X-Git-Url: https://git.dogcows.com/gitweb?a=blobdiff_plain;f=doc%2Ftar.texi;h=62a65cf37532350d5173f47c7245fd9f190daf17;hb=cd7bdd4076ca154575bbef85eb2157e59befcfe2;hp=72e1551e44419d8a1445b666882c28d990d201ac;hpb=7ac3cfedacb2f9a113fd80fd57443c703e3567e9;p=chaz%2Ftar diff --git a/doc/tar.texi b/doc/tar.texi index 72e1551..4a49282 100644 --- a/doc/tar.texi +++ b/doc/tar.texi @@ -1,3114 +1,11082 @@ -\input texinfo @c -*-texinfo-*- -@c %**start of header +\input texinfo @c -*-texinfo-*- +@comment %**start of header @setfilename tar.info -@settitle The Tar Manual: DRAFT +@include version.texi +@settitle GNU tar @value{VERSION} @setchapternewpage odd + +@finalout + +@smallbook @c %**end of header -@c Note: the edition number and date is listed in *two* places; please update. -@c subtitle and top node; search for !!set +@c Maintenance notes: +@c 1. Pay attention to @FIXME{}s and @UNREVISED{}s +@c 2. Before creating final variant: +@c 2.1. Run 'make check-options' to make sure all options are properly +@c documented; +@c 2.2. Run 'make master-menu' (see comment before the master menu). -@c Search for comments marked with !! or <<< (or >>>) +@include rendition.texi +@include value.texi -@c <<< CONVENTIONS: this manual refers to "ordinary files" , "directory -files" (or "directories"), "archive files", "archive members", and -various I/O devices (which have names and file names).>>> +@defcodeindex op +@defcodeindex kw -@c <<< it's "file name" (not filename) unless we are talking about an -argument, ie. @var{file-name}. also, you "use" a "file-name argument" -to "specify" a "file".>>> +@c Put everything in one index (arbitrarily chosen to be the concept index). +@syncodeindex fn cp +@syncodeindex ky cp +@syncodeindex pg cp +@syncodeindex vr cp +@syncodeindex kw cp -@c <<< @code{tar} is always lower case, in bold. >>> +@copying -@c <<< it's "operations of tar", "options to tar" also, it's " @samp{tar -+foo}" or "the @samp{+foo} operation". MIB doesn't like using -operations and options as separate concepts. I disagree --- would be a -mess to explain otherwise +This manual is for @acronym{GNU} @command{tar} (version +@value{VERSION}, @value{UPDATED}), which creates and extracts files +from archives. -@c <<< (don't forget to comment these out in final draft) -ringo +Copyright @copyright{} 1992, 1994--1997, 1999--2001, 2003--2013 Free +Software Foundation, Inc. -@c <<< please dont' change this without sending me e-mail. some things -@c are in progress or waiting to be edited in hardcopy. -ringo -@c smallbook +@quotation +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'', with the +Front-Cover Texts being ``A GNU Manual'', and with the Back-Cover Texts +as in (a) below. A copy of the license is included in the section +entitled ``GNU Free Documentation License''. + +(a) The FSF's Back-Cover Text is: ``You have the freedom to +copy and modify this GNU manual.'' +@end quotation +@end copying -@iftex -@c finalout -@end iftex +@dircategory Archiving +@direntry +* Tar: (tar). Making tape (or disk) archives. +@end direntry -@ifinfo -This file documents @code{tar}, a utility used to store, backup, and -transport files. +@dircategory Individual utilities +@direntry +* tar: (tar)tar invocation. Invoking @GNUTAR{}. +@end direntry -Copyright (C) 1992 Free Software Foundation, Inc. DRAFT! -@c Need to put distribution information here when ready. -@end ifinfo +@shorttitlepage @acronym{GNU} @command{tar} -@c !!set edition number and date here @titlepage -@title @code{tar} -@subtitle The GNU Tape Archiver -@subtitle Edition 0.01, for @code{tar} Version 1.10 -@subtitle @today{} -@c remove preceding today line when ready -@sp 1 -@subtitle DRAFT -@c subtitle insert month here when ready - -@author Amy Gorin and Jay Fenlason -@c <<>>> +@title @acronym{GNU} tar: an archiver tool +@subtitle @value{RENDITION} @value{VERSION}, @value{UPDATED} +@author John Gilmore, Jay Fenlason et al. @page @vskip 0pt plus 1filll -Copyright @copyright{} 1992 Free Software Foundation, Inc. - -@sp 2 -This draft is not yet ready for distribution. +@insertcopying @end titlepage -@ifinfo -@node Top, Introduction, (dir), (dir) -@top @code{tar} - -This file documents @code{tar}, a utility used to store, backup, and -transport files. - -@c !!set edition number and date here -This is DRAFT Edition 0.01 of the @code{tar} documentation, @today{}, for @code{tar} -version 1.12. -@end ifinfo +@ifnottex +@node Top +@top @acronym{GNU} tar: an archiver tool -@c <<< The menus need to be gone over, and node names fixed. -@menu -* Introduction:: @code{tar}: The GNU Tape Archiver -* Invoking @code{tar}:: How to invoke @code{tar} -* Tutorial:: Getting started -* Wizardry:: Some More Advanced Uses for @code{tar} -* Archive Structure:: The structure of an archive -* Reading and Writing:: Reading and writing archives -* Insuring Accuracy:: How to insure the accuracy of an archive -* Selecting Archive Members:: How to select archive members -* User Interaction:: How @code{tar} interacts with people. -* Backups and Restoration:: How to restore files and perform backups -* Media:: Using tapes and other archive media -* Quick Reference:: A quick reference guide to - @code{tar} operations and options -* Data Format Details:: Details of the archive data format -* Concept Index:: Concept Index -@end menu +@insertcopying -@node Introduction, Invoking @code{tar}, Top, Top -@chapter @code{tar}: The GNU Tape Archiver +@cindex file archival +@cindex archiving files -You can use @code{tar} to create an @dfn{archive}---a single file -which contains other file's contents as well as a listing of those -files' characteristics. You can also use @code{tar} to read, add to, -or manipulate already existing archives. Because an archive created -by @code{tar} is capable of preserving file information and directory -structure, @code{tar} is ideal for performing full and incremental -backups, as well as for transferring groups of files between disks and -over networks. +The first part of this master menu lists the major nodes in this Info +document. The rest of the menu lists all the lower level nodes. +@end ifnottex -Despite the utility's name, which comes from the words @samp{T(ape)} -@samp{AR(chiver)}, @code{tar}'s output can be directed to any -available device. For instance, @code{tar} archives can be stored in -a file or sent to another program via a pipe. +@c The master menu goes here. +@c +@c NOTE: To update it from within Emacs, make sure mastermenu.el is +@c loaded and run texinfo-master-menu. +@c To update it from the command line, run +@c +@c make master-menu -@c <<< this menu will conflict with menu above in info mode. -ringo @menu -* Invoking @code{tar}:: How to invoke @code{tar} and specify arguments. -* Tutorial:: An introduction to @code{tar}. -* Operations:: What you can use @code{tar} to do. -* Options:: How to change the way @code{tar} behaves. -* Problems:: Common problems with @code{tar}. -@end menu +* Introduction:: +* Tutorial:: +* tar invocation:: +* operations:: +* Backups:: +* Choosing:: +* Date input formats:: +* Formats:: +* Media:: +* Reliability and security:: + +Appendices + +* Changes:: +* Configuring Help Summary:: +* Fixing Snapshot Files:: +* Tar Internals:: +* Genfile:: +* Free Software Needs Free Documentation:: +* GNU Free Documentation License:: +* Index of Command Line Options:: +* Index:: + +@detailmenu + --- The Detailed Node Listing --- + +Introduction + +* Book Contents:: What this Book Contains +* Definitions:: Some Definitions +* What tar Does:: What @command{tar} Does +* Naming tar Archives:: How @command{tar} Archives are Named +* Authors:: @GNUTAR{} Authors +* Reports:: Reporting bugs or suggestions -@node Invoking @code{tar}, Tutorial, Introduction, Top -@chapter How To Invoke @code{tar} +Tutorial Introduction to @command{tar} + +* assumptions:: +* stylistic conventions:: +* basic tar options:: Basic @command{tar} Operations and Options +* frequent operations:: +* Two Frequent Options:: +* create:: How to Create Archives +* list:: How to List Archives +* extract:: How to Extract Members from an Archive +* going further:: -You can use @code{tar} to store files in an archive, to extract them -from an archive, and to do other types of archive manipulation. The -primary argument to @code{tar}, which is called the @dfn{operation}, -specifies which action to take. The other arguments to @code{tar} are -either @dfn{options}, which change the way @code{tar} performs an -operation, or @dfn{file-names}, which specify the files @code{tar} is -to act on. The typical @code{tar} command line syntax is: +Two Frequently Used Options -@example -@code{tar} @var{operation} [@var{options}...] [@var{file-names}...] -@end example +* file tutorial:: +* verbose tutorial:: +* help tutorial:: + +How to Create Archives + +* prepare for examples:: +* Creating the archive:: +* create verbose:: +* short create:: +* create dir:: + +How to List Archives -Note: You can actually type in arguments in any order. In this manual -the operation is always first, the options second and the file-name -arguments last, to make examples easier to understand. +* list dir:: -@menu -* Argument Functions:: The Functions of Arguments -* Argument Form:: The Forms of Arguments -* Old Syntax for Commands:: An Old, but Still Supported, Syntax - for @code{tar} Commands -@end menu +How to Extract Members from an Archive -@node Argument Functions, Argument Form, Invoking @code{tar}, Invoking @code{tar} -@section The Functions of Arguments +* extracting archives:: +* extracting files:: +* extract dir:: +* extracting untrusted archives:: +* failing commands:: + +Invoking @GNUTAR{} -The primary argument to @code{tar} is the @dfn{operation}, which -specifies what @code{tar} does. @code{tar} can be used to: +* Synopsis:: +* using tar options:: +* Styles:: +* All Options:: +* help:: +* defaults:: +* verbose:: +* checkpoints:: +* warnings:: +* interactive:: + +The Three Option Styles + +* Long Options:: Long Option Style +* Short Options:: Short Option Style +* Old Options:: Old Option Style +* Mixing:: Mixing Option Styles + +All @command{tar} Options + +* Operation Summary:: +* Option Summary:: +* Short Option Summary:: + +@GNUTAR{} Operations + +* Basic tar:: +* Advanced tar:: +* create options:: +* extract options:: +* backup:: +* Applications:: +* looking ahead:: -@itemize -@item -Add files to an existing archive (@samp{+add-file}, @samp+{append} or -@samp{-r}) +Advanced @GNUTAR{} Operations -@item -Compare files in an archive with files in the file system -(@samp{+compare}, @samp{+diff} or @samp{-d}) -@c !!! is diff still working?? --- yes -ringo +* Operations:: +* append:: +* update:: +* concatenate:: +* delete:: +* compare:: -@item -Add archives to another archive (@samp{+add-archive}, @samp{+catenate} -or @samp{-A}) -@c was +concatenate. -ringo +How to Add Files to Existing Archives: @option{--append} -@item -Create an archive (@samp{+create} or @samp{-c}) +* appending files:: Appending Files to an Archive +* multiple:: -@item -Delete files from an archive (@samp{+delete}) -@c -D should have been removed -ringo +Updating an Archive -@item -Extract files from an archive (@samp{+extract}, @samp{+get} or @samp{-x}) +* how to update:: -@item -List the files in an archive (@samp{+list} or @samp{-t}) +Options Used by @option{--create} -@item -Update an archive by appending newer versions of already stored files -(@samp{+update} or @samp{-u}) -@end itemize +* override:: Overriding File Metadata. +* Ignore Failed Read:: -@xref{Reading and Writing}, for more information about these -operations. - -@dfn{Option} arguments to @code{tar} change details of the operation, -such as archive format, archive name, or level of user interaction. -You can specify more than one option. All options are optional. - -@dfn{File-name} arguments specify which files (including directory -files) to archive, extract, delete or otherwise operate on. - -If you don't use any file-name arguments, @samp{+add-file}, -@samp{+update} and @samp{+delete} will do nothing. The other -operations of @code{tar} will act on defaults. - -When you use a file-name argument to specify a directory file, -@code{tar} acts on all the files in that directory, including -sub-directories. - -@node Argument Form, Old Syntax for Commands, Argument Functions, Invoking @code{tar} -@section The Forms of Arguments - -Most operations of @code{tar} have a single letter form (a single -letter preceded by a @samp{-}), and at least one mnemonic form (a -word or abbreviation preceded by a @samp{+}). The forms are -identical in function. For example, you can use either @samp{tar -t} -or @samp{tar +list} to list the contents of an archive - -Options, like operations, have both single letter and mnemonic forms. -Options, however, may also incorporate an argument. Single letter -options are separated from their arguments by a space. Mnemonic -options are separated from their arguments by an @samp{=} sign. For -example, to create an an archive file named @file{george}, use either -@samp{tar +create +file=george} or @samp{tar +create -f george}. Both -@samp{+file=@var{archive-name}} and @samp{-f @var{archive-name}} -denote the option to give the archive a non-default name, which in the -example is @samp{george}. - -You can mix single letter and mnemonic forms in the same command. You -could type the above example as @samp{tar -c +file=george} or -@samp{tar +create -f george}. However, @code{tar} operations and -options are case sensitive. You would not type the above example as -@samp{tar -C +file=george}, because @samp{-C} is an option that causes -@code{tar} to change directories, not an operation that creates an -archive. +Options Used by @option{--extract} -File-name arguments are the names of files (including directories). -These names can be specified on the command line or read from a text -file in the file system (using the @samp{+files-from} option). Files -stored in an archive are called @dfn{archive members}. The operations -@samp{+delete}, @samp{+extract}, @samp{+list}, @samp{+compare} and -@samp{+update} take the names of archive members as file-name -arguments. The other operations take the names of files in the file -system. +* Reading:: Options to Help Read Archives +* Writing:: Changing How @command{tar} Writes Files +* Scarce:: Coping with Scarce Resources -@code{tar} interprets relative file names as being relative to the -working directory. @code{tar} will make all file names relative (by -removing leading @samp{/}s when archiving or restoring files), unless -you specify otherwise (using the @samp{+absolute-paths} option). -@xref{File Name Interpretation}, for more information about -@samp{+absolute-paths}. -@c >>> yet another node name that is probably wrong. +Options to Help Read Archives -@node Old Syntax for Commands, , Argument Form, Invoking @code{tar} -@section An Old, but Still Supported, Syntax for @code{tar} Commands +* read full records:: +* Ignore Zeros:: -For historical reasons, GNU @code{tar} also accepts a syntax for -commands which splits options that include arguments into two parts. -That syntax is of the form: +Changing How @command{tar} Writes Files -@example -@code{tar} @var{operation}[@var{option-letters}...] [@var{option-arguments}...] [@var{file-names}...]@refill -@end example +* Dealing with Old Files:: +* Overwrite Old Files:: +* Keep Old Files:: +* Keep Newer Files:: +* Unlink First:: +* Recursive Unlink:: +* Data Modification Times:: +* Setting Access Permissions:: +* Directory Modification Times and Permissions:: +* Writing to Standard Output:: +* Writing to an External Program:: +* remove files:: -@noindent -where arguments to the options appear in the same order as the letters -to which they correspond, and the operation and all the option letters -appear as a single argument, without separating spaces. +Coping with Scarce Resources -This command syntax is useful because it lets you type the single -letter forms of the operation and options as a single argument to -@code{tar}, without writing preceding @samp{-}s or inserting spaces -between letters. @samp{tar cv} or @samp{tar -cv} are equivalent to -@samp{tar -c -v}. +* Starting File:: +* Same Order:: -This old style syntax makes it difficult to match option letters with -their corresponding arguments, and is often confusing. In the command -@samp{tar cvbf 20 /dev/rmt0}, for example, @samp{20} is the argument -for @samp{-b}, @samp{/dev/rmt0} is the argument for @samp{-f}, and -@samp{-v} does not have a corresponding argument. The modern -syntax---@samp{tar -c -v -b 20 -f /dev/rmt0}---is clearer. +Performing Backups and Restoring Files -@node Tutorial, Wizardry, Invoking @code{tar}, Top -@chapter Getting Started With @code{tar} +* Full Dumps:: Using @command{tar} to Perform Full Dumps +* Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps +* Backup Levels:: Levels of Backups +* Backup Parameters:: Setting Parameters for Backups and Restoration +* Scripted Backups:: Using the Backup Scripts +* Scripted Restoration:: Using the Restore Script -This chapter guides you through some basic examples of @code{tar} -operations. In the examples, the lines you should type are preceded -by a @samp{%}, which is a typical shell prompt. We use mnemonic forms -of operations and options in the examples, and in discussions in the -text, but short forms produce the same result. +Setting Parameters for Backups and Restoration -@menu -* Creating Archives:: Creating Archives -* Extracting Files:: Extracting Files from an Archive -* Listing Archive Contents:: Listing the Contents of an Archive -* Comparing Files:: Comparing Archives with the File System -* Adding to Archives:: Adding Files to Existing Archives -* Concatenate:: Concatenating Archives -* Deleting Files:: Deleting Files From an Archive -@end menu +* General-Purpose Variables:: +* Magnetic Tape Control:: +* User Hooks:: +* backup-specs example:: An Example Text of @file{Backup-specs} -@node Creating Archives, Listing Archive Contents, Tutorial, Tutorial -@section Creating Archives +Choosing Files and Names for @command{tar} -To create a new archive, use @code{tar +create} (or @code{tar -c}). -You can use options to specify the name and format of the archive (as -well as other characteristics), and you can use file-name arguments to -specify which files to put in the archive. If you don't use any -options or file-name arguments, @code{tar} will use default values. -@xref{Creating Example}, for more information about the @samp{+create} -operation. +* file:: Choosing the Archive's Name +* Selecting Archive Members:: +* files:: Reading Names from a File +* exclude:: Excluding Some Files +* wildcards:: Wildcards Patterns and Matching +* quoting styles:: Ways of Quoting Special Characters in Names +* transform:: Modifying File and Member Names +* after:: Operating Only on New Files +* recurse:: Descending into Directories +* one:: Crossing File System Boundaries -@menu -* Creating Example:: Creating Archives of Files -* Subdirectory:: Creating an Archive of a Subdirectory -@end menu +Reading Names from a File -@node Creating Example, Subdirectory, Creating Archives, Creating Archives -@subsection Creating Archives of Files +* nul:: -This example shows you how to create an archive file in the working -directory containing other files in the working directory. The three -files you archive in this example are called @file{blues}, -@file{folk}, and @file{jazz}. The archive file is called -@file{records}. While the archive in this example is written to the -file system, it could also be written to any other device. +Excluding Some Files -(If you want to follow along with this and future examples, create a -directory called @file{practice} containing files called @file{blues}, -@file{folk} and @file{jazz}. To create the directory, type -@samp{mkdir practice} at the system prompt. It will probably be -easiest to create the files using a text editor, such as Emacs.) +* problems with exclude:: -First, change into the directory containing the files you want to -archive: +Wildcards Patterns and Matching -@example -% cd practice -@end example +* controlling pattern-matching:: -@noindent -@file{~/practice} is now your working directory. +Crossing File System Boundaries -Then, check that the files to be archived do in fact exist in the -working directory, and make sure there isn't already a file in the -working directory with the archive name you intend to use. If you -specify an archive file name that is already in use, @code{tar} will -overwrite the old file and its contents will be lost. +* directory:: Changing Directory +* absolute:: Absolute File Names -To list the names of files in the working directory, type: +Date input formats -@example -% ls -@end example +* General date syntax:: Common rules. +* Calendar date items:: 19 Dec 1994. +* Time of day items:: 9:20pm. +* Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}. +* Day of week items:: Monday and others. +* Relative items in date strings:: next tuesday, 2 years ago. +* Pure numbers in date strings:: 19931219, 1440. +* Seconds since the Epoch:: @@1078100502. +* Specifying time zone rules:: TZ="America/New_York", TZ="UTC0". +* Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al. -The system responds: +Controlling the Archive Format -@example -blues folk jazz -% -@end example +* Compression:: Using Less Space through Compression +* Attributes:: Handling File Attributes +* Portability:: Making @command{tar} Archives More Portable +* cpio:: Comparison of @command{tar} and @command{cpio} -@noindent -Then, -@itemize @bullet -@item -Create a new archive (@samp{tar -c} or @samp{tar +create}) +Using Less Space through Compression -@item -Explicitly name the archive file being created (@samp{-f -@var{archive-name}} or @samp{+file=@var{archive-name}}). If you don't -use this option @code{tar} will write the archive to the default -storage device, which varies from system to system. -@c <<< this syntax may change. OK now---check before printing -ringo +* gzip:: Creating and Reading Compressed Archives +* sparse:: Archiving Sparse Files -@code{tar} interprets archive file names relative to the working -directory. Make sure you have write access to the working directory -before using @code{tar}. +Creating and Reading Compressed Archives -@item -Specify which files to put into the archive (@code{tar} interprets -file names relative to the working directory). If you don't use any -@var{file-name} arguments, @code{tar} will archive everything in the -working directory. -@end itemize +* lbzip2:: Using lbzip2 with @GNUTAR{}. -@noindent -Type: -@example -% tar +create +file=records blues folk jazz -@end example +Making @command{tar} Archives More Portable -@noindent -If you now list the contents of the working directory (@samp{ls}), you -will find the archive file listed as well as the files you saw -previously. +* Portable Names:: Portable Names +* dereference:: Symbolic Links +* hard links:: Hard Links +* old:: Old V7 Archives +* ustar:: Ustar Archives +* gnu:: GNU and old GNU format archives. +* posix:: @acronym{POSIX} archives +* Checksumming:: Checksumming Problems +* Large or Negative Values:: Large files, negative time stamps, etc. +* Other Tars:: How to Extract GNU-Specific Data Using + Other @command{tar} Implementations -@example -% ls -blues folk jazz records -% -@end example +@GNUTAR{} and @acronym{POSIX} @command{tar} -@menu -* Listing Files:: Listing files in an archive -* Verbose:: Using @code{tar} in Verbose Mode -@end menu +* PAX keywords:: Controlling Extended Header Keywords. -@node Listing Files, Verbose, Creating Example, Creating Example -@subsubsection Listing files in an archive +How to Extract GNU-Specific Data Using Other @command{tar} Implementations -You can list the contents of an archive with another operation of -@code{tar}---@samp{+list} or @samp{-l}. To list the contents of the -archive you just created, type: +* Split Recovery:: Members Split Between Volumes +* Sparse Recovery:: Sparse Members -@example -% tar +list +file=records -@end example +Tapes and Other Archive Media -@noindent -@code{tar} will respond: +* Device:: Device selection and switching +* Remote Tape Server:: +* Common Problems and Solutions:: +* Blocking:: Blocking +* Many:: Many archives on one tape +* Using Multiple Tapes:: Using Multiple Tapes +* label:: Including a Label in the Archive +* verify:: +* Write Protection:: -@example -blues folk jazz -@end example +Blocking -@xref{Listing Archive Contents}, for a more detailed tutorial of the -@samp{+list} operation. @xref{Listing Contents}, for more information -about the @samp{+list} operation. +* Format Variations:: Format Variations +* Blocking Factor:: The Blocking Factor of an Archive -@node Verbose, , Listing Files, Creating Example -@subsubsection Using @code{tar} in Verbose Mode +Many Archives on One Tape -If you include the @samp{+verbose} or @samp{-v} option on the command -line, @code{tar} will list the files it is acting on as it is working. -In verbose mode, the creation example above would appear as: -@cindex Verbose mode example -@findex -v (verbose mode example) +* Tape Positioning:: Tape Positions and Tape Marks +* mt:: The @command{mt} Utility -@example -% tar +create +file=records +verbose blues folk jazz -blues -folk -jazz -@end example +Using Multiple Tapes -@noindent -The first line is the command typed in by the user. The remaining -lines are generated by @code{tar}. In the following examples we -usually use verbose mode, though it is almost never required. +* Multi-Volume Archives:: Archives Longer than One Tape or Disk +* Tape Files:: Tape Files +* Tarcat:: Concatenate Volumes into a Single Archive -@node Subdirectory, Changing, Creating Example, Creating Archives -@subsection Creating an Archive of a Subdirectory -You can store a directory in an archive by using the directory name as -a file-name argument to @code{tar}. When you specify a directory -file, @code{tar} archives the directory file and all the files it -contains. The names of the directory and the files it contains are -stored in the archive relative to the current working directory---when -the directory is extracted they will be written into the file system -relative to the working directory at that time. -@c <<< add an xref to +absolute-paths -ringo +Tar Internals -To archive a directory, first move to its superior directory. If you -have been following the tutorial, you should type: +* Standard:: Basic Tar Format +* Extensions:: @acronym{GNU} Extensions to the Archive Format +* Sparse Formats:: Storing Sparse Files +* Snapshot Files:: +* Dumpdir:: -@example -% cd .. -% -@end example +Storing Sparse Files -Once in the superior directory, specify the subdirectory using a -file-name argument. To store the directory file @file{~/practice} in -the archive file @file{music}, type: +* Old GNU Format:: +* PAX 0:: PAX Format, Versions 0.0 and 0.1 +* PAX 1:: PAX Format, Version 1.0 -@example -% tar +create +verbose +file=music practice -@end example +Genfile -@noindent -@code{tar} should respond: +* Generate Mode:: File Generation Mode. +* Status Mode:: File Status Mode. +* Exec Mode:: Synchronous Execution mode. -@example -practice/ -practice/blues -practice/folk -practice/jazz -practice/records -@end example +Copying This Manual + +* GNU Free Documentation License:: License for copying this manual -Note that @file{~/practice/records}, another archive file, has -itself been archived. @code{tar} will accept any file as a file to be -archived, even an archive file. +@end detailmenu +@end menu -@c >>> symbolic links and changing directories are now in main body, not in -@c >>> tutorial. -ringo +@node Introduction +@chapter Introduction -@node Extracting Files -@section Extracting Files from an Archive +@GNUTAR{} creates +and manipulates @dfn{archives} which are actually collections of +many other files; the program provides users with an organized and +systematic method for controlling a large amount of data. +The name ``tar'' originally came from the phrase ``Tape ARchive'', but +archives need not (and these days, typically do not) reside on tapes. -Creating an archive is only half the job---there would be no point in -storing files in an archive if you couldn't retrieve them. To extract -files from an archive, use the @samp{+extract} or @samp{-x} operation. +@menu +* Book Contents:: What this Book Contains +* Definitions:: Some Definitions +* What tar Does:: What @command{tar} Does +* Naming tar Archives:: How @command{tar} Archives are Named +* Authors:: @GNUTAR{} Authors +* Reports:: Reporting bugs or suggestions +@end menu -To extract specific files, use their names as file-name arguments. If -you use a directory name as a file-name argument, @code{tar} extracts -all the files (including subdirectories) in that directory. If you -don't use any file-name arguments, @code{tar} extracts all the files -in the archive. +@node Book Contents +@section What this Book Contains + +The first part of this chapter introduces you to various terms that will +recur throughout the book. It also tells you who has worked on @GNUTAR{} +and its documentation, and where you should send bug reports +or comments. + +The second chapter is a tutorial (@pxref{Tutorial}) which provides a +gentle introduction for people who are new to using @command{tar}. It is +meant to be self-contained, not requiring any reading from subsequent +chapters to make sense. It moves from topic to topic in a logical, +progressive order, building on information already explained. + +Although the tutorial is paced and structured to allow beginners to +learn how to use @command{tar}, it is not intended solely for beginners. +The tutorial explains how to use the three most frequently used +operations (@samp{create}, @samp{list}, and @samp{extract}) as well as +two frequently used options (@samp{file} and @samp{verbose}). The other +chapters do not refer to the tutorial frequently; however, if a section +discusses something which is a complex variant of a basic concept, there +may be a cross-reference to that basic concept. (The entire book, +including the tutorial, assumes that the reader understands some basic +concepts of using a Unix-type operating system; @pxref{Tutorial}.) + +The third chapter presents the remaining five operations, and +information about using @command{tar} options and option syntax. + +The other chapters are meant to be used as a reference. Each chapter +presents everything that needs to be said about a specific topic. + +One of the chapters (@pxref{Date input formats}) exists in its +entirety in other @acronym{GNU} manuals, and is mostly self-contained. +In addition, one section of this manual (@pxref{Standard}) contains a +big quote which is taken directly from @command{tar} sources. + +In general, we give both long and short (abbreviated) option names +at least once in each section where the relevant option is covered, so +that novice readers will become familiar with both styles. (A few +options have no short versions, and the relevant sections will +indicate this.) + +@node Definitions +@section Some Definitions + +@cindex archive +@cindex tar archive +The @command{tar} program is used to create and manipulate @command{tar} +archives. An @dfn{archive} is a single file which contains the contents +of many files, while still identifying the names of the files, their +owner(s), and so forth. (In addition, archives record access +permissions, user and group, size in bytes, and data modification time. +Some archives also record the file names in each archived directory, as +well as other file and directory information.) You can use @command{tar} +to @dfn{create} a new archive in a specified directory. + +@cindex member +@cindex archive member +@cindex file name +@cindex member name +The files inside an archive are called @dfn{members}. Within this +manual, we use the term @dfn{file} to refer only to files accessible in +the normal ways (by @command{ls}, @command{cat}, and so forth), and the term +@dfn{member} to refer only to the members of an archive. Similarly, a +@dfn{file name} is the name of a file, as it resides in the file system, +and a @dfn{member name} is the name of an archive member within the +archive. -Note: @code{tar} will extract an archive member into the file system -without checking to see if there is already a file with the archive -member's file name. If there is a file with that name, @code{tar} -will @strong{overwrite} that file and its contents will be lost. -@c << @var{link-name} +The file or archive member is a @dfn{symbolic link} and +@var{link-name} is the name of file it links to. + +@item link to @var{link-name} +The file or archive member is a @dfn{hard link} and @var{link-name} is +the name of file it links to. + +@item --Long Link-- +The archive member is an old GNU format long link. You will normally +not encounter this. + +@item --Long Name-- +The archive member is an old GNU format long name. You will normally +not encounter this. + +@item --Volume Header-- +The archive member is a GNU @dfn{volume header} (@pxref{Tape Files}). + +@item --Continued at byte @var{n}-- +Encountered only at the beginning of a multi-volume archive +(@pxref{Using Multiple Tapes}). This archive member is a continuation +from the previous volume. The number @var{n} gives the offset where +the original file was split. + +@item unknown file type @var{c} +An archive member of unknown type. @var{c} is the type character from +the archive header. If you encounter such a message, it means that +either your archive contains proprietary member types @GNUTAR{} is not +able to handle, or the archive is corrupted. +@end table -To to see if a particular file is in an archive, use the name of the -file in question as a file-name argument while specifying the -@samp{+list} operation. For example, to see whether the file -@file{folk} is in the archive file @file{music}, do the following: +@end itemize -@itemize @bullet -@item -Invoke @code{tar}, and specify the @samp{+list} operation -(@samp{+list} or @samp{-t}). +For example, here is an archive listing containing most of the special +suffixes explained above: + +@smallexample +@group +V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header-- +-rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at byte 32456-- +-rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple +lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple +-rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues +hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues +@end group +@end smallexample + +@smallexample +@end smallexample + +@node help tutorial +@unnumberedsubsec Getting Help: Using the @option{--help} Option + +@table @option +@opindex help +@item --help + +The @option{--help} option to @command{tar} prints out a very brief list of +all operations and option available for the current version of +@command{tar} available on your system. +@end table -@item -Specify the archive file to be acted on (@samp{+file -@var{archive-name}} or @samp{-f @var{archive-name}}). +@node create +@section How to Create Archives +@UNREVISED + +@cindex Creation of the archive +@cindex Archive, creation of +One of the basic operations of @command{tar} is @option{--create} (@option{-c}), which +you use to create a @command{tar} archive. We will explain +@option{--create} first because, in order to learn about the other +operations, you will find it useful to have an archive available to +practice on. + +To make this easier, in this section you will first create a directory +containing three files. Then, we will show you how to create an +@emph{archive} (inside the new directory). Both the directory, and +the archive are specifically for you to practice on. The rest of this +chapter and the next chapter will show many examples using this +directory and the files you will create: some of those files may be +other directories and other archives. + +The three files you will archive in this example are called +@file{blues}, @file{folk}, and @file{jazz}. The archive is called +@file{collection.tar}. + +This section will proceed slowly, detailing how to use @option{--create} +in @code{verbose} mode, and showing examples using both short and long +forms. In the rest of the tutorial, and in the examples in the next +chapter, we will proceed at a slightly quicker pace. This section +moves more slowly to allow beginning users to understand how +@command{tar} works. -@item -Specify the files to look for, by typing their names as file-name -arguments. You have to type the file name as it appears in the -archive (normally, as it is relative to the relative to the directory -from which the archive was created). <<< xref absolute-paths -ringo -@end itemize +@menu +* prepare for examples:: +* Creating the archive:: +* create verbose:: +* short create:: +* create dir:: +@end menu -Type: +@node prepare for examples +@subsection Preparing a Practice Directory for Examples + +To follow along with this and future examples, create a new directory +called @file{practice} containing files called @file{blues}, @file{folk} +and @file{jazz}. The files can contain any information you like: +ideally, they should contain information which relates to their names, +and be of different lengths. Our examples assume that @file{practice} +is a subdirectory of your home directory. + +Now @command{cd} to the directory named @file{practice}; @file{practice} +is now your @dfn{working directory}. (@emph{Please note}: Although +the full file name of this directory is +@file{/@var{homedir}/practice}, in our examples we will refer to +this directory as @file{practice}; the @var{homedir} is presumed.) + +In general, you should check that the files to be archived exist where +you think they do (in the working directory) by running @command{ls}. +Because you just created the directory and the files and have changed to +that directory, you probably don't need to do that this time. + +It is very important to make sure there isn't already a file in the +working directory with the archive name you intend to use (in this case, +@samp{collection.tar}), or that you don't care about its contents. +Whenever you use @samp{create}, @command{tar} will erase the current +contents of the file named by @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) if it exists. @command{tar} +will not tell you if you are about to overwrite an archive unless you +specify an option which does this (@pxref{backup}, for the +information on how to do so). To add files to an existing archive, +you need to use a different option, such as @option{--append} (@option{-r}); see +@ref{append} for information on how to do this. + +@node Creating the archive +@subsection Creating the Archive + +@xopindex{create, introduced} +To place the files @file{blues}, @file{folk}, and @file{jazz} into an +archive named @file{collection.tar}, use the following command: + +@smallexample +$ @kbd{tar --create --file=collection.tar blues folk jazz} +@end smallexample + +The order of the arguments is not very important, @emph{when using long +option forms}. You could also say: + +@smallexample +$ @kbd{tar blues --create folk --file=collection.tar jazz} +@end smallexample -@example -% tar +list +file=music practice/folk -@end example +@noindent +However, you can see that this order is harder to understand; this is +why we will list the arguments in the order that makes the commands +easiest to understand (and we encourage you to do the same when you use +@command{tar}, to avoid errors). + +Note that the sequence +@option{--file=@-collection.tar} is considered to be @emph{one} argument. +If you substituted any other string of characters for +@kbd{collection.tar}, then that string would become the name of the +archive file you create. + +The order of the options becomes more important when you begin to use +short forms. With short forms, if you type commands in the wrong order +(even if you type them correctly in all other ways), you may end up with +results you don't expect. For this reason, it is a good idea to get +into the habit of typing options in the order that makes inherent sense. +@xref{short create}, for more information on this. + +In this example, you type the command as shown above: @option{--create} +is the operation which creates the new archive +(@file{collection.tar}), and @option{--file} is the option which lets +you give it the name you chose. The files, @file{blues}, @file{folk}, +and @file{jazz}, are now members of the archive, @file{collection.tar} +(they are @dfn{file name arguments} to the @option{--create} operation. +@xref{Choosing}, for the detailed discussion on these.) Now that they are +in the archive, they are called @emph{archive members}, not files. +(@pxref{Definitions,members}). + +When you create an archive, you @emph{must} specify which files you +want placed in the archive. If you do not specify any archive +members, @GNUTAR{} will complain. + +If you now list the contents of the working directory (@command{ls}), you will +find the archive file listed as well as the files you saw previously: + +@smallexample +blues folk jazz collection.tar +@end smallexample -@noindent -@code{tar} responds: +@noindent +Creating the archive @samp{collection.tar} did not destroy the copies of +the files in the directory. -@example -practice/folk -@end example +Keep in mind that if you don't indicate an operation, @command{tar} will not +run and will prompt you for one. If you don't name any files, @command{tar} +will complain. You must have write access to the working directory, +or else you will not be able to create an archive in that directory. -@noindent -If the file were not stored in the archive (for example, the file -@file{practice/rock}), the example above would look like: +@emph{Caution}: Do not attempt to use @option{--create} (@option{-c}) to add files to +an existing archive; it will delete the archive and write a new one. +Use @option{--append} (@option{-r}) instead. @xref{append}. -@example -% tar +list +file=music practice/rock -tar: practice/rock not found in archive -@end example +@node create verbose +@subsection Running @option{--create} with @option{--verbose} -@noindent -If you had used @samp{+verbose} mode, the example above would look -like: +@xopindex{create, using with @option{--verbose}} +@xopindex{verbose, using with @option{--create}} +If you include the @option{--verbose} (@option{-v}) option on the command line, +@command{tar} will list the files it is acting on as it is working. In +verbose mode, the @code{create} example above would appear as: -@example -% tar +list +file=music practice/folk --rw-rw-rw- myself/user 62 May 23 10:55 1990 practice/folk -@end example +@smallexample +$ @kbd{tar --create --verbose --file=collection.tar blues folk jazz} +blues +folk +jazz +@end smallexample -@node Listing Directories, , , -@subsection Listing the Contents of a Stored Directory +This example is just like the example we showed which did not use +@option{--verbose}, except that @command{tar} generated the remaining +@iftex +lines (note the different font styles). +@end iftex +@ifinfo +lines. +@end ifinfo -To get information about the contents of an archived directory, use -the directory name as a file-name argument in conjunction with -@samp{+list}. To find out file attributes, include the -@samp{+verbose} option. +In the rest of the examples in this chapter, we will frequently use +@code{verbose} mode so we can show actions or @command{tar} responses that +you would otherwise not see, and which are important for you to +understand. -For example, to find out about files in the directory @file{practice}, -in the archive file @file{music}, type: +@node short create +@subsection Short Forms with @samp{create} -@example -% tar +list +file=music practice -@end example +As we said before, the @option{--create} (@option{-c}) operation is one of the most +basic uses of @command{tar}, and you will use it countless times. +Eventually, you will probably want to use abbreviated (or ``short'') +forms of options. A full discussion of the three different forms that +options can take appears in @ref{Styles}; for now, here is what the +previous example (including the @option{--verbose} (@option{-v}) option) looks like +using short option forms: -@noindent @code{tar} responds: +@smallexample +$ @kbd{tar -cvf collection.tar blues folk jazz} +blues +folk +jazz +@end smallexample -@example -drwxrwxrwx myself/user 0 May 31 21:49 1990 practice/ --rw-rw-rw- myself/user 42 May 21 13:29 1990 practice/blues --rw-rw-rw- myself/user 62 May 23 10:55 1990 practice/folk --rw-rw-rw- myself/user 40 May 21 13:30 1990 practice/jazz --rw-rw-rw- myself/user 10240 May 31 21:49 1990 practice/records -@end example +@noindent +As you can see, the system responds the same no matter whether you use +long or short option forms. -When you use a directory name as a file-name argument, @code{tar} acts -on all the files (including sub-directories) in that directory. - -@node Comparing Files, , , -@section Comparing Files in an Archive with Files in the File System - -To compare the attributes of archive members with the attributes of -their counterparts in the file system, use the @samp{+compare}, -@samp{+diff}, or @samp{-d}) operation. While you could use -@samp{+list +verbose} to manually compare some file attributes, it is -simpler to have @code{tar} itself compare file attributes and report -back on file differences. -@c <<<"manually"? suggestions? -ringo - -The @samp{+compare} operation, as its name implies, compares archive -members with files of the same name in the file system, and reports -back differences in file size, mode, owner and modification date. -@samp{tar +compare} acts only on archive members---it ignores files in -the file system that are not stored in the archive. If you give -@samp{tar +compare} a file-name argument that does not correspond to -the name of an archive member, @code{tar} responds with an error -message. - -To compare archive members in the archive file @file{records} with -files in the @file{~/practice} directory, first change into the -@file{practice} directory. Then: +@FIXME{i don't like how this is worded:} One difference between using +short and long option forms is that, although the exact placement of +arguments following options is no more specific when using short forms, +it is easier to become confused and make a mistake when using short +forms. For example, suppose you attempted the above example in the +following way: -@itemize @bullet -@item -Invoke @code{tar} and specify the @samp{+compare} operation. -(@samp{+compare}, @samp{+diff}, or @samp{-d}). +@smallexample +$ @kbd{tar -cfv collection.tar blues folk jazz} +@end smallexample -@item -Specify the archive where the files to be compared are stored -(@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}}) +@noindent +In this case, @command{tar} will make an archive file called @file{v}, +containing the files @file{blues}, @file{folk}, and @file{jazz}, because +the @samp{v} is the closest ``file name'' to the @option{-f} option, and +is thus taken to be the chosen archive file name. @command{tar} will try +to add a file called @file{collection.tar} to the @file{v} archive file; +if the file @file{collection.tar} did not already exist, @command{tar} will +report an error indicating that this file does not exist. If the file +@file{collection.tar} does already exist (e.g., from a previous command +you may have run), then @command{tar} will add this file to the archive. +Because the @option{-v} option did not get registered, @command{tar} will not +run under @samp{verbose} mode, and will not report its progress. + +The end result is that you may be quite confused about what happened, +and possibly overwrite a file. To illustrate this further, we will show +you how an example we showed previously would look using short forms. + +This example, + +@smallexample +$ @kbd{tar blues --create folk --file=collection.tar jazz} +@end smallexample -@item -Specify the archive members to be compared. (In this example you are -comparing all the archive members in the archive. Since this is the -default, you don't need to use any file-name arguments). -@end itemize +@noindent +is confusing as it is. When shown using short forms, however, it +becomes much more so: -@example -% tar +compare +file=records -% -@end example +@smallexample +$ @kbd{tar blues -c folk -f collection.tar jazz} +@end smallexample @noindent -While it looks like nothing has happened, @code{tar} has, in fact, -done the comparison---and found nothing to report. +It would be very easy to put the wrong string of characters +immediately following the @option{-f}, but doing that could sacrifice +valuable data. + +For this reason, we recommend that you pay very careful attention to +the order of options and placement of file and archive names, +especially when using short option forms. Not having the option name +written out mnemonically can affect how well you remember which option +does what, and therefore where different names have to be placed. + +@node create dir +@subsection Archiving Directories + +@cindex Archiving Directories +@cindex Directories, Archiving +You can archive a directory by specifying its directory name as a +file name argument to @command{tar}. The files in the directory will be +archived relative to the working directory, and the directory will be +re-created along with its contents when the archive is extracted. -Use the @samp{+verbose} option to list the names of archive members as -they are being compared with their counterparts of the same name in -the file system: +To archive a directory, first move to its superior directory. If you +have followed the previous instructions in this tutorial, you should +type: -@example -% tar +compare +verbose +file=records -blues -folk -jazz -% -@end example +@smallexample +$ @kbd{cd ..} +$ +@end smallexample @noindent -If @code{tar} had had anything to report, it would have done so as it -was comparing each file. +This will put you into the directory which contains @file{practice}, +i.e., your home directory. Once in the superior directory, you can +specify the subdirectory, @file{practice}, as a file name argument. To +store @file{practice} in the new archive file @file{music.tar}, type: -If you remove the file @file{jazz} from the file system (@samp{rm -jazz}), and modify the file @file{blues} (for instance, by adding text -to it with an editor such as Emacs), the above example would look -like: +@smallexample +$ @kbd{tar --create --verbose --file=music.tar practice} +@end smallexample -@example -% tar +compare +verbose +file=records -blues -blues: mod time differs -blues: size differs -folk -jazz -jazz: does not exist -% -@end example +@noindent +@command{tar} should output: -Note again that while @samp{tar +compare} reports the names of archive -members that do not have counterparts in the file system, @samp{tar -+compare} ignores files in the file system that do not have -counterparts in the archive. To demonstrate this, create a file in -the @file{practice} directory called @file{rock} (using any text -editor). The new file appears when you list the directory's contents: +@smallexample +practice/ +practice/blues +practice/folk +practice/jazz +practice/collection.tar +@end smallexample + +Note that the archive thus created is not in the subdirectory +@file{practice}, but rather in the current working directory---the +directory from which @command{tar} was invoked. Before trying to archive a +directory from its superior directory, you should make sure you have +write access to the superior directory itself, not only the directory +you are trying archive with @command{tar}. For example, you will probably +not be able to store your home directory in an archive by invoking +@command{tar} from the root directory; @xref{absolute}. (Note +also that @file{collection.tar}, the original archive file, has itself +been archived. @command{tar} will accept any file as a file to be +archived, regardless of its content. When @file{music.tar} is +extracted, the archive file @file{collection.tar} will be re-written +into the file system). + +If you give @command{tar} a command such as + +@smallexample +$ @kbd{tar --create --file=foo.tar .} +@end smallexample -@example -% ls -blues folk records rock -@end example +@noindent +@command{tar} will report @samp{tar: ./foo.tar is the archive; not +dumped}. This happens because @command{tar} creates the archive +@file{foo.tar} in the current directory before putting any files into +it. Then, when @command{tar} attempts to add all the files in the +directory @file{.} to the archive, it notices that the file +@file{./foo.tar} is the same as the archive @file{foo.tar}, and skips +it. (It makes no sense to put an archive into itself.) @GNUTAR{} +will continue in this case, and create the archive +normally, except for the exclusion of that one file. (@emph{Please +note:} Other implementations of @command{tar} may not be so clever; +they will enter an infinite loop when this happens, so you should not +depend on this behavior unless you are certain you are running +@GNUTAR{}. In general, it is wise to always place the archive outside +of the directory being dumped.) + +@node list +@section How to List Archives + +@opindex list +Frequently, you will find yourself wanting to determine exactly what a +particular archive contains. You can use the @option{--list} +(@option{-t}) operation to get the member names as they currently +appear in the archive, as well as various attributes of the files at +the time they were archived. For example, you can examine the archive +@file{collection.tar} that you created in the last section with the +command, + +@smallexample +$ @kbd{tar --list --file=collection.tar} +@end smallexample @noindent -If you type the @samp{+compare} example again, @code{tar} prints the -following: +The output of @command{tar} would then be: -@example -% tar +compare +verbose +file=records +@smallexample blues -blues: mod time differs -blues: size differs folk jazz -jazz: does not exist -% -@end example +@end smallexample @noindent -@code{tar} ignores the file @file{rock} because @code{tar} is -comparing archive members to files in the file system, not vice versa. +The archive @file{bfiles.tar} would list as follows: -If you specify @file{rock} explicitly (using a file-name argument), -@code{tar} prints an error message: +@smallexample +./birds +baboon +./box +@end smallexample -@example -% tar +compare +verbose +file=records rock -tar: rock not found in archive -% -@end example +@noindent +Be sure to use a @option{--file=@var{archive-name}} (@option{-f +@var{archive-name}}) option just as with @option{--create} +(@option{-c}) to specify the name of the archive. + +@xopindex{list, using with @option{--verbose}} +@xopindex{verbose, using with @option{--list}} +If you use the @option{--verbose} (@option{-v}) option with +@option{--list}, then @command{tar} will print out a listing +reminiscent of @w{@samp{ls -l}}, showing owner, file size, and so +forth. This output is described in detail in @ref{verbose member listing}. + +If you had used @option{--verbose} (@option{-v}) mode, the example +above would look like: + +@smallexample +$ @kbd{tar --list --verbose --file=collection.tar folk} +-rw-r--r-- myself/user 62 1990-05-23 10:55 folk +@end smallexample + +@cindex listing member and file names +@anchor{listing member and file names} +It is important to notice that the output of @kbd{tar --list +--verbose} does not necessarily match that produced by @kbd{tar +--create --verbose} while creating the archive. It is because +@GNUTAR{}, unless told explicitly not to do so, removes some directory +prefixes from file names before storing them in the archive +(@xref{absolute}, for more information). In other +words, in verbose mode @GNUTAR{} shows @dfn{file names} when creating +an archive and @dfn{member names} when listing it. Consider this +example: + +@smallexample +@group +$ @kbd{tar --create --verbose --file archive /etc/mail} +tar: Removing leading '/' from member names +/etc/mail/ +/etc/mail/sendmail.cf +/etc/mail/aliases +$ @kbd{tar --test --file archive} +etc/mail/ +etc/mail/sendmail.cf +etc/mail/aliases +@end group +@end smallexample + +@opindex show-stored-names + This default behavior can sometimes be inconvenient. You can force +@GNUTAR{} show member names when creating archive by supplying +@option{--show-stored-names} option. + +@table @option +@item --show-stored-names +Print member (as opposed to @emph{file}) names when creating the archive. +@end table + +@cindex File name arguments, using @option{--list} with +@xopindex{list, using with file name arguments} +You can specify one or more individual member names as arguments when +using @samp{list}. In this case, @command{tar} will only list the +names of members you identify. For example, @w{@kbd{tar --list +--file=afiles.tar apple}} would only print @file{apple}. + +Because @command{tar} preserves file names, these must be specified as +they appear in the archive (i.e., relative to the directory from which +the archive was created). Therefore, it is essential when specifying +member names to @command{tar} that you give the exact member names. +For example, @w{@kbd{tar --list --file=bfiles.tar birds}} would produce an +error message something like @samp{tar: birds: Not found in archive}, +because there is no member named @file{birds}, only one named +@file{./birds}. While the names @file{birds} and @file{./birds} name +the same file, @emph{member} names by default are compared verbatim. + +However, @w{@kbd{tar --list --file=bfiles.tar baboon}} would respond +with @file{baboon}, because this exact member name is in the archive file +@file{bfiles.tar}. If you are not sure of the exact file name, +use @dfn{globbing patterns}, for example: + +@smallexample +$ @kbd{tar --list --file=bfiles.tar --wildcards '*b*'} +@end smallexample + +@noindent +will list all members whose name contains @samp{b}. @xref{wildcards}, +for a detailed discussion of globbing patterns and related +@command{tar} command line options. @menu -* Comparing Directories:: Using Compare on Directories +* list dir:: @end menu -@node Comparing Directories, , , -@subsubsection Using Compare on Directories +@node list dir +@unnumberedsubsec Listing the Contents of a Stored Directory -In addition to using @samp{+compare} to compare text files, you can -use @samp{+compare} to compare directories. To illustrate this, -re-create the examples above using your home directory as the working -directory, and using the archive file @file{~/music} instead of the -archive file @file{~/practice/records}. +To get information about the contents of an archived directory, +use the directory name as a file name argument in conjunction with +@option{--list} (@option{-t}). To find out file attributes, include the +@option{--verbose} (@option{-v}) option. -First, change into your home directory (@samp{cd ~}). Then, try the -above example using @file{music} as the specified archive file, and -@file{practice} as a file-name argument. - -@example -% tar +compare +verbose +file=music practice -@end example +For example, to find out about files in the directory @file{practice}, in +the archive file @file{music.tar}, type: -@noindent -If you have been following along with the tutorial, @code{tar} will -respond: +@smallexample +$ @kbd{tar --list --verbose --file=music.tar practice} +@end smallexample -@example -practice -practice/blues -practice/blues: mod time differs -practice/blues: size differs -practice/folk -practice/jazz -practice/jazz: does not exist -practice/records -@end example +@command{tar} responds: -@node Adding to Archives, Concatenate, Listing Archive Contents, Tutorial -@section Adding Files to Existing Archives +@smallexample +drwxrwxrwx myself/user 0 1990-05-31 21:49 practice/ +-rw-r--r-- myself/user 42 1990-05-21 13:29 practice/blues +-rw-r--r-- myself/user 62 1990-05-23 10:55 practice/folk +-rw-r--r-- myself/user 40 1990-05-21 13:30 practice/jazz +-rw-r--r-- myself/user 10240 1990-05-31 21:49 practice/collection.tar +@end smallexample -@c >>> we want people to use the script for backups, so I an not going to -@c >>> use backups as an explanation in the tutorial. (people can still -@c >>> do it if they really want to) -ringo +When you use a directory name as a file name argument, @command{tar} acts on +all the files (including sub-directories) in that directory. -While you can use @code{tar} to create a new archive every time you -want to store a file, it is more sometimes efficient to add files to -an existing archive. +@node extract +@section How to Extract Members from an Archive +@cindex Extraction +@cindex Retrieving files from an archive +@cindex Resurrecting files from an archive -To add new files to an existing archive, use the @samp{+add-file}, -@samp{+append} or @samp{-r} operation. To add newer versions of -archive members to an archive, use the @samp{+update} or @samp{-u} -operation. +@opindex extract +Creating an archive is only half the job---there is no point in storing +files in an archive if you can't retrieve them. The act of retrieving +members from an archive so they can be used and manipulated as +unarchived files again is called @dfn{extraction}. To extract files +from an archive, use the @option{--extract} (@option{--get} or +@option{-x}) operation. As with @option{--create}, specify the name +of the archive with @option{--file} (@option{-f}) option. Extracting +an archive does not modify the archive in any way; you can extract it +multiple times if you want or need to. + +Using @option{--extract}, you can extract an entire archive, or specific +files. The files can be directories containing other files, or not. As +with @option{--create} (@option{-c}) and @option{--list} (@option{-t}), you may use the short or the +long form of the operation without affecting the performance. @menu -* Append:: Appending Files to an Archive -* Update:: Updating Files in an Archive +* extracting archives:: +* extracting files:: +* extract dir:: +* extracting untrusted archives:: +* failing commands:: @end menu -@node Append, Update, Adding to Archives, Adding to Archives -@subsection Appending Files to an Archive +@node extracting archives +@subsection Extracting an Entire Archive -The simplest method of adding a file to an existing archive is the -@samp{+add-file}, @samp{-r} or @samp{+append} operation, which writes -files into the archive without regard to whether or not they are -already archive members. When you use @samp{+add-file} you must use -file-name arguments; there is no default. If you specify a file that -is already stored in the archive, @code{tar} adds another copy of the -file to the archive. +To extract an entire archive, specify the archive file name only, with +no individual file names as arguments. For example, -If you have been following the previous examples, you should have a -text file called @file{~/practice/rock} which has not been stored in -either the archive file @file{~/practice/records}, or the archive file -@file{~/music}. To add @file{rock} to @file{records}, first make -@file{practice} the working directory (@samp{cd practice}). Then: +@smallexample +$ @kbd{tar -xvf collection.tar} +@end smallexample -@itemize @bullet -@item -Invoke @code{tar} and specify the @samp{+add-file} operation -(@samp{+add-file}, @samp{-r} or @samp{+append}) +@noindent +produces this: -@item -Specify the archive to which the file will be added -(@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}}) +@smallexample +-rw-r--r-- me/user 28 1996-10-18 16:31 jazz +-rw-r--r-- me/user 21 1996-09-23 16:44 blues +-rw-r--r-- me/user 20 1996-09-23 16:44 folk +@end smallexample -@item -Specify the files to be added to the archive, using file-name -arguments -@end itemize +@node extracting files +@subsection Extracting Specific Files + +To extract specific archive members, give their exact member names as +arguments, as printed by @option{--list} (@option{-t}). If you had +mistakenly deleted one of the files you had placed in the archive +@file{collection.tar} earlier (say, @file{blues}), you can extract it +from the archive without changing the archive's structure. Its +contents will be identical to the original file @file{blues} that you +deleted. + +First, make sure you are in the @file{practice} directory, and list the +files in the directory. Now, delete the file, @samp{blues}, and list +the files in the directory again. + +You can now extract the member @file{blues} from the archive file +@file{collection.tar} like this: + +@smallexample +$ @kbd{tar --extract --file=collection.tar blues} +@end smallexample @noindent -For example: +If you list the files in the directory again, you will see that the file +@file{blues} has been restored, with its original permissions, data +modification times, and owner.@footnote{This is only accidentally +true, but not in general. Whereas modification times are always +restored, in most cases, one has to be root for restoring the owner, +and use a special option for restoring permissions. Here, it just +happens that the restoring user is also the owner of the archived +members, and that the current @code{umask} is compatible with original +permissions.} (These parameters will be identical to those which +the file had when you originally placed it in the archive; any changes +you may have made before deleting the file from the file system, +however, will @emph{not} have been made to the archive member.) The +archive file, @samp{collection.tar}, is the same as it was before you +extracted @samp{blues}. You can confirm this by running @command{tar} with +@option{--list} (@option{-t}). + +Remember that as with other operations, specifying the exact member +name is important. @w{@kbd{tar --extract --file=bfiles.tar birds}} +will fail, because there is no member named @file{birds}. To extract +the member named @file{./birds}, you must specify @w{@kbd{tar +--extract --file=bfiles.tar ./birds}}. If you don't remember the +exact member names, use @option{--list} (@option{-t}) option +(@pxref{list}). You can also extract those members that match a +specific @dfn{globbing pattern}. For example, to extract from +@file{bfiles.tar} all files that begin with @samp{b}, no matter their +directory prefix, you could type: + +@smallexample +$ @kbd{tar -x -f bfiles.tar --wildcards --no-anchored 'b*'} +@end smallexample -@example -% tar +add-file +file=records rock -@end example +@noindent +Here, @option{--wildcards} instructs @command{tar} to treat +command line arguments as globbing patterns and @option{--no-anchored} +informs it that the patterns apply to member names after any @samp{/} +delimiter. The use of globbing patterns is discussed in detail in +@xref{wildcards}. + +You can extract a file to standard output by combining the above options +with the @option{--to-stdout} (@option{-O}) option (@pxref{Writing to Standard +Output}). + +If you give the @option{--verbose} option, then @option{--extract} +will print the names of the archive members as it extracts them. + +@node extract dir +@subsection Extracting Files that are Directories + +Extracting directories which are members of an archive is similar to +extracting other files. The main difference to be aware of is that if +the extracted directory has the same name as any directory already in +the working directory, then files in the extracted directory will be +placed into the directory of the same name. Likewise, if there are +files in the pre-existing directory with the same names as the members +which you extract, the files from the extracted archive will replace +the files already in the working directory (and possible +subdirectories). This will happen regardless of whether or not the +files in the working directory were more recent than those extracted +(there exist, however, special options that alter this behavior +@pxref{Writing}). + +However, if a file was stored with a directory name as part of its file +name, and that directory does not exist under the working directory when +the file is extracted, @command{tar} will create the directory. + +We can demonstrate how to use @option{--extract} to extract a directory +file with an example. Change to the @file{practice} directory if you +weren't there, and remove the files @file{folk} and @file{jazz}. Then, +go back to the parent directory and extract the archive +@file{music.tar}. You may either extract the entire archive, or you may +extract only the files you just deleted. To extract the entire archive, +don't give any file names as arguments after the archive name +@file{music.tar}. To extract only the files you deleted, use the +following command: + +@smallexample +$ @kbd{tar -xvf music.tar practice/folk practice/jazz} +practice/folk +practice/jazz +@end smallexample @noindent -If you list the archive members in @file{records}, you will see that -@file{rock} has been added to the archive: +If you were to specify two @option{--verbose} (@option{-v}) options, @command{tar} +would have displayed more detail about the extracted files, as shown +in the example below: -@example -% tar +list +file=records -blues -folk -jazz -rock -@end example +@smallexample +$ @kbd{tar -xvvf music.tar practice/folk practice/jazz} +-rw-r--r-- me/user 28 1996-10-18 16:31 practice/jazz +-rw-r--r-- me/user 20 1996-09-23 16:44 practice/folk +@end smallexample -@c <<< this should be some kind of node. +@noindent +Because you created the directory with @file{practice} as part of the +file names of each of the files by archiving the @file{practice} +directory as @file{practice}, you must give @file{practice} as part +of the file names when you extract those files from the archive. -You can use @samp{+add-file} to keep archive members current with -active files. Because @samp{+add-file} stores a file whether or not -there is already an archive member with the same file name, you can -use @samp{+add-file} to add newer versions of archive members to an -archive. When you extract the file, only the version stored last will -wind up in the file system. Because @samp{tar +extract} extracts -files from an archive in sequence, and overwrites files with the same -name in the file system, if a file name appears more than once in an -archive the last version of the file will overwrite the previous -versions which have just been extracted. +@node extracting untrusted archives +@subsection Extracting Archives from Untrusted Sources -If you recall from the examples using @samp{+compare} above, -@file{blues} was changed after the archive @file{records} was created. -It is simple, however, to use @samp{+add-file} to add the new version -of @file{blues} to @file{records}: +Extracting files from archives can overwrite files that already exist. +If you receive an archive from an untrusted source, you should make a +new directory and extract into that directory, so that you don't have +to worry about the extraction overwriting one of your existing files. +For example, if @file{untrusted.tar} came from somewhere else on the +Internet, and you don't necessarily trust its contents, you can +extract it as follows: -@example -% tar +add-file +verbose +file=records blues -blues -@end example +@smallexample +$ @kbd{mkdir newdir} +$ @kbd{cd newdir} +$ @kbd{tar -xvf ../untrusted.tar} +@end smallexample -@noindent -If you now list the contents of the archive, you will obtain the following: +It is also a good practice to examine contents of the archive +before extracting it, using @option{--list} (@option{-t}) option, possibly combined +with @option{--verbose} (@option{-v}). -@example -% tar +list -f records -blues -folk -jazz -rock -blues -@end example +@node failing commands +@subsection Commands That Will Fail + +Here are some sample commands you might try which will not work, and why +they won't work. + +If you try to use this command, + +@smallexample +$ @kbd{tar -xvf music.tar folk jazz} +@end smallexample @noindent -The newest version of @file{blues} is at the end of the archive. When -the files in @file{records} are extracted, the newer version of -@file{blues} (which has the same name as the older) will overwrite the -version stored first. When @samp{tar +extract} is finished, only the -newer version of @file{blues} is in the file system. <<>> - -@node Update, , Append, Adding to Archives -@subsection Updating Files in an Archive - -To keep archive members up to date with their counterparts of the same -name in the file system, use the @samp{+update} or @samp{-u} -operation. @samp{tar +update} adds a specified file to an archive if -no file of that name is already stored in the archive. If there is -already an archive member with the same name, @code{tar} checks the -modification date of the archive member, and adds the file only if its -modification date is later. If a file is stored in the archive but no -longer exists under the same name in the active file system, -@code{tar} reports an error. - -You could use the @samp{+add-file} option to keep an archive current, -but do so you would either have to use the @samp{+compare} and -@samp{+list} options to determine what files needed to be re-archived -(which could waste a lot of time), or you would have to be willing to -add identical copies of already archived files to the archive (which -could waste a lot of space). - -You must use file-name arguments with the @samp{+update} -operation---if you don't specify any files, @code{tar} won't act on -any files. - -To see the @samp{+update} option at work, create a new file, -@file{~/practice/classical}, and modify the file -@file{~/practice/blues} (you can use a text editor, such as Emacs, to -do both these things). Then, with @file{practice} as your working -directory, invoke @samp{tar +update} using the names of all the files -in the practice directory as file-name arguments, and specifying the -@samp{+verbose} option: +you will get the following response: -@example -% tar +update +verbose +file=records blues folk rock classical -blues -classical -% -@end example +@smallexample +tar: folk: Not found in archive +tar: jazz: Not found in archive +@end smallexample @noindent -Because you specified verbose mode, @code{tar} printed out the names -of the files it acted on. If you now list the archive members of the -archive, (@samp{tar +list +file=records}), you will see that the file -@file{classical} and another version of the file @file{blues} have -been added to @file{records}. - -Note: When you update an archive, @code{tar} does not overwrite old -archive members when it stores newer versions of a file. This is -because archive members appear in an archive in the order in which -they are stored, and some archive devices do not allow writing in the -middle of an archive. - -@node Concatenate, Extracting Files Example, Adding to Archives, Tutorial -@comment node-name, next, previous, up -@section Concatenating Archives - -To concatenate archive files, use @samp{tar +concatenate} or @samp{tar --A}. This operation adds other archives to the end of an archive. -While it may seem intuitive to concatenate archives using @code{cat}, -the utility for adding files together, archive files which have been -"catted" together cannot be read properly by @code{tar}. Archive -files incorporate an end of file marker---if archives are concatenated -using @code{cat}, this marker will appear before the end of the new -archive. This will interfere with operations on that archive. -@c <<>> - -In earlier examples, you stored the @file{~/practice} directory in an -archive file, @file{~/music}. If you have been following the -examples, you have since changed the contents of the @file{~/practice} -directory. There is a current version of the files in the -@file{practice} directory, however, stored in the archive file -@file{~/practice/records}. - -To store current versions of the files in @file{practice} in the -archive file @file{music}, you can use @samp{tar +concatenate} to add -the archive file @file{~/practice/records} to @file{music}. First, -make sure you are in your home directory (@samp{cd ~}). Then: +This is because these files were not originally @emph{in} the parent +directory @file{..}, where the archive is located; they were in the +@file{practice} directory, and their file names reflect this: -@itemize @bullet -@item -Invoke @code{tar}, and specify the @samp{+concatenate} operation -(@samp{-A} or @samp{+concatenate}) +@smallexample +$ @kbd{tar -tvf music.tar} +practice/blues +practice/folk +practice/jazz +@end smallexample -@item -Specify the archive file to be added to -(@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}}) +@FIXME{make sure the above works when going through the examples in +order...} -@item -Specify the archives to be added, using file-name arguments. In this -case, the file-name arguments are, unusually, the names of archive -files. (Remember to include the path in the archive name, if the -archive file is not in your working directory.) -@end itemize +@noindent +Likewise, if you try to use this command, -@example -% cd ~ -% tar +concatenate +file=music practice/records -@end example +@smallexample +$ @kbd{tar -tvf music.tar folk jazz} +@end smallexample -If you now list the contents of the @file{music}, you see it now -contains the archive members of @file{practice/records}: +@noindent +you would get a similar response. Members with those names are not in the +archive. You must use the correct member names, or wildcards, in order +to extract the files from the archive. + +If you have forgotten the correct names of the files in the archive, +use @w{@kbd{tar --list --verbose}} to list them correctly. + +@FIXME{more examples, here? hag thinks it's a good idea.} + +@node going further +@section Going Further Ahead in this Manual +@UNREVISED + +@FIXME{need to write up a node here about the things that are going to +be in the rest of the manual.} + +@node tar invocation +@chapter Invoking @GNUTAR{} + +This chapter is about how one invokes the @GNUTAR{} +command, from the command synopsis (@pxref{Synopsis}). There are +numerous options, and many styles for writing them. One mandatory +option specifies the operation @command{tar} should perform +(@pxref{Operation Summary}), other options are meant to detail how +this operation should be performed (@pxref{Option Summary}). +Non-option arguments are not always interpreted the same way, +depending on what the operation is. + +You will find in this chapter everything about option styles and rules for +writing them (@pxref{Styles}). On the other hand, operations and options +are fully described elsewhere, in other chapters. Here, you will find +only synthetic descriptions for operations and options, together with +pointers to other parts of the @command{tar} manual. + +Some options are so special they are fully described right in this +chapter. They have the effect of inhibiting the normal operation of +@command{tar} or else, they globally alter the amount of feedback the user +receives about what is going on. These are the @option{--help} and +@option{--version} (@pxref{help}), @option{--verbose} (@pxref{verbose}) +and @option{--interactive} options (@pxref{interactive}). -@example -%tar +list +file=music -blues -folk -jazz -rock -blues -practice/blues -practice/folk -practice/jazz -practice/rock -practice/blues -practice/classical -@end example +@menu +* Synopsis:: +* using tar options:: +* Styles:: +* All Options:: +* help:: +* defaults:: +* verbose:: +* checkpoints:: +* warnings:: +* interactive:: +@end menu -@node Deleting Files, , , Tutorial -@comment node-name, next, previous, up -@section Deleting Files From an Archive +@node Synopsis +@section General Synopsis of @command{tar} + +The @GNUTAR{} program is invoked as either one of: + +@smallexample +@kbd{tar @var{option}@dots{} [@var{name}]@dots{}} +@kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}} +@end smallexample + +The second form is for when old options are being used. + +You can use @command{tar} to store files in an archive, to extract them from +an archive, and to do other types of archive manipulation. The primary +argument to @command{tar}, which is called the @dfn{operation}, specifies +which action to take. The other arguments to @command{tar} are either +@dfn{options}, which change the way @command{tar} performs an operation, +or file names or archive members, which specify the files or members +@command{tar} is to act on. + +You can actually type in arguments in any order, even if in this manual +the options always precede the other arguments, to make examples easier +to understand. Further, the option stating the main operation mode +(the @command{tar} main command) is usually given first. + +Each @var{name} in the synopsis above is interpreted as an archive member +name when the main command is one of @option{--compare} +(@option{--diff}, @option{-d}), @option{--delete}, @option{--extract} +(@option{--get}, @option{-x}), @option{--list} (@option{-t}) or +@option{--update} (@option{-u}). When naming archive members, you +must give the exact name of the member in the archive, as it is +printed by @option{--list}. For @option{--append} (@option{-r}) and +@option{--create} (@option{-c}), these @var{name} arguments specify +the names of either files or directory hierarchies to place in the archive. +These files or hierarchies should already exist in the file system, +prior to the execution of the @command{tar} command. + +@command{tar} interprets relative file names as being relative to the +working directory. @command{tar} will make all file names relative +(by removing leading slashes when archiving or restoring files), +unless you specify otherwise (using the @option{--absolute-names} +option). @xref{absolute}, for more information about +@option{--absolute-names}. + +If you give the name of a directory as either a file name or a member +name, then @command{tar} acts recursively on all the files and directories +beneath that directory. For example, the name @file{/} identifies all +the files in the file system to @command{tar}. + +The distinction between file names and archive member names is especially +important when shell globbing is used, and sometimes a source of confusion +for newcomers. @xref{wildcards}, for more information about globbing. +The problem is that shells may only glob using existing files in the +file system. Only @command{tar} itself may glob on archive members, so when +needed, you must ensure that wildcard characters reach @command{tar} without +being interpreted by the shell first. Using a backslash before @samp{*} +or @samp{?}, or putting the whole argument between quotes, is usually +sufficient for this. + +Even if @var{name}s are often specified on the command line, they +can also be read from a text file in the file system, using the +@option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option. + +If you don't use any file name arguments, @option{--append} (@option{-r}), +@option{--delete} and @option{--concatenate} (@option{--catenate}, +@option{-A}) will do nothing, while @option{--create} (@option{-c}) +will usually yield a diagnostic and inhibit @command{tar} execution. +The other operations of @command{tar} (@option{--list}, +@option{--extract}, @option{--compare}, and @option{--update}) +will act on the entire contents of the archive. + +@anchor{exit status} +@cindex exit status +@cindex return status +Besides successful exits, @GNUTAR{} may fail for +many reasons. Some reasons correspond to bad usage, that is, when the +@command{tar} command line is improperly written. Errors may be +encountered later, while processing the archive or the files. Some +errors are recoverable, in which case the failure is delayed until +@command{tar} has completed all its work. Some errors are such that +it would be not meaningful, or at least risky, to continue processing: +@command{tar} then aborts processing immediately. All abnormal exits, +whether immediate or delayed, should always be clearly diagnosed on +@code{stderr}, after a line stating the nature of the error. + +Possible exit codes of @GNUTAR{} are summarized in the following +table: + +@table @asis +@item 0 +@samp{Successful termination}. + +@item 1 +@samp{Some files differ}. If tar was invoked with @option{--compare} +(@option{--diff}, @option{-d}) command line option, this means that +some files in the archive differ from their disk counterparts +(@pxref{compare}). If tar was given @option{--create}, +@option{--append} or @option{--update} option, this exit code means +that some files were changed while being archived and so the resulting +archive does not contain the exact copy of the file set. + +@item 2 +@samp{Fatal error}. This means that some fatal, unrecoverable error +occurred. +@end table -In some instances, you may want to remove some files from an archive -stored on disk +If @command{tar} has invoked a subprocess and that subprocess exited with a +nonzero exit code, @command{tar} exits with that code as well. +This can happen, for example, if @command{tar} was given some +compression option (@pxref{gzip}) and the external compressor program +failed. Another example is @command{rmt} failure during backup to the +remote device (@pxref{Remote Tape Server}). + +@node using tar options +@section Using @command{tar} Options + +@GNUTAR{} has a total of eight operating modes which +allow you to perform a variety of tasks. You are required to choose +one operating mode each time you employ the @command{tar} program by +specifying one, and only one operation as an argument to the +@command{tar} command (the corresponding options may be found +at @ref{frequent operations} and @ref{Operations}). Depending on +circumstances, you may also wish to customize how the chosen operating +mode behaves. For example, you may wish to change the way the output +looks, or the format of the files that you wish to archive may require +you to do something special in order to make the archive look right. + +You can customize and control @command{tar}'s performance by running +@command{tar} with one or more options (such as @option{--verbose} +(@option{-v}), which we used in the tutorial). As we said in the +tutorial, @dfn{options} are arguments to @command{tar} which are (as +their name suggests) optional. Depending on the operating mode, you +may specify one or more options. Different options will have different +effects, but in general they all change details of the operation, such +as archive format, archive name, or level of user interaction. Some +options make sense with all operating modes, while others are +meaningful only with particular modes. You will likely use some +options frequently, while you will only use others infrequently, or +not at all. (A full list of options is available in @pxref{All Options}.) + +@vrindex TAR_OPTIONS, environment variable +@anchor{TAR_OPTIONS} +The @env{TAR_OPTIONS} environment variable specifies default options to +be placed in front of any explicit options. For example, if +@code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as +if the two options @option{-v} and @option{--unlink-first} had been +specified before any explicit options. Option specifications are +separated by whitespace. A backslash escapes the next character, so it +can be used to specify an option containing whitespace or a backslash. + +Note that @command{tar} options are case sensitive. For example, the +options @option{-T} and @option{-t} are different; the first requires an +argument for stating the name of a file providing a list of @var{name}s, +while the second does not require an argument and is another way to +write @option{--list} (@option{-t}). + +In addition to the eight operations, there are many options to +@command{tar}, and three different styles for writing both: long (mnemonic) +form, short form, and old style. These styles are discussed below. +Both the options and the operations can be written in any of these three +styles. + +@FIXME{menu at end of this node. need to think of an actual outline +for this chapter; probably do that after stuff from chapter 4 is +incorporated.} + +@node Styles +@section The Three Option Styles + +There are three styles for writing operations and options to the command +line invoking @command{tar}. The different styles were developed at +different times during the history of @command{tar}. These styles will be +presented below, from the most recent to the oldest. + +Some options must take an argument@footnote{For example, @option{--file} +(@option{-f}) takes the name of an archive file as an argument. If +you do not supply an archive file name, @command{tar} will use a +default, but this can be confusing; thus, we recommend that you always +supply a specific archive file name.}. Where you @emph{place} the +arguments generally depends on which style of options you choose. We +will detail specific information relevant to each option style in the +sections on the different option styles, below. The differences are +subtle, yet can often be very important; incorrect option placement +can cause you to overwrite a number of important files. We urge you +to note these differences, and only use the option style(s) which +makes the most sense to you until you feel comfortable with the others. + +Some options @emph{may} take an argument. Such options may have at +most long and short forms, they do not have old style equivalent. The +rules for specifying an argument for such options are stricter than +those for specifying mandatory arguments. Please, pay special +attention to them. -@quotation -@emph{Caution:} you should never delete files from an archive stored -on tape---because of the linear nature of tape storage, doing this is -likely to scramble the archive. -@end quotation +@menu +* Long Options:: Long Option Style +* Short Options:: Short Option Style +* Old Options:: Old Option Style +* Mixing:: Mixing Option Styles +@end menu -To remove archive members from an archive, use the @samp{+delete} -operation. You must specify the names of files to be removed as -file-name arguments. All versions of the named file are removed from -the archive. +@node Long Options +@subsection Long Option Style + +@cindex long options +@cindex options, long style +@cindex options, GNU style +@cindex options, mnemonic names +Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two +dashes in a row, e.g., @option{--list}. The long names are more clear than +their corresponding short or old names. It sometimes happens that a +single long option has many different names which are +synonymous, such as @option{--compare} and @option{--diff}. In addition, +long option names can be given unique abbreviations. For example, +@option{--cre} can be used in place of @option{--create} because there is no +other long option which begins with @samp{cre}. (One way to find +this out is by trying it and seeing what happens; if a particular +abbreviation could represent more than one option, @command{tar} will tell +you that that abbreviation is ambiguous and you'll know that that +abbreviation won't work. You may also choose to run @samp{tar --help} +to see a list of options. Be aware that if you run @command{tar} with a +unique abbreviation for the long name of an option you didn't want to +use, you are stuck; @command{tar} will perform the command as ordered.) + +Long options are meant to be obvious and easy to remember, and their +meanings are generally easier to discern than those of their +corresponding short options (see below). For example: + +@smallexample +$ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0} +@end smallexample -Execution of the @samp{+delete} operation can be very slow. +@noindent +gives a fairly good set of hints about what the command does, even +for those not fully acquainted with @command{tar}. + +@cindex arguments to long options +@cindex long options with mandatory arguments +Long options which require arguments take those arguments +immediately following the option name. There are two ways of +specifying a mandatory argument. It can be separated from the +option name either by an equal sign, or by any amount of +white space characters. For example, the @option{--file} option (which +tells the name of the @command{tar} archive) is given a file such as +@file{archive.tar} as argument by using any of the following notations: +@option{--file=archive.tar} or @option{--file archive.tar}. + +@cindex optional arguments to long options +@cindex long options with optional arguments +In contrast, optional arguments must always be introduced using +an equal sign. For example, the @option{--backup} option takes +an optional argument specifying backup type. It must be used +as @option{--backup=@var{backup-type}}. + +@node Short Options +@subsection Short Option Style + +@cindex short options +@cindex options, short style +@cindex options, traditional +Most options also have a @dfn{short option} name. Short options start with +a single dash, and are followed by a single character, e.g., @option{-t} +(which is equivalent to @option{--list}). The forms are absolutely +identical in function; they are interchangeable. + +The short option names are faster to type than long option names. + +@cindex arguments to short options +@cindex short options with mandatory arguments +Short options which require arguments take their arguments immediately +following the option, usually separated by white space. It is also +possible to stick the argument right after the short option name, using +no intervening space. For example, you might write @w{@option{-f +archive.tar}} or @option{-farchive.tar} instead of using +@option{--file=archive.tar}. Both @option{--file=@var{archive-name}} and +@w{@option{-f @var{archive-name}}} denote the option which indicates a +specific archive, here named @file{archive.tar}. + +@cindex optional arguments to short options +@cindex short options with optional arguments +Short options which take optional arguments take their arguments +immediately following the option letter, @emph{without any intervening +white space characters}. + +Short options' letters may be clumped together, but you are not +required to do this (as compared to old options; see below). When +short options are clumped as a set, use one (single) dash for them +all, e.g., @w{@samp{@command{tar} -cvf}}. Only the last option in +such a set is allowed to have an argument@footnote{Clustering many +options, the last of which has an argument, is a rather opaque way to +write options. Some wonder if @acronym{GNU} @code{getopt} should not +even be made helpful enough for considering such usages as invalid.}. + +When the options are separated, the argument for each option which requires +an argument directly follows that option, as is usual for Unix programs. +For example: -To delete all versions of the file @file{blues} from the archive -@file{records} in the @file{practice} directory, make sure you are in -that directory, and then: +@smallexample +$ @kbd{tar -c -v -b 20 -f /dev/rmt0} +@end smallexample + +If you reorder short options' locations, be sure to move any arguments +that belong to them. If you do not move the arguments properly, you may +end up overwriting files. + +@node Old Options +@subsection Old Option Style +@cindex options, old style +@cindex old option style +@cindex option syntax, traditional + +As far as we know, all @command{tar} programs, @acronym{GNU} and +non-@acronym{GNU}, support @dfn{old options}: that is, if the first +argument does not start with @samp{-}, it is assumed to specify option +letters. @GNUTAR{} supports old options not only for historical +reasons, but also because many people are used to them. If the first +argument does not start with a dash, you are announcing the old option +style instead of the short option style; old options are decoded +differently. + +Like short options, old options are single letters. However, old options +must be written together as a single clumped set, without spaces separating +them or dashes preceding them. This set +of letters must be the first to appear on the command line, after the +@command{tar} program name and some white space; old options cannot appear +anywhere else. The letter of an old option is exactly the same letter as +the corresponding short option. For example, the old option @samp{t} is +the same as the short option @option{-t}, and consequently, the same as the +long option @option{--list}. So for example, the command @w{@samp{tar +cv}} specifies the option @option{-v} in addition to the operation @option{-c}. + +@cindex arguments to old options +@cindex old options with mandatory arguments +When options that need arguments are given together with the command, +all the associated arguments follow, in the same order as the options. +Thus, the example given previously could also be written in the old +style as follows: + +@smallexample +$ @kbd{tar cvbf 20 /dev/rmt0} +@end smallexample -@itemize @bullet -@item -List the contents of the archive file @file{records} (see above for -the steps involved) to insure that the file(s) you wish to delete are -stored in the archive. (This step is optional) +@noindent +Here, @samp{20} is the argument of @option{-b} and @samp{/dev/rmt0} is +the argument of @option{-f}. -@item -Invoke @code{tar} and specify the @samp{+delete} operation -(@samp{+delete}). +The old style syntax can make it difficult to match +option letters with their corresponding arguments, and is often +confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example, +@samp{20} is the argument for @option{-b}, @samp{/dev/rmt0} is the +argument for @option{-f}, and @option{-v} does not have a corresponding +argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f +/dev/rmt0}} is clearer, putting all arguments next to the option they +pertain to. -@item -Specify the name of the archive file that the file(s) will be deleted -from (@samp{+file=@var{archive-name}} or @samp{-f @var{archive-name}}) +If you want to reorder the letters in the old option argument, be +sure to reorder any corresponding argument appropriately. -@item -Specify the files to be deleted, using file-name arguments. +This old way of writing @command{tar} options can surprise even experienced +users. For example, the two commands: -@item -List the contents of the archive file again---note that the files have -been removed. (this step is also optional) -@end itemize +@smallexample +@kbd{tar cfz archive.tar.gz file} +@kbd{tar -cfz archive.tar.gz file} +@end smallexample -@example -% tar +list +file=records -blues -folk -jazz -% tar +delete +file=records blues -% tar +list +file=records -folk -jazz -% -@end example +@noindent +are quite different. The first example uses @file{archive.tar.gz} as +the value for option @samp{f} and recognizes the option @samp{z}. The +second example, however, uses @file{z} as the value for option +@samp{f} --- probably not what was intended. + +This second example could be corrected in many ways, among which the +following are equivalent: + +@smallexample +@kbd{tar -czf archive.tar.gz file} +@kbd{tar -cf archive.tar.gz -z file} +@kbd{tar cf archive.tar.gz -z file} +@end smallexample + +@node Mixing +@subsection Mixing Option Styles + +@cindex options, mixing different styles +All three styles may be intermixed in a single @command{tar} command, +so long as the rules for each style are fully +respected@footnote{Before @GNUTAR{} version 1.11.6, +a bug prevented intermixing old style options with long options in +some cases.}. Old style options and either of the modern styles of +options may be mixed within a single @command{tar} command. However, +old style options must be introduced as the first arguments only, +following the rule for old options (old options must appear directly +after the @command{tar} command and some white space). Modern options +may be given only after all arguments to the old options have been +collected. If this rule is not respected, a modern option might be +falsely interpreted as the value of the argument to one of the old +style options. + +For example, all the following commands are wholly equivalent, and +illustrate the many combinations and orderings of option styles. + +@smallexample +@kbd{tar --create --file=archive.tar} +@kbd{tar --create -f archive.tar} +@kbd{tar --create -farchive.tar} +@kbd{tar --file=archive.tar --create} +@kbd{tar --file=archive.tar -c} +@kbd{tar -c --file=archive.tar} +@kbd{tar -c -f archive.tar} +@kbd{tar -c -farchive.tar} +@kbd{tar -cf archive.tar} +@kbd{tar -cfarchive.tar} +@kbd{tar -f archive.tar --create} +@kbd{tar -f archive.tar -c} +@kbd{tar -farchive.tar --create} +@kbd{tar -farchive.tar -c} +@kbd{tar c --file=archive.tar} +@kbd{tar c -f archive.tar} +@kbd{tar c -farchive.tar} +@kbd{tar cf archive.tar} +@kbd{tar f archive.tar --create} +@kbd{tar f archive.tar -c} +@kbd{tar fc archive.tar} +@end smallexample + +On the other hand, the following commands are @emph{not} equivalent to +the previous set: + +@smallexample +@kbd{tar -f -c archive.tar} +@kbd{tar -fc archive.tar} +@kbd{tar -fcarchive.tar} +@kbd{tar -farchive.tarc} +@kbd{tar cfarchive.tar} +@end smallexample -@node Wizardry, Archive Structure, Tutorial, Top -@chapter Wizardry +@noindent +These last examples mean something completely different from what the +user intended (judging based on the example in the previous set which +uses long options, whose intent is therefore very clear). The first +four specify that the @command{tar} archive would be a file named +@option{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc}, +respectively. The first two examples also specify a single non-option, +@var{name} argument having the value @samp{archive.tar}. The last +example contains only old style option letters (repeating option +@samp{c} twice), not all of which are meaningful (eg., @samp{.}, +@samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked +the first sentence of this paragraph..} + +@node All Options +@section All @command{tar} Options + +The coming manual sections contain an alphabetical listing of all +@command{tar} operations and options, with brief descriptions and +cross-references to more in-depth explanations in the body of the manual. +They also contain an alphabetically arranged table of the short option +forms with their corresponding long option. You can use this table as +a reference for deciphering @command{tar} commands in scripts. -<<>>>> +Appends other @command{tar} archives to the end of the archive. +@xref{concatenate}. -@node Archive Structure, Reading and Writing, Wizardry, Top -@chapter The Structure of an Archive +@opsummary{create} +@item --create +@itemx -c -While an archive may contain many files, the archive itself is a -single ordinary file. Like any other file, an archive file can be -written to a storage device such as a tape or disk, sent through a -pipe or over a network, saved on the active file system, or even -stored in another archive. An archive file is not easy to read or -manipulate without using the @code{tar} utility or Tar mode in Emacs. +Creates a new @command{tar} archive. @xref{create}. +@opsummary{delete} +@item --delete -Physically, an archive consists of a series of file entries terminated -by an end-of-archive entry, which consists of 512 zero bytes. A file -entry usually describes one of the files in the archive (an -@dfn{archive member}), and consists of a file header and the contents -of the file. File headers contain file names and statistics, checksum -information which @code{tar} uses to detect file corruption, and -information about file types. +Deletes members from the archive. Don't try this on an archive on a +tape! @xref{delete}. -More than archive member can have the same file name. One way this -situation can occur is if more than one version of a file has been -stored in the archive. For information about adding new versions of a -file to an archive, @pxref{Modifying}. +@opsummary{diff} +@item --diff +@itemx -d -In addition to entries describing archive members, an archive may contain -entries which @code{tar} itself uses to store information. -@xref{Archive Label}, for an example of such an archive entry. +Same @option{--compare}. @xref{compare}. -@menu -* Old Style File Information:: Old Style File Information -* Archive Label:: -* Format Variations:: -@end menu +@opsummary{extract} +@item --extract +@itemx -x -@node Old Style File Information, Archive Label, Archive Structure, Archive Structure -@section Old Style File Information -@cindex Format, old style -@cindex Old style format -@cindex Old style archives +Extracts members from the archive into the file system. @xref{extract}. -Archives record not only an archive member's contents, but also its -file name or names, its access permissions, user and group, size in -bytes, and last modification time. Some archives also record the file -names in each archived directory, as well as other file and directory -information. - -Certain old versions of @code{tar} cannot handle additional -information recorded by newer @code{tar} programs. To create an -archive which can be read by these old versions, specify the -@samp{+old-archive} option in conjunction with the @samp{tar +create} -operation. When you specify this option, @code{tar} leaves out -information about directories, pipes, fifos, contiguous files, and -device files, and specifies file ownership by group and user ids -instead of names. - -The @samp{+old-archive} option is needed only if the archive must be -readable by an older tape archive program which cannot handle the new format. -Most @code{tar} programs do not have this limitation, so this option -is seldom needed. +@opsummary{get} +@item --get +@itemx -x -@table @samp -@item +old-archive -@itemx -o -@itemx +old -@itemx +portable -@c has portability been changed to portable? -Creates an archive that can be read by an old @code{tar} program. -Used in conjunction with the @samp{tar +create} operation. -@end table +Same as @option{--extract}. @xref{extract}. -@node Archive Label, Format Variations, Old Style File Information, Archive Structure -@section Including a Label in the Archive -@cindex Labeling an archive -@cindex Labels on the archive media +@opsummary{list} +@item --list +@itemx -t -@c !! Should the arg to +label be a quoted string?? no - ringo -To avoid problems caused by misplaced paper labels on the archive -media, you can include a @dfn{label} entry---an archive member which -contains the name of the archive---in the archive itself. Use the -@samp{+label=@var{archive-label}} option in conjunction with the -@samp{+create} operation to include a label entry in the archive as it -is being created. - -If you create an archive using both @samp{+label=@var{archive-label}} -and @samp{+multi-volume}, each volume of the archive will have an -archive label of the form @samp{@var{archive-label} Volume @var{n}}, -where @var{n} is 1 for the first volume, 2 for the next, and so on. -@xref{Multi-Volume Archives}, for information on creating multiple -volume archives. - -If you extract an archive using @samp{+label=@var{archive-label}}, -@code{tar} will print an error if the archive label doesn't match the -@var{archive-label} specified, and will then not extract the archive. -You can include a regular expression in @var{archive-label}, in this -case only. -@c >>> why is a reg. exp. useful here? (to limit extraction to a -@c >>>specific group? ie for multi-volume??? -ringo - -To find out an archive's label entry (or to find out if an archive has -a label at all), use @samp{tar +list +verbose}. @code{tar} will print the -label first, and then print archive member information, as in the -example below: +Lists the members in an archive. @xref{list}. -@example -% tar +verbose +list +file=iamanarchive -V--------- 0/0 0 Mar 7 12:01 1992 iamalabel--Volume Header-- --rw-rw-rw- ringo/user 40 May 21 13:30 1990 iamafilename -@end example +@opsummary{update} +@item --update +@itemx -u + +Adds files to the end of the archive, but only if they are newer than +their counterparts already in the archive, or if they do not already +exist in the archive. @xref{update}. -@table @samp -@item +label=@var{archive-label} -@itemx -V @var{archive-label} -Includes an @dfn{archive-label} at the beginning of the archive when -the archive is being created (when used in conjunction with the -@samp{tar +create} operation). Checks to make sure the archive label -matches the one specified (when used in conjunction with the @samp{tar -+extract} operation. @end table -@c was +volume -@node Format Variations, , Archive Label, Archive Structure -@section Format Variations -@cindex Format Parameters -@cindex Format Options -@cindex Options to specify archive format. +@node Option Summary +@subsection @command{tar} Options + +@table @option + +@opsummary{absolute-names} +@item --absolute-names +@itemx -P + +Normally when creating an archive, @command{tar} strips an initial +@samp{/} from member names, and when extracting from an archive @command{tar} +treats names specially if they have initial @samp{/} or internal +@samp{..}. This option disables that behavior. @xref{absolute}. + +@opsummary{after-date} +@item --after-date + +(See @option{--newer}, @pxref{after}) + +@opsummary{anchored} +@item --anchored +A pattern must match an initial subsequence of the name's components. +@xref{controlling pattern-matching}. + +@opsummary{atime-preserve} +@item --atime-preserve +@itemx --atime-preserve=replace +@itemx --atime-preserve=system + +Attempt to preserve the access time of files when reading them. This +option currently is effective only on files that you own, unless you +have superuser privileges. + +@option{--atime-preserve=replace} remembers the access time of a file +before reading it, and then restores the access time afterwards. This +may cause problems if other programs are reading the file at the same +time, as the times of their accesses will be lost. On most platforms +restoring the access time also requires @command{tar} to restore the +data modification time too, so this option may also cause problems if +other programs are writing the file at the same time (@command{tar} attempts +to detect this situation, but cannot do so reliably due to race +conditions). Worse, on most platforms restoring the access time also +updates the status change time, which means that this option is +incompatible with incremental backups. + +@option{--atime-preserve=system} avoids changing time stamps on files, +without interfering with time stamp updates +caused by other programs, so it works better with incremental backups. +However, it requires a special @code{O_NOATIME} option from the +underlying operating and file system implementation, and it also requires +that searching directories does not update their access times. As of +this writing (November 2005) this works only with Linux, and only with +Linux kernels 2.6.8 and later. Worse, there is currently no reliable +way to know whether this feature actually works. Sometimes +@command{tar} knows that it does not work, and if you use +@option{--atime-preserve=system} then @command{tar} complains and +exits right away. But other times @command{tar} might think that the +option works when it actually does not. + +Currently @option{--atime-preserve} with no operand defaults to +@option{--atime-preserve=replace}, but this may change in the future +as support for @option{--atime-preserve=system} improves. + +If your operating or file system does not support +@option{--atime-preserve=@-system}, you might be able to preserve access +times reliably by using the @command{mount} command. For example, +you can mount the file system read-only, or access the file system via +a read-only loopback mount, or use the @samp{noatime} mount option +available on some systems. However, mounting typically requires +superuser privileges and can be a pain to manage. + +@opsummary{auto-compress} +@item --auto-compress +@itemx -a + +During a @option{--create} operation, enables automatic compressed +format recognition based on the archive suffix. The effect of this +option is cancelled by @option{--no-auto-compress}. @xref{gzip}. + +@opsummary{backup} +@item --backup=@var{backup-type} + +Rather than deleting files from the file system, @command{tar} will +back them up using simple or numbered backups, depending upon +@var{backup-type}. @xref{backup}. + +@opsummary{block-number} +@item --block-number +@itemx -R + +With this option present, @command{tar} prints error messages for read errors +with the block number in the archive file. @xref{block-number}. + +@opsummary{blocking-factor} +@item --blocking-factor=@var{blocking} +@itemx -b @var{blocking} + +Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per +record. @xref{Blocking Factor}. + +@opsummary{bzip2} +@item --bzip2 +@itemx -j + +This option tells @command{tar} to read or write archives through +@code{bzip2}. @xref{gzip}. + +@opsummary{check-device} +@item --check-device +Check device numbers when creating a list of modified files for +incremental archiving. This is the default. @xref{device numbers}, +for a detailed description. + +@opsummary{checkpoint} +@item --checkpoint[=@var{number}] + +This option directs @command{tar} to print periodic checkpoint +messages as it reads through the archive. It is intended for when you +want a visual indication that @command{tar} is still running, but +don't want to see @option{--verbose} output. You can also instruct +@command{tar} to execute a list of actions on each checkpoint, see +@option{--checkpoint-action} below. For a detailed description, see +@ref{checkpoints}. + +@opsummary{checkpoint-action} +@item --checkpoint-action=@var{action} +Instruct @command{tar} to execute an action upon hitting a +breakpoint. Here we give only a brief outline. @xref{checkpoints}, +for a complete description. + +The @var{action} argument can be one of the following: + +@table @asis +@item bell +Produce an audible bell on the console. + +@item dot +@itemx . +Print a single dot on the standard listing stream. + +@item echo +Display a textual message on the standard error, with the status and +number of the checkpoint. This is the default. + +@item echo=@var{string} +Display @var{string} on the standard error. Before output, the string +is subject to meta-character expansion. + +@item exec=@var{command} +Execute the given @var{command}. + +@item sleep=@var{time} +Wait for @var{time} seconds. + +@item ttyout=@var{string} +Output @var{string} on the current console (@file{/dev/tty}). +@end table -Format parameters specify how an archive is written on the archive -media. The best choice of format parameters will vary depending on -the type and number of files being archived, and on the media used to -store the archive. +Several @option{--checkpoint-action} options can be specified. The +supplied actions will be executed in order of their appearance in the +command line. -To specify format parameters when accessing or creating an archive, -you can use the options described in the following sections. If you -do not specify any format parameters, @code{tar} uses default -parameters. You cannot modify a compressed archive. If you create an -archive with the @samp{+block-size} option specified (@pxref{Blocking -Factor}), you must specify that block-size when operating on the -archive. @xref{Matching Format Parameters}, for other examples of -format parameter considerations. +Using @option{--checkpoint-action} without @option{--checkpoint} +assumes default checkpoint frequency of one checkpoint per 10 records. +@opsummary{check-links} +@item --check-links +@itemx -l +If this option was given, @command{tar} will check the number of links +dumped for each processed file. If this number does not match the +total number of hard links for the file, a warning message will be +output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a +synonym for @option{--one-file-system}. The current semantics, which +complies to UNIX98, was introduced with version +1.15.91. @xref{Changes}, for more information.}. + +@xref{hard links}. + +@opsummary{compress} +@opsummary{uncompress} +@item --compress +@itemx --uncompress +@itemx -Z -@menu -* Multi-Volume Archives:: -* Sparse Files:: -* Blocking Factor:: -* Compressed Archives:: -@end menu +@command{tar} will use the @command{compress} program when reading or +writing the archive. This allows you to directly act on archives +while saving space. @xref{gzip}. -@node Multi-Volume Archives, Sparse Files, Format Variations, Format Variations -@subsection Archives Longer than One Tape or Disk -@cindex Multi-volume archives +@opsummary{confirmation} +@item --confirmation -To create an archive that is larger than will fit on a single unit of -the media, use the @samp{+multi-volume} option in conjunction with the -@samp{tar +create} operation (@pxref{Creating Archives}). A -@dfn{multi-volume} archive can be manipulated like any other archive -(provided the @samp{+multi-volume} option is specified), but is stored -on more than one tape or disk. +(See @option{--interactive}.) @xref{interactive}. -When you specify @samp{+multi-volume}, @code{tar} does not report an -error when it comes to the end of an archive volume (when reading), or -the end of the media (when writing). Instead, it prompts you to load -a new storage volume. If the archive is on a magnetic tape, you -should change tapes when you see the prompt; if the archive is on a -floppy disk, you should change disks; etc. +@opsummary{delay-directory-restore} +@item --delay-directory-restore -You can read each individual volume of a multi-volume archive as if it -were an archive by itself. For example, to list the contents of one -volume, use @samp{tar +list}, without @samp{+multi-volume} specified. -To extract an archive member from one volume (assuming it is described -that volume), use @samp{tar +extract}, again without -@samp{+multi-volume}. +Delay setting modification times and permissions of extracted +directories until the end of extraction. @xref{Directory Modification Times and Permissions}. -If an archive member is split across volumes (ie. its entry begins on -one volume of the media and ends on another), you need to specify -@samp{+multi-volume} to extract it successfully. In this case, you -should load the volume where the archive member starts, and use -@samp{tar +extract +multi-volume}---@code{tar} will prompt for later -volumes as it needs them. @xref{Extracting From Archives} for more -information about extracting archives. +@opsummary{dereference} +@item --dereference +@itemx -h -@samp{+info-script=@var{program-file}} is like @samp{+multi-volume}, -except that @code{tar} does not prompt you directly to change media -volumes when a volume is full---instead, @code{tar} runs commands you -have stored in @var{program-file}. This option can be used to -broadcast messages such as @samp{someone please come change my tape} -when performing unattended backups. When @var{program-file} is done, -@code{tar} will assume that the media has been changed. +When reading or writing a file to be archived, @command{tar} accesses +the file that a symbolic link points to, rather than the symlink +itself. @xref{dereference}. +@opsummary{directory} +@item --directory=@var{dir} +@itemx -C @var{dir} -<<< There should be a sample program here, including an exit before -<<< end. +When this option is specified, @command{tar} will change its current directory +to @var{dir} before performing any operations. When this option is used +during archive creation, it is order sensitive. @xref{directory}. -@table @samp -@item +multi-volume -@itemx -M -Creates a multi-volume archive, when used in conjunction with -@samp{tar +create}. To perform any other operation on a multi-volume -archive, specify @samp{+multi-volume} in conjunction with that -operation. +@opsummary{exclude} +@item --exclude=@var{pattern} -@item +info-script=@var{program-file} -@itemx -F @var{program-file} -Creates a multi-volume archive via a script. Used in conjunction with -@samp{tar +create}. -@end table +When performing operations, @command{tar} will skip files that match +@var{pattern}. @xref{exclude}. -@node Sparse Files, Blocking Factor, Multi-Volume Archives, Format Variations -@subsection Archiving Sparse Files -@cindex Sparse Files +@opsummary{exclude-backups} +@item --exclude-backups +Exclude backup and lock files. @xref{exclude,, exclude-backups}. -A file is sparse if it contains blocks of zeros whose existance is -recorded, but that have no space allocated on disk. When you specify -the @samp{+sparse} option in conjunction with the @samp{+create} -operation, @code{tar} tests all files for sparseness while archiving. -If @code{tar} finds a file to be sparse, it uses a sparse -representation of the file in the archive. @xref{Creating Archives}, -for more information about creating archives. +@opsummary{exclude-from} +@item --exclude-from=@var{file} +@itemx -X @var{file} -@samp{+sparse} is useful when archiving files, such as dbm files, -likely to contain many nulls. This option dramatically -decreases the amount of space needed to store such an archive. +Similar to @option{--exclude}, except @command{tar} will use the list of +patterns in the file @var{file}. @xref{exclude}. -@quotation -@strong{Please Note:} Always use @samp{+sparse} when performing file -system backups, to avoid archiving the expanded forms of files stored -sparsely in the system.@refill +@opsummary{exclude-caches} +@item --exclude-caches -Even if your system has no no sparse files currently, some may be -created in the future. If you use @samp{+sparse} while making file -system backups as a matter of course, you can be assured the archive -will always take no more space on the media than the files take on -disk (otherwise, archiving a disk filled with sparse files might take -hundreds of tapes).@refill -<<< xref incremental when node name is set. -@end quotation +Exclude from dump any directory containing a valid cache directory +tag file, but still dump the directory node and the tag file itself. -@code{tar} ignores the @samp{+sparse} option when reading an archive. +@xref{exclude,, exclude-caches}. -@table @samp -@item +sparse -@itemx -S -Files stored sparsely in the file system are represented sparsely in -the archive. Use in conjunction with write operations. -@end table +@opsummary{exclude-caches-under} +@item --exclude-caches-under -@node Blocking Factor, Compressed Archives, Sparse Files, Format Variations -@subsection The Blocking Factor of an Archive -@cindex Blocking Factor -@cindex Block Size -@cindex Number of records per block -@cindex Number of bytes per block -@cindex Bytes per block -@cindex Records per block - -The data in an archive is grouped into records, which are 512 bytes. -Records are read and written in whole number multiples called -@dfn{blocks}. The number of records in a block (ie. the size of a -block in units of 512 bytes) is called the @dfn{blocking factor}. The -@samp{+block-size=@var{number}} option specifies the blocking factor -of an archive. The default blocking factor is typically 20 (ie.@: -10240 bytes), but can be specified at installation. To find out the -blocking factor of an existing archive, use @samp {tar +list -+file=@var{archive-name}}. This may not work on some devices. - -Blocks are seperated by gaps, which waste space on the archive media. -If you are archiving on magnetic tape, using a larger blocking factor -(and therefore larger blocks) provides faster throughput and allows -you to fit more data on a tape (because there are fewer gaps). If you -are archiving on cartridge, a very large blocking factor (say 126 or -more) greatly increases performance. A -smaller blocking factor, on the other hand, may be usefull when -archiving small files, to avoid archiving lots of nulls as @code{tar} -fills out the archive to the end of the block. In general, the ideal block size -depends on the size of the inter-block gaps on the tape you are using, -and the average size of the files you are archiving. @xref{Creating -Archives}, for information on writing archives. - -Archives with blocking factors larger than 20 cannot be read by very -old versions of @code{tar}, or by some newer versions of @code{tar} -running on old machines with small address spaces. With GNU -@code{tar}, the blocking factor of an archive is limited only by the -maximum block size of the device containing the archive, or by the -amount of available virtual memory. - -If you use a non-default blocking factor when you create an archive, -you must specify the same blocking factor when you modify that -archive. Some archive devices will also require you to specify the -blocking factor when reading that archive, however this is not -typically the case. Usually, you can use @samp{tar +list} without -specifying a blocking factor---@code{tar} reports a non-default block -size and then lists the archive members as it would normally. To -extract files from an archive with a non-standard blocking factor -(particularly if you're not sure what the blocking factor is), you can -usually use the {+read-full-blocks} option while specifying a blocking -factor larger then the blocking factor of the archive (ie. @samp{tar -+extract +read-full-blocks +block-size=300}. @xref{Listing Contents} -for more information on the @samp{+list} operation. -@xref{read-full-blocks} for a more detailed explanation of that -option. +Exclude from dump any directory containing a valid cache directory +tag file, but still dump the directory node itself. -@table @samp -@item +block-size=@var{number} -@itemx -b @var{number} -Specifies the blocking factor of an archive. Can be used with any -operation, but is usually not necessary with @samp{tar +list}. -@end table +@xref{exclude}. -@node Compressed Archives, , Blocking Factor, Format Variations -@subsection Creating and Reading Compressed Archives -@cindex Compressed archives -@cindex Storing archives in compressed format +@opsummary{exclude-caches-all} +@item --exclude-caches-all -@samp{+compress} indicates an archive stored in compressed format. -The @samp{+compress} option is useful in saving time over networks and -space in pipes, and when storage space is at a premium. -@samp{+compress} causes @code{tar} to compress when writing the -archive, or to uncompress when reading the archive. - -To perform compression and uncompression on the archive, @code{tar} -runs the @code{compress} utility. @code{tar} uses the default -compression parameters; if you need to override them, avoid the -@samp{+compress} option and run the @code{compress} utility -explicitly. It is useful to be able to call the @code{compress} -utility from within @code{tar} because the @code{compress} utility by -itself cannot access remote tape drives. - -The @samp{+compress} option will not work in conjunction with the -@samp{+multi-volume} option or the @samp{+add-file}, @samp{+update}, -@samp{+add-file} and @samp{+delete} operations. @xref{Modifying}, for -more information on these operations. - -If there is no compress utility available, @code{tar} will report an -error. +Exclude from dump any directory containing a valid cache directory +tag file. @xref{exclude}. -@samp{+compress-block} is like @samp{+compress}, but when used in -conjunction with @samp{+create} also causes @code{tar} to pad the last -block of the archive out to the next block boundary as it is written. -This is useful with certain devices which require all write operations -be a multiple of a specific size. +@opsummary{exclude-tag} +@item --exclude-tag=@var{file} -@quotation -@strong{Please Note:} The @code{compress} program may be covered by a patent, -and therefore we recommend you stop using it. We hope to have a -different compress program in the future. We may change the name of -this option at that time. -@end quotation +Exclude from dump any directory containing file named @var{file}, but +dump the directory node and @var{file} itself. @xref{exclude,, exclude-tag}. -@table @samp -@item +compress -@itemx +uncompress -@itemx -z -@itemx -Z -When this option is specified, @code{tar} will compress (when writing -an archive), or uncompress (when reading an archive). Used in -conjunction with the @samp{+create}, @samp{+extract}, @samp{+list} and -@samp{+compare} operations. +@opsummary{exclude-tag-under} +@item --exclude-tag-under=@var{file} -@item +compress-block -@itemx -z -z -Acts like @samp{+compress}, but pads the archive out to the next block -boundary as it is written when used in conjunction with the -@samp{+create} operation. -@end table +Exclude from dump the contents of any directory containing file +named @var{file}, but dump the directory node itself. @xref{exclude,, +exclude-tag-under}. -@c >>> MIB -- why not use -Z instead of -z -z ? -ringo +@opsummary{exclude-tag-all} +@item --exclude-tag-all=@var{file} -@node Reading and Writing, Insuring Accuracy, Archive Structure, Top -@chapter Reading and Writing Archives +Exclude from dump any directory containing file named @var{file}. +@xref{exclude,,exclude-tag-all}. -The @samp{+create} operation writes a new archive, and the -@samp{+extract} operation reads files from an archive and writes them -into the file system. You can use other @code{tar} operations to -write new information into an existing archive (adding files to it, -adding another archive to it, or deleting files from it), and you can -read a list of the files in an archive without extracting it using the -@samp{+list} operation. +@opsummary{exclude-vcs} +@item --exclude-vcs -@menu -* Archive Name:: The name of an archive -* Creating in Detail:: Creating in detail -* Modifying:: Modifying archives -* Listing Contents:: Listing the contents of an archive -* Extracting From Archives:: Extracting files from an archive -@end menu +Exclude from dump directories and files, that are internal for some +widely used version control systems. -@node Archive Name, Creating in Detail, Reading and Writing, Reading and Writing -@section The Name of an Archive -@cindex Naming an archive -@cindex Archive Name -@cindex Directing output -@cindex Where is the archive? +@xref{exclude,,exclude-vcs}. -An archive can be saved as a file in the file system, sent through a -pipe or over a network, or written to an I/O device such as a tape or -disk drive. To specify the name of the archive, use the -@samp{+file=@var{archive-name}} option. - -An archive name can be the name of an ordinary file or the name of an -I/O device. @code{tar} always needs an archive name---if you do not -specify an archive name, the archive name comes from the environment -variable @code{TAPE} or, if that variable is not specified, a default -archive name, which is usually the name of tape unit zero (ie. -/dev/tu00). - -If you use @file{-} as an @var{archive-name}, @code{tar} reads the -archive from standard input (when listing or extracting files), or -writes it to standard output (when creating an archive). If you use -@file{-} as an @var{archive-name} when modifying an archive, -@code{tar} reads the original archive from its standard input and -writes the entire new archive to its standard output. +@opsummary{file} +@item --file=@var{archive} +@itemx -f @var{archive} -@c >>> MIB--does standard input and output redirection work with all -@c >>> operations? -@c >>> need example for standard input and output (screen and keyboard?) +@command{tar} will use the file @var{archive} as the @command{tar} archive it +performs operations on, rather than @command{tar}'s compilation dependent +default. @xref{file tutorial}. -@cindex Standard input and output -@cindex tar to standard input and output +@opsummary{files-from} +@item --files-from=@var{file} +@itemx -T @var{file} -To specify an archive file on a device attached to a remote machine, -use the following: +@command{tar} will use the contents of @var{file} as a list of archive members +or files to operate on, in addition to those specified on the +command-line. @xref{files}. -@example -+file=@var{hostname}:/@var{dev}/@var{file name} -@end example +@opsummary{force-local} +@item --force-local -@noindent -@code{tar} will complete the remote connection, if possible, and -prompt you for a username and password. If you use -@samp{+file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @code{tar} -will complete the remote connection, if possible, using your username -as the username on the remote machine. +Forces @command{tar} to interpret the file name given to @option{--file} +as a local file, even if it looks like a remote tape drive name. +@xref{local and remote archives}. + +@opsummary{format} +@item --format=@var{format} +@itemx -H @var{format} -@c >>>MIB --- is this clear? +Selects output archive format. @var{Format} may be one of the +following: @table @samp -@item +file=@var{archive-name} -@itemx -f @var{archive-name} -Names the archive to create or operate on. Use in conjunction with -any operation. +@item v7 +Creates an archive that is compatible with Unix V7 @command{tar}. + +@item oldgnu +Creates an archive that is compatible with GNU @command{tar} version +1.12 or earlier. + +@item gnu +Creates archive in GNU tar 1.13 format. Basically it is the same as +@samp{oldgnu} with the only difference in the way it handles long +numeric fields. + +@item ustar +Creates a @acronym{POSIX.1-1988} compatible archive. + +@item posix +Creates a @acronym{POSIX.1-2001 archive}. + @end table -@node Creating in Detail, Modifying, Archive Name, Reading and Writing -@section Creating in Detail -@c operations should probably have examples, not tables. -@cindex Writing new archives -@cindex Archive creation +@xref{Formats}, for a detailed discussion of these formats. -To create an archive, use @samp{tar +create}. To name the archive, -use @samp{+file=@var{archive-name}} in conjunction with the -@samp{+create} operation (@pxref{Archive Name}). If you do not name -the archive, @code{tar} uses the value of the environment variable -@code{TAPE} as the file name for the archive, or, if that is not -available, @code{tar} uses a default archive name, usually that for tape -unit zero. @xref{Archive Name}, for more information about specifying -an archive name. +@opsummary{full-time} +@item --full-time +This option instructs @command{tar} to print file times to their full +resolution. Usually this means 1-second resolution, but that depends +on the underlying file system. The @option{--full-time} option takes +effect only when detailed output (verbosity level 2 or higher) has +been requested using the @option{--verbose} option, e.g., when listing +or extracting archives: -The following example creates an archive named @file{stooges}, -containing the files @file{larry}, @file{moe} and @file{curley}: +@smallexample +$ @kbd{tar -t -v --full-time -f archive.tar} +@end smallexample -@example -tar +create +file=stooges larry moe curley -@end example +@noindent +or, when creating an archive: -If you specify a directory name as a file-name argument, @code{tar} -will archive all the files in that directory. The following example -creates an archive named @file{hail/hail/fredonia}, containing the -contents of the directory @file{marx}: +@smallexample +$ @kbd{tar -c -vv --full-time -f archive.tar .} +@end smallexample -@example -tar +create +file=hail/hail/fredonia marx -@end example +Notice, thar when creating the archive you need to specify +@option{--verbose} twice to get a detailed output (@pxref{verbose +tutorial}). -If you don't specify files to put in the archive, @code{tar} archives -all the files in the working directory. The following example creates -an archive named @file{home} containing all the files in the working -directory: +@opsummary{group} +@item --group=@var{group} -@example -tar +create +file=home -@end example +Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group}, +rather than the group from the source file. @var{group} can specify a +symbolic name, or a numeric @acronym{ID}, or both as +@var{name}:@var{id}. @xref{override}. -@xref{File Name Lists}, for other ways to specify files to archive. +Also see the comments for the @option{--owner=@var{user}} option. -Note: In the example above, an archive containing all the files in the -working directory is being written to the working directory. GNU -@code{tar} stores files in the working directory in an archive which -is itself in the working directory without falling into an infinite -loop. Other versions of @code{tar} may fall into this trap. +@opsummary{gzip} +@opsummary{gunzip} +@opsummary{ungzip} +@item --gzip +@itemx --gunzip +@itemx --ungzip +@itemx -z -@node Modifying, Listing Contents, Creating in Detail, Reading and Writing -@section Modifying Archives -@cindex Modifying archives +This option tells @command{tar} to read or write archives through +@command{gzip}, allowing @command{tar} to directly operate on several +kinds of compressed archives transparently. @xref{gzip}. -Once an archive is created, you can add new archive members to it, add -the contents of another archive, add newer versions of members already -stored, or delete archive members already stored. +@opsummary{hard-dereference} +@item --hard-dereference +When creating an archive, dereference hard links and store the files +they refer to, instead of creating usual hard link members. -To find out what files are already stored in an archive, use @samp{tar -+list +file=@var{archive-name}}. @xref{Listing Contents}. +@xref{hard links}. -@menu -* Adding Files:: -* Appending Archives:: -* Deleting Archive Files:: Deleting Files From an Archive -* Matching Format Parameters:: -@end menu +@opsummary{help} +@item --help +@itemx -? -@node Adding Files, Appending Archives, Modifying, Modifying -@subsection Adding Files to an Archive -@cindex Adding files to an archive -@cindex Updating an archive +@command{tar} will print out a short message summarizing the operations and +options to @command{tar} and exit. @xref{help}. -To add files to an archive, use @samp{tar +add-file}. The archive to -be added to must already exist and be in proper archive format (which -normally means it was created previously using @code{tar}). If the -archive was created with a different block size than now specified, -@code{tar} will report an error (@pxref{Blocking Factor}). If the -archive is not a valid @code{tar} archive, the results will be -unpredictable. You cannot add files to a compressed archive, however -you can add files to the last volume of a multi-volume archive. -@xref{Matching Format Parameters}. +@opsummary{ignore-case} +@item --ignore-case +Ignore case when matching member or file names with +patterns. @xref{controlling pattern-matching}. -The following example adds the file @file{shemp} to the archive -@file{stooges} created above: +@opsummary{ignore-command-error} +@item --ignore-command-error +Ignore exit codes of subprocesses. @xref{Writing to an External Program}. -@example -tar +add-file +file=stooges shemp -@end example +@opsummary{ignore-failed-read} +@item --ignore-failed-read -You must specify the files to be added; there is no default. +Do not exit unsuccessfully merely because an unreadable file was encountered. +@xref{Ignore Failed Read}. -@samp{tar +update} acts like @samp{tar +add-file}, but does not add -files to the archive if there is already a file entry with that name -in the archive that has the same modification time. +@opsummary{ignore-zeros} +@item --ignore-zeros +@itemx -i -Both @samp{+update} and @samp{+add-file} work by adding to the end of -the archive. When you extract a file from the archive, only the -version stored last will wind up in the file system. Because -@samp{tar +extract} extracts files from an archive in sequence, and -overwrites files with the same name in the file system, if a file name -appears more than once in an archive the last version of the file will -overwrite the previous versions which have just been extracted. You -should avoid storing older versions of a file later in the archive. +With this option, @command{tar} will ignore zeroed blocks in the +archive, which normally signals EOF. @xref{Reading}. -Note: @samp{+update} is not suitable for performing backups, because -it doesn't change directory content entries, and because it lengthens -the archive every time it is used. -@c <<< xref to scripted backup, listed incremental, for info on backups. +@opsummary{incremental} +@item --incremental +@itemx -G -@node Appending Archives, Deleting Archive Files, Adding Files, Modifying -@subsection Appending One Archive's Contents to Another Archive -@cindex Adding archives to an archive -@cindex Concatenating Archives +Informs @command{tar} that it is working with an old +@acronym{GNU}-format incremental backup archive. It is intended +primarily for backwards compatibility only. @xref{Incremental Dumps}, +for a detailed discussion of incremental archives. -To append copies of an archive or archives to the end of another -archive, use @samp{tar +add-archive}. The source and target archives -must already exist and have been created using compatable format -parameters (@pxref{Matching Format Parameters}). +@opsummary{index-file} +@item --index-file=@var{file} -@code{tar} will stop reading an archive if it encounters an -end-of-archive marker. The @code{cat} utility does not remove -end-of-archive markers, and is therefore unsuitable for concatenating -archives. @samp{tar +add-archive} removes the end-of-archive marker -from the target archive before each new archive is appended. -@c <<< xref ignore-zeros +Send verbose output to @var{file} instead of to standard output. -You must specify the source archives using -@samp{+file=@var{archive-name}} (@pxref{Archive Name}). If you do not -specify the target archive , @code{tar} uses the value of the -environment variable @code{TAPE}, or, if this has not been set, the -default archive name. +@opsummary{info-script} +@opsummary{new-volume-script} +@item --info-script=@var{script-file} +@itemx --new-volume-script=@var{script-file} +@itemx -F @var{script-file} -The following example adds the contents of the archive -@file{hail/hail/fredonia} to the archive @file{stooges} (both archives -were created in examples above): +When @command{tar} is performing multi-tape backups, @var{script-file} is run +at the end of each tape. If @var{script-file} exits with nonzero status, +@command{tar} fails immediately. @xref{info-script}, for a detailed +discussion of @var{script-file}. -@example -tar +add-archive +file=stooges hail/hail/fredonia -@end example +@opsummary{interactive} +@item --interactive +@itemx --confirmation +@itemx -w -If you need to retrieve files from an archive that was added to using -the @code{cat} utility, use the @samp{+ignore-zeros} option -(@pxref{Archive Reading Options}). +Specifies that @command{tar} should ask the user for confirmation before +performing potentially destructive options, such as overwriting files. +@xref{interactive}. -@node Deleting Archive Files, Matching Format Parameters, Appending Archives, Modifying -@subsection Deleting Files From an Archive -@cindex Deleting files from an archive -@cindex Removing files from an archive +@opsummary{keep-newer-files} +@item --keep-newer-files -To delete archive members from an archive, use @samp{tar +delete}. -You must specify the file names of the members to be deleted. All -archive members with the specified file names will be removed from the -archive. +Do not replace existing files that are newer than their archive copies +when extracting files from an archive. -The following example removes the file @file{curley} from the archive -@file{stooges}: +@opsummary{keep-old-files} +@item --keep-old-files +@itemx -k -@example -tar +delete +file=stooges curley -@end example +Do not overwrite existing files when extracting files from an +archive. Return error if such files exist. See also +@ref{--skip-old-files}. -You can only use @samp{tar +delete} on an archive if the archive -device allows you to write to any point on the media. +@xref{Keep Old Files}. -@quotation -@strong{Warning:} Don't try to delete an archive member from a -magnetic tape, lest you scramble the archive. There is no safe way -(except by completely re-writing the archive) to delete files from -most kinds of magnetic tape. -@end quotation +@opsummary{label} +@item --label=@var{name} +@itemx -V @var{name} -@c <<< MIB -- how about automatic detection of archive media? give error -@c <<< unless the archive device is either an ordinary file or different -@c <<< input and output (+file=-). +When creating an archive, instructs @command{tar} to write @var{name} +as a name record in the archive. When extracting or listing archives, +@command{tar} will only operate on archives that have a label matching +the pattern specified in @var{name}. @xref{Tape Files}. -@node Matching Format Parameters, , Deleting Archive Files, Modifying -@subsection Matching the Format Parameters +@opsummary{level} +@item --level=@var{n} +Force incremental backup of level @var{n}. As of @GNUTAR version +@value{VERSION}, the option @option{--level=0} truncates the snapshot +file, thereby forcing the level 0 dump. Other values of @var{n} are +effectively ignored. @xref{--level=0}, for details and examples. -Some format parameters must be taken into consideration when modifying -an archive: +The use of this option is valid only in conjunction with the +@option{--listed-incremental} option. @xref{Incremental Dumps}, +for a detailed description. -Compressed archives cannot be modified. +@opsummary{listed-incremental} +@item --listed-incremental=@var{snapshot-file} +@itemx -g @var{snapshot-file} -You have to specify the block size of the archive when modifying an -archive with a non-default block size. +During a @option{--create} operation, specifies that the archive that +@command{tar} creates is a new @acronym{GNU}-format incremental +backup, using @var{snapshot-file} to determine which files to backup. +With other operations, informs @command{tar} that the archive is in +incremental format. @xref{Incremental Dumps}. -Multi-volume archives can be modified like any other archive. To add -files to a multi-volume archive, you need to only mount the last -volume of the archive media (and new volumes, if needed). For all -other operations, you need to use the entire archive. +@opsummary{lzip} +@item --lzip -If a multi-volume archive was labeled using @samp{+label} -(@pxref{Archive Label}) when it was created, @code{tar} will not -automatically label volumes which are added later. To label -subsequent volumes, specify @samp{+label=@var{archive-label}} again in -conjunction with the @samp{+add-file}, @samp{+update} or -@samp{+add-archive} operation. -@cindex Labelling multi-volume archives -@c <<< example +This option tells @command{tar} to read or write archives through +@command{lzip}. @xref{gzip}. -@c <<< xref somewhere, for more information about format parameters. +@opsummary{lzma} +@item --lzma -@node Listing Contents, Extracting From Archives, Modifying, Reading and Writing -@section Listing the Contents of an Archive -@cindex Names of the files in an archive -@cindex Archive contents, list of -@cindex Archive members, list of +This option tells @command{tar} to read or write archives through +@command{lzma}. @xref{gzip}. -@samp{tar +list} prints a list of the file names of the archive -members on the standard output. If you specify @var{file-name} -arguments on the command line (or using the @samp{+files-from} option, -@pxref{File Name Lists}), only the files you specify will be listed, -and only if they exist in the archive. Files not specified will be -ignored, unless they are under a specific directory. +@item --lzop -If you include the @samp{+verbose} option, @code{tar} prints an -@samp{ls -l} type listing for the archive. @pxref{Additional -Information}, for a description of the @samp{+verbose} option. +This option tells @command{tar} to read or write archives through +@command{lzop}. @xref{gzip}. -If the blocking factor of the archive differs from the default, -@code{tar} reports this. @xref{Blocking Factor}. +@opsummary{mode} +@item --mode=@var{permissions} -@xref{Archive Reading Options} for a list of options which can be used -to modify @samp{+list}'s operation. +When adding files to an archive, @command{tar} will use +@var{permissions} for the archive members, rather than the permissions +from the files. @var{permissions} can be specified either as an octal +number or as symbolic permissions, like with +@command{chmod}. @xref{override}. -This example prints a list of the archive members of the archive -@file{stooges}: +@opsummary{mtime} +@item --mtime=@var{date} -@example -tar +list +file=stooges -@end example +When adding files to an archive, @command{tar} will use @var{date} as +the modification time of members when creating archives, instead of +their actual modification times. The value of @var{date} can be +either a textual date representation (@pxref{Date input formats}) or a +name of the existing file, starting with @samp{/} or @samp{.}. In the +latter case, the modification time of that file is used. @xref{override}. -@noindent -@code{tar} responds: +@opsummary{multi-volume} +@item --multi-volume +@itemx -M -@example -larry -moe -shemp -marx/julius -marx/alexander -marx/karl -@end example +Informs @command{tar} that it should create or otherwise operate on a +multi-volume @command{tar} archive. @xref{Using Multiple Tapes}. -This example generates a verbose list of the archive members of the -archive file @file{dwarves}, which has a blocking factor of two: +@opsummary{new-volume-script} +@item --new-volume-script -@example -tar +list -v +file=blocks -@end example +(see @option{--info-script}) -@noindent -@code{tar} responds: +@opsummary{newer} +@item --newer=@var{date} +@itemx --after-date=@var{date} +@itemx -N -@example -tar: Blocksize = 2 records --rw------- ringo/user 42 May 1 13:29 1990 .bashful --rw-rw-rw- ringo/user 42 Oct 4 13:29 1990 doc --rw-rw-rw- ringo/user 42 Jul 20 18:01 1969 dopey --rw-rw---- ringo/user 42 Nov 26 13:42 1963 grumpy --rw-rw-rw- ringo/user 42 May 5 13:29 1990 happy --rw-rw-rw- ringo/user 42 May 1 12:00 1868 sleepy --rw-rw-rw- ringo/user 42 Jul 4 17:29 1776 sneezy -@end example +When creating an archive, @command{tar} will only add files that have changed +since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it +is taken to be the name of a file whose data modification time specifies +the date. @xref{after}. -@node Extracting From Archives, , Listing Contents, Reading and Writing -@section Extracting Files from an Archive -@cindex Extraction -@cindex Retrieving files from an archive -@cindex Resurrecting files from an archive +@opsummary{newer-mtime} +@item --newer-mtime=@var{date} -To read archive members from the archive and write them into the file -system, use @samp{tar +extract}. The archive itself is left -unchanged. +Like @option{--newer}, but add only files whose +contents have changed (as opposed to just @option{--newer}, which will +also back up files for which any status information has +changed). @xref{after}. -If you do not specify the files to extract, @code{tar} extracts all -the files in the archive. If you specify the name of a directory as a -file-name argument, @code{tar} will extract all files which have been -stored as part of that directory. If a file was stored with a -directory name as part of its file name, and that directory does not -exist under the working directory when the file is extracted, -@code{tar} will create the directory. @xref{Selecting Archive -Members}, for information on specifying files to extract. +@opsummary{no-anchored} +@item --no-anchored +An exclude pattern can match any subsequence of the name's components. +@xref{controlling pattern-matching}. -The following example shows the extraction of the archive -@file{stooges} into an empty directory: +@opsummary{no-auto-compress} +@item --no-auto-compress -@example -tar +extract +file=stooges -@end example +Disables automatic compressed format recognition based on the archive +suffix. @xref{--auto-compress}. @xref{gzip}. -@noindent -Generating a listing of the directory (@samp{ls}) produces: +@opsummary{no-check-device} +@item --no-check-device +Do not check device numbers when creating a list of modified files +for incremental archiving. @xref{device numbers}, for +a detailed description. -@example -larry -moe -shemp -marx -@end example +@opsummary{no-delay-directory-restore} +@item --no-delay-directory-restore -@noindent -The subdirectory @file{marx} contains the files @file{julius}, -@file{alexander} and @file{karl}. +Modification times and permissions of extracted +directories are set when all files from this directory have been +extracted. This is the default. +@xref{Directory Modification Times and Permissions}. -If you wanted to just extract the files in the subdirectory -@file{marx}, you could specify that directory as a file-name argument -in conjunction with the @samp{+extract} operation: +@opsummary{no-ignore-case} +@item --no-ignore-case +Use case-sensitive matching. +@xref{controlling pattern-matching}. -@example -tar +extract +file=stooges marx -@end example +@opsummary{no-ignore-command-error} +@item --no-ignore-command-error +Print warnings about subprocesses that terminated with a nonzero exit +code. @xref{Writing to an External Program}. -@quotation -@strong{Warning:} Extraction can overwrite files in the file system. -To avoid losing files in the file system when extracting files from -the archive with the same name, use the @samp{+keep-old-files} option -(@pxref{File Writing Options}). -@end quotation +@opsummary{no-null} +@item --no-null -If the archive was created using @samp{+block-size}, @samp{+compress} -or @samp{+multi-volume}, you must specify those format options again -when extracting files from the archive (@pxref{Format Variations}). +If the @option{--null} option was given previously, this option +cancels its effect, so that any following @option{--files-from} +options will expect their file lists to be newline-terminated. -@menu -* Archive Reading Options:: -* File Writing Options:: -* Scarce Disk Space:: Recovering From Scarce Disk Space -@end menu +@opsummary{no-overwrite-dir} +@item --no-overwrite-dir -@node Archive Reading Options, File Writing Options, Extracting From Archives, Extracting From Archives -@subsection Options to Help Read Archives -@cindex Options when reading archives -@cindex Reading incomplete blocks -@cindex Blocks, incomplete -@cindex End of archive markers, ignoring -@cindex Ignoring end of archive markers -@cindex Large lists of file names on small machines -@cindex Small memory -@cindex Running out of space +Preserve metadata of existing directories when extracting files +from an archive. @xref{Overwrite Old Files}. -@c <<< each option wants its own node. summary after menu - -Normally, @code{tar} will request data in full block increments from -an archive storage device. If the device cannot return a full block, -@code{tar} will report an error. However, some devices do not always -return full blocks, or do not require the last block of an archive to -be padded out to the next block boundary. To keep reading until you -obtain a full block, or to accept an incomplete block if it contains -an end-of-archive marker, specify the @samp{+read-full-blocks} option -in conjunction with the @samp{+extract} or @samp{+list} operations. -@xref{Listing Contents}. - -The @samp{+read-full-blocks} option is turned on by default when -@code{tar} reads an archive from standard input, or from a remote -machine. This is because on BSD Unix systems, attempting to read a -pipe returns however much happens to be in the pipe, even if it is -less than was requested. If this option were not enabled, @code{tar} -would fail as soon as it read an incomplete block from the pipe. +@opsummary{no-quote-chars} +@item --no-quote-chars=@var{string} +Remove characters listed in @var{string} from the list of quoted +characters set by the previous @option{--quote-chars} option +(@pxref{quoting styles}). -If you're not sure of the blocking factor of an archive, you can read -the archive by specifying @samp{+read-full-blocks} and -@samp{+block-size=@var{n}}, where @var{n} is a blocking factor larger -than the blocking factor of the archive. This lets you avoid having -to determine the blocking factor of an archive. @xref{Blocking -Factor}. +@opsummary{no-recursion} +@item --no-recursion -@table @samp -@item +read-full-blocks -@item -B -Use in conjunction with @samp{tar +extract} to read an archive which -contains incomplete blocks, or one which has a blocking factor less -than the one specified. -@end table +With this option, @command{tar} will not recurse into directories. +@xref{recurse}. -Normally @code{tar} stops reading when it encounters a block of zeros -between file entries (which usually indicates the end of the archive). -@samp{+ignore-zeros} allows @code{tar} to completely read an archive -which contains a block of zeros before the end (i.e.@: a damaged -archive, or one which was created by @code{cat}-ing several archives -together). +@opsummary{no-same-owner} +@item --no-same-owner +@itemx -o -The @samp{+ignore-zeros} option is turned off by default because many -versions of @code{tar} write garbage after the end of archive entry, -since that part of the media is never supposed to be read. GNU -@code{tar} does not write after the end of an archive, but seeks to -maintain compatablity among archiving utilities. +When extracting an archive, do not attempt to preserve the owner +specified in the @command{tar} archive. This the default behavior +for ordinary users. -@table @samp -@item +ignore-zeros -@itemx -i -To ignore blocks of zeros (ie.@: end-of-archive entries) which may be -encountered while reading an archive. Use in conjunction with -@samp{tar +extract} or @samp{tar +list}. -@end table +@opsummary{no-same-permissions} +@item --no-same-permissions -If you are using a machine with a small amount of memory, and you need -to process large list of file-names, you can reduce the amount of -space @code{tar} needs to process the list. To do so, specify the -@samp{+same-order} option and provide an ordered list of file names. -This option tells @code{tar} that the @file{file-name} arguments -(provided on the command line, or read from a file using the -@samp{+files-from} option) are listed in the same order as the files -in the archive. +When extracting an archive, subtract the user's umask from files from +the permissions specified in the archive. This is the default behavior +for ordinary users. -You can create a file containing an ordered list of files in the -archive by storing the output produced by @samp{tar +list -+file=@var{archive-name}}. @xref{Listing Contents}, for information -on the @samp{+list} operation. +@opsummary{no-seek} +@item --no-seek -This option is probably never needed on modern computer systems. +The archive media does not support seeks to arbitrary +locations. Usually @command{tar} determines automatically whether +the archive can be seeked or not. Use this option to disable this +mechanism. -@table @samp -@item +same-order -@itemx +preserve-order -@itemx -s -To process large lists of file-names on machines with small amounts of -memory. Use in conjunction with @samp{tar +compare}, @samp{tar +list} -or @samp{tar +extract}. -@end table +@opsummary{no-unquote} +@item --no-unquote +Treat all input file or member names literally, do not interpret +escape sequences. @xref{input name quoting}. -@c we don't need/want +preserve to exist any more +@opsummary{no-wildcards} +@item --no-wildcards +Do not use wildcards. +@xref{controlling pattern-matching}. -@node File Writing Options, Scarce Disk Space, Archive Reading Options, Extracting From Archives -@subsection Changing How @code{tar} Writes Files -@c <<< find a better title -@cindex Overwriting old files, prevention -@cindex Protecting old files -@cindex Modification times of extracted files -@cindex Permissions of extracted files -@cindex Modes of extracted files -@cindex Writing extracted files to standard output -@cindex Standard output, writing extracted files to +@opsummary{no-wildcards-match-slash} +@item --no-wildcards-match-slash +Wildcards do not match @samp{/}. +@xref{controlling pattern-matching}. -Normally, @code{tar} writes extracted files into the file system -without regard to the files already on the system---files with the -same name as archive members are overwritten. To prevent @code{tar} -from extracting an archive member from an archive, if doing so will -overwrite a file in the file system, use @samp{+keep-old-files} in -conjunction with the @samp{+extract} operation. When this option is -specified, @code{tar} reports an error stating the name of the files -in conflict, instead of writing the file from the archive. +@opsummary{null} +@item --null -@table @samp -@item +keep-old files -@itemx -k -Prevents @code{tar} from overwriting files in the file system during -extraction. -@end table +When @command{tar} is using the @option{--files-from} option, this option +instructs @command{tar} to expect file names terminated with @acronym{NUL}, so +@command{tar} can correctly work with file names that contain newlines. +@xref{nul}. -Normally, @code{tar} sets the modification times of extracted files to -the modification times recorded for the files in the archive, but -limits the permissions of extracted files by the current @code{umask} -setting. +@opsummary{numeric-owner} +@item --numeric-owner -To set the modification times of extracted files to the time when -the files were extracted, use the @samp{+modification-time} option in -conjunction with @samp{tar +extract}. +This option will notify @command{tar} that it should use numeric user +and group IDs when creating a @command{tar} file, rather than names. +@xref{Attributes}. -@table @samp -@item +modification-time -@itemx -m -Sets the modification time of extracted archive members to the time -they were extracted, not the time recorded for them in the archive. -Use in conjunction with @samp{+extract}. -@end table +@item -o +The function of this option depends on the action @command{tar} is +performing. When extracting files, @option{-o} is a synonym for +@option{--no-same-owner}, i.e., it prevents @command{tar} from +restoring ownership of files being extracted. -To set the modes (access permissions) of extracted files to those -recorded for those files in the archive, use the -@samp{+preserve-permissions} option in conjunction with the -@samp{+extract} operation. -@c <<>> should be an example in the tutorial/wizardry section using this -@c >>> to transfer files between systems. +@opsummary{sparse} +@item --sparse +@itemx -S -@c >>> is write access an issue? +Invokes a @acronym{GNU} extension when adding files to an archive that handles +sparse files efficiently. @xref{sparse}. -@table @samp -@item +absolute-paths -Preserves full file names (inclusing superior dirctory names) when -archiving files. Preserves leading slash when extracting files. -@end table +@opsummary{sparse-version} +@item --sparse-version=@var{version} -@node Changing Working Directory, Archiving with Symbolic Links, Absolute File Names, File Name Interpretation -@subsection Changing the Working Directory Within a List of File-names -@cindex Directory, changing in mid-stream -@cindex Working directory, specifying +Specifies the @dfn{format version} to use when archiving sparse +files. Implies @option{--sparse}. @xref{sparse}. For the description +of the supported sparse formats, @xref{Sparse Formats}. -To change working directory in the middle of a list of file names, -(either on the command line or in a file specified using -@samp{+files-from}), use @samp{+directory=@var{directory}}. This will -change the working directory to the directory @var{directory} after -that point in the list. For example, +@opsummary{starting-file} +@item --starting-file=@var{name} +@itemx -K @var{name} -@example -tar +create iggy ziggy +directory=baz melvin -@end example +This option affects extraction only; @command{tar} will skip extracting +files in the archive until it finds one that matches @var{name}. +@xref{Scarce}. + +@opsummary{strip-components} +@item --strip-components=@var{number} +Strip given @var{number} of leading components from file names before +extraction. For example, if archive @file{archive.tar} contained +@file{/some/file/name}, then running + +@smallexample +tar --extract --file archive.tar --strip-components=2 +@end smallexample @noindent -will place the files @file{iggy} and @file{ziggy} from the current -directory into the archive, followed by the file @file{melvin} from -the directory @file{baz}. This option is especially useful when you -have several widely separated files that you want to store in the same -directory in the archive. +would extract this file to file @file{name}. -Note that the file @file{melvin} is recorded in the archive under the -precise name @file{melvin}, @emph{not} @file{baz/melvin}. Thus, the -archive will contain three files that all appear to have come from the -same directory; if the archive is extracted with plain @samp{tar -+extract}, all three files will be written in the current directory. +@opsummary{suffix} +@item --suffix=@var{suffix} -Contrast this with the command +Alters the suffix @command{tar} uses when backing up files from the default +@samp{~}. @xref{backup}. -@example -tar -c iggy ziggy bar/melvin -@end example +@opsummary{tape-length} +@item --tape-length=@var{num}[@var{suf}] +@itemx -L @var{num}[@var{suf}] + +Specifies the length of tapes that @command{tar} is writing as being +@w{@var{num} x 1024} bytes long. If optional @var{suf} is given, it +specifies a multiplicative factor to be used instead of 1024. For +example, @samp{-L2M} means 2 megabytes. @xref{size-suffixes}, for a +list of allowed suffixes. @xref{Using Multiple Tapes}, for a detailed +discussion of this option. + +@opsummary{test-label} +@item --test-label + +Reads the volume label. If an argument is specified, test whether it +matches the volume label. @xref{--test-label option}. + +@opsummary{to-command} +@item --to-command=@var{command} + +During extraction @command{tar} will pipe extracted files to the +standard input of @var{command}. @xref{Writing to an External Program}. + +@opsummary{to-stdout} +@item --to-stdout +@itemx -O + +During extraction, @command{tar} will extract files to stdout rather +than to the file system. @xref{Writing to Standard Output}. + +@opsummary{totals} +@item --totals[=@var{signo}] + +Displays the total number of bytes transferred when processing an +archive. If an argument is given, these data are displayed on +request, when signal @var{signo} is delivered to @command{tar}. +@xref{totals}. + +@opsummary{touch} +@item --touch +@itemx -m + +Sets the data modification time of extracted files to the extraction time, +rather than the data modification time stored in the archive. +@xref{Data Modification Times}. + +@opsummary{transform} +@opsummary{xform} +@item --transform=@var{sed-expr} +@itemx --xform=@var{sed-expr} +Transform file or member names using @command{sed} replacement expression +@var{sed-expr}. For example, + +@smallexample +$ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .} +@end smallexample @noindent -which records the third file in the archive under the name -@file{bar/melvin} so that, if the archive is extracted using @samp{tar -+extract}, the third file will be written in a subdirectory named -@file{bar}. +will add to @file{archive} files from the current working directory, +replacing initial @samp{./} prefix with @samp{usr/}. For the detailed +discussion, @xref{transform}. -@table @samp -@item +directory=@file{directory} -@itemx -C @file{directory} -Changes the working directory. -@end table +To see transformed member names in verbose listings, use +@option{--show-transformed-names} option +(@pxref{show-transformed-names}). -@c <<>> +@item -C @tab @ref{--directory}. -@node User Interaction, Backups and Restoration, Selecting Archive Members, Top -@chapter User Interaction -@cindex Getting more information during the operation -@cindex Information during operation -@cindex Feedback from @code{tar} +@item -F @tab @ref{--info-script}. -Once you have typed a @code{tar}command, it is usually performed -without any further information required of the user, or provided by -@code{tar}. The following options allow you to generate progress and -status information during an operation, or to confirm operations on -files as they are performed. +@item -G @tab @ref{--incremental}. -@menu -* Additional Information:: -* Interactive Operation:: -@end menu +@item -J @tab @ref{--xz}. -@node Additional Information, Interactive Operation, User Interaction, User Interaction -@section Progress and Status Information -@cindex Progress information -@cindex Status information -@cindex Information on progress and status of operations -@cindex Verbose operation -@cindex Record number where error occured -@cindex Error message, record number of -@cindex Version of the @code{tar} program - -Typically, @code{tar} performs most operations without reporting any -information to the user except error messages. If you have -encountered a problem when operating on an archive, however, you may -need more information than just an error message in order to solve the -problem. The following options can be helpful diagnostic tools. - -When used with most operations, @samp{+verbose} causes @code{tar} to -print the file names of the files or archive members it is operating -on. When used with @samp{tar +list}, the verbose option causes -@code{tar} to print out an @samp{ls -l} type listing of the files in -the archive. - -Verbose output appears on the standard output except when an archive -is being written to the standard output (as with @samp{tar +create -+file=- +verbose}). In that case @code{tar} writes verbose output to -the standard error stream. +@item -K @tab @ref{--starting-file}. -@table @samp -@item +verbose -@itemx -v -Prints the names of files or archive members as they are being -operated on. Can be used in conjunction with any operation. When -used with @samp{+list}, generates an @samp{ls -l} type listing. -@end table +@item -L @tab @ref{--tape-length}. -To find out where in an archive a message was triggered, use -@samp{+record-number}. @samp{+record-number} causes @code{tar} to -print, along with every message it produces, the record number within -the archive where the message was triggered. +@item -M @tab @ref{--multi-volume}. -This option is especially useful when reading damaged archives, since -it helps pinpoint the damaged sections. It can also be used with -@samp{tar +list} when listing a file-system backup tape, allowing you -to choose among several backup tapes when retrieving a file later, in -favor of the tape where the file appears earliest (closest to the -front of the tape). -@c <<< xref when the node name is set and the backup section written +@item -N @tab @ref{--newer}. -@table @samp -@item +record-number -@itemx -R -Prints the record number whenever a message is generated by -@code{tar}. Use in conjunction with any operation. -@end table +@item -O @tab @ref{--to-stdout}. -@c rewrite below -To print the version number of the @code{tar} program, use @samp{tar -+version}. @code{tar} prints the version number to the standard -error. For example: +@item -P @tab @ref{--absolute-names}. -@example -tar +version -@end example +@item -R @tab @ref{--block-number}. -@noindent -might return: +@item -S @tab @ref{--sparse}. -@example -GNU tar version 1.09 -@end example -@c used to be an option. has been fixed. +@item -T @tab @ref{--files-from}. -@node Interactive Operation, , Additional Information, User Interaction -@section Asking for Confirmation During Operations -@cindex Interactive operation +@item -U @tab @ref{--unlink-first}. -Typically, @code{tar} carries out a command without stopping for -further instructions. In some situations however, you -may want to exclude some files and archive members from the operation -(for instance if disk or storage space is tight). You can do this by -excluding certain files automatically (@pxref{File Exclusion}), or by -performing an operation interactively, using the @samp{+interactive} -operation. - -When the @samp{+interactive} option is specified, @code{tar} asks for -confirmation before reading, writing, or deleting each file it -encounters while carrying out an operation. To confirm the action you -must type a line of input beginning with @samp{y}. If your input line -begins with anything other than @samp{y}, @code{tar} skips that file. - -Commands which might be useful to perform interactively include -appending files to an archive, extracting files from an archive, -deleting a file from an archive, and deleting a file from disk during -an incremental restore. - -If @code{tar} is reading the archive from the standard input, -@code{tar} opens the file @file{/dev/tty} to support the interactive -communications. -<<< this aborts if you won't OK the working directory. this is a bug. -ringo +@item -V @tab @ref{--label}. -@table @samp -@item +interactive -@itemx +confirmation -@itemx -w -Asks for confirmation before reading, writing or deleting an archive -member (when listing, comparing or writing an archive or deleting -archive members), or before writing or deleting a file (when -extracting an archive). -@end table +@item -W @tab @ref{--verify}. -@node Backups and Restoration, Media, User Interaction, Top -@chapter Performing Backups and Restoring Files +@item -X @tab @ref{--exclude-from}. -To @dfn{back up} a file system means to create archives that contain -all the files in that file system. Those archives can then be used to -restore any or all of those files (for instance if a disk crashes or a -file is accidently deleted). File system @dfn{backups} are also -called @dfn{dumps}. +@item -Z @tab @ref{--compress}. -@menu -* Backup Levels:: Levels of backups -* Backup Scripts:: Using scripts to perform backups - and restoration -* incremental and listed-incremental:: The +incremental - and +listed-incremental Options -* Problems:: Some common problems and their solutions -@end menu +@item -b @tab @ref{--blocking-factor}. -@node Backup Levels, Backup Scripts, Backups and Restoration, Backups and Restoration -@section Levels of Backups +@item -c @tab @ref{--create}. -An archive containing all the files in the file system is called a -@dfn{full backup} or @dfn{full dump}. You could insure your data by -creating a full dump every day. This strategy, however, would waste a -substantial amount of archive media and user time, as unchanged files -are daily re-archived. +@item -d @tab @ref{--compare}. -It is more efficient to do a full dump only occasionally. To back up -files between full dumps, you can a incremental dump. A @dfn{level -one} dump archives all the files that have changed since the last full -dump. +@item -f @tab @ref{--file}. -A typical dump strategy would be to perform a full dump once a week, -and a level one dump once a day. This means some versions of files -will in fact be archived more than once, but this dump strategy makes -it possible to restore a file system to within one day of accuracy by -only extracting two archives---the last weekly (full) dump and the -last daily (level one) dump. The only information lost would be in -files changed or created since the last daily backup. (Doing dumps -more than once a day is usually not worth the trouble). +@item -g @tab @ref{--listed-incremental}. -@node Backup Scripts, incremental and listed-incremental, Backup Levels, Backups and Restoration -@section Using Scripts to Perform Backups and Restoration +@item -h @tab @ref{--dereference}. -GNU @code{tar} comes with scripts you can use to do full and level-one -dumps. Using scripts (shell programs) to perform backups and -restoration is a convenient and reliable alternative to typing out -file name lists and @code{tar} commands by hand. +@item -i @tab @ref{--ignore-zeros}. -Before you use these scripts, you need to edit the file -@file{backup-specs}, which specifies parameters used by the backup -scripts and by the restore script. @xref{Script Syntax}. -Once the backup parameters are set, you can perform backups or -restoration by running the appropriate script. - -The name of the restore script is @code{restore}. The names of the -level one and full backup scripts are, respectively, @code{level-1} and -@code{level-0}. The @code{level-0} script also exists under the name -@code{weekly}, and the @code{level-1} under the name -@code{daily}---these additional names can be changed according to your -backup schedule. @xref{Scripted Restoration}, for more information -on running the restoration script. @xref{Scripted Backups}, for more -information on running the backup scripts. - -@emph{Please Note:} The backup scripts and the restoration scripts are -designed to be used together. While it is possible to restore files -by hand from an archive which was created using a backup script, and -to create an archive by hand which could then be extracted using the -restore script, it is easier to use the scripts. @xref{incremental -and listed-incremental}, before making such an attempt. - -@c shorten node names -@menu -* Backup Parameters:: Setting parameters for backups and restoration -* Scripted Backups:: Using the backup scripts -* Scripted Restoration:: Using the restore script -@end menu +@item -j @tab @ref{--bzip2}. -@node Backup Parameters, Scripted Backups, Backup Scripts, Backup Scripts -@subsection Setting Parameters for Backups and Restoration +@item -k @tab @ref{--keep-old-files}. -The file @file{backup-specs} specifies backup parameters for the -backup and restoration scripts provided with @code{tar}. You must -edit @file{backup-specs} to fit your system configuration and schedule -before using these scripts. +@item -l @tab @ref{--check-links}. -@c <<< This about backup scripts needs to be written: -@c <<. +This is free software: you are free to change and redistribute it. +There is NO WARRANTY, to the extent permitted by law. + +Written by John Gilmore and Jay Fenlason. +@end smallexample + +@noindent +The first occurrence of @samp{tar} in the result above is the program +name in the package (for example, @command{rmt} is another program), +while the second occurrence of @samp{tar} is the name of the package +itself, containing possibly many programs. The package is currently +named @samp{tar}, after the name of the main program it +contains@footnote{There are plans to merge the @command{cpio} and +@command{tar} packages into a single one which would be called +@code{paxutils}. So, who knows if, one of this days, the +@option{--version} would not output @w{@samp{tar (@acronym{GNU} +paxutils) 3.2}}.}. + +@cindex Obtaining help +@cindex Listing all @command{tar} options +@xopindex{help, introduction} +Another thing you might want to do is checking the spelling or meaning +of some particular @command{tar} option, without resorting to this +manual, for once you have carefully read it. @GNUTAR{} +has a short help feature, triggerable through the +@option{--help} option. By using this option, @command{tar} will +print a usage message listing all available options on standard +output, then exit successfully, without doing anything else and +ignoring all other options. Even if this is only a brief summary, it +may be several screens long. So, if you are not using some kind of +scrollable window, you might prefer to use something like: + +@smallexample +$ @kbd{tar --help | less} +@end smallexample + +@noindent +presuming, here, that you like using @command{less} for a pager. Other +popular pagers are @command{more} and @command{pg}. If you know about some +@var{keyword} which interests you and do not want to read all the +@option{--help} output, another common idiom is doing: + +@smallexample +tar --help | grep @var{keyword} +@end smallexample + +@noindent +for getting only the pertinent lines. Notice, however, that some +@command{tar} options have long description lines and the above +command will list only the first of them. + +The exact look of the option summary displayed by @kbd{tar --help} is +configurable. @xref{Configuring Help Summary}, for a detailed description. + +@opindex usage +If you only wish to check the spelling of an option, running @kbd{tar +--usage} may be a better choice. This will display a terse list of +@command{tar} options without accompanying explanations. + +The short help output is quite succinct, and you might have to get +back to the full documentation for precise points. If you are reading +this paragraph, you already have the @command{tar} manual in some +form. This manual is available in a variety of forms from +@url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{} +distribution, provided you have @TeX{} already installed somewhere, +and a laser printer around. Just configure the distribution, execute +the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the +usual way (contact your local guru to know how). If @GNUTAR{} +has been conveniently installed at your place, this +manual is also available in interactive, hypertextual form as an Info +file. Just call @w{@samp{info tar}} or, if you do not have the +@command{info} program handy, use the Info reader provided within +@acronym{GNU} Emacs, calling @samp{tar} from the main Info menu. + +There is currently no @code{man} page for @GNUTAR{}. +If you observe such a @code{man} page on the system you are running, +either it does not belong to @GNUTAR{}, or it has not +been produced by @acronym{GNU}. Some package maintainers convert +@kbd{tar --help} output to a man page, using @command{help2man}. In +any case, please bear in mind that the authoritative source of +information about @GNUTAR{} is this Texinfo documentation. + +@node defaults +@section Obtaining @GNUTAR{} default values + +@opindex show-defaults +@GNUTAR{} has some predefined defaults that are used when you do not +explicitly specify another values. To obtain a list of such +defaults, use @option{--show-defaults} option. This will output the +values in the form of @command{tar} command line options: + +@smallexample +@group +$ @kbd{tar --show-defaults} +--format=gnu -f- -b20 --quoting-style=escape +--rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh +@end group +@end smallexample + +@noindent +Notice, that this option outputs only one line. The example output above +has been split to fit page boundaries. -@item BACKUP_FILES -A list of individual files to be dumped. These should be accessible -from the machine on which the backup script is run. -@c << small-files} +$ @kbd{tar -c -v -z -T small-files -f little.tgz} +@end smallexample + +@noindent +In the file list given by @option{-T} option, any file name beginning +with @samp{-} character is considered a @command{tar} option and is +processed accordingly@footnote{Versions of @GNUTAR{} up to 1.15.1 +recognized only @option{-C} option in file lists, and only if the +option and its argument occupied two consecutive lines.}. For example, +the common use of this feature is to change to another directory by +specifying @option{-C} option: + +@smallexample +@group +$ @kbd{cat list} +-C/etc +passwd +hosts +-C/lib +libc.a +$ @kbd{tar -c -f foo.tar --files-from list} +@end group +@end smallexample + +@noindent +In this example, @command{tar} will first switch to @file{/etc} +directory and add files @file{passwd} and @file{hosts} to the +archive. Then it will change to @file{/lib} directory and will archive +the file @file{libc.a}. Thus, the resulting archive @file{foo.tar} will +contain: + +@smallexample +@group +$ @kbd{tar tf foo.tar} +passwd +hosts +libc.a +@end group +@end smallexample + +@noindent +@xopindex{directory, using in @option{--files-from} argument} +Notice that the option parsing algorithm used with @option{-T} is +stricter than the one used by shell. Namely, when specifying option +arguments, you should observe the following rules: + +@itemize @bullet +@item +When using short (single-letter) option form, its argument must +immediately follow the option letter, without any intervening +whitespace. For example: @code{-Cdir}. + +@item +When using long option form, the option argument must be separated +from the option by a single equal sign. No whitespace is allowed on +any side of the equal sign. For example: @code{--directory=dir}. + +@item +For both short and long option forms, the option argument can be given +on the next line after the option name, e.g.: + +@smallexample +@group +--directory +dir +@end group +@end smallexample + +@noindent +and + +@smallexample +@group +-C +dir +@end group +@end smallexample +@end itemize + +@opindex add-file +If you happen to have a file whose name starts with @samp{-}, +precede it with @option{--add-file} option to prevent it from +being recognized as an option. For example: @code{--add-file=--my-file}. + +@menu +* nul:: +@end menu + +@node nul +@subsection @code{NUL}-Terminated File Names + +@cindex File names, terminated by @code{NUL} +@cindex @code{NUL}-terminated file names +The @option{--null} option causes +@option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) +to read file names terminated by a @code{NUL} instead of a newline, so +files whose names contain newlines can be archived using +@option{--files-from}. + +@table @option +@xopindex{null, described} +@item --null +Only consider @code{NUL}-terminated file names, instead of files that +terminate in a newline. + +@xopindex{no-null, described} +@item --no-null +Undo the effect of any previous @option{--null} option. +@end table + +The @option{--null} option is just like the one in @acronym{GNU} +@command{xargs} and @command{cpio}, and is useful with the +@option{-print0} predicate of @acronym{GNU} @command{find}. In +@command{tar}, @option{--null} also disables special handling for +file names that begin with dash. + +This example shows how to use @command{find} to generate a list of files +larger than 800K in length and put that list into a file called +@file{long-files}. The @option{-print0} option to @command{find} is just +like @option{-print}, except that it separates files with a @code{NUL} +rather than with a newline. You can then run @command{tar} with both the +@option{--null} and @option{-T} options to specify that @command{tar} gets the +files from that file, @file{long-files}, to create the archive +@file{big.tgz}. The @option{--null} option to @command{tar} will cause +@command{tar} to recognize the @code{NUL} separator between files. + +@smallexample +$ @kbd{find . -size +800 -print0 > long-files} +$ @kbd{tar -c -v --null --files-from=long-files --file=big.tar} +@end smallexample + +The @option{--no-null} option can be used if you need to read both +@code{NUL}-terminated and newline-terminated files on the same command line. +For example, if @file{flist} is a newline-terminated file, then the +following command can be used to combine it with the above command: + +@smallexample +@group +$ @kbd{find . -size +800 -print0 | + tar -c -f big.tar --null -T - --no-null -T flist} +@end group +@end smallexample + +This example uses short options for typographic reasons, to avoid +very long lines. + +@GNUTAR is able to automatically detect @code{NUL}-terminated file lists, so +it is safe to use them even without the @option{--null} option. In +this case @command{tar} will print a warning and continue reading such +a file as if @option{--null} were actually given: + +@smallexample +@group +$ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -} +tar: -: file name read contains nul character +@end group +@end smallexample + +The null terminator, however, remains in effect only for this +particular file, any following @option{-T} options will assume +newline termination. Of course, the null autodetection applies +to these eventual surplus @option{-T} options as well. + +@node exclude +@section Excluding Some Files + +@cindex File names, excluding files by +@cindex Excluding files by name and pattern +@cindex Excluding files by file system +@opindex exclude +@opindex exclude-from +To avoid operating on files whose names match a particular pattern, +use the @option{--exclude} or @option{--exclude-from} options. + +@table @option +@opindex exclude +@item --exclude=@var{pattern} +Causes @command{tar} to ignore files that match the @var{pattern}. +@end table + +@findex exclude +The @option{--exclude=@var{pattern}} option prevents any file or +member whose name matches the shell wildcard (@var{pattern}) from +being operated on. +For example, to create an archive with all the contents of the directory +@file{src} except for files whose names end in @file{.o}, use the +command @samp{tar -cf src.tar --exclude='*.o' src}. + +You may give multiple @option{--exclude} options. + +@table @option +@opindex exclude-from +@item --exclude-from=@var{file} +@itemx -X @var{file} +Causes @command{tar} to ignore files that match the patterns listed in +@var{file}. +@end table + +@findex exclude-from +Use the @option{--exclude-from} option to read a +list of patterns, one per line, from @var{file}; @command{tar} will +ignore files matching those patterns. Thus if @command{tar} is +called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a +single line @file{*.o}, no files whose names end in @file{.o} will be +added to the archive. + +Notice, that lines from @var{file} are read verbatim. One of the +frequent errors is leaving some extra whitespace after a file name, +which is difficult to catch using text editors. + +However, empty lines are OK. + +@table @option +@cindex version control system, excluding files +@cindex VCS, excluding files +@cindex SCCS, excluding files +@cindex RCS, excluding files +@cindex CVS, excluding files +@cindex SVN, excluding files +@cindex git, excluding files +@cindex Bazaar, excluding files +@cindex Arch, excluding files +@cindex Mercurial, excluding files +@cindex Darcs, excluding files +@opindex exclude-vcs +@item --exclude-vcs +Exclude files and directories used by following version control +systems: @samp{CVS}, @samp{RCS}, @samp{SCCS}, @samp{SVN}, @samp{Arch}, +@samp{Bazaar}, @samp{Mercurial}, and @samp{Darcs}. + +As of version @value{VERSION}, the following files are excluded: + +@itemize @bullet +@item @file{CVS/}, and everything under it +@item @file{RCS/}, and everything under it +@item @file{SCCS/}, and everything under it +@item @file{.git/}, and everything under it +@item @file{.gitignore} +@item @file{.cvsignore} +@item @file{.svn/}, and everything under it +@item @file{.arch-ids/}, and everything under it +@item @file{@{arch@}/}, and everything under it +@item @file{=RELEASE-ID} +@item @file{=meta-update} +@item @file{=update} +@item @file{.bzr} +@item @file{.bzrignore} +@item @file{.bzrtags} +@item @file{.hg} +@item @file{.hgignore} +@item @file{.hgrags} +@item @file{_darcs} +@end itemize + +@opindex exclude-backups +@item --exclude-backups +Exclude backup and lock files. This option causes exclusion of files +that match the following shell globbing patterns: + +@table @asis +@item .#* +@item *~ +@item #*# +@end table + +@end table + +@findex exclude-caches +When creating an archive, the @option{--exclude-caches} option family +causes @command{tar} to exclude all directories that contain a @dfn{cache +directory tag}. A cache directory tag is a short file with the +well-known name @file{CACHEDIR.TAG} and having a standard header +specified in @url{http://www.brynosaurus.com/cachedir/spec.html}. +Various applications write cache directory tags into directories they +use to hold regenerable, non-precious data, so that such data can be +more easily excluded from backups. + +There are three @samp{exclude-caches} options, each providing a different +exclusion semantics: + +@table @option +@opindex exclude-caches +@item --exclude-caches +Do not archive the contents of the directory, but archive the +directory itself and the @file{CACHEDIR.TAG} file. + +@opindex exclude-caches-under +@item --exclude-caches-under +Do not archive the contents of the directory, nor the +@file{CACHEDIR.TAG} file, archive only the directory itself. + +@opindex exclude-caches-all +@item --exclude-caches-all +Omit directories containing @file{CACHEDIR.TAG} file entirely. +@end table + +@findex exclude-tag +Another option family, @option{--exclude-tag}, provides a generalization of +this concept. It takes a single argument, a file name to look for. +Any directory that contains this file will be excluded from the dump. +Similarly to @samp{exclude-caches}, there are three options in this +option family: + +@table @option +@opindex exclude-tag +@item --exclude-tag=@var{file} +Do not dump the contents of the directory, but dump the +directory itself and the @var{file}. + +@opindex exclude-tag-under +@item --exclude-tag-under=@var{file} +Do not dump the contents of the directory, nor the +@var{file}, archive only the directory itself. + +@opindex exclude-tag-all +@item --exclude-tag-all=@var{file} +Omit directories containing @var{file} file entirely. +@end table + +Multiple @option{--exclude-tag*} options can be given. + +For example, given this directory: + +@smallexample +@group +$ @kbd{find dir} +dir +dir/blues +dir/jazz +dir/folk +dir/folk/tagfile +dir/folk/sanjuan +dir/folk/trote +@end group +@end smallexample + +The @option{--exclude-tag} will produce the following: + +@smallexample +$ @kbd{tar -cf archive.tar --exclude-tag=tagfile -v dir} +dir/ +dir/blues +dir/jazz +dir/folk/ +tar: dir/folk/: contains a cache directory tag tagfile; + contents not dumped +dir/folk/tagfile +@end smallexample + +Both the @file{dir/folk} directory and its tagfile are preserved in +the archive, however the rest of files in this directory are not. + +Now, using the @option{--exclude-tag-under} option will exclude +@file{tagfile} from the dump, while still preserving the directory +itself, as shown in this example: + +@smallexample +$ @kbd{tar -cf archive.tar --exclude-tag-under=tagfile -v dir} +dir/ +dir/blues +dir/jazz +dir/folk/ +./tar: dir/folk/: contains a cache directory tag tagfile; + contents not dumped +@end smallexample + +Finally, using @option{--exclude-tag-all} omits the @file{dir/folk} +directory entirely: + +@smallexample +$ @kbd{tar -cf archive.tar --exclude-tag-all=tagfile -v dir} +dir/ +dir/blues +dir/jazz +./tar: dir/folk/: contains a cache directory tag tagfile; + directory not dumped +@end smallexample + +@menu +* problems with exclude:: +@end menu + +@node problems with exclude +@unnumberedsubsec Problems with Using the @code{exclude} Options + +@xopindex{exclude, potential problems with} +Some users find @samp{exclude} options confusing. Here are some common +pitfalls: + +@itemize @bullet +@item +The main operating mode of @command{tar} does not act on a file name +explicitly listed on the command line, if one of its file name +components is excluded. In the example above, if +you create an archive and exclude files that end with @samp{*.o}, but +explicitly name the file @samp{dir.o/foo} after all the options have been +listed, @samp{dir.o/foo} will be excluded from the archive. + +@item +You can sometimes confuse the meanings of @option{--exclude} and +@option{--exclude-from}. Be careful: use @option{--exclude} when files +to be excluded are given as a pattern on the command line. Use +@option{--exclude-from} to introduce the name of a file which contains +a list of patterns, one per line; each of these patterns can exclude +zero, one, or many files. + +@item +When you use @option{--exclude=@var{pattern}}, be sure to quote the +@var{pattern} parameter, so @GNUTAR{} sees wildcard characters +like @samp{*}. If you do not do this, the shell might expand the +@samp{*} itself using files at hand, so @command{tar} might receive a +list of files instead of one pattern, or none at all, making the +command somewhat illegal. This might not correspond to what you want. + +For example, write: + +@smallexample +$ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}} +@end smallexample + +@noindent +rather than: + +@smallexample +# @emph{Wrong!} +$ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}} +@end smallexample + +@item +You must use use shell syntax, or globbing, rather than @code{regexp} +syntax, when using exclude options in @command{tar}. If you try to use +@code{regexp} syntax to describe files to be excluded, your command +might fail. + +@item +@FIXME{The change in semantics must have occurred before 1.11, +so I doubt if it is worth mentioning at all. Anyway, should at +least specify in which version the semantics changed.} +In earlier versions of @command{tar}, what is now the +@option{--exclude-from} option was called @option{--exclude} instead. +Now, @option{--exclude} applies to patterns listed on the command +line and @option{--exclude-from} applies to patterns listed in a +file. + +@end itemize + +@node wildcards +@section Wildcards Patterns and Matching + +@dfn{Globbing} is the operation by which @dfn{wildcard} characters, +@samp{*} or @samp{?} for example, are replaced and expanded into all +existing files matching the given pattern. @GNUTAR{} can use wildcard +patterns for matching (or globbing) archive members when extracting +from or listing an archive. Wildcard patterns are also used for +verifying volume labels of @command{tar} archives. This section has the +purpose of explaining wildcard syntax for @command{tar}. + +@FIXME{the next few paragraphs need work.} + +A @var{pattern} should be written according to shell syntax, using wildcard +characters to effect globbing. Most characters in the pattern stand +for themselves in the matched string, and case is significant: @samp{a} +will match only @samp{a}, and not @samp{A}. The character @samp{?} in the +pattern matches any single character in the matched string. The character +@samp{*} in the pattern matches zero, one, or more single characters in +the matched string. The character @samp{\} says to take the following +character of the pattern @emph{literally}; it is useful when one needs to +match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves. + +The character @samp{[}, up to the matching @samp{]}, introduces a character +class. A @dfn{character class} is a list of acceptable characters +for the next single character of the matched string. For example, +@samp{[abcde]} would match any of the first five letters of the alphabet. +Note that within a character class, all of the ``special characters'' +listed above other than @samp{\} lose their special meaning; for example, +@samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\}, +@samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints, +the characters @samp{-} and @samp{]} must either come @emph{first} or +@emph{last} in a character class.) + +@cindex Excluding characters from a character class +@cindex Character class, excluding characters from +If the first character of the class after the opening @samp{[} +is @samp{!} or @samp{^}, then the meaning of the class is reversed. +Rather than listing character to match, it lists those characters which +are @emph{forbidden} as the next single character of the matched string. + +Other characters of the class stand for themselves. The special +construction @samp{[@var{a}-@var{e}]}, using an hyphen between two +letters, is meant to represent all characters between @var{a} and +@var{e}, inclusive. + +@FIXME{need to add a sentence or so here to make this clear for those +who don't have dan around.} + +Periods (@samp{.}) or forward slashes (@samp{/}) are not considered +special for wildcard matches. However, if a pattern completely matches +a directory prefix of a matched string, then it matches the full matched +string: thus, excluding a directory also excludes all the files beneath it. + +@menu +* controlling pattern-matching:: +@end menu + +@node controlling pattern-matching +@unnumberedsubsec Controlling Pattern-Matching + +For the purposes of this section, we call @dfn{exclusion members} all +member names obtained while processing @option{--exclude} and +@option{--exclude-from} options, and @dfn{inclusion members} those +member names that were given in the command line or read from the file +specified with @option{--files-from} option. + +These two pairs of member lists are used in the following operations: +@option{--diff}, @option{--extract}, @option{--list}, +@option{--update}. + +There are no inclusion members in create mode (@option{--create} and +@option{--append}), since in this mode the names obtained from the +command line refer to @emph{files}, not archive members. + +By default, inclusion members are compared with archive members +literally @footnote{Notice that earlier @GNUTAR{} versions used +globbing for inclusion members, which contradicted to UNIX98 +specification and was not documented. @xref{Changes}, for more +information on this and other changes.} and exclusion members are +treated as globbing patterns. For example: + +@smallexample +@group +$ @kbd{tar tf foo.tar} +a.c +b.c +a.txt +[remarks] +# @i{Member names are used verbatim:} +$ @kbd{tar -xf foo.tar -v '[remarks]'} +[remarks] +# @i{Exclude member names are globbed:} +$ @kbd{tar -xf foo.tar -v --exclude '*.c'} +a.txt +[remarks] +@end group +@end smallexample + +This behavior can be altered by using the following options: + +@table @option +@opindex wildcards +@item --wildcards +Treat all member names as wildcards. + +@opindex no-wildcards +@item --no-wildcards +Treat all member names as literal strings. +@end table + +Thus, to extract files whose names end in @samp{.c}, you can use: + +@smallexample +$ @kbd{tar -xf foo.tar -v --wildcards '*.c'} +a.c +b.c +@end smallexample + +@noindent +Notice quoting of the pattern to prevent the shell from interpreting +it. + +The effect of @option{--wildcards} option is canceled by +@option{--no-wildcards}. This can be used to pass part of +the command line arguments verbatim and other part as globbing +patterns. For example, the following invocation: + +@smallexample +$ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'} +@end smallexample + +@noindent +instructs @command{tar} to extract from @file{foo.tar} all files whose +names end in @samp{.txt} and the file named @file{[remarks]}. + +Normally, a pattern matches a name if an initial subsequence of the +name's components matches the pattern, where @samp{*}, @samp{?}, and +@samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards, +and wildcards can match @samp{/}. + +Other than optionally stripping leading @samp{/} from names +(@pxref{absolute}), patterns and names are used as-is. For +example, trailing @samp{/} is not trimmed from a user-specified name +before deciding whether to exclude it. + +However, this matching procedure can be altered by the options listed +below. These options accumulate. For example: + +@smallexample +--ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme' +@end smallexample + +@noindent +ignores case when excluding @samp{makefile}, but not when excluding +@samp{readme}. + +@table @option +@opindex anchored +@opindex no-anchored +@item --anchored +@itemx --no-anchored +If anchored, a pattern must match an initial subsequence +of the name's components. Otherwise, the pattern can match any +subsequence. Default is @option{--no-anchored} for exclusion members +and @option{--anchored} inclusion members. + +@opindex ignore-case +@opindex no-ignore-case +@item --ignore-case +@itemx --no-ignore-case +When ignoring case, upper-case patterns match lower-case names and vice versa. +When not ignoring case (the default), matching is case-sensitive. + +@opindex wildcards-match-slash +@opindex no-wildcards-match-slash +@item --wildcards-match-slash +@itemx --no-wildcards-match-slash +When wildcards match slash (the default for exclusion members), a +wildcard like @samp{*} in the pattern can match a @samp{/} in the +name. Otherwise, @samp{/} is matched only by @samp{/}. + +@end table + +The @option{--recursion} and @option{--no-recursion} options +(@pxref{recurse}) also affect how member patterns are interpreted. If +recursion is in effect, a pattern matches a name if it matches any of +the name's parent directories. + +The following table summarizes pattern-matching default values: + +@multitable @columnfractions .3 .7 +@headitem Members @tab Default settings +@item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash} +@item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash} +@end multitable + +@node quoting styles +@section Quoting Member Names + +When displaying member names, @command{tar} takes care to avoid +ambiguities caused by certain characters. This is called @dfn{name +quoting}. The characters in question are: + +@itemize @bullet +@item Non-printable control characters: +@anchor{escape sequences} +@multitable @columnfractions 0.20 0.10 0.60 +@headitem Character @tab @acronym{ASCII} @tab Character name +@item \a @tab 7 @tab Audible bell +@item \b @tab 8 @tab Backspace +@item \f @tab 12 @tab Form feed +@item \n @tab 10 @tab New line +@item \r @tab 13 @tab Carriage return +@item \t @tab 9 @tab Horizontal tabulation +@item \v @tab 11 @tab Vertical tabulation +@end multitable + +@item Space (@acronym{ASCII} 32) + +@item Single and double quotes (@samp{'} and @samp{"}) + +@item Backslash (@samp{\}) +@end itemize + +The exact way @command{tar} uses to quote these characters depends on +the @dfn{quoting style}. The default quoting style, called +@dfn{escape} (see below), uses backslash notation to represent control +characters, space and backslash. Using this quoting style, control +characters are represented as listed in column @samp{Character} in the +above table, a space is printed as @samp{\ } and a backslash as @samp{\\}. + +@GNUTAR{} offers seven distinct quoting styles, which can be selected +using @option{--quoting-style} option: + +@table @option +@item --quoting-style=@var{style} +@opindex quoting-style + +Sets quoting style. Valid values for @var{style} argument are: +literal, shell, shell-always, c, escape, locale, clocale. +@end table + +These styles are described in detail below. To illustrate their +effect, we will use an imaginary tar archive @file{arch.tar} +containing the following members: + +@smallexample +@group +# 1. Contains horizontal tabulation character. +a tab +# 2. Contains newline character +a +newline +# 3. Contains a space +a space +# 4. Contains double quotes +a"double"quote +# 5. Contains single quotes +a'single'quote +# 6. Contains a backslash character: +a\backslash +@end group +@end smallexample + +Here is how usual @command{ls} command would have listed them, if they +had existed in the current working directory: + +@smallexample +@group +$ @kbd{ls} +a\ttab +a\nnewline +a\ space +a"double"quote +a'single'quote +a\\backslash +@end group +@end smallexample + +Quoting styles: + +@table @samp +@item literal +No quoting, display each character as is: + +@smallexample +@group +$ @kbd{tar tf arch.tar --quoting-style=literal} +./ +./a space +./a'single'quote +./a"double"quote +./a\backslash +./a tab +./a +newline +@end group +@end smallexample + +@item shell +Display characters the same way Bourne shell does: +control characters, except @samp{\t} and @samp{\n}, are printed using +backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a +single quote is printed as @samp{\'}. If a name contains any quoted +characters, it is enclosed in single quotes. In particular, if a name +contains single quotes, it is printed as several single-quoted strings: + +@smallexample +@group +$ @kbd{tar tf arch.tar --quoting-style=shell} +./ +'./a space' +'./a'\''single'\''quote' +'./a"double"quote' +'./a\backslash' +'./a tab' +'./a +newline' +@end group +@end smallexample + +@item shell-always +Same as @samp{shell}, but the names are always enclosed in single +quotes: + +@smallexample +@group +$ @kbd{tar tf arch.tar --quoting-style=shell-always} +'./' +'./a space' +'./a'\''single'\''quote' +'./a"double"quote' +'./a\backslash' +'./a tab' +'./a +newline' +@end group +@end smallexample + +@item c +Use the notation of the C programming language. All names are +enclosed in double quotes. Control characters are quoted using +backslash notations, double quotes are represented as @samp{\"}, +backslash characters are represented as @samp{\\}. Single quotes and +spaces are not quoted: + +@smallexample +@group +$ @kbd{tar tf arch.tar --quoting-style=c} +"./" +"./a space" +"./a'single'quote" +"./a\"double\"quote" +"./a\\backslash" +"./a\ttab" +"./a\nnewline" +@end group +@end smallexample + +@item escape +Control characters are printed using backslash notation, a space is +printed as @samp{\ } and a backslash as @samp{\\}. This is the +default quoting style, unless it was changed when configured the +package. + +@smallexample +@group +$ @kbd{tar tf arch.tar --quoting-style=escape} +./ +./a space +./a'single'quote +./a"double"quote +./a\\backslash +./a\ttab +./a\nnewline +@end group +@end smallexample + +@item locale +Control characters, single quote and backslash are printed using +backslash notation. All names are quoted using left and right +quotation marks, appropriate to the current locale. If it does not +define quotation marks, use @samp{'} as left and as right +quotation marks. Any occurrences of the right quotation mark in a +name are escaped with @samp{\}, for example: + +For example: + +@smallexample +@group +$ @kbd{tar tf arch.tar --quoting-style=locale} +'./' +'./a space' +'./a\'single\'quote' +'./a"double"quote' +'./a\\backslash' +'./a\ttab' +'./a\nnewline' +@end group +@end smallexample + +@item clocale +Same as @samp{locale}, but @samp{"} is used for both left and right +quotation marks, if not provided by the currently selected locale: + +@smallexample +@group +$ @kbd{tar tf arch.tar --quoting-style=clocale} +"./" +"./a space" +"./a'single'quote" +"./a\"double\"quote" +"./a\\backslash" +"./a\ttab" +"./a\nnewline" +@end group +@end smallexample +@end table + +You can specify which characters should be quoted in addition to those +implied by the current quoting style: + +@table @option +@item --quote-chars=@var{string} +Always quote characters from @var{string}, even if the selected +quoting style would not quote them. +@end table + +For example, using @samp{escape} quoting (compare with the usual +escape listing above): + +@smallexample +@group +$ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'} +./ +./a\ space +./a'single'quote +./a\"double\"quote +./a\\backslash +./a\ttab +./a\nnewline +@end group +@end smallexample + +To disable quoting of such additional characters, use the following +option: + +@table @option +@item --no-quote-chars=@var{string} +Remove characters listed in @var{string} from the list of quoted +characters set by the previous @option{--quote-chars} option. +@end table + +This option is particularly useful if you have added +@option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS}) +and wish to disable it for the current invocation. + +Note, that @option{--no-quote-chars} does @emph{not} disable those +characters that are quoted by default in the selected quoting style. + +@node transform +@section Modifying File and Member Names + +@command{Tar} archives contain detailed information about files stored +in them and full file names are part of that information. When +storing a file to an archive, its file name is recorded in it, +along with the actual file contents. When restoring from an archive, +a file is created on disk with exactly the same name as that stored +in the archive. In the majority of cases this is the desired behavior +of a file archiver. However, there are some cases when it is not. + +First of all, it is often unsafe to extract archive members with +absolute file names or those that begin with a @file{../}. @GNUTAR{} +takes special precautions when extracting such names and provides a +special option for handling them, which is described in +@ref{absolute}. + +Secondly, you may wish to extract file names without some leading +directory components, or with otherwise modified names. In other +cases it is desirable to store files under differing names in the +archive. + +@GNUTAR{} provides several options for these needs. + +@table @option +@opindex strip-components +@item --strip-components=@var{number} +Strip given @var{number} of leading components from file names before +extraction. +@end table + +For example, suppose you have archived whole @file{/usr} hierarchy to +a tar archive named @file{usr.tar}. Among other files, this archive +contains @file{usr/include/stdlib.h}, which you wish to extract to +the current working directory. To do so, you type: + +@smallexample +$ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h} +@end smallexample + +The option @option{--strip=2} instructs @command{tar} to strip the +two leading components (@file{usr/} and @file{include/}) off the file +name. + +If you add the @option{--verbose} (@option{-v}) option to the invocation +above, you will note that the verbose listing still contains the +full file name, with the two removed components still in place. This +can be inconvenient, so @command{tar} provides a special option for +altering this behavior: + +@anchor{show-transformed-names} +@table @option +@opindex show-transformed-names +@item --show-transformed-names +Display file or member names with all requested transformations +applied. +@end table + +@noindent +For example: + +@smallexample +@group +$ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h} +usr/include/stdlib.h +$ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h} +stdlib.h +@end group +@end smallexample + +Notice that in both cases the file @file{stdlib.h} is extracted to the +current working directory, @option{--show-transformed-names} affects +only the way its name is displayed. + +This option is especially useful for verifying whether the invocation +will have the desired effect. Thus, before running + +@smallexample +$ @kbd{tar -x --strip=@var{n}} +@end smallexample + +@noindent +it is often advisable to run + +@smallexample +$ @kbd{tar -t -v --show-transformed --strip=@var{n}} +@end smallexample + +@noindent +to make sure the command will produce the intended results. + +In case you need to apply more complex modifications to the file name, +@GNUTAR{} provides a general-purpose transformation option: + +@table @option +@opindex transform +@opindex xform +@item --transform=@var{expression} +@itemx --xform=@var{expression} +Modify file names using supplied @var{expression}. +@end table + +@noindent +The @var{expression} is a @command{sed}-like replace expression of the +form: + +@smallexample +s/@var{regexp}/@var{replace}/[@var{flags}] +@end smallexample + +@noindent +where @var{regexp} is a @dfn{regular expression}, @var{replace} is a +replacement for each file name part that matches @var{regexp}. Both +@var{regexp} and @var{replace} are described in detail in +@ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}. + +Any delimiter can be used in lieu of @samp{/}, the only requirement being +that it be used consistently throughout the expression. For example, +the following two expressions are equivalent: + +@smallexample +@group +s/one/two/ +s,one,two, +@end group +@end smallexample + +Changing delimiters is often useful when the @var{regex} contains +slashes. For example, it is more convenient to write @code{s,/,-,} than +@code{s/\//-/}. + +As in @command{sed}, you can give several replace expressions, +separated by a semicolon. + +Supported @var{flags} are: + +@table @samp +@item g +Apply the replacement to @emph{all} matches to the @var{regexp}, not +just the first. + +@item i +Use case-insensitive matching. + +@item x +@var{regexp} is an @dfn{extended regular expression} (@pxref{Extended +regexps, Extended regular expressions, Extended regular expressions, +sed, GNU sed}). + +@item @var{number} +Only replace the @var{number}th match of the @var{regexp}. + +Note: the @acronym{POSIX} standard does not specify what should happen +when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{} +follows the GNU @command{sed} implementation in this regard, so +the interaction is defined to be: ignore matches before the +@var{number}th, and then match and replace all matches from the +@var{number}th on. + +@end table + +In addition, several @dfn{transformation scope} flags are supported, +that control to what files transformations apply. These are: + +@table @samp +@item r +Apply transformation to regular archive members. + +@item R +Do not apply transformation to regular archive members. + +@item s +Apply transformation to symbolic link targets. + +@item S +Do not apply transformation to symbolic link targets. + +@item h +Apply transformation to hard link targets. + +@item H +Do not apply transformation to hard link targets. +@end table + +Default is @samp{rsh}, which means to apply tranformations to both archive +members and targets of symbolic and hard links. + +Default scope flags can also be changed using @samp{flags=} statement +in the transform expression. The flags set this way remain in force +until next @samp{flags=} statement or end of expression, whichever +occurs first. For example: + +@smallexample + --transform 'flags=S;s|^|/usr/local/|' +@end smallexample + +Here are several examples of @option{--transform} usage: + +@enumerate +@item Extract @file{usr/} hierarchy into @file{usr/local/}: + +@smallexample +$ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar} +@end smallexample + +@item Strip two leading directory components (equivalent to +@option{--strip-components=2}): + +@smallexample +$ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar} +@end smallexample + +@item Convert each file name to lower case: -The second file is a log file containing the names of the file systems -and files dumped, what time the backup was made, and any error -messages that were generated, as well as how much space was left in -the media volume after the last volume of the archive was written. -You should check this log file after every backup. The file name is -@file{log-@var{mmm-ddd-yyyy}-level-1} or -@file{log-@var{mmm-ddd-yyyy}-full}. +@smallexample +$ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar} +@end smallexample + +@item Prepend @file{/prefix/} to each file name: + +@smallexample +$ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar} +@end smallexample + +@item Archive the @file{/lib} directory, prepending @samp{/usr/local} +to each archive member: + +@smallexample +$ @kbd{tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib} +@end smallexample +@end enumerate + +Notice the use of flags in the last example. The @file{/lib} +directory often contains many symbolic links to files within it. +It may look, for example, like this: + +@smallexample +$ @kbd{ls -l} +drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/ +-rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so +lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so +... +@end smallexample + +Using the expression @samp{s,^,/usr/local/,} would mean adding +@samp{/usr/local} to both regular archive members and to link +targets. In this case, @file{/lib/libc.so.6} would become: + +@smallexample + /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so +@end smallexample + +This is definitely not desired. To avoid this, the @samp{S} flag +is used, which excludes symbolic link targets from filename +transformations. The result is: + +@smallexample +$ @kbd{tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \ + --show-transformed /lib} +drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/ +-rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so +lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 \ + -> libc-2.3.2.so +@end smallexample + +Unlike @option{--strip-components}, @option{--transform} can be used +in any @GNUTAR{} operation mode. For example, the following command +adds files to the archive while replacing the leading @file{usr/} +component with @file{var/}: + +@smallexample +$ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /} +@end smallexample + +To test @option{--transform} effect we suggest using +@option{--show-transformed-names} option: + +@smallexample +$ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \ + --verbose --show-transformed-names /} +@end smallexample + +If both @option{--strip-components} and @option{--transform} are used +together, then @option{--transform} is applied first, and the required +number of components is then stripped from its result. + +You can use as many @option{--transform} options in a single command +line as you want. The specified expressions will then be applied in +order of their appearance. For example, the following two invocations +are equivalent: + +@smallexample +$ @kbd{tar -cf arch.tar --transform='s,/usr/var,/var/' \ + --transform='s,/usr/local,/usr/,'} +$ @kbd{tar -cf arch.tar \ + --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'} +@end smallexample + +@node after +@section Operating Only on New Files + +@cindex Excluding file by age +@cindex Data Modification time, excluding files by +@cindex Modification time, excluding files by +@cindex Age, excluding files by +The @option{--after-date=@var{date}} (@option{--newer=@var{date}}, +@option{-N @var{date}}) option causes @command{tar} to only work on +files whose data modification or status change times are newer than +the @var{date} given. If @var{date} starts with @samp{/} or @samp{.}, +it is taken to be a file name; the data modification time of that file +is used as the date. If you use this option when creating or appending +to an archive, the archive will only include new files. If you use +@option{--after-date} when extracting an archive, @command{tar} will +only extract files newer than the @var{date} you specify. + +If you only want @command{tar} to make the date comparison based on +modification of the file's data (rather than status +changes), then use the @option{--newer-mtime=@var{date}} option. + +@cindex --after-date and --update compared +@cindex --newer-mtime and --update compared +You may use these options with any operation. Note that these options +differ from the @option{--update} (@option{-u}) operation in that they +allow you to specify a particular date against which @command{tar} can +compare when deciding whether or not to archive the files. + +@table @option +@opindex after-date +@opindex newer +@item --after-date=@var{date} +@itemx --newer=@var{date} +@itemx -N @var{date} +Only store files newer than @var{date}. + +Acts on files only if their data modification or status change times are +later than @var{date}. Use in conjunction with any operation. + +If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file +name; the data modification time of that file is used as the date. + +@opindex newer-mtime +@item --newer-mtime=@var{date} +Acts like @option{--after-date}, but only looks at data modification times. +@end table + +These options limit @command{tar} to operate only on files which have +been modified after the date specified. A file's status is considered to have +changed if its contents have been modified, or if its owner, +permissions, and so forth, have been changed. (For more information on +how to specify a date, see @ref{Date input formats}; remember that the +entire date argument must be quoted if it contains any spaces.) + +Gurus would say that @option{--after-date} tests both the data +modification time (@code{mtime}, the time the contents of the file +were last modified) and the status change time (@code{ctime}, the time +the file's status was last changed: owner, permissions, etc.@:) +fields, while @option{--newer-mtime} tests only the @code{mtime} +field. + +To be precise, @option{--after-date} checks @emph{both} @code{mtime} and +@code{ctime} and processes the file if either one is more recent than +@var{date}, while @option{--newer-mtime} only checks @code{mtime} and +disregards @code{ctime}. Neither does it use @code{atime} (the last time the +contents of the file were looked at). + +Date specifiers can have embedded spaces. Because of this, you may need +to quote date arguments to keep the shell from parsing them as separate +arguments. For example, the following command will add to the archive +all the files modified less than two days ago: + +@smallexample +$ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'} +@end smallexample + +When any of these options is used with the option @option{--verbose} +(@pxref{verbose tutorial}) @GNUTAR{} will try to convert the specified +date back to its textual representation and compare that with the +one given with the option. If the two dates differ, @command{tar} will +print a warning saying what date it will use. This is to help user +ensure he is using the right date. For example: + +@smallexample +@group +$ @kbd{tar -c -f archive.tar --after-date='10 days ago' .} +tar: Option --after-date: Treating date '10 days ago' as 2006-06-11 +13:19:37.232434 +@end group +@end smallexample + +@quotation +@strong{Please Note:} @option{--after-date} and @option{--newer-mtime} +should not be used for incremental backups. @xref{Incremental Dumps}, +for proper way of creating incremental backups. +@end quotation + +@node recurse +@section Descending into Directories +@cindex Avoiding recursion in directories +@cindex Descending directories, avoiding +@cindex Directories, avoiding recursion +@cindex Recursion in directories, avoiding + +Usually, @command{tar} will recursively explore all directories (either +those given on the command line or through the @option{--files-from} +option) for the various files they contain. However, you may not always +want @command{tar} to act this way. + +@opindex no-recursion +@cindex @command{find}, using with @command{tar} +The @option{--no-recursion} option inhibits @command{tar}'s recursive descent +into specified directories. If you specify @option{--no-recursion}, you can +use the @command{find} (@pxref{Top,, find, find, GNU Find Manual}) +utility for hunting through levels of directories to +construct a list of file names which you could then pass to @command{tar}. +@command{find} allows you to be more selective when choosing which files to +archive; see @ref{files}, for more information on using @command{find} with +@command{tar}. + +@table @option +@item --no-recursion +Prevents @command{tar} from recursively descending directories. + +@opindex recursion +@item --recursion +Requires @command{tar} to recursively descend directories. +This is the default. +@end table + +When you use @option{--no-recursion}, @GNUTAR{} grabs +directory entries themselves, but does not descend on them +recursively. Many people use @command{find} for locating files they +want to back up, and since @command{tar} @emph{usually} recursively +descends on directories, they have to use the @samp{@w{-not -type d}} +test in their @command{find} invocation (@pxref{Type, Type, Type test, +find, Finding Files}), as they usually do not want all the files in a +directory. They then use the @option{--files-from} option to archive +the files located via @command{find}. + +The problem when restoring files archived in this manner is that the +directories themselves are not in the archive; so the +@option{--same-permissions} (@option{--preserve-permissions}, +@option{-p}) option does not affect them---while users might really +like it to. Specifying @option{--no-recursion} is a way to tell +@command{tar} to grab only the directory entries given to it, adding +no new files on its own. To summarize, if you use @command{find} to +create a list of files to be stored in an archive, use it as follows: + +@smallexample +@group +$ @kbd{find @var{dir} @var{tests} | \ + tar -cf @var{archive} -T - --no-recursion} +@end group +@end smallexample + +The @option{--no-recursion} option also applies when extracting: it +causes @command{tar} to extract only the matched directory entries, not +the files under those directories. + +The @option{--no-recursion} option also affects how globbing patterns +are interpreted (@pxref{controlling pattern-matching}). + +The @option{--no-recursion} and @option{--recursion} options apply to +later options and operands, and can be overridden by later occurrences +of @option{--no-recursion} and @option{--recursion}. For example: + +@smallexample +$ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord} +@end smallexample + +@noindent +creates an archive with one entry for @file{grape}, and the recursive +contents of @file{grape/concord}, but no entries under @file{grape} +other than @file{grape/concord}. + +@node one +@section Crossing File System Boundaries +@cindex File system boundaries, not crossing + +@command{tar} will normally automatically cross file system boundaries in +order to archive files which are part of a directory tree. You can +change this behavior by running @command{tar} and specifying +@option{--one-file-system}. This option only affects files that are +archived because they are in a directory that is being archived; +@command{tar} will still archive files explicitly named on the command line +or through @option{--files-from}, regardless of where they reside. + +@table @option +@opindex one-file-system +@item --one-file-system +Prevents @command{tar} from crossing file system boundaries when +archiving. Use in conjunction with any write operation. +@end table + +The @option{--one-file-system} option causes @command{tar} to modify its +normal behavior in archiving the contents of directories. If a file in +a directory is not on the same file system as the directory itself, then +@command{tar} will not archive that file. If the file is a directory +itself, @command{tar} will not archive anything beneath it; in other words, +@command{tar} will not cross mount points. + +This option is useful for making full or incremental archival backups of +a file system. If this option is used in conjunction with +@option{--verbose} (@option{-v}), files that are excluded are +mentioned by name on the standard error. + +@menu +* directory:: Changing Directory +* absolute:: Absolute File Names +@end menu + +@node directory +@subsection Changing the Working Directory + +@FIXME{need to read over this node now for continuity; i've switched +things around some.} + +@cindex Changing directory mid-stream +@cindex Directory, changing mid-stream +@cindex Working directory, specifying +To change the working directory in the middle of a list of file names, +either on the command line or in a file specified using +@option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}). +This will change the working directory to the specified directory +after that point in the list. + +@table @option +@opindex directory +@item --directory=@var{directory} +@itemx -C @var{directory} +Changes the working directory in the middle of a command line. +@end table + +For example, + +@smallexample +$ @kbd{tar -c -f jams.tar grape prune -C food cherry} +@end smallexample + +@noindent +will place the files @file{grape} and @file{prune} from the current +directory into the archive @file{jams.tar}, followed by the file +@file{cherry} from the directory @file{food}. This option is especially +useful when you have several widely separated files that you want to +store in the same archive. + +Note that the file @file{cherry} is recorded in the archive under the +precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the +archive will contain three files that all appear to have come from the +same directory; if the archive is extracted with plain @samp{tar +--extract}, all three files will be written in the current directory. + +Contrast this with the command, + +@smallexample +$ @kbd{tar -c -f jams.tar grape prune -C food red/cherry} +@end smallexample + +@noindent +which records the third file in the archive under the name +@file{red/cherry} so that, if the archive is extracted using +@samp{tar --extract}, the third file will be written in a subdirectory +named @file{red}. + +You can use the @option{--directory} option to make the archive +independent of the original name of the directory holding the files. +The following command places the files @file{/etc/passwd}, +@file{/etc/hosts}, and @file{/lib/libc.a} into the archive +@file{foo.tar}: + +@smallexample +$ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a} +@end smallexample + +@noindent +However, the names of the archive members will be exactly what they were +on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}. +They will not appear to be related by file name to the original +directories where those files were located. + +Note that @option{--directory} options are interpreted consecutively. If +@option{--directory} specifies a relative file name, it is interpreted +relative to the then current directory, which might not be the same as +the original current working directory of @command{tar}, due to a previous +@option{--directory} option. + +When using @option{--files-from} (@pxref{files}), you can put various +@command{tar} options (including @option{-C}) in the file list. Notice, +however, that in this case the option and its argument may not be +separated by whitespace. If you use short option, its argument must +either follow the option letter immediately, without any intervening +whitespace, or occupy the next line. Otherwise, if you use long +option, separate its argument by an equal sign. + +For instance, the file list for the above example will be: + +@smallexample +@group +-C/etc +passwd +hosts +--directory=/lib +libc.a +@end group +@end smallexample + +@noindent +To use it, you would invoke @command{tar} as follows: + +@smallexample +$ @kbd{tar -c -f foo.tar --files-from list} +@end smallexample + +The interpretation of @option{--directory} is disabled by +@option{--null} option. + +@node absolute +@subsection Absolute File Names +@cindex absolute file names +@cindex file names, absolute + +By default, @GNUTAR{} drops a leading @samp{/} on +input or output, and complains about file names containing a @file{..} +component. There is an option that turns off this behavior: + +@table @option +@opindex absolute-names +@item --absolute-names +@itemx -P +Do not strip leading slashes from file names, and permit file names +containing a @file{..} file name component. +@end table + +When @command{tar} extracts archive members from an archive, it strips any +leading slashes (@samp{/}) from the member name. This causes absolute +member names in the archive to be treated as relative file names. This +allows you to have such members extracted wherever you want, instead of +being restricted to extracting the member in the exact directory named +in the archive. For example, if the archive member has the name +@file{/etc/passwd}, @command{tar} will extract it as if the name were +really @file{etc/passwd}. + +File names containing @file{..} can cause problems when extracting, so +@command{tar} normally warns you about such files when creating an +archive, and rejects attempts to extracts such files. + +Other @command{tar} programs do not do this. As a result, if you +create an archive whose member names start with a slash, they will be +difficult for other people with a non-@GNUTAR{} +program to use. Therefore, @GNUTAR{} also strips +leading slashes from member names when putting members into the +archive. For example, if you ask @command{tar} to add the file +@file{/bin/ls} to an archive, it will do so, but the member name will +be @file{bin/ls}@footnote{A side effect of this is that when +@option{--create} is used with @option{--verbose} the resulting output +is not, generally speaking, the same as the one you'd get running +@kbd{tar --list} command. This may be important if you use some +scripts for comparing both outputs. @xref{listing member and file names}, +for the information on how to handle this case.}. + +Symbolic links containing @file{..} or leading @samp{/} can also cause +problems when extracting, so @command{tar} normally extracts them last; +it may create empty files as placeholders during extraction. + +If you use the @option{--absolute-names} (@option{-P}) option, +@command{tar} will do none of these transformations. + +To archive or extract files relative to the root directory, specify +the @option{--absolute-names} (@option{-P}) option. + +Normally, @command{tar} acts on files relative to the working +directory---ignoring superior directory names when archiving, and +ignoring leading slashes when extracting. + +When you specify @option{--absolute-names} (@option{-P}), +@command{tar} stores file names including all superior directory +names, and preserves leading slashes. If you only invoked +@command{tar} from the root directory you would never need the +@option{--absolute-names} option, but using this option +may be more convenient than switching to root. + +@FIXME{Should be an example in the tutorial/wizardry section using this +to transfer files between systems.} + +@table @option +@item --absolute-names +Preserves full file names (including superior directory names) when +archiving and extracting files. + +@end table + +@command{tar} prints out a message about removing the @samp{/} from +file names. This message appears once per @GNUTAR{} +invocation. It represents something which ought to be told; ignoring +what it means can cause very serious surprises, later. + +Some people, nevertheless, do not want to see this message. Wanting to +play really dangerously, one may of course redirect @command{tar} standard +error to the sink. For example, under @command{sh}: + +@smallexample +$ @kbd{tar -c -f archive.tar /home 2> /dev/null} +@end smallexample + +@noindent +Another solution, both nicer and simpler, would be to change to +the @file{/} directory first, and then avoid absolute notation. +For example: + +@smallexample +$ @kbd{tar -c -f archive.tar -C / home} +@end smallexample + +@xref{Integrity}, for some of the security-related implications +of using this option. + +@include parse-datetime.texi + +@node Formats +@chapter Controlling the Archive Format + +@cindex Tar archive formats +Due to historical reasons, there are several formats of tar archives. +All of them are based on the same principles, but have some subtle +differences that often make them incompatible with each other. + +GNU tar is able to create and handle archives in a variety of formats. +The most frequently used formats are (in alphabetical order): + +@table @asis +@item gnu +Format used by @GNUTAR{} versions up to 1.13.25. This format derived +from an early @acronym{POSIX} standard, adding some improvements such as +sparse file handling and incremental archives. Unfortunately these +features were implemented in a way incompatible with other archive +formats. + +Archives in @samp{gnu} format are able to hold file names of unlimited +length. + +@item oldgnu +Format used by @GNUTAR{} of versions prior to 1.12. + +@item v7 +Archive format, compatible with the V7 implementation of tar. This +format imposes a number of limitations. The most important of them +are: + +@enumerate +@item The maximum length of a file name is limited to 99 characters. +@item The maximum length of a symbolic link is limited to 99 characters. +@item It is impossible to store special files (block and character +devices, fifos etc.) +@item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777 +octal) +@item V7 archives do not contain symbolic ownership information (user +and group name of the file owner). +@end enumerate + +This format has traditionally been used by Automake when producing +Makefiles. This practice will change in the future, in the meantime, +however this means that projects containing file names more than 99 +characters long will not be able to use @GNUTAR{} @value{VERSION} and +Automake prior to 1.9. + +@item ustar +Archive format defined by @acronym{POSIX.1-1988} specification. It stores +symbolic ownership information. It is also able to store +special files. However, it imposes several restrictions as well: + +@enumerate +@item The maximum length of a file name is limited to 256 characters, +provided that the file name can be split at a directory separator in +two parts, first of them being at most 155 bytes long. So, in most +cases the maximum file name length will be shorter than 256 +characters. +@item The maximum length of a symbolic link name is limited to +100 characters. +@item Maximum size of a file the archive is able to accommodate +is 8GB +@item Maximum value of UID/GID is 2097151. +@item Maximum number of bits in device major and minor numbers is 21. +@end enumerate + +@item star +Format used by J@"org Schilling @command{star} +implementation. @GNUTAR{} is able to read @samp{star} archives but +currently does not produce them. + +@item posix +Archive format defined by @acronym{POSIX.1-2001} specification. This is the +most flexible and feature-rich format. It does not impose any +restrictions on file sizes or file name lengths. This format is quite +recent, so not all tar implementations are able to handle it properly. +However, this format is designed in such a way that any tar +implementation able to read @samp{ustar} archives will be able to read +most @samp{posix} archives as well, with the only exception that any +additional information (such as long file names etc.) will in such +case be extracted as plain text files along with the files it refers to. + +This archive format will be the default format for future versions +of @GNUTAR{}. + +@end table + +The following table summarizes the limitations of each of these +formats: + +@multitable @columnfractions .10 .20 .20 .20 .20 +@headitem Format @tab UID @tab File Size @tab File Name @tab Devn +@item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63 +@item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63 +@item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a +@item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21 +@item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited +@end multitable + +The default format for @GNUTAR{} is defined at compilation +time. You may check it by running @command{tar --help}, and examining +the last lines of its output. Usually, @GNUTAR{} is configured +to create archives in @samp{gnu} format, however, future version will +switch to @samp{posix}. + +@menu +* Compression:: Using Less Space through Compression +* Attributes:: Handling File Attributes +* Portability:: Making @command{tar} Archives More Portable +* cpio:: Comparison of @command{tar} and @command{cpio} +@end menu + +@node Compression +@section Using Less Space through Compression + +@menu +* gzip:: Creating and Reading Compressed Archives +* sparse:: Archiving Sparse Files +@end menu + +@node gzip +@subsection Creating and Reading Compressed Archives +@cindex Compressed archives +@cindex Storing archives in compressed format + +@cindex gzip +@cindex bzip2 +@cindex lzip +@cindex lzma +@cindex lzop +@cindex compress +@GNUTAR{} is able to create and read compressed archives. It supports +a wide variety of compression programs, namely: @command{gzip}, +@command{bzip2}, @command{lzip}, @command{lzma}, @command{lzop}, +@command{xz} and traditional @command{compress}. The latter is +supported mostly for backward compatibility, and we recommend +against using it, because it is by far less effective than the other +compression programs@footnote{It also had patent problems in the past.}. + +Creating a compressed archive is simple: you just specify a +@dfn{compression option} along with the usual archive creation +commands. The compression option is @option{-z} (@option{--gzip}) to +create a @command{gzip} compressed archive, @option{-j} +(@option{--bzip2}) to create a @command{bzip2} compressed archive, +@option{--lzip} to create an @asis{lzip} compressed archive, +@option{-J} (@option{--xz}) to create an @asis{XZ} archive, +@option{--lzma} to create an @asis{LZMA} compressed +archive, @option{--lzop} to create an @asis{LSOP} archive, and +@option{-Z} (@option{--compress}) to use @command{compress} program. +For example: + +@smallexample +$ @kbd{tar czf archive.tar.gz .} +@end smallexample + +You can also let @GNUTAR{} select the compression program based on +the suffix of the archive file name. This is done using +@option{--auto-compress} (@option{-a}) command line option. For +example, the following invocation will use @command{bzip2} for +compression: + +@smallexample +$ @kbd{tar caf archive.tar.bz2 .} +@end smallexample + +@noindent +whereas the following one will use @command{lzma}: + +@smallexample +$ @kbd{tar caf archive.tar.lzma .} +@end smallexample + +For a complete list of file name suffixes recognized by @GNUTAR{}, +see @ref{auto-compress}. + +Reading compressed archive is even simpler: you don't need to specify +any additional options as @GNUTAR{} recognizes its format +automatically. Thus, the following commands will list and extract the +archive created in previous example: + +@smallexample +# List the compressed archive +$ @kbd{tar tf archive.tar.gz} +# Extract the compressed archive +$ @kbd{tar xf archive.tar.gz} +@end smallexample + +The format recognition algorithm is based on @dfn{signatures}, a +special byte sequences in the beginning of file, that are specific for +certain compression formats. If this approach fails, @command{tar} +falls back to using archive name suffix to determine its format +(@pxref{auto-compress}, for a list of recognized suffixes). + +@anchor{alternative decompression programs} +@cindex alternative decompression programs +Some compression programs are able to handle different compression +formats. @GNUTAR{} uses this, if the principal decompressor for the +given format is not available. For example, if @command{compress} is +not installed, @command{tar} will try to use @command{gzip}. As of +version @value{VERSION} the following alternatives are +tried@footnote{To verbosely trace the decompressor selection, use the +@option{--warning=decompress-program} option +(@pxref{warnings,decompress-program}).}: + +@multitable @columnfractions 0.3 0.3 0.3 +@headitem Format @tab Main decompressor @tab Alternatives +@item compress @tab compress @tab gzip +@item lzma @tab lzma @tab xz +@item bzip2 @tab bzip2 @tab lbzip2 +@end multitable + +The only case when you have to specify a decompression option while +reading the archive is when reading from a pipe or from a tape drive +that does not support random access. However, in this case @GNUTAR{} +will indicate which option you should use. For example: + +@smallexample +$ @kbd{cat archive.tar.gz | tar tf -} +tar: Archive is compressed. Use -z option +tar: Error is not recoverable: exiting now +@end smallexample + +If you see such diagnostics, just add the suggested option to the +invocation of @GNUTAR{}: + +@smallexample +$ @kbd{cat archive.tar.gz | tar tzf -} +@end smallexample + +Notice also, that there are several restrictions on operations on +compressed archives. First of all, compressed archives cannot be +modified, i.e., you cannot update (@option{--update}, alias @option{-u}) +them or delete (@option{--delete}) members from them or +add (@option{--append}, alias @option{-r}) members to them. Likewise, you +cannot append another @command{tar} archive to a compressed archive using +@option{--concatenate} (@option{-A}). Secondly, multi-volume +archives cannot be compressed. + +The following options allow to select a particular compressor program: + +@table @option +@opindex gzip +@opindex ungzip +@item -z +@itemx --gzip +@itemx --ungzip +Filter the archive through @command{gzip}. + +@opindex xz +@item -J +@itemx --xz +Filter the archive through @code{xz}. + +@item -j +@itemx --bzip2 +Filter the archive through @code{bzip2}. + +@opindex lzip +@item --lzip +Filter the archive through @command{lzip}. + +@opindex lzma +@item --lzma +Filter the archive through @command{lzma}. + +@opindex lzop +@item --lzop +Filter the archive through @command{lzop}. + +@opindex compress +@opindex uncompress +@item -Z +@itemx --compress +@itemx --uncompress +Filter the archive through @command{compress}. +@end table + +When any of these options is given, @GNUTAR{} searches the compressor +binary in the current path and invokes it. The name of the compressor +program is specified at compilation time using a corresponding +@option{--with-@var{compname}} option to @command{configure}, e.g. +@option{--with-bzip2} to select a specific @command{bzip2} binary. +@xref{lbzip2}, for a detailed discussion. + +The output produced by @command{tar --help} shows the actual +compressor names along with each of these options. + +You can use any of these options on physical devices (tape drives, +etc.) and remote files as well as on normal files; data to or from +such devices or remote files is reblocked by another copy of the +@command{tar} program to enforce the specified (or default) record +size. The default compression parameters are used. Most compression +programs let you override these by setting a program-specific +environment variable. For example, with @command{gzip} you can set +@env{GZIP}: + +@smallexample +$ @kbd{GZIP='-9 -n' tar czf archive.tar.gz subdir} +@end smallexample + +@noindent +The traditional way to do this is to use a pipe: + +@smallexample +$ @kbd{tar cf - subdir | gzip -9 -n > archive.tar.gz} +@end smallexample + +@cindex corrupted archives +Compressed archives are easily corrupted, because compressed files +have little redundancy. The adaptive nature of the +compression scheme means that the compression tables are implicitly +spread all over the archive. If you lose a few blocks, the dynamic +construction of the compression tables becomes unsynchronized, and there +is little chance that you could recover later in the archive. + +Other compression options provide better control over creating +compressed archives. These are: + +@table @option +@anchor{auto-compress} +@opindex auto-compress +@item --auto-compress +@itemx -a +Select a compression program to use by the archive file name +suffix. The following suffixes are recognized: + +@multitable @columnfractions 0.3 0.6 +@headitem Suffix @tab Compression program +@item @samp{.gz} @tab @command{gzip} +@item @samp{.tgz} @tab @command{gzip} +@item @samp{.taz} @tab @command{gzip} +@item @samp{.Z} @tab @command{compress} +@item @samp{.taZ} @tab @command{compress} +@item @samp{.bz2} @tab @command{bzip2} +@item @samp{.tz2} @tab @command{bzip2} +@item @samp{.tbz2} @tab @command{bzip2} +@item @samp{.tbz} @tab @command{bzip2} +@item @samp{.lz} @tab @command{lzip} +@item @samp{.lzma} @tab @command{lzma} +@item @samp{.tlz} @tab @command{lzma} +@item @samp{.lzo} @tab @command{lzop} +@item @samp{.xz} @tab @command{xz} +@end multitable + +@opindex use-compress-program +@item --use-compress-program=@var{prog} +@itemx -I=@var{prog} +Use external compression program @var{prog}. Use this option if you +are not happy with the compression program associated with the suffix +at compile time or if you have a compression program that @GNUTAR{} +does not support. The program should follow two conventions: + +First, when invoked without options, it should read data from standard +input, compress it and output it on standard output. + +Secondly, if invoked with the @option{-d} option, it should do exactly +the opposite, i.e., read the compressed data from the standard input +and produce uncompressed data on the standard output. +@end table + +@cindex gpg, using with tar +@cindex gnupg, using with tar +@cindex Using encrypted archives +The @option{--use-compress-program} option, in particular, lets you +implement your own filters, not necessarily dealing with +compression/decompression. For example, suppose you wish to implement +PGP encryption on top of compression, using @command{gpg} (@pxref{Top, +gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard +Manual}). The following script does that: + +@smallexample +@group +#! /bin/sh +case $1 in +-d) gpg --decrypt - | gzip -d -c;; +'') gzip -c | gpg -s;; +*) echo "Unknown option $1">&2; exit 1;; +esac +@end group +@end smallexample + +Suppose you name it @file{gpgz} and save it somewhere in your +@env{PATH}. Then the following command will create a compressed +archive signed with your private key: + +@smallexample +$ @kbd{tar -cf foo.tar.gpgz -Igpgz .} +@end smallexample + +@noindent +Likewise, the command below will list its contents: + +@smallexample +$ @kbd{tar -tf foo.tar.gpgz -Igpgz .} +@end smallexample -The script also prints the name of each system being dumped to the -standard output. -@c <<> longfile} +$ rm -f GNUFileParts.27962 +@end group +@end smallexample + +Notice, that if the @command{tar} implementation you use supports PAX +format archives, it will probably emit warnings about unknown keywords +during extraction. They will look like this: + +@smallexample +@group +Tar file too small +Unknown extended header keyword 'GNU.volume.filename' ignored. +Unknown extended header keyword 'GNU.volume.size' ignored. +Unknown extended header keyword 'GNU.volume.offset' ignored. +@end group +@end smallexample + +@noindent +You can safely ignore these warnings. + +If your @command{tar} implementation is not PAX-aware, you will get +more warnings and more files generated on your disk, e.g.: + +@smallexample +@group +$ @kbd{tar xf vol-1.tar} +var/PaxHeaders.27962/longfile: Unknown file type 'x', extracted as +normal file +Unexpected EOF in archive +$ @kbd{tar xf vol-2.tar} +tmp/GlobalHead.27962.1: Unknown file type 'g', extracted as normal file +GNUFileParts.27962/PaxHeaders.27962/sparsefile.1: Unknown file type +'x', extracted as normal file +@end group +@end smallexample + +Ignore these warnings. The @file{PaxHeaders.*} directories created +will contain files with @dfn{extended header keywords} describing the +extracted files. You can delete them, unless they describe sparse +members. Read further to learn more about them. + +@node Sparse Recovery +@subsubsection Extracting Sparse Members + +@cindex sparse files, extracting with non-GNU tars +Any @command{tar} implementation will be able to extract sparse members from a +PAX archive. However, the extracted files will be @dfn{condensed}, +i.e., any zero blocks will be removed from them. When we restore such +a condensed file to its original form, by adding zero blocks (or +@dfn{holes}) back to their original locations, we call this process +@dfn{expanding} a compressed sparse file. + +@pindex xsparse +To expand a file, you will need a simple auxiliary program called +@command{xsparse}. It is available in source form from +@uref{http://www.gnu.org/@/software/@/tar/@/utils/@/xsparse.html, @GNUTAR{} +home page}. + +@cindex sparse files v.1.0, extracting with non-GNU tars +Let's begin with archive members in @dfn{sparse format +version 1.0}@footnote{@xref{PAX 1}.}, which are the easiest to expand. +The condensed file will contain both file map and file data, so no +additional data will be needed to restore it. If the original file +name was @file{@var{dir}/@var{name}}, then the condensed file will be +named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where +@var{n} is a decimal number@footnote{Technically speaking, @var{n} is a +@dfn{process @acronym{ID}} of the @command{tar} process which created the +archive (@pxref{PAX keywords}).}. + +To expand a version 1.0 file, run @command{xsparse} as follows: + +@smallexample +$ @kbd{xsparse @file{cond-file}} +@end smallexample + +@noindent +where @file{cond-file} is the name of the condensed file. The utility +will deduce the name for the resulting expanded file using the +following algorithm: + +@enumerate 1 +@item If @file{cond-file} does not contain any directories, +@file{../cond-file} will be used; + +@item If @file{cond-file} has the form +@file{@var{dir}/@var{t}/@var{name}}, where both @var{t} and @var{name} +are simple names, with no @samp{/} characters in them, the output file +name will be @file{@var{dir}/@var{name}}. + +@item Otherwise, if @file{cond-file} has the form +@file{@var{dir}/@var{name}}, the output file name will be +@file{@var{name}}. +@end enumerate + +In the unlikely case when this algorithm does not suit your needs, +you can explicitly specify output file name as a second argument to +the command: + +@smallexample +$ @kbd{xsparse @file{cond-file} @file{out-file}} +@end smallexample + +It is often a good idea to run @command{xsparse} in @dfn{dry run} mode +first. In this mode, the command does not actually expand the file, +but verbosely lists all actions it would be taking to do so. The dry +run mode is enabled by @option{-n} command line argument: + +@smallexample +@group +$ @kbd{xsparse -n /home/gray/GNUSparseFile.6058/sparsefile} +Reading v.1.0 sparse map +Expanding file '/home/gray/GNUSparseFile.6058/sparsefile' to +'/home/gray/sparsefile' +Finished dry run +@end group +@end smallexample + +To actually expand the file, you would run: + +@smallexample +$ @kbd{xsparse /home/gray/GNUSparseFile.6058/sparsefile} +@end smallexample + +@noindent +The program behaves the same way all UNIX utilities do: it will keep +quiet unless it has simething important to tell you (e.g. an error +condition or something). If you wish it to produce verbose output, +similar to that from the dry run mode, use @option{-v} option: + +@smallexample +@group +$ @kbd{xsparse -v /home/gray/GNUSparseFile.6058/sparsefile} +Reading v.1.0 sparse map +Expanding file '/home/gray/GNUSparseFile.6058/sparsefile' to +'/home/gray/sparsefile' +Done +@end group +@end smallexample + +Additionally, if your @command{tar} implementation has extracted the +@dfn{extended headers} for this file, you can instruct @command{xstar} +to use them in order to verify the integrity of the expanded file. +The option @option{-x} sets the name of the extended header file to +use. Continuing our example: + +@smallexample +@group +$ @kbd{xsparse -v -x /home/gray/PaxHeaders.6058/sparsefile \ + /home/gray/GNUSparseFile.6058/sparsefile} +Reading extended header file +Found variable GNU.sparse.major = 1 +Found variable GNU.sparse.minor = 0 +Found variable GNU.sparse.name = sparsefile +Found variable GNU.sparse.realsize = 217481216 +Reading v.1.0 sparse map +Expanding file '/home/gray/GNUSparseFile.6058/sparsefile' to +'/home/gray/sparsefile' +Done +@end group +@end smallexample + +@anchor{extracting sparse v.0.x} +@cindex sparse files v.0.1, extracting with non-GNU tars +@cindex sparse files v.0.0, extracting with non-GNU tars +An @dfn{extended header} is a special @command{tar} archive header +that precedes an archive member and contains a set of +@dfn{variables}, describing the member properties that cannot be +stored in the standard @code{ustar} header. While optional for +expanding sparse version 1.0 members, the use of extended headers is +mandatory when expanding sparse members in older sparse formats: v.0.0 +and v.0.1 (The sparse formats are described in detail in @ref{Sparse +Formats}.) So, for these formats, the question is: how to obtain +extended headers from the archive? + +If you use a @command{tar} implementation that does not support PAX +format, extended headers for each member will be extracted as a +separate file. If we represent the member name as +@file{@var{dir}/@var{name}}, then the extended header file will be +named @file{@var{dir}/@/PaxHeaders.@var{n}/@/@var{name}}, where +@var{n} is an integer number. + +Things become more difficult if your @command{tar} implementation +does support PAX headers, because in this case you will have to +manually extract the headers. We recommend the following algorithm: + +@enumerate 1 +@item +Consult the documentation of your @command{tar} implementation for an +option that prints @dfn{block numbers} along with the archive +listing (analogous to @GNUTAR{}'s @option{-R} option). For example, +@command{star} has @option{-block-number}. + +@item +Obtain verbose listing using the @samp{block number} option, and +find block numbers of the sparse member in question and the member +immediately following it. For example, running @command{star} on our +archive we obtain: + +@smallexample +@group +$ @kbd{star -t -v -block-number -f arc.tar} +@dots{} +star: Unknown extended header keyword 'GNU.sparse.size' ignored. +star: Unknown extended header keyword 'GNU.sparse.numblocks' ignored. +star: Unknown extended header keyword 'GNU.sparse.name' ignored. +star: Unknown extended header keyword 'GNU.sparse.map' ignored. +block 56: 425984 -rw-r--r-- gray/users Jun 25 14:46 2006 GNUSparseFile.28124/sparsefile +block 897: 65391 -rw-r--r-- gray/users Jun 24 20:06 2006 README +@dots{} +@end group +@end smallexample + +@noindent +(as usual, ignore the warnings about unknown keywords.) + +@item +Let @var{size} be the size of the sparse member, @var{Bs} be its block number +and @var{Bn} be the block number of the next member. +Compute: + +@smallexample +@var{N} = @var{Bs} - @var{Bn} - @var{size}/512 - 2 +@end smallexample + +@noindent +This number gives the size of the extended header part in tar @dfn{blocks}. +In our example, this formula gives: @code{897 - 56 - 425984 / 512 - 2 += 7}. + +@item +Use @command{dd} to extract the headers: + +@smallexample +@kbd{dd if=@var{archive} of=@var{hname} bs=512 skip=@var{Bs} count=@var{N}} +@end smallexample + +@noindent +where @var{archive} is the archive name, @var{hname} is a name of the +file to store the extended header in, @var{Bs} and @var{N} are +computed in previous steps. + +In our example, this command will be + +@smallexample +$ @kbd{dd if=arc.tar of=xhdr bs=512 skip=56 count=7} +@end smallexample +@end enumerate + +Finally, you can expand the condensed file, using the obtained header: + +@smallexample +@group +$ @kbd{xsparse -v -x xhdr GNUSparseFile.6058/sparsefile} +Reading extended header file +Found variable GNU.sparse.size = 217481216 +Found variable GNU.sparse.numblocks = 208 +Found variable GNU.sparse.name = sparsefile +Found variable GNU.sparse.map = 0,2048,1050624,2048,@dots{} +Expanding file 'GNUSparseFile.28124/sparsefile' to 'sparsefile' +Done +@end group +@end smallexample + +@node cpio +@section Comparison of @command{tar} and @command{cpio} +@UNREVISED + +@FIXME{Reorganize the following material} + +The @command{cpio} archive formats, like @command{tar}, do have maximum +file name lengths. The binary and old @acronym{ASCII} formats have a maximum file +length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max +file length of 1024. @acronym{GNU} @command{cpio} can read and write archives +with arbitrary file name lengths, but other @command{cpio} implementations +may crash unexplainedly trying to read them. + +@command{tar} handles symbolic links in the form in which it comes in @acronym{BSD}; +@command{cpio} doesn't handle symbolic links in the form in which it comes +in System V prior to SVR4, and some vendors may have added symlinks +to their system without enhancing @command{cpio} to know about them. +Others may have enhanced it in a way other than the way I did it +at Sun, and which was adopted by AT&T (and which is, I think, also +present in the @command{cpio} that Berkeley picked up from AT&T and put +into a later @acronym{BSD} release---I think I gave them my changes). + +(SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio} +can handle @command{tar} format input, and write it on output, and it +probably handles symbolic links. They may not have bothered doing +anything to enhance @command{tar} as a result.) + +@command{cpio} handles special files; traditional @command{tar} doesn't. + +@command{tar} comes with V7, System III, System V, and @acronym{BSD} source; +@command{cpio} comes only with System III, System V, and later @acronym{BSD} +(4.3-tahoe and later). + +@command{tar}'s way of handling multiple hard links to a file can handle +file systems that support 32-bit i-numbers (e.g., the @acronym{BSD} file system); +@command{cpio}s way requires you to play some games (in its ``binary'' +format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format, +they're 18 bits---it would have to play games with the "file system @acronym{ID}" +field of the header to make sure that the file system @acronym{ID}/i-number pairs +of different files were always different), and I don't know which +@command{cpio}s, if any, play those games. Those that don't might get +confused and think two files are the same file when they're not, and +make hard links between them. + +@command{tar}s way of handling multiple hard links to a file places only +one copy of the link on the tape, but the name attached to that copy +is the @emph{only} one you can use to retrieve the file; @command{cpio}s +way puts one copy for every link, but you can retrieve it using any +of the names. + +@quotation +What type of check sum (if any) is used, and how is this calculated. +@end quotation + +See the attached manual pages for @command{tar} and @command{cpio} format. +@command{tar} uses a checksum which is the sum of all the bytes in the +@command{tar} header for a file; @command{cpio} uses no checksum. + +@quotation +If anyone knows why @command{cpio} was made when @command{tar} was present +at the unix scene, +@end quotation + +It wasn't. @command{cpio} first showed up in PWB/UNIX 1.0; no +generally-available version of UNIX had @command{tar} at the time. I don't +know whether any version that was generally available @emph{within AT&T} +had @command{tar}, or, if so, whether the people within AT&T who did +@command{cpio} knew about it. + +On restore, if there is a corruption on a tape @command{tar} will stop at +that point, while @command{cpio} will skip over it and try to restore the +rest of the files. + +The main difference is just in the command syntax and header format. + +@command{tar} is a little more tape-oriented in that everything is blocked +to start on a record boundary. + +@quotation +Is there any differences between the ability to recover crashed +archives between the two of them. (Is there any chance of recovering +crashed archives at all.) +@end quotation + +Theoretically it should be easier under @command{tar} since the blocking +lets you find a header with some variation of @samp{dd skip=@var{nn}}. +However, modern @command{cpio}'s and variations have an option to just +search for the next file header after an error with a reasonable chance +of resyncing. However, lots of tape driver software won't allow you to +continue past a media error which should be the only reason for getting +out of sync unless a file changed sizes while you were writing the +archive. + +@quotation +If anyone knows why @command{cpio} was made when @command{tar} was present +at the unix scene, please tell me about this too. +@end quotation + +Probably because it is more media efficient (by not blocking everything +and using only the space needed for the headers where @command{tar} +always uses 512 bytes per file header) and it knows how to archive +special files. + +You might want to look at the freely available alternatives. The +major ones are @command{afio}, @GNUTAR{}, and +@command{pax}, each of which have their own extensions with some +backwards compatibility. + +Sparse files were @command{tar}red as sparse files (which you can +easily test, because the resulting archive gets smaller, and +@acronym{GNU} @command{cpio} can no longer read it). + +@node Media +@chapter Tapes and Other Archive Media +@UNREVISED + +A few special cases about tape handling warrant more detailed +description. These special cases are discussed below. + +Many complexities surround the use of @command{tar} on tape drives. Since +the creation and manipulation of archives located on magnetic tape was +the original purpose of @command{tar}, it contains many features making +such manipulation easier. + +Archives are usually written on dismountable media---tape cartridges, +mag tapes, or floppy disks. -To restore files that were archived using a scripted backup, use the -@code{restore} script. The syntax for the script is: +The amount of data a tape or disk holds depends not only on its size, +but also on how it is formatted. A 2400 foot long reel of mag tape +holds 40 megabytes of data when formatted at 1600 bits per inch. The +physically smaller EXABYTE tape cartridge holds 2.3 gigabytes. +Magnetic media are re-usable---once the archive on a tape is no longer +needed, the archive can be erased and the tape or disk used over. +Media quality does deteriorate with use, however. Most tapes or disks +should be discarded when they begin to produce data errors. EXABYTE +tape cartridges should be discarded when they generate an @dfn{error +count} (number of non-usable bits) of more than 10k. -where ##### are the file systems to restore from, and -##### is a regular expression which specifies which files to -restore. If you specify +all, the script restores all the files -in the file system. +Magnetic media are written and erased using magnetic fields, and +should be protected from such fields to avoid damage to stored data. +Sticking a floppy disk to a filing cabinet using a magnet is probably +not a good idea. -You should start the restore script with the media containing the -first volume of the archive mounted. The script will prompt for other -volumes as they are needed. If the archive is on tape, you don't need -to rewind the tape to to its beginning---if the tape head is -positioned past the beginning of the archive, the script will rewind -the tape as needed. @xref{Media}, for a discussion of tape -positioning. +@menu +* Device:: Device selection and switching +* Remote Tape Server:: +* Common Problems and Solutions:: +* Blocking:: Blocking +* Many:: Many archives on one tape +* Using Multiple Tapes:: Using Multiple Tapes +* label:: Including a Label in the Archive +* verify:: +* Write Protection:: +@end menu -If you specify @samp{+all} as the @var{files} argument, the -@code{restore} script extracts all the files in the archived file -system into the active file system. +@node Device +@section Device Selection and Switching +@UNREVISED -@quotation -@strong{Warning:}The script will delete files from the active file -system if they were not in the file system when the archive was made. -@end quotation +@table @option +@item -f [@var{hostname}:]@var{file} +@itemx --file=[@var{hostname}:]@var{file} +Use archive file or device @var{file} on @var{hostname}. +@end table -@xref{incremental and listed-incremental}, for an explanation of how -the script makes that determination. -@c this may be an option, not a given -@end ignore +This option is used to specify the file name of the archive @command{tar} +works on. + +If the file name is @samp{-}, @command{tar} reads the archive from standard +input (when listing or extracting), or writes it to standard output +(when creating). If the @samp{-} file name is given when updating an +archive, @command{tar} will read the original archive from its standard +input, and will write the entire new archive to its standard output. + +If the file name contains a @samp{:}, it is interpreted as +@samp{hostname:file name}. If the @var{hostname} contains an @dfn{at} +sign (@samp{@@}), it is treated as @samp{user@@hostname:file name}. In +either case, @command{tar} will invoke the command @command{rsh} (or +@command{remsh}) to start up an @command{/usr/libexec/rmt} on the remote +machine. If you give an alternate login name, it will be given to the +@command{rsh}. +Naturally, the remote machine must have an executable +@command{/usr/libexec/rmt}. This program is free software from the +University of California, and a copy of the source code can be found +with the sources for @command{tar}; it's compiled and installed by default. +The exact path to this utility is determined when configuring the package. +It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for +your installation prefix. This location may also be overridden at +runtime by using the @option{--rmt-command=@var{command}} option (@xref{Option Summary, +---rmt-command}, for detailed description of this option. @xref{Remote +Tape Server}, for the description of @command{rmt} command). + +If this option is not given, but the environment variable @env{TAPE} +is set, its value is used; otherwise, old versions of @command{tar} +used a default archive name (which was picked when @command{tar} was +compiled). The default is normally set up to be the @dfn{first} tape +drive or other transportable I/O medium on the system. + +Starting with version 1.11.5, @GNUTAR{} uses +standard input and standard output as the default device, and I will +not try anymore supporting automatic device detection at installation +time. This was failing really in too many cases, it was hopeless. +This is now completely left to the installer to override standard +input and standard output for default device, if this seems +preferable. Further, I think @emph{most} actual usages of +@command{tar} are done with pipes or disks, not really tapes, +cartridges or diskettes. + +Some users think that using standard input and output is running +after trouble. This could lead to a nasty surprise on your screen if +you forget to specify an output file name---especially if you are going +through a network or terminal server capable of buffering large amounts +of output. We had so many bug reports in that area of configuring +default tapes automatically, and so many contradicting requests, that +we finally consider the problem to be portably intractable. We could +of course use something like @samp{/dev/tape} as a default, but this +is @emph{also} running after various kind of trouble, going from hung +processes to accidental destruction of real tapes. After having seen +all this mess, using standard input and output as a default really +sounds like the only clean choice left, and a very useful one too. + +@GNUTAR{} reads and writes archive in records, I +suspect this is the main reason why block devices are preferred over +character devices. Most probably, block devices are more efficient +too. The installer could also check for @samp{DEFTAPE} in +@file{}. + +@table @option +@xopindex{force-local, short description} +@item --force-local +Archive file is local even if it contains a colon. + +@opindex rsh-command +@item --rsh-command=@var{command} +Use remote @var{command} instead of @command{rsh}. This option exists +so that people who use something other than the standard @command{rsh} +(e.g., a Kerberized @command{rsh}) can access a remote device. + +When this command is not used, the shell command found when +the @command{tar} program was installed is used instead. This is +the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh}, +@file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}. +The installer may have overridden this by defining the environment +variable @env{RSH} @emph{at installation time}. + +@item -[0-7][lmh] +Specify drive and density. + +@xopindex{multi-volume, short description} +@item -M +@itemx --multi-volume +Create/list/extract multi-volume archive. + +This option causes @command{tar} to write a @dfn{multi-volume} archive---one +that may be larger than will fit on the medium used to hold it. +@xref{Multi-Volume Archives}. + +@xopindex{tape-length, short description} +@item -L @var{num} +@itemx --tape-length=@var{size}[@var{suf}] +Change tape after writing @var{size} units of data. Unless @var{suf} is +given, @var{size} is treated as kilobytes, i.e. @samp{@var{size} x +1024} bytes. The following suffixes alter this behavior: + +@float Table, size-suffixes +@caption{Size Suffixes} +@multitable @columnfractions 0.2 0.3 0.3 +@headitem Suffix @tab Units @tab Byte Equivalent +@item b @tab Blocks @tab @var{size} x 512 +@item B @tab Kilobytes @tab @var{size} x 1024 +@item c @tab Bytes @tab @var{size} +@item G @tab Gigabytes @tab @var{size} x 1024^3 +@item K @tab Kilobytes @tab @var{size} x 1024 +@item k @tab Kilobytes @tab @var{size} x 1024 +@item M @tab Megabytes @tab @var{size} x 1024^2 +@item P @tab Petabytes @tab @var{size} x 1024^5 +@item T @tab Terabytes @tab @var{size} x 1024^4 +@item w @tab Words @tab @var{size} x 2 +@end multitable +@end float + +This option might be useful when your tape drivers do not properly +detect end of physical tapes. By being slightly conservative on the +maximum tape length, you might avoid the problem entirely. + +@xopindex{info-script, short description} +@xopindex{new-volume-script, short description} +@item -F @var{file} +@itemx --info-script=@var{file} +@itemx --new-volume-script=@var{file} +Execute @file{file} at end of each tape. This implies +@option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed +description of this option. +@end table -@node incremental and listed-incremental, Problems, Backup Scripts, Backups and Restoration -@section The @code{+incremental} and @code{+listed-incremental} Options - -@samp{+incremental} is used in conjunction with @samp{+create}, -@samp{+extract} or @samp{+list} when backing up and restoring file -systems. An archive cannot be extracted or listed with the -@samp{+incremental} option specified unless it was created with the -option specified. This option should only be used by a script, not by -the user, and is usually disregarded in favor of -@samp{+listed-incremental}, which is described below. - -@samp{+incremental} in conjunction with @samp{+create} causes -@code{tar} to write, at the beginning of the archive, an entry for -each of the directories that will be archived. The entry for a -directory includes a list of all the files in the directory at the -time the archive was created and a flag for each file indicating -whether or not the file is going to be put in the archive. - -Note that this option causes @code{tar} to create a non-standard -archive that may not be readable by non-GNU versions of the @code{tar} -program. - -@samp{+incremental} in conjunction with @samp{+extract} causes -@code{tar} to read the lists of directory contents previously stored -in the archive, @emph{delete} files in the file system that did not -exist in their directories when the archive was created, and then -extract the files in the archive. - -This behavior is convenient when restoring a damaged file system from -a succession of incremental backups: it restores the entire state of -the file system to that which obtained when the backup was made. If -@samp{+incremental} isn't specified, the file system will probably -fill up with files that shouldn't exist any more. - -@samp{+incremental} in conjunction with @samp{+list}, causes -@code{tar} to print, for each directory in the archive, the list of -files in that directory at the time the archive was created. This -information is put out in a format that is not easy for humans to -read, but which is unambiguous for a program: each file name is -preceded by either a @samp{Y} if the file is present in the archive, -an @samp{N} if the file is not included in the archive, or a @samp{D} -if the file is a directory (and is included in the archive). Each -file name is terminated by a null character. The last file is followed -by an additional null and a newline to indicate the end of the data. - -@samp{+listed-incremental}=@var{file} acts like @samp{+incremental}, -but when used in conjunction with @samp{+create} will also cause -@code{tar} to use the file @var{file}, which contains information -about the state of the file system at the time of the last backup, to -decide which files to include in the archive being created. That file -will then be updated by @code{tar}. If the file @var{file} does not -exist when this option is specified, @code{tar} will create it, and -include all appropriate files in the archive. - -The file @var{file}, which is archive independent, contains the date -it was last modified and a list of devices, inode numbers and -directory names. @code{tar} will archive files with newer mod dates -or inode change times, and directories with an unchanged inode number -and device but a changed directory name. The file is updated after -the files to be archived are determined, but before the new archive is -actually created. - -@c <<< this section needs to be written -@node Problems, , incremental and listed-incremental, Backups and Restoration +@node Remote Tape Server +@section Remote Tape Server + +@cindex remote tape drive +@pindex rmt +In order to access the tape drive on a remote machine, @command{tar} +uses the remote tape server written at the University of California at +Berkeley. The remote tape server must be installed as +@file{@var{prefix}/libexec/rmt} on any machine whose tape drive you +want to use. @command{tar} calls @command{rmt} by running an +@command{rsh} or @command{remsh} to the remote machine, optionally +using a different login name if one is supplied. + +A copy of the source for the remote tape server is provided. Its +source code can be freely distributed. It is compiled and +installed by default. + +@cindex absolute file names +Unless you use the @option{--absolute-names} (@option{-P}) option, +@GNUTAR{} will not allow you to create an archive that contains +absolute file names (a file name beginning with @samp{/}.) If you try, +@command{tar} will automatically remove the leading @samp{/} from the +file names it stores in the archive. It will also type a warning +message telling you what it is doing. + +When reading an archive that was created with a different +@command{tar} program, @GNUTAR{} automatically +extracts entries in the archive which have absolute file names as if +the file names were not absolute. This is an important feature. A +visitor here once gave a @command{tar} tape to an operator to restore; +the operator used Sun @command{tar} instead of @GNUTAR{}, +and the result was that it replaced large portions of +our @file{/bin} and friends with versions from the tape; needless to +say, we were unhappy about having to recover the file system from +backup tapes. + +For example, if the archive contained a file @file{/usr/bin/computoy}, +@GNUTAR{} would extract the file to @file{usr/bin/computoy}, +relative to the current directory. If you want to extract the files in +an archive to the same absolute names that they had when the archive +was created, you should do a @samp{cd /} before extracting the files +from the archive, or you should either use the @option{--absolute-names} +option, or use the command @samp{tar -C / @dots{}}. + +@cindex Ultrix 3.1 and write failure +Some versions of Unix (Ultrix 3.1 is known to have this problem), +can claim that a short write near the end of a tape succeeded, +when it actually failed. This will result in the -M option not +working correctly. The best workaround at the moment is to use a +significantly larger blocking factor than the default 20. + +In order to update an archive, @command{tar} must be able to backspace the +archive in order to reread or rewrite a record that was just read (or +written). This is currently possible only on two kinds of files: normal +disk files (or any other file that can be backspaced with @samp{lseek}), +and industry-standard 9-track magnetic tape (or any other kind of tape +that can be backspaced with the @code{MTIOCTOP} @code{ioctl}). + +This means that the @option{--append}, @option{--concatenate}, and +@option{--delete} commands will not work on any other kind of file. +Some media simply cannot be backspaced, which means these commands and +options will never be able to work on them. These non-backspacing +media include pipes and cartridge tape drives. + +Some other media can be backspaced, and @command{tar} will work on them +once @command{tar} is modified to do so. + +Archives created with the @option{--multi-volume}, @option{--label}, and +@option{--incremental} (@option{-G}) options may not be readable by other version +of @command{tar}. In particular, restoring a file that was split over +a volume boundary will require some careful work with @command{dd}, if +it can be done at all. Other versions of @command{tar} may also create +an empty file whose name is that of the volume header. Some versions +of @command{tar} may create normal files instead of directories archived +with the @option{--incremental} (@option{-G}) option. + +@node Common Problems and Solutions @section Some Common Problems and their Solutions +@ifclear PUBLISH + +@format errors from system: permission denied no such file or directory not owner -errors from tar: +errors from @command{tar}: directory checksum error header format error errors from media/system: i/o error device busy +@end format -@node Media, Quick Reference, Backups and Restoration, Top -@chapter Tapes and Other Archive Media +@end ifclear -Archives are usually written on dismountable media---tape cartridges, -mag tapes, or floppy disks. +@node Blocking +@section Blocking +@cindex block +@cindex record -The amount of data a tape or disk holds depends not only on its size, -but also on how it is formatted. A 2400 foot long reel of mag tape -holds 40 megabytes of data when formated at 1600 bits per inch. The -physically smaller EXABYTE tape cartridge holds 2.3 gigabytes. +@dfn{Block} and @dfn{record} terminology is rather confused, and it +is also confusing to the expert reader. On the other hand, readers +who are new to the field have a fresh mind, and they may safely skip +the next two paragraphs, as the remainder of this manual uses those +two terms in a quite consistent way. -Magnetic media are re-usable---once the archive on a tape is no longer -needed, the archive can be erased and the tape or disk used over. -Media quality does deteriorate with use, however. Most tapes or disks -should be disgarded when they begin to produce data errors. EXABYTE -tape cartridges should be disgarded when they generate an @dfn{error -count} (number of non-usable bits) of more than 10k. +John Gilmore, the writer of the public domain @command{tar} from which +@GNUTAR{} was originally derived, wrote (June 1995): -Magnetic media are written and erased using magnetic fields, and -should be protected from such fields to avoid damage to stored data. -Sticking a floppy disk to a filing cabinet using a magnet is probably -not a good idea. +@quotation +The nomenclature of tape drives comes from IBM, where I believe +they were invented for the IBM 650 or so. On IBM mainframes, what +is recorded on tape are tape blocks. The logical organization of +data is into records. There are various ways of putting records into +blocks, including @code{F} (fixed sized records), @code{V} (variable +sized records), @code{FB} (fixed blocked: fixed size records, @var{n} +to a block), @code{VB} (variable size records, @var{n} to a block), +@code{VSB} (variable spanned blocked: variable sized records that can +occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=} +parameter specified this to the operating system. + +The Unix man page on @command{tar} was totally confused about this. +When I wrote @code{PD TAR}, I used the historically correct terminology +(@command{tar} writes data records, which are grouped into blocks). +It appears that the bogus terminology made it into @acronym{POSIX} (no surprise +here), and now Fran@,{c}ois has migrated that terminology back +into the source code too. +@end quotation +The term @dfn{physical block} means the basic transfer chunk from or +to a device, after which reading or writing may stop without anything +being lost. In this manual, the term @dfn{block} usually refers to +a disk physical block, @emph{assuming} that each disk block is 512 +bytes in length. It is true that some disk devices have different +physical blocks, but @command{tar} ignore these differences in its own +format, which is meant to be portable, so a @command{tar} block is always +512 bytes in length, and @dfn{block} always mean a @command{tar} block. +The term @dfn{logical block} often represents the basic chunk of +allocation of many disk blocks as a single entity, which the operating +system treats somewhat atomically; this concept is only barely used +in @GNUTAR{}. + +The term @dfn{physical record} is another way to speak of a physical +block, those two terms are somewhat interchangeable. In this manual, +the term @dfn{record} usually refers to a tape physical block, +@emph{assuming} that the @command{tar} archive is kept on magnetic tape. +It is true that archives may be put on disk or used with pipes, +but nevertheless, @command{tar} tries to read and write the archive one +@dfn{record} at a time, whatever the medium in use. One record is made +up of an integral number of blocks, and this operation of putting many +disk blocks into a single tape block is called @dfn{reblocking}, or +more simply, @dfn{blocking}. The term @dfn{logical record} refers to +the logical organization of many characters into something meaningful +to the application. The term @dfn{unit record} describes a small set +of characters which are transmitted whole to or by the application, +and often refers to a line of text. Those two last terms are unrelated +to what we call a @dfn{record} in @GNUTAR{}. + +When writing to tapes, @command{tar} writes the contents of the archive +in chunks known as @dfn{records}. To change the default blocking +factor, use the @option{--blocking-factor=@var{512-size}} (@option{-b +@var{512-size}}) option. Each record will then be composed of +@var{512-size} blocks. (Each @command{tar} block is 512 bytes. +@xref{Standard}.) Each file written to the archive uses at least one +full record. As a result, using a larger record size can result in +more wasted space for small files. On the other hand, a larger record +size can often be read and written much more efficiently. + +Further complicating the problem is that some tape drives ignore the +blocking entirely. For these, a larger record size can still improve +performance (because the software layers above the tape drive still +honor the blocking), but not as dramatically as on tape drives that +honor blocking. + +When reading an archive, @command{tar} can usually figure out the +record size on itself. When this is the case, and a non-standard +record size was used when the archive was created, @command{tar} will +print a message about a non-standard blocking factor, and then operate +normally. On some tape devices, however, @command{tar} cannot figure +out the record size itself. On most of those, you can specify a +blocking factor (with @option{--blocking-factor}) larger than the +actual blocking factor, and then use the @option{--read-full-records} +(@option{-B}) option. (If you specify a blocking factor with +@option{--blocking-factor} and don't use the +@option{--read-full-records} option, then @command{tar} will not +attempt to figure out the recording size itself.) On some devices, +you must always specify the record size exactly with +@option{--blocking-factor} when reading, because @command{tar} cannot +figure it out. In any case, use @option{--list} (@option{-t}) before +doing any extractions to see whether @command{tar} is reading the archive +correctly. + +@command{tar} blocks are all fixed size (512 bytes), and its scheme for +putting them into records is to put a whole number of them (one or +more) into each record. @command{tar} records are all the same size; +at the end of the file there's a block containing all zeros, which +is how you tell that the remainder of the last record(s) are garbage. + +In a standard @command{tar} file (no options), the block size is 512 +and the record size is 10240, for a blocking factor of 20. What the +@option{--blocking-factor} option does is sets the blocking factor, +changing the record size while leaving the block size at 512 bytes. +20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives; +most tape drives these days prefer much bigger records in order to +stream and not waste tape. When writing tapes for myself, some tend +to use a factor of the order of 2048, say, giving a record size of +around one megabyte. + +If you use a blocking factor larger than 20, older @command{tar} +programs might not be able to read the archive, so we recommend this +as a limit to use in practice. @GNUTAR{}, however, +will support arbitrarily large record sizes, limited only by the +amount of virtual memory or the physical characteristics of the tape +device. @menu -* Write Protection:: Write Protection -* Tape Positioning:: Tape Positions and Tape Marks +* Format Variations:: Format Variations +* Blocking Factor:: The Blocking Factor of an Archive @end menu -@node Write Protection, Tape Positioning, Media, Media -@section Write Protection +@node Format Variations +@subsection Format Variations +@cindex Format Parameters +@cindex Format Options +@cindex Options, archive format specifying +@cindex Options, format specifying +@UNREVISED + +Format parameters specify how an archive is written on the archive +media. The best choice of format parameters will vary depending on +the type and number of files being archived, and on the media used to +store the archive. -All tapes and disks can be @dfn{write protected}, to protect data on -them from being changed. Once an archive is written, you should write -protect the media to prevent the archive from being accidently -overwritten or deleted. (This will protect the archive from being -changed with a tape or floppy drive---it will not protect it from -magnet fields or other physical hazards). +To specify format parameters when accessing or creating an archive, +you can use the options described in the following sections. +If you do not specify any format parameters, @command{tar} uses +default parameters. You cannot modify a compressed archive. +If you create an archive with the @option{--blocking-factor} option +specified (@pxref{Blocking Factor}), you must specify that +blocking-factor when operating on the archive. @xref{Formats}, for other +examples of format parameter considerations. + +@node Blocking Factor +@subsection The Blocking Factor of an Archive +@cindex Blocking Factor +@cindex Record Size +@cindex Number of blocks per record +@cindex Number of bytes per record +@cindex Bytes per record +@cindex Blocks per record +@UNREVISED + +@opindex blocking-factor +The data in an archive is grouped into blocks, which are 512 bytes. +Blocks are read and written in whole number multiples called +@dfn{records}. The number of blocks in a record (i.e., the size of a +record in units of 512 bytes) is called the @dfn{blocking factor}. +The @option{--blocking-factor=@var{512-size}} (@option{-b +@var{512-size}}) option specifies the blocking factor of an archive. +The default blocking factor is typically 20 (i.e., 10240 bytes), but +can be specified at installation. To find out the blocking factor of +an existing archive, use @samp{tar --list --file=@var{archive-name}}. +This may not work on some devices. + +Records are separated by gaps, which waste space on the archive media. +If you are archiving on magnetic tape, using a larger blocking factor +(and therefore larger records) provides faster throughput and allows you +to fit more data on a tape (because there are fewer gaps). If you are +archiving on cartridge, a very large blocking factor (say 126 or more) +greatly increases performance. A smaller blocking factor, on the other +hand, may be useful when archiving small files, to avoid archiving lots +of nulls as @command{tar} fills out the archive to the end of the record. +In general, the ideal record size depends on the size of the +inter-record gaps on the tape you are using, and the average size of the +files you are archiving. @xref{create}, for information on +writing archives. + +@FIXME{Need example of using a cartridge with blocking factor=126 or more.} + +Archives with blocking factors larger than 20 cannot be read +by very old versions of @command{tar}, or by some newer versions +of @command{tar} running on old machines with small address spaces. +With @GNUTAR{}, the blocking factor of an archive is limited +only by the maximum record size of the device containing the archive, +or by the amount of available virtual memory. + +Also, on some systems, not using adequate blocking factors, as sometimes +imposed by the device drivers, may yield unexpected diagnostics. For +example, this has been reported: + +@smallexample +Cannot write to /dev/dlt: Invalid argument +@end smallexample -The write protection device itself is usually an integral part of the -physical media, and can be a two position (write enabled/write -disabled) switch, a notch which can be popped out or covered, a ring -which can be removed from the center of a tape reel, or some other -changeable feature. +@noindent +In such cases, it sometimes happen that the @command{tar} bundled by +the system is aware of block size idiosyncrasies, while @GNUTAR{} +requires an explicit specification for the block size, +which it cannot guess. This yields some people to consider +@GNUTAR{} is misbehaving, because by comparison, +@cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}}, +for example, might resolve the problem. + +If you use a non-default blocking factor when you create an archive, you +must specify the same blocking factor when you modify that archive. Some +archive devices will also require you to specify the blocking factor when +reading that archive, however this is not typically the case. Usually, you +can use @option{--list} (@option{-t}) without specifying a blocking factor---@command{tar} +reports a non-default record size and then lists the archive members as +it would normally. To extract files from an archive with a non-standard +blocking factor (particularly if you're not sure what the blocking factor +is), you can usually use the @option{--read-full-records} (@option{-B}) option while +specifying a blocking factor larger then the blocking factor of the archive +(i.e., @samp{tar --extract --read-full-records --blocking-factor=300}). +@xref{list}, for more information on the @option{--list} (@option{-t}) +operation. @xref{Reading}, for a more detailed explanation of that option. + +@table @option +@item --blocking-factor=@var{number} +@itemx -b @var{number} +Specifies the blocking factor of an archive. Can be used with any +operation, but is usually not necessary with @option{--list} (@option{-t}). +@end table -@node Tape Positioning, , Write Protection, Media -@section Tape Positions and Tape Marks +Device blocking + +@table @option +@item -b @var{blocks} +@itemx --blocking-factor=@var{blocks} +Set record size to @math{@var{blocks}*512} bytes. + +This option is used to specify a @dfn{blocking factor} for the archive. +When reading or writing the archive, @command{tar}, will do reads and writes +of the archive in records of @math{@var{block}*512} bytes. This is true +even when the archive is compressed. Some devices requires that all +write operations be a multiple of a certain size, and so, @command{tar} +pads the archive out to the next record boundary. + +The default blocking factor is set when @command{tar} is compiled, and is +typically 20. Blocking factors larger than 20 cannot be read by very +old versions of @command{tar}, or by some newer versions of @command{tar} +running on old machines with small address spaces. + +With a magnetic tape, larger records give faster throughput and fit +more data on a tape (because there are fewer inter-record gaps). +If the archive is in a disk file or a pipe, you may want to specify +a smaller blocking factor, since a large one will result in a large +number of null bytes at the end of the archive. + +When writing cartridge or other streaming tapes, a much larger +blocking factor (say 126 or more) will greatly increase performance. +However, you must specify the same blocking factor when reading or +updating the archive. + +Apparently, Exabyte drives have a physical block size of 8K bytes. +If we choose our blocksize as a multiple of 8k bytes, then the problem +seems to disappear. Id est, we are using block size of 112 right +now, and we haven't had the problem since we switched@dots{} + +With @GNUTAR{} the blocking factor is limited only +by the maximum record size of the device containing the archive, or by +the amount of available virtual memory. + +However, deblocking or reblocking is virtually avoided in a special +case which often occurs in practice, but which requires all the +following conditions to be simultaneously true: +@itemize @bullet +@item +the archive is subject to a compression option, +@item +the archive is not handled through standard input or output, nor +redirected nor piped, +@item +the archive is directly handled to a local disk, instead of any special +device, +@item +@option{--blocking-factor} is not explicitly specified on the @command{tar} +invocation. +@end itemize + +If the output goes directly to a local disk, and not through +stdout, then the last write is not extended to a full record size. +Otherwise, reblocking occurs. Here are a few other remarks on this +topic: + +@itemize @bullet + +@item +@command{gzip} will complain about trailing garbage if asked to +uncompress a compressed archive on tape, there is an option to turn +the message off, but it breaks the regularity of simply having to use +@samp{@var{prog} -d} for decompression. It would be nice if gzip was +silently ignoring any number of trailing zeros. I'll ask Jean-loup +Gailly, by sending a copy of this message to him. + +@item +@command{compress} does not show this problem, but as Jean-loup pointed +out to Michael, @samp{compress -d} silently adds garbage after +the result of decompression, which tar ignores because it already +recognized its end-of-file indicator. So this bug may be safely +ignored. + +@item +@samp{gzip -d -q} will be silent about the trailing zeros indeed, +but will still return an exit status of 2 which tar reports in turn. +@command{tar} might ignore the exit status returned, but I hate doing +that, as it weakens the protection @command{tar} offers users against +other possible problems at decompression time. If @command{gzip} was +silently skipping trailing zeros @emph{and} also avoiding setting the +exit status in this innocuous case, that would solve this situation. + +@item +@command{tar} should become more solid at not stopping to read a pipe at +the first null block encountered. This inelegantly breaks the pipe. +@command{tar} should rather drain the pipe out before exiting itself. +@end itemize + +@xopindex{ignore-zeros, short description} +@item -i +@itemx --ignore-zeros +Ignore blocks of zeros in archive (means EOF). + +The @option{--ignore-zeros} (@option{-i}) option causes @command{tar} to ignore blocks +of zeros in the archive. Normally a block of zeros indicates the +end of the archive, but when reading a damaged archive, or one which +was created by concatenating several archives together, this option +allows @command{tar} to read the entire archive. This option is not on +by default because many versions of @command{tar} write garbage after +the zeroed blocks. + +Note that this option causes @command{tar} to read to the end of the +archive file, which may sometimes avoid problems when multiple files +are stored on a single physical tape. + +@xopindex{read-full-records, short description} +@item -B +@itemx --read-full-records +Reblock as we read (for reading 4.2@acronym{BSD} pipes). + +If @option{--read-full-records} is used, @command{tar} +will not panic if an attempt to read a record from the archive does +not return a full record. Instead, @command{tar} will keep reading +until it has obtained a full +record. + +This option is turned on by default when @command{tar} is reading +an archive from standard input, or from a remote machine. This is +because on @acronym{BSD} Unix systems, a read of a pipe will return however +much happens to be in the pipe, even if it is less than @command{tar} +requested. If this option was not used, @command{tar} would fail as +soon as it read an incomplete record from the pipe. + +This option is also useful with the commands for updating an archive. + +@end table + +Tape blocking + +@FIXME{Appropriate options should be moved here from elsewhere.} + +@cindex blocking factor +@cindex tape blocking + +When handling various tapes or cartridges, you have to take care of +selecting a proper blocking, that is, the number of disk blocks you +put together as a single tape block on the tape, without intervening +tape gaps. A @dfn{tape gap} is a small landing area on the tape +with no information on it, used for decelerating the tape to a +full stop, and for later regaining the reading or writing speed. +When the tape driver starts reading a record, the record has to +be read whole without stopping, as a tape gap is needed to stop the +tape motion without losing information. + +@cindex Exabyte blocking +@cindex DAT blocking +Using higher blocking (putting more disk blocks per tape block) will use +the tape more efficiently as there will be less tape gaps. But reading +such tapes may be more difficult for the system, as more memory will be +required to receive at once the whole record. Further, if there is a +reading error on a huge record, this is less likely that the system will +succeed in recovering the information. So, blocking should not be too +low, nor it should be too high. @command{tar} uses by default a blocking of +20 for historical reasons, and it does not really matter when reading or +writing to disk. Current tape technology would easily accommodate higher +blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs. +We were told that for some DLT drives, the blocking should be a multiple +of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance. +Other manufacturers may use different recommendations for the same tapes. +This might also depends of the buffering techniques used inside modern +tape controllers. Some imposes a minimum blocking, or a maximum blocking. +Others request blocking to be some exponent of two. + +So, there is no fixed rule for blocking. But blocking at read time +should ideally be the same as blocking used at write time. At one place +I know, with a wide variety of equipment, they found it best to use a +blocking of 32 to guarantee that their tapes are fully interchangeable. + +I was also told that, for recycled tapes, prior erasure (by the same +drive unit that will be used to create the archives) sometimes lowers +the error rates observed at rewriting time. + +I might also use @option{--number-blocks} instead of +@option{--block-number}, so @option{--block} will then expand to +@option{--blocking-factor} unambiguously. + +@node Many +@section Many Archives on One Tape + +@FIXME{Appropriate options should be moved here from elsewhere.} + +@findex ntape @r{device} +Most tape devices have two entries in the @file{/dev} directory, or +entries that come in pairs, which differ only in the minor number for +this device. Let's take for example @file{/dev/tape}, which often +points to the only or usual tape device of a given system. There might +be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler +name is the @emph{rewinding} version of the device, while the name +having @samp{nr} in it is the @emph{no rewinding} version of the same +device. + +A rewinding tape device will bring back the tape to its beginning point +automatically when this device is opened or closed. Since @command{tar} +opens the archive file before using it and closes it afterwards, this +means that a simple: + +@smallexample +$ @kbd{tar cf /dev/tape @var{directory}} +@end smallexample + +@noindent +will reposition the tape to its beginning both prior and after saving +@var{directory} contents to it, thus erasing prior tape contents and +making it so that any subsequent write operation will destroy what has +just been saved. + +@cindex tape positioning +So, a rewinding device is normally meant to hold one and only one file. +If you want to put more than one @command{tar} archive on a given tape, you +will need to avoid using the rewinding version of the tape device. You +will also have to pay special attention to tape positioning. Errors in +positioning may overwrite the valuable data already on your tape. Many +people, burnt by past experiences, will only use rewinding devices and +limit themselves to one file per tape, precisely to avoid the risk of +such errors. Be fully aware that writing at the wrong position on a +tape loses all information past this point and most probably until the +end of the tape, and this destroyed information @emph{cannot} be +recovered. + +To save @var{directory-1} as a first archive at the beginning of a +tape, and leave that tape ready for a second archive, you should use: + +@smallexample +$ @kbd{mt -f /dev/nrtape rewind} +$ @kbd{tar cf /dev/nrtape @var{directory-1}} +@end smallexample + +@cindex tape marks +@dfn{Tape marks} are special magnetic patterns written on the tape +media, which are later recognizable by the reading hardware. These +marks are used after each file, when there are many on a single tape. +An empty file (that is to say, two tape marks in a row) signal the +logical end of the tape, after which no file exist. Usually, +non-rewinding tape device drivers will react to the close request issued +by @command{tar} by first writing two tape marks after your archive, and by +backspacing over one of these. So, if you remove the tape at that time +from the tape drive, it is properly terminated. But if you write +another file at the current position, the second tape mark will be +erased by the new information, leaving only one tape mark between files. + +So, you may now save @var{directory-2} as a second archive after the +first on the same tape by issuing the command: + +@smallexample +$ @kbd{tar cf /dev/nrtape @var{directory-2}} +@end smallexample + +@noindent +and so on for all the archives you want to put on the same tape. + +Another usual case is that you do not write all the archives the same +day, and you need to remove and store the tape between two archive +sessions. In general, you must remember how many files are already +saved on your tape. Suppose your tape already has 16 files on it, and +that you are ready to write the 17th. You have to take care of skipping +the first 16 tape marks before saving @var{directory-17}, say, by using +these commands: + +@smallexample +$ @kbd{mt -f /dev/nrtape rewind} +$ @kbd{mt -f /dev/nrtape fsf 16} +$ @kbd{tar cf /dev/nrtape @var{directory-17}} +@end smallexample + +In all the previous examples, we put aside blocking considerations, but +you should do the proper things for that as well. @xref{Blocking}. + +@menu +* Tape Positioning:: Tape Positions and Tape Marks +* mt:: The @command{mt} Utility +@end menu + +@node Tape Positioning +@subsection Tape Positions and Tape Marks +@UNREVISED Just as archives can store more than one file from the file system, tapes can store more than one archive file. To keep track of where @@ -3117,26 +11085,25 @@ end, tape archive devices write magnetic @dfn{tape marks} on the archive media. Tape drives write one tape mark between files, two at the end of all the file entries. -If you think of data as a series of "0000"'s, and tape marks as "x"'s, -a tape might look like the following: +If you think of data as a series of records "rrrr"'s, and tape marks as +"*"'s, a tape might look like the following: -@example -0000x000000x00000x00x00000xx------------------------- -@end example +@smallexample +rrrr*rrrrrr*rrrrr*rr*rrrrr**------------------------- +@end smallexample Tape devices read and write tapes using a read/write @dfn{tape -head}---a physical part of the device which can only access one point -on the tape at a time. When you use @code{tar} to read or write -archive data from a tape device, the device will begin reading or -writing from wherever on the tape the tape head happens to be, -regardless of which archive or what part of the archive the tape head -is on. Before writing an archive, you should make sure that no data -on the tape will be overwritten (unless it is no longer needed). +head}---a physical part of the device which can only access one +point on the tape at a time. When you use @command{tar} to read or +write archive data from a tape device, the device will begin reading +or writing from wherever on the tape the tape head happens to be, +regardless of which archive or what part of the archive the tape +head is on. Before writing an archive, you should make sure that no +data on the tape will be overwritten (unless it is no longer needed). Before reading an archive, you should make sure the tape head is at -the beginning of the archive you want to read. (The @code{restore} -script will find the archive automatically. @xref{Scripted -Restoration}). @xref{mt}, for an explanation of the tape moving -utility. +the beginning of the archive you want to read. You can do it manually +via @code{mt} utility (@pxref{mt}). The @code{restore} script does +that automatically (@pxref{Scripted Restoration}). If you want to add new archive file entries to a tape, you should advance the tape to the end of the existing file entries, backspace @@ -3144,813 +11111,1310 @@ over the last tape mark, and write the new archive file. If you were to add two archives to the example above, the tape might look like the following: -@example -0000x000000x00000x00x00000x000x0000xx---------------- -@end example - -@menu -* mt:: The @code{mt} Utility -@end menu +@smallexample +rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**---------------- +@end smallexample -@node mt, , Tape Positioning, Tape Positioning -@subsection The @code{mt} Utility +@node mt +@subsection The @command{mt} Utility +@UNREVISED -<<< is it true that this only works on non-block devices? should -<<< explain the difference, xref to block-size (fixed or variable). +@FIXME{Is it true that this only works on non-block devices? +should explain the difference, (fixed or variable).} +@xref{Blocking Factor}. -You can use the @code{mt} utility to advance or rewind a tape past a -specified number of archive files on the tape. This will allow you to -move to the beginning of an archive before extracting or reading it, -or to the end of all the archives before writing a new one. -@c why isn't there an "advance 'til you find two tape marks together"? +You can use the @command{mt} utility to advance or rewind a tape past a +specified number of archive files on the tape. This will allow you +to move to the beginning of an archive before extracting or reading +it, or to the end of all the archives before writing a new one. +@FIXME{Why isn't there an "advance 'til you find two tape marks +together"?} -The syntax of the @code{mt} command is: +The syntax of the @command{mt} command is: -@example -mt [-f @var{tapename}] @var{operation} [@var{number}] -@end example +@smallexample +@kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]} +@end smallexample where @var{tapename} is the name of the tape device, @var{number} is the number of times an operation is performed (with a default of one), and @var{operation} is one of the following: -@table @code +@FIXME{is there any use for record operations?} + +@table @option @item eof @itemx weof Writes @var{number} tape marks at the current position on the tape. - -@item fsf +@item fsf Moves tape position forward @var{number} files. - @item bsf Moves tape position back @var{number} files. - @item rewind -Rewinds the tape. (Ignores @var{number}). - +Rewinds the tape. (Ignores @var{number}.) @item offline @itemx rewoff1 -Rewinds the tape and takes the tape device off-line. (Ignores @var{number}). - +Rewinds the tape and takes the tape device off-line. (Ignores @var{number}.) @item status Prints status information about the tape unit. + @end table -<<< is there a better way to frob the spacing on the list? -ringo -If you don't specify a @var{tapename}, @code{mt} uses the environment -variable TAPE; if TAPE does not exist, @code{mt} uses the device -@file{/dev/rmt12}. +If you don't specify a @var{tapename}, @command{mt} uses the environment +variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use +the default device specified in your @file{sys/mtio.h} file +(@code{DEFTAPE} variable). If this is not defined, the program will +display a descriptive error message and exit with code 1. -@code{mt} returns a 0 exit status when the operation(s) were +@command{mt} returns a 0 exit status when the operation(s) were successful, 1 if the command was unrecognized, and 2 if an operation failed. -@c <<< new node on how to find an archive? -ringo -If you use @code{tar +extract} with the -@samp{+label=@var{archive-name}} option specified, @code{tar} will -read an archive label (the tape head has to be positioned on it) and -print an error if the archive label doesn't match the -@var{archive-name} specified. @var{archive-name} can be any regular -expression. If the labels match, @code{tar} extracts the archive. -@xref{Archive Label}. @xref{Matching Format Parameters}. -<<< fix cross references - -@code{tar +list +label} will cause @code{tar} to print the label. - -@c <<< MIB -- program to list all the labels on a tape? - -@node Quick Reference, Data Format Details, Media, Top -@appendix A Quick Reference Guide to @code{tar} Operations and Options -@c put in proper form for appendix. (unnumbered?) +@node Using Multiple Tapes +@section Using Multiple Tapes + +Often you might want to write a large archive, one larger than will fit +on the actual tape you are using. In such a case, you can run multiple +@command{tar} commands, but this can be inconvenient, particularly if you +are using options like @option{--exclude=@var{pattern}} or dumping entire file systems. +Therefore, @command{tar} provides a special mode for creating +multi-volume archives. + +@dfn{Multi-volume} archive is a single @command{tar} archive, stored +on several media volumes of fixed size. Although in this section we will +often call @samp{volume} a @dfn{tape}, there is absolutely no +requirement for multi-volume archives to be stored on tapes. Instead, +they can use whatever media type the user finds convenient, they can +even be located on files. + +When creating a multi-volume archive, @GNUTAR{} continues to fill +current volume until it runs out of space, then it switches to +next volume (usually the operator is queried to replace the tape on +this point), and continues working on the new volume. This operation +continues until all requested files are dumped. If @GNUTAR{} detects +end of media while dumping a file, such a file is archived in split +form. Some very big files can even be split across several volumes. + +Each volume is itself a valid @GNUTAR{} archive, so it can be read +without any special options. Consequently any file member residing +entirely on one volume can be extracted or otherwise operated upon +without needing the other volume. Sure enough, to extract a split +member you would need all volumes its parts reside on. + +Multi-volume archives suffer from several limitations. In particular, +they cannot be compressed. + +@GNUTAR{} is able to create multi-volume archives of two formats +(@pxref{Formats}): @samp{GNU} and @samp{POSIX}. @menu -* Operations:: A Table of Operations -* Options:: Table of Options -@end menu - -@node Operations, Options, Quick Reference, Quick Reference -@appendixsec A Table of Operations -@c add xrefs, note synonyms - -The operation argument to @code{tar} specifies which action you want to -take. - -@table @samp -@item -A -Adds copies of an archive or archives to the end of another archive. - -@item -c -Creates a new archive. - -@item -d -Compares files in the archive with their counterparts in the file -system, and reports differences in file size, mode, owner, -modification date and contents. +* Multi-Volume Archives:: Archives Longer than One Tape or Disk +* Tape Files:: Tape Files +* Tarcat:: Concatenate Volumes into a Single Archive -@item -r -Adds files to the end of the archive. - -@item -t -Prints a list of the contents of the archive. - -@item -x -Reads files from the archive and writes them into the active file -system. - -@item -u -Adds files to the end of the archive, but only if they are newer than -their counterparts already in the archive, or if they do not already -exist in the archive. - -@item +add-archive -Adds copies of an archive or archives to the end of another archive. - -@item +add-file -Adds files to the end of the archive. - -@item +append -Adds files to the end of the archive. - -@item +catenate -Adds copies of an archive or archives to the end of another archive. - -@item +compare -Compares files in the archive with their counterparts in the file -system, and reports differences in file size, mode, owner, -modification date and contents. - -@item +concatenate -Adds copies of an archive or archives to the end of another archive. - -@item +create -Creates a new archive. +@end menu -@item +delete -Deletes files from the archive. All versions of the files are deleted. +@node Multi-Volume Archives +@subsection Archives Longer than One Tape or Disk +@cindex Multi-volume archives -@item +diff -Compares files in the archive with their counterparts in the file -system, and reports differences in file size, mode, owner, -modification date and contents. +@opindex multi-volume +To create an archive that is larger than will fit on a single unit of +the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with +the @option{--create} option (@pxref{create}). A @dfn{multi-volume} +archive can be manipulated like any other archive (provided the +@option{--multi-volume} option is specified), but is stored on more +than one tape or file. -@item +extract -Reads files from the archive and writes them into the active file -system. +When you specify @option{--multi-volume}, @command{tar} does not report an +error when it comes to the end of an archive volume (when reading), or +the end of the media (when writing). Instead, it prompts you to load +a new storage volume. If the archive is on a magnetic tape, you +should change tapes when you see the prompt; if the archive is on a +floppy disk, you should change disks; etc. -@item +get -Reads files from the archive and writes them into the active file -system. +@table @option +@item --multi-volume +@itemx -M +Creates a multi-volume archive, when used in conjunction with +@option{--create} (@option{-c}). To perform any other operation on a multi-volume +archive, specify @option{--multi-volume} in conjunction with that +operation. +For example: -@item +help -Prints a list of @code{tar} operations and options. +@smallexample +$ @kbd{tar --create --multi-volume --file=/dev/tape @var{files}} +@end smallexample +@end table -@item +list -Prints a list of the contents of the archive. +The method @command{tar} uses to detect end of tape is not perfect, and +fails on some operating systems or on some devices. If @command{tar} +cannot detect the end of the tape itself, you can use +@option{--tape-length} option to inform it about the capacity of the +tape: + +@anchor{tape-length} +@table @option +@opindex tape-length +@item --tape-length=@var{size}[@var{suf}] +@itemx -L @var{size}[@var{suf}] +Set maximum length of a volume. The @var{suf}, if given, specifies +units in which @var{size} is expressed, e.g. @samp{2M} mean 2 +megabytes (@pxref{size-suffixes}, for a list of allowed size +suffixes). Without @var{suf}, units of 1024 bytes (kilobyte) are +assumed. + +This option selects @option{--multi-volume} automatically. For example: + +@smallexample +$ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}} +@end smallexample -@item +update -Adds files to the end of the archive, but only if they are newer than -their counterparts already in the archive, or if they do not already -exist in the archive. +@noindent +or, which is equivalent: -@item +version -Prints the version number of the @code{tar} program to the standard -error. +@smallexample +$ @kbd{tar --create --tape-length=4G --file=/dev/tape @var{files}} +@end smallexample @end table -@node Options, , Operations, Quick Reference -@appendixsec Table of Options - -Options change the way @code{tar} performs an operation. +@anchor{change volume prompt} +When @GNUTAR{} comes to the end of a storage media, it asks you to +change the volume. The built-in prompt for POSIX locale +is@footnote{If you run @GNUTAR{} under a different locale, the +translation to the locale's language will be used.}: -@table @samp -@item +absolute-paths -WILL BE INPUT WHEN QUESTION IS RESOLVED - -@item +after-date=@var{date} -Limit the operation to files changed after the given date. -@xref{File Exclusion}. +@smallexample +Prepare volume #@var{n} for '@var{archive}' and hit return: +@end smallexample -@item +block-size=@var{number} -Specify the blocking factor of an archive. @xref{Blocking Factor}. +@noindent +where @var{n} is the ordinal number of the volume to be created and +@var{archive} is archive file or device name. + +When prompting for a new tape, @command{tar} accepts any of the following +responses: + +@table @kbd +@item ? +Request @command{tar} to explain possible responses. +@item q +Request @command{tar} to exit immediately. +@item n @var{file-name} +Request @command{tar} to write the next volume on the file @var{file-name}. +@item ! +Request @command{tar} to run a subshell. This option can be disabled +by giving @option{--restrict} command line option to +@command{tar}@footnote{@xref{--restrict}, for more information about +this option.}. +@item y +Request @command{tar} to begin writing the next volume. +@end table -@item +compress -Specify a compressed archive. @xref{Compressed Archives}. +(You should only type @samp{y} after you have changed the tape; +otherwise @command{tar} will write over the volume it just finished.) + +@cindex Volume number file +@cindex volno file +@anchor{volno-file} +@opindex volno-file +The volume number used by @command{tar} in its tape-changing prompt +can be changed; if you give the +@option{--volno-file=@var{file-of-number}} option, then +@var{file-of-number} should be an non-existing file to be created, or +else, a file already containing a decimal number. That number will be +used as the volume number of the first volume written. When +@command{tar} is finished, it will rewrite the file with the +now-current volume number. (This does not change the volume number +written on a tape label, as per @ref{label}, it @emph{only} affects +the number used in the prompt.) + +@cindex End-of-archive info script +@cindex Info script +@anchor{info-script} +@opindex info-script +@opindex new-volume-script +If you want more elaborate behavior than this, you can write a special +@dfn{new volume script}, that will be responsible for changing the +volume, and instruct @command{tar} to use it instead of its normal +prompting procedure: + +@table @option +@item --info-script=@var{script-name} +@itemx --new-volume-script=@var{script-name} +@itemx -F @var{script-name} +Specify the full name of the volume script to use. The script can be +used to eject cassettes, or to broadcast messages such as +@samp{Someone please come change my tape} when performing unattended +backups. +@end table -@item +compress-block. -Create a whole block sized compressed archive. @xref{Compressed Archives}. +The @var{script-name} is executed without any command line +arguments. It inherits @command{tar}'s shell environment. +Additional data is passed to it via the following +environment variables: + +@table @env +@vrindex TAR_VERSION, info script environment variable +@item TAR_VERSION +@GNUTAR{} version number. + +@vrindex TAR_ARCHIVE, info script environment variable +@item TAR_ARCHIVE +The name of the archive @command{tar} is processing. + +@vrindex TAR_BLOCKING_FACTOR, info script environment variable +@item TAR_BLOCKING_FACTOR +Current blocking factor (@pxref{Blocking}). + +@vrindex TAR_VOLUME, info script environment variable +@item TAR_VOLUME +Ordinal number of the volume @command{tar} is about to start. + +@vrindex TAR_SUBCOMMAND, info script environment variable +@item TAR_SUBCOMMAND +A short option describing the operation @command{tar} is executing. +@xref{Operations}, for a complete list of subcommand options. + +@vrindex TAR_FORMAT, info script environment variable +@item TAR_FORMAT +Format of the archive being processed. @xref{Formats}, for a complete +list of archive format names. + +@vrindex TAR_FD, info script environment variable +@item TAR_FD +File descriptor which can be used to communicate the new volume +name to @command{tar}. +@end table -@item +confirmation -Solicit confirmation for each file. @xref{Interactive Operation} -<<< +selective should be a synonym. +The volume script can instruct @command{tar} to use new archive name, +by writing in to file descriptor @env{$TAR_FD} (see below for an example). + +If the info script fails, @command{tar} exits; otherwise, it begins +writing the next volume. + +If you want @command{tar} to cycle through a series of files or tape +drives, there are three approaches to choose from. First of all, you +can give @command{tar} multiple @option{--file} options. In this case +the specified files will be used, in sequence, as the successive +volumes of the archive. Only when the first one in the sequence needs +to be used again will @command{tar} prompt for a tape change (or run +the info script). For example, suppose someone has two tape drives on +a system named @file{/dev/tape0} and @file{/dev/tape1}. For having +@GNUTAR{} to switch to the second drive when it needs to write the +second tape, and then back to the first tape, etc., just do either of: + +@smallexample +$ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}} +$ @kbd{tar -cM -f /dev/tape0 -f /dev/tape1 @var{files}} +@end smallexample + +The second method is to use the @samp{n} response to the tape-change +prompt. + +Finally, the most flexible approach is to use a volume script, that +writes new archive name to the file descriptor @env{$TAR_FD}. For example, the +following volume script will create a series of archive files, named +@file{@var{archive}-@var{vol}}, where @var{archive} is the name of the +archive being created (as given by @option{--file} option) and +@var{vol} is the ordinal number of the archive being created: + +@smallexample +@group +#! /bin/bash +# For this script it's advisable to use a shell, such as Bash, +# that supports a TAR_FD value greater than 9. + +echo Preparing volume $TAR_VOLUME of $TAR_ARCHIVE. + +name=`expr $TAR_ARCHIVE : '\(.*\)-.*'` +case $TAR_SUBCOMMAND in +-c) ;; +-d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1 + ;; +*) exit 1 +esac + +echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&$TAR_FD +@end group +@end smallexample + +The same script can be used while listing, comparing or extracting +from the created archive. For example: + +@smallexample +@group +# @r{Create a multi-volume archive:} +$ @kbd{tar -c -L1024 -f archive.tar -F new-volume .} +# @r{Extract from the created archive:} +$ @kbd{tar -x -f archive.tar -F new-volume .} +@end group +@end smallexample -@item +dereference -Treat a symbolic link as an alternate name for the file the link -points to. @xref{Symbolic Links}. +@noindent +Notice, that the first command had to use @option{-L} option, since +otherwise @GNUTAR{} will end up writing everything to file +@file{archive.tar}. -@item +directory=@file{directory} -Change the working directory. @xref{Changing Working Directory}. +You can read each individual volume of a multi-volume archive as if it +were an archive by itself. For example, to list the contents of one +volume, use @option{--list}, without @option{--multi-volume} specified. +To extract an archive member from one volume (assuming it is described +that volume), use @option{--extract}, again without +@option{--multi-volume}. -@item +exclude=@var{pattern} -Exclude files which match the regular expression @var{pattern}. -@xref{File Exclusion}. +If an archive member is split across volumes (i.e., its entry begins on +one volume of the media and ends on another), you need to specify +@option{--multi-volume} to extract it successfully. In this case, you +should load the volume where the archive member starts, and use +@samp{tar --extract --multi-volume}---@command{tar} will prompt for later +volumes as it needs them. @xref{extracting archives}, for more +information about extracting archives. -@item +exclude-from=@file{file} -Exclude files which match any of the regular expressions listed in -the file @file{file}. @xref{File Exclusion}. +Multi-volume archives can be modified like any other archive. To add +files to a multi-volume archive, you need to only mount the last +volume of the archive media (and new volumes, if needed). For all +other operations, you need to use the entire archive. + +If a multi-volume archive was labeled using +@option{--label=@var{archive-label}} (@pxref{label}) when it was +created, @command{tar} will not automatically label volumes which are +added later. To label subsequent volumes, specify +@option{--label=@var{archive-label}} again in conjunction with the +@option{--append}, @option{--update} or @option{--concatenate} operation. + +Notice that multi-volume support is a GNU extension and the archives +created in this mode should be read only using @GNUTAR{}. If you +absolutely have to process such archives using a third-party @command{tar} +implementation, read @ref{Split Recovery}. + +@node Tape Files +@subsection Tape Files +@cindex labeling archives +@opindex label +@UNREVISED + +To give the archive a name which will be recorded in it, use the +@option{--label=@var{volume-label}} (@option{-V @var{volume-label}}) +option. This will write a special block identifying +@var{volume-label} as the name of the archive to the front of the +archive which will be displayed when the archive is listed with +@option{--list}. If you are creating a multi-volume archive with +@option{--multi-volume} (@pxref{Using Multiple Tapes}), then the +volume label will have @samp{Volume @var{nnn}} appended to the name +you give, where @var{nnn} is the number of the volume of the archive. +If you use the @option{--label=@var{volume-label}} option when +reading an archive, it checks to make sure the label on the tape +matches the one you gave. @xref{label}. + +When @command{tar} writes an archive to tape, it creates a single +tape file. If multiple archives are written to the same tape, one +after the other, they each get written as separate tape files. When +extracting, it is necessary to position the tape at the right place +before running @command{tar}. To do this, use the @command{mt} command. +For more information on the @command{mt} command and on the organization +of tapes into a sequence of tape files, see @ref{mt}. + +People seem to often do: + +@smallexample +@kbd{--label="@var{some-prefix} `date +@var{some-format}`"} +@end smallexample + +or such, for pushing a common date in all volumes or an archive set. + +@node Tarcat +@subsection Concatenate Volumes into a Single Archive + +@pindex tarcat + Sometimes it is necessary to convert existing @GNUTAR{} multi-volume +archive to a single @command{tar} archive. Simply concatenating all +volumes into one will not work, since each volume carries an additional +information at the beginning. @GNUTAR{} is shipped with the shell +script @command{tarcat} designed for this purpose. + + The script takes a list of files comprising a multi-volume archive +and creates the resulting archive at the standard output. For example: + +@smallexample +@kbd{tarcat vol.1 vol.2 vol.3 | tar tf -} +@end smallexample + + The script implements a simple heuristics to determine the format of +the first volume file and to decide how to process the rest of the +files. However, it makes no attempt to verify whether the files are +given in order or even if they are valid @command{tar} archives. +It uses @command{dd} and does not filter its standard error, so you +will usually see lots of spurious messages. + +@FIXME{The script is not installed. Should we install it?} + +@node label +@section Including a Label in the Archive +@cindex Labeling an archive +@cindex Labels on the archive media +@cindex Labeling multi-volume archives + +@opindex label + To avoid problems caused by misplaced paper labels on the archive +media, you can include a @dfn{label} entry --- an archive member which +contains the name of the archive --- in the archive itself. Use the +@option{--label=@var{archive-label}} (@option{-V @var{archive-label}}) +option@footnote{Until version 1.10, that option was called +@option{--volume}, but is not available under that name anymore.} in +conjunction with the @option{--create} operation to include a label +entry in the archive as it is being created. + +@table @option +@item --label=@var{archive-label} +@itemx -V @var{archive-label} +Includes an @dfn{archive-label} at the beginning of the archive when +the archive is being created, when used in conjunction with the +@option{--create} operation. Checks to make sure the archive label +matches the one specified (when used in conjunction with any other +operation). +@end table -@item +file=@var{archive-name} -Name the archive. @xref{Archive Name}). + If you create an archive using both +@option{--label=@var{archive-label}} (@option{-V @var{archive-label}}) +and @option{--multi-volume} (@option{-M}), each volume of the archive +will have an archive label of the form @samp{@var{archive-label} +Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the +next, and so on. @xref{Using Multiple Tapes}, for information on +creating multiple volume archives. + +@cindex Volume label, listing +@cindex Listing volume label + The volume label will be displayed by @option{--list} along with +the file contents. If verbose display is requested, it will also be +explicitly marked as in the example below: + +@smallexample +@group +$ @kbd{tar --verbose --list --file=iamanarchive} +V--------- 0/0 0 1992-03-07 12:01 iamalabel--Volume Header-- +-rw-r--r-- ringo/user 40 1990-05-21 13:30 iamafilename +@end group +@end smallexample + +@opindex test-label +@anchor{--test-label option} + However, @option{--list} option will cause listing entire +contents of the archive, which may be undesirable (for example, if the +archive is stored on a tape). You can request checking only the volume +label by specifying @option{--test-label} option. This option reads only the +first block of an archive, so it can be used with slow storage +devices. For example: + +@smallexample +@group +$ @kbd{tar --test-label --file=iamanarchive} +iamalabel +@end group +@end smallexample + + If @option{--test-label} is used with one or more command line +arguments, @command{tar} compares the volume label with each +argument. It exits with code 0 if a match is found, and with code 1 +otherwise@footnote{Note that @GNUTAR{} versions up to 1.23 indicated +mismatch with an exit code 2 and printed a spurious diagnostics on +stderr.}. No output is displayed, unless you also used the +@option{--verbose} option. For example: + +@smallexample +@group +$ @kbd{tar --test-label --file=iamanarchive 'iamalabel'} +@result{} 0 +$ @kbd{tar --test-label --file=iamanarchive 'alabel'} +@result{} 1 +@end group +@end smallexample + + When used with the @option{--verbose} option, @command{tar} +prints the actual volume label (if any), and a verbose diagnostics in +case of a mismatch: + +@smallexample +@group +$ @kbd{tar --test-label --verbose --file=iamanarchive 'iamalabel'} +iamalabel +@result{} 0 +$ @kbd{tar --test-label --verbose --file=iamanarchive 'alabel'} +iamalabel +tar: Archive label mismatch +@result{} 1 +@end group +@end smallexample + + If you request any operation, other than @option{--create}, along +with using @option{--label} option, @command{tar} will first check if +the archive label matches the one specified and will refuse to proceed +if it does not. Use this as a safety precaution to avoid accidentally +overwriting existing archives. For example, if you wish to add files +to @file{archive}, presumably labeled with string @samp{My volume}, +you will get: + +@smallexample +@group +$ @kbd{tar -rf archive --label 'My volume' .} +tar: Archive not labeled to match 'My volume' +@end group +@end smallexample -@item +files-from=@file{file} -Read file-name arguments from a file on the file system. -@xref{File Name Lists}. +@noindent +in case its label does not match. This will work even if +@file{archive} is not labeled at all. + + Similarly, @command{tar} will refuse to list or extract the +archive if its label doesn't match the @var{archive-label} +specified. In those cases, @var{archive-label} argument is interpreted +as a globbing-style pattern which must match the actual magnetic +volume label. @xref{exclude}, for a precise description of how match +is attempted@footnote{Previous versions of @command{tar} used full +regular expression matching, or before that, only exact string +matching, instead of wildcard matchers. We decided for the sake of +simplicity to use a uniform matching device through +@command{tar}.}. If the switch @option{--multi-volume} (@option{-M}) is being used, +the volume label matcher will also suffix @var{archive-label} by +@w{@samp{ Volume [1-9]*}} if the initial match fails, before giving +up. Since the volume numbering is automatically added in labels at +creation time, it sounded logical to equally help the user taking care +of it when the archive is being read. + + You can also use @option{--label} to get a common information on +all tapes of a series. For having this information different in each +series created through a single script used on a regular basis, just +manage to get some date string as part of the label. For example: + +@smallexample +@group +$ @kbd{tar -cM -f /dev/tape -V "Daily backup for `date +%Y-%m-%d`"} +$ @kbd{tar --create --file=/dev/tape --multi-volume \ + --label="Daily backup for `date +%Y-%m-%d`"} +@end group +@end smallexample + + Some more notes about volume labels: -@item +ignore-umask -Set modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. +@itemize @bullet +@item Each label has its own date and time, which corresponds +to the time when @GNUTAR{} initially attempted to write it, +often soon after the operator launches @command{tar} or types the +carriage return telling that the next tape is ready. + +@item Comparing date labels to get an idea of tape throughput is +unreliable. It gives correct results only if the delays for rewinding +tapes and the operator switching them were negligible, which is +usually not the case. +@end itemize -@item +ignore-zeros -Ignore end-of-archive entries. @xref{Archive Reading Options}. -<<< this should be changed to +ignore-end +@node verify +@section Verifying Data as It is Stored +@cindex Verifying a write operation +@cindex Double-checking a write operation -@item +listed-incremental=@var{file-name} (-g) -Take a file name argument always. If the file doesn't exist, run a level -zero dump, creating the file. If the file exists, uses that file to see -what has changed. +@table @option +@item -W +@itemx --verify +@opindex verify, short description +Attempt to verify the archive after writing. +@end table -@item +incremental (-G) -@c <<>> +This option causes @command{tar} to verify the archive after writing it. +Each volume is checked after it is written, and any discrepancies +are recorded on the standard error output. -@item +tape-length=@var{n} (-L) -@c <<>> -@c <<< this needs to be written into main body as well -ringo +Verification requires that the archive be on a back-space-able medium. +This means pipes, some cartridge tape drives, and some other devices +cannot be verified. -@item +info-script=@var{program-file} -Create a multi-volume archive via a script. @xref{Multi-Volume Archives}. +You can insure the accuracy of an archive by comparing files in the +system with archive members. @command{tar} can compare an archive to the +file system as the archive is being written, to verify a write +operation, or can compare a previously written archive, to insure that +it is up to date. -@item +interactive -Ask for confirmation before performing any operation on a file or -archive member. +@xopindex{verify, using with @option{--create}} +@xopindex{create, using with @option{--verify}} +To check for discrepancies in an archive immediately after it is +written, use the @option{--verify} (@option{-W}) option in conjunction with +the @option{--create} operation. When this option is +specified, @command{tar} checks archive members against their counterparts +in the file system, and reports discrepancies on the standard error. -@item +keep-old-files -Prevent overwriting during extraction. @xref{File Writing Options}. +To verify an archive, you must be able to read it from before the end +of the last written entry. This option is useful for detecting data +errors on some tapes. Archives written to pipes, some cartridge tape +drives, and some other devices cannot be verified. -@item +label=@var{archive-label} -Include an archive-label in the archive being created. @xref{Archive -Label}. +One can explicitly compare an already made archive with the file +system by using the @option{--compare} (@option{--diff}, @option{-d}) +option, instead of using the more automatic @option{--verify} option. +@xref{compare}. + +Note that these two options have a slightly different intent. The +@option{--compare} option checks how identical are the logical contents of some +archive with what is on your disks, while the @option{--verify} option is +really for checking if the physical contents agree and if the recording +media itself is of dependable quality. So, for the @option{--verify} +operation, @command{tar} tries to defeat all in-memory cache pertaining to +the archive, while it lets the speed optimization undisturbed for the +@option{--compare} option. If you nevertheless use @option{--compare} for +media verification, you may have to defeat the in-memory cache yourself, +maybe by opening and reclosing the door latch of your recording unit, +forcing some doubt in your operating system about the fact this is really +the same volume as the one just written or read. + +The @option{--verify} option would not be necessary if drivers were indeed +able to detect dependably all write failures. This sometimes require many +magnetic heads, some able to read after the writes occurred. One would +not say that drivers unable to detect all cases are necessarily flawed, +as long as programming is concerned. + +The @option{--verify} (@option{-W}) option will not work in +conjunction with the @option{--multi-volume} (@option{-M}) option or +the @option{--append} (@option{-r}), @option{--update} (@option{-u}) +and @option{--delete} operations. @xref{Operations}, for more +information on these operations. + +Also, since @command{tar} normally strips leading @samp{/} from file +names (@pxref{absolute}), a command like @samp{tar --verify -cf +/tmp/foo.tar /etc} will work as desired only if the working directory is +@file{/}, as @command{tar} uses the archive's relative member names +(e.g., @file{etc/motd}) when verifying the archive. + +@node Write Protection +@section Write Protection -@item +modification-time -Set the modification time of extracted files to the time they were -extracted. @xref{File Writing Options}. +Almost all tapes and diskettes, and in a few rare cases, even disks can +be @dfn{write protected}, to protect data on them from being changed. +Once an archive is written, you should write protect the media to prevent +the archive from being accidentally overwritten or deleted. (This will +protect the archive from being changed with a tape or floppy drive---it +will not protect it from magnet fields or other physical hazards.) -@item +multi-volume -Specify a multi-volume archive. @xref{Multi-Volume Archives}. +The write protection device itself is usually an integral part of the +physical media, and can be a two position (write enabled/write +disabled) switch, a notch which can be popped out or covered, a ring +which can be removed from the center of a tape reel, or some other +changeable feature. -@item +newer=@var{date} -Limit the operation to files changed after the given date. -@xref{File Exclusion}. +@node Reliability and security +@chapter Reliability and Security -@item +newer-mtime=@var{date} -Limit the operation to files modified after the given date. @xref{File -Exclusion}. +The @command{tar} command reads and writes files as any other +application does, and is subject to the usual caveats about +reliability and security. This section contains some commonsense +advice on the topic. -@item +old -Create an old format archive. @xref{Old Style File Information}. -@c <<< did we agree this should go away as a synonym? +@menu +* Reliability:: +* Security:: +@end menu -@item +old-archive -Create an old format archive. @xref{Old Style File Information}. +@node Reliability +@section Reliability -@item +one-file-system -Prevent @code{tar} from crossing file system boundaries when -archiving. @xref{File Exclusion}. +Ideally, when @command{tar} is creating an archive, it reads from a +file system that is not being modified, and encounters no errors or +inconsistencies while reading and writing. If this is the case, the +archive should faithfully reflect what was read. Similarly, when +extracting from an archive, ideally @command{tar} ideally encounters +no errors and the extracted files faithfully reflect what was in the +archive. -@item +portable -Create an old format archive. @xref{Old Style File Information}. -@c <<< was portability, may still need to be changed +However, when reading or writing real-world file systems, several +things can go wrong; these include permissions problems, corruption of +data, and race conditions. -@item +preserve-order -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. +@menu +* Permissions problems:: +* Data corruption and repair:: +* Race conditions:: +@end menu -@item +preserve-permission -Set modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. +@node Permissions problems +@subsection Permissions Problems + +If @command{tar} encounters errors while reading or writing files, it +normally reports an error and exits with nonzero status. The work it +does may therefore be incomplete. For example, when creating an +archive, if @command{tar} cannot read a file then it cannot copy the +file into the archive. + +@node Data corruption and repair +@subsection Data Corruption and Repair + +If an archive becomes corrupted by an I/O error, this may corrupt the +data in an extracted file. Worse, it may corrupt the file's metadata, +which may cause later parts of the archive to become misinterpreted. +An tar-format archive contains a checksum that most likely will detect +errors in the metadata, but it will not detect errors in the data. + +If data corruption is a concern, you can compute and check your own +checksums of an archive by using other programs, such as +@command{cksum}. + +When attempting to recover from a read error or data corruption in an +archive, you may need to skip past the questionable data and read the +rest of the archive. This requires some expertise in the archive +format and in other software tools. + +@node Race conditions +@subsection Race conditions + +If some other process is modifying the file system while @command{tar} +is reading or writing files, the result may well be inconsistent due +to race conditions. For example, if another process creates some +files in a directory while @command{tar} is creating an archive +containing the directory's files, @command{tar} may see some of the +files but not others, or it may see a file that is in the process of +being created. The resulting archive may not be a snapshot of the +file system at any point in time. If an application such as a +database system depends on an accurate snapshot, restoring from the +@command{tar} archive of a live file system may therefore break that +consistency and may break the application. The simplest way to avoid +the consistency issues is to avoid making other changes to the file +system while tar is reading it or writing it. + +When creating an archive, several options are available to avoid race +conditions. Some hosts have a way of snapshotting a file system, or +of temporarily suspending all changes to a file system, by (say) +suspending the only virtual machine that can modify a file system; if +you use these facilities and have @command{tar -c} read from a +snapshot when creating an archive, you can avoid inconsistency +problems. More drastically, before starting @command{tar} you could +suspend or shut down all processes other than @command{tar} that have +access to the file system, or you could unmount the file system and +then mount it read-only. + +When extracting from an archive, one approach to avoid race conditions +is to create a directory that no other process can write to, and +extract into that. + +@node Security +@section Security + +In some cases @command{tar} may be used in an adversarial situation, +where an untrusted user is attempting to gain information about or +modify otherwise-inaccessible files. Dealing with untrusted data +(that is, data generated by an untrusted user) typically requires +extra care, because even the smallest mistake in the use of +@command{tar} is more likely to be exploited by an adversary than by a +race condition. -@item +read-full-blocks -Read an archive with a smaller than specified block size or which -contains incomplete blocks. @xref{Archive Reading Options}). -@c should be +partial-blocks (!!!) - -@item +record-number -Print the record number where a message is generated. -@xref{Additional Information}. +@menu +* Privacy:: +* Integrity:: +* Live untrusted data:: +* Security rules of thumb:: +@end menu -@item +same-order -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. +@node Privacy +@subsection Privacy + +Standard privacy concerns apply when using @command{tar}. For +example, suppose you are archiving your home directory into a file +@file{/archive/myhome.tar}. Any secret information in your home +directory, such as your SSH secret keys, are copied faithfully into +the archive. Therefore, if your home directory contains any file that +should not be read by some other user, the archive itself should be +not be readable by that user. And even if the archive's data are +inaccessible to untrusted users, its metadata (such as size or +last-modified date) may reveal some information about your home +directory; if the metadata are intended to be private, the archive's +parent directory should also be inaccessible to untrusted users. + +One precaution is to create @file{/archive} so that it is not +accessible to any user, unless that user also has permission to access +all the files in your home directory. + +Similarly, when extracting from an archive, take care that the +permissions of the extracted files are not more generous than what you +want. Even if the archive itself is readable only to you, files +extracted from it have their own permissions that may differ. + +@node Integrity +@subsection Integrity + +When creating archives, take care that they are not writable by a +untrusted user; otherwise, that user could modify the archive, and +when you later extract from the archive you will get incorrect data. + +When @command{tar} extracts from an archive, by default it writes into +files relative to the working directory. If the archive was generated +by an untrusted user, that user therefore can write into any file +under the working directory. If the working directory contains a +symbolic link to another directory, the untrusted user can also write +into any file under the referenced directory. When extracting from an +untrusted archive, it is therefore good practice to create an empty +directory and run @command{tar} in that directory. + +When extracting from two or more untrusted archives, each one should +be extracted independently, into different empty directories. +Otherwise, the first archive could create a symbolic link into an area +outside the working directory, and the second one could follow the +link and overwrite data that is not under the working directory. For +example, when restoring from a series of incremental dumps, the +archives should have been created by a trusted process, as otherwise +the incremental restores might alter data outside the working +directory. + +If you use the @option{--absolute-names} (@option{-P}) option when +extracting, @command{tar} respects any file names in the archive, even +file names that begin with @file{/} or contain @file{..}. As this +lets the archive overwrite any file in your system that you can write, +the @option{--absolute-names} (@option{-P}) option should be used only +for trusted archives. + +Conversely, with the @option{--keep-old-files} (@option{-k}) and +@option{--skip-old-files} options, @command{tar} refuses to replace +existing files when extracting. The difference between the two +options is that the former treats existing files as errors whereas the +latter just silently ignores them. + +Finally, with the @option{--no-overwrite-dir} option, @command{tar} +refuses to replace the permissions or ownership of already-existing +directories. These options may help when extracting from untrusted +archives. + +@node Live untrusted data +@subsection Dealing with Live Untrusted Data + +Extra care is required when creating from or extracting into a file +system that is accessible to untrusted users. For example, superusers +who invoke @command{tar} must be wary about its actions being hijacked +by an adversary who is reading or writing the file system at the same +time that @command{tar} is operating. + +When creating an archive from a live file system, @command{tar} is +vulnerable to denial-of-service attacks. For example, an adversarial +user could create the illusion of an indefinitely-deep directory +hierarchy @file{d/e/f/g/...} by creating directories one step ahead of +@command{tar}, or the illusion of an indefinitely-long file by +creating a sparse file but arranging for blocks to be allocated just +before @command{tar} reads them. There is no easy way for +@command{tar} to distinguish these scenarios from legitimate uses, so +you may need to monitor @command{tar}, just as you'd need to monitor +any other system service, to detect such attacks. + +While a superuser is extracting from an archive into a live file +system, an untrusted user might replace a directory with a symbolic +link, in hopes that @command{tar} will follow the symbolic link and +extract data into files that the untrusted user does not have access +to. Even if the archive was generated by the superuser, it may +contain a file such as @file{d/etc/passwd} that the untrusted user +earlier created in order to break in; if the untrusted user replaces +the directory @file{d/etc} with a symbolic link to @file{/etc} while +@command{tar} is running, @command{tar} will overwrite +@file{/etc/passwd}. This attack can be prevented by extracting into a +directory that is inaccessible to untrusted users. + +Similar attacks via symbolic links are also possible when creating an +archive, if the untrusted user can modify an ancestor of a top-level +argument of @command{tar}. For example, an untrusted user that can +modify @file{/home/eve} can hijack a running instance of @samp{tar -cf +- /home/eve/Documents/yesterday} by replacing +@file{/home/eve/Documents} with a symbolic link to some other +location. Attacks like these can be prevented by making sure that +untrusted users cannot modify any files that are top-level arguments +to @command{tar}, or any ancestor directories of these files. + +@node Security rules of thumb +@subsection Security Rules of Thumb + +This section briefly summarizes rules of thumb for avoiding security +pitfalls. -@item +same-permission -Set the modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. +@itemize @bullet -@item +sparse -Archive sparse files sparsely. @xref{Sparse Files}. +@item +Protect archives at least as much as you protect any of the files +being archived. -@item +starting-file=@var{file-name} -Begin reading in the middle of an archive. @xref{Scarce Disk Space}. +@item +Extract from an untrusted archive only into an otherwise-empty +directory. This directory and its parent should be accessible only to +trusted users. For example: -@item +to-stdout -Write files to the standard output. @xref{File Writing Options}. +@example +@group +$ @kbd{chmod go-rwx .} +$ @kbd{mkdir -m go-rwx dir} +$ @kbd{cd dir} +$ @kbd{tar -xvf /archives/got-it-off-the-net.tar.gz} +@end group +@end example -@item +uncompress -Specifdo a compressed archive. @xref{Compressed Archives}. +As a corollary, do not do an incremental restore from an untrusted archive. -@item -V @var{archive-label} -Include an archive-label in the archive being created. @xref{Archive -Label}. -@c was +volume +@item +Do not let untrusted users access files extracted from untrusted +archives without checking first for problems such as setuid programs. -@item +verbose -Print the names of files or archive members as they are being -operated on. @xref{Additional Information}. +@item +Do not let untrusted users modify directories that are ancestors of +top-level arguments of @command{tar}. For example, while you are +executing @samp{tar -cf /archive/u-home.tar /u/home}, do not let an +untrusted user modify @file{/}, @file{/archive}, or @file{/u}. -@item +verify -Check for discrepancies in the archive immediately after it is -written. @xref{Write Verification}. +@item +Pay attention to the diagnostics and exit status of @command{tar}. -@item -B -Read an archive with a smaller than specified block size or which -contains incomplete blocks. @xref{Archive Reading Options}). +@item +When archiving live file systems, monitor running instances of +@command{tar} to detect denial-of-service attacks. -@item -K @var{file-name} -Begin reading in the middle of an archive. @xref{Scarce Disk Space}. +@item +Avoid unusual options such as @option{--absolute-names} (@option{-P}), +@option{--dereference} (@option{-h}), @option{--overwrite}, +@option{--recursive-unlink}, and @option{--remove-files} unless you +understand their security implications. -@item -M -Specify a multi-volume archive. @xref{Multi-Volume Archives}. +@end itemize -@item -N @var{date} -Limit operation to files changed after the given date. @xref{File Exclusion}. +@node Changes +@appendix Changes -@item -O -Write files to the standard output. @xref{File Writing Options}. +This appendix lists some important user-visible changes between +version @GNUTAR{} @value{VERSION} and previous versions. An up-to-date +version of this document is available at +@uref{http://www.gnu.org/@/software/@/tar/manual/changes.html,the +@GNUTAR{} documentation page}. -@c <<<<- P is absolute paths, add when resolved. -ringo>>> +@table @asis +@item Use of globbing patterns when listing and extracting. -@item -R -Print the record number where a message is generated. -@xref{Additional Information}. +Previous versions of GNU tar assumed shell-style globbing when +extracting from or listing an archive. For example: -@item -S -Archive sparse files sparsely. @xref{Sparse Files}. +@smallexample +$ @kbd{tar xf foo.tar '*.c'} +@end smallexample -@item -T @var{file} -Read file-name arguments from a file on the file system. -@xref{File Name Lists}. +would extract all files whose names end in @samp{.c}. This behavior +was not documented and was incompatible with traditional tar +implementations. Therefore, starting from version 1.15.91, GNU tar +no longer uses globbing by default. For example, the above invocation +is now interpreted as a request to extract from the archive the file +named @file{*.c}. -@item -W -Check for discrepancies in the archive immediately after it is -written. @xref{Write Verification}. +To facilitate transition to the new behavior for those users who got +used to the previous incorrect one, @command{tar} will print a warning +if it finds out that a requested member was not found in the archive +and its name looks like a globbing pattern. For example: -@item -Z -Specify a compressed archive. @xref{Compressed Archives}. +@smallexample +$ @kbd{tar xf foo.tar '*.c'} +tar: Pattern matching characters used in file names. Please, +tar: use --wildcards to enable pattern matching, or --no-wildcards to +tar: suppress this warning. +tar: *.c: Not found in archive +tar: Error exit delayed from previous errors +@end smallexample -@item -b @var{number} -Specify the blocking factor of an archive. @xref{Blocking Factor}. +To treat member names as globbing patterns, use the @option{--wildcards} option. +If you want to tar to mimic the behavior of versions prior to 1.15.91, +add this option to your @env{TAR_OPTIONS} variable. -@item -f @var{archive-name} -Name the archive. @xref{Archive Name}). +@xref{wildcards}, for the detailed discussion of the use of globbing +patterns by @GNUTAR{}. -@item -h -Treat a symbolic link as an alternate name for the file the link -points to. @xref{Symbolic Links}. +@item Use of short option @option{-o}. -@item -i -Ignore end-of-archive entries. @xref{Archive Reading Options}. +Earlier versions of @GNUTAR{} understood @option{-o} command line +option as a synonym for @option{--old-archive}. -@item -k -Prevent overwriting during extraction. @xref{File Writing Options}. +@GNUTAR{} starting from version 1.13.90 understands this option as +a synonym for @option{--no-same-owner}. This is compatible with +UNIX98 @command{tar} implementations. -@item -l -Prevent @code{tar} from crossing file system boundaries when -archiving. @xref{File Exclusion}. +However, to facilitate transition, @option{-o} option retains its +old semantics when it is used with one of archive-creation commands. +Users are encouraged to use @option{--format=oldgnu} instead. -@item -m -Set the modification time of extracted files to the time they were -extracted. @xref{File Writing Options}. +It is especially important, since versions of @acronym{GNU} Automake +up to and including 1.8.4 invoke tar with this option to produce +distribution tarballs. @xref{Formats,v7}, for the detailed discussion +of this issue and its implications. -@item -o -Create an old format archive. @xref{Old Style File Information}. +@xref{Options, tar-formats, Changing Automake's Behavior, +automake, GNU Automake}, for a description on how to use various +archive formats with @command{automake}. -@item -p -Set the modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. +Future versions of @GNUTAR{} will understand @option{-o} only as a +synonym for @option{--no-same-owner}. -@item -s -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. +@item Use of short option @option{-l} -@item -v -Print the names of files or archive members they are being operated -on. @xref{Additional Information}. +Earlier versions of @GNUTAR{} understood @option{-l} option as a +synonym for @option{--one-file-system}. Since such usage contradicted +to UNIX98 specification and harmed compatibility with other +implementations, it was declared deprecated in version 1.14. However, +to facilitate transition to its new semantics, it was supported by +versions 1.15 and 1.15.90. The present use of @option{-l} as a short +variant of @option{--check-links} was introduced in version 1.15.91. -@item -w -@c <<>> +@item Use of options @option{--portability} and @option{--old-archive} -@item -z -Specify a compressed archive. @xref{Compressed Archives}. +These options are deprecated. Please use @option{--format=v7} instead. -@item -z -z -Create a whole block sized compressed archive. @xref{Compressed Archives}. -@c I would rather this were -Z. it is the only double letter short -@c form. +@item Use of option @option{--posix} -@item -C @file{directory} -Change the working directory. @xref{Changing Working Directory}. +This option is deprecated. Please use @option{--format=posix} instead. +@end table -@item -F @var{program-file} -Create a multi-volume archive via a script. @xref{Multi-Volume Archives}. +@node Configuring Help Summary +@appendix Configuring Help Summary + +Running @kbd{tar --help} displays the short @command{tar} option +summary (@pxref{help}). This summary is organized by @dfn{groups} of +semantically close options. The options within each group are printed +in the following order: a short option, eventually followed by a list +of corresponding long option names, followed by a short description of +the option. For example, here is an excerpt from the actual @kbd{tar +--help} output: + +@verbatim + Main operation mode: + + -A, --catenate, --concatenate append tar files to an archive + -c, --create create a new archive + -d, --diff, --compare find differences between archive and + file system + --delete delete from the archive +@end verbatim + +@vrindex ARGP_HELP_FMT, environment variable +The exact visual representation of the help output is configurable via +@env{ARGP_HELP_FMT} environment variable. The value of this variable +is a comma-separated list of @dfn{format variable} assignments. There +are two kinds of format variables. An @dfn{offset variable} keeps the +offset of some part of help output text from the leftmost column on +the screen. A @dfn{boolean} variable is a flag that toggles some +output feature on or off. Depending on the type of the corresponding +variable, there are two kinds of assignments: + +@table @asis +@item Offset assignment + +The assignment to an offset variable has the following syntax: + +@smallexample +@var{variable}=@var{value} +@end smallexample -@item -X @file{file} -Exclude files which match any of the regular expressions listed in -the file @file{file}. @xref{File Exclusion}. +@noindent +where @var{variable} is the variable name, and @var{value} is a +numeric value to be assigned to the variable. + +@item Boolean assignment + +To assign @code{true} value to a variable, simply put this variable name. To +assign @code{false} value, prefix the variable name with @samp{no-}. For +example: + +@smallexample +@group +# Assign @code{true} value: +dup-args +# Assign @code{false} value: +no-dup-args +@end group +@end smallexample @end table -@node Data Format Details, Concept Index, Quick Reference, Top -@appendix Details of the Archive Data Format +Following variables are declared: -This chapter is based heavily on John Gilmore's @i{tar}(5) manual page -for the public domain @code{tar} that GNU @code{tar} is based on. -@c it's been majorly edited since, we may be able to lose this. +@deftypevr {Help Output} boolean dup-args +If true, arguments for an option are shown with both short and long +options, even when a given option has both forms, for example: -The archive media contains a series of records, each of which contains -512 bytes. Each archive member is represented by a header record, -which describes the file, followed by zero or more records which -represent the contents of the file. At the end of the archive file -there may be a record consisting of a series of binary zeros, as an -end-of-archive marker. GNU @code{tar} writes a record of zeros at the -end of an archive, but does not assume that such a record exists when -reading an archive. +@smallexample + -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE +@end smallexample -Records may be grouped into @dfn{blocks} for I/O operations. A block -of records is written with a single @code{write()} operation. The -number of records in a block is specified using the @samp{+block-size} -option. @xref{Blocking Factor}, for more information about specifying -block size. +If false, then if an option has both short and long forms, the +argument is only shown with the long one, for example: -@menu -* Header Data:: The Distribution of Data in the Header -* Header Fields:: The Meaning of Header Fields -* Sparse File Handling:: Fields to Handle Sparse Files -@end menu +@smallexample + -f, --file=ARCHIVE use archive file or device ARCHIVE +@end smallexample -@node Header Data, Header Fields, Data Format Details, Data Format Details -@appendixsec The Distribution of Data in the Header +@noindent +and a message indicating that the argument is applicable to both +forms is printed below the options. This message can be disabled +using @code{dup-args-note} (see below). -The header record is defined in C as follows: -@c I am taking the following code on faith. +The default is false. +@end deftypevr -@example -@r{Standard Archive Format - Standard TAR - USTAR} - -#define RECORDSIZE 512 -#define NAMSIZ 100 -#define TUNMLEN 32 -#define TGNMLEN 32 -#define SPARSE_EXT_HDR 21 -#define SPARSE_IN_HDR 4 - -struct sparse @{ - char offset[12]; - char numbytes[12]; -@}; - -union record @{ - char charptr[RECORDSIZE]; - struct header @{ - char name[NAMSIZ]; - char mode[8]; - char uid[8]; - char gid[8]; - char size[12]; - char mtime[12]; - char chksum[8]; - char linkflag; - char linkname[NAMSIZ]; - char magic[8]; - char uname[TUNMLEN]; - char gname[TGNMLEN]; - char devmajor[8]; - char devminor[8]; - -@r{The following fields were added by gnu and are not used by other} -@r{versions of @code{tar}}. - char atime[12]; - char ctime[12]; - char offset[12]; - char longnames[4]; -@r{The next three fields were added by gnu to deal with shrinking down} -@r{sparse files.} - struct sparse sp[SPARSE_IN_HDR]; - char isextended; -@r{This is the number of nulls at the end of the file, if any.} - char ending_blanks[12]; - - @} header; - - struct extended_header @{ - struct sparse sp[21]; - char isextended; - @} ext_hdr; - -@}; -@c <<< this whole thing needs to be put into better english - -@r{The checksum field is filled with this while the checksum is computed.} -#define CHKBLANKS " " @r{8 blanks, no null} - -@r{Inclusion of this field marks an archive as being in standard} -@r{Posix format (though GNU tar itself is not Posix conforming). GNU} -@r{tar puts "ustar" in this field if uname and gname are valid.} -#define TMAGIC "ustar " @r{7 chars and a null} - -@r{The magic field is filled with this if this is a GNU format dump entry.} -#define GNUMAGIC "GNUtar " @r{7 chars and a null} - -@r{The linkflag defines the type of file.} -#define LF_OLDNORMAL '\0' @r{Normal disk file, Unix compatible} -#define LF_NORMAL '0' @r{Normal disk file} -#define LF_LINK '1' @r{Link to previously dumped file} -#define LF_SYMLINK '2' @r{Symbolic link} -#define LF_CHR '3' @r{Character special file} -#define LF_BLK '4' @r{Block special file} -#define LF_DIR '5' @r{Directory} -#define LF_FIFO '6' @r{FIFO special file} -#define LF_CONTIG '7' @r{Contiguous file} - -@r{hhe following are further link types which were defined later.} - -@r{This is a dir entry that contains the names of files that were in} -@r{the dir at the time the dump was made.} -#define LF_DUMPDIR 'D' - -@r{This is the continuation of a file that began on another volume} -#define LF_MULTIVOL 'M' - -@r{This is for sparse files} -#define LF_SPARSE 'S' - -@r{This file is a tape/volume header. Ignore it on extraction.} -#define LF_VOLHDR 'V' - -@r{These are bits used in the mode field - the values are in octal} -#define TSUID 04000 @r{Set UID on execution} -#define TSGID 02000 @r{Set GID on execution} -#define TSVTX 01000 @r{Save text (sticky bit)} - -@r{These are file permissions} -#define TUREAD 00400 @r{read by owner} -#define TUWRITE 00200 @r{write by owner} -#define TUEXEC 00100 @r{execute/search by owner} -#define TGREAD 00040 @r{read by group} -#define TGWRITE 00020 @r{write by group} -#define TGEXEC 00010 @r{execute/search by group} -#define TOREAD 00004 @r{read by other} -#define TOWRITE 00002 @r{write by other} -#define TOEXEC 00001 @r{execute/search by other} -@end example +@deftypevr {Help Output} boolean dup-args-note +If this variable is true, which is the default, the following notice +is displayed at the end of the help output: +@quotation +Mandatory or optional arguments to long options are also mandatory or +optional for any corresponding short options. +@end quotation -All characters in headers are 8-bit characters in the local variant of -ASCII. Each field in the header is contiguous; that is, there is no -padding in the header format. - -Data representing the contents of files is not translated in any way -and is not constrained to represent characters in any character set. -@code{tar} does not distinguish between text files and binary files. - -The @code{name}, @code{linkname}, @code{magic}, @code{uname}, and -@code{gname} fields contain null-terminated character strings. All -other fields contain zero-filled octal numbers in ASCII. Each numeric -field of width @var{w} contains @var{w} @minus{} 2 digits, a space, and a -null, except @code{size} and @code{mtime}, which do not contain the -trailing null. - -@node Header Fields, Sparse File Handling, Header Data, Data Format Details -@appendixsec The Meaning of Header Fields - -The @code{name} field contains the name of the file. -<<< how big a name before field overflows? - -The @code{mode} field contains nine bits which specify file -permissions, and three bits which specify the Set UID, Set GID, and -Save Text (``stick'') modes. Values for these bits are defined above. -@xref{File Writing Options}, for information on how file permissions -and modes are used by @code{tar}. - -The @code{uid} and @code{gid} fields contain the numeric user and -group IDs of the file owners. If the operating system does not -support numeric user or group IDs, these fields should be ignored. -@c but are they? - -The @code{size} field contains the size of the file in bytes; this -field contains a zero if the header describes a link to a file. - -The @code{mtime} field contains the modification time of the file. -This is the ASCII representation of the octal value of the last time -the file was modified, represented as an integer number of seconds -since January 1, 1970, 00:00 Coordinated Universal Time. -@xref{File Writing Options}, for a description of how @code{tar} uses -this information. - -The @code{chksum} field contains the ASCII representation of the octal -value of the simple sum of all bytes in the header record. To -generate this sum, each 8-bit byte in the header is added to an -unsigned integer, which has been initialized to zero. The precision -of the integer is seventeen bits. When calculating the checksum, the -@code{chksum} field itself is treated as blank. - -The @code{atime} and @code{ctime} fields are used when making -incremental backups; they store, respectively, the file's access time -and last inode-change time. - -The value in the @code{offset} field is used when making a -multi-volume archive. The offset is number of bytes into the file -that we need to go to pick up where we left off in the previous -volume, i.e the location that a continued file is continued from. - -The @code{longnames} field supports a feature that is not yet -implemented. This field should be empty. - -The @code{magic} field indicates that this archive was output in the -P1003 archive format. If this field contains @code{TMAGIC}, the -@code{uname} and @code{gname} fields will contain the ASCII -representation of the owner and group of the file respectively. If -found, the user and group IDs are used rather than the values in the -@code{uid} and @code{gid} fields. - -The @code{sp} field is used to archive sparse files efficiently. -@xref{Sparse File Handling}, for a description of this field, and -other fields it may imply. - -The @code{typeflag} field specifies the file's type. If a particular -implementation does not recognize or permit the specified type, -@code{tar} extracts the file as if it were a regular file, and reports -the discrepancy on the standard error. @xref{File Types}. @xref{GNU -File Types}. +Setting @code{no-dup-args-note} inhibits this message. Normally, only one of +variables @code{dup-args} or @code{dup-args-note} should be set. +@end deftypevr + +@deftypevr {Help Output} offset short-opt-col +Column in which short options start. Default is 2. + +@smallexample +@group +$ @kbd{tar --help|grep ARCHIVE} + -f, --file=ARCHIVE use archive file or device ARCHIVE +$ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE} + -f, --file=ARCHIVE use archive file or device ARCHIVE +@end group +@end smallexample +@end deftypevr + +@deftypevr {Help Output} offset long-opt-col +Column in which long options start. Default is 6. For example: + +@smallexample +@group +$ @kbd{tar --help|grep ARCHIVE} + -f, --file=ARCHIVE use archive file or device ARCHIVE +$ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE} + -f, --file=ARCHIVE use archive file or device ARCHIVE +@end group +@end smallexample +@end deftypevr + +@deftypevr {Help Output} offset doc-opt-col +Column in which @dfn{doc options} start. A doc option isn't actually +an option, but rather an arbitrary piece of documentation that is +displayed in much the same manner as the options. For example, in +the description of @option{--format} option: + +@smallexample +@group + -H, --format=FORMAT create archive of the given format. + + FORMAT is one of the following: + + gnu GNU tar 1.13.x format + oldgnu GNU format as per tar <= 1.12 + pax POSIX 1003.1-2001 (pax) format + posix same as pax + ustar POSIX 1003.1-1988 (ustar) format + v7 old V7 tar format +@end group +@end smallexample -@menu -* File Types:: File Types -* GNU File Types:: Additional File Types Supported by GNU -@end menu +@noindent +the format names are doc options. Thus, if you set +@kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output +will look as follows: + +@smallexample +@group + -H, --format=FORMAT create archive of the given format. + + FORMAT is one of the following: + + gnu GNU tar 1.13.x format + oldgnu GNU format as per tar <= 1.12 + pax POSIX 1003.1-2001 (pax) format + posix same as pax + ustar POSIX 1003.1-1988 (ustar) format + v7 old V7 tar format +@end group +@end smallexample +@end deftypevr + +@deftypevr {Help Output} offset opt-doc-col +Column in which option description starts. Default is 29. + +@smallexample +@group +$ @kbd{tar --help|grep ARCHIVE} + -f, --file=ARCHIVE use archive file or device ARCHIVE +$ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE} + -f, --file=ARCHIVE use archive file or device ARCHIVE +$ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE} + -f, --file=ARCHIVE + use archive file or device ARCHIVE +@end group +@end smallexample -@node File Types, GNU File Types, Header Fields, Header Fields -@appendixsubsec File Types +@noindent +Notice, that the description starts on a separate line if +@code{opt-doc-col} value is too small. +@end deftypevr + +@deftypevr {Help Output} offset header-col +Column in which @dfn{group headers} are printed. A group header is a +descriptive text preceding an option group. For example, in the +following text: + +@verbatim + Main operation mode: + + -A, --catenate, --concatenate append tar files to + an archive + -c, --create create a new archive +@end verbatim +@noindent +@samp{Main operation mode:} is the group header. -The following flags are used to describe file types: +The default value is 1. +@end deftypevr -@table @code -@item LF_NORMAL -@itemx LF_OLDNORMAL -Indicates a regular file. In order to be compatible with older -versions of @code{tar}, a @code{typeflag} value of @code{LF_OLDNORMAL} -should be silently recognized as a regular file. New archives should -be created using @code{LF_NORMAL} for regular files. For backward -compatibility, @code{tar} treats a regular file whose name ends with a -slash as a directory. - -@item LF_LINK -Indicates a link to another file, of any type, which has been -previously archived. @code{tar} identifies linked files in Unix by -matching device and inode numbers. The linked-to name is specified in -the @code{linkname} field with a trailing null. - -@item LF_SYMLINK -Indicates a symbolic link to another file. The linked-to -name is specified in the @code{linkname} field with a trailing null. -@xref{File Writing Options}, for information on archiving files -referenced by a symbolic link. - -@item LF_CHR -@itemx LF_BLK -Indicate character special files and block special files, -respectively. In this case the @code{devmajor} and @code{devminor} -fields will contain the major and minor device numbers. Operating -systems may map the device specifications to their own local -specification, or may ignore the entry. - -@item LF_DIR -Indicates a directory or sub-directory. The directory name in the -@code{name} field should end with a slash. On systems where disk -allocation is performed on a directory basis, the @code{size} field -will contain the maximum number of bytes (which may be rounded to the -nearest disk block allocation unit) that the directory can hold. A -@code{size} field of zero indicates no size limitations. Systems that -do not support size limiting in this manner should ignore the -@code{size} field. - -@item LF_FIFO -Indicates a FIFO special file. Note that archiving a FIFO file -archives the existence of the file and not its contents. - -@item LF_CONTIG -Indicates a contiguous file. Contiguous files are the same as normal -files except that, in operating systems that support it, all the -files' disk space is allocated contiguously. Operating systems which -do not allow contiguous allocation should silently treat this type as -a normal file. - -@item 'A' @dots{} -@itemx 'Z' -These are reserved for custom implementations. Some of these are used -in the GNU modified format, which is described below. @xref{GNU File -Types}. -@end table - -Certain other flag values are reserved for specification in future -revisions of the P1003 standard, and should not be used by any -@code{tar} program. - -@node GNU File Types, , File Types, Header Fields -@appendixsubsec Additional File Types Supported by GNU - -GNU @code{tar} uses additional file types to describe new types of -files in an archive. These are listed below. +@deftypevr {Help Output} offset usage-indent +Indentation of wrapped usage lines. Affects @option{--usage} +output. Default is 12. +@end deftypevr -@table @code -@item LF_DUMPDIR -@itemx 'D' -Indicates a directory and a list of files created by the -@samp{+incremental} option. The @code{size} field gives the total -size of the associated list of files. Each file name is preceded by -either a @code{'Y'} (the file should be in this archive) or an -@code{'N'} (the file is a directory, or is not stored in the archive). -Each file name is terminated by a null. There is an additional null -after the last file name. - -@item LF_MULTIVOL -@itemx 'M' -Indicates a file continued from another volume of a multi-volume -archive (@pxref{Multi-Volume Archives}). The original type of the file is not -given here. The @code{size} field gives the maximum size of this -piece of the file (assuming the volume does not end before the file is -written out). The @code{offset} field gives the offset from the -beginning of the file where this part of the file begins. Thus -@code{size} plus @code{offset} should equal the original size of the -file. +@deftypevr {Help Output} offset rmargin +Right margin of the text output. Used for wrapping. +@end deftypevr -@item LF_SPARSE -@itemx 'S' -Indicates a sparse file. @xref{Sparse Files}. @xref{Sparse File -Handling}. +@node Fixing Snapshot Files +@appendix Fixing Snapshot Files +@include tar-snapshot-edit.texi -@item LF_VOLHDR -@itemx 'V' -Marks an archive label that was created using the @samp{+label} option -when the archive was created (@pxref{Archive Label}. The @code{name} -field contains the argument to the option. The @code{size} field is -zero. Only the first file in each volume of an archive should have -this type. -@end table +@node Tar Internals +@appendix Tar Internals +@include intern.texi -@node Sparse File Handling, , Header Fields, Data Format Details -@appendixsec Fields to Handle Sparse Files +@node Genfile +@appendix Genfile +@include genfile.texi -The following header information was added to deal with sparse files -(@pxref{Sparse Files}): +@node Free Software Needs Free Documentation +@appendix Free Software Needs Free Documentation +@include freemanuals.texi -@c TALK TO MIB -The @code{sp} field (fields? something else?) is an array of -@code{struct sparse}. Each @code{struct sparse} contains two -12-character strings, which represent the offset into the file and the -number of bytes to be written at that offset. The offset is absolute, -and not relative to the offset in preceding array elements. +@node GNU Free Documentation License +@appendix GNU Free Documentation License -The header can contain four of these @code{struct sparse}; if more are -needed, they are not stored in the header, instead, the flag -@code{isextended} is set and the next record is an -@code{extended_header}. -@c @code{extended_header} or @dfn{extended_header} ??? the next -@c record after the header, or in the middle of it. +@include fdl.texi -The @code{isextended} flag is only set for sparse files, and then only -if extended header records are needed when archiving the file. +@node Index of Command Line Options +@appendix Index of Command Line Options -Each extended header record can contain an array of 21 sparse -structures, as well as another @code{isextended} flag. There is no -limit (except that implied by the archive media) on the number of -extended header records that can be used to describe a sparse file. +This appendix contains an index of all @GNUTAR{} long command line +options. The options are listed without the preceding double-dash. +For a cross-reference of short command line options, see +@ref{Short Option Summary}. -@c so is @code{extended_header} the right way to write this? +@printindex op -@node Concept Index, , Data Format Details, Top -@unnumbered Concept Index +@node Index +@appendix Index @printindex cp @@ -3958,4 +12422,6 @@ extended header records that can be used to describe a sparse file. @contents @bye - +@c Local variables: +@c texinfo-column-for-description: 32 +@c End: