1 \input texinfo @c -*-texinfo-*-
2 @comment %**start of header
5 @settitle GNU tar @value{VERSION}
14 @c 1. Pay attention to @FIXME{}s and @UNREVISED{}s
15 @c 2. Before creating final variant:
16 @c 2.1. Run `make check-options' to make sure all options are properly
18 @c 2.2. Run `make master-menu' (see comment before the master menu).
20 @include rendition.texi
25 @c Put everything in one index (arbitrarily chosen to be the concept index).
33 This manual is for @acronym{GNU} @command{tar} (version
34 @value{VERSION}, @value{UPDATED}), which creates and extracts files
37 Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
38 2003, 2004, 2005, 2006, 2007 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::
112 * Fixing Snapshot Files::
115 * Free Software Needs Free Documentation::
116 * Copying This Manual::
117 * Index of Command Line Options::
121 --- The Detailed Node Listing ---
125 * Book Contents:: What this Book Contains
126 * Definitions:: Some Definitions
127 * What tar Does:: What @command{tar} Does
128 * Naming tar Archives:: How @command{tar} Archives are Named
129 * Authors:: @GNUTAR{} Authors
130 * Reports:: Reporting bugs or suggestions
132 Tutorial Introduction to @command{tar}
135 * stylistic conventions::
136 * basic tar options:: Basic @command{tar} Operations and Options
137 * frequent operations::
138 * Two Frequent Options::
139 * create:: How to Create Archives
140 * list:: How to List Archives
141 * extract:: How to Extract Members from an Archive
144 Two Frequently Used Options
150 How to Create Archives
152 * prepare for examples::
153 * Creating the archive::
162 How to Extract Members from an Archive
164 * extracting archives::
167 * extracting untrusted archives::
173 * using tar options::
181 The Three Option Styles
183 * Long Options:: Long Option Style
184 * Short Options:: Short Option Style
185 * Old Options:: Old Option Style
186 * Mixing:: Mixing Option Styles
188 All @command{tar} Options
190 * Operation Summary::
192 * Short Option Summary::
204 Advanced @GNUTAR{} Operations
213 How to Add Files to Existing Archives: @option{--append}
215 * appending files:: Appending Files to an Archive
222 Options Used by @option{--create}
224 * override:: Overriding File Metadata.
225 * Ignore Failed Read::
227 Options Used by @option{--extract}
229 * Reading:: Options to Help Read Archives
230 * Writing:: Changing How @command{tar} Writes Files
231 * Scarce:: Coping with Scarce Resources
233 Options to Help Read Archives
235 * read full records::
238 Changing How @command{tar} Writes Files
240 * Dealing with Old Files::
241 * Overwrite Old Files::
246 * Data Modification Times::
247 * Setting Access Permissions::
248 * Directory Modification Times and Permissions::
249 * Writing to Standard Output::
250 * Writing to an External Program::
253 Coping with Scarce Resources
258 Performing Backups and Restoring Files
260 * Full Dumps:: Using @command{tar} to Perform Full Dumps
261 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
262 * Backup Levels:: Levels of Backups
263 * Backup Parameters:: Setting Parameters for Backups and Restoration
264 * Scripted Backups:: Using the Backup Scripts
265 * Scripted Restoration:: Using the Restore Script
267 Setting Parameters for Backups and Restoration
269 * General-Purpose Variables::
270 * Magnetic Tape Control::
272 * backup-specs example:: An Example Text of @file{Backup-specs}
274 Choosing Files and Names for @command{tar}
276 * file:: Choosing the Archive's Name
277 * Selecting Archive Members::
278 * files:: Reading Names from a File
279 * exclude:: Excluding Some Files
280 * wildcards:: Wildcards Patterns and Matching
281 * quoting styles:: Ways of Quoting Special Characters in Names
282 * transform:: Modifying File and Member Names
283 * after:: Operating Only on New Files
284 * recurse:: Descending into Directories
285 * one:: Crossing File System Boundaries
287 Reading Names from a File
293 * problems with exclude::
295 Wildcards Patterns and Matching
297 * controlling pattern-matching::
299 Crossing File System Boundaries
301 * directory:: Changing Directory
302 * absolute:: Absolute File Names
306 * General date syntax:: Common rules.
307 * Calendar date items:: 19 Dec 1994.
308 * Time of day items:: 9:20pm.
309 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
310 * Day of week items:: Monday and others.
311 * Relative items in date strings:: next tuesday, 2 years ago.
312 * Pure numbers in date strings:: 19931219, 1440.
313 * Seconds since the Epoch:: @@1078100502.
314 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
315 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
317 Controlling the Archive Format
319 * Compression:: Using Less Space through Compression
320 * Attributes:: Handling File Attributes
321 * Portability:: Making @command{tar} Archives More Portable
322 * cpio:: Comparison of @command{tar} and @command{cpio}
324 Using Less Space through Compression
326 * gzip:: Creating and Reading Compressed Archives
327 * sparse:: Archiving Sparse Files
329 Making @command{tar} Archives More Portable
331 * Portable Names:: Portable Names
332 * dereference:: Symbolic Links
333 * old:: Old V7 Archives
334 * ustar:: Ustar Archives
335 * gnu:: GNU and old GNU format archives.
336 * posix:: @acronym{POSIX} archives
337 * Checksumming:: Checksumming Problems
338 * Large or Negative Values:: Large files, negative time stamps, etc.
339 * Other Tars:: How to Extract GNU-Specific Data Using
340 Other @command{tar} Implementations
342 @GNUTAR{} and @acronym{POSIX} @command{tar}
344 * PAX keywords:: Controlling Extended Header Keywords.
346 How to Extract GNU-Specific Data Using Other @command{tar} Implementations
348 * Split Recovery:: Members Split Between Volumes
349 * Sparse Recovery:: Sparse Members
351 Tapes and Other Archive Media
353 * Device:: Device selection and switching
354 * Remote Tape Server::
355 * Common Problems and Solutions::
356 * Blocking:: Blocking
357 * Many:: Many archives on one tape
358 * Using Multiple Tapes:: Using Multiple Tapes
359 * label:: Including a Label in the Archive
365 * Format Variations:: Format Variations
366 * Blocking Factor:: The Blocking Factor of an Archive
368 Many Archives on One Tape
370 * Tape Positioning:: Tape Positions and Tape Marks
371 * mt:: The @command{mt} Utility
375 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
376 * Tape Files:: Tape Files
377 * Tarcat:: Concatenate Volumes into a Single Archive
382 * Standard:: Basic Tar Format
383 * Extensions:: @acronym{GNU} Extensions to the Archive Format
384 * Sparse Formats:: Storing Sparse Files
391 * PAX 0:: PAX Format, Versions 0.0 and 0.1
392 * PAX 1:: PAX Format, Version 1.0
396 * Generate Mode:: File Generation Mode.
397 * Status Mode:: File Status Mode.
398 * Exec Mode:: Synchronous Execution mode.
402 * GNU Free Documentation License:: License for copying this manual
408 @chapter Introduction
411 and manipulates @dfn{archives} which are actually collections of
412 many other files; the program provides users with an organized and
413 systematic method for controlling a large amount of data.
414 The name ``tar'' originally came from the phrase ``Tape ARchive'', but
415 archives need not (and these days, typically do not) reside on tapes.
418 * Book Contents:: What this Book Contains
419 * Definitions:: Some Definitions
420 * What tar Does:: What @command{tar} Does
421 * Naming tar Archives:: How @command{tar} Archives are Named
422 * Authors:: @GNUTAR{} Authors
423 * Reports:: Reporting bugs or suggestions
427 @section What this Book Contains
429 The first part of this chapter introduces you to various terms that will
430 recur throughout the book. It also tells you who has worked on @GNUTAR{}
431 and its documentation, and where you should send bug reports
434 The second chapter is a tutorial (@pxref{Tutorial}) which provides a
435 gentle introduction for people who are new to using @command{tar}. It is
436 meant to be self contained, not requiring any reading from subsequent
437 chapters to make sense. It moves from topic to topic in a logical,
438 progressive order, building on information already explained.
440 Although the tutorial is paced and structured to allow beginners to
441 learn how to use @command{tar}, it is not intended solely for beginners.
442 The tutorial explains how to use the three most frequently used
443 operations (@samp{create}, @samp{list}, and @samp{extract}) as well as
444 two frequently used options (@samp{file} and @samp{verbose}). The other
445 chapters do not refer to the tutorial frequently; however, if a section
446 discusses something which is a complex variant of a basic concept, there
447 may be a cross reference to that basic concept. (The entire book,
448 including the tutorial, assumes that the reader understands some basic
449 concepts of using a Unix-type operating system; @pxref{Tutorial}.)
451 The third chapter presents the remaining five operations, and
452 information about using @command{tar} options and option syntax.
454 @FIXME{this sounds more like a @acronym{GNU} Project Manuals Concept [tm] more
455 than the reality. should think about whether this makes sense to say
456 here, or not.} The other chapters are meant to be used as a
457 reference. Each chapter presents everything that needs to be said
458 about a specific topic.
460 One of the chapters (@pxref{Date input formats}) exists in its
461 entirety in other @acronym{GNU} manuals, and is mostly self-contained.
462 In addition, one section of this manual (@pxref{Standard}) contains a
463 big quote which is taken directly from @command{tar} sources.
465 In general, we give both long and short (abbreviated) option names
466 at least once in each section where the relevant option is covered, so
467 that novice readers will become familiar with both styles. (A few
468 options have no short versions, and the relevant sections will
472 @section Some Definitions
476 The @command{tar} program is used to create and manipulate @command{tar}
477 archives. An @dfn{archive} is a single file which contains the contents
478 of many files, while still identifying the names of the files, their
479 owner(s), and so forth. (In addition, archives record access
480 permissions, user and group, size in bytes, and data modification time.
481 Some archives also record the file names in each archived directory, as
482 well as other file and directory information.) You can use @command{tar}
483 to @dfn{create} a new archive in a specified directory.
486 @cindex archive member
489 The files inside an archive are called @dfn{members}. Within this
490 manual, we use the term @dfn{file} to refer only to files accessible in
491 the normal ways (by @command{ls}, @command{cat}, and so forth), and the term
492 @dfn{member} to refer only to the members of an archive. Similarly, a
493 @dfn{file name} is the name of a file, as it resides in the file system,
494 and a @dfn{member name} is the name of an archive member within the
499 The term @dfn{extraction} refers to the process of copying an archive
500 member (or multiple members) into a file in the file system. Extracting
501 all the members of an archive is often called @dfn{extracting the
502 archive}. The term @dfn{unpack} can also be used to refer to the
503 extraction of many or all the members of an archive. Extracting an
504 archive does not destroy the archive's structure, just as creating an
505 archive does not destroy the copies of the files that exist outside of
506 the archive. You may also @dfn{list} the members in a given archive
507 (this is often thought of as ``printing'' them to the standard output,
508 or the command line), or @dfn{append} members to a pre-existing archive.
509 All of these operations can be performed using @command{tar}.
512 @section What @command{tar} Does
515 The @command{tar} program provides the ability to create @command{tar}
516 archives, as well as various other kinds of manipulation. For example,
517 you can use @command{tar} on previously created archives to extract files,
518 to store additional files, or to update or list files which were already
521 Initially, @command{tar} archives were used to store files conveniently on
522 magnetic tape. The name @command{tar} comes from this use; it stands for
523 @code{t}ape @code{ar}chiver. Despite the utility's name, @command{tar} can
524 direct its output to available devices, files, or other programs (using
525 pipes). @command{tar} may even access remote devices or files (as archives).
527 You can use @command{tar} archives in many ways. We want to stress a few
528 of them: storage, backup, and transportation.
530 @FIXME{the following table entries need a bit of work.}
533 Often, @command{tar} archives are used to store related files for
534 convenient file transfer over a network. For example, the
535 @acronym{GNU} Project distributes its software bundled into
536 @command{tar} archives, so that all the files relating to a particular
537 program (or set of related programs) can be transferred as a single
540 A magnetic tape can store several files in sequence. However, the tape
541 has no names for these files; it only knows their relative position on
542 the tape. One way to store several files on one tape and retain their
543 names is by creating a @command{tar} archive. Even when the basic transfer
544 mechanism can keep track of names, as FTP can, the nuisance of handling
545 multiple files, directories, and multiple links makes @command{tar}
548 Archive files are also used for long-term storage. You can think of
549 this as transportation from the present into the future. (It is a
550 science-fiction idiom that you can move through time as well as in
551 space; the idea here is that @command{tar} can be used to move archives in
552 all dimensions, even time!)
555 Because the archive created by @command{tar} is capable of preserving
556 file information and directory structure, @command{tar} is commonly
557 used for performing full and incremental backups of disks. A backup
558 puts a collection of files (possibly pertaining to many users and
559 projects) together on a disk or a tape. This guards against
560 accidental destruction of the information in those files.
561 @GNUTAR{} has special features that allow it to be
562 used to make incremental and full dumps of all the files in a
566 You can create an archive on one system, transfer it to another system,
567 and extract the contents there. This allows you to transport a group of
568 files from one system to another.
571 @node Naming tar Archives
572 @section How @command{tar} Archives are Named
574 Conventionally, @command{tar} archives are given names ending with
575 @samp{.tar}. This is not necessary for @command{tar} to operate properly,
576 but this manual follows that convention in order to accustom readers to
577 it and to make examples more clear.
582 Often, people refer to @command{tar} archives as ``@command{tar} files,'' and
583 archive members as ``files'' or ``entries''. For people familiar with
584 the operation of @command{tar}, this causes no difficulty. However, in
585 this manual, we consistently refer to ``archives'' and ``archive
586 members'' to make learning to use @command{tar} easier for novice users.
589 @section @GNUTAR{} Authors
591 @GNUTAR{} was originally written by John Gilmore,
592 and modified by many people. The @acronym{GNU} enhancements were
593 written by Jay Fenlason, then Joy Kendall, and the whole package has
594 been further maintained by Thomas Bushnell, n/BSG, Fran@,{c}ois
595 Pinard, Paul Eggert, and finally Sergey Poznyakoff with the help of
596 numerous and kind users.
598 We wish to stress that @command{tar} is a collective work, and owes much to
599 all those people who reported problems, offered solutions and other
600 insights, or shared their thoughts and suggestions. An impressive, yet
601 partial list of those contributors can be found in the @file{THANKS}
602 file from the @GNUTAR{} distribution.
604 @FIXME{i want all of these names mentioned, Absolutely. BUT, i'm not
605 sure i want to spell out the history in this detail, at least not for
606 the printed book. i'm just not sure it needs to be said this way.
607 i'll think about it.}
609 @FIXME{History is more important, and surely more interesting, than
610 actual names. Quoting names without history would be meaningless. FP}
612 Jay Fenlason put together a draft of a @GNUTAR{}
613 manual, borrowing notes from the original man page from John Gilmore.
614 This was withdrawn in version 1.11. Thomas Bushnell, n/BSG and Amy
615 Gorin worked on a tutorial and manual for @GNUTAR{}.
616 Fran@,{c}ois Pinard put version 1.11.8 of the manual together by
617 taking information from all these sources and merging them. Melissa
618 Weisshaus finally edited and redesigned the book to create version
619 1.12. The book for versions from 1.14 up to @value{VERSION} were edited
620 by the current maintainer, Sergey Poznyakoff.
622 For version 1.12, Daniel Hagerty contributed a great deal of technical
623 consulting. In particular, he is the primary author of @ref{Backups}.
625 In July, 2003 @GNUTAR{} was put on CVS at savannah.gnu.org
626 (see @url{http://savannah.gnu.org/projects/tar}), and
627 active development and maintenance work has started
628 again. Currently @GNUTAR{} is being maintained by Paul Eggert, Sergey
629 Poznyakoff and Jeff Bailey.
631 Support for @acronym{POSIX} archives was added by Sergey Poznyakoff.
634 @section Reporting bugs or suggestions
637 @cindex reporting bugs
638 If you find problems or have suggestions about this program or manual,
639 please report them to @file{bug-tar@@gnu.org}.
641 When reporting a bug, please be sure to include as much detail as
642 possible, in order to reproduce it. @FIXME{Be more specific, I'd
643 like to make this node as detailed as 'Bug reporting' node in Emacs
647 @chapter Tutorial Introduction to @command{tar}
649 This chapter guides you through some basic examples of three @command{tar}
650 operations: @option{--create}, @option{--list}, and @option{--extract}. If
651 you already know how to use some other version of @command{tar}, then you
652 may not need to read this chapter. This chapter omits most complicated
653 details about how @command{tar} works.
657 * stylistic conventions::
658 * basic tar options:: Basic @command{tar} Operations and Options
659 * frequent operations::
660 * Two Frequent Options::
661 * create:: How to Create Archives
662 * list:: How to List Archives
663 * extract:: How to Extract Members from an Archive
668 @section Assumptions this Tutorial Makes
670 This chapter is paced to allow beginners to learn about @command{tar}
671 slowly. At the same time, we will try to cover all the basic aspects of
672 these three operations. In order to accomplish both of these tasks, we
673 have made certain assumptions about your knowledge before reading this
674 manual, and the hardware you will be using:
678 Before you start to work through this tutorial, you should understand
679 what the terms ``archive'' and ``archive member'' mean
680 (@pxref{Definitions}). In addition, you should understand something
681 about how Unix-type operating systems work, and you should know how to
682 use some basic utilities. For example, you should know how to create,
683 list, copy, rename, edit, and delete files and directories; how to
684 change between directories; and how to figure out where you are in the
685 file system. You should have some basic understanding of directory
686 structure and how files are named according to which directory they are
687 in. You should understand concepts such as standard output and standard
688 input, what various definitions of the term ``argument'' mean, and the
689 differences between relative and absolute file names. @FIXME{and what
693 This manual assumes that you are working from your own home directory
694 (unless we state otherwise). In this tutorial, you will create a
695 directory to practice @command{tar} commands in. When we show file names,
696 we will assume that those names are relative to your home directory.
697 For example, my home directory is @file{/home/fsf/melissa}. All of
698 my examples are in a subdirectory of the directory named by that file
699 name; the subdirectory is called @file{practice}.
702 In general, we show examples of archives which exist on (or can be
703 written to, or worked with from) a directory on a hard disk. In most
704 cases, you could write those archives to, or work with them on any other
705 device, such as a tape drive. However, some of the later examples in
706 the tutorial and next chapter will not work on tape drives.
707 Additionally, working with tapes is much more complicated than working
708 with hard disks. For these reasons, the tutorial does not cover working
709 with tape drives. @xref{Media}, for complete information on using
710 @command{tar} archives with tape drives.
712 @FIXME{this is a cop out. need to add some simple tape drive info.}
715 @node stylistic conventions
716 @section Stylistic Conventions
718 In the examples, @samp{$} represents a typical shell prompt. It
719 precedes lines you should type; to make this more clear, those lines are
720 shown in @kbd{this font}, as opposed to lines which represent the
721 computer's response; those lines are shown in @code{this font}, or
722 sometimes @samp{like this}.
724 @c When we have lines which are too long to be
725 @c displayed in any other way, we will show them like this:
727 @node basic tar options
728 @section Basic @command{tar} Operations and Options
730 @command{tar} can take a wide variety of arguments which specify and define
731 the actions it will have on the particular set of files or the archive.
732 The main types of arguments to @command{tar} fall into one of two classes:
733 operations, and options.
735 Some arguments fall into a class called @dfn{operations}; exactly one of
736 these is both allowed and required for any instance of using @command{tar};
737 you may @emph{not} specify more than one. People sometimes speak of
738 @dfn{operating modes}. You are in a particular operating mode when you
739 have specified the operation which specifies it; there are eight
740 operations in total, and thus there are eight operating modes.
742 The other arguments fall into the class known as @dfn{options}. You are
743 not required to specify any options, and you are allowed to specify more
744 than one at a time (depending on the way you are using @command{tar} at
745 that time). Some options are used so frequently, and are so useful for
746 helping you type commands more carefully that they are effectively
747 ``required''. We will discuss them in this chapter.
749 You can write most of the @command{tar} operations and options in any
750 of three forms: long (mnemonic) form, short form, and old style. Some
751 of the operations and options have no short or ``old'' forms; however,
752 the operations and options which we will cover in this tutorial have
753 corresponding abbreviations. @FIXME{make sure this is still the case,
754 at the end}We will indicate those abbreviations appropriately to get
755 you used to seeing them. (Note that the ``old style'' option forms
756 exist in @GNUTAR{} for compatibility with Unix
757 @command{tar}. In this book we present a full discussion of this way
758 of writing options and operations (@pxref{Old Options}), and we discuss
759 the other two styles of writing options (@xref{Long Options}, and
760 @pxref{Short Options}).
762 In the examples and in the text of this tutorial, we usually use the
763 long forms of operations and options; but the ``short'' forms produce
764 the same result and can make typing long @command{tar} commands easier.
765 For example, instead of typing
768 @kbd{tar --create --verbose --file=afiles.tar apple angst aspic}
774 @kbd{tar -c -v -f afiles.tar apple angst aspic}
780 @kbd{tar -cvf afiles.tar apple angst aspic}
784 For more information on option syntax, see @ref{Advanced tar}. In
785 discussions in the text, when we name an option by its long form, we
786 also give the corresponding short option in parentheses.
788 The term, ``option'', can be confusing at times, since ``operations''
789 are often lumped in with the actual, @emph{optional} ``options'' in certain
790 general class statements. For example, we just talked about ``short and
791 long forms of options and operations''. However, experienced @command{tar}
792 users often refer to these by shorthand terms such as, ``short and long
793 options''. This term assumes that the ``operations'' are included, also.
794 Context will help you determine which definition of ``options'' to use.
796 Similarly, the term ``command'' can be confusing, as it is often used in
797 two different ways. People sometimes refer to @command{tar} ``commands''.
798 A @command{tar} @dfn{command} is the entire command line of user input
799 which tells @command{tar} what to do --- including the operation, options,
800 and any arguments (file names, pipes, other commands, etc.). However,
801 you will also sometimes hear the term ``the @command{tar} command''. When
802 the word ``command'' is used specifically like this, a person is usually
803 referring to the @command{tar} @emph{operation}, not the whole line.
804 Again, use context to figure out which of the meanings the speaker
807 @node frequent operations
808 @section The Three Most Frequently Used Operations
810 Here are the three most frequently used operations (both short and long
811 forms), as well as a brief description of their meanings. The rest of
812 this chapter will cover how to use these operations in detail. We will
813 present the rest of the operations in the next chapter.
818 Create a new @command{tar} archive.
821 List the contents of an archive.
824 Extract one or more members from an archive.
827 @node Two Frequent Options
828 @section Two Frequently Used Options
830 To understand how to run @command{tar} in the three operating modes listed
831 previously, you also need to understand how to use two of the options to
832 @command{tar}: @option{--file} (which takes an archive file as an argument)
833 and @option{--verbose}. (You are usually not @emph{required} to specify
834 either of these options when you run @command{tar}, but they can be very
835 useful in making things more clear and helping you avoid errors.)
844 @unnumberedsubsec The @option{--file} Option
847 @xopindex{file, tutorial}
848 @item --file=@var{archive-name}
849 @itemx -f @var{archive-name}
850 Specify the name of an archive file.
853 You can specify an argument for the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option whenever you
854 use @command{tar}; this option determines the name of the archive file
855 that @command{tar} will work on.
858 If you don't specify this argument, then @command{tar} will examine
859 the environment variable @env{TAPE}. If it is set, its value will be
860 used as the archive name. Otherwise, @command{tar} will use the
861 default archive, determined at the compile time. Usually it is
862 standard output or some physical tape drive attached to your machine
863 (you can verify what the default is by running @kbd{tar
864 --show-defaults}, @pxref{defaults}). If there is no tape drive
865 attached, or the default is not meaningful, then @command{tar} will
866 print an error message. The error message might look roughly like one
870 tar: can't open /dev/rmt8 : No such device or address
871 tar: can't open /dev/rsmt0 : I/O error
875 To avoid confusion, we recommend that you always specify an archive file
876 name by using @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) when writing your @command{tar} commands.
877 For more information on using the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option, see
880 @node verbose tutorial
881 @unnumberedsubsec The @option{--verbose} Option
884 @xopindex{verbose, introduced}
887 Show the files being worked on as @command{tar} is running.
890 @option{--verbose} (@option{-v}) shows details about the results of running
891 @command{tar}. This can be especially useful when the results might not be
892 obvious. For example, if you want to see the progress of @command{tar} as
893 it writes files into the archive, you can use the @option{--verbose}
894 option. In the beginning, you may find it useful to use
895 @option{--verbose} at all times; when you are more accustomed to
896 @command{tar}, you will likely want to use it at certain times but not at
897 others. We will use @option{--verbose} at times to help make something
898 clear, and we will give many examples both using and not using
899 @option{--verbose} to show the differences.
901 Each instance of @option{--verbose} on the command line increases the
902 verbosity level by one, so if you need more details on the output,
905 When reading archives (@option{--list}, @option{--extract},
906 @option{--diff}), @command{tar} by default prints only the names of
907 the members being extracted. Using @option{--verbose} will show a full,
908 @command{ls} style member listing.
910 In contrast, when writing archives (@option{--create}, @option{--append},
911 @option{--update}), @command{tar} does not print file names by
912 default. So, a single @option{--verbose} option shows the file names
913 being added to the archive, while two @option{--verbose} options
914 enable the full listing.
916 For example, to create an archive in verbose mode:
919 $ @kbd{tar -cvf afiles.tar apple angst aspic}
926 Creating the same archive with the verbosity level 2 could give:
929 $ @kbd{tar -cvvf afiles.tar apple angst aspic}
930 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
931 -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst
932 -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
936 This works equally well using short or long forms of options. Using
937 long forms, you would simply write out the mnemonic form of the option
941 $ @kbd{tar --create --verbose --verbose @dots{}}
945 Note that you must double the hyphens properly each time.
947 Later in the tutorial, we will give examples using @w{@option{--verbose
950 @anchor{verbose member listing}
951 The full output consists of six fields:
954 @item File type and permissions in symbolic form.
955 These are displayed in the same format as the first column of
956 @command{ls -l} output (@pxref{What information is listed,
957 format=verbose, Verbose listing, fileutils, GNU file utilities}).
959 @item Owner name and group separated by a slash character.
960 If these data are not available (for example, when listing a @samp{v7} format
961 archive), numeric @acronym{ID} values are printed instead.
963 @item Size of the file, in bytes.
965 @item File modification date in ISO 8601 format.
967 @item File modification time.
970 If the name contains any special characters (white space, newlines,
971 etc.) these are displayed in an unambiguous form using so called
972 @dfn{quoting style}. For the detailed discussion of available styles
973 and on how to use them, see @ref{quoting styles}.
975 Depending on the file type, the name can be followed by some
976 additional information, described in the following table:
979 @item -> @var{link-name}
980 The file or archive member is a @dfn{symbolic link} and
981 @var{link-name} is the name of file it links to.
983 @item link to @var{link-name}
984 The file or archive member is a @dfn{hard link} and @var{link-name} is
985 the name of file it links to.
988 The archive member is an old GNU format long link. You will normally
992 The archive member is an old GNU format long name. You will normally
995 @item --Volume Header--
996 The archive member is a GNU @dfn{volume header} (@pxref{Tape Files}).
998 @item --Continued at byte @var{n}--
999 Encountered only at the beginning of a multi-volume archive
1000 (@pxref{Using Multiple Tapes}). This archive member is a continuation
1001 from the previous volume. The number @var{n} gives the offset where
1002 the original file was split.
1004 @item unknown file type @var{c}
1005 An archive member of unknown type. @var{c} is the type character from
1006 the archive header. If you encounter such a message, it means that
1007 either your archive contains proprietary member types @GNUTAR{} is not
1008 able to handle, or the archive is corrupted.
1013 For example, here is an archive listing containing most of the special
1014 suffixes explained above:
1018 V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header--
1019 -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at
1021 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
1022 lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple
1023 -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues
1024 hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
1032 @unnumberedsubsec Getting Help: Using the @option{--help} Option
1038 The @option{--help} option to @command{tar} prints out a very brief list of
1039 all operations and option available for the current version of
1040 @command{tar} available on your system.
1044 @section How to Create Archives
1047 @cindex Creation of the archive
1048 @cindex Archive, creation of
1049 One of the basic operations of @command{tar} is @option{--create} (@option{-c}), which
1050 you use to create a @command{tar} archive. We will explain
1051 @option{--create} first because, in order to learn about the other
1052 operations, you will find it useful to have an archive available to
1055 To make this easier, in this section you will first create a directory
1056 containing three files. Then, we will show you how to create an
1057 @emph{archive} (inside the new directory). Both the directory, and
1058 the archive are specifically for you to practice on. The rest of this
1059 chapter and the next chapter will show many examples using this
1060 directory and the files you will create: some of those files may be
1061 other directories and other archives.
1063 The three files you will archive in this example are called
1064 @file{blues}, @file{folk}, and @file{jazz}. The archive is called
1065 @file{collection.tar}.
1067 This section will proceed slowly, detailing how to use @option{--create}
1068 in @code{verbose} mode, and showing examples using both short and long
1069 forms. In the rest of the tutorial, and in the examples in the next
1070 chapter, we will proceed at a slightly quicker pace. This section
1071 moves more slowly to allow beginning users to understand how
1072 @command{tar} works.
1075 * prepare for examples::
1076 * Creating the archive::
1082 @node prepare for examples
1083 @subsection Preparing a Practice Directory for Examples
1085 To follow along with this and future examples, create a new directory
1086 called @file{practice} containing files called @file{blues}, @file{folk}
1087 and @file{jazz}. The files can contain any information you like:
1088 ideally, they should contain information which relates to their names,
1089 and be of different lengths. Our examples assume that @file{practice}
1090 is a subdirectory of your home directory.
1092 Now @command{cd} to the directory named @file{practice}; @file{practice}
1093 is now your @dfn{working directory}. (@emph{Please note}: Although
1094 the full file name of this directory is
1095 @file{/@var{homedir}/practice}, in our examples we will refer to
1096 this directory as @file{practice}; the @var{homedir} is presumed.
1098 In general, you should check that the files to be archived exist where
1099 you think they do (in the working directory) by running @command{ls}.
1100 Because you just created the directory and the files and have changed to
1101 that directory, you probably don't need to do that this time.
1103 It is very important to make sure there isn't already a file in the
1104 working directory with the archive name you intend to use (in this case,
1105 @samp{collection.tar}), or that you don't care about its contents.
1106 Whenever you use @samp{create}, @command{tar} will erase the current
1107 contents of the file named by @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) if it exists. @command{tar}
1108 will not tell you if you are about to overwrite an archive unless you
1109 specify an option which does this (@pxref{backup}, for the
1110 information on how to do so). To add files to an existing archive,
1111 you need to use a different option, such as @option{--append} (@option{-r}); see
1112 @ref{append} for information on how to do this.
1114 @node Creating the archive
1115 @subsection Creating the Archive
1117 @xopindex{create, introduced}
1118 To place the files @file{blues}, @file{folk}, and @file{jazz} into an
1119 archive named @file{collection.tar}, use the following command:
1122 $ @kbd{tar --create --file=collection.tar blues folk jazz}
1125 The order of the arguments is not very important, @emph{when using long
1126 option forms}. You could also say:
1129 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1133 However, you can see that this order is harder to understand; this is
1134 why we will list the arguments in the order that makes the commands
1135 easiest to understand (and we encourage you to do the same when you use
1136 @command{tar}, to avoid errors).
1138 Note that the sequence
1139 @option{--file=@-collection.tar} is considered to be @emph{one} argument.
1140 If you substituted any other string of characters for
1141 @kbd{collection.tar}, then that string would become the name of the
1142 archive file you create.
1144 The order of the options becomes more important when you begin to use
1145 short forms. With short forms, if you type commands in the wrong order
1146 (even if you type them correctly in all other ways), you may end up with
1147 results you don't expect. For this reason, it is a good idea to get
1148 into the habit of typing options in the order that makes inherent sense.
1149 @xref{short create}, for more information on this.
1151 In this example, you type the command as shown above: @option{--create}
1152 is the operation which creates the new archive
1153 (@file{collection.tar}), and @option{--file} is the option which lets
1154 you give it the name you chose. The files, @file{blues}, @file{folk},
1155 and @file{jazz}, are now members of the archive, @file{collection.tar}
1156 (they are @dfn{file name arguments} to the @option{--create} operation.
1157 @xref{Choosing}, for the detailed discussion on these.) Now that they are
1158 in the archive, they are called @emph{archive members}, not files.
1159 (@pxref{Definitions,members}).
1161 When you create an archive, you @emph{must} specify which files you
1162 want placed in the archive. If you do not specify any archive
1163 members, @GNUTAR{} will complain.
1165 If you now list the contents of the working directory (@command{ls}), you will
1166 find the archive file listed as well as the files you saw previously:
1169 blues folk jazz collection.tar
1173 Creating the archive @samp{collection.tar} did not destroy the copies of
1174 the files in the directory.
1176 Keep in mind that if you don't indicate an operation, @command{tar} will not
1177 run and will prompt you for one. If you don't name any files, @command{tar}
1178 will complain. You must have write access to the working directory,
1179 or else you will not be able to create an archive in that directory.
1181 @emph{Caution}: Do not attempt to use @option{--create} (@option{-c}) to add files to
1182 an existing archive; it will delete the archive and write a new one.
1183 Use @option{--append} (@option{-r}) instead. @xref{append}.
1185 @node create verbose
1186 @subsection Running @option{--create} with @option{--verbose}
1188 @xopindex{create, using with @option{--verbose}}
1189 @xopindex{verbose, using with @option{--create}}
1190 If you include the @option{--verbose} (@option{-v}) option on the command line,
1191 @command{tar} will list the files it is acting on as it is working. In
1192 verbose mode, the @code{create} example above would appear as:
1195 $ @kbd{tar --create --verbose --file=collection.tar blues folk jazz}
1201 This example is just like the example we showed which did not use
1202 @option{--verbose}, except that @command{tar} generated the remaining lines
1204 (note the different font styles).
1210 In the rest of the examples in this chapter, we will frequently use
1211 @code{verbose} mode so we can show actions or @command{tar} responses that
1212 you would otherwise not see, and which are important for you to
1216 @subsection Short Forms with @samp{create}
1218 As we said before, the @option{--create} (@option{-c}) operation is one of the most
1219 basic uses of @command{tar}, and you will use it countless times.
1220 Eventually, you will probably want to use abbreviated (or ``short'')
1221 forms of options. A full discussion of the three different forms that
1222 options can take appears in @ref{Styles}; for now, here is what the
1223 previous example (including the @option{--verbose} (@option{-v}) option) looks like
1224 using short option forms:
1227 $ @kbd{tar -cvf collection.tar blues folk jazz}
1234 As you can see, the system responds the same no matter whether you use
1235 long or short option forms.
1237 @FIXME{i don't like how this is worded:} One difference between using
1238 short and long option forms is that, although the exact placement of
1239 arguments following options is no more specific when using short forms,
1240 it is easier to become confused and make a mistake when using short
1241 forms. For example, suppose you attempted the above example in the
1245 $ @kbd{tar -cfv collection.tar blues folk jazz}
1249 In this case, @command{tar} will make an archive file called @file{v},
1250 containing the files @file{blues}, @file{folk}, and @file{jazz}, because
1251 the @samp{v} is the closest ``file name'' to the @option{-f} option, and
1252 is thus taken to be the chosen archive file name. @command{tar} will try
1253 to add a file called @file{collection.tar} to the @file{v} archive file;
1254 if the file @file{collection.tar} did not already exist, @command{tar} will
1255 report an error indicating that this file does not exist. If the file
1256 @file{collection.tar} does already exist (e.g., from a previous command
1257 you may have run), then @command{tar} will add this file to the archive.
1258 Because the @option{-v} option did not get registered, @command{tar} will not
1259 run under @samp{verbose} mode, and will not report its progress.
1261 The end result is that you may be quite confused about what happened,
1262 and possibly overwrite a file. To illustrate this further, we will show
1263 you how an example we showed previously would look using short forms.
1268 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1272 is confusing as it is. When shown using short forms, however, it
1273 becomes much more so:
1276 $ @kbd{tar blues -c folk -f collection.tar jazz}
1280 It would be very easy to put the wrong string of characters
1281 immediately following the @option{-f}, but doing that could sacrifice
1284 For this reason, we recommend that you pay very careful attention to
1285 the order of options and placement of file and archive names,
1286 especially when using short option forms. Not having the option name
1287 written out mnemonically can affect how well you remember which option
1288 does what, and therefore where different names have to be placed.
1291 @subsection Archiving Directories
1293 @cindex Archiving Directories
1294 @cindex Directories, Archiving
1295 You can archive a directory by specifying its directory name as a
1296 file name argument to @command{tar}. The files in the directory will be
1297 archived relative to the working directory, and the directory will be
1298 re-created along with its contents when the archive is extracted.
1300 To archive a directory, first move to its superior directory. If you
1301 have followed the previous instructions in this tutorial, you should
1310 This will put you into the directory which contains @file{practice},
1311 i.e., your home directory. Once in the superior directory, you can
1312 specify the subdirectory, @file{practice}, as a file name argument. To
1313 store @file{practice} in the new archive file @file{music.tar}, type:
1316 $ @kbd{tar --create --verbose --file=music.tar practice}
1320 @command{tar} should output:
1327 practice/collection.tar
1330 Note that the archive thus created is not in the subdirectory
1331 @file{practice}, but rather in the current working directory---the
1332 directory from which @command{tar} was invoked. Before trying to archive a
1333 directory from its superior directory, you should make sure you have
1334 write access to the superior directory itself, not only the directory
1335 you are trying archive with @command{tar}. For example, you will probably
1336 not be able to store your home directory in an archive by invoking
1337 @command{tar} from the root directory; @xref{absolute}. (Note
1338 also that @file{collection.tar}, the original archive file, has itself
1339 been archived. @command{tar} will accept any file as a file to be
1340 archived, regardless of its content. When @file{music.tar} is
1341 extracted, the archive file @file{collection.tar} will be re-written
1342 into the file system).
1344 If you give @command{tar} a command such as
1347 $ @kbd{tar --create --file=foo.tar .}
1351 @command{tar} will report @samp{tar: ./foo.tar is the archive; not
1352 dumped}. This happens because @command{tar} creates the archive
1353 @file{foo.tar} in the current directory before putting any files into
1354 it. Then, when @command{tar} attempts to add all the files in the
1355 directory @file{.} to the archive, it notices that the file
1356 @file{./foo.tar} is the same as the archive @file{foo.tar}, and skips
1357 it. (It makes no sense to put an archive into itself.) @GNUTAR{}
1358 will continue in this case, and create the archive
1359 normally, except for the exclusion of that one file. (@emph{Please
1360 note:} Other implementations of @command{tar} may not be so clever;
1361 they will enter an infinite loop when this happens, so you should not
1362 depend on this behavior unless you are certain you are running
1363 @GNUTAR{}. In general, it is wise to always place the archive outside
1364 of the directory being dumped.
1367 @section How to List Archives
1370 Frequently, you will find yourself wanting to determine exactly what a
1371 particular archive contains. You can use the @option{--list}
1372 (@option{-t}) operation to get the member names as they currently
1373 appear in the archive, as well as various attributes of the files at
1374 the time they were archived. For example, you can examine the archive
1375 @file{collection.tar} that you created in the last section with the
1379 $ @kbd{tar --list --file=collection.tar}
1383 The output of @command{tar} would then be:
1392 The archive @file{bfiles.tar} would list as follows:
1401 Be sure to use a @option{--file=@var{archive-name}} (@option{-f
1402 @var{archive-name}}) option just as with @option{--create}
1403 (@option{-c}) to specify the name of the archive.
1405 @xopindex{list, using with @option{--verbose}}
1406 @xopindex{verbose, using with @option{--list}}
1407 If you use the @option{--verbose} (@option{-v}) option with
1408 @option{--list}, then @command{tar} will print out a listing
1409 reminiscent of @w{@samp{ls -l}}, showing owner, file size, and so
1410 forth. This output is described in detail in @ref{verbose member listing}.
1412 If you had used @option{--verbose} (@option{-v}) mode, the example
1413 above would look like:
1416 $ @kbd{tar --list --verbose --file=collection.tar folk}
1417 -rw-r--r-- myself user 62 1990-05-23 10:55 folk
1420 @cindex listing member and file names
1421 @anchor{listing member and file names}
1422 It is important to notice that the output of @kbd{tar --list
1423 --verbose} does not necessarily match that produced by @kbd{tar
1424 --create --verbose} while creating the archive. It is because
1425 @GNUTAR{}, unless told explicitly not to do so, removes some directory
1426 prefixes from file names before storing them in the archive
1427 (@xref{absolute}, for more information). In other
1428 words, in verbose mode @GNUTAR{} shows @dfn{file names} when creating
1429 an archive and @dfn{member names} when listing it. Consider this
1434 $ @kbd{tar cfv archive /etc/mail}
1435 tar: Removing leading `/' from member names
1437 /etc/mail/sendmail.cf
1439 $ @kbd{tar tf archive}
1441 etc/mail/sendmail.cf
1446 @opindex show-stored-names
1447 This default behavior can sometimes be inconvenient. You can force
1448 @GNUTAR{} show member names when creating archive by supplying
1449 @option{--show-stored-names} option.
1452 @item --show-stored-names
1453 Print member (as opposed to @emph{file}) names when creating the archive.
1456 @cindex File name arguments, using @option{--list} with
1457 @xopindex{list, using with file name arguments}
1458 You can specify one or more individual member names as arguments when
1459 using @samp{list}. In this case, @command{tar} will only list the
1460 names of members you identify. For example, @w{@kbd{tar --list
1461 --file=afiles.tar apple}} would only print @file{apple}.
1463 Because @command{tar} preserves file names, these must be specified as
1464 they appear in the archive (i.e., relative to the directory from which
1465 the archive was created). Therefore, it is essential when specifying
1466 member names to @command{tar} that you give the exact member names.
1467 For example, @w{@kbd{tar --list --file=bfiles.tar birds}} would produce an
1468 error message something like @samp{tar: birds: Not found in archive},
1469 because there is no member named @file{birds}, only one named
1470 @file{./birds}. While the names @file{birds} and @file{./birds} name
1471 the same file, @emph{member} names by default are compared verbatim.
1473 However, @w{@kbd{tar --list --file=bfiles.tar baboon}} would respond
1474 with @file{baboon}, because this exact member name is in the archive file
1475 @file{bfiles.tar}. If you are not sure of the exact file name,
1476 use @dfn{globbing patterns}, for example:
1479 $ @kbd{tar --list --file=bfiles.tar --wildcards '*b*'}
1483 will list all members whose name contains @samp{b}. @xref{wildcards},
1484 for a detailed discussion of globbing patterns and related
1485 @command{tar} command line options.
1492 @unnumberedsubsec Listing the Contents of a Stored Directory
1494 To get information about the contents of an archived directory,
1495 use the directory name as a file name argument in conjunction with
1496 @option{--list} (@option{-t}). To find out file attributes, include the
1497 @option{--verbose} (@option{-v}) option.
1499 For example, to find out about files in the directory @file{practice}, in
1500 the archive file @file{music.tar}, type:
1503 $ @kbd{tar --list --verbose --file=music.tar practice}
1506 @command{tar} responds:
1509 drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
1510 -rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues
1511 -rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk
1512 -rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz
1513 -rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar
1516 When you use a directory name as a file name argument, @command{tar} acts on
1517 all the files (including sub-directories) in that directory.
1520 @section How to Extract Members from an Archive
1523 @cindex Retrieving files from an archive
1524 @cindex Resurrecting files from an archive
1527 Creating an archive is only half the job---there is no point in storing
1528 files in an archive if you can't retrieve them. The act of retrieving
1529 members from an archive so they can be used and manipulated as
1530 unarchived files again is called @dfn{extraction}. To extract files
1531 from an archive, use the @option{--extract} (@option{--get} or
1532 @option{-x}) operation. As with @option{--create}, specify the name
1533 of the archive with @option{--file} (@option{-f}) option. Extracting
1534 an archive does not modify the archive in any way; you can extract it
1535 multiple times if you want or need to.
1537 Using @option{--extract}, you can extract an entire archive, or specific
1538 files. The files can be directories containing other files, or not. As
1539 with @option{--create} (@option{-c}) and @option{--list} (@option{-t}), you may use the short or the
1540 long form of the operation without affecting the performance.
1543 * extracting archives::
1544 * extracting files::
1546 * extracting untrusted archives::
1547 * failing commands::
1550 @node extracting archives
1551 @subsection Extracting an Entire Archive
1553 To extract an entire archive, specify the archive file name only, with
1554 no individual file names as arguments. For example,
1557 $ @kbd{tar -xvf collection.tar}
1564 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
1565 -rw-r--r-- me user 21 1996-09-23 16:44 blues
1566 -rw-r--r-- me user 20 1996-09-23 16:44 folk
1569 @node extracting files
1570 @subsection Extracting Specific Files
1572 To extract specific archive members, give their exact member names as
1573 arguments, as printed by @option{--list} (@option{-t}). If you had
1574 mistakenly deleted one of the files you had placed in the archive
1575 @file{collection.tar} earlier (say, @file{blues}), you can extract it
1576 from the archive without changing the archive's structure. Its
1577 contents will be identical to the original file @file{blues} that you
1580 First, make sure you are in the @file{practice} directory, and list the
1581 files in the directory. Now, delete the file, @samp{blues}, and list
1582 the files in the directory again.
1584 You can now extract the member @file{blues} from the archive file
1585 @file{collection.tar} like this:
1588 $ @kbd{tar --extract --file=collection.tar blues}
1592 If you list the files in the directory again, you will see that the file
1593 @file{blues} has been restored, with its original permissions, data
1594 modification times, and owner.@footnote{This is only accidentally
1595 true, but not in general. Whereas modification times are always
1596 restored, in most cases, one has to be root for restoring the owner,
1597 and use a special option for restoring permissions. Here, it just
1598 happens that the restoring user is also the owner of the archived
1599 members, and that the current @code{umask} is compatible with original
1600 permissions.} (These parameters will be identical to those which
1601 the file had when you originally placed it in the archive; any changes
1602 you may have made before deleting the file from the file system,
1603 however, will @emph{not} have been made to the archive member.) The
1604 archive file, @samp{collection.tar}, is the same as it was before you
1605 extracted @samp{blues}. You can confirm this by running @command{tar} with
1606 @option{--list} (@option{-t}).
1608 Remember that as with other operations, specifying the exact member
1609 name is important. @w{@kbd{tar --extract --file=bfiles.tar birds}}
1610 will fail, because there is no member named @file{birds}. To extract
1611 the member named @file{./birds}, you must specify @w{@kbd{tar
1612 --extract --file=bfiles.tar ./birds}}. If you don't remember the
1613 exact member names, use @option{--list} (@option{-t}) option
1614 (@pxref{list}). You can also extract those members that match a
1615 specific @dfn{globbing pattern}. For example, to extract from
1616 @file{bfiles.tar} all files that begin with @samp{b}, no matter their
1617 directory prefix, you could type:
1620 $ @kbd{tar -x -f bfiles.tar --wildcards --no-anchored 'b*'}
1624 Here, @option{--wildcards} instructs @command{tar} to treat
1625 command line arguments as globbing patterns and @option{--no-anchored}
1626 informs it that the patterns apply to member names after any @samp{/}
1627 delimiter. The use of globbing patterns is discussed in detail in
1630 You can extract a file to standard output by combining the above options
1631 with the @option{--to-stdout} (@option{-O}) option (@pxref{Writing to Standard
1634 If you give the @option{--verbose} option, then @option{--extract}
1635 will print the names of the archive members as it extracts them.
1638 @subsection Extracting Files that are Directories
1640 Extracting directories which are members of an archive is similar to
1641 extracting other files. The main difference to be aware of is that if
1642 the extracted directory has the same name as any directory already in
1643 the working directory, then files in the extracted directory will be
1644 placed into the directory of the same name. Likewise, if there are
1645 files in the pre-existing directory with the same names as the members
1646 which you extract, the files from the extracted archive will replace
1647 the files already in the working directory (and possible
1648 subdirectories). This will happen regardless of whether or not the
1649 files in the working directory were more recent than those extracted
1650 (there exist, however, special options that alter this behavior
1653 However, if a file was stored with a directory name as part of its file
1654 name, and that directory does not exist under the working directory when
1655 the file is extracted, @command{tar} will create the directory.
1657 We can demonstrate how to use @option{--extract} to extract a directory
1658 file with an example. Change to the @file{practice} directory if you
1659 weren't there, and remove the files @file{folk} and @file{jazz}. Then,
1660 go back to the parent directory and extract the archive
1661 @file{music.tar}. You may either extract the entire archive, or you may
1662 extract only the files you just deleted. To extract the entire archive,
1663 don't give any file names as arguments after the archive name
1664 @file{music.tar}. To extract only the files you deleted, use the
1668 $ @kbd{tar -xvf music.tar practice/folk practice/jazz}
1674 If you were to specify two @option{--verbose} (@option{-v}) options, @command{tar}
1675 would have displayed more detail about the extracted files, as shown
1676 in the example below:
1679 $ @kbd{tar -xvvf music.tar practice/folk practice/jazz}
1680 -rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz
1681 -rw-r--r-- me user 20 1996-09-23 16:44 practice/folk
1685 Because you created the directory with @file{practice} as part of the
1686 file names of each of the files by archiving the @file{practice}
1687 directory as @file{practice}, you must give @file{practice} as part
1688 of the file names when you extract those files from the archive.
1690 @node extracting untrusted archives
1691 @subsection Extracting Archives from Untrusted Sources
1693 Extracting files from archives can overwrite files that already exist.
1694 If you receive an archive from an untrusted source, you should make a
1695 new directory and extract into that directory, so that you don't have
1696 to worry about the extraction overwriting one of your existing files.
1697 For example, if @file{untrusted.tar} came from somewhere else on the
1698 Internet, and you don't necessarily trust its contents, you can
1699 extract it as follows:
1702 $ @kbd{mkdir newdir}
1704 $ @kbd{tar -xvf ../untrusted.tar}
1707 It is also a good practice to examine contents of the archive
1708 before extracting it, using @option{--list} (@option{-t}) option, possibly combined
1709 with @option{--verbose} (@option{-v}).
1711 @node failing commands
1712 @subsection Commands That Will Fail
1714 Here are some sample commands you might try which will not work, and why
1717 If you try to use this command,
1720 $ @kbd{tar -xvf music.tar folk jazz}
1724 you will get the following response:
1727 tar: folk: Not found in archive
1728 tar: jazz: Not found in archive
1733 This is because these files were not originally @emph{in} the parent
1734 directory @file{..}, where the archive is located; they were in the
1735 @file{practice} directory, and their file names reflect this:
1738 $ @kbd{tar -tvf music.tar}
1744 @FIXME{make sure the above works when going through the examples in
1748 Likewise, if you try to use this command,
1751 $ @kbd{tar -tvf music.tar folk jazz}
1755 you would get a similar response. Members with those names are not in the
1756 archive. You must use the correct member names, or wildcards, in order
1757 to extract the files from the archive.
1759 If you have forgotten the correct names of the files in the archive,
1760 use @w{@kbd{tar --list --verbose}} to list them correctly.
1762 @FIXME{more examples, here? hag thinks it's a good idea.}
1765 @section Going Further Ahead in this Manual
1767 @FIXME{need to write up a node here about the things that are going to
1768 be in the rest of the manual.}
1770 @node tar invocation
1771 @chapter Invoking @GNUTAR{}
1774 This chapter is about how one invokes the @GNUTAR{}
1775 command, from the command synopsis (@pxref{Synopsis}). There are
1776 numerous options, and many styles for writing them. One mandatory
1777 option specifies the operation @command{tar} should perform
1778 (@pxref{Operation Summary}), other options are meant to detail how
1779 this operation should be performed (@pxref{Option Summary}).
1780 Non-option arguments are not always interpreted the same way,
1781 depending on what the operation is.
1783 You will find in this chapter everything about option styles and rules for
1784 writing them (@pxref{Styles}). On the other hand, operations and options
1785 are fully described elsewhere, in other chapters. Here, you will find
1786 only synthetic descriptions for operations and options, together with
1787 pointers to other parts of the @command{tar} manual.
1789 Some options are so special they are fully described right in this
1790 chapter. They have the effect of inhibiting the normal operation of
1791 @command{tar} or else, they globally alter the amount of feedback the user
1792 receives about what is going on. These are the @option{--help} and
1793 @option{--version} (@pxref{help}), @option{--verbose} (@pxref{verbose})
1794 and @option{--interactive} options (@pxref{interactive}).
1798 * using tar options::
1808 @section General Synopsis of @command{tar}
1810 The @GNUTAR{} program is invoked as either one of:
1813 @kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
1814 @kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
1817 The second form is for when old options are being used.
1819 You can use @command{tar} to store files in an archive, to extract them from
1820 an archive, and to do other types of archive manipulation. The primary
1821 argument to @command{tar}, which is called the @dfn{operation}, specifies
1822 which action to take. The other arguments to @command{tar} are either
1823 @dfn{options}, which change the way @command{tar} performs an operation,
1824 or file names or archive members, which specify the files or members
1825 @command{tar} is to act on.
1827 You can actually type in arguments in any order, even if in this manual
1828 the options always precede the other arguments, to make examples easier
1829 to understand. Further, the option stating the main operation mode
1830 (the @command{tar} main command) is usually given first.
1832 Each @var{name} in the synopsis above is interpreted as an archive member
1833 name when the main command is one of @option{--compare}
1834 (@option{--diff}, @option{-d}), @option{--delete}, @option{--extract}
1835 (@option{--get}, @option{-x}), @option{--list} (@option{-t}) or
1836 @option{--update} (@option{-u}). When naming archive members, you
1837 must give the exact name of the member in the archive, as it is
1838 printed by @option{--list}. For @option{--append} (@option{-r}) and
1839 @option{--create} (@option{-c}), these @var{name} arguments specify
1840 the names of either files or directory hierarchies to place in the archive.
1841 These files or hierarchies should already exist in the file system,
1842 prior to the execution of the @command{tar} command.
1844 @command{tar} interprets relative file names as being relative to the
1845 working directory. @command{tar} will make all file names relative
1846 (by removing leading slashes when archiving or restoring files),
1847 unless you specify otherwise (using the @option{--absolute-names}
1848 option). @xref{absolute}, for more information about
1849 @option{--absolute-names}.
1851 If you give the name of a directory as either a file name or a member
1852 name, then @command{tar} acts recursively on all the files and directories
1853 beneath that directory. For example, the name @file{/} identifies all
1854 the files in the file system to @command{tar}.
1856 The distinction between file names and archive member names is especially
1857 important when shell globbing is used, and sometimes a source of confusion
1858 for newcomers. @xref{wildcards}, for more information about globbing.
1859 The problem is that shells may only glob using existing files in the
1860 file system. Only @command{tar} itself may glob on archive members, so when
1861 needed, you must ensure that wildcard characters reach @command{tar} without
1862 being interpreted by the shell first. Using a backslash before @samp{*}
1863 or @samp{?}, or putting the whole argument between quotes, is usually
1864 sufficient for this.
1866 Even if @var{name}s are often specified on the command line, they
1867 can also be read from a text file in the file system, using the
1868 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option.
1870 If you don't use any file name arguments, @option{--append} (@option{-r}),
1871 @option{--delete} and @option{--concatenate} (@option{--catenate},
1872 @option{-A}) will do nothing, while @option{--create} (@option{-c})
1873 will usually yield a diagnostic and inhibit @command{tar} execution.
1874 The other operations of @command{tar} (@option{--list},
1875 @option{--extract}, @option{--compare}, and @option{--update})
1876 will act on the entire contents of the archive.
1879 @cindex return status
1880 Besides successful exits, @GNUTAR{} may fail for
1881 many reasons. Some reasons correspond to bad usage, that is, when the
1882 @command{tar} command is improperly written. Errors may be
1883 encountered later, while encountering an error processing the archive
1884 or the files. Some errors are recoverable, in which case the failure
1885 is delayed until @command{tar} has completed all its work. Some
1886 errors are such that it would not meaningful, or at least risky, to
1887 continue processing: @command{tar} then aborts processing immediately.
1888 All abnormal exits, whether immediate or delayed, should always be
1889 clearly diagnosed on @code{stderr}, after a line stating the nature of
1892 Possible exit codes of @GNUTAR{} are summarized in the following
1897 @samp{Successful termination}.
1900 @samp{Some files differ}. If tar was invoked with @option{--compare}
1901 (@option{--diff}, @option{-d}) command line option, this means that
1902 some files in the archive differ from their disk counterparts
1903 (@pxref{compare}). If tar was given @option{--create},
1904 @option{--append} or @option{--update} option, this exit code means
1905 that some files were changed while being archived and so the resulting
1906 archive does not contain the exact copy of the file set.
1909 @samp{Fatal error}. This means that some fatal, unrecoverable error
1913 If @command{tar} has invoked a subprocess and that subprocess exited with a
1914 nonzero exit code, @command{tar} exits with that code as well.
1915 This can happen, for example, if @command{tar} was given some
1916 compression option (@pxref{gzip}) and the external compressor program
1917 failed. Another example is @command{rmt} failure during backup to the
1918 remote device (@pxref{Remote Tape Server}).
1920 @node using tar options
1921 @section Using @command{tar} Options
1923 @GNUTAR{} has a total of eight operating modes which
1924 allow you to perform a variety of tasks. You are required to choose
1925 one operating mode each time you employ the @command{tar} program by
1926 specifying one, and only one operation as an argument to the
1927 @command{tar} command (two lists of four operations each may be found
1928 at @ref{frequent operations} and @ref{Operations}). Depending on
1929 circumstances, you may also wish to customize how the chosen operating
1930 mode behaves. For example, you may wish to change the way the output
1931 looks, or the format of the files that you wish to archive may require
1932 you to do something special in order to make the archive look right.
1934 You can customize and control @command{tar}'s performance by running
1935 @command{tar} with one or more options (such as @option{--verbose}
1936 (@option{-v}), which we used in the tutorial). As we said in the
1937 tutorial, @dfn{options} are arguments to @command{tar} which are (as
1938 their name suggests) optional. Depending on the operating mode, you
1939 may specify one or more options. Different options will have different
1940 effects, but in general they all change details of the operation, such
1941 as archive format, archive name, or level of user interaction. Some
1942 options make sense with all operating modes, while others are
1943 meaningful only with particular modes. You will likely use some
1944 options frequently, while you will only use others infrequently, or
1945 not at all. (A full list of options is available in @pxref{All Options}.)
1947 @vrindex TAR_OPTIONS, environment variable
1948 @anchor{TAR_OPTIONS}
1949 The @env{TAR_OPTIONS} environment variable specifies default options to
1950 be placed in front of any explicit options. For example, if
1951 @code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as
1952 if the two options @option{-v} and @option{--unlink-first} had been
1953 specified before any explicit options. Option specifications are
1954 separated by whitespace. A backslash escapes the next character, so it
1955 can be used to specify an option containing whitespace or a backslash.
1957 Note that @command{tar} options are case sensitive. For example, the
1958 options @option{-T} and @option{-t} are different; the first requires an
1959 argument for stating the name of a file providing a list of @var{name}s,
1960 while the second does not require an argument and is another way to
1961 write @option{--list} (@option{-t}).
1963 In addition to the eight operations, there are many options to
1964 @command{tar}, and three different styles for writing both: long (mnemonic)
1965 form, short form, and old style. These styles are discussed below.
1966 Both the options and the operations can be written in any of these three
1969 @FIXME{menu at end of this node. need to think of an actual outline
1970 for this chapter; probably do that after stuff from chapter 4 is
1974 @section The Three Option Styles
1976 There are three styles for writing operations and options to the command
1977 line invoking @command{tar}. The different styles were developed at
1978 different times during the history of @command{tar}. These styles will be
1979 presented below, from the most recent to the oldest.
1981 Some options must take an argument. (For example, @option{--file}
1982 (@option{-f})) takes the name of an archive file as an argument. If
1983 you do not supply an archive file name, @command{tar} will use a
1984 default, but this can be confusing; thus, we recommend that you always
1985 supply a specific archive file name.) Where you @emph{place} the
1986 arguments generally depends on which style of options you choose. We
1987 will detail specific information relevant to each option style in the
1988 sections on the different option styles, below. The differences are
1989 subtle, yet can often be very important; incorrect option placement
1990 can cause you to overwrite a number of important files. We urge you
1991 to note these differences, and only use the option style(s) which
1992 makes the most sense to you until you feel comfortable with the others.
1994 Some options @emph{may} take an argument. Such options may have at
1995 most long and short forms, they do not have old style equivalent. The
1996 rules for specifying an argument for such options are stricter than
1997 those for specifying mandatory arguments. Please, pay special
2001 * Long Options:: Long Option Style
2002 * Short Options:: Short Option Style
2003 * Old Options:: Old Option Style
2004 * Mixing:: Mixing Option Styles
2008 @subsection Long Option Style
2010 Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
2011 dashes in a row, e.g., @option{--list}. The long names are more clear than
2012 their corresponding short or old names. It sometimes happens that a
2013 single long option has many different names which are
2014 synonymous, such as @option{--compare} and @option{--diff}. In addition,
2015 long option names can be given unique abbreviations. For example,
2016 @option{--cre} can be used in place of @option{--create} because there is no
2017 other long option which begins with @samp{cre}. (One way to find
2018 this out is by trying it and seeing what happens; if a particular
2019 abbreviation could represent more than one option, @command{tar} will tell
2020 you that that abbreviation is ambiguous and you'll know that that
2021 abbreviation won't work. You may also choose to run @samp{tar --help}
2022 to see a list of options. Be aware that if you run @command{tar} with a
2023 unique abbreviation for the long name of an option you didn't want to
2024 use, you are stuck; @command{tar} will perform the command as ordered.)
2026 Long options are meant to be obvious and easy to remember, and their
2027 meanings are generally easier to discern than those of their
2028 corresponding short options (see below). For example:
2031 $ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
2035 gives a fairly good set of hints about what the command does, even
2036 for those not fully acquainted with @command{tar}.
2038 Long options which require arguments take those arguments
2039 immediately following the option name. There are two ways of
2040 specifying a mandatory argument. It can be separated from the
2041 option name either by an equal sign, or by any amount of
2042 white space characters. For example, the @option{--file} option (which
2043 tells the name of the @command{tar} archive) is given a file such as
2044 @file{archive.tar} as argument by using any of the following notations:
2045 @option{--file=archive.tar} or @option{--file archive.tar}.
2047 In contrast, optional arguments must always be introduced using
2048 an equal sign. For example, the @option{--backup} option takes
2049 an optional argument specifying backup type. It must be used
2050 as @option{--backup=@var{backup-type}}.
2053 @subsection Short Option Style
2055 Most options also have a @dfn{short option} name. Short options start with
2056 a single dash, and are followed by a single character, e.g., @option{-t}
2057 (which is equivalent to @option{--list}). The forms are absolutely
2058 identical in function; they are interchangeable.
2060 The short option names are faster to type than long option names.
2062 Short options which require arguments take their arguments immediately
2063 following the option, usually separated by white space. It is also
2064 possible to stick the argument right after the short option name, using
2065 no intervening space. For example, you might write @w{@option{-f
2066 archive.tar}} or @option{-farchive.tar} instead of using
2067 @option{--file=archive.tar}. Both @option{--file=@var{archive-name}} and
2068 @w{@option{-f @var{archive-name}}} denote the option which indicates a
2069 specific archive, here named @file{archive.tar}.
2071 Short options which take optional arguments take their arguments
2072 immediately following the option letter, @emph{without any intervening
2073 white space characters}.
2075 Short options' letters may be clumped together, but you are not
2076 required to do this (as compared to old options; see below). When
2077 short options are clumped as a set, use one (single) dash for them
2078 all, e.g., @w{@samp{@command{tar} -cvf}}. Only the last option in
2079 such a set is allowed to have an argument@footnote{Clustering many
2080 options, the last of which has an argument, is a rather opaque way to
2081 write options. Some wonder if @acronym{GNU} @code{getopt} should not
2082 even be made helpful enough for considering such usages as invalid.}.
2084 When the options are separated, the argument for each option which requires
2085 an argument directly follows that option, as is usual for Unix programs.
2089 $ @kbd{tar -c -v -b 20 -f /dev/rmt0}
2092 If you reorder short options' locations, be sure to move any arguments
2093 that belong to them. If you do not move the arguments properly, you may
2094 end up overwriting files.
2097 @subsection Old Option Style
2100 Like short options, @dfn{old options} are single letters. However, old options
2101 must be written together as a single clumped set, without spaces separating
2102 them or dashes preceding them@footnote{Beware that if you precede options
2103 with a dash, you are announcing the short option style instead of the
2104 old option style; short options are decoded differently.}. This set
2105 of letters must be the first to appear on the command line, after the
2106 @command{tar} program name and some white space; old options cannot appear
2107 anywhere else. The letter of an old option is exactly the same letter as
2108 the corresponding short option. For example, the old option @samp{t} is
2109 the same as the short option @option{-t}, and consequently, the same as the
2110 long option @option{--list}. So for example, the command @w{@samp{tar
2111 cv}} specifies the option @option{-v} in addition to the operation @option{-c}.
2113 When options that need arguments are given together with the command,
2114 all the associated arguments follow, in the same order as the options.
2115 Thus, the example given previously could also be written in the old
2119 $ @kbd{tar cvbf 20 /dev/rmt0}
2123 Here, @samp{20} is the argument of @option{-b} and @samp{/dev/rmt0} is
2124 the argument of @option{-f}.
2126 On the other hand, this old style syntax makes it difficult to match
2127 option letters with their corresponding arguments, and is often
2128 confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example,
2129 @samp{20} is the argument for @option{-b}, @samp{/dev/rmt0} is the
2130 argument for @option{-f}, and @option{-v} does not have a corresponding
2131 argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f
2132 /dev/rmt0}} is clearer, putting all arguments next to the option they
2135 If you want to reorder the letters in the old option argument, be
2136 sure to reorder any corresponding argument appropriately.
2138 This old way of writing @command{tar} options can surprise even experienced
2139 users. For example, the two commands:
2142 @kbd{tar cfz archive.tar.gz file}
2143 @kbd{tar -cfz archive.tar.gz file}
2147 are quite different. The first example uses @file{archive.tar.gz} as
2148 the value for option @samp{f} and recognizes the option @samp{z}. The
2149 second example, however, uses @file{z} as the value for option
2150 @samp{f} --- probably not what was intended.
2152 Old options are kept for compatibility with old versions of @command{tar}.
2154 This second example could be corrected in many ways, among which the
2155 following are equivalent:
2158 @kbd{tar -czf archive.tar.gz file}
2159 @kbd{tar -cf archive.tar.gz -z file}
2160 @kbd{tar cf archive.tar.gz -z file}
2163 @cindex option syntax, traditional
2164 As far as we know, all @command{tar} programs, @acronym{GNU} and
2165 non-@acronym{GNU}, support old options. @GNUTAR{}
2166 supports them not only for historical reasons, but also because many
2167 people are used to them. For compatibility with Unix @command{tar},
2168 the first argument is always treated as containing command and option
2169 letters even if it doesn't start with @samp{-}. Thus, @samp{tar c} is
2170 equivalent to @w{@samp{tar -c}:} both of them specify the
2171 @option{--create} (@option{-c}) command to create an archive.
2174 @subsection Mixing Option Styles
2176 All three styles may be intermixed in a single @command{tar} command,
2177 so long as the rules for each style are fully
2178 respected@footnote{Before @GNUTAR{} version 1.11.6,
2179 a bug prevented intermixing old style options with long options in
2180 some cases.}. Old style options and either of the modern styles of
2181 options may be mixed within a single @command{tar} command. However,
2182 old style options must be introduced as the first arguments only,
2183 following the rule for old options (old options must appear directly
2184 after the @command{tar} command and some white space). Modern options
2185 may be given only after all arguments to the old options have been
2186 collected. If this rule is not respected, a modern option might be
2187 falsely interpreted as the value of the argument to one of the old
2190 For example, all the following commands are wholly equivalent, and
2191 illustrate the many combinations and orderings of option styles.
2194 @kbd{tar --create --file=archive.tar}
2195 @kbd{tar --create -f archive.tar}
2196 @kbd{tar --create -farchive.tar}
2197 @kbd{tar --file=archive.tar --create}
2198 @kbd{tar --file=archive.tar -c}
2199 @kbd{tar -c --file=archive.tar}
2200 @kbd{tar -c -f archive.tar}
2201 @kbd{tar -c -farchive.tar}
2202 @kbd{tar -cf archive.tar}
2203 @kbd{tar -cfarchive.tar}
2204 @kbd{tar -f archive.tar --create}
2205 @kbd{tar -f archive.tar -c}
2206 @kbd{tar -farchive.tar --create}
2207 @kbd{tar -farchive.tar -c}
2208 @kbd{tar c --file=archive.tar}
2209 @kbd{tar c -f archive.tar}
2210 @kbd{tar c -farchive.tar}
2211 @kbd{tar cf archive.tar}
2212 @kbd{tar f archive.tar --create}
2213 @kbd{tar f archive.tar -c}
2214 @kbd{tar fc archive.tar}
2217 On the other hand, the following commands are @emph{not} equivalent to
2221 @kbd{tar -f -c archive.tar}
2222 @kbd{tar -fc archive.tar}
2223 @kbd{tar -fcarchive.tar}
2224 @kbd{tar -farchive.tarc}
2225 @kbd{tar cfarchive.tar}
2229 These last examples mean something completely different from what the
2230 user intended (judging based on the example in the previous set which
2231 uses long options, whose intent is therefore very clear). The first
2232 four specify that the @command{tar} archive would be a file named
2233 @option{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc},
2234 respectively. The first two examples also specify a single non-option,
2235 @var{name} argument having the value @samp{archive.tar}. The last
2236 example contains only old style option letters (repeating option
2237 @samp{c} twice), not all of which are meaningful (eg., @samp{.},
2238 @samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked
2239 the first sentence of this paragraph..}
2242 @section All @command{tar} Options
2244 The coming manual sections contain an alphabetical listing of all
2245 @command{tar} operations and options, with brief descriptions and cross
2246 references to more in-depth explanations in the body of the manual.
2247 They also contain an alphabetically arranged table of the short option
2248 forms with their corresponding long option. You can use this table as
2249 a reference for deciphering @command{tar} commands in scripts.
2252 * Operation Summary::
2254 * Short Option Summary::
2257 @node Operation Summary
2258 @subsection Operations
2266 Appends files to the end of the archive. @xref{append}.
2268 @opsummary{catenate}
2272 Same as @option{--concatenate}. @xref{concatenate}.
2278 Compares archive members with their counterparts in the file
2279 system, and reports differences in file size, mode, owner,
2280 modification date and contents. @xref{compare}.
2282 @opsummary{concatenate}
2286 Appends other @command{tar} archives to the end of the archive.
2293 Creates a new @command{tar} archive. @xref{create}.
2298 Deletes members from the archive. Don't try this on a archive on a
2299 tape! @xref{delete}.
2305 Same @option{--compare}. @xref{compare}.
2311 Extracts members from the archive into the file system. @xref{extract}.
2317 Same as @option{--extract}. @xref{extract}.
2323 Lists the members in an archive. @xref{list}.
2329 Adds files to the end of the archive, but only if they are newer than
2330 their counterparts already in the archive, or if they do not already
2331 exist in the archive. @xref{update}.
2335 @node Option Summary
2336 @subsection @command{tar} Options
2340 @opsummary{absolute-names}
2341 @item --absolute-names
2344 Normally when creating an archive, @command{tar} strips an initial
2345 @samp{/} from member names. This option disables that behavior.
2348 @opsummary{after-date}
2351 (See @option{--newer}, @pxref{after})
2353 @opsummary{anchored}
2355 A pattern must match an initial subsequence of the name's components.
2356 @xref{controlling pattern-matching}.
2358 @opsummary{atime-preserve}
2359 @item --atime-preserve
2360 @itemx --atime-preserve=replace
2361 @itemx --atime-preserve=system
2363 Attempt to preserve the access time of files when reading them. This
2364 option currently is effective only on files that you own, unless you
2365 have superuser privileges.
2367 @option{--atime-preserve=replace} remembers the access time of a file
2368 before reading it, and then restores the access time afterwards. This
2369 may cause problems if other programs are reading the file at the same
2370 time, as the times of their accesses will be lost. On most platforms
2371 restoring the access time also requires @command{tar} to restore the
2372 data modification time too, so this option may also cause problems if
2373 other programs are writing the file at the same time. (Tar attempts
2374 to detect this situation, but cannot do so reliably due to race
2375 conditions.) Worse, on most platforms restoring the access time also
2376 updates the status change time, which means that this option is
2377 incompatible with incremental backups.
2379 @option{--atime-preserve=system} avoids changing time stamps on files,
2380 without interfering with time stamp updates
2381 caused by other programs, so it works better with incremental backups.
2382 However, it requires a special @code{O_NOATIME} option from the
2383 underlying operating and file system implementation, and it also requires
2384 that searching directories does not update their access times. As of
2385 this writing (November 2005) this works only with Linux, and only with
2386 Linux kernels 2.6.8 and later. Worse, there is currently no reliable
2387 way to know whether this feature actually works. Sometimes
2388 @command{tar} knows that it does not work, and if you use
2389 @option{--atime-preserve=system} then @command{tar} complains and
2390 exits right away. But other times @command{tar} might think that the
2391 option works when it actually does not.
2393 Currently @option{--atime-preserve} with no operand defaults to
2394 @option{--atime-preserve=replace}, but this may change in the future
2395 as support for @option{--atime-preserve=system} improves.
2397 If your operating system does not support
2398 @option{--atime-preserve=@-system}, you might be able to preserve access
2399 times reliably by by using the @command{mount} command. For example,
2400 you can mount the file system read-only, or access the file system via
2401 a read-only loopback mount, or use the @samp{noatime} mount option
2402 available on some systems. However, mounting typically requires
2403 superuser privileges and can be a pain to manage.
2406 @item --backup=@var{backup-type}
2408 Rather than deleting files from the file system, @command{tar} will
2409 back them up using simple or numbered backups, depending upon
2410 @var{backup-type}. @xref{backup}.
2412 @opsummary{block-number}
2413 @item --block-number
2416 With this option present, @command{tar} prints error messages for read errors
2417 with the block number in the archive file. @xref{block-number}.
2419 @opsummary{blocking-factor}
2420 @item --blocking-factor=@var{blocking}
2421 @itemx -b @var{blocking}
2423 Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
2424 record. @xref{Blocking Factor}.
2430 This option tells @command{tar} to read or write archives through
2431 @code{bzip2}. @xref{gzip}.
2433 @opsummary{checkpoint}
2434 @item --checkpoint[=@var{number}]
2436 This option directs @command{tar} to print periodic checkpoint
2437 messages as it reads through the archive. It is intended for when you
2438 want a visual indication that @command{tar} is still running, but
2439 don't want to see @option{--verbose} output. For a detailed
2440 description, see @ref{Progress information}.
2442 @opsummary{check-links}
2445 If this option was given, @command{tar} will check the number of links
2446 dumped for each processed file. If this number does not match the
2447 total number of hard links for the file, a warning message will be
2448 output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2449 synonym for @option{--one-file-system}. The current semantics, which
2450 complies to UNIX98, was introduced with version
2451 1.15.91. @xref{Changes}, for more information.}.
2453 @opsummary{compress}
2454 @opsummary{uncompress}
2459 @command{tar} will use the @command{compress} program when reading or
2460 writing the archive. This allows you to directly act on archives
2461 while saving space. @xref{gzip}.
2463 @opsummary{confirmation}
2464 @item --confirmation
2466 (See @option{--interactive}.) @xref{interactive}.
2468 @opsummary{delay-directory-restore}
2469 @item --delay-directory-restore
2471 Delay setting modification times and permissions of extracted
2472 directories until the end of extraction. @xref{Directory Modification Times and Permissions}.
2474 @opsummary{dereference}
2478 When creating a @command{tar} archive, @command{tar} will archive the
2479 file that a symbolic link points to, rather than archiving the
2480 symlink. @xref{dereference}.
2482 @opsummary{directory}
2483 @item --directory=@var{dir}
2486 When this option is specified, @command{tar} will change its current directory
2487 to @var{dir} before performing any operations. When this option is used
2488 during archive creation, it is order sensitive. @xref{directory}.
2491 @item --exclude=@var{pattern}
2493 When performing operations, @command{tar} will skip files that match
2494 @var{pattern}. @xref{exclude}.
2496 @opsummary{exclude-from}
2497 @item --exclude-from=@var{file}
2498 @itemx -X @var{file}
2500 Similar to @option{--exclude}, except @command{tar} will use the list of
2501 patterns in the file @var{file}. @xref{exclude}.
2503 @opsummary{exclude-caches}
2504 @item --exclude-caches
2506 Exclude from dump any directory containing a valid cache directory
2507 tag file, but still dump the directory node and the tag file itself.
2511 @opsummary{exclude-caches-under}
2512 @item --exclude-caches-under
2514 Exclude from dump any directory containing a valid cache directory
2515 tag file, but still dump the directory node itself.
2519 @opsummary{exclude-caches-all}
2520 @item --exclude-caches-all
2522 Exclude from dump any directory containing a valid cache directory
2523 tag file. @xref{exclude}.
2525 @opsummary{exclude-tag}
2526 @item --exclude-tag=@var{file}
2528 Exclude from dump any directory containing file named @var{file}, but
2529 dump the directory node and @var{file} itself. @xref{exclude}.
2531 @opsummary{exclude-tag-under}
2532 @item --exclude-tag-under=@var{file}
2534 Exclude from dump the contents of any directory containing file
2535 named @var{file}, but dump the directory node itself. @xref{exclude}.
2537 @opsummary{exclude-tag-all}
2538 @item --exclude-tag-all=@var{file}
2540 Exclude from dump any directory containing file named @var{file}.
2544 @item --file=@var{archive}
2545 @itemx -f @var{archive}
2547 @command{tar} will use the file @var{archive} as the @command{tar} archive it
2548 performs operations on, rather than @command{tar}'s compilation dependent
2549 default. @xref{file tutorial}.
2551 @opsummary{files-from}
2552 @item --files-from=@var{file}
2553 @itemx -T @var{file}
2555 @command{tar} will use the contents of @var{file} as a list of archive members
2556 or files to operate on, in addition to those specified on the
2557 command-line. @xref{files}.
2559 @opsummary{force-local}
2562 Forces @command{tar} to interpret the file name given to @option{--file}
2563 as a local file, even if it looks like a remote tape drive name.
2564 @xref{local and remote archives}.
2567 @item --format=@var{format}
2568 @itemx -H @var{format}
2570 Selects output archive format. @var{Format} may be one of the
2575 Creates an archive that is compatible with Unix V7 @command{tar}.
2578 Creates an archive that is compatible with GNU @command{tar} version
2582 Creates archive in GNU tar 1.13 format. Basically it is the same as
2583 @samp{oldgnu} with the only difference in the way it handles long
2587 Creates a @acronym{POSIX.1-1988} compatible archive.
2590 Creates a @acronym{POSIX.1-2001 archive}.
2594 @xref{Formats}, for a detailed discussion of these formats.
2597 @item --group=@var{group}
2599 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
2600 rather than the group from the source file. @var{group} is first decoded
2601 as a group symbolic name, but if this interpretation fails, it has to be
2602 a decimal numeric group @acronym{ID}. @xref{override}.
2604 Also see the comments for the @option{--owner=@var{user}} option.
2614 This option tells @command{tar} to read or write archives through
2615 @command{gzip}, allowing @command{tar} to directly operate on several
2616 kinds of compressed archives transparently. @xref{gzip}.
2622 @command{tar} will print out a short message summarizing the operations and
2623 options to @command{tar} and exit. @xref{help}.
2625 @opsummary{ignore-case}
2627 Ignore case when matching member or file names with
2628 patterns. @xref{controlling pattern-matching}.
2630 @opsummary{ignore-command-error}
2631 @item --ignore-command-error
2632 Ignore exit codes of subprocesses. @xref{Writing to an External Program}.
2634 @opsummary{ignore-failed-read}
2635 @item --ignore-failed-read
2637 Do not exit unsuccessfully merely because an unreadable file was encountered.
2640 @opsummary{ignore-zeros}
2641 @item --ignore-zeros
2644 With this option, @command{tar} will ignore zeroed blocks in the
2645 archive, which normally signals EOF. @xref{Reading}.
2647 @opsummary{incremental}
2651 Informs @command{tar} that it is working with an old
2652 @acronym{GNU}-format incremental backup archive. It is intended
2653 primarily for backwards compatibility only. @xref{Incremental Dumps},
2654 for a detailed discussion of incremental archives.
2656 @opsummary{index-file}
2657 @item --index-file=@var{file}
2659 Send verbose output to @var{file} instead of to standard output.
2661 @opsummary{info-script}
2662 @opsummary{new-volume-script}
2663 @item --info-script=@var{script-file}
2664 @itemx --new-volume-script=@var{script-file}
2665 @itemx -F @var{script-file}
2667 When @command{tar} is performing multi-tape backups, @var{script-file} is run
2668 at the end of each tape. If @var{script-file} exits with nonzero status,
2669 @command{tar} fails immediately. @xref{info-script}, for a detailed
2670 discussion of @var{script-file}.
2672 @opsummary{interactive}
2674 @itemx --confirmation
2677 Specifies that @command{tar} should ask the user for confirmation before
2678 performing potentially destructive options, such as overwriting files.
2681 @opsummary{keep-newer-files}
2682 @item --keep-newer-files
2684 Do not replace existing files that are newer than their archive copies
2685 when extracting files from an archive.
2687 @opsummary{keep-old-files}
2688 @item --keep-old-files
2691 Do not overwrite existing files when extracting files from an archive.
2692 @xref{Keep Old Files}.
2695 @item --label=@var{name}
2696 @itemx -V @var{name}
2698 When creating an archive, instructs @command{tar} to write @var{name}
2699 as a name record in the archive. When extracting or listing archives,
2700 @command{tar} will only operate on archives that have a label matching
2701 the pattern specified in @var{name}. @xref{Tape Files}.
2703 @opsummary{listed-incremental}
2704 @item --listed-incremental=@var{snapshot-file}
2705 @itemx -g @var{snapshot-file}
2707 During a @option{--create} operation, specifies that the archive that
2708 @command{tar} creates is a new @acronym{GNU}-format incremental
2709 backup, using @var{snapshot-file} to determine which files to backup.
2710 With other operations, informs @command{tar} that the archive is in
2711 incremental format. @xref{Incremental Dumps}.
2714 @item --mode=@var{permissions}
2716 When adding files to an archive, @command{tar} will use
2717 @var{permissions} for the archive members, rather than the permissions
2718 from the files. @var{permissions} can be specified either as an octal
2719 number or as symbolic permissions, like with
2720 @command{chmod}. @xref{override}.
2723 @item --mtime=@var{date}
2725 When adding files to an archive, @command{tar} will use @var{date} as
2726 the modification time of members when creating archives, instead of
2727 their actual modification times. The value of @var{date} can be
2728 either a textual date representation (@pxref{Date input formats}) or a
2729 name of the existing file, starting with @samp{/} or @samp{.}. In the
2730 latter case, the modification time of that file is used. @xref{override}.
2732 @opsummary{multi-volume}
2733 @item --multi-volume
2736 Informs @command{tar} that it should create or otherwise operate on a
2737 multi-volume @command{tar} archive. @xref{Using Multiple Tapes}.
2739 @opsummary{new-volume-script}
2740 @item --new-volume-script
2745 @item --newer=@var{date}
2746 @itemx --after-date=@var{date}
2749 When creating an archive, @command{tar} will only add files that have changed
2750 since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it
2751 is taken to be the name of a file whose data modification time specifies
2752 the date. @xref{after}.
2754 @opsummary{newer-mtime}
2755 @item --newer-mtime=@var{date}
2757 Like @option{--newer}, but add only files whose
2758 contents have changed (as opposed to just @option{--newer}, which will
2759 also back up files for which any status information has
2760 changed). @xref{after}.
2762 @opsummary{no-anchored}
2764 An exclude pattern can match any subsequence of the name's components.
2765 @xref{controlling pattern-matching}.
2767 @opsummary{no-delay-directory-restore}
2768 @item --no-delay-directory-restore
2770 Modification times and permissions of extracted
2771 directories are set when all files from this directory have been
2772 extracted. This is the default.
2773 @xref{Directory Modification Times and Permissions}.
2775 @opsummary{no-ignore-case}
2776 @item --no-ignore-case
2777 Use case-sensitive matching.
2778 @xref{controlling pattern-matching}.
2780 @opsummary{no-ignore-command-error}
2781 @item --no-ignore-command-error
2782 Print warnings about subprocesses that terminated with a nonzero exit
2783 code. @xref{Writing to an External Program}.
2785 @opsummary{no-overwrite-dir}
2786 @item --no-overwrite-dir
2788 Preserve metadata of existing directories when extracting files
2789 from an archive. @xref{Overwrite Old Files}.
2791 @opsummary{no-quote-chars}
2792 @item --no-quote-chars=@var{string}
2793 Remove characters listed in @var{string} from the list of quoted
2794 characters set by the previous @option{--quote-chars} option
2795 (@pxref{quoting styles}).
2797 @opsummary{no-recursion}
2798 @item --no-recursion
2800 With this option, @command{tar} will not recurse into directories.
2803 @opsummary{no-same-owner}
2804 @item --no-same-owner
2807 When extracting an archive, do not attempt to preserve the owner
2808 specified in the @command{tar} archive. This the default behavior
2811 @opsummary{no-same-permissions}
2812 @item --no-same-permissions
2814 When extracting an archive, subtract the user's umask from files from
2815 the permissions specified in the archive. This is the default behavior
2818 @opsummary{no-unquote}
2820 Treat all input file or member names literally, do not interpret
2821 escape sequences. @xref{input name quoting}.
2823 @opsummary{no-wildcards}
2824 @item --no-wildcards
2825 Do not use wildcards.
2826 @xref{controlling pattern-matching}.
2828 @opsummary{no-wildcards-match-slash}
2829 @item --no-wildcards-match-slash
2830 Wildcards do not match @samp{/}.
2831 @xref{controlling pattern-matching}.
2836 When @command{tar} is using the @option{--files-from} option, this option
2837 instructs @command{tar} to expect file names terminated with @acronym{NUL}, so
2838 @command{tar} can correctly work with file names that contain newlines.
2841 @opsummary{numeric-owner}
2842 @item --numeric-owner
2844 This option will notify @command{tar} that it should use numeric user
2845 and group IDs when creating a @command{tar} file, rather than names.
2849 The function of this option depends on the action @command{tar} is
2850 performing. When extracting files, @option{-o} is a synonym for
2851 @option{--no-same-owner}, i.e., it prevents @command{tar} from
2852 restoring ownership of files being extracted.
2854 When creating an archive, it is a synonym for
2855 @option{--old-archive}. This behavior is for compatibility
2856 with previous versions of @GNUTAR{}, and will be
2857 removed in future releases.
2859 @xref{Changes}, for more information.
2861 @opsummary{occurrence}
2862 @item --occurrence[=@var{number}]
2864 This option can be used in conjunction with one of the subcommands
2865 @option{--delete}, @option{--diff}, @option{--extract} or
2866 @option{--list} when a list of files is given either on the command
2867 line or via @option{-T} option.
2869 This option instructs @command{tar} to process only the @var{number}th
2870 occurrence of each named file. @var{Number} defaults to 1, so
2873 tar -x -f archive.tar --occurrence filename
2877 will extract the first occurrence of the member @file{filename} from @file{archive.tar}
2878 and will terminate without scanning to the end of the archive.
2880 @opsummary{old-archive}
2882 Synonym for @option{--format=v7}.
2884 @opsummary{one-file-system}
2885 @item --one-file-system
2886 Used when creating an archive. Prevents @command{tar} from recursing into
2887 directories that are on different file systems from the current
2888 directory @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2889 synonym for @option{--one-file-system}. This has changed in version
2890 1.15.91. @xref{Changes}, for more information.}.
2892 @opsummary{overwrite}
2895 Overwrite existing files and directory metadata when extracting files
2896 from an archive. @xref{Overwrite Old Files}.
2898 @opsummary{overwrite-dir}
2899 @item --overwrite-dir
2901 Overwrite the metadata of existing directories when extracting files
2902 from an archive. @xref{Overwrite Old Files}.
2905 @item --owner=@var{user}
2907 Specifies that @command{tar} should use @var{user} as the owner of members
2908 when creating archives, instead of the user associated with the source
2909 file. @var{user} is first decoded as a user symbolic name, but if
2910 this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
2913 This option does not affect extraction from archives.
2915 @opsummary{pax-option}
2916 @item --pax-option=@var{keyword-list}
2917 This option is meaningful only with @acronym{POSIX.1-2001} archives
2918 (@pxref{posix}). It modifies the way @command{tar} handles the
2919 extended header keywords. @var{Keyword-list} is a comma-separated
2920 list of keyword options. @xref{PAX keywords}, for a detailed
2923 @opsummary{portability}
2925 @itemx --old-archive
2926 Synonym for @option{--format=v7}.
2930 Same as @option{--format=posix}.
2932 @opsummary{preserve}
2935 Synonymous with specifying both @option{--preserve-permissions} and
2936 @option{--same-order}. @xref{Setting Access Permissions}.
2938 @opsummary{preserve-order}
2939 @item --preserve-order
2941 (See @option{--same-order}; @pxref{Reading}.)
2943 @opsummary{preserve-permissions}
2944 @opsummary{same-permissions}
2945 @item --preserve-permissions
2946 @itemx --same-permissions
2949 When @command{tar} is extracting an archive, it normally subtracts the
2950 users' umask from the permissions specified in the archive and uses
2951 that number as the permissions to create the destination file.
2952 Specifying this option instructs @command{tar} that it should use the
2953 permissions directly from the archive. @xref{Setting Access Permissions}.
2955 @opsummary{quote-chars}
2956 @item --quote-chars=@var{string}
2957 Always quote characters from @var{string}, even if the selected
2958 quoting style would not quote them (@pxref{quoting styles}).
2960 @opsummary{quoting-style}
2961 @item --quoting-style=@var{style}
2962 Set quoting style to use when printing member and file names
2963 (@pxref{quoting styles}). Valid @var{style} values are:
2964 @code{literal}, @code{shell}, @code{shell-always}, @code{c},
2965 @code{escape}, @code{locale}, and @code{clocale}. Default quoting
2966 style is @code{escape}, unless overridden while configuring the
2969 @opsummary{read-full-records}
2970 @item --read-full-records
2973 Specifies that @command{tar} should reblock its input, for reading
2974 from pipes on systems with buggy implementations. @xref{Reading}.
2976 @opsummary{record-size}
2977 @item --record-size=@var{size}
2979 Instructs @command{tar} to use @var{size} bytes per record when accessing the
2980 archive. @xref{Blocking Factor}.
2982 @opsummary{recursion}
2985 With this option, @command{tar} recurses into directories (default).
2988 @opsummary{recursive-unlink}
2989 @item --recursive-unlink
2992 directory hierarchies before extracting directories of the same name
2993 from the archive. @xref{Recursive Unlink}.
2995 @opsummary{remove-files}
2996 @item --remove-files
2998 Directs @command{tar} to remove the source file from the file system after
2999 appending it to an archive. @xref{remove files}.
3001 @opsummary{restrict}
3004 Disable use of some potentially harmful @command{tar} options.
3005 Currently this option disables shell invocation from multi-volume menu
3006 (@pxref{Using Multiple Tapes}).
3008 @opsummary{rmt-command}
3009 @item --rmt-command=@var{cmd}
3011 Notifies @command{tar} that it should use @var{cmd} instead of
3012 the default @file{/usr/libexec/rmt} (@pxref{Remote Tape Server}).
3014 @opsummary{rsh-command}
3015 @item --rsh-command=@var{cmd}
3017 Notifies @command{tar} that is should use @var{cmd} to communicate with remote
3018 devices. @xref{Device}.
3020 @opsummary{same-order}
3022 @itemx --preserve-order
3025 This option is an optimization for @command{tar} when running on machines with
3026 small amounts of memory. It informs @command{tar} that the list of file
3027 arguments has already been sorted to match the order of files in the
3028 archive. @xref{Reading}.
3030 @opsummary{same-owner}
3033 When extracting an archive, @command{tar} will attempt to preserve the owner
3034 specified in the @command{tar} archive with this option present.
3035 This is the default behavior for the superuser; this option has an
3036 effect only for ordinary users. @xref{Attributes}.
3038 @opsummary{same-permissions}
3039 @item --same-permissions
3041 (See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
3047 Assume that the archive media supports seeks to arbitrary
3048 locations. Usually @command{tar} determines automatically whether
3049 the archive can be seeked or not. This option is intended for use
3050 in cases when such recognition fails.
3052 @opsummary{show-defaults}
3053 @item --show-defaults
3055 Displays the default options used by @command{tar} and exits
3056 successfully. This option is intended for use in shell scripts.
3057 Here is an example of what you can see using this option:
3060 $ tar --show-defaults
3061 --format=gnu -f- -b20 --quoting-style=escape \
3062 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
3065 @opsummary{show-omitted-dirs}
3066 @item --show-omitted-dirs
3068 Instructs @command{tar} to mention the directories it is skipping when
3069 operating on a @command{tar} archive. @xref{show-omitted-dirs}.
3071 @opsummary{show-transformed-names}
3072 @opsummary{show-stored-names}
3073 @item --show-transformed-names
3074 @itemx --show-stored-names
3076 Display file or member names after applying any transformations
3077 (@pxref{transform}). In particular, when used in conjunction with one of
3078 the archive creation operations it instructs @command{tar} to list the
3079 member names stored in the archive, as opposed to the actual file
3080 names. @xref{listing member and file names}.
3086 Invokes a @acronym{GNU} extension when adding files to an archive that handles
3087 sparse files efficiently. @xref{sparse}.
3089 @opsummary{sparse-version}
3090 @item --sparse-version=@var{version}
3092 Specifies the @dfn{format version} to use when archiving sparse
3093 files. Implies @option{--sparse}. @xref{sparse}. For the description
3094 of the supported sparse formats, @xref{Sparse Formats}.
3096 @opsummary{starting-file}
3097 @item --starting-file=@var{name}
3098 @itemx -K @var{name}
3100 This option affects extraction only; @command{tar} will skip extracting
3101 files in the archive until it finds one that matches @var{name}.
3104 @opsummary{strip-components}
3105 @item --strip-components=@var{number}
3106 Strip given @var{number} of leading components from file names before
3107 extraction. For example, if archive @file{archive.tar} contained
3108 @file{/some/file/name}, then running
3111 tar --extract --file archive.tar --strip-components=2
3115 would extract this file to file @file{name}.
3117 @opsummary{suffix}, summary
3118 @item --suffix=@var{suffix}
3120 Alters the suffix @command{tar} uses when backing up files from the default
3121 @samp{~}. @xref{backup}.
3123 @opsummary{tape-length}
3124 @item --tape-length=@var{num}
3127 Specifies the length of tapes that @command{tar} is writing as being
3128 @w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
3130 @opsummary{test-label}
3133 Reads the volume label. If an argument is specified, test whether it
3134 matches the volume label. @xref{--test-label option}.
3136 @opsummary{to-command}
3137 @item --to-command=@var{command}
3139 During extraction @command{tar} will pipe extracted files to the
3140 standard input of @var{command}. @xref{Writing to an External Program}.
3142 @opsummary{to-stdout}
3146 During extraction, @command{tar} will extract files to stdout rather
3147 than to the file system. @xref{Writing to Standard Output}.
3150 @item --totals[=@var{signo}]
3152 Displays the total number of bytes transferred when processing an
3153 archive. If an argument is given, these data are displayed on
3154 request, when signal @var{signo} is delivered to @command{tar}.
3161 Sets the data modification time of extracted files to the extraction time,
3162 rather than the data modification time stored in the archive.
3163 @xref{Data Modification Times}.
3165 @opsummary{transform}
3166 @item --transform=@var{sed-expr}
3168 Transform file or member names using @command{sed} replacement expression
3169 @var{sed-expr}. For example,
3172 $ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
3176 will add to @file{archive} files from the current working directory,
3177 replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
3178 discussion, @xref{transform}.
3180 To see transformed member names in verbose listings, use
3181 @option{--show-transformed-names} option
3182 (@pxref{show-transformed-names}).
3184 @opsummary{uncompress}
3187 (See @option{--compress}. @pxref{gzip})
3192 (See @option{--gzip}. @pxref{gzip})
3194 @opsummary{unlink-first}
3195 @item --unlink-first
3198 Directs @command{tar} to remove the corresponding file from the file
3199 system before extracting it from the archive. @xref{Unlink First}.
3203 Enable unquoting input file or member names (default). @xref{input
3206 @opsummary{use-compress-program}
3207 @item --use-compress-program=@var{prog}
3209 Instructs @command{tar} to access the archive through @var{prog}, which is
3210 presumed to be a compression program of some sort. @xref{gzip}.
3215 Display file modification dates in @acronym{UTC}. This option implies
3222 Specifies that @command{tar} should be more verbose about the
3223 operations it is performing. This option can be specified multiple
3224 times for some operations to increase the amount of information displayed.
3231 Verifies that the archive was correctly written when creating an
3232 archive. @xref{verify}.
3237 Print information about the program's name, version, origin and legal
3238 status, all on standard output, and then exit successfully.
3241 @opsummary{volno-file}
3242 @item --volno-file=@var{file}
3244 Used in conjunction with @option{--multi-volume}. @command{tar} will
3245 keep track of which volume of a multi-volume archive it is working in
3246 @var{file}. @xref{volno-file}.
3248 @opsummary{wildcards}
3250 Use wildcards when matching member names with patterns.
3251 @xref{controlling pattern-matching}.
3253 @opsummary{wildcards-match-slash}
3254 @item --wildcards-match-slash
3255 Wildcards match @samp{/}.
3256 @xref{controlling pattern-matching}.
3259 @node Short Option Summary
3260 @subsection Short Options Cross Reference
3262 Here is an alphabetized list of all of the short option forms, matching
3263 them with the equivalent long option.
3265 @multitable @columnfractions 0.20 0.80
3266 @headitem Short Option @tab Reference
3268 @item -A @tab @ref{--concatenate}.
3270 @item -B @tab @ref{--read-full-records}.
3272 @item -C @tab @ref{--directory}.
3274 @item -F @tab @ref{--info-script}.
3276 @item -G @tab @ref{--incremental}.
3278 @item -K @tab @ref{--starting-file}.
3280 @item -L @tab @ref{--tape-length}.
3282 @item -M @tab @ref{--multi-volume}.
3284 @item -N @tab @ref{--newer}.
3286 @item -O @tab @ref{--to-stdout}.
3288 @item -P @tab @ref{--absolute-names}.
3290 @item -R @tab @ref{--block-number}.
3292 @item -S @tab @ref{--sparse}.
3294 @item -T @tab @ref{--files-from}.
3296 @item -U @tab @ref{--unlink-first}.
3298 @item -V @tab @ref{--label}.
3300 @item -W @tab @ref{--verify}.
3302 @item -X @tab @ref{--exclude-from}.
3304 @item -Z @tab @ref{--compress}.
3306 @item -b @tab @ref{--blocking-factor}.
3308 @item -c @tab @ref{--create}.
3310 @item -d @tab @ref{--compare}.
3312 @item -f @tab @ref{--file}.
3314 @item -g @tab @ref{--listed-incremental}.
3316 @item -h @tab @ref{--dereference}.
3318 @item -i @tab @ref{--ignore-zeros}.
3320 @item -j @tab @ref{--bzip2}.
3322 @item -k @tab @ref{--keep-old-files}.
3324 @item -l @tab @ref{--check-links}.
3326 @item -m @tab @ref{--touch}.
3328 @item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
3329 @ref{--portability}.
3331 The later usage is deprecated. It is retained for compatibility with
3332 the earlier versions of @GNUTAR{}. In future releases
3333 @option{-o} will be equivalent to @option{--no-same-owner} only.
3335 @item -p @tab @ref{--preserve-permissions}.
3337 @item -r @tab @ref{--append}.
3339 @item -s @tab @ref{--same-order}.
3341 @item -t @tab @ref{--list}.
3343 @item -u @tab @ref{--update}.
3345 @item -v @tab @ref{--verbose}.
3347 @item -w @tab @ref{--interactive}.
3349 @item -x @tab @ref{--extract}.
3351 @item -z @tab @ref{--gzip}.
3356 @section @GNUTAR{} documentation
3358 @cindex Getting program version number
3360 @cindex Version of the @command{tar} program
3361 Being careful, the first thing is really checking that you are using
3362 @GNUTAR{}, indeed. The @option{--version} option
3363 causes @command{tar} to print information about its name, version,
3364 origin and legal status, all on standard output, and then exit
3365 successfully. For example, @w{@samp{tar --version}} might print:
3368 tar (GNU tar) @value{VERSION}
3369 Copyright (C) 2006 Free Software Foundation, Inc.
3370 This is free software. You may redistribute copies of it under the terms
3371 of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
3372 There is NO WARRANTY, to the extent permitted by law.
3374 Written by John Gilmore and Jay Fenlason.
3378 The first occurrence of @samp{tar} in the result above is the program
3379 name in the package (for example, @command{rmt} is another program),
3380 while the second occurrence of @samp{tar} is the name of the package
3381 itself, containing possibly many programs. The package is currently
3382 named @samp{tar}, after the name of the main program it
3383 contains@footnote{There are plans to merge the @command{cpio} and
3384 @command{tar} packages into a single one which would be called
3385 @code{paxutils}. So, who knows if, one of this days, the
3386 @option{--version} would not output @w{@samp{tar (@acronym{GNU}
3389 @cindex Obtaining help
3390 @cindex Listing all @command{tar} options
3391 @xopindex{help, introduction}
3392 Another thing you might want to do is checking the spelling or meaning
3393 of some particular @command{tar} option, without resorting to this
3394 manual, for once you have carefully read it. @GNUTAR{}
3395 has a short help feature, triggerable through the
3396 @option{--help} option. By using this option, @command{tar} will
3397 print a usage message listing all available options on standard
3398 output, then exit successfully, without doing anything else and
3399 ignoring all other options. Even if this is only a brief summary, it
3400 may be several screens long. So, if you are not using some kind of
3401 scrollable window, you might prefer to use something like:
3404 $ @kbd{tar --help | less}
3408 presuming, here, that you like using @command{less} for a pager. Other
3409 popular pagers are @command{more} and @command{pg}. If you know about some
3410 @var{keyword} which interests you and do not want to read all the
3411 @option{--help} output, another common idiom is doing:
3414 tar --help | grep @var{keyword}
3418 for getting only the pertinent lines. Notice, however, that some
3419 @command{tar} options have long description lines and the above
3420 command will list only the first of them.
3422 The exact look of the option summary displayed by @kbd{tar --help} is
3423 configurable. @xref{Configuring Help Summary}, for a detailed description.
3426 If you only wish to check the spelling of an option, running @kbd{tar
3427 --usage} may be a better choice. This will display a terse list of
3428 @command{tar} option without accompanying explanations.
3430 The short help output is quite succinct, and you might have to get
3431 back to the full documentation for precise points. If you are reading
3432 this paragraph, you already have the @command{tar} manual in some
3433 form. This manual is available in a variety of forms from
3434 @url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{}
3435 distribution, provided you have @TeX{} already installed somewhere,
3436 and a laser printer around. Just configure the distribution, execute
3437 the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the
3438 usual way (contact your local guru to know how). If @GNUTAR{}
3439 has been conveniently installed at your place, this
3440 manual is also available in interactive, hypertextual form as an Info
3441 file. Just call @w{@samp{info tar}} or, if you do not have the
3442 @command{info} program handy, use the Info reader provided within
3443 @acronym{GNU} Emacs, calling @samp{tar} from the main Info menu.
3445 There is currently no @code{man} page for @GNUTAR{}.
3446 If you observe such a @code{man} page on the system you are running,
3447 either it does not belong to @GNUTAR{}, or it has not
3448 been produced by @acronym{GNU}. Some package maintainers convert
3449 @kbd{tar --help} output to a man page, using @command{help2man}. In
3450 any case, please bear in mind that the authoritative source of
3451 information about @GNUTAR{} is this Texinfo documentation.
3454 @section Obtaining @GNUTAR{} default values
3456 @opindex show-defaults
3457 @GNUTAR{} has some predefined defaults that are used when you do not
3458 explicitly specify another values. To obtain a list of such
3459 defaults, use @option{--show-defaults} option. This will output the
3460 values in the form of @command{tar} command line options:
3464 @kbd{tar --show-defaults}
3465 --format=gnu -f- -b20 --quoting-style=escape
3466 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3471 Notice, that this option outputs only one line. The example output above
3472 has been split to fit page boundaries.
3475 The above output shows that this version of @GNUTAR{} defaults to
3476 using @samp{gnu} archive format (@pxref{Formats}), it uses standard
3477 output as the archive, if no @option{--file} option has been given
3478 (@pxref{file tutorial}), the default blocking factor is 20
3479 (@pxref{Blocking Factor}). It also shows the default locations where
3480 @command{tar} will look for @command{rmt} and @command{rsh} binaries.
3483 @section Checking @command{tar} progress
3485 Typically, @command{tar} performs most operations without reporting any
3486 information to the user except error messages. When using @command{tar}
3487 with many options, particularly ones with complicated or
3488 difficult-to-predict behavior, it is possible to make serious mistakes.
3489 @command{tar} provides several options that make observing @command{tar}
3490 easier. These options cause @command{tar} to print information as it
3491 progresses in its job, and you might want to use them just for being
3492 more careful about what is going on, or merely for entertaining
3493 yourself. If you have encountered a problem when operating on an
3494 archive, however, you may need more information than just an error
3495 message in order to solve the problem. The following options can be
3496 helpful diagnostic tools.
3498 @cindex Verbose operation
3500 Normally, the @option{--list} (@option{-t}) command to list an archive
3501 prints just the file names (one per line) and the other commands are
3502 silent. When used with most operations, the @option{--verbose}
3503 (@option{-v}) option causes @command{tar} to print the name of each
3504 file or archive member as it is processed. This and the other options
3505 which make @command{tar} print status information can be useful in
3506 monitoring @command{tar}.
3508 With @option{--create} or @option{--extract}, @option{--verbose} used
3509 once just prints the names of the files or members as they are processed.
3510 Using it twice causes @command{tar} to print a longer listing
3511 (@xref{verbose member listing}, for the description) for each member.
3512 Since @option{--list} already prints the names of the members,
3513 @option{--verbose} used once with @option{--list} causes @command{tar}
3514 to print an @samp{ls -l} type listing of the files in the archive.
3515 The following examples both extract members with long list output:
3518 $ @kbd{tar --extract --file=archive.tar --verbose --verbose}
3519 $ @kbd{tar xvvf archive.tar}
3522 Verbose output appears on the standard output except when an archive is
3523 being written to the standard output, as with @samp{tar --create
3524 --file=- --verbose} (@samp{tar cfv -}, or even @samp{tar cv}---if the
3525 installer let standard output be the default archive). In that case
3526 @command{tar} writes verbose output to the standard error stream.
3528 If @option{--index-file=@var{file}} is specified, @command{tar} sends
3529 verbose output to @var{file} rather than to standard output or standard
3533 @cindex Obtaining total status information
3535 The @option{--totals} option causes @command{tar} to print on the
3536 standard error the total amount of bytes transferred when processing
3537 an archive. When creating or appending to an archive, this option
3538 prints the number of bytes written to the archive and the average
3539 speed at which they have been written, e.g.:
3543 $ @kbd{tar -c -f archive.tar --totals /home}
3544 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3548 When reading an archive, this option displays the number of bytes
3553 $ @kbd{tar -x -f archive.tar --totals}
3554 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3558 Finally, when deleting from an archive, the @option{--totals} option
3559 displays both numbers plus number of bytes removed from the archive:
3563 $ @kbd{tar --delete -f foo.tar --totals --wildcards '*~'}
3564 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3565 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3566 Total bytes deleted: 1474048
3570 You can also obtain this information on request. When
3571 @option{--totals} is used with an argument, this argument is
3572 interpreted as a symbolic name of a signal, upon delivery of which the
3573 statistics is to be printed:
3576 @item --totals=@var{signo}
3577 Print statistics upon delivery of signal @var{signo}. Valid arguments
3578 are: @code{SIGHUP}, @code{SIGQUIT}, @code{SIGINT}, @code{SIGUSR1} and
3579 @code{SIGUSR2}. Shortened names without @samp{SIG} prefix are also
3583 Both forms of @option{--totals} option can be used simultaneously.
3584 Thus, @kbd{tar -x --totals --totals=USR1} instructs @command{tar} to
3585 extract all members from its default archive and print statistics
3586 after finishing the extraction, as well as when receiving signal
3589 @anchor{Progress information}
3590 @cindex Progress information
3592 The @option{--checkpoint} option prints an occasional message
3593 as @command{tar} reads or writes the archive. It is designed for
3594 those who don't need the more detailed (and voluminous) output of
3595 @option{--block-number} (@option{-R}), but do want visual confirmation
3596 that @command{tar} is actually making forward progress. By default it
3597 prints a message each 10 records read or written. This can be changed
3598 by giving it a numeric argument after an equal sign:
3601 $ @kbd{tar -c --checkpoint=1000} /var
3602 tar: Write checkpoint 1000
3603 tar: Write checkpoint 2000
3604 tar: Write checkpoint 3000
3607 This example shows the default checkpoint message used by
3608 @command{tar}. If you place a dot immediately after the equal
3609 sign, it will print a @samp{.} at each checkpoint. For example:
3612 $ @kbd{tar -c --checkpoint=.1000} /var
3616 @opindex show-omitted-dirs
3617 @anchor{show-omitted-dirs}
3618 The @option{--show-omitted-dirs} option, when reading an archive---with
3619 @option{--list} or @option{--extract}, for example---causes a message
3620 to be printed for each directory in the archive which is skipped.
3621 This happens regardless of the reason for skipping: the directory might
3622 not have been named on the command line (implicitly or explicitly),
3623 it might be excluded by the use of the
3624 @option{--exclude=@var{pattern}} option, or some other reason.
3626 @opindex block-number
3627 @cindex Block number where error occurred
3628 @anchor{block-number}
3629 If @option{--block-number} (@option{-R}) is used, @command{tar} prints, along with
3630 every message it would normally produce, the block number within the
3631 archive where the message was triggered. Also, supplementary messages
3632 are triggered when reading blocks full of NULs, or when hitting end of
3633 file on the archive. As of now, if the archive if properly terminated
3634 with a NUL block, the reading of the file may stop before end of file
3635 is met, so the position of end of file will not usually show when
3636 @option{--block-number} (@option{-R}) is used. Note that @GNUTAR{}
3637 drains the archive before exiting when reading the
3638 archive from a pipe.
3640 @cindex Error message, block number of
3641 This option is especially useful when reading damaged archives, since
3642 it helps pinpoint the damaged sections. It can also be used with
3643 @option{--list} (@option{-t}) when listing a file-system backup tape, allowing you to
3644 choose among several backup tapes when retrieving a file later, in
3645 favor of the tape where the file appears earliest (closest to the
3646 front of the tape). @xref{backup}.
3649 @section Asking for Confirmation During Operations
3650 @cindex Interactive operation
3652 Typically, @command{tar} carries out a command without stopping for
3653 further instructions. In some situations however, you may want to
3654 exclude some files and archive members from the operation (for instance
3655 if disk or storage space is tight). You can do this by excluding
3656 certain files automatically (@pxref{Choosing}), or by performing
3657 an operation interactively, using the @option{--interactive} (@option{-w}) option.
3658 @command{tar} also accepts @option{--confirmation} for this option.
3660 @opindex interactive
3661 When the @option{--interactive} (@option{-w}) option is specified, before
3662 reading, writing, or deleting files, @command{tar} first prints a message
3663 for each such file, telling what operation it intends to take, then asks
3664 for confirmation on the terminal. The actions which require
3665 confirmation include adding a file to the archive, extracting a file
3666 from the archive, deleting a file from the archive, and deleting a file
3667 from disk. To confirm the action, you must type a line of input
3668 beginning with @samp{y}. If your input line begins with anything other
3669 than @samp{y}, @command{tar} skips that file.
3671 If @command{tar} is reading the archive from the standard input,
3672 @command{tar} opens the file @file{/dev/tty} to support the interactive
3675 Verbose output is normally sent to standard output, separate from
3676 other error messages. However, if the archive is produced directly
3677 on standard output, then verbose output is mixed with errors on
3678 @code{stderr}. Producing the archive on standard output may be used
3679 as a way to avoid using disk space, when the archive is soon to be
3680 consumed by another process reading it, say. Some people felt the need
3681 of producing an archive on stdout, still willing to segregate between
3682 verbose output and error output. A possible approach would be using a
3683 named pipe to receive the archive, and having the consumer process to
3684 read from that named pipe. This has the advantage of letting standard
3685 output free to receive verbose output, all separate from errors.
3688 @chapter @GNUTAR{} Operations
3701 @section Basic @GNUTAR{} Operations
3703 The basic @command{tar} operations, @option{--create} (@option{-c}),
3704 @option{--list} (@option{-t}) and @option{--extract} (@option{--get},
3705 @option{-x}), are currently presented and described in the tutorial
3706 chapter of this manual. This section provides some complementary notes
3707 for these operations.
3710 @xopindex{create, complementary notes}
3714 Creating an empty archive would have some kind of elegance. One can
3715 initialize an empty archive and later use @option{--append}
3716 (@option{-r}) for adding all members. Some applications would not
3717 welcome making an exception in the way of adding the first archive
3718 member. On the other hand, many people reported that it is
3719 dangerously too easy for @command{tar} to destroy a magnetic tape with
3720 an empty archive@footnote{This is well described in @cite{Unix-haters
3721 Handbook}, by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG
3722 Books, ISBN 1-56884-203-1.}. The two most common errors are:
3726 Mistakingly using @code{create} instead of @code{extract}, when the
3727 intent was to extract the full contents of an archive. This error
3728 is likely: keys @kbd{c} and @kbd{x} are right next to each other on
3729 the QWERTY keyboard. Instead of being unpacked, the archive then
3730 gets wholly destroyed. When users speak about @dfn{exploding} an
3731 archive, they usually mean something else :-).
3734 Forgetting the argument to @code{file}, when the intent was to create
3735 an archive with a single file in it. This error is likely because a
3736 tired user can easily add the @kbd{f} key to the cluster of option
3737 letters, by the mere force of habit, without realizing the full
3738 consequence of doing so. The usual consequence is that the single
3739 file, which was meant to be saved, is rather destroyed.
3742 So, recognizing the likelihood and the catastrophic nature of these
3743 errors, @GNUTAR{} now takes some distance from elegance, and
3744 cowardly refuses to create an archive when @option{--create} option is
3745 given, there are no arguments besides options, and
3746 @option{--files-from} (@option{-T}) option is @emph{not} used. To get
3747 around the cautiousness of @GNUTAR{} and nevertheless create an
3748 archive with nothing in it, one may still use, as the value for the
3749 @option{--files-from} option, a file with no names in it, as shown in
3750 the following commands:
3753 @kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
3754 @kbd{tar cfT empty-archive.tar /dev/null}
3757 @xopindex{extract, complementary notes}
3762 A socket is stored, within a @GNUTAR{} archive, as a pipe.
3764 @item @option{--list} (@option{-t})
3766 @GNUTAR{} now shows dates as @samp{1996-08-30},
3767 while it used to show them as @samp{Aug 30 1996}. Preferably,
3768 people should get used to ISO 8601 dates. Local American dates should
3769 be made available again with full date localization support, once
3770 ready. In the meantime, programs not being localizable for dates
3771 should prefer international dates, that's really the way to go.
3773 Look up @url{http://www.cl.cam.ac.uk/@/~mgk25/@/iso-time.html} if you
3774 are curious, it contains a detailed explanation of the ISO 8601 standard.
3779 @section Advanced @GNUTAR{} Operations
3781 Now that you have learned the basics of using @GNUTAR{}, you may want
3782 to learn about further ways in which @command{tar} can help you.
3784 This chapter presents five, more advanced operations which you probably
3785 won't use on a daily basis, but which serve more specialized functions.
3786 We also explain the different styles of options and why you might want
3787 to use one or another, or a combination of them in your @command{tar}
3788 commands. Additionally, this chapter includes options which allow you to
3789 define the output from @command{tar} more carefully, and provide help and
3790 error correction in special circumstances.
3792 @FIXME{check this after the chapter is actually revised to make sure
3793 it still introduces the info in the chapter correctly : ).}
3805 @subsection The Five Advanced @command{tar} Operations
3808 In the last chapter, you learned about the first three operations to
3809 @command{tar}. This chapter presents the remaining five operations to
3810 @command{tar}: @option{--append}, @option{--update}, @option{--concatenate},
3811 @option{--delete}, and @option{--compare}.
3813 You are not likely to use these operations as frequently as those
3814 covered in the last chapter; however, since they perform specialized
3815 functions, they are quite useful when you do need to use them. We
3816 will give examples using the same directory and files that you created
3817 in the last chapter. As you may recall, the directory is called
3818 @file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk},
3819 @samp{rock}, and the two archive files you created are
3820 @samp{collection.tar} and @samp{music.tar}.
3822 We will also use the archive files @samp{afiles.tar} and
3823 @samp{bfiles.tar}. The archive @samp{afiles.tar} contains the members @samp{apple},
3824 @samp{angst}, and @samp{aspic}; @samp{bfiles.tar} contains the members
3825 @samp{./birds}, @samp{baboon}, and @samp{./box}.
3827 Unless we state otherwise, all practicing you do and examples you follow
3828 in this chapter will take place in the @file{practice} directory that
3829 you created in the previous chapter; see @ref{prepare for examples}.
3830 (Below in this section, we will remind you of the state of the examples
3831 where the last chapter left them.)
3833 The five operations that we will cover in this chapter are:
3838 Add new entries to an archive that already exists.
3841 Add more recent copies of archive members to the end of an archive, if
3846 Add one or more pre-existing archives to the end of another archive.
3848 Delete items from an archive (does not work on tapes).
3852 Compare archive members to their counterparts in the file system.
3856 @subsection How to Add Files to Existing Archives: @option{--append}
3860 If you want to add files to an existing archive, you don't need to
3861 create a new archive; you can use @option{--append} (@option{-r}).
3862 The archive must already exist in order to use @option{--append}. (A
3863 related operation is the @option{--update} operation; you can use this
3864 to add newer versions of archive members to an existing archive. To learn how to
3865 do this with @option{--update}, @pxref{update}.)
3867 If you use @option{--append} to add a file that has the same name as an
3868 archive member to an archive containing that archive member, then the
3869 old member is not deleted. What does happen, however, is somewhat
3870 complex. @command{tar} @emph{allows} you to have infinite number of files
3871 with the same name. Some operations treat these same-named members no
3872 differently than any other set of archive members: for example, if you
3873 view an archive with @option{--list} (@option{-t}), you will see all
3874 of those members listed, with their data modification times, owners, etc.
3876 Other operations don't deal with these members as perfectly as you might
3877 prefer; if you were to use @option{--extract} to extract the archive,
3878 only the most recently added copy of a member with the same name as four
3879 other members would end up in the working directory. This is because
3880 @option{--extract} extracts an archive in the order the members appeared
3881 in the archive; the most recently archived members will be extracted
3882 last. Additionally, an extracted member will @emph{replace} a file of
3883 the same name which existed in the directory already, and @command{tar}
3884 will not prompt you about this@footnote{Unless you give it
3885 @option{--keep-old-files} option, or the disk copy is newer than the
3886 the one in the archive and you invoke @command{tar} with
3887 @option{--keep-newer-files} option}. Thus, only the most recently archived
3888 member will end up being extracted, as it will replace the one
3889 extracted before it, and so on.
3891 There exists a special option that allows you to get around this
3892 behavior and extract (or list) only a particular copy of the file.
3893 This is @option{--occurrence} option. If you run @command{tar} with
3894 this option, it will extract only the first copy of the file. You
3895 may also give this option an argument specifying the number of
3896 copy to be extracted. Thus, for example if the archive
3897 @file{archive.tar} contained three copies of file @file{myfile}, then
3901 tar --extract --file archive.tar --occurrence=2 myfile
3905 would extract only the second copy. @xref{Option
3906 Summary,---occurrence}, for the description of @option{--occurrence}
3909 @FIXME{ hag -- you might want to incorporate some of the above into the
3910 MMwtSN node; not sure. i didn't know how to make it simpler...
3912 There are a few ways to get around this. (maybe xref Multiple Members
3913 with the Same Name.}
3915 @cindex Members, replacing with other members
3916 @cindex Replacing members with other members
3917 If you want to replace an archive member, use @option{--delete} to
3918 delete the member you want to remove from the archive, , and then use
3919 @option{--append} to add the member you want to be in the archive. Note
3920 that you can not change the order of the archive; the most recently
3921 added member will still appear last. In this sense, you cannot truly
3922 ``replace'' one member with another. (Replacing one member with another
3923 will not work on certain types of media, such as tapes; see @ref{delete}
3924 and @ref{Media}, for more information.)
3927 * appending files:: Appending Files to an Archive
3931 @node appending files
3932 @subsubsection Appending Files to an Archive
3934 @cindex Adding files to an Archive
3935 @cindex Appending files to an Archive
3936 @cindex Archives, Appending files to
3938 The simplest way to add a file to an already existing archive is the
3939 @option{--append} (@option{-r}) operation, which writes specified
3940 files into the archive whether or not they are already among the
3943 When you use @option{--append}, you @emph{must} specify file name
3944 arguments, as there is no default. If you specify a file that already
3945 exists in the archive, another copy of the file will be added to the
3946 end of the archive. As with other operations, the member names of the
3947 newly added files will be exactly the same as their names given on the
3948 command line. The @option{--verbose} (@option{-v}) option will print
3949 out the names of the files as they are written into the archive.
3951 @option{--append} cannot be performed on some tape drives, unfortunately,
3952 due to deficiencies in the formats those tape drives use. The archive
3953 must be a valid @command{tar} archive, or else the results of using this
3954 operation will be unpredictable. @xref{Media}.
3956 To demonstrate using @option{--append} to add a file to an archive,
3957 create a file called @file{rock} in the @file{practice} directory.
3958 Make sure you are in the @file{practice} directory. Then, run the
3959 following @command{tar} command to add @file{rock} to
3960 @file{collection.tar}:
3963 $ @kbd{tar --append --file=collection.tar rock}
3967 If you now use the @option{--list} (@option{-t}) operation, you will see that
3968 @file{rock} has been added to the archive:
3971 $ @kbd{tar --list --file=collection.tar}
3972 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
3973 -rw-r--r-- me user 21 1996-09-23 16:44 blues
3974 -rw-r--r-- me user 20 1996-09-23 16:44 folk
3975 -rw-r--r-- me user 20 1996-09-23 16:44 rock
3979 @subsubsection Multiple Members with the Same Name
3981 You can use @option{--append} (@option{-r}) to add copies of files
3982 which have been updated since the archive was created. (However, we
3983 do not recommend doing this since there is another @command{tar}
3984 option called @option{--update}; @xref{update}, for more information.
3985 We describe this use of @option{--append} here for the sake of
3986 completeness.) When you extract the archive, the older version will
3987 be effectively lost. This works because files are extracted from an
3988 archive in the order in which they were archived. Thus, when the
3989 archive is extracted, a file archived later in time will replace a
3990 file of the same name which was archived earlier, even though the
3991 older version of the file will remain in the archive unless you delete
3992 all versions of the file.
3994 Supposing you change the file @file{blues} and then append the changed
3995 version to @file{collection.tar}. As you saw above, the original
3996 @file{blues} is in the archive @file{collection.tar}. If you change the
3997 file and append the new version of the file to the archive, there will
3998 be two copies in the archive. When you extract the archive, the older
3999 version of the file will be extracted first, and then replaced by the
4000 newer version when it is extracted.
4002 You can append the new, changed copy of the file @file{blues} to the
4003 archive in this way:
4006 $ @kbd{tar --append --verbose --file=collection.tar blues}
4011 Because you specified the @option{--verbose} option, @command{tar} has
4012 printed the name of the file being appended as it was acted on. Now
4013 list the contents of the archive:
4016 $ @kbd{tar --list --verbose --file=collection.tar}
4017 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4018 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4019 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4020 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4021 -rw-r--r-- me user 58 1996-10-24 18:30 blues
4025 The newest version of @file{blues} is now at the end of the archive
4026 (note the different creation dates and file sizes). If you extract
4027 the archive, the older version of the file @file{blues} will be
4028 replaced by the newer version. You can confirm this by extracting
4029 the archive and running @samp{ls} on the directory.
4031 If you wish to extract the first occurrence of the file @file{blues}
4032 from the archive, use @option{--occurrence} option, as shown in
4033 the following example:
4036 $ @kbd{tar --extract -vv --occurrence --file=collection.tar blues}
4037 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4040 @xref{Writing}, for more information on @option{--extract} and
4041 @xref{Option Summary, --occurrence}, for the description of
4042 @option{--occurrence} option.
4045 @subsection Updating an Archive
4047 @cindex Updating an archive
4050 In the previous section, you learned how to use @option{--append} to
4051 add a file to an existing archive. A related operation is
4052 @option{--update} (@option{-u}). The @option{--update} operation
4053 updates a @command{tar} archive by comparing the date of the specified
4054 archive members against the date of the file with the same name. If
4055 the file has been modified more recently than the archive member, then
4056 the newer version of the file is added to the archive (as with
4059 Unfortunately, you cannot use @option{--update} with magnetic tape drives.
4060 The operation will fail.
4062 @FIXME{other examples of media on which --update will fail? need to ask
4063 charles and/or mib/thomas/dave shevett..}
4065 Both @option{--update} and @option{--append} work by adding to the end
4066 of the archive. When you extract a file from the archive, only the
4067 version stored last will wind up in the file system, unless you use
4068 the @option{--backup} option. @xref{multiple}, for a detailed discussion.
4075 @subsubsection How to Update an Archive Using @option{--update}
4077 You must use file name arguments with the @option{--update}
4078 (@option{-u}) operation. If you don't specify any files,
4079 @command{tar} won't act on any files and won't tell you that it didn't
4080 do anything (which may end up confusing you).
4082 @c note: the above parenthetical added because in fact, this
4083 @c behavior just confused the author. :-)
4085 To see the @option{--update} option at work, create a new file,
4086 @file{classical}, in your practice directory, and some extra text to the
4087 file @file{blues}, using any text editor. Then invoke @command{tar} with
4088 the @samp{update} operation and the @option{--verbose} (@option{-v})
4089 option specified, using the names of all the files in the practice
4090 directory as file name arguments:
4093 $ @kbd{tar --update -v -f collection.tar blues folk rock classical}
4100 Because we have specified verbose mode, @command{tar} prints out the names
4101 of the files it is working on, which in this case are the names of the
4102 files that needed to be updated. If you run @samp{tar --list} and look
4103 at the archive, you will see @file{blues} and @file{classical} at its
4104 end. There will be a total of two versions of the member @samp{blues};
4105 the one at the end will be newer and larger, since you added text before
4108 (The reason @command{tar} does not overwrite the older file when updating
4109 it is because writing to the middle of a section of tape is a difficult
4110 process. Tapes are not designed to go backward. @xref{Media}, for more
4111 information about tapes.
4113 @option{--update} (@option{-u}) is not suitable for performing backups for two
4114 reasons: it does not change directory content entries, and it
4115 lengthens the archive every time it is used. The @GNUTAR{}
4116 options intended specifically for backups are more
4117 efficient. If you need to run backups, please consult @ref{Backups}.
4120 @subsection Combining Archives with @option{--concatenate}
4122 @cindex Adding archives to an archive
4123 @cindex Concatenating Archives
4124 @opindex concatenate
4126 @c @cindex @option{-A} described
4127 Sometimes it may be convenient to add a second archive onto the end of
4128 an archive rather than adding individual files to the archive. To add
4129 one or more archives to the end of another archive, you should use the
4130 @option{--concatenate} (@option{--catenate}, @option{-A}) operation.
4132 To use @option{--concatenate}, give the first archive with
4133 @option{--file} option and name the rest of archives to be
4134 concatenated on the command line. The members, and their member
4135 names, will be copied verbatim from those archives to the first one.
4136 @footnote{This can cause multiple members to have the same name, for
4137 information on how this affects reading the archive, @ref{multiple}.}
4138 The new, concatenated archive will be called by the same name as the
4139 one given with the @option{--file} option. As usual, if you omit
4140 @option{--file}, @command{tar} will use the value of the environment
4141 variable @env{TAPE}, or, if this has not been set, the default archive name.
4143 @FIXME{There is no way to specify a new name...}
4145 To demonstrate how @option{--concatenate} works, create two small archives
4146 called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
4147 files from @file{practice}:
4150 $ @kbd{tar -cvf bluesrock.tar blues rock}
4153 $ @kbd{tar -cvf folkjazz.tar folk jazz}
4159 If you like, You can run @samp{tar --list} to make sure the archives
4160 contain what they are supposed to:
4163 $ @kbd{tar -tvf bluesrock.tar}
4164 -rw-r--r-- melissa user 105 1997-01-21 19:42 blues
4165 -rw-r--r-- melissa user 33 1997-01-20 15:34 rock
4166 $ @kbd{tar -tvf jazzfolk.tar}
4167 -rw-r--r-- melissa user 20 1996-09-23 16:44 folk
4168 -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
4171 We can concatenate these two archives with @command{tar}:
4175 $ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
4178 If you now list the contents of the @file{bluesrock.tar}, you will see
4179 that now it also contains the archive members of @file{jazzfolk.tar}:
4182 $ @kbd{tar --list --file=bluesrock.tar}
4189 When you use @option{--concatenate}, the source and target archives must
4190 already exist and must have been created using compatible format
4191 parameters. Notice, that @command{tar} does not check whether the
4192 archives it concatenates have compatible formats, it does not
4193 even check if the files are really tar archives.
4195 Like @option{--append} (@option{-r}), this operation cannot be performed on some
4196 tape drives, due to deficiencies in the formats those tape drives use.
4198 @cindex @code{concatenate} vs @command{cat}
4199 @cindex @command{cat} vs @code{concatenate}
4200 It may seem more intuitive to you to want or try to use @command{cat} to
4201 concatenate two archives instead of using the @option{--concatenate}
4202 operation; after all, @command{cat} is the utility for combining files.
4204 However, @command{tar} archives incorporate an end-of-file marker which
4205 must be removed if the concatenated archives are to be read properly as
4206 one archive. @option{--concatenate} removes the end-of-archive marker
4207 from the target archive before each new archive is appended. If you use
4208 @command{cat} to combine the archives, the result will not be a valid
4209 @command{tar} format archive. If you need to retrieve files from an
4210 archive that was added to using the @command{cat} utility, use the
4211 @option{--ignore-zeros} (@option{-i}) option. @xref{Ignore Zeros}, for further
4212 information on dealing with archives improperly combined using the
4213 @command{cat} shell utility.
4216 @subsection Removing Archive Members Using @option{--delete}
4218 @cindex Deleting files from an archive
4219 @cindex Removing files from an archive
4222 You can remove members from an archive by using the @option{--delete}
4223 option. Specify the name of the archive with @option{--file}
4224 (@option{-f}) and then specify the names of the members to be deleted;
4225 if you list no member names, nothing will be deleted. The
4226 @option{--verbose} option will cause @command{tar} to print the names
4227 of the members as they are deleted. As with @option{--extract}, you
4228 must give the exact member names when using @samp{tar --delete}.
4229 @option{--delete} will remove all versions of the named file from the
4230 archive. The @option{--delete} operation can run very slowly.
4232 Unlike other operations, @option{--delete} has no short form.
4234 @cindex Tapes, using @option{--delete} and
4235 @cindex Deleting from tape archives
4236 This operation will rewrite the archive. You can only use
4237 @option{--delete} on an archive if the archive device allows you to
4238 write to any point on the media, such as a disk; because of this, it
4239 does not work on magnetic tapes. Do not try to delete an archive member
4240 from a magnetic tape; the action will not succeed, and you will be
4241 likely to scramble the archive and damage your tape. There is no safe
4242 way (except by completely re-writing the archive) to delete files from
4243 most kinds of magnetic tape. @xref{Media}.
4245 To delete all versions of the file @file{blues} from the archive
4246 @file{collection.tar} in the @file{practice} directory, make sure you
4247 are in that directory, and then,
4250 $ @kbd{tar --list --file=collection.tar}
4255 $ @kbd{tar --delete --file=collection.tar blues}
4256 $ @kbd{tar --list --file=collection.tar}
4263 @FIXME{Check if the above listing is actually produced after running
4264 all the examples on collection.tar.}
4266 The @option{--delete} option has been reported to work properly when
4267 @command{tar} acts as a filter from @code{stdin} to @code{stdout}.
4270 @subsection Comparing Archive Members with the File System
4271 @cindex Verifying the currency of an archive
4275 The @option{--compare} (@option{-d}), or @option{--diff} operation compares
4276 specified archive members against files with the same names, and then
4277 reports differences in file size, mode, owner, modification date and
4278 contents. You should @emph{only} specify archive member names, not file
4279 names. If you do not name any members, then @command{tar} will compare the
4280 entire archive. If a file is represented in the archive but does not
4281 exist in the file system, @command{tar} reports a difference.
4283 You have to specify the record size of the archive when modifying an
4284 archive with a non-default record size.
4286 @command{tar} ignores files in the file system that do not have
4287 corresponding members in the archive.
4289 The following example compares the archive members @file{rock},
4290 @file{blues} and @file{funk} in the archive @file{bluesrock.tar} with
4291 files of the same name in the file system. (Note that there is no file,
4292 @file{funk}; @command{tar} will report an error message.)
4295 $ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
4298 tar: funk not found in archive
4301 The spirit behind the @option{--compare} (@option{--diff},
4302 @option{-d}) option is to check whether the archive represents the
4303 current state of files on disk, more than validating the integrity of
4304 the archive media. For this later goal, @xref{verify}.
4306 @node create options
4307 @section Options Used by @option{--create}
4309 @xopindex{create, additional options}
4310 The previous chapter described the basics of how to use
4311 @option{--create} (@option{-c}) to create an archive from a set of files.
4312 @xref{create}. This section described advanced options to be used with
4316 * override:: Overriding File Metadata.
4317 * Ignore Failed Read::
4321 @subsection Overriding File Metadata
4323 As described above, a @command{tar} archive keeps, for each member it contains,
4324 its @dfn{metadata}, such as modification time, mode and ownership of
4325 the file. @GNUTAR{} allows to replace these data with other values
4326 when adding files to the archive. The options described in this
4327 section affect creation of archives of any type. For POSIX archives,
4328 see also @ref{PAX keywords}, for additional ways of controlling
4329 metadata, stored in the archive.
4333 @item --mode=@var{permissions}
4335 When adding files to an archive, @command{tar} will use
4336 @var{permissions} for the archive members, rather than the permissions
4337 from the files. @var{permissions} can be specified either as an octal
4338 number or as symbolic permissions, like with
4339 @command{chmod} (@xref{File permissions, Permissions, File
4340 permissions, fileutils, @acronym{GNU} file utilities}. This reference
4341 also has useful information for those not being overly familiar with
4342 the UNIX permission system). Using latter syntax allows for
4343 more flexibility. For example, the value @samp{a+rw} adds read and write
4344 permissions for everybody, while retaining executable bits on directories
4345 or on any other file already marked as executable:
4348 $ @kbd{tar -c -f archive.tar --mode='a+rw' .}
4351 @item --mtime=@var{date}
4354 When adding files to an archive, @command{tar} will use @var{date} as
4355 the modification time of members when creating archives, instead of
4356 their actual modification times. The argument @var{date} can be
4357 either a textual date representation in almost arbitrary format
4358 (@pxref{Date input formats}) or a name of the existing file, starting
4359 with @samp{/} or @samp{.}. In the latter case, the modification time
4360 of that file will be used.
4362 The following example will set the modification date to 00:00:00 UTC,
4366 $ @kbd{tar -c -f archive.tar --mtime='1970-01-01' .}
4370 When used with @option{--verbose} (@pxref{verbose tutorial}) @GNUTAR{}
4371 will try to convert the specified date back to its textual
4372 representation and compare it with the one given with
4373 @option{--mtime} options. If the two dates differ, @command{tar} will
4374 print a warning saying what date it will use. This is to help user
4375 ensure he is using the right date.
4380 $ @kbd{tar -c -f archive.tar -v --mtime=yesterday .}
4381 tar: Option --mtime: Treating date `yesterday' as 2006-06-20
4386 @item --owner=@var{user}
4389 Specifies that @command{tar} should use @var{user} as the owner of members
4390 when creating archives, instead of the user associated with the source
4391 file. The argument @var{user} can be either an existing user symbolic
4392 name, or a decimal numeric user @acronym{ID}.
4394 There is no value indicating a missing number, and @samp{0} usually means
4395 @code{root}. Some people like to force @samp{0} as the value to offer in
4396 their distributions for the owner of files, because the @code{root} user is
4397 anonymous anyway, so that might as well be the owner of anonymous
4398 archives. For example:
4402 $ @kbd{tar -c -f archive.tar --owner=0 .}
4404 $ @kbd{tar -c -f archive.tar --owner=root .}
4408 @item --group=@var{group}
4411 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
4412 rather than the group from the source file. The argument @var{group}
4413 can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
4416 @node Ignore Failed Read
4417 @subsection Ignore Fail Read
4420 @item --ignore-failed-read
4421 @opindex ignore-failed-read
4422 Do not exit with nonzero on unreadable files or directories.
4425 @node extract options
4426 @section Options Used by @option{--extract}
4429 @xopindex{extract, additional options}
4430 The previous chapter showed how to use @option{--extract} to extract
4431 an archive into the file system. Various options cause @command{tar} to
4432 extract more information than just file contents, such as the owner,
4433 the permissions, the modification date, and so forth. This section
4434 presents options to be used with @option{--extract} when certain special
4435 considerations arise. You may review the information presented in
4436 @ref{extract} for more basic information about the
4437 @option{--extract} operation.
4440 * Reading:: Options to Help Read Archives
4441 * Writing:: Changing How @command{tar} Writes Files
4442 * Scarce:: Coping with Scarce Resources
4446 @subsection Options to Help Read Archives
4447 @cindex Options when reading archives
4450 @cindex Reading incomplete records
4451 @cindex Records, incomplete
4452 @opindex read-full-records
4453 Normally, @command{tar} will request data in full record increments from
4454 an archive storage device. If the device cannot return a full record,
4455 @command{tar} will report an error. However, some devices do not always
4456 return full records, or do not require the last record of an archive to
4457 be padded out to the next record boundary. To keep reading until you
4458 obtain a full record, or to accept an incomplete record if it contains
4459 an end-of-archive marker, specify the @option{--read-full-records} (@option{-B}) option
4460 in conjunction with the @option{--extract} or @option{--list} operations.
4463 The @option{--read-full-records} (@option{-B}) option is turned on by default when
4464 @command{tar} reads an archive from standard input, or from a remote
4465 machine. This is because on @acronym{BSD} Unix systems, attempting to read a
4466 pipe returns however much happens to be in the pipe, even if it is
4467 less than was requested. If this option were not enabled, @command{tar}
4468 would fail as soon as it read an incomplete record from the pipe.
4470 If you're not sure of the blocking factor of an archive, you can
4471 read the archive by specifying @option{--read-full-records} (@option{-B}) and
4472 @option{--blocking-factor=@var{512-size}} (@option{-b
4473 @var{512-size}}), using a blocking factor larger than what the archive
4474 uses. This lets you avoid having to determine the blocking factor
4475 of an archive. @xref{Blocking Factor}.
4478 * read full records::
4482 @node read full records
4483 @unnumberedsubsubsec Reading Full Records
4485 @FIXME{need sentence or so of intro here}
4488 @opindex read-full-records
4489 @item --read-full-records
4491 Use in conjunction with @option{--extract} (@option{--get},
4492 @option{-x}) to read an archive which contains incomplete records, or
4493 one which has a blocking factor less than the one specified.
4497 @unnumberedsubsubsec Ignoring Blocks of Zeros
4499 @cindex End-of-archive blocks, ignoring
4500 @cindex Ignoring end-of-archive blocks
4501 @opindex ignore-zeros
4502 Normally, @command{tar} stops reading when it encounters a block of zeros
4503 between file entries (which usually indicates the end of the archive).
4504 @option{--ignore-zeros} (@option{-i}) allows @command{tar} to
4505 completely read an archive which contains a block of zeros before the
4506 end (i.e., a damaged archive, or one that was created by concatenating
4507 several archives together).
4509 The @option{--ignore-zeros} (@option{-i}) option is turned off by default because many
4510 versions of @command{tar} write garbage after the end-of-archive entry,
4511 since that part of the media is never supposed to be read. @GNUTAR{}
4512 does not write after the end of an archive, but seeks to
4513 maintain compatibility among archiving utilities.
4516 @item --ignore-zeros
4518 To ignore blocks of zeros (i.e., end-of-archive entries) which may be
4519 encountered while reading an archive. Use in conjunction with
4520 @option{--extract} or @option{--list}.
4524 @subsection Changing How @command{tar} Writes Files
4527 @FIXME{Introductory paragraph}
4530 * Dealing with Old Files::
4531 * Overwrite Old Files::
4533 * Keep Newer Files::
4535 * Recursive Unlink::
4536 * Data Modification Times::
4537 * Setting Access Permissions::
4538 * Directory Modification Times and Permissions::
4539 * Writing to Standard Output::
4540 * Writing to an External Program::
4544 @node Dealing with Old Files
4545 @unnumberedsubsubsec Options Controlling the Overwriting of Existing Files
4547 @xopindex{overwrite-dir, introduced}
4548 When extracting files, if @command{tar} discovers that the extracted
4549 file already exists, it normally replaces the file by removing it before
4550 extracting it, to prevent confusion in the presence of hard or symbolic
4551 links. (If the existing file is a symbolic link, it is removed, not
4552 followed.) However, if a directory cannot be removed because it is
4553 nonempty, @command{tar} normally overwrites its metadata (ownership,
4554 permission, etc.). The @option{--overwrite-dir} option enables this
4555 default behavior. To be more cautious and preserve the metadata of
4556 such a directory, use the @option{--no-overwrite-dir} option.
4558 @cindex Overwriting old files, prevention
4559 @xopindex{keep-old-files, introduced}
4560 To be even more cautious and prevent existing files from being replaced, use
4561 the @option{--keep-old-files} (@option{-k}) option. It causes @command{tar} to refuse
4562 to replace or update a file that already exists, i.e., a file with the
4563 same name as an archive member prevents extraction of that archive
4564 member. Instead, it reports an error.
4566 @xopindex{overwrite, introduced}
4567 To be more aggressive about altering existing files, use the
4568 @option{--overwrite} option. It causes @command{tar} to overwrite
4569 existing files and to follow existing symbolic links when extracting.
4571 @cindex Protecting old files
4572 Some people argue that @GNUTAR{} should not hesitate
4573 to overwrite files with other files when extracting. When extracting
4574 a @command{tar} archive, they expect to see a faithful copy of the
4575 state of the file system when the archive was created. It is debatable
4576 that this would always be a proper behavior. For example, suppose one
4577 has an archive in which @file{usr/local} is a link to
4578 @file{usr/local2}. Since then, maybe the site removed the link and
4579 renamed the whole hierarchy from @file{/usr/local2} to
4580 @file{/usr/local}. Such things happen all the time. I guess it would
4581 not be welcome at all that @GNUTAR{} removes the
4582 whole hierarchy just to make room for the link to be reinstated
4583 (unless it @emph{also} simultaneously restores the full
4584 @file{/usr/local2}, of course!) @GNUTAR{} is indeed
4585 able to remove a whole hierarchy to reestablish a symbolic link, for
4586 example, but @emph{only if} @option{--recursive-unlink} is specified
4587 to allow this behavior. In any case, single files are silently
4590 @xopindex{unlink-first, introduced}
4591 Finally, the @option{--unlink-first} (@option{-U}) option can improve performance in
4592 some cases by causing @command{tar} to remove files unconditionally
4593 before extracting them.
4595 @node Overwrite Old Files
4596 @unnumberedsubsubsec Overwrite Old Files
4601 Overwrite existing files and directory metadata when extracting files
4604 This causes @command{tar} to write extracted files into the file system without
4605 regard to the files already on the system; i.e., files with the same
4606 names as archive members are overwritten when the archive is extracted.
4607 It also causes @command{tar} to extract the ownership, permissions,
4608 and time stamps onto any preexisting files or directories.
4609 If the name of a corresponding file name is a symbolic link, the file
4610 pointed to by the symbolic link will be overwritten instead of the
4611 symbolic link itself (if this is possible). Moreover, special devices,
4612 empty directories and even symbolic links are automatically removed if
4613 they are in the way of extraction.
4615 Be careful when using the @option{--overwrite} option, particularly when
4616 combined with the @option{--absolute-names} (@option{-P}) option, as this combination
4617 can change the contents, ownership or permissions of any file on your
4618 system. Also, many systems do not take kindly to overwriting files that
4619 are currently being executed.
4621 @opindex overwrite-dir
4622 @item --overwrite-dir
4623 Overwrite the metadata of directories when extracting files from an
4624 archive, but remove other files before extracting.
4627 @node Keep Old Files
4628 @unnumberedsubsubsec Keep Old Files
4631 @opindex keep-old-files
4632 @item --keep-old-files
4634 Do not replace existing files from archive. The
4635 @option{--keep-old-files} (@option{-k}) option prevents @command{tar}
4636 from replacing existing files with files with the same name from the
4637 archive. The @option{--keep-old-files} option is meaningless with
4638 @option{--list} (@option{-t}). Prevents @command{tar} from replacing
4639 files in the file system during extraction.
4642 @node Keep Newer Files
4643 @unnumberedsubsubsec Keep Newer Files
4646 @opindex keep-newer-files
4647 @item --keep-newer-files
4648 Do not replace existing files that are newer than their archive
4649 copies. This option is meaningless with @option{--list} (@option{-t}).
4653 @unnumberedsubsubsec Unlink First
4656 @opindex unlink-first
4657 @item --unlink-first
4659 Remove files before extracting over them.
4660 This can make @command{tar} run a bit faster if you know in advance
4661 that the extracted files all need to be removed. Normally this option
4662 slows @command{tar} down slightly, so it is disabled by default.
4665 @node Recursive Unlink
4666 @unnumberedsubsubsec Recursive Unlink
4669 @opindex recursive-unlink
4670 @item --recursive-unlink
4671 When this option is specified, try removing files and directory hierarchies
4672 before extracting over them. @emph{This is a dangerous option!}
4675 If you specify the @option{--recursive-unlink} option,
4676 @command{tar} removes @emph{anything} that keeps you from extracting a file
4677 as far as current permissions will allow it. This could include removal
4678 of the contents of a full directory hierarchy.
4680 @node Data Modification Times
4681 @unnumberedsubsubsec Setting Data Modification Times
4683 @cindex Data modification times of extracted files
4684 @cindex Modification times of extracted files
4685 Normally, @command{tar} sets the data modification times of extracted
4686 files to the corresponding times recorded for the files in the archive, but
4687 limits the permissions of extracted files by the current @code{umask}
4690 To set the data modification times of extracted files to the time when
4691 the files were extracted, use the @option{--touch} (@option{-m}) option in
4692 conjunction with @option{--extract} (@option{--get}, @option{-x}).
4698 Sets the data modification time of extracted archive members to the time
4699 they were extracted, not the time recorded for them in the archive.
4700 Use in conjunction with @option{--extract} (@option{--get}, @option{-x}).
4703 @node Setting Access Permissions
4704 @unnumberedsubsubsec Setting Access Permissions
4706 @cindex Permissions of extracted files
4707 @cindex Modes of extracted files
4708 To set the modes (access permissions) of extracted files to those
4709 recorded for those files in the archive, use @option{--same-permissions}
4710 in conjunction with the @option{--extract} (@option{--get},
4711 @option{-x}) operation.
4714 @opindex preserve-permissions
4715 @opindex same-permissions
4716 @item --preserve-permissions
4717 @itemx --same-permissions
4718 @c @itemx --ignore-umask
4720 Set modes of extracted archive members to those recorded in the
4721 archive, instead of current umask settings. Use in conjunction with
4722 @option{--extract} (@option{--get}, @option{-x}).
4725 @node Directory Modification Times and Permissions
4726 @unnumberedsubsubsec Directory Modification Times and Permissions
4728 After successfully extracting a file member, @GNUTAR{} normally
4729 restores its permissions and modification times, as described in the
4730 previous sections. This cannot be done for directories, because
4731 after extracting a directory @command{tar} will almost certainly
4732 extract files into that directory and this will cause the directory
4733 modification time to be updated. Moreover, restoring that directory
4734 permissions may not permit file creation within it. Thus, restoring
4735 directory permissions and modification times must be delayed at least
4736 until all files have been extracted into that directory. @GNUTAR{}
4737 restores directories using the following approach.
4739 The extracted directories are created with the mode specified in the
4740 archive, as modified by the umask of the user, which gives sufficient
4741 permissions to allow file creation. The meta-information about the
4742 directory is recorded in the temporary list of directories. When
4743 preparing to extract next archive member, @GNUTAR{} checks if the
4744 directory prefix of this file contains the remembered directory. If
4745 it does not, the program assumes that all files have been extracted
4746 into that directory, restores its modification time and permissions
4747 and removes its entry from the internal list. This approach allows
4748 to correctly restore directory meta-information in the majority of
4749 cases, while keeping memory requirements sufficiently small. It is
4750 based on the fact, that most @command{tar} archives use the predefined
4751 order of members: first the directory, then all the files and
4752 subdirectories in that directory.
4754 However, this is not always true. The most important exception are
4755 incremental archives (@pxref{Incremental Dumps}). The member order in
4756 an incremental archive is reversed: first all directory members are
4757 stored, followed by other (non-directory) members. So, when extracting
4758 from incremental archives, @GNUTAR{} alters the above procedure. It
4759 remembers all restored directories, and restores their meta-data
4760 only after the entire archive has been processed. Notice, that you do
4761 not need to specify any special options for that, as @GNUTAR{}
4762 automatically detects archives in incremental format.
4764 There may be cases, when such processing is required for normal archives
4765 too. Consider the following example:
4769 $ @kbd{tar --no-recursion -cvf archive \
4770 foo foo/file1 bar bar/file foo/file2}
4779 During the normal operation, after encountering @file{bar}
4780 @GNUTAR{} will assume that all files from the directory @file{foo}
4781 were already extracted and will therefore restore its timestamp and
4782 permission bits. However, after extracting @file{foo/file2} the
4783 directory timestamp will be offset again.
4785 To correctly restore directory meta-information in such cases, use
4786 @option{delay-directory-restore} command line option:
4789 @opindex delay-directory-restore
4790 @item --delay-directory-restore
4791 Delays restoring of the modification times and permissions of extracted
4792 directories until the end of extraction. This way, correct
4793 meta-information is restored even if the archive has unusual member
4796 @opindex no-delay-directory-restore
4797 @item --no-delay-directory-restore
4798 Cancel the effect of the previous @option{--delay-directory-restore}.
4799 Use this option if you have used @option{--delay-directory-restore} in
4800 @env{TAR_OPTIONS} variable (@pxref{TAR_OPTIONS}) and wish to
4801 temporarily disable it.
4804 @node Writing to Standard Output
4805 @unnumberedsubsubsec Writing to Standard Output
4807 @cindex Writing extracted files to standard output
4808 @cindex Standard output, writing extracted files to
4809 To write the extracted files to the standard output, instead of
4810 creating the files on the file system, use @option{--to-stdout} (@option{-O}) in
4811 conjunction with @option{--extract} (@option{--get}, @option{-x}). This option is useful if you are
4812 extracting files to send them through a pipe, and do not need to
4813 preserve them in the file system. If you extract multiple members,
4814 they appear on standard output concatenated, in the order they are
4815 found in the archive.
4821 Writes files to the standard output. Use only in conjunction with
4822 @option{--extract} (@option{--get}, @option{-x}). When this option is
4823 used, instead of creating the files specified, @command{tar} writes
4824 the contents of the files extracted to its standard output. This may
4825 be useful if you are only extracting the files in order to send them
4826 through a pipe. This option is meaningless with @option{--list}
4830 This can be useful, for example, if you have a tar archive containing
4831 a big file and don't want to store the file on disk before processing
4832 it. You can use a command like this:
4835 tar -xOzf foo.tgz bigfile | process
4838 or even like this if you want to process the concatenation of the files:
4841 tar -xOzf foo.tgz bigfile1 bigfile2 | process
4844 However, @option{--to-command} may be more convenient for use with
4845 multiple files. See the next section.
4847 @node Writing to an External Program
4848 @unnumberedsubsubsec Writing to an External Program
4850 You can instruct @command{tar} to send the contents of each extracted
4851 file to the standard input of an external program:
4855 @item --to-command=@var{command}
4856 Extract files and pipe their contents to the standard input of
4857 @var{command}. When this option is used, instead of creating the
4858 files specified, @command{tar} invokes @var{command} and pipes the
4859 contents of the files to its standard output. @var{Command} may
4860 contain command line arguments. The program is executed via
4861 @code{sh -c}. Notice, that @var{command} is executed once for each regular file
4862 extracted. Non-regular files (directories, etc.) are ignored when this
4866 The command can obtain the information about the file it processes
4867 from the following environment variables:
4870 @vrindex TAR_FILETYPE, to-command environment
4872 Type of the file. It is a single letter with the following meaning:
4874 @multitable @columnfractions 0.10 0.90
4875 @item f @tab Regular file
4876 @item d @tab Directory
4877 @item l @tab Symbolic link
4878 @item h @tab Hard link
4879 @item b @tab Block device
4880 @item c @tab Character device
4883 Currently only regular files are supported.
4885 @vrindex TAR_MODE, to-command environment
4887 File mode, an octal number.
4889 @vrindex TAR_FILENAME, to-command environment
4891 The name of the file.
4893 @vrindex TAR_REALNAME, to-command environment
4895 Name of the file as stored in the archive.
4897 @vrindex TAR_UNAME, to-command environment
4899 Name of the file owner.
4901 @vrindex TAR_GNAME, to-command environment
4903 Name of the file owner group.
4905 @vrindex TAR_ATIME, to-command environment
4907 Time of last access. It is a decimal number, representing seconds
4908 since the epoch. If the archive provides times with nanosecond
4909 precision, the nanoseconds are appended to the timestamp after a
4912 @vrindex TAR_MTIME, to-command environment
4914 Time of last modification.
4916 @vrindex TAR_CTIME, to-command environment
4918 Time of last status change.
4920 @vrindex TAR_SIZE, to-command environment
4924 @vrindex TAR_UID, to-command environment
4926 UID of the file owner.
4928 @vrindex TAR_GID, to-command environment
4930 GID of the file owner.
4933 In addition to these variables, @env{TAR_VERSION} contains the
4934 @GNUTAR{} version number.
4936 If @var{command} exits with a non-0 status, @command{tar} will print
4937 an error message similar to the following:
4940 tar: 2345: Child returned status 1
4943 Here, @samp{2345} is the PID of the finished process.
4945 If this behavior is not wanted, use @option{--ignore-command-error}:
4948 @opindex ignore-command-error
4949 @item --ignore-command-error
4950 Ignore exit codes of subprocesses. Notice that if the program
4951 exits on signal or otherwise terminates abnormally, the error message
4952 will be printed even if this option is used.
4954 @opindex no-ignore-command-error
4955 @item --no-ignore-command-error
4956 Cancel the effect of any previous @option{--ignore-command-error}
4957 option. This option is useful if you have set
4958 @option{--ignore-command-error} in @env{TAR_OPTIONS}
4959 (@pxref{TAR_OPTIONS}) and wish to temporarily cancel it.
4963 @unnumberedsubsubsec Removing Files
4965 @FIXME{The section is too terse. Something more to add? An example,
4969 @opindex remove-files
4970 @item --remove-files
4971 Remove files after adding them to the archive.
4975 @subsection Coping with Scarce Resources
4978 @cindex Small memory
4979 @cindex Running out of space
4987 @unnumberedsubsubsec Starting File
4990 @opindex starting-file
4991 @item --starting-file=@var{name}
4992 @itemx -K @var{name}
4993 Starts an operation in the middle of an archive. Use in conjunction
4994 with @option{--extract} (@option{--get}, @option{-x}) or @option{--list} (@option{-t}).
4997 @cindex Middle of the archive, starting in the
4998 If a previous attempt to extract files failed due to lack of disk
4999 space, you can use @option{--starting-file=@var{name}} (@option{-K
5000 @var{name}}) to start extracting only after member @var{name} of the
5001 archive. This assumes, of course, that there is now free space, or
5002 that you are now extracting into a different file system. (You could
5003 also choose to suspend @command{tar}, remove unnecessary files from
5004 the file system, and then restart the same @command{tar} operation.
5005 In this case, @option{--starting-file} is not necessary.
5006 @xref{Incremental Dumps}, @xref{interactive}, and @ref{exclude}.)
5009 @unnumberedsubsubsec Same Order
5012 @cindex Large lists of file names on small machines
5014 @opindex preserve-order
5016 @itemx --preserve-order
5018 To process large lists of file names on machines with small amounts of
5019 memory. Use in conjunction with @option{--compare} (@option{--diff},
5020 @option{-d}), @option{--list} (@option{-t}) or @option{--extract}
5021 (@option{--get}, @option{-x}).
5024 The @option{--same-order} (@option{--preserve-order}, @option{-s}) option tells @command{tar} that the list of file
5025 names to be listed or extracted is sorted in the same order as the
5026 files in the archive. This allows a large list of names to be used,
5027 even on a small machine that would not otherwise be able to hold all
5028 the names in memory at the same time. Such a sorted list can easily be
5029 created by running @samp{tar -t} on the archive and editing its output.
5031 This option is probably never needed on modern computer systems.
5034 @section Backup options
5036 @cindex backup options
5038 @GNUTAR{} offers options for making backups of files
5039 before writing new versions. These options control the details of
5040 these backups. They may apply to the archive itself before it is
5041 created or rewritten, as well as individual extracted members. Other
5042 @acronym{GNU} programs (@command{cp}, @command{install}, @command{ln},
5043 and @command{mv}, for example) offer similar options.
5045 Backup options may prove unexpectedly useful when extracting archives
5046 containing many members having identical name, or when extracting archives
5047 on systems having file name limitations, making different members appear
5048 has having similar names through the side-effect of name truncation.
5049 (This is true only if we have a good scheme for truncated backup names,
5050 which I'm not sure at all: I suspect work is needed in this area.)
5051 When any existing file is backed up before being overwritten by extraction,
5052 then clashing files are automatically be renamed to be unique, and the
5053 true name is kept for only the last file of a series of clashing files.
5054 By using verbose mode, users may track exactly what happens.
5056 At the detail level, some decisions are still experimental, and may
5057 change in the future, we are waiting comments from our users. So, please
5058 do not learn to depend blindly on the details of the backup features.
5059 For example, currently, directories themselves are never renamed through
5060 using these options, so, extracting a file over a directory still has
5061 good chances to fail. Also, backup options apply to created archives,
5062 not only to extracted members. For created archives, backups will not
5063 be attempted when the archive is a block or character device, or when it
5064 refers to a remote file.
5066 For the sake of simplicity and efficiency, backups are made by renaming old
5067 files prior to creation or extraction, and not by copying. The original
5068 name is restored if the file creation fails. If a failure occurs after a
5069 partial extraction of a file, both the backup and the partially extracted
5073 @item --backup[=@var{method}]
5075 @vindex VERSION_CONTROL
5077 Back up files that are about to be overwritten or removed.
5078 Without this option, the original versions are destroyed.
5080 Use @var{method} to determine the type of backups made.
5081 If @var{method} is not specified, use the value of the @env{VERSION_CONTROL}
5082 environment variable. And if @env{VERSION_CONTROL} is not set,
5083 use the @samp{existing} method.
5085 @vindex version-control @r{Emacs variable}
5086 This option corresponds to the Emacs variable @samp{version-control};
5087 the same values for @var{method} are accepted as in Emacs. This option
5088 also allows more descriptive names. The valid @var{method}s are:
5093 @cindex numbered @r{backup method}
5094 Always make numbered backups.
5098 @cindex existing @r{backup method}
5099 Make numbered backups of files that already have them, simple backups
5104 @cindex simple @r{backup method}
5105 Always make simple backups.
5109 @item --suffix=@var{suffix}
5111 @cindex backup suffix
5112 @vindex SIMPLE_BACKUP_SUFFIX
5113 Append @var{suffix} to each backup file made with @option{--backup}. If this
5114 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
5115 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
5116 set, the default is @samp{~}, just as in Emacs.
5121 @section Notable @command{tar} Usages
5124 @FIXME{Using Unix file linking capability to recreate directory
5125 structures---linking files into one subdirectory and then
5126 @command{tar}ring that directory.}
5128 @FIXME{Nice hairy example using absolute-names, newer, etc.}
5131 You can easily use archive files to transport a group of files from
5132 one system to another: put all relevant files into an archive on one
5133 computer system, transfer the archive to another system, and extract
5134 the contents there. The basic transfer medium might be magnetic tape,
5135 Internet FTP, or even electronic mail (though you must encode the
5136 archive with @command{uuencode} in order to transport it properly by
5137 mail). Both machines do not have to use the same operating system, as
5138 long as they both support the @command{tar} program.
5140 For example, here is how you might copy a directory's contents from
5141 one disk to another, while preserving the dates, modes, owners and
5142 link-structure of all the files therein. In this case, the transfer
5143 medium is a @dfn{pipe}, which is one a Unix redirection mechanism:
5146 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
5150 You can avoid subshells by using @option{-C} option:
5153 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xf -}
5157 The command also works using short option forms:
5160 $ @kbd{(cd sourcedir; tar --create --file=- . ) \
5161 | (cd targetdir; tar --extract --file=-)}
5163 $ @kbd{tar --directory sourcedir --create --file=- . ) \
5164 | tar --directory targetdir --extract --file=-}
5168 This is one of the easiest methods to transfer a @command{tar} archive.
5171 @section Looking Ahead: The Rest of this Manual
5173 You have now seen how to use all eight of the operations available to
5174 @command{tar}, and a number of the possible options. The next chapter
5175 explains how to choose and change file and archive names, how to use
5176 files to store names of other files which you can then call as
5177 arguments to @command{tar} (this can help you save time if you expect to
5178 archive the same list of files a number of times), and so forth.
5179 @FIXME{in case it's not obvious, i'm making this up in some sense
5180 based on my limited memory of what the next chapter *really* does. i
5181 just wanted to flesh out this final section a little bit so i'd
5182 remember to stick it in here. :-)}
5184 If there are too many files to conveniently list on the command line,
5185 you can list the names in a file, and @command{tar} will read that file.
5188 There are various ways of causing @command{tar} to skip over some files,
5189 and not archive them. @xref{Choosing}.
5192 @chapter Performing Backups and Restoring Files
5195 @GNUTAR{} is distributed along with the scripts
5196 which the Free Software Foundation uses for performing backups. There
5197 is no corresponding scripts available yet for doing restoration of
5198 files. Even if there is a good chance those scripts may be satisfying
5199 to you, they are not the only scripts or methods available for doing
5200 backups and restore. You may well create your own, or use more
5201 sophisticated packages dedicated to that purpose.
5203 Some users are enthusiastic about @code{Amanda} (The Advanced Maryland
5204 Automatic Network Disk Archiver), a backup system developed by James
5205 da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
5206 This is free software, and it is available at these places:
5209 http://www.cs.umd.edu/projects/amanda/amanda.html
5210 ftp://ftp.cs.umd.edu/pub/amanda
5215 Here is a possible plan for a future documentation about the backuping
5216 scripts which are provided within the @GNUTAR{}
5222 @item what are dumps
5223 @item different levels of dumps
5225 @item full dump = dump everything
5226 @item level 1, level 2 dumps etc
5227 A level @var{n} dump dumps everything changed since the last level
5230 @item how to use scripts for dumps (ie, the concept)
5232 @item scripts to run after editing backup specs (details)
5234 @item Backup Specs, what is it.
5236 @item how to customize
5237 @item actual text of script [/sp/dump/backup-specs]
5241 @item rsh doesn't work
5242 @item rtape isn't installed
5245 @item the @option{--incremental} option of tar
5248 @item write protection
5249 @item types of media, different sizes and types, useful for different things
5250 @item files and tape marks
5251 one tape mark between files, two at end.
5252 @item positioning the tape
5253 MT writes two at end of write,
5254 backspaces over one when writing again.
5260 This chapter documents both the provided shell scripts and @command{tar}
5261 options which are more specific to usage as a backup tool.
5263 To @dfn{back up} a file system means to create archives that contain
5264 all the files in that file system. Those archives can then be used to
5265 restore any or all of those files (for instance if a disk crashes or a
5266 file is accidentally deleted). File system @dfn{backups} are also
5270 * Full Dumps:: Using @command{tar} to Perform Full Dumps
5271 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
5272 * Backup Levels:: Levels of Backups
5273 * Backup Parameters:: Setting Parameters for Backups and Restoration
5274 * Scripted Backups:: Using the Backup Scripts
5275 * Scripted Restoration:: Using the Restore Script
5279 @section Using @command{tar} to Perform Full Dumps
5285 @cindex corrupted archives
5286 Full dumps should only be made when no other people or programs
5287 are modifying files in the file system. If files are modified while
5288 @command{tar} is making the backup, they may not be stored properly in
5289 the archive, in which case you won't be able to restore them if you
5290 have to. (Files not being modified are written with no trouble, and do
5291 not corrupt the entire archive.)
5293 You will want to use the @option{--label=@var{archive-label}}
5294 (@option{-V @var{archive-label}}) option to give the archive a
5295 volume label, so you can tell what this archive is even if the label
5296 falls off the tape, or anything like that.
5298 Unless the file system you are dumping is guaranteed to fit on
5299 one volume, you will need to use the @option{--multi-volume} (@option{-M}) option.
5300 Make sure you have enough tapes on hand to complete the backup.
5302 If you want to dump each file system separately you will need to use
5303 the @option{--one-file-system} option to prevent
5304 @command{tar} from crossing file system boundaries when storing
5307 The @option{--incremental} (@option{-G}) (@pxref{Incremental Dumps})
5308 option is not needed, since this is a complete copy of everything in
5309 the file system, and a full restore from this backup would only be
5310 done onto a completely
5313 Unless you are in a hurry, and trust the @command{tar} program (and your
5314 tapes), it is a good idea to use the @option{--verify} (@option{-W})
5315 option, to make sure your files really made it onto the dump properly.
5316 This will also detect cases where the file was modified while (or just
5317 after) it was being archived. Not all media (notably cartridge tapes)
5318 are capable of being verified, unfortunately.
5320 @node Incremental Dumps
5321 @section Using @command{tar} to Perform Incremental Dumps
5323 @dfn{Incremental backup} is a special form of @GNUTAR{} archive that
5324 stores additional metadata so that exact state of the file system
5325 can be restored when extracting the archive.
5327 @GNUTAR{} currently offers two options for handling incremental
5328 backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
5329 @var{snapshot-file}}) and @option{--incremental} (@option{-G}).
5331 @opindex listed-incremental
5332 The option @option{--listed-incremental} instructs tar to operate on
5333 an incremental archive with additional metadata stored in a standalone
5334 file, called a @dfn{snapshot file}. The purpose of this file is to help
5335 determine which files have been changed, added or deleted since the
5336 last backup, so that the next incremental backup will contain only
5337 modified files. The name of the snapshot file is given as an argument
5341 @item --listed-incremental=@var{file}
5342 @itemx -g @var{file}
5343 Handle incremental backups with snapshot data in @var{file}.
5346 To create an incremental backup, you would use
5347 @option{--listed-incremental} together with @option{--create}
5348 (@pxref{create}). For example:
5351 $ @kbd{tar --create \
5352 --file=archive.1.tar \
5353 --listed-incremental=/var/log/usr.snar \
5357 This will create in @file{archive.1.tar} an incremental backup of
5358 the @file{/usr} file system, storing additional metadata in the file
5359 @file{/var/log/usr.snar}. If this file does not exist, it will be
5360 created. The created archive will then be a @dfn{level 0 backup};
5361 please see the next section for more on backup levels.
5363 Otherwise, if the file @file{/var/log/usr.snar} exists, it
5364 determines which files are modified. In this case only these files will be
5365 stored in the archive. Suppose, for example, that after running the
5366 above command, you delete file @file{/usr/doc/old} and create
5367 directory @file{/usr/local/db} with the following contents:
5370 $ @kbd{ls /usr/local/db}
5375 Some time later you create another incremental backup. You will
5379 $ @kbd{tar --create \
5380 --file=archive.2.tar \
5381 --listed-incremental=/var/log/usr.snar \
5383 tar: usr/local/db: Directory is new
5390 The created archive @file{archive.2.tar} will contain only these
5391 three members. This archive is called a @dfn{level 1 backup}. Notice
5392 that @file{/var/log/usr.snar} will be updated with the new data, so if
5393 you plan to create more @samp{level 1} backups, it is necessary to
5394 create a working copy of the snapshot file before running
5395 @command{tar}. The above example will then be modified as follows:
5398 $ @kbd{cp /var/log/usr.snar /var/log/usr.snar-1}
5399 $ @kbd{tar --create \
5400 --file=archive.2.tar \
5401 --listed-incremental=/var/log/usr.snar-1 \
5405 Incremental dumps depend crucially on time stamps, so the results are
5406 unreliable if you modify a file's time stamps during dumping (e.g.,
5407 with the @option{--atime-preserve=replace} option), or if you set the clock
5410 @cindex Device numbers, using in incremental backups
5411 Metadata stored in snapshot files include device numbers, which,
5412 obviously is supposed to be a non-volatile value. However, it turns
5413 out that NFS devices have undependable values when an automounter
5414 gets in the picture. This can lead to a great deal of spurious
5415 redumping in incremental dumps, so it is somewhat useless to compare
5416 two NFS devices numbers over time. The solution implemented currently
5417 is to considers all NFS devices as being equal when it comes to
5418 comparing directories; this is fairly gross, but there does not seem
5419 to be a better way to go.
5421 If you are using the @i{Linux} kernel, the device numbers can also
5422 change when upgrading to some newer versions of the kernel. This can
5423 cause the next backup to be full backup on the affected filesystems.
5424 @xref{Fixing Snapshot Files}, for the information on how to handle this case.
5426 Note that incremental archives use @command{tar} extensions and may
5427 not be readable by non-@acronym{GNU} versions of the @command{tar} program.
5429 @xopindex{listed-incremental, using with @option{--extract}}
5430 @xopindex{extract, using with @option{--listed-incremental}}
5431 To extract from the incremental dumps, use
5432 @option{--listed-incremental} together with @option{--extract}
5433 option (@pxref{extracting files}). In this case, @command{tar} does
5434 not need to access snapshot file, since all the data necessary for
5435 extraction are stored in the archive itself. So, when extracting, you
5436 can give whatever argument to @option{--listed-incremental}, the usual
5437 practice is to use @option{--listed-incremental=/dev/null}.
5438 Alternatively, you can use @option{--incremental}, which needs no
5439 arguments. In general, @option{--incremental} (@option{-G}) can be
5440 used as a shortcut for @option{--listed-incremental} when listing or
5441 extracting incremental backups (for more information, regarding this
5442 option, @pxref{incremental-op}).
5444 When extracting from the incremental backup @GNUTAR{} attempts to
5445 restore the exact state the file system had when the archive was
5446 created. In particular, it will @emph{delete} those files in the file
5447 system that did not exist in their directories when the archive was
5448 created. If you have created several levels of incremental files,
5449 then in order to restore the exact contents the file system had when
5450 the last level was created, you will need to restore from all backups
5451 in turn. Continuing our example, to restore the state of @file{/usr}
5452 file system, one would do@footnote{Notice, that since both archives
5453 were created without @option{-P} option (@pxref{absolute}), these
5454 commands should be run from the root file system.}:
5457 $ @kbd{tar --extract \
5458 --listed-incremental=/dev/null \
5459 --file archive.1.tar}
5460 $ @kbd{tar --extract \
5461 --listed-incremental=/dev/null \
5462 --file archive.2.tar}
5465 To list the contents of an incremental archive, use @option{--list}
5466 (@pxref{list}), as usual. To obtain more information about the
5467 archive, use @option{--listed-incremental} or @option{--incremental}
5468 combined with two @option{--verbose} options@footnote{Two
5469 @option{--verbose} options were selected to avoid breaking usual
5470 verbose listing output (@option{--list --verbose}) when using in
5473 @xopindex{incremental, using with @option{--list}}
5474 @xopindex{listed-incremental, using with @option{--list}}
5475 @xopindex{list, using with @option{--incremental}}
5476 @xopindex{list, using with @option{--listed-incremental}}
5477 Versions of @GNUTAR{} up to 1.15.1 used to dump verbatim binary
5478 contents of the DUMPDIR header (with terminating nulls) when
5479 @option{--incremental} or @option{--listed-incremental} option was
5480 given, no matter what the verbosity level. This behavior, and,
5481 especially, the binary output it produced were considered inconvenient
5482 and were changed in version 1.16}:
5485 @kbd{tar --list --incremental --verbose --verbose archive.tar}
5488 This command will print, for each directory in the archive, the list
5489 of files in that directory at the time the archive was created. This
5490 information is put out in a format which is both human-readable and
5491 unambiguous for a program: each file name is printed as
5498 where @var{x} is a letter describing the status of the file: @samp{Y}
5499 if the file is present in the archive, @samp{N} if the file is not
5500 included in the archive, or a @samp{D} if the file is a directory (and
5501 is included in the archive). @xref{Dumpdir}, for the detailed
5502 description of dumpdirs and status codes. Each such
5503 line is terminated by a newline character. The last line is followed
5504 by an additional newline to indicate the end of the data.
5506 @anchor{incremental-op}The option @option{--incremental} (@option{-G})
5507 gives the same behavior as @option{--listed-incremental} when used
5508 with @option{--list} and @option{--extract} options. When used with
5509 @option{--create} option, it creates an incremental archive without
5510 creating snapshot file. Thus, it is impossible to create several
5511 levels of incremental backups with @option{--incremental} option.
5514 @section Levels of Backups
5516 An archive containing all the files in the file system is called a
5517 @dfn{full backup} or @dfn{full dump}. You could insure your data by
5518 creating a full dump every day. This strategy, however, would waste a
5519 substantial amount of archive media and user time, as unchanged files
5520 are daily re-archived.
5522 It is more efficient to do a full dump only occasionally. To back up
5523 files between full dumps, you can use @dfn{incremental dumps}. A @dfn{level
5524 one} dump archives all the files that have changed since the last full
5527 A typical dump strategy would be to perform a full dump once a week,
5528 and a level one dump once a day. This means some versions of files
5529 will in fact be archived more than once, but this dump strategy makes
5530 it possible to restore a file system to within one day of accuracy by
5531 only extracting two archives---the last weekly (full) dump and the
5532 last daily (level one) dump. The only information lost would be in
5533 files changed or created since the last daily backup. (Doing dumps
5534 more than once a day is usually not worth the trouble).
5536 @GNUTAR{} comes with scripts you can use to do full
5537 and level-one (actually, even level-two and so on) dumps. Using
5538 scripts (shell programs) to perform backups and restoration is a
5539 convenient and reliable alternative to typing out file name lists
5540 and @command{tar} commands by hand.
5542 Before you use these scripts, you need to edit the file
5543 @file{backup-specs}, which specifies parameters used by the backup
5544 scripts and by the restore script. This file is usually located
5545 in @file{/etc/backup} directory. @xref{Backup Parameters}, for its
5546 detailed description. Once the backup parameters are set, you can
5547 perform backups or restoration by running the appropriate script.
5549 The name of the backup script is @code{backup}. The name of the
5550 restore script is @code{restore}. The following sections describe
5551 their use in detail.
5553 @emph{Please Note:} The backup and restoration scripts are
5554 designed to be used together. While it is possible to restore files by
5555 hand from an archive which was created using a backup script, and to create
5556 an archive by hand which could then be extracted using the restore script,
5557 it is easier to use the scripts. @xref{Incremental Dumps}, before
5558 making such an attempt.
5560 @node Backup Parameters
5561 @section Setting Parameters for Backups and Restoration
5563 The file @file{backup-specs} specifies backup parameters for the
5564 backup and restoration scripts provided with @command{tar}. You must
5565 edit @file{backup-specs} to fit your system configuration and schedule
5566 before using these scripts.
5568 Syntactically, @file{backup-specs} is a shell script, containing
5569 mainly variable assignments. However, any valid shell construct
5570 is allowed in this file. Particularly, you may wish to define
5571 functions within that script (e.g., see @code{RESTORE_BEGIN} below).
5572 For more information about shell script syntax, please refer to
5573 @url{http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
5574 g_02, the definition of the Shell Command Language}. See also
5575 @ref{Top,,Bash Features,bashref,Bash Reference Manual}.
5577 The shell variables controlling behavior of @code{backup} and
5578 @code{restore} are described in the following subsections.
5581 * General-Purpose Variables::
5582 * Magnetic Tape Control::
5584 * backup-specs example:: An Example Text of @file{Backup-specs}
5587 @node General-Purpose Variables
5588 @subsection General-Purpose Variables
5590 @defvr {Backup variable} ADMINISTRATOR
5591 The user name of the backup administrator. @code{Backup} scripts
5592 sends a backup report to this address.
5595 @defvr {Backup variable} BACKUP_HOUR
5596 The hour at which the backups are done. This can be a number from 0
5597 to 23, or the time specification in form @var{hours}:@var{minutes},
5598 or the string @samp{now}.
5600 This variable is used by @code{backup}. Its value may be overridden
5601 using @option{--time} option (@pxref{Scripted Backups}).
5604 @defvr {Backup variable} TAPE_FILE
5606 The device @command{tar} writes the archive to. If @var{TAPE_FILE}
5607 is a remote archive (@pxref{remote-dev}), backup script will suppose
5608 that your @command{mt} is able to access remote devices. If @var{RSH}
5609 (@pxref{RSH}) is set, @option{--rsh-command} option will be added to
5610 invocations of @command{mt}.
5613 @defvr {Backup variable} BLOCKING
5615 The blocking factor @command{tar} will use when writing the dump archive.
5616 @xref{Blocking Factor}.
5619 @defvr {Backup variable} BACKUP_DIRS
5621 A list of file systems to be dumped (for @code{backup}), or restored
5622 (for @code{restore}). You can include any directory
5623 name in the list --- subdirectories on that file system will be
5624 included, regardless of how they may look to other networked machines.
5625 Subdirectories on other file systems will be ignored.
5627 The host name specifies which host to run @command{tar} on, and should
5628 normally be the host that actually contains the file system. However,
5629 the host machine must have @GNUTAR{} installed, and
5630 must be able to access the directory containing the backup scripts and
5631 their support files using the same file name that is used on the
5632 machine where the scripts are run (i.e., what @command{pwd} will print
5633 when in that directory on that machine). If the host that contains
5634 the file system does not have this capability, you can specify another
5635 host as long as it can access the file system through NFS.
5637 If the list of file systems is very long you may wish to put it
5638 in a separate file. This file is usually named
5639 @file{/etc/backup/dirs}, but this name may be overridden in
5640 @file{backup-specs} using @code{DIRLIST} variable.
5643 @defvr {Backup variable} DIRLIST
5645 The name of the file that contains a list of file systems to backup
5646 or restore. By default it is @file{/etc/backup/dirs}.
5649 @defvr {Backup variable} BACKUP_FILES
5651 A list of individual files to be dumped (for @code{backup}), or restored
5652 (for @code{restore}). These should be accessible from the machine on
5653 which the backup script is run.
5655 If the list of file systems is very long you may wish to store it
5656 in a separate file. This file is usually named
5657 @file{/etc/backup/files}, but this name may be overridden in
5658 @file{backup-specs} using @code{FILELIST} variable.
5661 @defvr {Backup variable} FILELIST
5663 The name of the file that contains a list of individual files to backup
5664 or restore. By default it is @file{/etc/backup/files}.
5667 @defvr {Backup variable} MT
5669 Full file name of @command{mt} binary.
5672 @defvr {Backup variable} RSH
5674 Full file name of @command{rsh} binary or its equivalent. You may wish to
5675 set it to @code{ssh}, to improve security. In this case you will have
5676 to use public key authentication.
5679 @defvr {Backup variable} RSH_COMMAND
5681 Full file name of @command{rsh} binary on remote machines. This will
5682 be passed via @option{--rsh-command} option to the remote invocation
5686 @defvr {Backup variable} VOLNO_FILE
5688 Name of temporary file to hold volume numbers. This needs to be accessible
5689 by all the machines which have file systems to be dumped.
5692 @defvr {Backup variable} XLIST
5694 Name of @dfn{exclude file list}. An @dfn{exclude file list} is a file
5695 located on the remote machine and containing the list of files to
5696 be excluded from the backup. Exclude file lists are searched in
5697 /etc/tar-backup directory. A common use for exclude file lists
5698 is to exclude files containing security-sensitive information
5699 (e.g., @file{/etc/shadow} from backups).
5701 This variable affects only @code{backup}.
5704 @defvr {Backup variable} SLEEP_TIME
5706 Time to sleep between dumps of any two successive file systems
5708 This variable affects only @code{backup}.
5711 @defvr {Backup variable} DUMP_REMIND_SCRIPT
5713 Script to be run when it's time to insert a new tape in for the next
5714 volume. Administrators may want to tailor this script for their site.
5715 If this variable isn't set, @GNUTAR{} will display its built-in
5716 prompt, and will expect confirmation from the console. For the
5717 description of the default prompt, see @ref{change volume prompt}.
5721 @defvr {Backup variable} SLEEP_MESSAGE
5723 Message to display on the terminal while waiting for dump time. Usually
5724 this will just be some literal text.
5727 @defvr {Backup variable} TAR
5729 Full file name of the @GNUTAR{} executable. If this is not set, backup
5730 scripts will search @command{tar} in the current shell path.
5733 @node Magnetic Tape Control
5734 @subsection Magnetic Tape Control
5736 Backup scripts access tape device using special @dfn{hook functions}.
5737 These functions take a single argument -- the name of the tape
5738 device. Their names are kept in the following variables:
5740 @defvr {Backup variable} MT_BEGIN
5741 The name of @dfn{begin} function. This function is called before
5742 accessing the drive. By default it retensions the tape:
5748 mt -f "$1" retension
5753 @defvr {Backup variable} MT_REWIND
5754 The name of @dfn{rewind} function. The default definition is as
5767 @defvr {Backup variable} MT_OFFLINE
5768 The name of the function switching the tape off line. By default
5769 it is defined as follows:
5772 MT_OFFLINE=mt_offline
5780 @defvr {Backup variable} MT_STATUS
5781 The name of the function used to obtain the status of the archive device,
5782 including error count. Default definition:
5794 @subsection User Hooks
5796 @dfn{User hooks} are shell functions executed before and after
5797 each @command{tar} invocation. Thus, there are @dfn{backup
5798 hooks}, which are executed before and after dumping each file
5799 system, and @dfn{restore hooks}, executed before and
5800 after restoring a file system. Each user hook is a shell function
5801 taking four arguments:
5803 @deffn {User Hook Function} hook @var{level} @var{host} @var{fs} @var{fsname}
5808 Current backup or restore level.
5811 Name or IP address of the host machine being dumped or restored.
5814 Full file name of the file system being dumped or restored.
5817 File system name with directory separators replaced with colons. This
5818 is useful, e.g., for creating unique files.
5822 Following variables keep the names of user hook functions
5824 @defvr {Backup variable} DUMP_BEGIN
5825 Dump begin function. It is executed before dumping the file system.
5828 @defvr {Backup variable} DUMP_END
5829 Executed after dumping the file system.
5832 @defvr {Backup variable} RESTORE_BEGIN
5833 Executed before restoring the file system.
5836 @defvr {Backup variable} RESTORE_END
5837 Executed after restoring the file system.
5840 @node backup-specs example
5841 @subsection An Example Text of @file{Backup-specs}
5843 The following is an example of @file{backup-specs}:
5846 # site-specific parameters for file system backup.
5848 ADMINISTRATOR=friedman
5850 TAPE_FILE=/dev/nrsmt0
5852 # Use @code{ssh} instead of the less secure @code{rsh}
5854 RSH_COMMAND=/usr/bin/ssh
5856 # Override MT_STATUS function:
5862 # Disable MT_OFFLINE function
5879 apple-gunkies:/com/mailer/gnu
5880 apple-gunkies:/com/archive/gnu"
5882 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
5886 @node Scripted Backups
5887 @section Using the Backup Scripts
5889 The syntax for running a backup script is:
5892 backup --level=@var{level} --time=@var{time}
5895 The @option{level} option requests the dump level. Thus, to produce
5896 a full dump, specify @code{--level=0} (this is the default, so
5897 @option{--level} may be omitted if its value is @code{0}).
5898 @footnote{For backward compatibility, the @code{backup} will also
5899 try to deduce the requested dump level from the name of the
5900 script itself. If the name consists of a string @samp{level-}
5901 followed by a single decimal digit, that digit is taken as
5902 the dump level number. Thus, you may create a link from @code{backup}
5903 to @code{level-1} and then run @code{level-1} whenever you need to
5904 create a level one dump.}
5906 The @option{--time} option determines when should the backup be
5907 run. @var{Time} may take three forms:
5910 @item @var{hh}:@var{mm}
5912 The dump must be run at @var{hh} hours @var{mm} minutes.
5916 The dump must be run at @var{hh} hours
5920 The dump must be run immediately.
5923 You should start a script with a tape or disk mounted. Once you
5924 start a script, it prompts you for new tapes or disks as it
5925 needs them. Media volumes don't have to correspond to archive
5926 files --- a multi-volume archive can be started in the middle of a
5927 tape that already contains the end of another multi-volume archive.
5928 The @code{restore} script prompts for media by its archive volume,
5929 so to avoid an error message you should keep track of which tape
5930 (or disk) contains which volume of the archive (@pxref{Scripted
5933 The backup scripts write two files on the file system. The first is a
5934 record file in @file{/etc/tar-backup/}, which is used by the scripts
5935 to store and retrieve information about which files were dumped. This
5936 file is not meant to be read by humans, and should not be deleted by
5937 them. @xref{Snapshot Files}, for a more detailed explanation of this
5940 The second file is a log file containing the names of the file systems
5941 and files dumped, what time the backup was made, and any error
5942 messages that were generated, as well as how much space was left in
5943 the media volume after the last volume of the archive was written.
5944 You should check this log file after every backup. The file name is
5945 @file{log-@var{mm-dd-yyyy}-level-@var{n}}, where @var{mm-dd-yyyy}
5946 represents current date, and @var{n} represents current dump level number.
5948 The script also prints the name of each system being dumped to the
5951 Following is the full list of options accepted by @code{backup}
5955 @item -l @var{level}
5956 @itemx --level=@var{level}
5957 Do backup level @var{level} (default 0).
5961 Force backup even if today's log file already exists.
5963 @item -v[@var{level}]
5964 @itemx --verbose[=@var{level}]
5965 Set verbosity level. The higher the level is, the more debugging
5966 information will be output during execution. Default @var{level}
5967 is 100, which means the highest debugging level.
5969 @item -t @var{start-time}
5970 @itemx --time=@var{start-time}
5971 Wait till @var{time}, then do backup.
5975 Display short help message and exit.
5979 Display information about the program's name, version, origin and legal
5980 status, all on standard output, and then exit successfully.
5984 @node Scripted Restoration
5985 @section Using the Restore Script
5987 To restore files that were archived using a scripted backup, use the
5988 @code{restore} script. Its usage is quite straightforward. In the
5989 simplest form, invoke @code{restore --all}, it will
5990 then restore all the file systems and files specified in
5991 @file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
5993 You may select the file systems (and/or files) to restore by
5994 giving @code{restore} list of @dfn{patterns} in its command
5995 line. For example, running
6002 will restore all file systems on the machine @samp{albert}. A more
6003 complicated example:
6006 restore 'albert:*' '*:/var'
6010 This command will restore all file systems on the machine @samp{albert}
6011 as well as @file{/var} file system on all machines.
6013 By default @code{restore} will start restoring files from the lowest
6014 available dump level (usually zero) and will continue through
6015 all available dump levels. There may be situations where such a
6016 thorough restore is not necessary. For example, you may wish to
6017 restore only files from the recent level one backup. To do so,
6018 use @option{--level} option, as shown in the example below:
6024 The full list of options accepted by @code{restore} follows:
6029 Restore all file systems and files specified in @file{backup-specs}
6031 @item -l @var{level}
6032 @itemx --level=@var{level}
6033 Start restoring from the given backup level, instead of the default 0.
6035 @item -v[@var{level}]
6036 @itemx --verbose[=@var{level}]
6037 Set verbosity level. The higher the level is, the more debugging
6038 information will be output during execution. Default @var{level}
6039 is 100, which means the highest debugging level.
6043 Display short help message and exit.
6047 Display information about the program's name, version, origin and legal
6048 status, all on standard output, and then exit successfully.
6051 You should start the restore script with the media containing the
6052 first volume of the archive mounted. The script will prompt for other
6053 volumes as they are needed. If the archive is on tape, you don't need
6054 to rewind the tape to to its beginning---if the tape head is
6055 positioned past the beginning of the archive, the script will rewind
6056 the tape as needed. @xref{Tape Positioning}, for a discussion of tape
6060 @strong{Warning:} The script will delete files from the active file
6061 system if they were not in the file system when the archive was made.
6064 @xref{Incremental Dumps}, for an explanation of how the script makes
6068 @chapter Choosing Files and Names for @command{tar}
6071 Certain options to @command{tar} enable you to specify a name for your
6072 archive. Other options let you decide which files to include or exclude
6073 from the archive, based on when or whether files were modified, whether
6074 the file names do or don't match specified patterns, or whether files
6075 are in specified directories.
6077 This chapter discusses these options in detail.
6080 * file:: Choosing the Archive's Name
6081 * Selecting Archive Members::
6082 * files:: Reading Names from a File
6083 * exclude:: Excluding Some Files
6084 * wildcards:: Wildcards Patterns and Matching
6085 * quoting styles:: Ways of Quoting Special Characters in Names
6086 * transform:: Modifying File and Member Names
6087 * after:: Operating Only on New Files
6088 * recurse:: Descending into Directories
6089 * one:: Crossing File System Boundaries
6093 @section Choosing and Naming Archive Files
6096 @cindex Naming an archive
6097 @cindex Archive Name
6098 @cindex Choosing an archive file
6099 @cindex Where is the archive?
6100 By default, @command{tar} uses an archive file name that was compiled when
6101 it was built on the system; usually this name refers to some physical
6102 tape drive on the machine. However, the person who installed @command{tar}
6103 on the system may not have set the default to a meaningful value as far as
6104 most users are concerned. As a result, you will usually want to tell
6105 @command{tar} where to find (or create) the archive. The
6106 @option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
6107 option allows you to either specify or name a file to use as the archive
6108 instead of the default archive file location.
6111 @xopindex{file, short description}
6112 @item --file=@var{archive-name}
6113 @itemx -f @var{archive-name}
6114 Name the archive to create or operate on. Use in conjunction with
6118 For example, in this @command{tar} command,
6121 $ @kbd{tar -cvf collection.tar blues folk jazz}
6125 @file{collection.tar} is the name of the archive. It must directly
6126 follow the @option{-f} option, since whatever directly follows @option{-f}
6127 @emph{will} end up naming the archive. If you neglect to specify an
6128 archive name, you may end up overwriting a file in the working directory
6129 with the archive you create since @command{tar} will use this file's name
6130 for the archive name.
6132 An archive can be saved as a file in the file system, sent through a
6133 pipe or over a network, or written to an I/O device such as a tape,
6134 floppy disk, or CD write drive.
6136 @cindex Writing new archives
6137 @cindex Archive creation
6138 If you do not name the archive, @command{tar} uses the value of the
6139 environment variable @env{TAPE} as the file name for the archive. If
6140 that is not available, @command{tar} uses a default, compiled-in archive
6141 name, usually that for tape unit zero (i.e., @file{/dev/tu00}).
6143 @cindex Standard input and output
6144 @cindex tar to standard input and output
6145 If you use @file{-} as an @var{archive-name}, @command{tar} reads the
6146 archive from standard input (when listing or extracting files), or
6147 writes it to standard output (when creating an archive). If you use
6148 @file{-} as an @var{archive-name} when modifying an archive,
6149 @command{tar} reads the original archive from its standard input and
6150 writes the entire new archive to its standard output.
6152 The following example is a convenient way of copying directory
6153 hierarchy from @file{sourcedir} to @file{targetdir}.
6156 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)}
6159 The @option{-C} option allows to avoid using subshells:
6162 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xpf -}
6165 In both examples above, the leftmost @command{tar} invocation archives
6166 the contents of @file{sourcedir} to the standard output, while the
6167 rightmost one reads this archive from its standard input and
6168 extracts it. The @option{-p} option tells it to restore permissions
6169 of the extracted files.
6171 @cindex Remote devices
6172 @cindex tar to a remote device
6174 To specify an archive file on a device attached to a remote machine,
6178 @kbd{--file=@var{hostname}:/@var{dev}/@var{file-name}}
6182 @command{tar} will complete the remote connection, if possible, and
6183 prompt you for a username and password. If you use
6184 @option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
6185 will complete the remote connection, if possible, using your username
6186 as the username on the remote machine.
6188 @cindex Local and remote archives
6189 @anchor{local and remote archives}
6190 If the archive file name includes a colon (@samp{:}), then it is assumed
6191 to be a file on another machine. If the archive file is
6192 @samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the
6193 host @var{host}. The remote host is accessed using the @command{rsh}
6194 program, with a username of @var{user}. If the username is omitted
6195 (along with the @samp{@@} sign), then your user name will be used.
6196 (This is the normal @command{rsh} behavior.) It is necessary for the
6197 remote machine, in addition to permitting your @command{rsh} access, to
6198 have the @file{rmt} program installed (This command is included in
6199 the @GNUTAR{} distribution and by default is installed under
6200 @file{@var{prefix}/libexec/rmt}, were @var{prefix} means your
6201 installation prefix). If you need to use a file whose name includes a
6202 colon, then the remote tape drive behavior
6203 can be inhibited by using the @option{--force-local} option.
6205 When the archive is being created to @file{/dev/null}, @GNUTAR{}
6206 tries to minimize input and output operations. The Amanda backup
6207 system, when used with @GNUTAR{}, has an initial sizing pass which
6210 @node Selecting Archive Members
6211 @section Selecting Archive Members
6212 @cindex Specifying files to act on
6213 @cindex Specifying archive members
6215 @dfn{File Name arguments} specify which files in the file system
6216 @command{tar} operates on, when creating or adding to an archive, or which
6217 archive members @command{tar} operates on, when reading or deleting from
6218 an archive. @xref{Operations}.
6220 To specify file names, you can include them as the last arguments on
6221 the command line, as follows:
6223 @kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
6226 If a file name begins with dash (@samp{-}), precede it with
6227 @option{--add-file} option to prevent it from being treated as an
6230 @anchor{input name quoting}
6231 By default @GNUTAR{} attempts to @dfn{unquote} each file or member
6232 name, replacing @dfn{escape sequences} according to the following
6235 @multitable @columnfractions 0.20 0.60
6236 @headitem Escape @tab Replaced with
6237 @item \a @tab Audible bell (@acronym{ASCII} 7)
6238 @item \b @tab Backspace (@acronym{ASCII} 8)
6239 @item \f @tab Form feed (@acronym{ASCII} 12)
6240 @item \n @tab New line (@acronym{ASCII} 10)
6241 @item \r @tab Carriage return (@acronym{ASCII} 13)
6242 @item \t @tab Horizontal tabulation (@acronym{ASCII} 9)
6243 @item \v @tab Vertical tabulation (@acronym{ASCII} 11)
6244 @item \? @tab @acronym{ASCII} 127
6245 @item \@var{n} @tab @acronym{ASCII} @var{n} (@var{n} should be an octal number
6249 A backslash followed by any other symbol is retained.
6251 This default behavior is controlled by the following command line
6257 Enable unquoting input file or member names (default).
6261 Disable unquoting input file or member names.
6264 If you specify a directory name as a file name argument, all the files
6265 in that directory are operated on by @command{tar}.
6267 If you do not specify files, @command{tar} behavior differs depending
6268 on the operation mode as described below:
6270 When @command{tar} is invoked with @option{--create} (@option{-c}),
6271 @command{tar} will stop immediately, reporting the following:
6275 $ @kbd{tar cf a.tar}
6276 tar: Cowardly refusing to create an empty archive
6277 Try `tar --help' or `tar --usage' for more information.
6281 If you specify either @option{--list} (@option{-t}) or
6282 @option{--extract} (@option{--get}, @option{-x}), @command{tar}
6283 operates on all the archive members in the archive.
6285 If run with @option{--diff} option, tar will compare the archive with
6286 the contents of the current working directory.
6288 If you specify any other operation, @command{tar} does nothing.
6290 By default, @command{tar} takes file names from the command line. However,
6291 there are other ways to specify file or member names, or to modify the
6292 manner in which @command{tar} selects the files or members upon which to
6293 operate. In general, these methods work both for specifying the names
6294 of files and archive members.
6297 @section Reading Names from a File
6299 @cindex Reading file names from a file
6300 @cindex Lists of file names
6301 @cindex File Name arguments, alternatives
6302 Instead of giving the names of files or archive members on the command
6303 line, you can put the names into a file, and then use the
6304 @option{--files-from=@var{file-of-names}} (@option{-T
6305 @var{file-of-names}}) option to @command{tar}. Give the name of the
6306 file which contains the list of files to include as the argument to
6307 @option{--files-from}. In the list, the file names should be separated by
6308 newlines. You will frequently use this option when you have generated
6309 the list of files to archive with the @command{find} utility.
6313 @item --files-from=@var{file-name}
6314 @itemx -T @var{file-name}
6315 Get names to extract or create from file @var{file-name}.
6318 If you give a single dash as a file name for @option{--files-from}, (i.e.,
6319 you specify either @code{--files-from=-} or @code{-T -}), then the file
6320 names are read from standard input.
6322 Unless you are running @command{tar} with @option{--create}, you can not use
6323 both @code{--files-from=-} and @code{--file=-} (@code{-f -}) in the same
6326 Any number of @option{-T} options can be given in the command line.
6328 The following example shows how to use @command{find} to generate a list of
6329 files smaller than 400K in length and put that list into a file
6330 called @file{small-files}. You can then use the @option{-T} option to
6331 @command{tar} to specify the files from that file, @file{small-files}, to
6332 create the archive @file{little.tgz}. (The @option{-z} option to
6333 @command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for
6337 $ @kbd{find . -size -400 -print > small-files}
6338 $ @kbd{tar -c -v -z -T small-files -f little.tgz}
6342 In the file list given by @option{-T} option, any file name beginning
6343 with @samp{-} character is considered a @command{tar} option and is
6344 processed accordingly.@footnote{Versions of @GNUTAR{} up to 1.15.1
6345 recognized only @option{-C} option in file lists, and only if the
6346 option and its argument occupied two consecutive lines.} For example,
6347 the common use of this feature is to change to another directory by
6348 specifying @option{-C} option:
6358 $ @kbd{tar -c -f foo.tar --files-from list}
6363 In this example, @command{tar} will first switch to @file{/etc}
6364 directory and add files @file{passwd} and @file{hosts} to the
6365 archive. Then it will change to @file{/lib} directory and will archive
6366 the file @file{libc.a}. Thus, the resulting archive @file{foo.tar} will
6371 $ @kbd{tar tf foo.tar}
6379 @xopindex{directory, using in @option{--files-from} argument}
6380 Notice that the option parsing algorithm used with @option{-T} is
6381 stricter than the one used by shell. Namely, when specifying option
6382 arguments, you should observe the following rules:
6386 When using short (single-letter) option form, its argument must
6387 immediately follow the option letter, without any intervening
6388 whitespace. For example: @code{-Cdir}.
6391 When using long option form, the option argument must be separated
6392 from the option by a single equal sign. No whitespace is allowed on
6393 any side of the equal sign. For example: @code{--directory=dir}.
6396 For both short and long option forms, the option argument can be given
6397 on the next line after the option name, e.g.:
6418 If you happen to have a file whose name starts with @samp{-},
6419 precede it with @option{--add-file} option to prevent it from
6420 being recognized as an option. For example: @code{--add-file=--my-file}.
6427 @subsection @code{NUL} Terminated File Names
6429 @cindex File names, terminated by @code{NUL}
6430 @cindex @code{NUL} terminated file names
6431 The @option{--null} option causes
6432 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
6433 to read file names terminated by a @code{NUL} instead of a newline, so
6434 files whose names contain newlines can be archived using
6435 @option{--files-from}.
6440 Only consider @code{NUL} terminated file names, instead of files that
6441 terminate in a newline.
6444 The @option{--null} option is just like the one in @acronym{GNU}
6445 @command{xargs} and @command{cpio}, and is useful with the
6446 @option{-print0} predicate of @acronym{GNU} @command{find}. In
6447 @command{tar}, @option{--null} also disables special handling for
6448 file names that begin with dash.
6450 This example shows how to use @command{find} to generate a list of files
6451 larger than 800K in length and put that list into a file called
6452 @file{long-files}. The @option{-print0} option to @command{find} is just
6453 like @option{-print}, except that it separates files with a @code{NUL}
6454 rather than with a newline. You can then run @command{tar} with both the
6455 @option{--null} and @option{-T} options to specify that @command{tar} get the
6456 files from that file, @file{long-files}, to create the archive
6457 @file{big.tgz}. The @option{--null} option to @command{tar} will cause
6458 @command{tar} to recognize the @code{NUL} separator between files.
6461 $ @kbd{find . -size +800 -print0 > long-files}
6462 $ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
6465 @FIXME{say anything else here to conclude the section?}
6468 @section Excluding Some Files
6471 @cindex File names, excluding files by
6472 @cindex Excluding files by name and pattern
6473 @cindex Excluding files by file system
6474 To avoid operating on files whose names match a particular pattern,
6475 use the @option{--exclude} or @option{--exclude-from} options.
6479 @item --exclude=@var{pattern}
6480 Causes @command{tar} to ignore files that match the @var{pattern}.
6484 The @option{--exclude=@var{pattern}} option prevents any file or
6485 member whose name matches the shell wildcard (@var{pattern}) from
6487 For example, to create an archive with all the contents of the directory
6488 @file{src} except for files whose names end in @file{.o}, use the
6489 command @samp{tar -cf src.tar --exclude='*.o' src}.
6491 You may give multiple @option{--exclude} options.
6494 @opindex exclude-from
6495 @item --exclude-from=@var{file}
6496 @itemx -X @var{file}
6497 Causes @command{tar} to ignore files that match the patterns listed in
6501 @findex exclude-from
6502 Use the @option{--exclude-from} option to read a
6503 list of patterns, one per line, from @var{file}; @command{tar} will
6504 ignore files matching those patterns. Thus if @command{tar} is
6505 called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a
6506 single line @file{*.o}, no files whose names end in @file{.o} will be
6507 added to the archive.
6509 @findex exclude-caches
6510 When creating an archive, the @option{--exclude-caches} option family
6511 causes @command{tar} to exclude all directories that contain a @dfn{cache
6512 directory tag}. A cache directory tag is a short file with the
6513 well-known name @file{CACHEDIR.TAG} and having a standard header
6514 specified in @url{http://www.brynosaurus.com/cachedir/spec.html}.
6515 Various applications write cache directory tags into directories they
6516 use to hold regenerable, non-precious data, so that such data can be
6517 more easily excluded from backups.
6519 There are three @samp{exclude-caches} option, providing a different
6520 exclusion semantics:
6523 @opindex exclude-caches
6524 @item --exclude-caches
6525 Do not archive the contents of the directory, but archive the
6526 directory itself and the @file{CACHEDIR.TAG} file.
6528 @opindex exclude-caches-under
6529 @item --exclude-caches-under
6530 Do not archive the contents of the directory, nor the
6531 @file{CACHEDIR.TAG} file, archive only the directory itself.
6533 @opindex exclude-caches-all
6534 @item --exclude-caches-all
6535 Omit directories containing @file{CACHEDIR.TAG} file entirely.
6539 Another option family, @option{--exclude-tag}, provides a generalization of
6540 this concept. It takes a single argument, a file name to look for.
6541 Any directory that contains this file will be excluded from the dump.
6542 Similarly to @samp{exclude-caches}, there are three options in this
6546 @opindex exclude-tag
6547 @item --exclude-tag=@var{file}
6548 Do not dump the contents of the directory, but dump the
6549 directory itself and the @var{file}.
6551 @opindex exclude-tag-under
6552 @item --exclude-tag-under=@var{file}
6553 Do not dump the contents of the directory, nor the
6554 @var{file}, archive only the directory itself.
6556 @opindex exclude-tag-all
6557 @item --exclude-tag-all=@var{file}
6558 Omit directories containing @var{file} file entirely.
6561 Multiple @option{--exclude-tag*} options can be given.
6563 For example, given this directory:
6578 The @option{--exclude-tag} will produce the following:
6581 $ @kbd{tar -cf archive.tar --exclude-tag=tagfile -v dir}
6586 tar: dir/folk/: contains a cache directory tag tagfile;
6591 Both the @file{dir/folk} directory and its tagfile are preserved in
6592 the archive, however the rest of files in this directory are not.
6594 Now, using the @option{--exclude-tag-under} option will exclude
6595 @file{tagfile} from the dump, while still preserving the directory
6596 itself, as shown in this example:
6599 $ @kbd{tar -cf archive.tar --exclude-tag-under=tagfile -v dir}
6604 ./tar: dir/folk/: contains a cache directory tag tagfile;
6608 Finally, using @option{--exclude-tag-all} omits the @file{dir/folk}
6612 $ @kbd{tar -cf archive.tar --exclude-tag-all=tagfile -v dir}
6616 ./tar: dir/folk/: contains a cache directory tag tagfile;
6617 directory not dumped
6621 * problems with exclude::
6624 @node problems with exclude
6625 @unnumberedsubsec Problems with Using the @code{exclude} Options
6627 @xopindex{exclude, potential problems with}
6628 Some users find @samp{exclude} options confusing. Here are some common
6633 The main operating mode of @command{tar} does not act on a file name
6634 explicitly listed on the command line, if one of its file name
6635 components is excluded. In the example above, if
6636 you create an archive and exclude files that end with @samp{*.o}, but
6637 explicitly name the file @samp{dir.o/foo} after all the options have been
6638 listed, @samp{dir.o/foo} will be excluded from the archive.
6641 You can sometimes confuse the meanings of @option{--exclude} and
6642 @option{--exclude-from}. Be careful: use @option{--exclude} when files
6643 to be excluded are given as a pattern on the command line. Use
6644 @option{--exclude-from} to introduce the name of a file which contains
6645 a list of patterns, one per line; each of these patterns can exclude
6646 zero, one, or many files.
6649 When you use @option{--exclude=@var{pattern}}, be sure to quote the
6650 @var{pattern} parameter, so @GNUTAR{} sees wildcard characters
6651 like @samp{*}. If you do not do this, the shell might expand the
6652 @samp{*} itself using files at hand, so @command{tar} might receive a
6653 list of files instead of one pattern, or none at all, making the
6654 command somewhat illegal. This might not correspond to what you want.
6659 $ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}}
6667 $ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
6671 You must use use shell syntax, or globbing, rather than @code{regexp}
6672 syntax, when using exclude options in @command{tar}. If you try to use
6673 @code{regexp} syntax to describe files to be excluded, your command
6677 @FIXME{The change in semantics must have occurred before 1.11,
6678 so I doubt if it is worth mentioning at all. Anyway, should at
6679 least specify in which version the semantics changed.}
6680 In earlier versions of @command{tar}, what is now the
6681 @option{--exclude-from} option was called @option{--exclude} instead.
6682 Now, @option{--exclude} applies to patterns listed on the command
6683 line and @option{--exclude-from} applies to patterns listed in a
6689 @section Wildcards Patterns and Matching
6691 @dfn{Globbing} is the operation by which @dfn{wildcard} characters,
6692 @samp{*} or @samp{?} for example, are replaced and expanded into all
6693 existing files matching the given pattern. @GNUTAR{} can use wildcard
6694 patterns for matching (or globbing) archive members when extracting
6695 from or listing an archive. Wildcard patterns are also used for
6696 verifying volume labels of @command{tar} archives. This section has the
6697 purpose of explaining wildcard syntax for @command{tar}.
6699 @FIXME{the next few paragraphs need work.}
6701 A @var{pattern} should be written according to shell syntax, using wildcard
6702 characters to effect globbing. Most characters in the pattern stand
6703 for themselves in the matched string, and case is significant: @samp{a}
6704 will match only @samp{a}, and not @samp{A}. The character @samp{?} in the
6705 pattern matches any single character in the matched string. The character
6706 @samp{*} in the pattern matches zero, one, or more single characters in
6707 the matched string. The character @samp{\} says to take the following
6708 character of the pattern @emph{literally}; it is useful when one needs to
6709 match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves.
6711 The character @samp{[}, up to the matching @samp{]}, introduces a character
6712 class. A @dfn{character class} is a list of acceptable characters
6713 for the next single character of the matched string. For example,
6714 @samp{[abcde]} would match any of the first five letters of the alphabet.
6715 Note that within a character class, all of the ``special characters''
6716 listed above other than @samp{\} lose their special meaning; for example,
6717 @samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\},
6718 @samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints,
6719 the characters @samp{-} and @samp{]} must either come @emph{first} or
6720 @emph{last} in a character class.)
6722 @cindex Excluding characters from a character class
6723 @cindex Character class, excluding characters from
6724 If the first character of the class after the opening @samp{[}
6725 is @samp{!} or @samp{^}, then the meaning of the class is reversed.
6726 Rather than listing character to match, it lists those characters which
6727 are @emph{forbidden} as the next single character of the matched string.
6729 Other characters of the class stand for themselves. The special
6730 construction @samp{[@var{a}-@var{e}]}, using an hyphen between two
6731 letters, is meant to represent all characters between @var{a} and
6734 @FIXME{need to add a sentence or so here to make this clear for those
6735 who don't have dan around.}
6737 Periods (@samp{.}) or forward slashes (@samp{/}) are not considered
6738 special for wildcard matches. However, if a pattern completely matches
6739 a directory prefix of a matched string, then it matches the full matched
6740 string: thus, excluding a directory also excludes all the files beneath it.
6743 * controlling pattern-matching::
6746 @node controlling pattern-matching
6747 @unnumberedsubsec Controlling Pattern-Matching
6749 For the purposes of this section, we call @dfn{exclusion members} all
6750 member names obtained while processing @option{--exclude} and
6751 @option{--exclude-from} options, and @dfn{inclusion members} those
6752 member names that were given in the command line or read from the file
6753 specified with @option{--files-from} option.
6755 These two pairs of member lists are used in the following operations:
6756 @option{--diff}, @option{--extract}, @option{--list},
6759 There are no inclusion members in create mode (@option{--create} and
6760 @option{--append}), since in this mode the names obtained from the
6761 command line refer to @emph{files}, not archive members.
6763 By default, inclusion members are compared with archive members
6764 literally @footnote{Notice that earlier @GNUTAR{} versions used
6765 globbing for inclusion members, which contradicted to UNIX98
6766 specification and was not documented. @xref{Changes}, for more
6767 information on this and other changes.} and exclusion members are
6768 treated as globbing patterns. For example:
6772 $ @kbd{tar tf foo.tar}
6777 # @i{Member names are used verbatim:}
6778 $ @kbd{tar -xf foo.tar -v '[remarks]'}
6780 # @i{Exclude member names are globbed:}
6781 $ @kbd{tar -xf foo.tar -v --exclude '*.c'}
6787 This behavior can be altered by using the following options:
6792 Treat all member names as wildcards.
6794 @opindex no-wildcards
6795 @item --no-wildcards
6796 Treat all member names as literal strings.
6799 Thus, to extract files whose names end in @samp{.c}, you can use:
6802 $ @kbd{tar -xf foo.tar -v --wildcards '*.c'}
6808 Notice quoting of the pattern to prevent the shell from interpreting
6811 The effect of @option{--wildcards} option is canceled by
6812 @option{--no-wildcards}. This can be used to pass part of
6813 the command line arguments verbatim and other part as globbing
6814 patterns. For example, the following invocation:
6817 $ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'}
6821 instructs @command{tar} to extract from @file{foo.tar} all files whose
6822 names end in @samp{.txt} and the file named @file{[remarks]}.
6824 Normally, a pattern matches a name if an initial subsequence of the
6825 name's components matches the pattern, where @samp{*}, @samp{?}, and
6826 @samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
6827 and wildcards can match @samp{/}.
6829 Other than optionally stripping leading @samp{/} from names
6830 (@pxref{absolute}), patterns and names are used as-is. For
6831 example, trailing @samp{/} is not trimmed from a user-specified name
6832 before deciding whether to exclude it.
6834 However, this matching procedure can be altered by the options listed
6835 below. These options accumulate. For example:
6838 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
6842 ignores case when excluding @samp{makefile}, but not when excluding
6847 @opindex no-anchored
6849 @itemx --no-anchored
6850 If anchored, a pattern must match an initial subsequence
6851 of the name's components. Otherwise, the pattern can match any
6852 subsequence. Default is @option{--no-anchored} for exclusion members
6853 and @option{--anchored} inclusion members.
6855 @opindex ignore-case
6856 @opindex no-ignore-case
6858 @itemx --no-ignore-case
6859 When ignoring case, upper-case patterns match lower-case names and vice versa.
6860 When not ignoring case (the default), matching is case-sensitive.
6862 @opindex wildcards-match-slash
6863 @opindex no-wildcards-match-slash
6864 @item --wildcards-match-slash
6865 @itemx --no-wildcards-match-slash
6866 When wildcards match slash (the default for exclusion members), a
6867 wildcard like @samp{*} in the pattern can match a @samp{/} in the
6868 name. Otherwise, @samp{/} is matched only by @samp{/}.
6872 The @option{--recursion} and @option{--no-recursion} options
6873 (@pxref{recurse}) also affect how member patterns are interpreted. If
6874 recursion is in effect, a pattern matches a name if it matches any of
6875 the name's parent directories.
6877 The following table summarizes pattern-matching default values:
6879 @multitable @columnfractions .3 .7
6880 @headitem Members @tab Default settings
6881 @item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash}
6882 @item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash}
6885 @node quoting styles
6886 @section Quoting Member Names
6888 When displaying member names, @command{tar} takes care to avoid
6889 ambiguities caused by certain characters. This is called @dfn{name
6890 quoting}. The characters in question are:
6893 @item Non-printable control characters:
6895 @multitable @columnfractions 0.20 0.10 0.60
6896 @headitem Character @tab @acronym{ASCII} @tab Character name
6897 @item \a @tab 7 @tab Audible bell
6898 @item \b @tab 8 @tab Backspace
6899 @item \f @tab 12 @tab Form feed
6900 @item \n @tab 10 @tab New line
6901 @item \r @tab 13 @tab Carriage return
6902 @item \t @tab 9 @tab Horizontal tabulation
6903 @item \v @tab 11 @tab Vertical tabulation
6906 @item Space (@acronym{ASCII} 32)
6908 @item Single and double quotes (@samp{'} and @samp{"})
6910 @item Backslash (@samp{\})
6913 The exact way @command{tar} uses to quote these characters depends on
6914 the @dfn{quoting style}. The default quoting style, called
6915 @dfn{escape} (see below), uses backslash notation to represent control
6916 characters, space and backslash. Using this quoting style, control
6917 characters are represented as listed in column @samp{Character} in the
6918 above table, a space is printed as @samp{\ } and a backslash as @samp{\\}.
6920 @GNUTAR{} offers seven distinct quoting styles, which can be selected
6921 using @option{--quoting-style} option:
6924 @item --quoting-style=@var{style}
6925 @opindex quoting-style
6927 Sets quoting style. Valid values for @var{style} argument are:
6928 literal, shell, shell-always, c, escape, locale, clocale.
6931 These styles are described in detail below. To illustrate their
6932 effect, we will use an imaginary tar archive @file{arch.tar}
6933 containing the following members:
6937 # 1. Contains horizontal tabulation character.
6939 # 2. Contains newline character
6942 # 3. Contains a space
6944 # 4. Contains double quotes
6946 # 5. Contains single quotes
6948 # 6. Contains a backslash character:
6953 Here is how usual @command{ls} command would have listed them, if they
6954 had existed in the current working directory:
6972 No quoting, display each character as is:
6976 $ @kbd{tar tf arch.tar --quoting-style=literal}
6989 Display characters the same way Bourne shell does:
6990 control characters, except @samp{\t} and @samp{\n}, are printed using
6991 backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a
6992 single quote is printed as @samp{\'}. If a name contains any quoted
6993 characters, it is enclosed in single quotes. In particular, if a name
6994 contains single quotes, it is printed as several single-quoted strings:
6998 $ @kbd{tar tf arch.tar --quoting-style=shell}
7001 './a'\''single'\''quote'
7011 Same as @samp{shell}, but the names are always enclosed in single
7016 $ @kbd{tar tf arch.tar --quoting-style=shell-always}
7019 './a'\''single'\''quote'
7029 Use the notation of the C programming language. All names are
7030 enclosed in double quotes. Control characters are quoted using
7031 backslash notations, double quotes are represented as @samp{\"},
7032 backslash characters are represented as @samp{\\}. Single quotes and
7033 spaces are not quoted:
7037 $ @kbd{tar tf arch.tar --quoting-style=c}
7041 "./a\"double\"quote"
7049 Control characters are printed using backslash notation, a space is
7050 printed as @samp{\ } and a backslash as @samp{\\}. This is the
7051 default quoting style, unless it was changed when configured the
7056 $ @kbd{tar tf arch.tar --quoting-style=escape}
7068 Control characters, single quote and backslash are printed using
7069 backslash notation. All names are quoted using left and right
7070 quotation marks, appropriate to the current locale. If it does not
7071 define quotation marks, use @samp{`} as left and @samp{'} as right
7072 quotation marks. Any occurrences of the right quotation mark in a
7073 name are escaped with @samp{\}, for example:
7079 $ @kbd{tar tf arch.tar --quoting-style=locale}
7082 `./a\'single\'quote'
7091 Same as @samp{locale}, but @samp{"} is used for both left and right
7092 quotation marks, if not provided by the currently selected locale:
7096 $ @kbd{tar tf arch.tar --quoting-style=clocale}
7100 "./a\"double\"quote"
7108 You can specify which characters should be quoted in addition to those
7109 implied by the current quoting style:
7112 @item --quote-chars=@var{string}
7113 Always quote characters from @var{string}, even if the selected
7114 quoting style would not quote them.
7117 For example, using @samp{escape} quoting (compare with the usual
7118 escape listing above):
7122 $ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'}
7133 To disable quoting of such additional characters, use the following
7137 @item --no-quote-chars=@var{string}
7138 Remove characters listed in @var{string} from the list of quoted
7139 characters set by the previous @option{--quote-chars} option.
7142 This option is particularly useful if you have added
7143 @option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS})
7144 and wish to disable it for the current invocation.
7146 Note, that @option{--no-quote-chars} does @emph{not} disable those
7147 characters that are quoted by default in the selected quoting style.
7150 @section Modifying File and Member Names
7152 @command{Tar} archives contain detailed information about files stored
7153 in them and full file names are part of that information. When
7154 storing file to an archive, its file name is recorded in the archive
7155 along with the actual file contents. When restoring from an archive,
7156 a file is created on disk with exactly the same name as that stored
7157 in the archive. In the majority of cases this is the desired behavior
7158 of a file archiver. However, there are some cases when it is not.
7160 First of all, it is often unsafe to extract archive members with
7161 absolute file names or those that begin with a @file{../}. @GNUTAR{}
7162 takes special precautions when extracting such names and provides a
7163 special option for handling them, which is described in
7166 Secondly, you may wish to extract file names without some leading
7167 directory components, or with otherwise modified names. In other
7168 cases it is desirable to store files under differing names in the
7171 @GNUTAR{} provides two options for these needs.
7174 @opindex strip-components
7175 @item --strip-components=@var{number}
7176 Strip given @var{number} of leading components from file names before
7180 For example, suppose you have archived whole @file{/usr} hierarchy to
7181 a tar archive named @file{usr.tar}. Among other files, this archive
7182 contains @file{usr/include/stdlib.h}, which you wish to extract to
7183 the current working directory. To do so, you type:
7186 $ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h}
7189 The option @option{--strip=2} instructs @command{tar} to strip the
7190 two leading components (@file{usr/} and @file{include/}) off the file
7193 If you add to the above invocation @option{--verbose} (@option{-v})
7194 option, you will note that the verbose listing still contains the
7195 full file name, with the two removed components still in place. This
7196 can be inconvenient, so @command{tar} provides a special option for
7197 altering this behavior:
7199 @anchor{show-transformed-names}
7201 @opindex show-transformed-names
7202 @item --show-transformed-names
7203 Display file or member names with all requested transformations
7212 $ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h}
7213 usr/include/stdlib.h
7214 $ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h}
7219 Notice that in both cases the file is @file{stdlib.h} extracted to the
7220 current working directory, @option{--show-transformed-names} affects
7221 only the way its name is displayed.
7223 This option is especially useful for verifying whether the invocation
7224 will have the desired effect. Thus, before running
7227 $ @kbd{tar -x --strip=@var{n}}
7231 it is often advisable to run
7234 $ @kbd{tar -t -v --show-transformed --strip=@var{n}}
7238 to make sure the command will produce the intended results.
7240 In case you need to apply more complex modifications to the file name,
7241 @GNUTAR{} provides a general-purpose transformation option:
7245 @item --transform=@var{expression}
7246 Modify file names using supplied @var{expression}.
7250 The @var{expression} is a @command{sed}-like replace expression of the
7254 s/@var{regexp}/@var{replace}/[@var{flags}]
7258 where @var{regexp} is a @dfn{regular expression}, @var{replace} is a
7259 replacement for each file name part that matches @var{regexp}. Both
7260 @var{regexp} and @var{replace} are described in detail in
7261 @ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
7263 Supported @var{flags} are:
7267 Apply the replacement to @emph{all} matches to the @var{regexp}, not
7271 Use case-insensitive matching
7274 @var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
7275 regexps, Extended regular expressions, Extended regular expressions,
7279 Only replace the @var{number}th match of the @var{regexp}.
7281 Note: the @var{posix} standard does not specify what should happen
7282 when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
7283 follows the GNU @command{sed} implementation in this regard, so
7284 the interaction is defined to be: ignore matches before the
7285 @var{number}th, and then match and replace all matches from the
7290 Any delimiter can be used in lieue of @samp{/}, the only requirement being
7291 that it be used consistently throughout the expression. For example,
7292 the following two expressions are equivalent:
7301 Changing delimiters is often useful when the @var{regex} contains
7302 slashes. For example, it is more convenient to write @code{s,/,-,} than
7305 Here are several examples of @option{--transform} usage:
7308 @item Extract @file{usr/} hierarchy into @file{usr/local/}:
7311 $ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar}
7314 @item Strip two leading directory components (equivalent to
7315 @option{--strip-components=2}):
7318 $ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
7321 @item Prepend @file{/prefix/} to each file name:
7324 $ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
7327 @item Convert each file name to lower case:
7330 $ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
7335 Unlike @option{--strip-components}, @option{--transform} can be used
7336 in any @GNUTAR{} operation mode. For example, the following command
7337 adds files to the archive while replacing the leading @file{usr/}
7338 component with @file{var/}:
7341 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /}
7344 To test @option{--transform} effect we suggest using
7345 @option{--show-transformed-names} option:
7348 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \
7349 --verbose --show-transformed-names /}
7352 If both @option{--strip-components} and @option{--transform} are used
7353 together, then @option{--transform} is applied first, and the required
7354 number of components is then stripped from its result.
7357 @section Operating Only on New Files
7360 @cindex Excluding file by age
7361 @cindex Data Modification time, excluding files by
7362 @cindex Modification time, excluding files by
7363 @cindex Age, excluding files by
7364 The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
7365 @option{-N @var{date}}) option causes @command{tar} to only work on
7366 files whose data modification or status change times are newer than
7367 the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
7368 it is taken to be a file name; the data modification time of that file
7369 is used as the date. If you use this option when creating or appending
7370 to an archive, the archive will only include new files. If you use
7371 @option{--after-date} when extracting an archive, @command{tar} will
7372 only extract files newer than the @var{date} you specify.
7374 If you only want @command{tar} to make the date comparison based on
7375 modification of the file's data (rather than status
7376 changes), then use the @option{--newer-mtime=@var{date}} option.
7378 You may use these options with any operation. Note that these options
7379 differ from the @option{--update} (@option{-u}) operation in that they
7380 allow you to specify a particular date against which @command{tar} can
7381 compare when deciding whether or not to archive the files.
7386 @item --after-date=@var{date}
7387 @itemx --newer=@var{date}
7388 @itemx -N @var{date}
7389 Only store files newer than @var{date}.
7391 Acts on files only if their data modification or status change times are
7392 later than @var{date}. Use in conjunction with any operation.
7394 If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
7395 name; the data modification time of that file is used as the date.
7397 @opindex newer-mtime
7398 @item --newer-mtime=@var{date}
7399 Acts like @option{--after-date}, but only looks at data modification times.
7402 These options limit @command{tar} to operate only on files which have
7403 been modified after the date specified. A file's status is considered to have
7404 changed if its contents have been modified, or if its owner,
7405 permissions, and so forth, have been changed. (For more information on
7406 how to specify a date, see @ref{Date input formats}; remember that the
7407 entire date argument must be quoted if it contains any spaces.)
7409 Gurus would say that @option{--after-date} tests both the data
7410 modification time (@code{mtime}, the time the contents of the file
7411 were last modified) and the status change time (@code{ctime}, the time
7412 the file's status was last changed: owner, permissions, etc.@:)
7413 fields, while @option{--newer-mtime} tests only the @code{mtime}
7416 To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
7417 @code{ctime} and processes the file if either one is more recent than
7418 @var{date}, while @option{--newer-mtime} only checks @code{mtime} and
7419 disregards @code{ctime}. Neither does it use @code{atime} (the last time the
7420 contents of the file were looked at).
7422 Date specifiers can have embedded spaces. Because of this, you may need
7423 to quote date arguments to keep the shell from parsing them as separate
7424 arguments. For example, the following command will add to the archive
7425 all the files modified less than two days ago:
7428 $ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'}
7431 When any of these options is used with the option @option{--verbose}
7432 (@pxref{verbose tutorial}) @GNUTAR{} will try to convert the specified
7433 date back to its textual representation and compare that with the
7434 one given with the option. If the two dates differ, @command{tar} will
7435 print a warning saying what date it will use. This is to help user
7436 ensure he is using the right date. For example:
7440 $ @kbd{tar -c -f archive.tar --after-date='10 days ago' .}
7441 tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
7447 @strong{Please Note:} @option{--after-date} and @option{--newer-mtime}
7448 should not be used for incremental backups. @xref{Incremental Dumps},
7449 for proper way of creating incremental backups.
7453 @section Descending into Directories
7455 @cindex Avoiding recursion in directories
7456 @cindex Descending directories, avoiding
7457 @cindex Directories, avoiding recursion
7458 @cindex Recursion in directories, avoiding
7460 @FIXME{arrggh! this is still somewhat confusing to me. :-< }
7462 Usually, @command{tar} will recursively explore all directories (either
7463 those given on the command line or through the @option{--files-from}
7464 option) for the various files they contain. However, you may not always
7465 want @command{tar} to act this way.
7467 @opindex no-recursion
7468 The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
7469 into specified directories. If you specify @option{--no-recursion}, you can
7470 use the @command{find} utility for hunting through levels of directories to
7471 construct a list of file names which you could then pass to @command{tar}.
7472 @command{find} allows you to be more selective when choosing which files to
7473 archive; see @ref{files}, for more information on using @command{find} with
7474 @command{tar}, or look.
7477 @item --no-recursion
7478 Prevents @command{tar} from recursively descending directories.
7482 Requires @command{tar} to recursively descend directories.
7483 This is the default.
7486 When you use @option{--no-recursion}, @GNUTAR{} grabs
7487 directory entries themselves, but does not descend on them
7488 recursively. Many people use @command{find} for locating files they
7489 want to back up, and since @command{tar} @emph{usually} recursively
7490 descends on directories, they have to use the @samp{@w{-not -type d}}
7491 test in their @command{find} invocation (@pxref{Type, Type, Type test,
7492 find, Finding Files}), as they usually do not want all the files in a
7493 directory. They then use the @option{--files-from} option to archive
7494 the files located via @command{find}.
7496 The problem when restoring files archived in this manner is that the
7497 directories themselves are not in the archive; so the
7498 @option{--same-permissions} (@option{--preserve-permissions},
7499 @option{-p}) option does not affect them---while users might really
7500 like it to. Specifying @option{--no-recursion} is a way to tell
7501 @command{tar} to grab only the directory entries given to it, adding
7502 no new files on its own. To summarize, if you use @command{find} to
7503 create a list of files to be stored in an archive, use it as follows:
7507 $ @kbd{find @var{dir} @var{tests} | \
7508 tar -cf @var{archive} -T - --no-recursion}
7512 The @option{--no-recursion} option also applies when extracting: it
7513 causes @command{tar} to extract only the matched directory entries, not
7514 the files under those directories.
7516 The @option{--no-recursion} option also affects how globbing patterns
7517 are interpreted (@pxref{controlling pattern-matching}).
7519 The @option{--no-recursion} and @option{--recursion} options apply to
7520 later options and operands, and can be overridden by later occurrences
7521 of @option{--no-recursion} and @option{--recursion}. For example:
7524 $ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
7528 creates an archive with one entry for @file{grape}, and the recursive
7529 contents of @file{grape/concord}, but no entries under @file{grape}
7530 other than @file{grape/concord}.
7533 @section Crossing File System Boundaries
7534 @cindex File system boundaries, not crossing
7537 @command{tar} will normally automatically cross file system boundaries in
7538 order to archive files which are part of a directory tree. You can
7539 change this behavior by running @command{tar} and specifying
7540 @option{--one-file-system}. This option only affects files that are
7541 archived because they are in a directory that is being archived;
7542 @command{tar} will still archive files explicitly named on the command line
7543 or through @option{--files-from}, regardless of where they reside.
7546 @opindex one-file-system
7547 @item --one-file-system
7548 Prevents @command{tar} from crossing file system boundaries when
7549 archiving. Use in conjunction with any write operation.
7552 The @option{--one-file-system} option causes @command{tar} to modify its
7553 normal behavior in archiving the contents of directories. If a file in
7554 a directory is not on the same file system as the directory itself, then
7555 @command{tar} will not archive that file. If the file is a directory
7556 itself, @command{tar} will not archive anything beneath it; in other words,
7557 @command{tar} will not cross mount points.
7559 This option is useful for making full or incremental archival backups of
7560 a file system. If this option is used in conjunction with
7561 @option{--verbose} (@option{-v}), files that are excluded are
7562 mentioned by name on the standard error.
7565 * directory:: Changing Directory
7566 * absolute:: Absolute File Names
7570 @subsection Changing the Working Directory
7572 @FIXME{need to read over this node now for continuity; i've switched
7573 things around some.}
7575 @cindex Changing directory mid-stream
7576 @cindex Directory, changing mid-stream
7577 @cindex Working directory, specifying
7578 To change the working directory in the middle of a list of file names,
7579 either on the command line or in a file specified using
7580 @option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
7581 This will change the working directory to the specified directory
7582 after that point in the list.
7586 @item --directory=@var{directory}
7587 @itemx -C @var{directory}
7588 Changes the working directory in the middle of a command line.
7594 $ @kbd{tar -c -f jams.tar grape prune -C food cherry}
7598 will place the files @file{grape} and @file{prune} from the current
7599 directory into the archive @file{jams.tar}, followed by the file
7600 @file{cherry} from the directory @file{food}. This option is especially
7601 useful when you have several widely separated files that you want to
7602 store in the same archive.
7604 Note that the file @file{cherry} is recorded in the archive under the
7605 precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the
7606 archive will contain three files that all appear to have come from the
7607 same directory; if the archive is extracted with plain @samp{tar
7608 --extract}, all three files will be written in the current directory.
7610 Contrast this with the command,
7613 $ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
7617 which records the third file in the archive under the name
7618 @file{red/cherry} so that, if the archive is extracted using
7619 @samp{tar --extract}, the third file will be written in a subdirectory
7620 named @file{orange-colored}.
7622 You can use the @option{--directory} option to make the archive
7623 independent of the original name of the directory holding the files.
7624 The following command places the files @file{/etc/passwd},
7625 @file{/etc/hosts}, and @file{/lib/libc.a} into the archive
7629 $ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
7633 However, the names of the archive members will be exactly what they were
7634 on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}.
7635 They will not appear to be related by file name to the original
7636 directories where those files were located.
7638 Note that @option{--directory} options are interpreted consecutively. If
7639 @option{--directory} specifies a relative file name, it is interpreted
7640 relative to the then current directory, which might not be the same as
7641 the original current working directory of @command{tar}, due to a previous
7642 @option{--directory} option.
7644 When using @option{--files-from} (@pxref{files}), you can put various
7645 @command{tar} options (including @option{-C}) in the file list. Notice,
7646 however, that in this case the option and its argument may not be
7647 separated by whitespace. If you use short option, its argument must
7648 either follow the option letter immediately, without any intervening
7649 whitespace, or occupy the next line. Otherwise, if you use long
7650 option, separate its argument by an equal sign.
7652 For instance, the file list for the above example will be:
7665 To use it, you would invoke @command{tar} as follows:
7668 $ @kbd{tar -c -f foo.tar --files-from list}
7671 The interpretation of @option{--directory} is disabled by
7672 @option{--null} option.
7675 @subsection Absolute File Names
7679 @opindex absolute-names
7680 @item --absolute-names
7682 Do not strip leading slashes from file names, and permit file names
7683 containing a @file{..} file name component.
7686 By default, @GNUTAR{} drops a leading @samp{/} on
7687 input or output, and complains about file names containing a @file{..}
7688 component. This option turns off this behavior.
7690 When @command{tar} extracts archive members from an archive, it strips any
7691 leading slashes (@samp{/}) from the member name. This causes absolute
7692 member names in the archive to be treated as relative file names. This
7693 allows you to have such members extracted wherever you want, instead of
7694 being restricted to extracting the member in the exact directory named
7695 in the archive. For example, if the archive member has the name
7696 @file{/etc/passwd}, @command{tar} will extract it as if the name were
7697 really @file{etc/passwd}.
7699 File names containing @file{..} can cause problems when extracting, so
7700 @command{tar} normally warns you about such files when creating an
7701 archive, and rejects attempts to extracts such files.
7703 Other @command{tar} programs do not do this. As a result, if you
7704 create an archive whose member names start with a slash, they will be
7705 difficult for other people with a non-@GNUTAR{}
7706 program to use. Therefore, @GNUTAR{} also strips
7707 leading slashes from member names when putting members into the
7708 archive. For example, if you ask @command{tar} to add the file
7709 @file{/bin/ls} to an archive, it will do so, but the member name will
7710 be @file{bin/ls}.@footnote{A side effect of this is that when
7711 @option{--create} is used with @option{--verbose} the resulting output
7712 is not, generally speaking, the same as the one you'd get running
7713 @kbd{tar --list} command. This may be important if you use some
7714 scripts for comparing both outputs. @xref{listing member and file names},
7715 for the information on how to handle this case.}
7717 If you use the @option{--absolute-names} (@option{-P}) option,
7718 @command{tar} will do none of these transformations.
7720 To archive or extract files relative to the root directory, specify
7721 the @option{--absolute-names} (@option{-P}) option.
7723 Normally, @command{tar} acts on files relative to the working
7724 directory---ignoring superior directory names when archiving, and
7725 ignoring leading slashes when extracting.
7727 When you specify @option{--absolute-names} (@option{-P}),
7728 @command{tar} stores file names including all superior directory
7729 names, and preserves leading slashes. If you only invoked
7730 @command{tar} from the root directory you would never need the
7731 @option{--absolute-names} option, but using this option
7732 may be more convenient than switching to root.
7734 @FIXME{Should be an example in the tutorial/wizardry section using this
7735 to transfer files between systems.}
7737 @FIXME{Is write access an issue?}
7740 @item --absolute-names
7741 Preserves full file names (including superior directory names) when
7742 archiving files. Preserves leading slash when extracting files.
7746 @FIXME{this is still horrible; need to talk with dan on monday.}
7748 @command{tar} prints out a message about removing the @samp{/} from
7749 file names. This message appears once per @GNUTAR{}
7750 invocation. It represents something which ought to be told; ignoring
7751 what it means can cause very serious surprises, later.
7753 Some people, nevertheless, do not want to see this message. Wanting to
7754 play really dangerously, one may of course redirect @command{tar} standard
7755 error to the sink. For example, under @command{sh}:
7758 $ @kbd{tar -c -f archive.tar /home 2> /dev/null}
7762 Another solution, both nicer and simpler, would be to change to
7763 the @file{/} directory first, and then avoid absolute notation.
7767 $ @kbd{(cd / && tar -c -f archive.tar home)}
7769 $ @kbd{tar -c -f archive.tar -C / home}
7772 @include getdate.texi
7775 @chapter Controlling the Archive Format
7777 @cindex Tar archive formats
7778 Due to historical reasons, there are several formats of tar archives.
7779 All of them are based on the same principles, but have some subtle
7780 differences that often make them incompatible with each other.
7782 GNU tar is able to create and handle archives in a variety of formats.
7783 The most frequently used formats are (in alphabetical order):
7787 Format used by @GNUTAR{} versions up to 1.13.25. This format derived
7788 from an early @acronym{POSIX} standard, adding some improvements such as
7789 sparse file handling and incremental archives. Unfortunately these
7790 features were implemented in a way incompatible with other archive
7793 Archives in @samp{gnu} format are able to hold file names of unlimited
7797 Format used by @GNUTAR{} of versions prior to 1.12.
7800 Archive format, compatible with the V7 implementation of tar. This
7801 format imposes a number of limitations. The most important of them
7805 @item The maximum length of a file name is limited to 99 characters.
7806 @item The maximum length of a symbolic link is limited to 99 characters.
7807 @item It is impossible to store special files (block and character
7808 devices, fifos etc.)
7809 @item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777
7811 @item V7 archives do not contain symbolic ownership information (user
7812 and group name of the file owner).
7815 This format has traditionally been used by Automake when producing
7816 Makefiles. This practice will change in the future, in the meantime,
7817 however this means that projects containing file names more than 99
7818 characters long will not be able to use @GNUTAR{} @value{VERSION} and
7819 Automake prior to 1.9.
7822 Archive format defined by @acronym{POSIX.1-1988} specification. It stores
7823 symbolic ownership information. It is also able to store
7824 special files. However, it imposes several restrictions as well:
7827 @item The maximum length of a file name is limited to 256 characters,
7828 provided that the file name can be split at a directory separator in
7829 two parts, first of them being at most 155 bytes long. So, in most
7830 cases the maximum file name length will be shorter than 256
7832 @item The maximum length of a symbolic link name is limited to
7834 @item Maximum size of a file the archive is able to accommodate
7836 @item Maximum value of UID/GID is 2097151.
7837 @item Maximum number of bits in device major and minor numbers is 21.
7841 Format used by J@"org Schilling @command{star}
7842 implementation. @GNUTAR{} is able to read @samp{star} archives but
7843 currently does not produce them.
7846 Archive format defined by @acronym{POSIX.1-2001} specification. This is the
7847 most flexible and feature-rich format. It does not impose any
7848 restrictions on file sizes or file name lengths. This format is quite
7849 recent, so not all tar implementations are able to handle it properly.
7850 However, this format is designed in such a way that any tar
7851 implementation able to read @samp{ustar} archives will be able to read
7852 most @samp{posix} archives as well, with the only exception that any
7853 additional information (such as long file names etc.) will in such
7854 case be extracted as plain text files along with the files it refers to.
7856 This archive format will be the default format for future versions
7861 The following table summarizes the limitations of each of these
7864 @multitable @columnfractions .10 .20 .20 .20 .20
7865 @headitem Format @tab UID @tab File Size @tab File Name @tab Devn
7866 @item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
7867 @item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
7868 @item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
7869 @item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
7870 @item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
7873 The default format for @GNUTAR{} is defined at compilation
7874 time. You may check it by running @command{tar --help}, and examining
7875 the last lines of its output. Usually, @GNUTAR{} is configured
7876 to create archives in @samp{gnu} format, however, future version will
7877 switch to @samp{posix}.
7880 * Compression:: Using Less Space through Compression
7881 * Attributes:: Handling File Attributes
7882 * Portability:: Making @command{tar} Archives More Portable
7883 * cpio:: Comparison of @command{tar} and @command{cpio}
7887 @section Using Less Space through Compression
7890 * gzip:: Creating and Reading Compressed Archives
7891 * sparse:: Archiving Sparse Files
7895 @subsection Creating and Reading Compressed Archives
7896 @cindex Compressed archives
7897 @cindex Storing archives in compressed format
7899 @GNUTAR{} is able to create and read compressed archives. It supports
7900 @command{gzip} and @command{bzip2} compression programs. For backward
7901 compatibility, it also supports @command{compress} command, although
7902 we strongly recommend against using it, since there is a patent
7903 covering the algorithm it uses and you could be sued for patent
7904 infringement merely by running @command{compress}! Besides, it is less
7905 effective than @command{gzip} and @command{bzip2}.
7907 Creating a compressed archive is simple: you just specify a
7908 @dfn{compression option} along with the usual archive creation
7909 commands. The compression option is @option{-z} (@option{--gzip}) to
7910 create a @command{gzip} compressed archive, @option{-j}
7911 (@option{--bzip2}) to create a @command{bzip2} compressed archive, and
7912 @option{-Z} (@option{--compress}) to use @command{compress} program.
7916 $ @kbd{tar cfz archive.tar.gz .}
7919 Reading compressed archive is even simpler: you don't need to specify
7920 any additional options as @GNUTAR{} recognizes its format
7921 automatically. Thus, the following commands will list and extract the
7922 archive created in previous example:
7925 # List the compressed archive
7926 $ @kbd{tar tf archive.tar.gz}
7927 # Extract the compressed archive
7928 $ @kbd{tar xf archive.tar.gz}
7931 The only case when you have to specify a decompression option while
7932 reading the archive is when reading from a pipe or from a tape drive
7933 that does not support random access. However, in this case @GNUTAR{}
7934 will indicate which option you should use. For example:
7937 $ @kbd{cat archive.tar.gz | tar tf -}
7938 tar: Archive is compressed. Use -z option
7939 tar: Error is not recoverable: exiting now
7942 If you see such diagnostics, just add the suggested option to the
7943 invocation of @GNUTAR{}:
7946 $ @kbd{cat archive.tar.gz | tar tfz -}
7949 Notice also, that there are several restrictions on operations on
7950 compressed archives. First of all, compressed archives cannot be
7951 modified, i.e., you cannot update (@option{--update} (@option{-u})) them or delete
7952 (@option{--delete}) members from them. Likewise, you cannot append
7953 another @command{tar} archive to a compressed archive using
7954 @option{--append} (@option{-r})). Secondly, multi-volume archives cannot be
7957 The following table summarizes compression options used by @GNUTAR{}.
7965 Filter the archive through @command{gzip}.
7967 You can use @option{--gzip} and @option{--gunzip} on physical devices
7968 (tape drives, etc.) and remote files as well as on normal files; data
7969 to or from such devices or remote files is reblocked by another copy
7970 of the @command{tar} program to enforce the specified (or default) record
7971 size. The default compression parameters are used; if you need to
7972 override them, set @env{GZIP} environment variable, e.g.:
7975 $ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
7979 Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
7980 @command{gzip} explicitly:
7983 $ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
7986 @cindex corrupted archives
7987 About corrupted compressed archives: @command{gzip}'ed files have no
7988 redundancy, for maximum compression. The adaptive nature of the
7989 compression scheme means that the compression tables are implicitly
7990 spread all over the archive. If you lose a few blocks, the dynamic
7991 construction of the compression tables becomes unsynchronized, and there
7992 is little chance that you could recover later in the archive.
7994 There are pending suggestions for having a per-volume or per-file
7995 compression in @GNUTAR{}. This would allow for viewing the
7996 contents without decompression, and for resynchronizing decompression at
7997 every volume or file, in case of corrupted archives. Doing so, we might
7998 lose some compressibility. But this would have make recovering easier.
7999 So, there are pros and cons. We'll see!
8004 Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
8011 Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
8013 The @acronym{GNU} Project recommends you not use
8014 @command{compress}, because there is a patent covering the algorithm it
8015 uses. You could be sued for patent infringement merely by running
8018 @opindex use-compress-program
8019 @item --use-compress-program=@var{prog}
8020 Use external compression program @var{prog}. Use this option if you
8021 have a compression program that @GNUTAR{} does not support. There
8022 are two requirements to which @var{prog} should comply:
8024 First, when called without options, it should read data from standard
8025 input, compress it and output it on standard output.
8027 Secondly, if called with @option{-d} argument, it should do exactly
8028 the opposite, i.e., read the compressed data from the standard input
8029 and produce uncompressed data on the standard output.
8032 @cindex gpg, using with tar
8033 @cindex gnupg, using with tar
8034 @cindex Using encrypted archives
8035 The @option{--use-compress-program} option, in particular, lets you
8036 implement your own filters, not necessarily dealing with
8037 compression/decompression. For example, suppose you wish to implement
8038 PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
8039 gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard
8040 Manual}). The following script does that:
8046 -d) gpg --decrypt - | gzip -d -c;;
8047 '') gzip -c | gpg -s ;;
8048 *) echo "Unknown option $1">&2; exit 1;;
8053 Suppose you name it @file{gpgz} and save it somewhere in your
8054 @env{PATH}. Then the following command will create a compressed
8055 archive signed with your private key:
8058 $ @kbd{tar -cf foo.tar.gpgz --use-compress=gpgz .}
8062 Likewise, the following command will list its contents:
8065 $ @kbd{tar -tf foo.tar.gpgz --use-compress=gpgz .}
8069 The above is based on the following discussion:
8071 I have one question, or maybe it's a suggestion if there isn't a way
8072 to do it now. I would like to use @option{--gzip}, but I'd also like
8073 the output to be fed through a program like @acronym{GNU}
8074 @command{ecc} (actually, right now that's @samp{exactly} what I'd like
8075 to use :-)), basically adding ECC protection on top of compression.
8076 It seems as if this should be quite easy to do, but I can't work out
8077 exactly how to go about it. Of course, I can pipe the standard output
8078 of @command{tar} through @command{ecc}, but then I lose (though I
8079 haven't started using it yet, I confess) the ability to have
8080 @command{tar} use @command{rmt} for it's I/O (I think).
8082 I think the most straightforward thing would be to let me specify a
8083 general set of filters outboard of compression (preferably ordered,
8084 so the order can be automatically reversed on input operations, and
8085 with the options they require specifiable), but beggars shouldn't be
8086 choosers and anything you decide on would be fine with me.
8088 By the way, I like @command{ecc} but if (as the comments say) it can't
8089 deal with loss of block sync, I'm tempted to throw some time at adding
8090 that capability. Supposing I were to actually do such a thing and
8091 get it (apparently) working, do you accept contributed changes to
8092 utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
8094 Isn't that exactly the role of the
8095 @option{--use-compress-prog=@var{program}} option?
8096 I never tried it myself, but I suspect you may want to write a
8097 @var{prog} script or program able to filter stdin to stdout to
8098 way you want. It should recognize the @option{-d} option, for when
8099 extraction is needed rather than creation.
8101 It has been reported that if one writes compressed data (through the
8102 @option{--gzip} or @option{--compress} options) to a DLT and tries to use
8103 the DLT compression mode, the data will actually get bigger and one will
8104 end up with less space on the tape.
8108 @subsection Archiving Sparse Files
8109 @cindex Sparse Files
8111 Files in the file system occasionally have @dfn{holes}. A @dfn{hole}
8112 in a file is a section of the file's contents which was never written.
8113 The contents of a hole reads as all zeros. On many operating systems,
8114 actual disk storage is not allocated for holes, but they are counted
8115 in the length of the file. If you archive such a file, @command{tar}
8116 could create an archive longer than the original. To have @command{tar}
8117 attempt to recognize the holes in a file, use @option{--sparse}
8118 (@option{-S}). When you use this option, then, for any file using
8119 less disk space than would be expected from its length, @command{tar}
8120 searches the file for consecutive stretches of zeros. It then records
8121 in the archive for the file where the consecutive stretches of zeros
8122 are, and only archives the ``real contents'' of the file. On
8123 extraction (using @option{--sparse} is not needed on extraction) any
8124 such files have holes created wherever the continuous stretches of zeros
8125 were found. Thus, if you use @option{--sparse}, @command{tar} archives
8126 won't take more space than the original.
8132 This option instructs @command{tar} to test each file for sparseness
8133 before attempting to archive it. If the file is found to be sparse it
8134 is treated specially, thus allowing to decrease the amount of space
8135 used by its image in the archive.
8137 This option is meaningful only when creating or updating archives. It
8138 has no effect on extraction.
8141 Consider using @option{--sparse} when performing file system backups,
8142 to avoid archiving the expanded forms of files stored sparsely in the
8145 Even if your system has no sparse files currently, some may be
8146 created in the future. If you use @option{--sparse} while making file
8147 system backups as a matter of course, you can be assured the archive
8148 will never take more space on the media than the files take on disk
8149 (otherwise, archiving a disk filled with sparse files might take
8150 hundreds of tapes). @xref{Incremental Dumps}.
8152 However, be aware that @option{--sparse} option presents a serious
8153 drawback. Namely, in order to determine if the file is sparse
8154 @command{tar} has to read it before trying to archive it, so in total
8155 the file is read @strong{twice}. So, always bear in mind that the
8156 time needed to process all files with this option is roughly twice
8157 the time needed to archive them without it.
8158 @FIXME{A technical note:
8160 Programs like @command{dump} do not have to read the entire file; by
8161 examining the file system directly, they can determine in advance
8162 exactly where the holes are and thus avoid reading through them. The
8163 only data it need read are the actual allocated data blocks.
8164 @GNUTAR{} uses a more portable and straightforward
8165 archiving approach, it would be fairly difficult that it does
8166 otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, on
8170 What I did say is that you cannot tell the difference between a hole and an
8171 equivalent number of nulls without reading raw blocks. @code{st_blocks} at
8172 best tells you how many holes there are; it doesn't tell you @emph{where}.
8173 Just as programs may, conceivably, care what @code{st_blocks} is (care
8174 to name one that does?), they may also care where the holes are (I have
8175 no examples of this one either, but it's equally imaginable).
8177 I conclude from this that good archivers are not portable. One can
8178 arguably conclude that if you want a portable program, you can in good
8179 conscience restore files with as many holes as possible, since you can't
8184 @cindex sparse formats, defined
8185 When using @samp{POSIX} archive format, @GNUTAR{} is able to store
8186 sparse files using in three distinct ways, called @dfn{sparse
8187 formats}. A sparse format is identified by its @dfn{number},
8188 consisting, as usual of two decimal numbers, delimited by a dot. By
8189 default, format @samp{1.0} is used. If, for some reason, you wish to
8190 use an earlier format, you can select it using
8191 @option{--sparse-version} option.
8194 @opindex sparse-version
8195 @item --sparse-version=@var{version}
8197 Select the format to store sparse files in. Valid @var{version} values
8198 are: @samp{0.0}, @samp{0.1} and @samp{1.0}. @xref{Sparse Formats},
8199 for a detailed description of each format.
8202 Using @option{--sparse-format} option implies @option{--sparse}.
8205 @section Handling File Attributes
8208 When @command{tar} reads files, it updates their access times. To
8209 avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
8210 reset the access time retroactively or avoid changing it in the first
8213 Handling of file attributes
8216 @opindex atime-preserve
8217 @item --atime-preserve
8218 @itemx --atime-preserve=replace
8219 @itemx --atime-preserve=system
8220 Preserve the access times of files that are read. This works only for
8221 files that you own, unless you have superuser privileges.
8223 @option{--atime-preserve=replace} works on most systems, but it also
8224 restores the data modification time and updates the status change
8225 time. Hence it doesn't interact with incremental dumps nicely
8226 (@pxref{Incremental Dumps}), and it can set access or data modification times
8227 incorrectly if other programs access the file while @command{tar} is
8230 @option{--atime-preserve=system} avoids changing the access time in
8231 the first place, if the operating system supports this.
8232 Unfortunately, this may or may not work on any given operating system
8233 or file system. If @command{tar} knows for sure it won't work, it
8234 complains right away.
8236 Currently @option{--atime-preserve} with no operand defaults to
8237 @option{--atime-preserve=replace}, but this is intended to change to
8238 @option{--atime-preserve=system} when the latter is better-supported.
8243 Do not extract data modification time.
8245 When this option is used, @command{tar} leaves the data modification times
8246 of the files it extracts as the times when the files were extracted,
8247 instead of setting it to the times recorded in the archive.
8249 This option is meaningless with @option{--list} (@option{-t}).
8253 Create extracted files with the same ownership they have in the
8256 This is the default behavior for the superuser,
8257 so this option is meaningful only for non-root users, when @command{tar}
8258 is executed on those systems able to give files away. This is
8259 considered as a security flaw by many people, at least because it
8260 makes quite difficult to correctly account users for the disk space
8261 they occupy. Also, the @code{suid} or @code{sgid} attributes of
8262 files are easily and silently lost when files are given away.
8264 When writing an archive, @command{tar} writes the user @acronym{ID} and user name
8265 separately. If it can't find a user name (because the user @acronym{ID} is not
8266 in @file{/etc/passwd}), then it does not write one. When restoring,
8267 it tries to look the name (if one was written) up in
8268 @file{/etc/passwd}. If it fails, then it uses the user @acronym{ID} stored in
8269 the archive instead.
8271 @opindex no-same-owner
8272 @item --no-same-owner
8274 Do not attempt to restore ownership when extracting. This is the
8275 default behavior for ordinary users, so this option has an effect
8276 only for the superuser.
8278 @opindex numeric-owner
8279 @item --numeric-owner
8280 The @option{--numeric-owner} option allows (ANSI) archives to be written
8281 without user/group name information or such information to be ignored
8282 when extracting. It effectively disables the generation and/or use
8283 of user/group name information. This option forces extraction using
8284 the numeric ids from the archive, ignoring the names.
8286 This is useful in certain circumstances, when restoring a backup from
8287 an emergency floppy with different passwd/group files for example.
8288 It is otherwise impossible to extract files with the right ownerships
8289 if the password file in use during the extraction does not match the
8290 one belonging to the file system(s) being extracted. This occurs,
8291 for example, if you are restoring your files after a major crash and
8292 had booted from an emergency floppy with no password file or put your
8293 disk into another machine to do the restore.
8295 The numeric ids are @emph{always} saved into @command{tar} archives.
8296 The identifying names are added at create time when provided by the
8297 system, unless @option{--old-archive} (@option{-o}) is used. Numeric ids could be
8298 used when moving archives between a collection of machines using
8299 a centralized management for attribution of numeric ids to users
8300 and groups. This is often made through using the NIS capabilities.
8302 When making a @command{tar} file for distribution to other sites, it
8303 is sometimes cleaner to use a single owner for all files in the
8304 distribution, and nicer to specify the write permission bits of the
8305 files as stored in the archive independently of their actual value on
8306 the file system. The way to prepare a clean distribution is usually
8307 to have some Makefile rule creating a directory, copying all needed
8308 files in that directory, then setting ownership and permissions as
8309 wanted (there are a lot of possible schemes), and only then making a
8310 @command{tar} archive out of this directory, before cleaning
8311 everything out. Of course, we could add a lot of options to
8312 @GNUTAR{} for fine tuning permissions and ownership.
8313 This is not the good way, I think. @GNUTAR{} is
8314 already crowded with options and moreover, the approach just explained
8315 gives you a great deal of control already.
8317 @xopindex{same-permissions, short description}
8318 @xopindex{preserve-permissions, short description}
8320 @itemx --same-permissions
8321 @itemx --preserve-permissions
8322 Extract all protection information.
8324 This option causes @command{tar} to set the modes (access permissions) of
8325 extracted files exactly as recorded in the archive. If this option
8326 is not used, the current @code{umask} setting limits the permissions
8327 on extracted files. This option is by default enabled when
8328 @command{tar} is executed by a superuser.
8331 This option is meaningless with @option{--list} (@option{-t}).
8335 Same as both @option{--same-permissions} and @option{--same-order}.
8337 The @option{--preserve} option has no equivalent short option name.
8338 It is equivalent to @option{--same-permissions} plus @option{--same-order}.
8340 @FIXME{I do not see the purpose of such an option. (Neither I. FP.)
8341 Neither do I. --Sergey}
8346 @section Making @command{tar} Archives More Portable
8348 Creating a @command{tar} archive on a particular system that is meant to be
8349 useful later on many other machines and with other versions of @command{tar}
8350 is more challenging than you might think. @command{tar} archive formats
8351 have been evolving since the first versions of Unix. Many such formats
8352 are around, and are not always compatible with each other. This section
8353 discusses a few problems, and gives some advice about making @command{tar}
8354 archives more portable.
8356 One golden rule is simplicity. For example, limit your @command{tar}
8357 archives to contain only regular files and directories, avoiding
8358 other kind of special files. Do not attempt to save sparse files or
8359 contiguous files as such. Let's discuss a few more problems, in turn.
8361 @FIXME{Discuss GNU extensions (incremental backups, multi-volume
8362 archives and archive labels) in GNU and PAX formats.}
8365 * Portable Names:: Portable Names
8366 * dereference:: Symbolic Links
8367 * old:: Old V7 Archives
8368 * ustar:: Ustar Archives
8369 * gnu:: GNU and old GNU format archives.
8370 * posix:: @acronym{POSIX} archives
8371 * Checksumming:: Checksumming Problems
8372 * Large or Negative Values:: Large files, negative time stamps, etc.
8373 * Other Tars:: How to Extract GNU-Specific Data Using
8374 Other @command{tar} Implementations
8377 @node Portable Names
8378 @subsection Portable Names
8380 Use portable file and member names. A name is portable if it contains
8381 only @acronym{ASCII} letters and digits, @samp{/}, @samp{.}, @samp{_}, and
8382 @samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
8383 contain @samp{/-}. Avoid deep directory nesting. For portability to
8384 old Unix hosts, limit your file name components to 14 characters or
8387 If you intend to have your @command{tar} archives to be read under
8388 MSDOS, you should not rely on case distinction for file names, and you
8389 might use the @acronym{GNU} @command{doschk} program for helping you
8390 further diagnosing illegal MSDOS names, which are even more limited
8394 @subsection Symbolic Links
8395 @cindex File names, using symbolic links
8396 @cindex Symbolic link as file name
8398 @opindex dereference
8399 Normally, when @command{tar} archives a symbolic link, it writes a
8400 block to the archive naming the target of the link. In that way, the
8401 @command{tar} archive is a faithful record of the file system contents.
8402 @option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
8403 @command{tar} to archive the files symbolic links point to, instead of
8404 the links themselves. When this option is used, when @command{tar}
8405 encounters a symbolic link, it will archive the linked-to file,
8406 instead of simply recording the presence of a symbolic link.
8408 The name under which the file is stored in the file system is not
8409 recorded in the archive. To record both the symbolic link name and
8410 the file name in the system, archive the file under both names. If
8411 all links were recorded automatically by @command{tar}, an extracted file
8412 might be linked to a file name that no longer exists in the file
8415 If a linked-to file is encountered again by @command{tar} while creating
8416 the same archive, an entire second copy of it will be stored. (This
8417 @emph{might} be considered a bug.)
8419 So, for portable archives, do not archive symbolic links as such,
8420 and use @option{--dereference} (@option{-h}): many systems do not support
8421 symbolic links, and moreover, your distribution might be unusable if
8422 it contains unresolved symbolic links.
8425 @subsection Old V7 Archives
8426 @cindex Format, old style
8427 @cindex Old style format
8428 @cindex Old style archives
8429 @cindex v7 archive format
8431 Certain old versions of @command{tar} cannot handle additional
8432 information recorded by newer @command{tar} programs. To create an
8433 archive in V7 format (not ANSI), which can be read by these old
8434 versions, specify the @option{--format=v7} option in
8435 conjunction with the @option{--create} (@option{-c}) (@command{tar} also
8436 accepts @option{--portability} or @option{--old-archive} for this
8437 option). When you specify it,
8438 @command{tar} leaves out information about directories, pipes, fifos,
8439 contiguous files, and device files, and specifies file ownership by
8440 group and user IDs instead of group and user names.
8442 When updating an archive, do not use @option{--format=v7}
8443 unless the archive was created using this option.
8445 In most cases, a @emph{new} format archive can be read by an @emph{old}
8446 @command{tar} program without serious trouble, so this option should
8447 seldom be needed. On the other hand, most modern @command{tar}s are
8448 able to read old format archives, so it might be safer for you to
8449 always use @option{--format=v7} for your distributions. Notice,
8450 however, that @samp{ustar} format is a better alternative, as it is
8451 free from many of @samp{v7}'s drawbacks.
8454 @subsection Ustar Archive Format
8456 @cindex ustar archive format
8457 Archive format defined by @acronym{POSIX}.1-1988 specification is called
8458 @code{ustar}. Although it is more flexible than the V7 format, it
8459 still has many restrictions (@xref{Formats,ustar}, for the detailed
8460 description of @code{ustar} format). Along with V7 format,
8461 @code{ustar} format is a good choice for archives intended to be read
8462 with other implementations of @command{tar}.
8464 To create archive in @code{ustar} format, use @option{--format=ustar}
8465 option in conjunction with the @option{--create} (@option{-c}).
8468 @subsection @acronym{GNU} and old @GNUTAR{} format
8470 @cindex GNU archive format
8471 @cindex Old GNU archive format
8472 @GNUTAR{} was based on an early draft of the
8473 @acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
8474 @command{tar}, such as the support for file names longer than 100
8475 characters, use portions of the @command{tar} header record which were
8476 specified in that @acronym{POSIX} draft as unused. Subsequent changes in
8477 @acronym{POSIX} have allocated the same parts of the header record for
8478 other purposes. As a result, @GNUTAR{} format is
8479 incompatible with the current @acronym{POSIX} specification, and with
8480 @command{tar} programs that follow it.
8482 In the majority of cases, @command{tar} will be configured to create
8483 this format by default. This will change in future releases, since
8484 we plan to make @samp{POSIX} format the default.
8486 To force creation a @GNUTAR{} archive, use option
8487 @option{--format=gnu}.
8490 @subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
8492 @cindex POSIX archive format
8493 @cindex PAX archive format
8494 Starting from version 1.14 @GNUTAR{} features full support for
8495 @acronym{POSIX.1-2001} archives.
8497 A @acronym{POSIX} conformant archive will be created if @command{tar}
8498 was given @option{--format=posix} (@option{--format=pax}) option. No
8499 special option is required to read and extract from a @acronym{POSIX}
8503 * PAX keywords:: Controlling Extended Header Keywords.
8507 @subsubsection Controlling Extended Header Keywords
8511 @item --pax-option=@var{keyword-list}
8512 Handle keywords in @acronym{PAX} extended headers. This option is
8513 equivalent to @option{-o} option of the @command{pax} utility.
8516 @var{Keyword-list} is a comma-separated
8517 list of keyword options, each keyword option taking one of
8518 the following forms:
8521 @item delete=@var{pattern}
8522 When used with one of archive-creation commands,
8523 this option instructs @command{tar} to omit from extended header records
8524 that it produces any keywords matching the string @var{pattern}.
8526 When used in extract or list mode, this option instructs tar
8527 to ignore any keywords matching the given @var{pattern} in the extended
8528 header records. In both cases, matching is performed using the pattern
8529 matching notation described in @acronym{POSIX 1003.2}, 3.13
8530 (@pxref{wildcards}). For example:
8533 --pax-option delete=security.*
8536 would suppress security-related information.
8538 @item exthdr.name=@var{string}
8540 This keyword allows user control over the name that is written into the
8541 ustar header blocks for the extended headers. The name is obtained
8542 from @var{string} after making the following substitutions:
8544 @multitable @columnfractions .25 .55
8545 @headitem Meta-character @tab Replaced By
8546 @item %d @tab The directory name of the file, equivalent to the
8547 result of the @command{dirname} utility on the translated file name.
8548 @item %f @tab The name of the file with the directory information
8549 stripped, equivalent to the result of the @command{basename} utility
8550 on the translated file name.
8551 @item %p @tab The process @acronym{ID} of the @command{tar} process.
8552 @item %% @tab A @samp{%} character.
8555 Any other @samp{%} characters in @var{string} produce undefined
8558 If no option @samp{exthdr.name=string} is specified, @command{tar}
8559 will use the following default value:
8565 @item globexthdr.name=@var{string}
8566 This keyword allows user control over the name that is written into
8567 the ustar header blocks for global extended header records. The name
8568 is obtained from the contents of @var{string}, after making
8569 the following substitutions:
8571 @multitable @columnfractions .25 .55
8572 @headitem Meta-character @tab Replaced By
8573 @item %n @tab An integer that represents the
8574 sequence number of the global extended header record in the archive,
8576 @item %p @tab The process @acronym{ID} of the @command{tar} process.
8577 @item %% @tab A @samp{%} character.
8580 Any other @samp{%} characters in @var{string} produce undefined results.
8582 If no option @samp{globexthdr.name=string} is specified, @command{tar}
8583 will use the following default value:
8586 $TMPDIR/GlobalHead.%p.%n
8590 where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
8591 environment variable. If @var{TMPDIR} is not set, @command{tar}
8594 @item @var{keyword}=@var{value}
8595 When used with one of archive-creation commands, these keyword/value pairs
8596 will be included at the beginning of the archive in a global extended
8597 header record. When used with one of archive-reading commands,
8598 @command{tar} will behave as if it has encountered these keyword/value
8599 pairs at the beginning of the archive in a global extended header
8602 @item @var{keyword}:=@var{value}
8603 When used with one of archive-creation commands, these keyword/value pairs
8604 will be included as records at the beginning of an extended header for
8605 each file. This is effectively equivalent to @var{keyword}=@var{value}
8606 form except that it creates no global extended header records.
8608 When used with one of archive-reading commands, @command{tar} will
8609 behave as if these keyword/value pairs were included as records at the
8610 end of each extended header; thus, they will override any global or
8611 file-specific extended header record keywords of the same names.
8612 For example, in the command:
8615 tar --format=posix --create \
8616 --file archive --pax-option gname:=user .
8619 the group name will be forced to a new value for all files
8620 stored in the archive.
8624 @subsection Checksumming Problems
8626 SunOS and HP-UX @command{tar} fail to accept archives created using
8627 @GNUTAR{} and containing non-@acronym{ASCII} file names, that
8628 is, file names having characters with the eight bit set, because they
8629 use signed checksums, while @GNUTAR{} uses unsigned
8630 checksums while creating archives, as per @acronym{POSIX} standards. On
8631 reading, @GNUTAR{} computes both checksums and
8632 accept any. It is somewhat worrying that a lot of people may go
8633 around doing backup of their files using faulty (or at least
8634 non-standard) software, not learning about it until it's time to
8635 restore their missing files with an incompatible file extractor, or
8638 @GNUTAR{} compute checksums both ways, and accept
8639 any on read, so @acronym{GNU} tar can read Sun tapes even with their
8640 wrong checksums. @GNUTAR{} produces the standard
8641 checksum, however, raising incompatibilities with Sun. That is to
8642 say, @GNUTAR{} has not been modified to
8643 @emph{produce} incorrect archives to be read by buggy @command{tar}'s.
8644 I've been told that more recent Sun @command{tar} now read standard
8645 archives, so maybe Sun did a similar patch, after all?
8647 The story seems to be that when Sun first imported @command{tar}
8648 sources on their system, they recompiled it without realizing that
8649 the checksums were computed differently, because of a change in
8650 the default signing of @code{char}'s in their compiler. So they
8651 started computing checksums wrongly. When they later realized their
8652 mistake, they merely decided to stay compatible with it, and with
8653 themselves afterwards. Presumably, but I do not really know, HP-UX
8654 has chosen that their @command{tar} archives to be compatible with Sun's.
8655 The current standards do not favor Sun @command{tar} format. In any
8656 case, it now falls on the shoulders of SunOS and HP-UX users to get
8657 a @command{tar} able to read the good archives they receive.
8659 @node Large or Negative Values
8660 @subsection Large or Negative Values
8661 @cindex large values
8662 @cindex future time stamps
8663 @cindex negative time stamps
8666 The above sections suggest to use @samp{oldest possible} archive
8667 format if in doubt. However, sometimes it is not possible. If you
8668 attempt to archive a file whose metadata cannot be represented using
8669 required format, @GNUTAR{} will print error message and ignore such a
8670 file. You will than have to switch to a format that is able to
8671 handle such values. The format summary table (@pxref{Formats}) will
8674 In particular, when trying to archive files larger than 8GB or with
8675 timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
8676 12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
8677 @acronym{POSIX} archive formats. When considering which format to
8678 choose, bear in mind that the @acronym{GNU} format uses
8679 two's-complement base-256 notation to store values that do not fit
8680 into standard @acronym{ustar} range. Such archives can generally be
8681 read only by a @GNUTAR{} implementation. Moreover, they sometimes
8682 cannot be correctly restored on another hosts even by @GNUTAR{}. For
8683 example, using two's complement representation for negative time
8684 stamps that assumes a signed 32-bit @code{time_t} generates archives
8685 that are not portable to hosts with differing @code{time_t}
8688 On the other hand, @acronym{POSIX} archives, generally speaking, can
8689 be extracted by any tar implementation that understands older
8690 @acronym{ustar} format. The only exception are files larger than 8GB.
8692 @FIXME{Describe how @acronym{POSIX} archives are extracted by non
8696 @subsection How to Extract GNU-Specific Data Using Other @command{tar} Implementations
8698 In previous sections you became acquainted with various quirks
8699 necessary to make your archives portable. Sometimes you may need to
8700 extract archives containing GNU-specific members using some
8701 third-party @command{tar} implementation or an older version of
8702 @GNUTAR{}. Of course your best bet is to have @GNUTAR{} installed,
8703 but if it is for some reason impossible, this section will explain
8704 how to cope without it.
8706 When we speak about @dfn{GNU-specific} members we mean two classes of
8707 them: members split between the volumes of a multi-volume archive and
8708 sparse members. You will be able to always recover such members if
8709 the archive is in PAX format. In addition split members can be
8710 recovered from archives in old GNU format. The following subsections
8711 describe the required procedures in detail.
8714 * Split Recovery:: Members Split Between Volumes
8715 * Sparse Recovery:: Sparse Members
8718 @node Split Recovery
8719 @subsubsection Extracting Members Split Between Volumes
8721 @cindex Mutli-volume archives, extracting using non-GNU tars
8722 If a member is split between several volumes of an old GNU format archive
8723 most third party @command{tar} implementation will fail to extract
8724 it. To extract it, use @command{tarcat} program (@pxref{Tarcat}).
8725 This program is available from
8726 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tarcat.html, @GNUTAR{}
8727 home page}. It concatenates several archive volumes into a single
8728 valid archive. For example, if you have three volumes named from
8729 @file{vol-1.tar} to @file{vol-3.tar}, you can do the following to
8730 extract them using a third-party @command{tar}:
8733 $ @kbd{tarcat vol-1.tar vol-2.tar vol-3.tar | tar xf -}
8736 @cindex Mutli-volume archives in PAX format, extracting using non-GNU tars
8737 You could use this approach for most (although not all) PAX
8738 format archives as well. However, extracting split members from a PAX
8739 archive is a much easier task, because PAX volumes are constructed in
8740 such a way that each part of a split member is extracted to a
8741 different file by @command{tar} implementations that are not aware of
8742 GNU extensions. More specifically, the very first part retains its
8743 original name, and all subsequent parts are named using the pattern:
8746 %d/GNUFileParts.%p/%f.%n
8750 where symbols preceeded by @samp{%} are @dfn{macro characters} that
8751 have the following meaning:
8753 @multitable @columnfractions .25 .55
8754 @headitem Meta-character @tab Replaced By
8755 @item %d @tab The directory name of the file, equivalent to the
8756 result of the @command{dirname} utility on its full name.
8757 @item %f @tab The file name of the file, equivalent to the result
8758 of the @command{basename} utility on its full name.
8759 @item %p @tab The process @acronym{ID} of the @command{tar} process that
8760 created the archive.
8761 @item %n @tab Ordinal number of this particular part.
8764 For example, if the file @file{var/longfile} was split during archive
8765 creation between three volumes, and the creator @command{tar} process
8766 had process @acronym{ID} @samp{27962}, then the member names will be:
8770 var/GNUFileParts.27962/longfile.1
8771 var/GNUFileParts.27962/longfile.2
8774 When you extract your archive using a third-party @command{tar}, these
8775 files will be created on your disk, and the only thing you will need
8776 to do to restore your file in its original form is concatenate them in
8777 the proper order, for example:
8782 $ @kbd{cat GNUFileParts.27962/longfile.1 \
8783 GNUFileParts.27962/longfile.2 >> longfile}
8784 $ rm -f GNUFileParts.27962
8788 Notice, that if the @command{tar} implementation you use supports PAX
8789 format archives, it will probably emit warnings about unknown keywords
8790 during extraction. They will look like this:
8795 Unknown extended header keyword 'GNU.volume.filename' ignored.
8796 Unknown extended header keyword 'GNU.volume.size' ignored.
8797 Unknown extended header keyword 'GNU.volume.offset' ignored.
8802 You can safely ignore these warnings.
8804 If your @command{tar} implementation is not PAX-aware, you will get
8805 more warnings and more files generated on your disk, e.g.:
8809 $ @kbd{tar xf vol-1.tar}
8810 var/PaxHeaders.27962/longfile: Unknown file type 'x', extracted as
8812 Unexpected EOF in archive
8813 $ @kbd{tar xf vol-2.tar}
8814 tmp/GlobalHead.27962.1: Unknown file type 'g', extracted as normal file
8815 GNUFileParts.27962/PaxHeaders.27962/sparsefile.1: Unknown file type
8816 'x', extracted as normal file
8820 Ignore these warnings. The @file{PaxHeaders.*} directories created
8821 will contain files with @dfn{extended header keywords} describing the
8822 extracted files. You can delete them, unless they describe sparse
8823 members. Read further to learn more about them.
8825 @node Sparse Recovery
8826 @subsubsection Extracting Sparse Members
8828 @cindex sparse files, extracting with non-GNU tars
8829 Any @command{tar} implementation will be able to extract sparse members from a
8830 PAX archive. However, the extracted files will be @dfn{condensed},
8831 i.e., any zero blocks will be removed from them. When we restore such
8832 a condensed file to its original form, by adding zero blocks (or
8833 @dfn{holes}) back to their original locations, we call this process
8834 @dfn{expanding} a compressed sparse file.
8837 To expand a file, you will need a simple auxiliary program called
8838 @command{xsparse}. It is available in source form from
8839 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/xsparse.html, @GNUTAR{}
8842 @cindex sparse files v.1.0, extracting with non-GNU tars
8843 Let's begin with archive members in @dfn{sparse format
8844 version 1.0}@footnote{@xref{PAX 1}.}, which are the easiest to expand.
8845 The condensed file will contain both file map and file data, so no
8846 additional data will be needed to restore it. If the original file
8847 name was @file{@var{dir}/@var{name}}, then the condensed file will be
8848 named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
8849 @var{n} is a decimal number@footnote{technically speaking, @var{n} is a
8850 @dfn{process @acronym{ID}} of the @command{tar} process which created the
8851 archive (@pxref{PAX keywords}).}.
8853 To expand a version 1.0 file, run @command{xsparse} as follows:
8856 $ @kbd{xsparse @file{cond-file}}
8860 where @file{cond-file} is the name of the condensed file. The utility
8861 will deduce the name for the resulting expanded file using the
8862 following algorithm:
8865 @item If @file{cond-file} does not contain any directories,
8866 @file{../cond-file} will be used;
8868 @item If @file{cond-file} has the form
8869 @file{@var{dir}/@var{t}/@var{name}}, where both @var{t} and @var{name}
8870 are simple names, with no @samp{/} characters in them, the output file
8871 name will be @file{@var{dir}/@var{name}}.
8873 @item Otherwise, if @file{cond-file} has the form
8874 @file{@var{dir}/@var{name}}, the output file name will be
8878 In the unlikely case when this algorithm does not suit your needs,
8879 you can explicitly specify output file name as a second argument to
8883 $ @kbd{xsparse @file{cond-file} @file{out-file}}
8886 It is often a good idea to run @command{xsparse} in @dfn{dry run} mode
8887 first. In this mode, the command does not actually expand the file,
8888 but verbosely lists all actions it would be taking to do so. The dry
8889 run mode is enabled by @option{-n} command line argument:
8893 $ @kbd{xsparse -n /home/gray/GNUSparseFile.6058/sparsefile}
8894 Reading v.1.0 sparse map
8895 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
8896 `/home/gray/sparsefile'
8901 To actually expand the file, you would run:
8904 $ @kbd{xsparse /home/gray/GNUSparseFile.6058/sparsefile}
8908 The program behaves the same way all UNIX utilities do: it will keep
8909 quiet unless it has simething important to tell you (e.g. an error
8910 condition or something). If you wish it to produce verbose output,
8911 similar to that from the dry run mode, use @option{-v} option:
8915 $ @kbd{xsparse -v /home/gray/GNUSparseFile.6058/sparsefile}
8916 Reading v.1.0 sparse map
8917 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
8918 `/home/gray/sparsefile'
8923 Additionally, if your @command{tar} implementation has extracted the
8924 @dfn{extended headers} for this file, you can instruct @command{xstar}
8925 to use them in order to verify the integrity of the expanded file.
8926 The option @option{-x} sets the name of the extended header file to
8927 use. Continuing our example:
8931 $ @kbd{xsparse -v -x /home/gray/PaxHeaders.6058/sparsefile \
8932 /home/gray/GNUSparseFile.6058/sparsefile}
8933 Reading extended header file
8934 Found variable GNU.sparse.major = 1
8935 Found variable GNU.sparse.minor = 0
8936 Found variable GNU.sparse.name = sparsefile
8937 Found variable GNU.sparse.realsize = 217481216
8938 Reading v.1.0 sparse map
8939 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
8940 `/home/gray/sparsefile'
8945 @anchor{extracting sparse v.0.x}
8946 @cindex sparse files v.0.1, extracting with non-GNU tars
8947 @cindex sparse files v.0.0, extracting with non-GNU tars
8948 An @dfn{extended header} is a special @command{tar} archive header
8949 that precedes an archive member and contains a set of
8950 @dfn{variables}, describing the member properties that cannot be
8951 stored in the standard @code{ustar} header. While optional for
8952 expanding sparse version 1.0 members, the use of extended headers is
8953 mandatory when expanding sparse members in older sparse formats: v.0.0
8954 and v.0.1 (The sparse formats are described in detail in @ref{Sparse
8955 Formats}.) So, for these formats, the question is: how to obtain
8956 extended headers from the archive?
8958 If you use a @command{tar} implementation that does not support PAX
8959 format, extended headers for each member will be extracted as a
8960 separate file. If we represent the member name as
8961 @file{@var{dir}/@var{name}}, then the extended header file will be
8962 named @file{@var{dir}/@/PaxHeaders.@var{n}/@/@var{name}}, where
8963 @var{n} is an integer number.
8965 Things become more difficult if your @command{tar} implementation
8966 does support PAX headers, because in this case you will have to
8967 manually extract the headers. We recommend the following algorithm:
8971 Consult the documentation of your @command{tar} implementation for an
8972 option that prints @dfn{block numbers} along with the archive
8973 listing (analogous to @GNUTAR{}'s @option{-R} option). For example,
8974 @command{star} has @option{-block-number}.
8977 Obtain verbose listing using the @samp{block number} option, and
8978 find block numbers of the sparse member in question and the member
8979 immediately following it. For example, running @command{star} on our
8984 $ @kbd{star -t -v -block-number -f arc.tar}
8986 star: Unknown extended header keyword 'GNU.sparse.size' ignored.
8987 star: Unknown extended header keyword 'GNU.sparse.numblocks' ignored.
8988 star: Unknown extended header keyword 'GNU.sparse.name' ignored.
8989 star: Unknown extended header keyword 'GNU.sparse.map' ignored.
8990 block 56: 425984 -rw-r--r-- gray/users Jun 25 14:46 2006 GNUSparseFile.28124/sparsefile
8991 block 897: 65391 -rw-r--r-- gray/users Jun 24 20:06 2006 README
8997 (as usual, ignore the warnings about unknown keywords.)
9000 Let @var{size} be the size of the sparse member, @var{Bs} be its block number
9001 and @var{Bn} be the block number of the next member.
9005 @var{N} = @var{Bs} - @var{Bn} - @var{size}/512 - 2
9009 This number gives the size of the extended header part in tar @dfn{blocks}.
9010 In our example, this formula gives: @code{897 - 56 - 425984 / 512 - 2
9014 Use @command{dd} to extract the headers:
9017 @kbd{dd if=@var{archive} of=@var{hname} bs=512 skip=@var{Bs} count=@var{N}}
9021 where @var{archive} is the archive name, @var{hname} is a name of the
9022 file to store the extended header in, @var{Bs} and @var{N} are
9023 computed in previous steps.
9025 In our example, this command will be
9028 $ @kbd{dd if=arc.tar of=xhdr bs=512 skip=56 count=7}
9032 Finally, you can expand the condensed file, using the obtained header:
9036 $ @kbd{xsparse -v -x xhdr GNUSparseFile.6058/sparsefile}
9037 Reading extended header file
9038 Found variable GNU.sparse.size = 217481216
9039 Found variable GNU.sparse.numblocks = 208
9040 Found variable GNU.sparse.name = sparsefile
9041 Found variable GNU.sparse.map = 0,2048,1050624,2048,@dots{}
9042 Expanding file `GNUSparseFile.28124/sparsefile' to `sparsefile'
9048 @section Comparison of @command{tar} and @command{cpio}
9051 @FIXME{Reorganize the following material}
9053 The @command{cpio} archive formats, like @command{tar}, do have maximum
9054 file name lengths. The binary and old @acronym{ASCII} formats have a maximum file
9055 length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max
9056 file length of 1024. @acronym{GNU} @command{cpio} can read and write archives
9057 with arbitrary file name lengths, but other @command{cpio} implementations
9058 may crash unexplainedly trying to read them.
9060 @command{tar} handles symbolic links in the form in which it comes in @acronym{BSD};
9061 @command{cpio} doesn't handle symbolic links in the form in which it comes
9062 in System V prior to SVR4, and some vendors may have added symlinks
9063 to their system without enhancing @command{cpio} to know about them.
9064 Others may have enhanced it in a way other than the way I did it
9065 at Sun, and which was adopted by AT&T (and which is, I think, also
9066 present in the @command{cpio} that Berkeley picked up from AT&T and put
9067 into a later @acronym{BSD} release---I think I gave them my changes).
9069 (SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
9070 can handle @command{tar} format input, and write it on output, and it
9071 probably handles symbolic links. They may not have bothered doing
9072 anything to enhance @command{tar} as a result.)
9074 @command{cpio} handles special files; traditional @command{tar} doesn't.
9076 @command{tar} comes with V7, System III, System V, and @acronym{BSD} source;
9077 @command{cpio} comes only with System III, System V, and later @acronym{BSD}
9078 (4.3-tahoe and later).
9080 @command{tar}'s way of handling multiple hard links to a file can handle
9081 file systems that support 32-bit inumbers (e.g., the @acronym{BSD} file system);
9082 @command{cpio}s way requires you to play some games (in its ``binary''
9083 format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
9084 they're 18 bits---it would have to play games with the "file system @acronym{ID}"
9085 field of the header to make sure that the file system @acronym{ID}/i-number pairs
9086 of different files were always different), and I don't know which
9087 @command{cpio}s, if any, play those games. Those that don't might get
9088 confused and think two files are the same file when they're not, and
9089 make hard links between them.
9091 @command{tar}s way of handling multiple hard links to a file places only
9092 one copy of the link on the tape, but the name attached to that copy
9093 is the @emph{only} one you can use to retrieve the file; @command{cpio}s
9094 way puts one copy for every link, but you can retrieve it using any
9098 What type of check sum (if any) is used, and how is this calculated.
9101 See the attached manual pages for @command{tar} and @command{cpio} format.
9102 @command{tar} uses a checksum which is the sum of all the bytes in the
9103 @command{tar} header for a file; @command{cpio} uses no checksum.
9106 If anyone knows why @command{cpio} was made when @command{tar} was present
9110 It wasn't. @command{cpio} first showed up in PWB/UNIX 1.0; no
9111 generally-available version of UNIX had @command{tar} at the time. I don't
9112 know whether any version that was generally available @emph{within AT&T}
9113 had @command{tar}, or, if so, whether the people within AT&T who did
9114 @command{cpio} knew about it.
9116 On restore, if there is a corruption on a tape @command{tar} will stop at
9117 that point, while @command{cpio} will skip over it and try to restore the
9120 The main difference is just in the command syntax and header format.
9122 @command{tar} is a little more tape-oriented in that everything is blocked
9123 to start on a record boundary.
9126 Is there any differences between the ability to recover crashed
9127 archives between the two of them. (Is there any chance of recovering
9128 crashed archives at all.)
9131 Theoretically it should be easier under @command{tar} since the blocking
9132 lets you find a header with some variation of @samp{dd skip=@var{nn}}.
9133 However, modern @command{cpio}'s and variations have an option to just
9134 search for the next file header after an error with a reasonable chance
9135 of resyncing. However, lots of tape driver software won't allow you to
9136 continue past a media error which should be the only reason for getting
9137 out of sync unless a file changed sizes while you were writing the
9141 If anyone knows why @command{cpio} was made when @command{tar} was present
9142 at the unix scene, please tell me about this too.
9145 Probably because it is more media efficient (by not blocking everything
9146 and using only the space needed for the headers where @command{tar}
9147 always uses 512 bytes per file header) and it knows how to archive
9150 You might want to look at the freely available alternatives. The
9151 major ones are @command{afio}, @GNUTAR{}, and
9152 @command{pax}, each of which have their own extensions with some
9153 backwards compatibility.
9155 Sparse files were @command{tar}red as sparse files (which you can
9156 easily test, because the resulting archive gets smaller, and
9157 @acronym{GNU} @command{cpio} can no longer read it).
9160 @chapter Tapes and Other Archive Media
9163 A few special cases about tape handling warrant more detailed
9164 description. These special cases are discussed below.
9166 Many complexities surround the use of @command{tar} on tape drives. Since
9167 the creation and manipulation of archives located on magnetic tape was
9168 the original purpose of @command{tar}, it contains many features making
9169 such manipulation easier.
9171 Archives are usually written on dismountable media---tape cartridges,
9172 mag tapes, or floppy disks.
9174 The amount of data a tape or disk holds depends not only on its size,
9175 but also on how it is formatted. A 2400 foot long reel of mag tape
9176 holds 40 megabytes of data when formatted at 1600 bits per inch. The
9177 physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
9179 Magnetic media are re-usable---once the archive on a tape is no longer
9180 needed, the archive can be erased and the tape or disk used over.
9181 Media quality does deteriorate with use, however. Most tapes or disks
9182 should be discarded when they begin to produce data errors. EXABYTE
9183 tape cartridges should be discarded when they generate an @dfn{error
9184 count} (number of non-usable bits) of more than 10k.
9186 Magnetic media are written and erased using magnetic fields, and
9187 should be protected from such fields to avoid damage to stored data.
9188 Sticking a floppy disk to a filing cabinet using a magnet is probably
9192 * Device:: Device selection and switching
9193 * Remote Tape Server::
9194 * Common Problems and Solutions::
9195 * Blocking:: Blocking
9196 * Many:: Many archives on one tape
9197 * Using Multiple Tapes:: Using Multiple Tapes
9198 * label:: Including a Label in the Archive
9200 * Write Protection::
9204 @section Device Selection and Switching
9208 @item -f [@var{hostname}:]@var{file}
9209 @itemx --file=[@var{hostname}:]@var{file}
9210 Use archive file or device @var{file} on @var{hostname}.
9213 This option is used to specify the file name of the archive @command{tar}
9216 If the file name is @samp{-}, @command{tar} reads the archive from standard
9217 input (when listing or extracting), or writes it to standard output
9218 (when creating). If the @samp{-} file name is given when updating an
9219 archive, @command{tar} will read the original archive from its standard
9220 input, and will write the entire new archive to its standard output.
9222 If the file name contains a @samp{:}, it is interpreted as
9223 @samp{hostname:file name}. If the @var{hostname} contains an @dfn{at}
9224 sign (@samp{@@}), it is treated as @samp{user@@hostname:file name}. In
9225 either case, @command{tar} will invoke the command @command{rsh} (or
9226 @command{remsh}) to start up an @command{/usr/libexec/rmt} on the remote
9227 machine. If you give an alternate login name, it will be given to the
9229 Naturally, the remote machine must have an executable
9230 @command{/usr/libexec/rmt}. This program is free software from the
9231 University of California, and a copy of the source code can be found
9232 with the sources for @command{tar}; it's compiled and installed by default.
9233 The exact path to this utility is determined when configuring the package.
9234 It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for
9235 your installation prefix. This location may also be overridden at
9236 runtime by using @option{rmt-command=@var{command}} option (@xref{Option Summary,
9237 ---rmt-command}, for detailed description of this option. @xref{Remote
9238 Tape Server}, for the description of @command{rmt} command).
9240 If this option is not given, but the environment variable @env{TAPE}
9241 is set, its value is used; otherwise, old versions of @command{tar}
9242 used a default archive name (which was picked when @command{tar} was
9243 compiled). The default is normally set up to be the @dfn{first} tape
9244 drive or other transportable I/O medium on the system.
9246 Starting with version 1.11.5, @GNUTAR{} uses
9247 standard input and standard output as the default device, and I will
9248 not try anymore supporting automatic device detection at installation
9249 time. This was failing really in too many cases, it was hopeless.
9250 This is now completely left to the installer to override standard
9251 input and standard output for default device, if this seems
9252 preferable. Further, I think @emph{most} actual usages of
9253 @command{tar} are done with pipes or disks, not really tapes,
9254 cartridges or diskettes.
9256 Some users think that using standard input and output is running
9257 after trouble. This could lead to a nasty surprise on your screen if
9258 you forget to specify an output file name---especially if you are going
9259 through a network or terminal server capable of buffering large amounts
9260 of output. We had so many bug reports in that area of configuring
9261 default tapes automatically, and so many contradicting requests, that
9262 we finally consider the problem to be portably intractable. We could
9263 of course use something like @samp{/dev/tape} as a default, but this
9264 is @emph{also} running after various kind of trouble, going from hung
9265 processes to accidental destruction of real tapes. After having seen
9266 all this mess, using standard input and output as a default really
9267 sounds like the only clean choice left, and a very useful one too.
9269 @GNUTAR{} reads and writes archive in records, I
9270 suspect this is the main reason why block devices are preferred over
9271 character devices. Most probably, block devices are more efficient
9272 too. The installer could also check for @samp{DEFTAPE} in
9273 @file{<sys/mtio.h>}.
9276 @xopindex{force-local, short description}
9278 Archive file is local even if it contains a colon.
9280 @opindex rsh-command
9281 @item --rsh-command=@var{command}
9282 Use remote @var{command} instead of @command{rsh}. This option exists
9283 so that people who use something other than the standard @command{rsh}
9284 (e.g., a Kerberized @command{rsh}) can access a remote device.
9286 When this command is not used, the shell command found when
9287 the @command{tar} program was installed is used instead. This is
9288 the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh},
9289 @file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}.
9290 The installer may have overridden this by defining the environment
9291 variable @env{RSH} @emph{at installation time}.
9294 Specify drive and density.
9296 @xopindex{multi-volume, short description}
9298 @itemx --multi-volume
9299 Create/list/extract multi-volume archive.
9301 This option causes @command{tar} to write a @dfn{multi-volume} archive---one
9302 that may be larger than will fit on the medium used to hold it.
9303 @xref{Multi-Volume Archives}.
9305 @xopindex{tape-length, short description}
9307 @itemx --tape-length=@var{num}
9308 Change tape after writing @var{num} x 1024 bytes.
9310 This option might be useful when your tape drivers do not properly
9311 detect end of physical tapes. By being slightly conservative on the
9312 maximum tape length, you might avoid the problem entirely.
9314 @xopindex{info-script, short description}
9315 @xopindex{new-volume-script, short description}
9317 @itemx --info-script=@var{file}
9318 @itemx --new-volume-script=@var{file}
9319 Execute @file{file} at end of each tape. This implies
9320 @option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed
9321 description of this option.
9324 @node Remote Tape Server
9325 @section The Remote Tape Server
9327 @cindex remote tape drive
9329 In order to access the tape drive on a remote machine, @command{tar}
9330 uses the remote tape server written at the University of California at
9331 Berkeley. The remote tape server must be installed as
9332 @file{@var{prefix}/libexec/rmt} on any machine whose tape drive you
9333 want to use. @command{tar} calls @command{rmt} by running an
9334 @command{rsh} or @command{remsh} to the remote machine, optionally
9335 using a different login name if one is supplied.
9337 A copy of the source for the remote tape server is provided. It is
9338 Copyright @copyright{} 1983 by the Regents of the University of
9339 California, but can be freely distributed. It is compiled and
9340 installed by default.
9342 @cindex absolute file names
9343 Unless you use the @option{--absolute-names} (@option{-P}) option,
9344 @GNUTAR{} will not allow you to create an archive that contains
9345 absolute file names (a file name beginning with @samp{/}.) If you try,
9346 @command{tar} will automatically remove the leading @samp{/} from the
9347 file names it stores in the archive. It will also type a warning
9348 message telling you what it is doing.
9350 When reading an archive that was created with a different
9351 @command{tar} program, @GNUTAR{} automatically
9352 extracts entries in the archive which have absolute file names as if
9353 the file names were not absolute. This is an important feature. A
9354 visitor here once gave a @command{tar} tape to an operator to restore;
9355 the operator used Sun @command{tar} instead of @GNUTAR{},
9356 and the result was that it replaced large portions of
9357 our @file{/bin} and friends with versions from the tape; needless to
9358 say, we were unhappy about having to recover the file system from
9361 For example, if the archive contained a file @file{/usr/bin/computoy},
9362 @GNUTAR{} would extract the file to @file{usr/bin/computoy},
9363 relative to the current directory. If you want to extract the files in
9364 an archive to the same absolute names that they had when the archive
9365 was created, you should do a @samp{cd /} before extracting the files
9366 from the archive, or you should either use the @option{--absolute-names}
9367 option, or use the command @samp{tar -C / @dots{}}.
9369 @cindex Ultrix 3.1 and write failure
9370 Some versions of Unix (Ultrix 3.1 is known to have this problem),
9371 can claim that a short write near the end of a tape succeeded,
9372 when it actually failed. This will result in the -M option not
9373 working correctly. The best workaround at the moment is to use a
9374 significantly larger blocking factor than the default 20.
9376 In order to update an archive, @command{tar} must be able to backspace the
9377 archive in order to reread or rewrite a record that was just read (or
9378 written). This is currently possible only on two kinds of files: normal
9379 disk files (or any other file that can be backspaced with @samp{lseek}),
9380 and industry-standard 9-track magnetic tape (or any other kind of tape
9381 that can be backspaced with the @code{MTIOCTOP} @code{ioctl}.
9383 This means that the @option{--append}, @option{--concatenate}, and
9384 @option{--delete} commands will not work on any other kind of file.
9385 Some media simply cannot be backspaced, which means these commands and
9386 options will never be able to work on them. These non-backspacing
9387 media include pipes and cartridge tape drives.
9389 Some other media can be backspaced, and @command{tar} will work on them
9390 once @command{tar} is modified to do so.
9392 Archives created with the @option{--multi-volume}, @option{--label}, and
9393 @option{--incremental} (@option{-G}) options may not be readable by other version
9394 of @command{tar}. In particular, restoring a file that was split over
9395 a volume boundary will require some careful work with @command{dd}, if
9396 it can be done at all. Other versions of @command{tar} may also create
9397 an empty file whose name is that of the volume header. Some versions
9398 of @command{tar} may create normal files instead of directories archived
9399 with the @option{--incremental} (@option{-G}) option.
9401 @node Common Problems and Solutions
9402 @section Some Common Problems and their Solutions
9409 no such file or directory
9412 errors from @command{tar}:
9413 directory checksum error
9416 errors from media/system:
9427 @dfn{Block} and @dfn{record} terminology is rather confused, and it
9428 is also confusing to the expert reader. On the other hand, readers
9429 who are new to the field have a fresh mind, and they may safely skip
9430 the next two paragraphs, as the remainder of this manual uses those
9431 two terms in a quite consistent way.
9433 John Gilmore, the writer of the public domain @command{tar} from which
9434 @GNUTAR{} was originally derived, wrote (June 1995):
9437 The nomenclature of tape drives comes from IBM, where I believe
9438 they were invented for the IBM 650 or so. On IBM mainframes, what
9439 is recorded on tape are tape blocks. The logical organization of
9440 data is into records. There are various ways of putting records into
9441 blocks, including @code{F} (fixed sized records), @code{V} (variable
9442 sized records), @code{FB} (fixed blocked: fixed size records, @var{n}
9443 to a block), @code{VB} (variable size records, @var{n} to a block),
9444 @code{VSB} (variable spanned blocked: variable sized records that can
9445 occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=}
9446 parameter specified this to the operating system.
9448 The Unix man page on @command{tar} was totally confused about this.
9449 When I wrote @code{PD TAR}, I used the historically correct terminology
9450 (@command{tar} writes data records, which are grouped into blocks).
9451 It appears that the bogus terminology made it into @acronym{POSIX} (no surprise
9452 here), and now Fran@,{c}ois has migrated that terminology back
9453 into the source code too.
9456 The term @dfn{physical block} means the basic transfer chunk from or
9457 to a device, after which reading or writing may stop without anything
9458 being lost. In this manual, the term @dfn{block} usually refers to
9459 a disk physical block, @emph{assuming} that each disk block is 512
9460 bytes in length. It is true that some disk devices have different
9461 physical blocks, but @command{tar} ignore these differences in its own
9462 format, which is meant to be portable, so a @command{tar} block is always
9463 512 bytes in length, and @dfn{block} always mean a @command{tar} block.
9464 The term @dfn{logical block} often represents the basic chunk of
9465 allocation of many disk blocks as a single entity, which the operating
9466 system treats somewhat atomically; this concept is only barely used
9469 The term @dfn{physical record} is another way to speak of a physical
9470 block, those two terms are somewhat interchangeable. In this manual,
9471 the term @dfn{record} usually refers to a tape physical block,
9472 @emph{assuming} that the @command{tar} archive is kept on magnetic tape.
9473 It is true that archives may be put on disk or used with pipes,
9474 but nevertheless, @command{tar} tries to read and write the archive one
9475 @dfn{record} at a time, whatever the medium in use. One record is made
9476 up of an integral number of blocks, and this operation of putting many
9477 disk blocks into a single tape block is called @dfn{reblocking}, or
9478 more simply, @dfn{blocking}. The term @dfn{logical record} refers to
9479 the logical organization of many characters into something meaningful
9480 to the application. The term @dfn{unit record} describes a small set
9481 of characters which are transmitted whole to or by the application,
9482 and often refers to a line of text. Those two last terms are unrelated
9483 to what we call a @dfn{record} in @GNUTAR{}.
9485 When writing to tapes, @command{tar} writes the contents of the archive
9486 in chunks known as @dfn{records}. To change the default blocking
9487 factor, use the @option{--blocking-factor=@var{512-size}} (@option{-b
9488 @var{512-size}}) option. Each record will then be composed of
9489 @var{512-size} blocks. (Each @command{tar} block is 512 bytes.
9490 @xref{Standard}.) Each file written to the archive uses at least one
9491 full record. As a result, using a larger record size can result in
9492 more wasted space for small files. On the other hand, a larger record
9493 size can often be read and written much more efficiently.
9495 Further complicating the problem is that some tape drives ignore the
9496 blocking entirely. For these, a larger record size can still improve
9497 performance (because the software layers above the tape drive still
9498 honor the blocking), but not as dramatically as on tape drives that
9501 When reading an archive, @command{tar} can usually figure out the
9502 record size on itself. When this is the case, and a non-standard
9503 record size was used when the archive was created, @command{tar} will
9504 print a message about a non-standard blocking factor, and then operate
9505 normally. On some tape devices, however, @command{tar} cannot figure
9506 out the record size itself. On most of those, you can specify a
9507 blocking factor (with @option{--blocking-factor}) larger than the
9508 actual blocking factor, and then use the @option{--read-full-records}
9509 (@option{-B}) option. (If you specify a blocking factor with
9510 @option{--blocking-factor} and don't use the
9511 @option{--read-full-records} option, then @command{tar} will not
9512 attempt to figure out the recording size itself.) On some devices,
9513 you must always specify the record size exactly with
9514 @option{--blocking-factor} when reading, because @command{tar} cannot
9515 figure it out. In any case, use @option{--list} (@option{-t}) before
9516 doing any extractions to see whether @command{tar} is reading the archive
9519 @command{tar} blocks are all fixed size (512 bytes), and its scheme for
9520 putting them into records is to put a whole number of them (one or
9521 more) into each record. @command{tar} records are all the same size;
9522 at the end of the file there's a block containing all zeros, which
9523 is how you tell that the remainder of the last record(s) are garbage.
9525 In a standard @command{tar} file (no options), the block size is 512
9526 and the record size is 10240, for a blocking factor of 20. What the
9527 @option{--blocking-factor} option does is sets the blocking factor,
9528 changing the record size while leaving the block size at 512 bytes.
9529 20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives;
9530 most tape drives these days prefer much bigger records in order to
9531 stream and not waste tape. When writing tapes for myself, some tend
9532 to use a factor of the order of 2048, say, giving a record size of
9533 around one megabyte.
9535 If you use a blocking factor larger than 20, older @command{tar}
9536 programs might not be able to read the archive, so we recommend this
9537 as a limit to use in practice. @GNUTAR{}, however,
9538 will support arbitrarily large record sizes, limited only by the
9539 amount of virtual memory or the physical characteristics of the tape
9543 * Format Variations:: Format Variations
9544 * Blocking Factor:: The Blocking Factor of an Archive
9547 @node Format Variations
9548 @subsection Format Variations
9549 @cindex Format Parameters
9550 @cindex Format Options
9551 @cindex Options, archive format specifying
9552 @cindex Options, format specifying
9555 Format parameters specify how an archive is written on the archive
9556 media. The best choice of format parameters will vary depending on
9557 the type and number of files being archived, and on the media used to
9560 To specify format parameters when accessing or creating an archive,
9561 you can use the options described in the following sections.
9562 If you do not specify any format parameters, @command{tar} uses
9563 default parameters. You cannot modify a compressed archive.
9564 If you create an archive with the @option{--blocking-factor} option
9565 specified (@pxref{Blocking Factor}), you must specify that
9566 blocking-factor when operating on the archive. @xref{Formats}, for other
9567 examples of format parameter considerations.
9569 @node Blocking Factor
9570 @subsection The Blocking Factor of an Archive
9571 @cindex Blocking Factor
9573 @cindex Number of blocks per record
9574 @cindex Number of bytes per record
9575 @cindex Bytes per record
9576 @cindex Blocks per record
9579 @opindex blocking-factor
9580 The data in an archive is grouped into blocks, which are 512 bytes.
9581 Blocks are read and written in whole number multiples called
9582 @dfn{records}. The number of blocks in a record (i.e., the size of a
9583 record in units of 512 bytes) is called the @dfn{blocking factor}.
9584 The @option{--blocking-factor=@var{512-size}} (@option{-b
9585 @var{512-size}}) option specifies the blocking factor of an archive.
9586 The default blocking factor is typically 20 (i.e., 10240 bytes), but
9587 can be specified at installation. To find out the blocking factor of
9588 an existing archive, use @samp{tar --list --file=@var{archive-name}}.
9589 This may not work on some devices.
9591 Records are separated by gaps, which waste space on the archive media.
9592 If you are archiving on magnetic tape, using a larger blocking factor
9593 (and therefore larger records) provides faster throughput and allows you
9594 to fit more data on a tape (because there are fewer gaps). If you are
9595 archiving on cartridge, a very large blocking factor (say 126 or more)
9596 greatly increases performance. A smaller blocking factor, on the other
9597 hand, may be useful when archiving small files, to avoid archiving lots
9598 of nulls as @command{tar} fills out the archive to the end of the record.
9599 In general, the ideal record size depends on the size of the
9600 inter-record gaps on the tape you are using, and the average size of the
9601 files you are archiving. @xref{create}, for information on
9604 @FIXME{Need example of using a cartridge with blocking factor=126 or more.}
9606 Archives with blocking factors larger than 20 cannot be read
9607 by very old versions of @command{tar}, or by some newer versions
9608 of @command{tar} running on old machines with small address spaces.
9609 With @GNUTAR{}, the blocking factor of an archive is limited
9610 only by the maximum record size of the device containing the archive,
9611 or by the amount of available virtual memory.
9613 Also, on some systems, not using adequate blocking factors, as sometimes
9614 imposed by the device drivers, may yield unexpected diagnostics. For
9615 example, this has been reported:
9618 Cannot write to /dev/dlt: Invalid argument
9622 In such cases, it sometimes happen that the @command{tar} bundled by
9623 the system is aware of block size idiosyncrasies, while @GNUTAR{}
9624 requires an explicit specification for the block size,
9625 which it cannot guess. This yields some people to consider
9626 @GNUTAR{} is misbehaving, because by comparison,
9627 @cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}},
9628 for example, might resolve the problem.
9630 If you use a non-default blocking factor when you create an archive, you
9631 must specify the same blocking factor when you modify that archive. Some
9632 archive devices will also require you to specify the blocking factor when
9633 reading that archive, however this is not typically the case. Usually, you
9634 can use @option{--list} (@option{-t}) without specifying a blocking factor---@command{tar}
9635 reports a non-default record size and then lists the archive members as
9636 it would normally. To extract files from an archive with a non-standard
9637 blocking factor (particularly if you're not sure what the blocking factor
9638 is), you can usually use the @option{--read-full-records} (@option{-B}) option while
9639 specifying a blocking factor larger then the blocking factor of the archive
9640 (i.e., @samp{tar --extract --read-full-records --blocking-factor=300}.
9641 @xref{list}, for more information on the @option{--list} (@option{-t})
9642 operation. @xref{Reading}, for a more detailed explanation of that option.
9645 @item --blocking-factor=@var{number}
9646 @itemx -b @var{number}
9647 Specifies the blocking factor of an archive. Can be used with any
9648 operation, but is usually not necessary with @option{--list} (@option{-t}).
9654 @item -b @var{blocks}
9655 @itemx --blocking-factor=@var{blocks}
9656 Set record size to @math{@var{blocks} * 512} bytes.
9658 This option is used to specify a @dfn{blocking factor} for the archive.
9659 When reading or writing the archive, @command{tar}, will do reads and writes
9660 of the archive in records of @math{@var{block}*512} bytes. This is true
9661 even when the archive is compressed. Some devices requires that all
9662 write operations be a multiple of a certain size, and so, @command{tar}
9663 pads the archive out to the next record boundary.
9665 The default blocking factor is set when @command{tar} is compiled, and is
9666 typically 20. Blocking factors larger than 20 cannot be read by very
9667 old versions of @command{tar}, or by some newer versions of @command{tar}
9668 running on old machines with small address spaces.
9670 With a magnetic tape, larger records give faster throughput and fit
9671 more data on a tape (because there are fewer inter-record gaps).
9672 If the archive is in a disk file or a pipe, you may want to specify
9673 a smaller blocking factor, since a large one will result in a large
9674 number of null bytes at the end of the archive.
9676 When writing cartridge or other streaming tapes, a much larger
9677 blocking factor (say 126 or more) will greatly increase performance.
9678 However, you must specify the same blocking factor when reading or
9679 updating the archive.
9681 Apparently, Exabyte drives have a physical block size of 8K bytes.
9682 If we choose our blocksize as a multiple of 8k bytes, then the problem
9683 seems to disappear. Id est, we are using block size of 112 right
9684 now, and we haven't had the problem since we switched@dots{}
9686 With @GNUTAR{} the blocking factor is limited only
9687 by the maximum record size of the device containing the archive, or by
9688 the amount of available virtual memory.
9690 However, deblocking or reblocking is virtually avoided in a special
9691 case which often occurs in practice, but which requires all the
9692 following conditions to be simultaneously true:
9695 the archive is subject to a compression option,
9697 the archive is not handled through standard input or output, nor
9698 redirected nor piped,
9700 the archive is directly handled to a local disk, instead of any special
9703 @option{--blocking-factor} is not explicitly specified on the @command{tar}
9707 If the output goes directly to a local disk, and not through
9708 stdout, then the last write is not extended to a full record size.
9709 Otherwise, reblocking occurs. Here are a few other remarks on this
9715 @command{gzip} will complain about trailing garbage if asked to
9716 uncompress a compressed archive on tape, there is an option to turn
9717 the message off, but it breaks the regularity of simply having to use
9718 @samp{@var{prog} -d} for decompression. It would be nice if gzip was
9719 silently ignoring any number of trailing zeros. I'll ask Jean-loup
9720 Gailly, by sending a copy of this message to him.
9723 @command{compress} does not show this problem, but as Jean-loup pointed
9724 out to Michael, @samp{compress -d} silently adds garbage after
9725 the result of decompression, which tar ignores because it already
9726 recognized its end-of-file indicator. So this bug may be safely
9730 @samp{gzip -d -q} will be silent about the trailing zeros indeed,
9731 but will still return an exit status of 2 which tar reports in turn.
9732 @command{tar} might ignore the exit status returned, but I hate doing
9733 that, as it weakens the protection @command{tar} offers users against
9734 other possible problems at decompression time. If @command{gzip} was
9735 silently skipping trailing zeros @emph{and} also avoiding setting the
9736 exit status in this innocuous case, that would solve this situation.
9739 @command{tar} should become more solid at not stopping to read a pipe at
9740 the first null block encountered. This inelegantly breaks the pipe.
9741 @command{tar} should rather drain the pipe out before exiting itself.
9744 @xopindex{ignore-zeros, short description}
9746 @itemx --ignore-zeros
9747 Ignore blocks of zeros in archive (means EOF).
9749 The @option{--ignore-zeros} (@option{-i}) option causes @command{tar} to ignore blocks
9750 of zeros in the archive. Normally a block of zeros indicates the
9751 end of the archive, but when reading a damaged archive, or one which
9752 was created by concatenating several archives together, this option
9753 allows @command{tar} to read the entire archive. This option is not on
9754 by default because many versions of @command{tar} write garbage after
9757 Note that this option causes @command{tar} to read to the end of the
9758 archive file, which may sometimes avoid problems when multiple files
9759 are stored on a single physical tape.
9761 @xopindex{read-full-records, short description}
9763 @itemx --read-full-records
9764 Reblock as we read (for reading 4.2@acronym{BSD} pipes).
9766 If @option{--read-full-records} is used, @command{tar}
9767 will not panic if an attempt to read a record from the archive does
9768 not return a full record. Instead, @command{tar} will keep reading
9769 until it has obtained a full
9772 This option is turned on by default when @command{tar} is reading
9773 an archive from standard input, or from a remote machine. This is
9774 because on @acronym{BSD} Unix systems, a read of a pipe will return however
9775 much happens to be in the pipe, even if it is less than @command{tar}
9776 requested. If this option was not used, @command{tar} would fail as
9777 soon as it read an incomplete record from the pipe.
9779 This option is also useful with the commands for updating an archive.
9785 @FIXME{Appropriate options should be moved here from elsewhere.}
9787 @cindex blocking factor
9788 @cindex tape blocking
9790 When handling various tapes or cartridges, you have to take care of
9791 selecting a proper blocking, that is, the number of disk blocks you
9792 put together as a single tape block on the tape, without intervening
9793 tape gaps. A @dfn{tape gap} is a small landing area on the tape
9794 with no information on it, used for decelerating the tape to a
9795 full stop, and for later regaining the reading or writing speed.
9796 When the tape driver starts reading a record, the record has to
9797 be read whole without stopping, as a tape gap is needed to stop the
9798 tape motion without loosing information.
9800 @cindex Exabyte blocking
9801 @cindex DAT blocking
9802 Using higher blocking (putting more disk blocks per tape block) will use
9803 the tape more efficiently as there will be less tape gaps. But reading
9804 such tapes may be more difficult for the system, as more memory will be
9805 required to receive at once the whole record. Further, if there is a
9806 reading error on a huge record, this is less likely that the system will
9807 succeed in recovering the information. So, blocking should not be too
9808 low, nor it should be too high. @command{tar} uses by default a blocking of
9809 20 for historical reasons, and it does not really matter when reading or
9810 writing to disk. Current tape technology would easily accommodate higher
9811 blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs.
9812 We were told that for some DLT drives, the blocking should be a multiple
9813 of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance.
9814 Other manufacturers may use different recommendations for the same tapes.
9815 This might also depends of the buffering techniques used inside modern
9816 tape controllers. Some imposes a minimum blocking, or a maximum blocking.
9817 Others request blocking to be some exponent of two.
9819 So, there is no fixed rule for blocking. But blocking at read time
9820 should ideally be the same as blocking used at write time. At one place
9821 I know, with a wide variety of equipment, they found it best to use a
9822 blocking of 32 to guarantee that their tapes are fully interchangeable.
9824 I was also told that, for recycled tapes, prior erasure (by the same
9825 drive unit that will be used to create the archives) sometimes lowers
9826 the error rates observed at rewriting time.
9828 I might also use @option{--number-blocks} instead of
9829 @option{--block-number}, so @option{--block} will then expand to
9830 @option{--blocking-factor} unambiguously.
9833 @section Many Archives on One Tape
9835 @FIXME{Appropriate options should be moved here from elsewhere.}
9837 @findex ntape @r{device}
9838 Most tape devices have two entries in the @file{/dev} directory, or
9839 entries that come in pairs, which differ only in the minor number for
9840 this device. Let's take for example @file{/dev/tape}, which often
9841 points to the only or usual tape device of a given system. There might
9842 be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler
9843 name is the @emph{rewinding} version of the device, while the name
9844 having @samp{nr} in it is the @emph{no rewinding} version of the same
9847 A rewinding tape device will bring back the tape to its beginning point
9848 automatically when this device is opened or closed. Since @command{tar}
9849 opens the archive file before using it and closes it afterwards, this
9850 means that a simple:
9853 $ @kbd{tar cf /dev/tape @var{directory}}
9857 will reposition the tape to its beginning both prior and after saving
9858 @var{directory} contents to it, thus erasing prior tape contents and
9859 making it so that any subsequent write operation will destroy what has
9862 @cindex tape positioning
9863 So, a rewinding device is normally meant to hold one and only one file.
9864 If you want to put more than one @command{tar} archive on a given tape, you
9865 will need to avoid using the rewinding version of the tape device. You
9866 will also have to pay special attention to tape positioning. Errors in
9867 positioning may overwrite the valuable data already on your tape. Many
9868 people, burnt by past experiences, will only use rewinding devices and
9869 limit themselves to one file per tape, precisely to avoid the risk of
9870 such errors. Be fully aware that writing at the wrong position on a
9871 tape loses all information past this point and most probably until the
9872 end of the tape, and this destroyed information @emph{cannot} be
9875 To save @var{directory-1} as a first archive at the beginning of a
9876 tape, and leave that tape ready for a second archive, you should use:
9879 $ @kbd{mt -f /dev/nrtape rewind}
9880 $ @kbd{tar cf /dev/nrtape @var{directory-1}}
9884 @dfn{Tape marks} are special magnetic patterns written on the tape
9885 media, which are later recognizable by the reading hardware. These
9886 marks are used after each file, when there are many on a single tape.
9887 An empty file (that is to say, two tape marks in a row) signal the
9888 logical end of the tape, after which no file exist. Usually,
9889 non-rewinding tape device drivers will react to the close request issued
9890 by @command{tar} by first writing two tape marks after your archive, and by
9891 backspacing over one of these. So, if you remove the tape at that time
9892 from the tape drive, it is properly terminated. But if you write
9893 another file at the current position, the second tape mark will be
9894 erased by the new information, leaving only one tape mark between files.
9896 So, you may now save @var{directory-2} as a second archive after the
9897 first on the same tape by issuing the command:
9900 $ @kbd{tar cf /dev/nrtape @var{directory-2}}
9904 and so on for all the archives you want to put on the same tape.
9906 Another usual case is that you do not write all the archives the same
9907 day, and you need to remove and store the tape between two archive
9908 sessions. In general, you must remember how many files are already
9909 saved on your tape. Suppose your tape already has 16 files on it, and
9910 that you are ready to write the 17th. You have to take care of skipping
9911 the first 16 tape marks before saving @var{directory-17}, say, by using
9915 $ @kbd{mt -f /dev/nrtape rewind}
9916 $ @kbd{mt -f /dev/nrtape fsf 16}
9917 $ @kbd{tar cf /dev/nrtape @var{directory-17}}
9920 In all the previous examples, we put aside blocking considerations, but
9921 you should do the proper things for that as well. @xref{Blocking}.
9924 * Tape Positioning:: Tape Positions and Tape Marks
9925 * mt:: The @command{mt} Utility
9928 @node Tape Positioning
9929 @subsection Tape Positions and Tape Marks
9932 Just as archives can store more than one file from the file system,
9933 tapes can store more than one archive file. To keep track of where
9934 archive files (or any other type of file stored on tape) begin and
9935 end, tape archive devices write magnetic @dfn{tape marks} on the
9936 archive media. Tape drives write one tape mark between files,
9937 two at the end of all the file entries.
9939 If you think of data as a series of records "rrrr"'s, and tape marks as
9940 "*"'s, a tape might look like the following:
9943 rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
9946 Tape devices read and write tapes using a read/write @dfn{tape
9947 head}---a physical part of the device which can only access one
9948 point on the tape at a time. When you use @command{tar} to read or
9949 write archive data from a tape device, the device will begin reading
9950 or writing from wherever on the tape the tape head happens to be,
9951 regardless of which archive or what part of the archive the tape
9952 head is on. Before writing an archive, you should make sure that no
9953 data on the tape will be overwritten (unless it is no longer needed).
9954 Before reading an archive, you should make sure the tape head is at
9955 the beginning of the archive you want to read. You can do it manually
9956 via @code{mt} utility (@pxref{mt}). The @code{restore} script does
9957 that automatically (@pxref{Scripted Restoration}).
9959 If you want to add new archive file entries to a tape, you should
9960 advance the tape to the end of the existing file entries, backspace
9961 over the last tape mark, and write the new archive file. If you were
9962 to add two archives to the example above, the tape might look like the
9966 rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
9970 @subsection The @command{mt} Utility
9973 @FIXME{Is it true that this only works on non-block devices?
9974 should explain the difference, (fixed or variable).}
9975 @xref{Blocking Factor}.
9977 You can use the @command{mt} utility to advance or rewind a tape past a
9978 specified number of archive files on the tape. This will allow you
9979 to move to the beginning of an archive before extracting or reading
9980 it, or to the end of all the archives before writing a new one.
9981 @FIXME{Why isn't there an "advance 'til you find two tape marks
9984 The syntax of the @command{mt} command is:
9987 @kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
9990 where @var{tapename} is the name of the tape device, @var{number} is
9991 the number of times an operation is performed (with a default of one),
9992 and @var{operation} is one of the following:
9994 @FIXME{is there any use for record operations?}
9999 Writes @var{number} tape marks at the current position on the tape.
10002 Moves tape position forward @var{number} files.
10005 Moves tape position back @var{number} files.
10008 Rewinds the tape. (Ignores @var{number}).
10012 Rewinds the tape and takes the tape device off-line. (Ignores @var{number}).
10015 Prints status information about the tape unit.
10019 @FIXME{Is there a better way to frob the spacing on the list?}
10021 If you don't specify a @var{tapename}, @command{mt} uses the environment
10022 variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
10023 the default device specified in your @file{sys/mtio.h} file
10024 (@code{DEFTAPE} variable). If this is not defined, the program will
10025 display a descriptive error message and exit with code 1.
10027 @command{mt} returns a 0 exit status when the operation(s) were
10028 successful, 1 if the command was unrecognized, and 2 if an operation
10031 @node Using Multiple Tapes
10032 @section Using Multiple Tapes
10034 Often you might want to write a large archive, one larger than will fit
10035 on the actual tape you are using. In such a case, you can run multiple
10036 @command{tar} commands, but this can be inconvenient, particularly if you
10037 are using options like @option{--exclude=@var{pattern}} or dumping entire file systems.
10038 Therefore, @command{tar} provides a special mode for creating
10039 multi-volume archives.
10041 @dfn{Multi-volume} archive is a single @command{tar} archive, stored
10042 on several media volumes of fixed size. Although in this section we will
10043 often call @samp{volume} a @dfn{tape}, there is absolutely no
10044 requirement for multi-volume archives to be stored on tapes. Instead,
10045 they can use whatever media type the user finds convenient, they can
10046 even be located on files.
10048 When creating a multi-volume archive, @GNUTAR{} continues to fill
10049 current volume until it runs out of space, then it switches to
10050 next volume (usually the operator is queried to replace the tape on
10051 this point), and continues working on the new volume. This operation
10052 continues until all requested files are dumped. If @GNUTAR{} detects
10053 end of media while dumping a file, such a file is archived in split
10054 form. Some very big files can even be split across several volumes.
10056 Each volume is itself a valid @GNUTAR{} archive, so it can be read
10057 without any special options. Consequently any file member residing
10058 entirely on one volume can be extracted or otherwise operated upon
10059 without needing the other volume. Sure enough, to extract a split
10060 member you would need all volumes its parts reside on.
10062 Multi-volume archives suffer from several limitations. In particular,
10063 they cannot be compressed.
10065 @GNUTAR{} is able to create multi-volume archives of two formats
10066 (@pxref{Formats}): @samp{GNU} and @samp{POSIX}.
10069 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
10070 * Tape Files:: Tape Files
10071 * Tarcat:: Concatenate Volumes into a Single Archive
10075 @node Multi-Volume Archives
10076 @subsection Archives Longer than One Tape or Disk
10077 @cindex Multi-volume archives
10079 @opindex multi-volume
10080 To create an archive that is larger than will fit on a single unit of
10081 the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
10082 the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
10083 archive can be manipulated like any other archive (provided the
10084 @option{--multi-volume} option is specified), but is stored on more
10085 than one tape or disk.
10087 When you specify @option{--multi-volume}, @command{tar} does not report an
10088 error when it comes to the end of an archive volume (when reading), or
10089 the end of the media (when writing). Instead, it prompts you to load
10090 a new storage volume. If the archive is on a magnetic tape, you
10091 should change tapes when you see the prompt; if the archive is on a
10092 floppy disk, you should change disks; etc.
10095 @item --multi-volume
10097 Creates a multi-volume archive, when used in conjunction with
10098 @option{--create} (@option{-c}). To perform any other operation on a multi-volume
10099 archive, specify @option{--multi-volume} in conjunction with that
10104 $ @kbd{tar --create --multi-volume --file=/dev/tape @var{files}}
10108 The method @command{tar} uses to detect end of tape is not perfect, and
10109 fails on some operating systems or on some devices. If @command{tar}
10110 cannot detect the end of the tape itself, you can use
10111 @option{--tape-length} option to inform it about the capacity of the
10114 @anchor{tape-length}
10116 @opindex tape-length
10117 @item --tape-length=@var{size}
10118 @itemx -L @var{size}
10119 Set maximum length of a volume. The @var{size} argument should then
10120 be the usable size of the tape in units of 1024 bytes. This option
10121 selects @option{--multi-volume} automatically. For example:
10124 $ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}}
10128 @anchor{change volume prompt}
10129 When @GNUTAR{} comes to the end of a storage media, it asks you to
10130 change the volume. The built-in prompt for POSIX locale
10131 is@footnote{If you run @GNUTAR{} under a different locale, the
10132 translation to the locale's language will be used.}:
10135 Prepare volume #@var{n} for `@var{archive}' and hit return:
10139 where @var{n} is the ordinal number of the volume to be created and
10140 @var{archive} is archive file or device name.
10142 When prompting for a new tape, @command{tar} accepts any of the following
10147 Request @command{tar} to explain possible responses
10149 Request @command{tar} to exit immediately.
10150 @item n @var{file-name}
10151 Request @command{tar} to write the next volume on the file @var{file-name}.
10153 Request @command{tar} to run a subshell. This option can be disabled
10154 by giving @option{--restrict} command line option to
10155 @command{tar}@footnote{@xref{--restrict}, for more information about
10158 Request @command{tar} to begin writing the next volume.
10161 (You should only type @samp{y} after you have changed the tape;
10162 otherwise @command{tar} will write over the volume it just finished.)
10164 @cindex Volume number file
10166 @anchor{volno-file}
10167 @opindex volno-file
10168 The volume number used by @command{tar} in its tape-changing prompt
10169 can be changed; if you give the
10170 @option{--volno-file=@var{file-of-number}} option, then
10171 @var{file-of-number} should be an non-existing file to be created, or
10172 else, a file already containing a decimal number. That number will be
10173 used as the volume number of the first volume written. When
10174 @command{tar} is finished, it will rewrite the file with the
10175 now-current volume number. (This does not change the volume number
10176 written on a tape label, as per @ref{label}, it @emph{only} affects
10177 the number used in the prompt.)
10179 @cindex End-of-archive info script
10180 @cindex Info script
10181 @anchor{info-script}
10182 @opindex info-script
10183 @opindex new-volume-script
10184 If you want more elaborate behavior than this, you can write a special
10185 @dfn{new volume script}, that will be responsible for changing the
10186 volume, and instruct @command{tar} to use it instead of its normal
10187 prompting procedure:
10190 @item --info-script=@var{script-name}
10191 @itemx --new-volume-script=@var{script-name}
10192 @itemx -F @var{script-name}
10193 Specify the full name of the volume script to use. The script can be
10194 used to eject cassettes, or to broadcast messages such as
10195 @samp{Someone please come change my tape} when performing unattended
10199 The @var{script-name} is executed without any command line
10200 arguments. It inherits @command{tar}'s shell environment.
10201 Additional data is passed to it via the following
10202 environment variables:
10205 @vrindex TAR_VERSION, info script environment variable
10207 @GNUTAR{} version number.
10209 @vrindex TAR_ARCHIVE, info script environment variable
10211 The name of the archive @command{tar} is processing.
10213 @vrindex TAR_VOLUME, info script environment variable
10215 Ordinal number of the volume @command{tar} is about to start.
10217 @vrindex TAR_SUBCOMMAND, info script environment variable
10218 @item TAR_SUBCOMMAND
10219 Short option describing the operation @command{tar} is executing
10220 @xref{Operations}, for a complete list of subcommand options.
10222 @vrindex TAR_FORMAT, info script environment variable
10224 Format of the archive being processed. @xref{Formats}, for a complete
10225 list of archive format names.
10227 @vrindex TAR_FD, info script environment variable
10229 File descriptor which can be used to communicate the new volume
10230 name to @command{tar}.
10233 The volume script can instruct @command{tar} to use new archive name,
10234 by writing in to file descriptor @env{$TAR_FD} (see below for an example).
10236 If the info script fails, @command{tar} exits; otherwise, it begins
10237 writing the next volume.
10239 If you want @command{tar} to cycle through a series of files or tape
10240 drives, there are three approaches to choose from. First of all, you
10241 can give @command{tar} multiple @option{--file} options. In this case
10242 the specified files will be used, in sequence, as the successive
10243 volumes of the archive. Only when the first one in the sequence needs
10244 to be used again will @command{tar} prompt for a tape change (or run
10245 the info script). For example, suppose someone has two tape drives on
10246 a system named @file{/dev/tape0} and @file{/dev/tape1}. For having
10247 @GNUTAR{} to switch to the second drive when it needs to write the
10248 second tape, and then back to the first tape, etc., just do either of:
10251 $ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
10252 $ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
10255 The second method is to use the @samp{n} response to the tape-change
10258 Finally, the most flexible approach is to use a volume script, that
10259 writes new archive name to the file descriptor @env{$TAR_FD}. For example, the
10260 following volume script will create a series of archive files, named
10261 @file{@var{archive}-@var{vol}}, where @var{archive} is the name of the
10262 archive being created (as given by @option{--file} option) and
10263 @var{vol} is the ordinal number of the archive being created:
10268 echo Preparing volume $TAR_VOLUME of $TAR_ARCHIVE.
10270 name=`expr $TAR_ARCHIVE : '\(.*\)-.*'`
10271 case $TAR_SUBCOMMAND in
10273 -d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
10278 echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&$TAR_FD
10282 The same script can be used while listing, comparing or extracting
10283 from the created archive. For example:
10287 # @r{Create a multi-volume archive:}
10288 $ @kbd{tar -c -L1024 -f archive.tar -F new-volume .}
10289 # @r{Extract from the created archive:}
10290 $ @kbd{tar -x -f archive.tar -F new-volume .}
10295 Notice, that the first command had to use @option{-L} option, since
10296 otherwise @GNUTAR{} will end up writing everything to file
10297 @file{archive.tar}.
10299 You can read each individual volume of a multi-volume archive as if it
10300 were an archive by itself. For example, to list the contents of one
10301 volume, use @option{--list}, without @option{--multi-volume} specified.
10302 To extract an archive member from one volume (assuming it is described
10303 that volume), use @option{--extract}, again without
10304 @option{--multi-volume}.
10306 If an archive member is split across volumes (i.e., its entry begins on
10307 one volume of the media and ends on another), you need to specify
10308 @option{--multi-volume} to extract it successfully. In this case, you
10309 should load the volume where the archive member starts, and use
10310 @samp{tar --extract --multi-volume}---@command{tar} will prompt for later
10311 volumes as it needs them. @xref{extracting archives}, for more
10312 information about extracting archives.
10314 Multi-volume archives can be modified like any other archive. To add
10315 files to a multi-volume archive, you need to only mount the last
10316 volume of the archive media (and new volumes, if needed). For all
10317 other operations, you need to use the entire archive.
10319 If a multi-volume archive was labeled using
10320 @option{--label=@var{archive-label}} (@pxref{label}) when it was
10321 created, @command{tar} will not automatically label volumes which are
10322 added later. To label subsequent volumes, specify
10323 @option{--label=@var{archive-label}} again in conjunction with the
10324 @option{--append}, @option{--update} or @option{--concatenate} operation.
10326 Notice that multi-volume support is a GNU extension and the archives
10327 created in this mode should be read only using @GNUTAR{}. If you
10328 absolutely have to process such archives using a third-party @command{tar}
10329 implementation, read @ref{Split Recovery}.
10332 @subsection Tape Files
10335 To give the archive a name which will be recorded in it, use the
10336 @option{--label=@var{volume-label}} (@option{-V @var{volume-label}})
10337 option. This will write a special block identifying
10338 @var{volume-label} as the name of the archive to the front of the
10339 archive which will be displayed when the archive is listed with
10340 @option{--list}. If you are creating a multi-volume archive with
10341 @option{--multi-volume} (@pxref{Using Multiple Tapes}), then the
10342 volume label will have @samp{Volume @var{nnn}} appended to the name
10343 you give, where @var{nnn} is the number of the volume of the archive.
10344 (If you use the @option{--label=@var{volume-label}}) option when
10345 reading an archive, it checks to make sure the label on the tape
10346 matches the one you give. @xref{label}.
10348 When @command{tar} writes an archive to tape, it creates a single
10349 tape file. If multiple archives are written to the same tape, one
10350 after the other, they each get written as separate tape files. When
10351 extracting, it is necessary to position the tape at the right place
10352 before running @command{tar}. To do this, use the @command{mt} command.
10353 For more information on the @command{mt} command and on the organization
10354 of tapes into a sequence of tape files, see @ref{mt}.
10356 People seem to often do:
10359 @kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
10362 or such, for pushing a common date in all volumes or an archive set.
10365 @subsection Concatenate Volumes into a Single Archive
10368 Sometimes it is necessary to convert existing @GNUTAR{} multi-volume
10369 archive to a single @command{tar} archive. Simply concatenating all
10370 volumes into one will not work, since each volume carries an additional
10371 information at the beginning. @GNUTAR{} is shipped with the shell
10372 script @command{tarcat} designed for this purpose.
10374 The script takes a list of files comprising a multi-volume archive
10375 and creates the resulting archive at the standard output. For example:
10378 @kbd{tarcat vol.1 vol.2 vol.3 | tar tf -}
10381 The script implements a simple heuristics to determine the format of
10382 the first volume file and to decide how to process the rest of the
10383 files. However, it makes no attempt to verify whether the files are
10384 given in order or even if they are valid @command{tar} archives.
10385 It uses @command{dd} and does not filter its standard error, so you
10386 will usually see lots of spurious messages.
10388 @FIXME{The script is not installed. Should we install it?}
10391 @section Including a Label in the Archive
10392 @cindex Labeling an archive
10393 @cindex Labels on the archive media
10394 @cindex Labeling multi-volume archives
10398 To avoid problems caused by misplaced paper labels on the archive
10399 media, you can include a @dfn{label} entry---an archive member which
10400 contains the name of the archive---in the archive itself. Use the
10401 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
10402 option in conjunction with the @option{--create} operation to include
10403 a label entry in the archive as it is being created.
10406 @item --label=@var{archive-label}
10407 @itemx -V @var{archive-label}
10408 Includes an @dfn{archive-label} at the beginning of the archive when
10409 the archive is being created, when used in conjunction with the
10410 @option{--create} operation. Checks to make sure the archive label
10411 matches the one specified (when used in conjunction with any other
10415 If you create an archive using both
10416 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
10417 and @option{--multi-volume} (@option{-M}), each volume of the archive
10418 will have an archive label of the form @samp{@var{archive-label}
10419 Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the
10420 next, and so on. @xref{Using Multiple Tapes}, for information on
10421 creating multiple volume archives.
10423 @cindex Volume label, listing
10424 @cindex Listing volume label
10425 The volume label will be displayed by @option{--list} along with
10426 the file contents. If verbose display is requested, it will also be
10427 explicitly marked as in the example below:
10431 $ @kbd{tar --verbose --list --file=iamanarchive}
10432 V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
10433 -rw-r--r-- ringo user 40 1990-05-21 13:30 iamafilename
10437 @opindex test-label
10438 @anchor{--test-label option}
10439 However, @option{--list} option will cause listing entire
10440 contents of the archive, which may be undesirable (for example, if the
10441 archive is stored on a tape). You can request checking only the volume
10442 by specifying @option{--test-label} option. This option reads only the
10443 first block of an archive, so it can be used with slow storage
10444 devices. For example:
10448 $ @kbd{tar --test-label --file=iamanarchive}
10453 If @option{--test-label} is used with a single command line
10454 argument, @command{tar} compares the volume label with the
10455 argument. It exits with code 0 if the two strings match, and with code
10456 2 otherwise. In this case no output is displayed. For example:
10460 $ @kbd{tar --test-label --file=iamanarchive 'iamalable'}
10462 $ @kbd{tar --test-label --file=iamanarchive 'iamalable' alabel}
10467 If you request any operation, other than @option{--create}, along
10468 with using @option{--label} option, @command{tar} will first check if
10469 the archive label matches the one specified and will refuse to proceed
10470 if it does not. Use this as a safety precaution to avoid accidentally
10471 overwriting existing archives. For example, if you wish to add files
10472 to @file{archive}, presumably labeled with string @samp{My volume},
10477 $ @kbd{tar -rf archive --label 'My volume' .}
10478 tar: Archive not labeled to match `My volume'
10483 in case its label does not match. This will work even if
10484 @file{archive} is not labeled at all.
10486 Similarly, @command{tar} will refuse to list or extract the
10487 archive if its label doesn't match the @var{archive-label}
10488 specified. In those cases, @var{archive-label} argument is interpreted
10489 as a globbing-style pattern which must match the actual magnetic
10490 volume label. @xref{exclude}, for a precise description of how match
10491 is attempted@footnote{Previous versions of @command{tar} used full
10492 regular expression matching, or before that, only exact string
10493 matching, instead of wildcard matchers. We decided for the sake of
10494 simplicity to use a uniform matching device through
10495 @command{tar}.}. If the switch @option{--multi-volume} (@option{-M}) is being used,
10496 the volume label matcher will also suffix @var{archive-label} by
10497 @w{@samp{ Volume [1-9]*}} if the initial match fails, before giving
10498 up. Since the volume numbering is automatically added in labels at
10499 creation time, it sounded logical to equally help the user taking care
10500 of it when the archive is being read.
10502 The @option{--label} was once called @option{--volume}, but is not
10503 available under that name anymore.
10505 You can also use @option{--label} to get a common information on
10506 all tapes of a series. For having this information different in each
10507 series created through a single script used on a regular basis, just
10508 manage to get some date string as part of the label. For example:
10512 $ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
10513 $ @kbd{tar --create --file=/dev/tape --multi-volume \
10514 --volume="Daily backup for `date +%Y-%m-%d`"}
10518 Also note that each label has its own date and time, which corresponds
10519 to when @GNUTAR{} initially attempted to write it,
10520 often soon after the operator launches @command{tar} or types the
10521 carriage return telling that the next tape is ready. Comparing date
10522 labels does give an idea of tape throughput only if the delays for
10523 rewinding tapes and the operator switching them were negligible, which
10524 is usually not the case.
10527 @section Verifying Data as It is Stored
10528 @cindex Verifying a write operation
10529 @cindex Double-checking a write operation
10534 @opindex verify, short description
10535 Attempt to verify the archive after writing.
10538 This option causes @command{tar} to verify the archive after writing it.
10539 Each volume is checked after it is written, and any discrepancies
10540 are recorded on the standard error output.
10542 Verification requires that the archive be on a back-space-able medium.
10543 This means pipes, some cartridge tape drives, and some other devices
10544 cannot be verified.
10546 You can insure the accuracy of an archive by comparing files in the
10547 system with archive members. @command{tar} can compare an archive to the
10548 file system as the archive is being written, to verify a write
10549 operation, or can compare a previously written archive, to insure that
10552 @xopindex{verify, using with @option{--create}}
10553 @xopindex{create, using with @option{--verify}}
10554 To check for discrepancies in an archive immediately after it is
10555 written, use the @option{--verify} (@option{-W}) option in conjunction with
10556 the @option{--create} operation. When this option is
10557 specified, @command{tar} checks archive members against their counterparts
10558 in the file system, and reports discrepancies on the standard error.
10560 To verify an archive, you must be able to read it from before the end
10561 of the last written entry. This option is useful for detecting data
10562 errors on some tapes. Archives written to pipes, some cartridge tape
10563 drives, and some other devices cannot be verified.
10565 One can explicitly compare an already made archive with the file
10566 system by using the @option{--compare} (@option{--diff}, @option{-d})
10567 option, instead of using the more automatic @option{--verify} option.
10570 Note that these two options have a slightly different intent. The
10571 @option{--compare} option checks how identical are the logical contents of some
10572 archive with what is on your disks, while the @option{--verify} option is
10573 really for checking if the physical contents agree and if the recording
10574 media itself is of dependable quality. So, for the @option{--verify}
10575 operation, @command{tar} tries to defeat all in-memory cache pertaining to
10576 the archive, while it lets the speed optimization undisturbed for the
10577 @option{--compare} option. If you nevertheless use @option{--compare} for
10578 media verification, you may have to defeat the in-memory cache yourself,
10579 maybe by opening and reclosing the door latch of your recording unit,
10580 forcing some doubt in your operating system about the fact this is really
10581 the same volume as the one just written or read.
10583 The @option{--verify} option would not be necessary if drivers were indeed
10584 able to detect dependably all write failures. This sometimes require many
10585 magnetic heads, some able to read after the writes occurred. One would
10586 not say that drivers unable to detect all cases are necessarily flawed,
10587 as long as programming is concerned.
10589 The @option{--verify} (@option{-W}) option will not work in
10590 conjunction with the @option{--multi-volume} (@option{-M}) option or
10591 the @option{--append} (@option{-r}), @option{--update} (@option{-u})
10592 and @option{--delete} operations. @xref{Operations}, for more
10593 information on these operations.
10595 Also, since @command{tar} normally strips leading @samp{/} from file
10596 names (@pxref{absolute}), a command like @samp{tar --verify -cf
10597 /tmp/foo.tar /etc} will work as desired only if the working directory is
10598 @file{/}, as @command{tar} uses the archive's relative member names
10599 (e.g., @file{etc/motd}) when verifying the archive.
10601 @node Write Protection
10602 @section Write Protection
10604 Almost all tapes and diskettes, and in a few rare cases, even disks can
10605 be @dfn{write protected}, to protect data on them from being changed.
10606 Once an archive is written, you should write protect the media to prevent
10607 the archive from being accidentally overwritten or deleted. (This will
10608 protect the archive from being changed with a tape or floppy drive---it
10609 will not protect it from magnet fields or other physical hazards).
10611 The write protection device itself is usually an integral part of the
10612 physical media, and can be a two position (write enabled/write
10613 disabled) switch, a notch which can be popped out or covered, a ring
10614 which can be removed from the center of a tape reel, or some other
10615 changeable feature.
10620 This appendix lists some important user-visible changes between
10621 version @GNUTAR{} @value{VERSION} and previous versions. An up-to-date
10622 version of this document is available at
10623 @uref{http://www.gnu.org/@/software/@/tar/manual/changes.html,the
10624 @GNUTAR{} documentation page}.
10627 @item Use of globbing patterns when listing and extracting.
10629 Previous versions of GNU tar assumed shell-style globbing when
10630 extracting from or listing an archive. For example:
10633 $ @kbd{tar xf foo.tar '*.c'}
10636 would extract all files whose names end in @samp{.c}. This behavior
10637 was not documented and was incompatible with traditional tar
10638 implementations. Therefore, starting from version 1.15.91, GNU tar
10639 no longer uses globbing by default. For example, the above invocation
10640 is now interpreted as a request to extract from the archive the file
10643 To facilitate transition to the new behavior for those users who got
10644 used to the previous incorrect one, @command{tar} will print a warning
10645 if it finds out that a requested member was not found in the archive
10646 and its name looks like a globbing pattern. For example:
10649 $ @kbd{tar xf foo.tar '*.c'}
10650 tar: Pattern matching characters used in file names. Please,
10651 tar: use --wildcards to enable pattern matching, or --no-wildcards to
10652 tar: suppress this warning.
10653 tar: *.c: Not found in archive
10654 tar: Error exit delayed from previous errors
10657 To treat member names as globbing patterns, use --wildcards option.
10658 If you want to tar to mimic the behavior of versions prior to 1.15.91,
10659 add this option to your @env{TAR_OPTIONS} variable.
10661 @xref{wildcards}, for the detailed discussion of the use of globbing
10662 patterns by @GNUTAR{}.
10664 @item Use of short option @option{-o}.
10666 Earlier versions of @GNUTAR{} understood @option{-o} command line
10667 option as a synonym for @option{--old-archive}.
10669 @GNUTAR{} starting from version 1.13.90 understands this option as
10670 a synonym for @option{--no-same-owner}. This is compatible with
10671 UNIX98 @command{tar} implementations.
10673 However, to facilitate transition, @option{-o} option retains its
10674 old semantics when it is used with one of archive-creation commands.
10675 Users are encouraged to use @option{--format=oldgnu} instead.
10677 It is especially important, since versions of @acronym{GNU} Automake
10678 up to and including 1.8.4 invoke tar with this option to produce
10679 distribution tarballs. @xref{Formats,v7}, for the detailed discussion
10680 of this issue and its implications.
10682 @FIXME{Change the first argument to tar-formats when the new Automake is
10683 out. The proposition to add @anchor{} to the appropriate place of its
10684 docs was accepted by Automake people --Sergey 2006-05-25}.
10685 @xref{Options, tar-v7, Changing Automake's Behavior,
10686 automake, GNU Automake}, for a description on how to use various
10687 archive formats with @command{automake}.
10689 Future versions of @GNUTAR{} will understand @option{-o} only as a
10690 synonym for @option{--no-same-owner}.
10692 @item Use of short option @option{-l}
10694 Earlier versions of @GNUTAR{} understood @option{-l} option as a
10695 synonym for @option{--one-file-system}. Since such usage contradicted
10696 to UNIX98 specification and harmed compatibility with other
10697 implementation, it was declared deprecated in version 1.14. However,
10698 to facilitate transition to its new semantics, it was supported by
10699 versions 1.15 and 1.15.90. The present use of @option{-l} as a short
10700 variant of @option{--check-links} was introduced in version 1.15.91.
10702 @item Use of options @option{--portability} and @option{--old-archive}
10704 These options are deprecated. Please use @option{--format=v7} instead.
10706 @item Use of option @option{--posix}
10708 This option is deprecated. Please use @option{--format=posix} instead.
10711 @node Configuring Help Summary
10712 @appendix Configuring Help Summary
10714 Running @kbd{tar --help} displays the short @command{tar} option
10715 summary (@pxref{help}). This summary is organized by @dfn{groups} of
10716 semantically close options. The options within each group are printed
10717 in the following order: a short option, eventually followed by a list
10718 of corresponding long option names, followed by a short description of
10719 the option. For example, here is an excerpt from the actual @kbd{tar
10723 Main operation mode:
10725 -A, --catenate, --concatenate append tar files to an archive
10726 -c, --create create a new archive
10727 -d, --diff, --compare find differences between archive and
10729 --delete delete from the archive
10732 @vrindex ARGP_HELP_FMT, environment variable
10733 The exact visual representation of the help output is configurable via
10734 @env{ARGP_HELP_FMT} environment variable. The value of this variable
10735 is a comma-separated list of @dfn{format variable} assignments. There
10736 are two kinds of format variables. An @dfn{offset variable} keeps the
10737 offset of some part of help output text from the leftmost column on
10738 the screen. A @dfn{boolean} variable is a flag that toggles some
10739 output feature on or off. Depending on the type of the corresponding
10740 variable, there are two kinds of assignments:
10743 @item Offset assignment
10745 The assignment to an offset variable has the following syntax:
10748 @var{variable}=@var{value}
10752 where @var{variable} is the variable name, and @var{value} is a
10753 numeric value to be assigned to the variable.
10755 @item Boolean assignment
10757 To assign @code{true} value to a variable, simply put this variable name. To
10758 assign @code{false} value, prefix the variable name with @samp{no-}. For
10763 # Assign @code{true} value:
10765 # Assign @code{false} value:
10771 Following variables are declared:
10773 @deftypevr {Help Output} boolean dup-args
10774 If true, arguments for an option are shown with both short and long
10775 options, even when a given option has both forms, for example:
10778 -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE
10781 If false, then if an option has both short and long forms, the
10782 argument is only shown with the long one, for example:
10785 -f, --file=ARCHIVE use archive file or device ARCHIVE
10789 and a message indicating that the argument is applicable to both
10790 forms is printed below the options. This message can be disabled
10791 using @code{dup-args-note} (see below).
10793 The default is false.
10796 @deftypevr {Help Output} boolean dup-args-note
10797 If this variable is true, which is the default, the following notice
10798 is displayed at the end of the help output:
10801 Mandatory or optional arguments to long options are also mandatory or
10802 optional for any corresponding short options.
10805 Setting @code{no-dup-args-note} inhibits this message. Normally, only one of
10806 variables @code{dup-args} or @code{dup-args-note} should be set.
10809 @deftypevr {Help Output} offset short-opt-col
10810 Column in which short options start. Default is 2.
10814 $ @kbd{tar --help|grep ARCHIVE}
10815 -f, --file=ARCHIVE use archive file or device ARCHIVE
10816 $ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE}
10817 -f, --file=ARCHIVE use archive file or device ARCHIVE
10822 @deftypevr {Help Output} offset long-opt-col
10823 Column in which long options start. Default is 6. For example:
10827 $ @kbd{tar --help|grep ARCHIVE}
10828 -f, --file=ARCHIVE use archive file or device ARCHIVE
10829 $ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE}
10830 -f, --file=ARCHIVE use archive file or device ARCHIVE
10835 @deftypevr {Help Output} offset doc-opt-col
10836 Column in which @dfn{doc options} start. A doc option isn't actually
10837 an option, but rather an arbitrary piece of documentation that is
10838 displayed in much the same manner as the options. For example, in
10839 the description of @option{--format} option:
10843 -H, --format=FORMAT create archive of the given format.
10845 FORMAT is one of the following:
10847 gnu GNU tar 1.13.x format
10848 oldgnu GNU format as per tar <= 1.12
10849 pax POSIX 1003.1-2001 (pax) format
10851 ustar POSIX 1003.1-1988 (ustar) format
10852 v7 old V7 tar format
10857 the format names are doc options. Thus, if you set
10858 @kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output
10859 will look as follows:
10863 -H, --format=FORMAT create archive of the given format.
10865 FORMAT is one of the following:
10867 gnu GNU tar 1.13.x format
10868 oldgnu GNU format as per tar <= 1.12
10869 pax POSIX 1003.1-2001 (pax) format
10871 ustar POSIX 1003.1-1988 (ustar) format
10872 v7 old V7 tar format
10877 @deftypevr {Help Output} offset opt-doc-col
10878 Column in which option description starts. Default is 29.
10882 $ @kbd{tar --help|grep ARCHIVE}
10883 -f, --file=ARCHIVE use archive file or device ARCHIVE
10884 $ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE}
10885 -f, --file=ARCHIVE use archive file or device ARCHIVE
10886 $ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE}
10888 use archive file or device ARCHIVE
10893 Notice, that the description starts on a separate line if
10894 @code{opt-doc-col} value is too small.
10897 @deftypevr {Help Output} offset header-col
10898 Column in which @dfn{group headers} are printed. A group header is a
10899 descriptive text preceding an option group. For example, in the
10903 Main operation mode:
10905 -A, --catenate, --concatenate append tar files to
10907 -c, --create create a new archive
10910 @samp{Main operation mode:} is the group header.
10912 The default value is 1.
10915 @deftypevr {Help Output} offset usage-indent
10916 Indentation of wrapped usage lines. Affects @option{--usage}
10917 output. Default is 12.
10920 @deftypevr {Help Output} offset rmargin
10921 Right margin of the text output. Used for wrapping.
10924 @node Fixing Snapshot Files
10925 @appendix Fixing Snapshot Files
10926 @include tar-snapshot-edit.texi
10928 @node Tar Internals
10929 @appendix Tar Internals
10930 @include intern.texi
10934 @include genfile.texi
10936 @node Free Software Needs Free Documentation
10937 @appendix Free Software Needs Free Documentation
10938 @include freemanuals.texi
10940 @node Copying This Manual
10941 @appendix Copying This Manual
10944 * GNU Free Documentation License:: License for copying this manual
10949 @node Index of Command Line Options
10950 @appendix Index of Command Line Options
10952 This appendix contains an index of all @GNUTAR{} long command line
10953 options. The options are listed without the preceding double-dash.
10954 For a cross-reference of short command line options, @ref{Short Option Summary}.
10967 @c Local variables:
10968 @c texinfo-column-for-description: 32
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