media quality does deteriorate with use, however. Most tapes or disks
8580 should be discarded when they begin to produce data errors. EXABYTE
8581 tape cartridges should be discarded when they generate an @dfn{error
8582 count} (number of non-usable bits) of more than 10k.
8584 Magnetic media are written and erased using magnetic fields, and
8585 should be protected from such fields to avoid damage to stored data.
8586 Sticking a floppy disk to a filing cabinet using a magnet is probably
8590 * Device:: Device selection and switching
8591 * Remote Tape Server::
8592 * Common Problems and Solutions::
8593 * Blocking:: Blocking
8594 * Many:: Many archives on one tape
8595 * Using Multiple Tapes:: Using Multiple Tapes
8596 * label:: Including a Label in the Archive
8598 * Write Protection::
8602 @section Device Selection and Switching
8606 @item -f [@var{hostname}:]@var{file}
8607 @itemx --file=[@var{hostname}:]@var{file}
8608 Use archive file or device @var{file} on @var{hostname}.
8611 This option is used to specify the file name of the archive @command{tar}
8614 If the file name is @samp{-}, @command{tar} reads the archive from standard
8615 input (when listing or extracting), or writes it to standard output
8616 (when creating). If the @samp{-} file name is given when updating an
8617 archive, @command{tar} will read the original archive from its standard
8618 input, and will write the entire new archive to its standard output.
8620 If the file name contains a @samp{:}, it is interpreted as
8621 @samp{hostname:file name}. If the @var{hostname} contains an @dfn{at}
8622 sign (@samp{@@}), it is treated as @samp{user@@hostname:file name}. In
8623 either case, @command{tar} will invoke the command @command{rsh} (or
8624 @command{remsh}) to start up an @command{/usr/libexec/rmt} on the remote
8625 machine. If you give an alternate login name, it will be given to the
8627 Naturally, the remote machine must have an executable
8628 @command{/usr/libexec/rmt}. This program is free software from the
8629 University of California, and a copy of the source code can be found
8630 with the sources for @command{tar}; it's compiled and installed by default.
8631 The exact path to this utility is determined when configuring the package.
8632 It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for
8633 your installation prefix. This location may also be overridden at
8634 runtime by using @option{rmt-command=@var{command}} option (@xref{Option Summary,
8635 ---rmt-command}, for detailed description of this option. @xref{Remote
8636 Tape Server}, for the description of @command{rmt} command).
8638 If this option is not given, but the environment variable @env{TAPE}
8639 is set, its value is used; otherwise, old versions of @command{tar}
8640 used a default archive name (which was picked when @command{tar} was
8641 compiled). The default is normally set up to be the @dfn{first} tape
8642 drive or other transportable I/O medium on the system.
8644 Starting with version 1.11.5, @GNUTAR{} uses
8645 standard input and standard output as the default device, and I will
8646 not try anymore supporting automatic device detection at installation
8647 time. This was failing really in too many cases, it was hopeless.
8648 This is now completely left to the installer to override standard
8649 input and standard output for default device, if this seems
8650 preferable. Further, I think @emph{most} actual usages of
8651 @command{tar} are done with pipes or disks, not really tapes,
8652 cartridges or diskettes.
8654 Some users think that using standard input and output is running
8655 after trouble. This could lead to a nasty surprise on your screen if
8656 you forget to specify an output file name---especially if you are going
8657 through a network or terminal server capable of buffering large amounts
8658 of output. We had so many bug reports in that area of configuring
8659 default tapes automatically, and so many contradicting requests, that
8660 we finally consider the problem to be portably intractable. We could
8661 of course use something like @samp{/dev/tape} as a default, but this
8662 is @emph{also} running after various kind of trouble, going from hung
8663 processes to accidental destruction of real tapes. After having seen
8664 all this mess, using standard input and output as a default really
8665 sounds like the only clean choice left, and a very useful one too.
8667 @GNUTAR{} reads and writes archive in records, I
8668 suspect this is the main reason why block devices are preferred over
8669 character devices. Most probably, block devices are more efficient
8670 too. The installer could also check for @samp{DEFTAPE} in
8671 @file{<sys/mtio.h>}.
8674 @xopindex{force-local, short description}
8676 Archive file is local even if it contains a colon.
8678 @opindex rsh-command
8679 @item --rsh-command=@var{command}
8680 Use remote @var{command} instead of @command{rsh}. This option exists
8681 so that people who use something other than the standard @command{rsh}
8682 (e.g., a Kerberized @command{rsh}) can access a remote device.
8684 When this command is not used, the shell command found when
8685 the @command{tar} program was installed is used instead. This is
8686 the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh},
8687 @file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}.
8688 The installer may have overridden this by defining the environment
8689 variable @env{RSH} @emph{at installation time}.
8692 Specify drive and density.
8694 @xopindex{multi-volume, short description}
8696 @itemx --multi-volume
8697 Create/list/extract multi-volume archive.
8699 This option causes @command{tar} to write a @dfn{multi-volume} archive---one
8700 that may be larger than will fit on the medium used to hold it.
8701 @xref{Multi-Volume Archives}.
8703 @xopindex{tape-length, short description}
8705 @itemx --tape-length=@var{num}
8706 Change tape after writing @var{num} x 1024 bytes.
8708 This option might be useful when your tape drivers do not properly
8709 detect end of physical tapes. By being slightly conservative on the
8710 maximum tape length, you might avoid the problem entirely.
8712 @xopindex{info-script, short description}
8713 @xopindex{new-volume-script, short description}
8715 @itemx --info-script=@var{file}
8716 @itemx --new-volume-script=@var{file}
8717 Execute @file{file} at end of each tape. This implies
8718 @option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed
8719 description of this option.
8722 @node Remote Tape Server
8723 @section The Remote Tape Server
8725 @cindex remote tape drive
8727 In order to access the tape drive on a remote machine, @command{tar}
8728 uses the remote tape server written at the University of California at
8729 Berkeley. The remote tape server must be installed as
8730 @file{@var{prefix}/libexec/rmt} on any machine whose tape drive you
8731 want to use. @command{tar} calls @command{rmt} by running an
8732 @command{rsh} or @command{remsh} to the remote machine, optionally
8733 using a different login name if one is supplied.
8735 A copy of the source for the remote tape server is provided. It is
8736 Copyright @copyright{} 1983 by the Regents of the University of
8737 California, but can be freely distributed. It is compiled and
8738 installed by default.
8740 @cindex absolute file names
8741 Unless you use the @option{--absolute-names} (@option{-P}) option,
8742 @GNUTAR{} will not allow you to create an archive that contains
8743 absolute file names (a file name beginning with @samp{/}.) If you try,
8744 @command{tar} will automatically remove the leading @samp{/} from the
8745 file names it stores in the archive. It will also type a warning
8746 message telling you what it is doing.
8748 When reading an archive that was created with a different
8749 @command{tar} program, @GNUTAR{} automatically
8750 extracts entries in the archive which have absolute file names as if
8751 the file names were not absolute. This is an important feature. A
8752 visitor here once gave a @command{tar} tape to an operator to restore;
8753 the operator used Sun @command{tar} instead of @GNUTAR{},
8754 and the result was that it replaced large portions of
8755 our @file{/bin} and friends with versions from the tape; needless to
8756 say, we were unhappy about having to recover the file system from
8759 For example, if the archive contained a file @file{/usr/bin/computoy},
8760 @GNUTAR{} would extract the file to @file{usr/bin/computoy},
8761 relative to the current directory. If you want to extract the files in
8762 an archive to the same absolute names that they had when the archive
8763 was created, you should do a @samp{cd /} before extracting the files
8764 from the archive, or you should either use the @option{--absolute-names}
8765 option, or use the command @samp{tar -C / @dots{}}.
8767 @cindex Ultrix 3.1 and write failure
8768 Some versions of Unix (Ultrix 3.1 is known to have this problem),
8769 can claim that a short write near the end of a tape succeeded,
8770 when it actually failed. This will result in the -M option not
8771 working correctly. The best workaround at the moment is to use a
8772 significantly larger blocking factor than the default 20.
8774 In order to update an archive, @command{tar} must be able to backspace the
8775 archive in order to reread or rewrite a record that was just read (or
8776 written). This is currently possible only on two kinds of files: normal
8777 disk files (or any other file that can be backspaced with @samp{lseek}),
8778 and industry-standard 9-track magnetic tape (or any other kind of tape
8779 that can be backspaced with the @code{MTIOCTOP} @code{ioctl}.
8781 This means that the @option{--append}, @option{--concatenate}, and
8782 @option{--delete} commands will not work on any other kind of file.
8783 Some media simply cannot be backspaced, which means these commands and
8784 options will never be able to work on them. These non-backspacing
8785 media include pipes and cartridge tape drives.
8787 Some other media can be backspaced, and @command{tar} will work on them
8788 once @command{tar} is modified to do so.
8790 Archives created with the @option{--multi-volume}, @option{--label}, and
8791 @option{--incremental} (@option{-G}) options may not be readable by other version
8792 of @command{tar}. In particular, restoring a file that was split over
8793 a volume boundary will require some careful work with @command{dd}, if
8794 it can be done at all. Other versions of @command{tar} may also create
8795 an empty file whose name is that of the volume header. Some versions
8796 of @command{tar} may create normal files instead of directories archived
8797 with the @option{--incremental} (@option{-G}) option.
8799 @node Common Problems and Solutions
8800 @section Some Common Problems and their Solutions
8807 no such file or directory
8810 errors from @command{tar}:
8811 directory checksum error
8814 errors from media/system:
8825 @dfn{Block} and @dfn{record} terminology is rather confused, and it
8826 is also confusing to the expert reader. On the other hand, readers
8827 who are new to the field have a fresh mind, and they may safely skip
8828 the next two paragraphs, as the remainder of this manual uses those
8829 two terms in a quite consistent way.
8831 John Gilmore, the writer of the public domain @command{tar} from which
8832 @GNUTAR{} was originally derived, wrote (June 1995):
8835 The nomenclature of tape drives comes from IBM, where I believe
8836 they were invented for the IBM 650 or so. On IBM mainframes, what
8837 is recorded on tape are tape blocks. The logical organization of
8838 data is into records. There are various ways of putting records into
8839 blocks, including @code{F} (fixed sized records), @code{V} (variable
8840 sized records), @code{FB} (fixed blocked: fixed size records, @var{n}
8841 to a block), @code{VB} (variable size records, @var{n} to a block),
8842 @code{VSB} (variable spanned blocked: variable sized records that can
8843 occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=}
8844 parameter specified this to the operating system.
8846 The Unix man page on @command{tar} was totally confused about this.
8847 When I wrote @code{PD TAR}, I used the historically correct terminology
8848 (@command{tar} writes data records, which are grouped into blocks).
8849 It appears that the bogus terminology made it into @acronym{POSIX} (no surprise
8850 here), and now Fran@,{c}ois has migrated that terminology back
8851 into the source code too.
8854 The term @dfn{physical block} means the basic transfer chunk from or
8855 to a device, after which reading or writing may stop without anything
8856 being lost. In this manual, the term @dfn{block} usually refers to
8857 a disk physical block, @emph{assuming} that each disk block is 512
8858 bytes in length. It is true that some disk devices have different
8859 physical blocks, but @command{tar} ignore these differences in its own
8860 format, which is meant to be portable, so a @command{tar} block is always
8861 512 bytes in length, and @dfn{block} always mean a @command{tar} block.
8862 The term @dfn{logical block} often represents the basic chunk of
8863 allocation of many disk blocks as a single entity, which the operating
8864 system treats somewhat atomically; this concept is only barely used
8867 The term @dfn{physical record} is another way to speak of a physical
8868 block, those two terms are somewhat interchangeable. In this manual,
8869 the term @dfn{record} usually refers to a tape physical block,
8870 @emph{assuming} that the @command{tar} archive is kept on magnetic tape.
8871 It is true that archives may be put on disk or used with pipes,
8872 but nevertheless, @command{tar} tries to read and write the archive one
8873 @dfn{record} at a time, whatever the medium in use. One record is made
8874 up of an integral number of blocks, and this operation of putting many
8875 disk blocks into a single tape block is called @dfn{reblocking}, or
8876 more simply, @dfn{blocking}. The term @dfn{logical record} refers to
8877 the logical organization of many characters into something meaningful
8878 to the application. The term @dfn{unit record} describes a small set
8879 of characters which are transmitted whole to or by the application,
8880 and often refers to a line of text. Those two last terms are unrelated
8881 to what we call a @dfn{record} in @GNUTAR{}.
8883 When writing to tapes, @command{tar} writes the contents of the archive
8884 in chunks known as @dfn{records}. To change the default blocking
8885 factor, use the @option{--blocking-factor=@var{512-size}} (@option{-b
8886 @var{512-size}}) option. Each record will then be composed of
8887 @var{512-size} blocks. (Each @command{tar} block is 512 bytes.
8888 @xref{Standard}.) Each file written to the archive uses at least one
8889 full record. As a result, using a larger record size can result in
8890 more wasted space for small files. On the other hand, a larger record
8891 size can often be read and written much more efficiently.
8893 Further complicating the problem is that some tape drives ignore the
8894 blocking entirely. For these, a larger record size can still improve
8895 performance (because the software layers above the tape drive still
8896 honor the blocking), but not as dramatically as on tape drives that
8899 When reading an archive, @command{tar} can usually figure out the
8900 record size on itself. When this is the case, and a non-standard
8901 record size was used when the archive was created, @command{tar} will
8902 print a message about a non-standard blocking factor, and then operate
8903 normally. On some tape devices, however, @command{tar} cannot figure
8904 out the record size itself. On most of those, you can specify a
8905 blocking factor (with @option{--blocking-factor}) larger than the
8906 actual blocking factor, and then use the @option{--read-full-records}
8907 (@option{-B}) option. (If you specify a blocking factor with
8908 @option{--blocking-factor} and don't use the
8909 @option{--read-full-records} option, then @command{tar} will not
8910 attempt to figure out the recording size itself.) On some devices,
8911 you must always specify the record size exactly with
8912 @option{--blocking-factor} when reading, because @command{tar} cannot
8913 figure it out. In any case, use @option{--list} (@option{-t}) before
8914 doing any extractions to see whether @command{tar} is reading the archive
8917 @command{tar} blocks are all fixed size (512 bytes), and its scheme for
8918 putting them into records is to put a whole number of them (one or
8919 more) into each record. @command{tar} records are all the same size;
8920 at the end of the file there's a block containing all zeros, which
8921 is how you tell that the remainder of the last record(s) are garbage.
8923 In a standard @command{tar} file (no options), the block size is 512
8924 and the record size is 10240, for a blocking factor of 20. What the
8925 @option{--blocking-factor} option does is sets the blocking factor,
8926 changing the record size while leaving the block size at 512 bytes.
8927 20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives;
8928 most tape drives these days prefer much bigger records in order to
8929 stream and not waste tape. When writing tapes for myself, some tend
8930 to use a factor of the order of 2048, say, giving a record size of
8931 around one megabyte.
8933 If you use a blocking factor larger than 20, older @command{tar}
8934 programs might not be able to read the archive, so we recommend this
8935 as a limit to use in practice. @GNUTAR{}, however,
8936 will support arbitrarily large record sizes, limited only by the
8937 amount of virtual memory or the physical characteristics of the tape
8941 * Format Variations:: Format Variations
8942 * Blocking Factor:: The Blocking Factor of an Archive
8945 @node Format Variations
8946 @subsection Format Variations
8947 @cindex Format Parameters
8948 @cindex Format Options
8949 @cindex Options, archive format specifying
8950 @cindex Options, format specifying
8953 Format parameters specify how an archive is written on the archive
8954 media. The best choice of format parameters will vary depending on
8955 the type and number of files being archived, and on the media used to
8958 To specify format parameters when accessing or creating an archive,
8959 you can use the options described in the following sections.
8960 If you do not specify any format parameters, @command{tar} uses
8961 default parameters. You cannot modify a compressed archive.
8962 If you create an archive with the @option{--blocking-factor} option
8963 specified (@pxref{Blocking Factor}), you must specify that
8964 blocking-factor when operating on the archive. @xref{Formats}, for other
8965 examples of format parameter considerations.
8967 @node Blocking Factor
8968 @subsection The Blocking Factor of an Archive
8969 @cindex Blocking Factor
8971 @cindex Number of blocks per record
8972 @cindex Number of bytes per record
8973 @cindex Bytes per record
8974 @cindex Blocks per record
8977 @opindex blocking-factor
8978 The data in an archive is grouped into blocks, which are 512 bytes.
8979 Blocks are read and written in whole number multiples called
8980 @dfn{records}. The number of blocks in a record (i.e. the size of a
8981 record in units of 512 bytes) is called the @dfn{blocking factor}.
8982 The @option{--blocking-factor=@var{512-size}} (@option{-b
8983 @var{512-size}}) option specifies the blocking factor of an archive.
8984 The default blocking factor is typically 20 (i.e., 10240 bytes), but
8985 can be specified at installation. To find out the blocking factor of
8986 an existing archive, use @samp{tar --list --file=@var{archive-name}}.
8987 This may not work on some devices.
8989 Records are separated by gaps, which waste space on the archive media.
8990 If you are archiving on magnetic tape, using a larger blocking factor
8991 (and therefore larger records) provides faster throughput and allows you
8992 to fit more data on a tape (because there are fewer gaps). If you are
8993 archiving on cartridge, a very large blocking factor (say 126 or more)
8994 greatly increases performance. A smaller blocking factor, on the other
8995 hand, may be useful when archiving small files, to avoid archiving lots
8996 of nulls as @command{tar} fills out the archive to the end of the record.
8997 In general, the ideal record size depends on the size of the
8998 inter-record gaps on the tape you are using, and the average size of the
8999 files you are archiving. @xref{create}, for information on
9002 @FIXME{Need example of using a cartridge with blocking factor=126 or more.}
9004 Archives with blocking factors larger than 20 cannot be read
9005 by very old versions of @command{tar}, or by some newer versions
9006 of @command{tar} running on old machines with small address spaces.
9007 With @GNUTAR{}, the blocking factor of an archive is limited
9008 only by the maximum record size of the device containing the archive,
9009 or by the amount of available virtual memory.
9011 Also, on some systems, not using adequate blocking factors, as sometimes
9012 imposed by the device drivers, may yield unexpected diagnostics. For
9013 example, this has been reported:
9016 Cannot write to /dev/dlt: Invalid argument
9020 In such cases, it sometimes happen that the @command{tar} bundled by
9021 the system is aware of block size idiosyncrasies, while @GNUTAR{}
9022 requires an explicit specification for the block size,
9023 which it cannot guess. This yields some people to consider
9024 @GNUTAR{} is misbehaving, because by comparison,
9025 @cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}},
9026 for example, might resolve the problem.
9028 If you use a non-default blocking factor when you create an archive, you
9029 must specify the same blocking factor when you modify that archive. Some
9030 archive devices will also require you to specify the blocking factor when
9031 reading that archive, however this is not typically the case. Usually, you
9032 can use @option{--list} (@option{-t}) without specifying a blocking factor---@command{tar}
9033 reports a non-default record size and then lists the archive members as
9034 it would normally. To extract files from an archive with a non-standard
9035 blocking factor (particularly if you're not sure what the blocking factor
9036 is), you can usually use the @option{--read-full-records} (@option{-B}) option while
9037 specifying a blocking factor larger then the blocking factor of the archive
9038 (i.e. @samp{tar --extract --read-full-records --blocking-factor=300}.
9039 @xref{list}, for more information on the @option{--list} (@option{-t})
9040 operation. @xref{Reading}, for a more detailed explanation of that option.
9043 @item --blocking-factor=@var{number}
9044 @itemx -b @var{number}
9045 Specifies the blocking factor of an archive. Can be used with any
9046 operation, but is usually not necessary with @option{--list} (@option{-t}).
9052 @item -b @var{blocks}
9053 @itemx --blocking-factor=@var{blocks}
9054 Set record size to @math{@var{blocks} * 512} bytes.
9056 This option is used to specify a @dfn{blocking factor} for the archive.
9057 When reading or writing the archive, @command{tar}, will do reads and writes
9058 of the archive in records of @math{@var{block}*512} bytes. This is true
9059 even when the archive is compressed. Some devices requires that all
9060 write operations be a multiple of a certain size, and so, @command{tar}
9061 pads the archive out to the next record boundary.
9063 The default blocking factor is set when @command{tar} is compiled, and is
9064 typically 20. Blocking factors larger than 20 cannot be read by very
9065 old versions of @command{tar}, or by some newer versions of @command{tar}
9066 running on old machines with small address spaces.
9068 With a magnetic tape, larger records give faster throughput and fit
9069 more data on a tape (because there are fewer inter-record gaps).
9070 If the archive is in a disk file or a pipe, you may want to specify
9071 a smaller blocking factor, since a large one will result in a large
9072 number of null bytes at the end of the archive.
9074 When writing cartridge or other streaming tapes, a much larger
9075 blocking factor (say 126 or more) will greatly increase performance.
9076 However, you must specify the same blocking factor when reading or
9077 updating the archive.
9079 Apparently, Exabyte drives have a physical block size of 8K bytes.
9080 If we choose our blocksize as a multiple of 8k bytes, then the problem
9081 seems to disappear. Id est, we are using block size of 112 right
9082 now, and we haven't had the problem since we switched@dots{}
9084 With @GNUTAR{} the blocking factor is limited only
9085 by the maximum record size of the device containing the archive, or by
9086 the amount of available virtual memory.
9088 However, deblocking or reblocking is virtually avoided in a special
9089 case which often occurs in practice, but which requires all the
9090 following conditions to be simultaneously true:
9093 the archive is subject to a compression option,
9095 the archive is not handled through standard input or output, nor
9096 redirected nor piped,
9098 the archive is directly handled to a local disk, instead of any special
9101 @option{--blocking-factor} is not explicitly specified on the @command{tar}
9105 If the output goes directly to a local disk, and not through
9106 stdout, then the last write is not extended to a full record size.
9107 Otherwise, reblocking occurs. Here are a few other remarks on this
9113 @command{gzip} will complain about trailing garbage if asked to
9114 uncompress a compressed archive on tape, there is an option to turn
9115 the message off, but it breaks the regularity of simply having to use
9116 @samp{@var{prog} -d} for decompression. It would be nice if gzip was
9117 silently ignoring any number of trailing zeros. I'll ask Jean-loup
9118 Gailly, by sending a copy of this message to him.
9121 @command{compress} does not show this problem, but as Jean-loup pointed
9122 out to Michael, @samp{compress -d} silently adds garbage after
9123 the result of decompression, which tar ignores because it already
9124 recognized its end-of-file indicator. So this bug may be safely
9128 @samp{gzip -d -q} will be silent about the trailing zeros indeed,
9129 but will still return an exit status of 2 which tar reports in turn.
9130 @command{tar} might ignore the exit status returned, but I hate doing
9131 that, as it weakens the protection @command{tar} offers users against
9132 other possible problems at decompression time. If @command{gzip} was
9133 silently skipping trailing zeros @emph{and} also avoiding setting the
9134 exit status in this innocuous case, that would solve this situation.
9137 @command{tar} should become more solid at not stopping to read a pipe at
9138 the first null block encountered. This inelegantly breaks the pipe.
9139 @command{tar} should rather drain the pipe out before exiting itself.
9142 @xopindex{ignore-zeros, short description}
9144 @itemx --ignore-zeros
9145 Ignore blocks of zeros in archive (means EOF).
9147 The @option{--ignore-zeros} (@option{-i}) option causes @command{tar} to ignore blocks
9148 of zeros in the archive. Normally a block of zeros indicates the
9149 end of the archive, but when reading a damaged archive, or one which
9150 was created by concatenating several archives together, this option
9151 allows @command{tar} to read the entire archive. This option is not on
9152 by default because many versions of @command{tar} write garbage after
9155 Note that this option causes @command{tar} to read to the end of the
9156 archive file, which may sometimes avoid problems when multiple files
9157 are stored on a single physical tape.
9159 @xopindex{read-full-records, short description}
9161 @itemx --read-full-records
9162 Reblock as we read (for reading 4.2BSD pipes).
9164 If @option{--read-full-records} is used, @command{tar}
9165 will not panic if an attempt to read a record from the archive does
9166 not return a full record. Instead, @command{tar} will keep reading
9167 until it has obtained a full
9170 This option is turned on by default when @command{tar} is reading
9171 an archive from standard input, or from a remote machine. This is
9172 because on BSD Unix systems, a read of a pipe will return however
9173 much happens to be in the pipe, even if it is less than @command{tar}
9174 requested. If this option was not used, @command{tar} would fail as
9175 soon as it read an incomplete record from the pipe.
9177 This option is also useful with the commands for updating an archive.
9183 @FIXME{Appropriate options should be moved here from elsewhere.}
9185 @cindex blocking factor
9186 @cindex tape blocking
9188 When handling various tapes or cartridges, you have to take care of
9189 selecting a proper blocking, that is, the number of disk blocks you
9190 put together as a single tape block on the tape, without intervening
9191 tape gaps. A @dfn{tape gap} is a small landing area on the tape
9192 with no information on it, used for decelerating the tape to a
9193 full stop, and for later regaining the reading or writing speed.
9194 When the tape driver starts reading a record, the record has to
9195 be read whole without stopping, as a tape gap is needed to stop the
9196 tape motion without loosing information.
9198 @cindex Exabyte blocking
9199 @cindex DAT blocking
9200 Using higher blocking (putting more disk blocks per tape block) will use
9201 the tape more efficiently as there will be less tape gaps. But reading
9202 such tapes may be more difficult for the system, as more memory will be
9203 required to receive at once the whole record. Further, if there is a
9204 reading error on a huge record, this is less likely that the system will
9205 succeed in recovering the information. So, blocking should not be too
9206 low, nor it should be too high. @command{tar} uses by default a blocking of
9207 20 for historical reasons, and it does not really matter when reading or
9208 writing to disk. Current tape technology would easily accommodate higher
9209 blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs.
9210 We were told that for some DLT drives, the blocking should be a multiple
9211 of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance.
9212 Other manufacturers may use different recommendations for the same tapes.
9213 This might also depends of the buffering techniques used inside modern
9214 tape controllers. Some imposes a minimum blocking, or a maximum blocking.
9215 Others request blocking to be some exponent of two.
9217 So, there is no fixed rule for blocking. But blocking at read time
9218 should ideally be the same as blocking used at write time. At one place
9219 I know, with a wide variety of equipment, they found it best to use a
9220 blocking of 32 to guarantee that their tapes are fully interchangeable.
9222 I was also told that, for recycled tapes, prior erasure (by the same
9223 drive unit that will be used to create the archives) sometimes lowers
9224 the error rates observed at rewriting time.
9226 I might also use @option{--number-blocks} instead of
9227 @option{--block-number}, so @option{--block} will then expand to
9228 @option{--blocking-factor} unambiguously.
9231 @section Many Archives on One Tape
9233 @FIXME{Appropriate options should be moved here from elsewhere.}
9235 @findex ntape @r{device}
9236 Most tape devices have two entries in the @file{/dev} directory, or
9237 entries that come in pairs, which differ only in the minor number for
9238 this device. Let's take for example @file{/dev/tape}, which often
9239 points to the only or usual tape device of a given system. There might
9240 be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler
9241 name is the @emph{rewinding} version of the device, while the name
9242 having @samp{nr} in it is the @emph{no rewinding} version of the same
9245 A rewinding tape device will bring back the tape to its beginning point
9246 automatically when this device is opened or closed. Since @command{tar}
9247 opens the archive file before using it and closes it afterwards, this
9248 means that a simple:
9251 $ @kbd{tar cf /dev/tape @var{directory}}
9255 will reposition the tape to its beginning both prior and after saving
9256 @var{directory} contents to it, thus erasing prior tape contents and
9257 making it so that any subsequent write operation will destroy what has
9260 @cindex tape positioning
9261 So, a rewinding device is normally meant to hold one and only one file.
9262 If you want to put more than one @command{tar} archive on a given tape, you
9263 will need to avoid using the rewinding version of the tape device. You
9264 will also have to pay special attention to tape positioning. Errors in
9265 positioning may overwrite the valuable data already on your tape. Many
9266 people, burnt by past experiences, will only use rewinding devices and
9267 limit themselves to one file per tape, precisely to avoid the risk of
9268 such errors. Be fully aware that writing at the wrong position on a
9269 tape loses all information past this point and most probably until the
9270 end of the tape, and this destroyed information @emph{cannot} be
9273 To save @var{directory-1} as a first archive at the beginning of a
9274 tape, and leave that tape ready for a second archive, you should use:
9277 $ @kbd{mt -f /dev/nrtape rewind}
9278 $ @kbd{tar cf /dev/nrtape @var{directory-1}}
9282 @dfn{Tape marks} are special magnetic patterns written on the tape
9283 media, which are later recognizable by the reading hardware. These
9284 marks are used after each file, when there are many on a single tape.
9285 An empty file (that is to say, two tape marks in a row) signal the
9286 logical end of the tape, after which no file exist. Usually,
9287 non-rewinding tape device drivers will react to the close request issued
9288 by @command{tar} by first writing two tape marks after your archive, and by
9289 backspacing over one of these. So, if you remove the tape at that time
9290 from the tape drive, it is properly terminated. But if you write
9291 another file at the current position, the second tape mark will be
9292 erased by the new information, leaving only one tape mark between files.
9294 So, you may now save @var{directory-2} as a second archive after the
9295 first on the same tape by issuing the command:
9298 $ @kbd{tar cf /dev/nrtape @var{directory-2}}
9302 and so on for all the archives you want to put on the same tape.
9304 Another usual case is that you do not write all the archives the same
9305 day, and you need to remove and store the tape between two archive
9306 sessions. In general, you must remember how many files are already
9307 saved on your tape. Suppose your tape already has 16 files on it, and
9308 that you are ready to write the 17th. You have to take care of skipping
9309 the first 16 tape marks before saving @var{directory-17}, say, by using
9313 $ @kbd{mt -f /dev/nrtape rewind}
9314 $ @kbd{mt -f /dev/nrtape fsf 16}
9315 $ @kbd{tar cf /dev/nrtape @var{directory-17}}
9318 In all the previous examples, we put aside blocking considerations, but
9319 you should do the proper things for that as well. @xref{Blocking}.
9322 * Tape Positioning:: Tape Positions and Tape Marks
9323 * mt:: The @command{mt} Utility
9326 @node Tape Positioning
9327 @subsection Tape Positions and Tape Marks
9330 Just as archives can store more than one file from the file system,
9331 tapes can store more than one archive file. To keep track of where
9332 archive files (or any other type of file stored on tape) begin and
9333 end, tape archive devices write magnetic @dfn{tape marks} on the
9334 archive media. Tape drives write one tape mark between files,
9335 two at the end of all the file entries.
9337 If you think of data as a series of records "rrrr"'s, and tape marks as
9338 "*"'s, a tape might look like the following:
9341 rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
9344 Tape devices read and write tapes using a read/write @dfn{tape
9345 head}---a physical part of the device which can only access one
9346 point on the tape at a time. When you use @command{tar} to read or
9347 write archive data from a tape device, the device will begin reading
9348 or writing from wherever on the tape the tape head happens to be,
9349 regardless of which archive or what part of the archive the tape
9350 head is on. Before writing an archive, you should make sure that no
9351 data on the tape will be overwritten (unless it is no longer needed).
9352 Before reading an archive, you should make sure the tape head is at
9353 the beginning of the archive you want to read. You can do it manually
9354 via @code{mt} utility (@pxref{mt}). The @code{restore} script does
9355 that automatically (@pxref{Scripted Restoration}).
9357 If you want to add new archive file entries to a tape, you should
9358 advance the tape to the end of the existing file entries, backspace
9359 over the last tape mark, and write the new archive file. If you were
9360 to add two archives to the example above, the tape might look like the
9364 rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
9368 @subsection The @command{mt} Utility
9371 @FIXME{Is it true that this only works on non-block devices?
9372 should explain the difference, (fixed or variable).}
9373 @xref{Blocking Factor}.
9375 You can use the @command{mt} utility to advance or rewind a tape past a
9376 specified number of archive files on the tape. This will allow you
9377 to move to the beginning of an archive before extracting or reading
9378 it, or to the end of all the archives before writing a new one.
9379 @FIXME{Why isn't there an "advance 'til you find two tape marks
9382 The syntax of the @command{mt} command is:
9385 @kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
9388 where @var{tapename} is the name of the tape device, @var{number} is
9389 the number of times an operation is performed (with a default of one),
9390 and @var{operation} is one of the following:
9392 @FIXME{is there any use for record operations?}
9397 Writes @var{number} tape marks at the current position on the tape.
9400 Moves tape position forward @var{number} files.
9403 Moves tape position back @var{number} files.
9406 Rewinds the tape. (Ignores @var{number}).
9410 Rewinds the tape and takes the tape device off-line. (Ignores @var{number}).
9413 Prints status information about the tape unit.
9417 @FIXME{Is there a better way to frob the spacing on the list?}
9419 If you don't specify a @var{tapename}, @command{mt} uses the environment
9420 variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
9421 the default device specified in your @file{sys/mtio.h} file
9422 (@code{DEFTAPE} variable). If this is not defined, the program will
9423 display a descriptive error message and exit with code 1.
9425 @command{mt} returns a 0 exit status when the operation(s) were
9426 successful, 1 if the command was unrecognized, and 2 if an operation
9429 @node Using Multiple Tapes
9430 @section Using Multiple Tapes
9433 Often you might want to write a large archive, one larger than will fit
9434 on the actual tape you are using. In such a case, you can run multiple
9435 @command{tar} commands, but this can be inconvenient, particularly if you
9436 are using options like @option{--exclude=@var{pattern}} or dumping entire file systems.
9437 Therefore, @command{tar} supports multiple tapes automatically.
9439 Use @option{--multi-volume} (@option{-M}) on the command line, and
9440 then @command{tar} will, when it reaches the end of the tape, prompt
9441 for another tape, and continue the archive. Each tape will have an
9442 independent archive, and can be read without needing the other. (As
9443 an exception to this, the file that @command{tar} was archiving when
9444 it ran out of tape will usually be split between the two archives; in
9445 this case you need to extract from the first archive, using
9446 @option{--multi-volume}, and then put in the second tape when
9447 prompted, so @command{tar} can restore both halves of the file.)
9449 @GNUTAR{} multi-volume archives do not use a truly portable format.
9450 You need @GNUTAR{} at both ends to process them properly.
9452 When prompting for a new tape, @command{tar} accepts any of the following
9457 Request @command{tar} to explain possible responses
9459 Request @command{tar} to exit immediately.
9460 @item n @var{file-name}
9461 Request @command{tar} to write the next volume on the file @var{file-name}.
9463 Request @command{tar} to run a subshell. This option can be disabled
9464 by giving @option{--restrict} command line option to @command{tar}.
9466 Request @command{tar} to begin writing the next volume.
9469 (You should only type @samp{y} after you have changed the tape;
9470 otherwise @command{tar} will write over the volume it just finished.)
9472 @cindex End-of-archive info script
9474 @anchor{info-script}
9475 @opindex info-script
9476 @opindex new-volume-script
9477 If you want more elaborate behavior than this, give @command{tar} the
9478 @option{--info-script=@var{script-name}}
9479 (@option{--new-volume-script=@var{script-name}}, @option{-F
9480 @var{script-name}}) option. The file @var{script-name} is expected to
9481 be a program (or shell script) to be run instead of the normal
9482 prompting procedure. It is executed without any command line
9483 arguments. Additional data is passed to it via the following
9484 environment variables:
9487 @vrindex TAR_VERSION, info script environment variable
9489 @GNUTAR{} version number.
9491 @vrindex TAR_ARCHIVE, info script environment variable
9493 The name of the archive @command{tar} is processing.
9495 @vrindex TAR_VOLUME, info script environment variable
9497 Ordinal number of the volume @command{tar} is about to start.
9499 @vrindex TAR_SUBCOMMAND, info script environment variable
9500 @item TAR_SUBCOMMAND
9501 Short option describing the operation @command{tar} is executing
9502 @xref{Operations}, for a complete list of subcommand options.
9504 @vrindex TAR_FORMAT, info script environment variable
9506 Format of the archive being processed. @xref{Formats}, for a complete
9507 list of archive format names.
9510 The info script can instruct @command{tar} to use new archive name,
9511 by writing in to file descriptor 3 (see below for an
9514 If the info script fails, @command{tar} exits; otherwise, it begins
9515 writing the next volume.
9517 The method @command{tar} uses to detect end of tape is not perfect, and
9518 fails on some operating systems or on some devices. You can use the
9519 @option{--tape-length=@var{size}} (@option{-L @var{size}}) option if
9520 @command{tar} can't detect the end of the tape itself. This option
9521 selects @option{--multi-volume} (@option{-M}) automatically. The
9522 @var{size} argument should then be the usable size of the tape in
9523 units of 1024 bytes. But for many devices, and floppy disks in
9524 particular, this option is never required for real, as far as we know.
9526 @cindex Volume number file
9530 The volume number used by @command{tar} in its tape-change prompt
9531 can be changed; if you give the
9532 @option{--volno-file=@var{file-of-number}} option, then
9533 @var{file-of-number} should be an unexisting file to be created, or
9534 else, a file already containing a decimal number. That number will be
9535 used as the volume number of the first volume written. When
9536 @command{tar} is finished, it will rewrite the file with the
9537 now-current volume number. (This does not change the volume number
9538 written on a tape label, as per @ref{label}, it @emph{only} affects
9539 the number used in the prompt.)
9541 If you want @command{tar} to cycle through a series of files or tape
9542 drives, there are three approaches to choose from. First of all, you
9543 can give @command{tar} multiple @option{--file} options. In this case
9544 the specified files will be used, in sequence, as the successive
9545 volumes of the archive. Only when the first one in the sequence needs
9546 to be used again will @command{tar} prompt for a tape change (or run
9547 the info script). Secondly, you can use the @samp{n} response to the
9548 tape-change prompt, and, finally, you can use an info script, that
9549 writes new archive name to file descriptor. The following example
9550 illustrates this approach:
9555 echo Preparing volume $TAR_VOLUME of $TAR_ARCHIVE.
9557 name=`expr $TAR_ARCHIVE : '\(.*\)-.*'`
9558 case $TAR_SUBCOMMAND in
9560 -d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
9565 echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&3
9569 Each volume of a multi-volume archive is an independent @command{tar}
9570 archive, complete in itself. For example, you can list or extract any
9571 volume alone; just don't specify @option{--multi-volume}
9572 (@option{-M}). However, if one file in the archive is split across
9573 volumes, the only way to extract it successfully is with a
9574 multi-volume extract command @option{--extract --multi-volume}
9575 (@option{-xM}) starting on or before the volume where the file begins.
9577 For example, let's presume someone has two tape drives on a system
9578 named @file{/dev/tape0} and @file{/dev/tape1}. For having @GNUTAR{}
9579 to switch to the second drive when it needs to write the
9580 second tape, and then back to the first tape, etc., just do either of:
9583 $ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
9584 $ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
9588 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
9589 * Tape Files:: Tape Files
9590 * Tarcat:: Concatenate Volumes into a Single Archive
9594 @node Multi-Volume Archives
9595 @subsection Archives Longer than One Tape or Disk
9596 @cindex Multi-volume archives
9599 @opindex multi-volume
9600 To create an archive that is larger than will fit on a single unit of
9601 the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
9602 the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
9603 archive can be manipulated like any other archive (provided the
9604 @option{--multi-volume} option is specified), but is stored on more
9605 than one tape or disk.
9607 When you specify @option{--multi-volume}, @command{tar} does not report an
9608 error when it comes to the end of an archive volume (when reading), or
9609 the end of the media (when writing). Instead, it prompts you to load
9610 a new storage volume. If the archive is on a magnetic tape, you
9611 should change tapes when you see the prompt; if the archive is on a
9612 floppy disk, you should change disks; etc.
9614 You can read each individual volume of a multi-volume archive as if it
9615 were an archive by itself. For example, to list the contents of one
9616 volume, use @option{--list}, without @option{--multi-volume} specified.
9617 To extract an archive member from one volume (assuming it is described
9618 that volume), use @option{--extract}, again without
9619 @option{--multi-volume}.
9621 If an archive member is split across volumes (i.e. its entry begins on
9622 one volume of the media and ends on another), you need to specify
9623 @option{--multi-volume} to extract it successfully. In this case, you
9624 should load the volume where the archive member starts, and use
9625 @samp{tar --extract --multi-volume}---@command{tar} will prompt for later
9626 volumes as it needs them. @xref{extracting archives}, for more
9627 information about extracting archives.
9629 @option{--info-script=@var{script-name}}
9630 (@option{--new-volume-script=@var{script-name}}, @option{-F
9631 @var{script-name}}) (@pxref{info-script}) is like
9632 @option{--multi-volume} (@option{-M}), except that @command{tar} does
9633 not prompt you directly to change media volumes when a volume is
9634 full---instead, @command{tar} runs commands you have stored in
9635 @var{script-name}. For example, this option can be used to eject
9636 cassettes, or to broadcast messages such as @samp{Someone please come
9637 change my tape} when performing unattended backups. When
9638 @var{script-name} is done, @command{tar} will assume that the media
9641 Multi-volume archives can be modified like any other archive. To add
9642 files to a multi-volume archive, you need to only mount the last
9643 volume of the archive media (and new volumes, if needed). For all
9644 other operations, you need to use the entire archive.
9646 If a multi-volume archive was labeled using
9647 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
9648 (@pxref{label}) when it was created, @command{tar} will not
9649 automatically label volumes which are added later. To label
9650 subsequent volumes, specify @option{--label=@var{archive-label}} again
9651 in conjunction with the @option{--append}, @option{--update} or
9652 @option{--concatenate} operation.
9654 @cindex Labeling multi-volume archives
9657 @FIXME{There should be a sample program here, including an exit
9658 before end. Is the exit status even checked in tar? :-(}
9661 @item --multi-volume
9663 Creates a multi-volume archive, when used in conjunction with
9664 @option{--create} (@option{-c}). To perform any other operation on a multi-volume
9665 archive, specify @option{--multi-volume} in conjunction with that
9668 @item --info-script=@var{program-file}
9669 @itemx --new-volume-script=@var{program-file}
9670 @itemx -F @var{program-file}
9671 Creates a multi-volume archive via a script. Used in conjunction with
9672 @option{--create} (@option{-c}). @xref{info-script}, dor a detailed discussion.
9675 Beware that there is @emph{no} real standard about the proper way, for
9676 a @command{tar} archive, to span volume boundaries. If you have a
9677 multi-volume created by some vendor's @command{tar}, there is almost
9678 no chance you could read all the volumes with @GNUTAR{}.
9679 The converse is also true: you may not expect
9680 multi-volume archives created by @GNUTAR{} to be
9681 fully recovered by vendor's @command{tar}. Since there is little
9682 chance that, in mixed system configurations, some vendor's
9683 @command{tar} will work on another vendor's machine, and there is a
9684 great chance that @GNUTAR{} will work on most of
9685 them, your best bet is to install @GNUTAR{} on all
9686 machines between which you know exchange of files is possible.
9689 @subsection Tape Files
9692 To give the archive a name which will be recorded in it, use the
9693 @option{--label=@var{volume-label}} (@option{-V @var{volume-label}})
9694 option. This will write a special block identifying
9695 @var{volume-label} as the name of the archive to the front of the
9696 archive which will be displayed when the archive is listed with
9697 @option{--list}. If you are creating a multi-volume archive with
9698 @option{--multi-volume} (@pxref{Using Multiple Tapes}), then the
9699 volume label will have @samp{Volume @var{nnn}} appended to the name
9700 you give, where @var{nnn} is the number of the volume of the archive.
9701 (If you use the @option{--label=@var{volume-label}}) option when
9702 reading an archive, it checks to make sure the label on the tape
9703 matches the one you give. @xref{label}.
9705 When @command{tar} writes an archive to tape, it creates a single
9706 tape file. If multiple archives are written to the same tape, one
9707 after the other, they each get written as separate tape files. When
9708 extracting, it is necessary to position the tape at the right place
9709 before running @command{tar}. To do this, use the @command{mt} command.
9710 For more information on the @command{mt} command and on the organization
9711 of tapes into a sequence of tape files, see @ref{mt}.
9713 People seem to often do:
9716 @kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
9719 or such, for pushing a common date in all volumes or an archive set.
9722 @subsection Concatenate Volumes into a Single Archive
9725 Sometimes it is necessary to convert existing @GNUTAR{} multi-volume
9726 archive to a single @command{tar} archive. Simply concatenating all
9727 volumes into one will not work, since each volume carries an additional
9728 information at the beginning. @GNUTAR{} is shipped with the shell
9729 script @command{tarcat} designed for this purpose.
9731 The script takes a list of files comprising a multi-volume archive
9732 and creates the resulting archive at the standard output. For example:
9735 @kbd{tarcat vol.1 vol.2 vol.3 | tar tf -}
9738 The script implements a simple heuristics to determine the format of
9739 the first volume file and to decide how to process the rest of the
9740 files. However, it makes no attempt to verify whether the files are
9741 given in order or even if they are valid @command{tar} archives.
9742 It uses @command{dd} and does not filter its standard error, so you
9743 will usually see lots of spurious messages.
9745 @FIXME{The script is not installed. Should we install it?}
9748 @section Including a Label in the Archive
9749 @cindex Labeling an archive
9750 @cindex Labels on the archive media
9754 To avoid problems caused by misplaced paper labels on the archive
9755 media, you can include a @dfn{label} entry---an archive member which
9756 contains the name of the archive---in the archive itself. Use the
9757 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
9758 option in conjunction with the @option{--create} operation to include
9759 a label entry in the archive as it is being created.
9762 @item --label=@var{archive-label}
9763 @itemx -V @var{archive-label}
9764 Includes an @dfn{archive-label} at the beginning of the archive when
9765 the archive is being created, when used in conjunction with the
9766 @option{--create} operation. Checks to make sure the archive label
9767 matches the one specified (when used in conjunction with any other
9771 If you create an archive using both
9772 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
9773 and @option{--multi-volume} (@option{-M}), each volume of the archive
9774 will have an archive label of the form @samp{@var{archive-label}
9775 Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the
9776 next, and so on. @xref{Using Multiple Tapes}, for information on
9777 creating multiple volume archives.
9779 @cindex Volume label, listing
9780 @cindex Listing volume label
9781 The volume label will be displayed by @option{--list} along with
9782 the file contents. If verbose display is requested, it will also be
9783 explicitely marked as in the example below:
9787 $ @kbd{tar --verbose --list --file=iamanarchive}
9788 V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
9789 -rw-r--r-- ringo user 40 1990-05-21 13:30 iamafilename
9794 @anchor{--test-label option}
9795 However, @option{--list} option will cause listing entire
9796 contents of the archive, which may be undesirable (for example, if the
9797 archive is stored on a tape). You can request checking only the volume
9798 by specifying @option{--test-label} option. This option reads only the
9799 first block of an archive, so it can be used with slow storage
9800 devices. For example:
9804 $ @kbd{tar --test-label --file=iamanarchive}
9809 If @option{--test-label} is used with a single command line
9810 argument, @command{tar} compares the volume label with the
9811 argument. It exits with code 0 if the two strings match, and with code
9812 2 otherwise. In this case no output is displayed. For example:
9816 $ @kbd{tar --test-label --file=iamanarchive 'iamalable'}
9818 $ @kbd{tar --test-label --file=iamanarchive 'iamalable' alabel}
9823 If you request any operation, other than @option{--create}, along
9824 with using @option{--label} option, @command{tar} will first check if
9825 the archive label matches the one specified and will refuse to proceed
9826 if it does not. Use this as a safety precaution to avoid accidentally
9827 overwriting existing archives. For example, if you wish to add files
9828 to @file{archive}, presumably labelled with string @samp{My volume},
9833 $ @kbd{tar -rf archive --label 'My volume' .}
9834 tar: Archive not labeled to match `My volume'
9839 in case its label does not match. This will work even if
9840 @file{archive} is not labelled at all.
9842 Similarly, @command{tar} will refuse to list or extract the
9843 archive if its label doesn't match the @var{archive-label}
9844 specified. In those cases, @var{archive-label} argument is interpreted
9845 as a globbing-style pattern which must match the actual magnetic
9846 volume label. @xref{exclude}, for a precise description of how match
9847 is attempted@footnote{Previous versions of @command{tar} used full
9848 regular expression matching, or before that, only exact string
9849 matching, instead of wildcard matchers. We decided for the sake of
9850 simplicity to use a uniform matching device through
9851 @command{tar}.}. If the switch @option{--multi-volume} (@option{-M}) is being used,
9852 the volume label matcher will also suffix @var{archive-label} by
9853 @w{@samp{ Volume [1-9]*}} if the initial match fails, before giving
9854 up. Since the volume numbering is automatically added in labels at
9855 creation time, it sounded logical to equally help the user taking care
9856 of it when the archive is being read.
9858 The @option{--label} was once called @option{--volume}, but is not
9859 available under that name anymore.
9861 You can also use @option{--label} to get a common information on
9862 all tapes of a series. For having this information different in each
9863 series created through a single script used on a regular basis, just
9864 manage to get some date string as part of the label. For example:
9868 $ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
9869 $ @kbd{tar --create --file=/dev/tape --multi-volume \
9870 --volume="Daily backup for `date +%Y-%m-%d`"}
9874 Also note that each label has its own date and time, which corresponds
9875 to when @GNUTAR{} initially attempted to write it,
9876 often soon after the operator launches @command{tar} or types the
9877 carriage return telling that the next tape is ready. Comparing date
9878 labels does give an idea of tape throughput only if the delays for
9879 rewinding tapes and the operator switching them were negligible, which
9880 is usually not the case.
9883 @section Verifying Data as It is Stored
9884 @cindex Verifying a write operation
9885 @cindex Double-checking a write operation
9890 @opindex verify, short description
9891 Attempt to verify the archive after writing.
9894 This option causes @command{tar} to verify the archive after writing it.
9895 Each volume is checked after it is written, and any discrepancies
9896 are recorded on the standard error output.
9898 Verification requires that the archive be on a back-space-able medium.
9899 This means pipes, some cartridge tape drives, and some other devices
9902 You can insure the accuracy of an archive by comparing files in the
9903 system with archive members. @command{tar} can compare an archive to the
9904 file system as the archive is being written, to verify a write
9905 operation, or can compare a previously written archive, to insure that
9908 @xopindex{verify, using with @option{--create}}
9909 @xopindex{create, using with @option{--verify}}
9910 To check for discrepancies in an archive immediately after it is
9911 written, use the @option{--verify} (@option{-W}) option in conjunction with
9912 the @option{--create} operation. When this option is
9913 specified, @command{tar} checks archive members against their counterparts
9914 in the file system, and reports discrepancies on the standard error.
9916 To verify an archive, you must be able to read it from before the end
9917 of the last written entry. This option is useful for detecting data
9918 errors on some tapes. Archives written to pipes, some cartridge tape
9919 drives, and some other devices cannot be verified.
9921 One can explicitly compare an already made archive with the file
9922 system by using the @option{--compare} (@option{--diff}, @option{-d})
9923 option, instead of using the more automatic @option{--verify} option.
9926 Note that these two options have a slightly different intent. The
9927 @option{--compare} option checks how identical are the logical contents of some
9928 archive with what is on your disks, while the @option{--verify} option is
9929 really for checking if the physical contents agree and if the recording
9930 media itself is of dependable quality. So, for the @option{--verify}
9931 operation, @command{tar} tries to defeat all in-memory cache pertaining to
9932 the archive, while it lets the speed optimization undisturbed for the
9933 @option{--compare} option. If you nevertheless use @option{--compare} for
9934 media verification, you may have to defeat the in-memory cache yourself,
9935 maybe by opening and reclosing the door latch of your recording unit,
9936 forcing some doubt in your operating system about the fact this is really
9937 the same volume as the one just written or read.
9939 The @option{--verify} option would not be necessary if drivers were indeed
9940 able to detect dependably all write failures. This sometimes require many
9941 magnetic heads, some able to read after the writes occurred. One would
9942 not say that drivers unable to detect all cases are necessarily flawed,
9943 as long as programming is concerned.
9945 The @option{--verify} (@option{-W}) option will not work in
9946 conjunction with the @option{--multi-volume} (@option{-M}) option or
9947 the @option{--append} (@option{-r}), @option{--update} (@option{-u})
9948 and @option{--delete} operations. @xref{Operations}, for more
9949 information on these operations.
9951 Also, since @command{tar} normally strips leading @samp{/} from file
9952 names (@pxref{absolute}), a command like @samp{tar --verify -cf
9953 /tmp/foo.tar /etc} will work as desired only if the working directory is
9954 @file{/}, as @command{tar} uses the archive's relative member names
9955 (e.g., @file{etc/motd}) when verifying the archive.
9957 @node Write Protection
9958 @section Write Protection
9960 Almost all tapes and diskettes, and in a few rare cases, even disks can
9961 be @dfn{write protected}, to protect data on them from being changed.
9962 Once an archive is written, you should write protect the media to prevent
9963 the archive from being accidentally overwritten or deleted. (This will
9964 protect the archive from being changed with a tape or floppy drive---it
9965 will not protect it from magnet fields or other physical hazards).
9967 The write protection device itself is usually an integral part of the
9968 physical media, and can be a two position (write enabled/write
9969 disabled) switch, a notch which can be popped out or covered, a ring
9970 which can be removed from the center of a tape reel, or some other
9976 This appendix lists some important user-visible changes between
9977 version @GNUTAR{} @value{VERSION} and previous versions. An up-to-date
9978 version of this document is available at
9979 @uref{http://www.gnu.org/@/software/@/tar/manual/changes.html,the
9980 @GNUTAR{} documentation page}.
9983 @item Use of globbing patterns when listing and extracting.
9985 Previous versions of GNU tar assumed shell-style globbing when
9986 extracting from or listing an archive. For example:
9989 $ @kbd{tar xf foo.tar '*.c'}
9992 would extract all files whose names end in @samp{.c}. This behavior
9993 was not documented and was incompatible with traditional tar
9994 implementations. Therefore, starting from version 1.15.91, GNU tar
9995 no longer uses globbing by default. For example, the above invocation
9996 is now interpreted as a request to extract from the archive the file
9999 To facilitate transition to the new behavior for those users who got
10000 used to the previous incorrect one, @command{tar} will print a warning
10001 if it finds out that a requested member was not found in the archive
10002 and its name looks like a globbing pattern. For example:
10005 $ @kbd{tar xf foo.tar '*.c'}
10006 tar: Pattern matching characters used in file names. Please,
10007 tar: use --wildcards to enable pattern matching, or --no-wildcards to
10008 tar: suppress this warning.
10009 tar: *.c: Not found in archive
10010 tar: Error exit delayed from previous errors
10013 To treat member names as globbing patterns, use --wildcards option.
10014 If you want to tar to mimic the behavior of versions prior to 1.15.91,
10015 add this option to your @env{TAR_OPTIONS} variable.
10017 @xref{wildcards}, for the detailed discussion of the use of globbing
10018 patterns by @GNUTAR{}.
10020 @item Use of short option @option{-o}.
10022 Earlier versions of @GNUTAR{} understood @option{-o} command line
10023 option as a synonym for @option{--old-archive}.
10025 @GNUTAR{} starting from version 1.13.90 understands this option as
10026 a synonym for @option{--no-same-owner}. This is compatible with
10027 UNIX98 @command{tar} implementations.
10029 However, to facilitate transition, @option{-o} option retains its
10030 old semantics when it is used with one of archive-creation commands.
10031 Users are encouraged to use @option{--format=oldgnu} instead.
10033 It is especially important, since versions of @acronym{GNU} Automake
10034 up to and including 1.8.4 invoke tar with this option to produce
10035 distribution tarballs. @xref{Formats,v7}, for the detailed discussion
10036 of this issue and its implications.
10038 @FIXME{Change the first argument to tar-formats when the new Automake is
10039 out. The proposition to add @anchor{} to the appropriate place of its
10040 docs was accepted by Automake people --Sergey 2006-05-25}.
10041 @xref{Options, tar-v7, Changing Automake's Behavior,
10042 automake, GNU Automake}, for a description on how to use various
10043 archive formats with @command{automake}.
10045 Future versions of @GNUTAR{} will understand @option{-o} only as a
10046 synonym for @option{--no-same-owner}.
10048 @item Use of short option @option{-l}
10050 Earlier versions of @GNUTAR{} understood @option{-l} option as a
10051 synonym for @option{--one-file-system}. Since such usage contradicted
10052 to UNIX98 specification and harmed compatibility with other
10053 implementation, it was declared deprecated in version 1.14. However,
10054 to facilitate transition to its new semantics, it was supported by
10055 versions 1.15 and 1.15.90. The present use of @option{-l} as a short
10056 variant of @option{--check-links} was introduced in version 1.15.91.
10058 @item Use of options @option{--portability} and @option{--old-archive}
10060 These options are deprecated. Please use @option{--format=v7} instead.
10062 @item Use of option @option{--posix}
10064 This option is deprecated. Please use @option{--format=posix} instead.
10067 @node Configuring Help Summary
10068 @appendix Configuring Help Summary
10070 Running @kbd{tar --help} displays the short @command{tar} option
10071 summary (@pxref{help}). This summary is organised by @dfn{groups} of
10072 semantically close options. The options within each group are printed
10073 in the following order: a short option, eventually followed by a list
10074 of corresponding long option names, followed by a short description of
10075 the option. For example, here is an excerpt from the actual @kbd{tar
10079 Main operation mode:
10081 -A, --catenate, --concatenate append tar files to an archive
10082 -c, --create create a new archive
10083 -d, --diff, --compare find differences between archive and
10085 --delete delete from the archive
10088 @vrindex ARGP_HELP_FMT, environment variable
10089 The exact visual representation of the help output is configurable via
10090 @env{ARGP_HELP_FMT} environment variable. The value of this variable
10091 is a comma-separated list of @dfn{format variable} assignments. There
10092 are two kinds of format variables. An @dfn{offset variable} keeps the
10093 offset of some part of help output text from the leftmost column on
10094 the screen. A @dfn{boolean} variable is a flag that toggles some
10095 output feature on or off. Depending on the type of the corresponding
10096 variable, there are two kinds of assignments:
10099 @item Offset assignment
10101 The assignment to an offset variable has the following syntax:
10104 @var{variable}=@var{value}
10108 where @var{variable} is the variable name, and @var{value} is a
10109 numeric value to be assigned to the variable.
10111 @item Boolean assignment
10113 To assign @code{true} value to a variable, simply put this variable name. To
10114 assign @code{false} value, prefix the variable name with @samp{no-}. For
10119 # Assign @code{true} value:
10121 # Assign @code{false} value:
10127 Following variables are declared:
10129 @deftypevr {Help Output} boolean dup-args
10130 If true, arguments for an option are shown with both short and long
10131 options, even when a given option has both forms, for example:
10134 -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE
10137 If false, then if an option has both short and long forms, the
10138 argument is only shown with the long one, for example:
10141 -f, --file=ARCHIVE use archive file or device ARCHIVE
10145 and a message indicating that the argument is applicable to both
10146 forms is printed below the options. This message can be disabled
10147 using @code{dup-args-note} (see below).
10149 The default is false.
10152 @deftypevr {Help Output} boolean dup-args-note
10153 If this variable is true, which is the default, the following notice
10154 is displayed at the end of the help output:
10157 Mandatory or optional arguments to long options are also mandatory or
10158 optional for any corresponding short options.
10161 Setting @code{no-dup-args-note} inhibits this message. Normally, only one of
10162 variables @code{dup-args} or @code{dup-args-note} should be set.
10165 @deftypevr {Help Output} offset short-opt-col
10166 Column in which short options start. Default is 2.
10170 $ @kbd{tar --help|grep ARCHIVE}
10171 -f, --file=ARCHIVE use archive file or device ARCHIVE
10172 $ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE}
10173 -f, --file=ARCHIVE use archive file or device ARCHIVE
10178 @deftypevr {Help Output} offset long-opt-col
10179 Column in which long options start. Default is 6. For example:
10183 $ @kbd{tar --help|grep ARCHIVE}
10184 -f, --file=ARCHIVE use archive file or device ARCHIVE
10185 $ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE}
10186 -f, --file=ARCHIVE use archive file or device ARCHIVE
10191 @deftypevr {Help Output} offset doc-opt-col
10192 Column in which @dfn{doc options} start. A doc option isn't actually
10193 an option, but rather an arbitrary piece of documentation that is
10194 displayed in much the same manner as the options. For example, in
10195 the description of @option{--format} option:
10199 -H, --format=FORMAT create archive of the given format.
10201 FORMAT is one of the following:
10203 gnu GNU tar 1.13.x format
10204 oldgnu GNU format as per tar <= 1.12
10205 pax POSIX 1003.1-2001 (pax) format
10207 ustar POSIX 1003.1-1988 (ustar) format
10208 v7 old V7 tar format
10213 the format names are doc options. Thus, if you set
10214 @kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output
10215 will look as follows:
10219 -H, --format=FORMAT create archive of the given format.
10221 FORMAT is one of the following:
10223 gnu GNU tar 1.13.x format
10224 oldgnu GNU format as per tar <= 1.12
10225 pax POSIX 1003.1-2001 (pax) format
10227 ustar POSIX 1003.1-1988 (ustar) format
10228 v7 old V7 tar format
10233 @deftypevr {Help Output} offset opt-doc-col
10234 Column in which option description starts. Default is 29.
10238 $ @kbd{tar --help|grep ARCHIVE}
10239 -f, --file=ARCHIVE use archive file or device ARCHIVE
10240 $ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE}
10241 -f, --file=ARCHIVE use archive file or device ARCHIVE
10242 $ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE}
10244 use archive file or device ARCHIVE
10249 Notice, that the description starts on a separate line if
10250 @code{opt-doc-col} value is too small.
10253 @deftypevr {Help Output} offset header-col
10254 Column in which @dfn{group headers} are printed. A group header is a
10255 descriptive text preceding an option group. For example, in the
10259 Main operation mode:
10261 -A, --catenate, --concatenate append tar files to
10263 -c, --create create a new archive
10266 @samp{Main operation mode:} is the group header.
10268 The default value is 1.
10271 @deftypevr {Help Output} offset usage-indent
10272 Indentation of wrapped usage lines. Affects @option{--usage}
10273 output. Default is 12.
10276 @deftypevr {Help Output} offset rmargin
10277 Right margin of the text output. Used for wrapping.
10282 @include genfile.texi
10284 @node Tar Internals
10285 @appendix Tar Internals
10286 @include intern.texi
10288 @node Free Software Needs Free Documentation
10289 @appendix Free Software Needs Free Documentation
10290 @include freemanuals.texi
10292 @node Copying This Manual
10293 @appendix Copying This Manual
10296 * GNU Free Documentation License:: License for copying this manual
10301 @node Index of Command Line Options
10302 @appendix Index of Command Line Options
10304 This appendix contains an index of all @GNUTAR{} long command line
10305 options. The options are listed without the preceeding double-dash.
10306 For a cross-reference of short command line options, @ref{Short Option Summary}.
10319 @c Local variables:
10320 @c texinfo-column-for-description: 32