X-Git-Url: https://git.dogcows.com/gitweb?a=blobdiff_plain;f=doc%2Ftar.texi;h=9c111a043b7d1fbd379c719210d136893458c78b;hb=9efbc4be3b8910063894d3ac933841edc683171a;hp=f55ea78873097d3a31511bf1cd0ffc29ff2ac35e;hpb=3112b152e66ed563ecbcca763ccd458b529ec208;p=chaz%2Ftar diff --git a/doc/tar.texi b/doc/tar.texi index f55ea78..9c111a0 100644 --- a/doc/tar.texi +++ b/doc/tar.texi @@ -1,3106 +1,7911 @@ -\input texinfo @c -*-texinfo-*- +\input texinfo @c %**start of header @setfilename tar.info -@settitle The Tar Manual: DRAFT +@settitle GNU tar +@finalout +@smallbook @setchapternewpage odd @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 ====================================================================== +@c This document has three levels of rendition: PUBLISH, DISTRIB or PROOF, +@c as decided by @set symbols. The PUBLISH rendition does not show +@c notes or marks asking for revision. Most users will prefer having more +@c information, even if this information is not fully revised for adequacy, +@c so DISTRIB is the default for tar distributions. The PROOF rendition +@c show all marks to the point of ugliness, but is nevertheless useful to +@c those working on the manual itself. +@c ====================================================================== + +@ifclear PUBLISH +@ifclear DISTRIB +@ifclear PROOF +@set DISTRIB +@end ifclear +@end ifclear +@end ifclear + +@ifset PUBLISH +@set RENDITION The book, version +@end ifset + +@ifset DISTRIB +@set RENDITION FTP release, version +@end ifset + +@ifset PROOF +@set RENDITION Proof reading version +@end ifset + +@c --------------------------------------------------------------------- +@c The @FIXME's, @UNREVISED and @c comments are part Fran@,{c}ois's work +@c plan. These annotations are somewhat precious to him; he asks that I +@c do not alter them inconsiderately. Much work is needed for GNU tar +@c internals (the sources, the programs themselves). Revising the +@c adequacy of the manual while revising the sources, and cleaning them +@c both at the same time, seems to him like a good way to proceed. +@c --------------------------------------------------------------------- + +@c Output marks for nodes needing revision, but not in PUBLISH rendition. + +@macro UNREVISED +@ifclear PUBLISH +@quotation +@emph{(This message will disappear, once this node revised.)} +@end quotation +@end ifclear +@end macro + +@c Output various FIXME information only in PROOF rendition. + +@macro FIXME{string} +@allow-recursion +@quote-arg +@ifset PROOF +@strong{} \string\ @strong{} +@end ifset + +@end macro + +@macro FIXME-ref{string} +@quote-arg +@ifset PROOF +@strong{} \string\ @strong{} +@end ifset + +@end macro + +@macro FIXME-pxref{string} +@quote-arg +@ifset PROOF +@strong{} \string\ @strong{} +@end ifset + +@end macro + +@macro FIXME-xref{string} +@quote-arg +@ifset PROOF +@strong{} \string\ @strong{} +@end ifset + +@end macro + +@c @macro option{entry} +@c @quote-arg +@c @opindex{--\entry\} +@c @value{\entry\} +@c @end macro + +@set op-absolute-names @kbd{--absolute-names} (@kbd{-P}) +@set ref-absolute-names @ref{absolute} +@set xref-absolute-names @xref{absolute} +@set pxref-absolute-names @pxref{absolute} + +@set op-after-date @kbd{--after-date=@var{date}} (@kbd{--newer=@var{date}}, @kbd{-N @var{date}}) +@set ref-after-date @ref{after} +@set xref-after-date @xref{after} +@set pxref-after-date @pxref{after} + +@set op-append @kbd{--append} (@kbd{-r}) +@set ref-append @ref{add} +@set xref-append @xref{add} +@set pxref-append @pxref{add} + +@set op-atime-preserve @kbd{--atime-preserve} +@set ref-atime-preserve @ref{Attributes} +@set xref-atime-preserve @xref{Attributes} +@set pxref-atime-preserve @pxref{Attributes} + +@set op-backup @kbd{--backup} +@set ref-backup @ref{Backup options} +@set xref-backup @xref{Backup options} +@set pxref-backup @pxref{Backup options} + +@set op-block-number @kbd{--block-number} (@kbd{-R}) +@set ref-block-number @ref{verbose} +@set xref-block-number @xref{verbose} +@set pxref-block-number @pxref{verbose} + +@set op-blocking-factor @kbd{--blocking-factor=@var{512-size}} (@kbd{-b @var{512-size}}) +@set ref-blocking-factor @ref{Blocking Factor} +@set xref-blocking-factor @xref{Blocking Factor} +@set pxref-blocking-factor @pxref{Blocking Factor} + +@set op-bzip2 @kbd{--bzip2} (@kbd{-j}) +@set ref-bzip2 @ref{gzip} +@set xref-bzip2 @xref{gzip} +@set pxref-bzip2 @pxref{gzip} + +@set op-checkpoint @kbd{--checkpoint} +@set ref-checkpoint @ref{verbose} +@set xref-checkpoint @xref{verbose} +@set pxref-checkpoint @pxref{verbose} + +@set op-compare @kbd{--compare} (@kbd{--diff}, @kbd{-d}) +@set ref-compare @ref{compare} +@set xref-compare @xref{compare} +@set pxref-compare @pxref{compare} + +@set op-compress @kbd{--compress} (@kbd{--uncompress}, @kbd{-Z}) +@set ref-compress @ref{gzip} +@set xref-compress @xref{gzip} +@set pxref-compress @pxref{gzip} + +@set op-concatenate @kbd{--concatenate} (@kbd{--catenate}, @kbd{-A}) +@set ref-concatenate @ref{concatenate} +@set xref-concatenate @xref{concatenate} +@set pxref-concatenate @pxref{concatenate} + +@set op-create @kbd{--create} (@kbd{-c}) +@set ref-create @ref{create} +@set xref-create @xref{create} +@set pxref-create @pxref{create} + +@set op-delete @kbd{--delete} +@set ref-delete @ref{delete} +@set xref-delete @xref{delete} +@set pxref-delete @pxref{delete} + +@set op-dereference @kbd{--dereference} (@kbd{-h}) +@set ref-dereference @ref{dereference} +@set xref-dereference @xref{dereference} +@set pxref-dereference @pxref{dereference} + +@set op-directory @kbd{--directory=@var{directory}} (@kbd{-C @var{directory}}) +@set ref-directory @ref{directory} +@set xref-directory @xref{directory} +@set pxref-directory @pxref{directory} + +@set op-exclude @kbd{--exclude=@var{pattern}} +@set ref-exclude @ref{exclude} +@set xref-exclude @xref{exclude} +@set pxref-exclude @pxref{exclude} + +@set op-exclude-from @kbd{--exclude-from=@var{file-of-patterns}} (@kbd{-X @var{file-of-patterns}}) +@set ref-exclude-from @ref{exclude} +@set xref-exclude-from @xref{exclude} +@set pxref-exclude-from @pxref{exclude} + +@set op-extract @kbd{--extract} (@kbd{--get}, @kbd{-x}) +@set ref-extract @ref{extract} +@set xref-extract @xref{extract} +@set pxref-extract @pxref{extract} + +@set op-file @kbd{--file=@var{archive-name}} (@kbd{-f @var{archive-name}}) +@set ref-file @ref{file} +@set xref-file @xref{file} +@set pxref-file @pxref{file} + +@set op-files-from @kbd{--files-from=@var{file-of-names}} (@kbd{-T @var{file-of-names}}) +@set ref-files-from @ref{files} +@set xref-files-from @xref{files} +@set pxref-files-from @pxref{files} + +@set op-force-local @kbd{--force-local} +@set ref-force-local @ref{file} +@set xref-force-local @xref{file} +@set pxref-force-local @pxref{file} + +@set op-group @kbd{--group=@var{group}} +@set ref-group @ref{Option Summary} +@set xref-group @xref{Option Summary} +@set pxref-group @pxref{Option Summary} + +@set op-gzip @kbd{--gzip} (@kbd{--gunzip}, @kbd{--ungzip}, @kbd{-z}) +@set ref-gzip @ref{gzip} +@set xref-gzip @xref{gzip} +@set pxref-gzip @pxref{gzip} + +@set op-help @kbd{--help} +@set ref-help @ref{help} +@set xref-help @xref{help} +@set pxref-help @pxref{help} + +@set op-ignore-failed-read @kbd{--ignore-failed-read} +@set ref-ignore-failed-read @ref{create options} +@set xref-ignore-failed-read @xref{create options} +@set pxref-ignore-failed-read @pxref{create options} + +@set op-ignore-zeros @kbd{--ignore-zeros} (@kbd{-i}) +@set ref-ignore-zeros @ref{Reading} +@set xref-ignore-zeros @xref{Reading} +@set pxref-ignore-zeros @pxref{Reading} + +@set op-incremental @kbd{--incremental} (@kbd{-G}) +@set ref-incremental @ref{Inc Dumps} +@set xref-incremental @xref{Inc Dumps} +@set pxref-incremental @pxref{Inc Dumps} + +@set op-info-script @kbd{--info-script=@var{script-name}} (@kbd{--new-volume-script=@var{script-name}}, @kbd{-F @var{script-name}}) +@set ref-info-script @ref{Multi-Volume Archives} +@set xref-info-script @xref{Multi-Volume Archives} +@set pxref-info-script @pxref{Multi-Volume Archives} + +@set op-interactive @kbd{--interactive} (@kbd{-w}) +@set ref-interactive @ref{interactive} +@set xref-interactive @xref{interactive} +@set pxref-interactive @pxref{interactive} + +@set op-keep-old-files @kbd{--keep-old-files} (@kbd{-k}) +@set ref-keep-old-files @ref{Writing} +@set xref-keep-old-files @xref{Writing} +@set pxref-keep-old-files @pxref{Writing} + +@set op-label @kbd{--label=@var{archive-label}} (@kbd{-V @var{archive-label}}) +@set ref-label @ref{label} +@set xref-label @xref{label} +@set pxref-label @pxref{label} + +@set op-list @kbd{--list} (@kbd{-t}) +@set ref-list @ref{list} +@set xref-list @xref{list} +@set pxref-list @pxref{list} + +@set op-listed-incremental @kbd{--listed-incremental=@var{snapshot-file}} (@kbd{-g @var{snapshot-file}}) +@set ref-listed-incremental @ref{Inc Dumps} +@set xref-listed-incremental @xref{Inc Dumps} +@set pxref-listed-incremental @pxref{Inc Dumps} + +@set op-mode @kbd{--mode=@var{permissions}} +@set ref-mode @ref{Option Summary} +@set xref-mode @xref{Option Summary} +@set pxref-mode @pxref{Option Summary} + +@set op-multi-volume @kbd{--multi-volume} (@kbd{-M}) +@set ref-multi-volume @ref{Multi-Volume Archives} +@set xref-multi-volume @xref{Multi-Volume Archives} +@set pxref-multi-volume @pxref{Multi-Volume Archives} + +@set op-newer-mtime @kbd{--newer-mtime=@var{date}} +@set ref-newer-mtime @ref{after} +@set xref-newer-mtime @xref{after} +@set pxref-newer-mtime @pxref{after} + +@set op-no-recursion @kbd{--no-recursion} +@set ref-no-recursion @ref{recurse} +@set xref-no-recursion @xref{recurse} +@set pxref-no-recursion @pxref{recurse} + +@set op-no-same-owner @kbd{--no-same-owner} +@set ref-no-same-owner @ref{Attributes} +@set xref-no-same-owner @xref{Attributes} +@set pxref-no-same-owner @pxref{Attributes} + +@set op-no-same-permissions @kbd{--no-same-permissions} +@set ref-no-same-permissions @ref{Attributes} +@set xref-no-same-permissions @xref{Attributes} +@set pxref-no-same-permissions @pxref{Attributes} + +@set op-null @kbd{--null} +@set ref-null @ref{files} +@set xref-null @xref{files} +@set pxref-null @pxref{files} + +@set op-numeric-owner @kbd{--numeric-owner} +@set ref-numeric-owner @ref{Attributes} +@set xref-numeric-owner @xref{Attributes} +@set pxref-numeric-owner @pxref{Attributes} + +@set op-old-archive @kbd{--old-archive} (@kbd{-o}) +@set ref-old-archive @ref{old} +@set xref-old-archive @xref{old} +@set pxref-old-archive @pxref{old} + +@set op-one-file-system @kbd{--one-file-system} (@kbd{-l}) +@set ref-one-file-system @ref{one} +@set xref-one-file-system @xref{one} +@set pxref-one-file-system @pxref{one} + +@set op-overwrite @kbd{--overwrite} +@set ref-overwrite @ref{Overwrite Old Files} +@set xref-overwrite @xref{Overwrite Old Files} +@set pxref-overwrite @pxref{Overwrite Old Files} + +@set op-owner @kbd{--owner=@var{user}} +@set ref-owner @ref{Option Summary} +@set xref-owner @xref{Option Summary} +@set pxref-owner @pxref{Option Summary} + +@set op-posix @kbd{--posix} +@set ref-posix @ref{posix} +@set xref-posix @xref{posix} +@set pxref-posix @pxref{posix} + +@set op-preserve @kbd{--preserve} +@set ref-preserve @ref{Attributes} +@set xref-preserve @xref{Attributes} +@set pxref-preserve @pxref{Attributes} + +@set op-record-size @kbd{--record-size=@var{size}} +@set ref-record-size @ref{Blocking} +@set xref-record-size @xref{Blocking} +@set pxref-record-size @pxref{Blocking} + +@set op-recursive-unlink @kbd{--recursive-unlink} +@set ref-recursive-unlink @ref{Writing} +@set xref-recursive-unlink @xref{Writing} +@set pxref-recursive-unlink @pxref{Writing} + +@set op-read-full-records @kbd{--read-full-records} (@kbd{-B}) +@set ref-read-full-records @ref{Blocking} +@set xref-read-full-records @xref{Blocking} +@set pxref-read-full-records @pxref{Blocking} +@c FIXME: or should it be Reading, or Blocking Factor + +@set op-remove-files @kbd{--remove-files} +@set ref-remove-files @ref{Writing} +@set xref-remove-files @xref{Writing} +@set pxref-remove-files @pxref{Writing} + +@set op-rsh-command @kbd{rsh-command=@var{command}} + +@set op-same-order @kbd{--same-order} (@kbd{--preserve-order}, @kbd{-s}) +@set ref-same-order @ref{Scarce} +@set xref-same-order @xref{Scarce} +@set pxref-same-order @pxref{Scarce} +@c FIXME: or should it be Reading, or Attributes? + +@set op-same-owner @kbd{--same-owner} +@set ref-same-owner @ref{Attributes} +@set xref-same-owner @xref{Attributes} +@set pxref-same-owner @pxref{Attributes} + +@set op-same-permissions @kbd{--same-permissions} (@kbd{--preserve-permissions}, @kbd{-p}) +@set ref-same-permissions @ref{Attributes} +@set xref-same-permissions @xref{Attributes} +@set pxref-same-permissions @pxref{Attributes} +@c FIXME: or should it be Writing? + +@set op-show-omitted-dirs @kbd{--show-omitted-dirs} +@set ref-show-omitted-dirs @ref{verbose} +@set xref-show-omitted-dirs @xref{verbose} +@set pxref-show-omitted-dirs @pxref{verbose} + +@set op-sparse @kbd{--sparse} (@kbd{-S}) +@set ref-sparse @ref{sparse} +@set xref-sparse @xref{sparse} +@set pxref-sparse @pxref{sparse} + +@set op-starting-file @kbd{--starting-file=@var{name}} (@kbd{-K @var{name}}) +@set ref-starting-file @ref{Scarce} +@set xref-starting-file @xref{Scarce} +@set pxref-starting-file @pxref{Scarce} + +@set op-suffix @kbd{--suffix=@var{suffix}} +@set ref-suffix @ref{Backup options} +@set xref-suffix @xref{Backup options} +@set pxref-suffix @pxref{Backup options} + +@set op-tape-length @kbd{--tape-length=@var{1024-size}} (@kbd{-L @var{1024-size}}) +@set ref-tape-length @ref{Using Multiple Tapes} +@set xref-tape-length @xref{Using Multiple Tapes} +@set pxref-tape-length @pxref{Using Multiple Tapes} + +@set op-to-stdout @kbd{--to-stdout} (@kbd{-O}) +@set ref-to-stdout @ref{Writing} +@set xref-to-stdout @xref{Writing} +@set pxref-to-stdout @pxref{Writing} + +@set op-totals @kbd{--totals} +@set ref-totals @ref{verbose} +@set xref-totals @xref{verbose} +@set pxref-totals @pxref{verbose} + +@set op-touch @kbd{--touch} (@kbd{-m}) +@set ref-touch @ref{Writing} +@set xref-touch @xref{Writing} +@set pxref-touch @pxref{Writing} + +@set op-unlink-first @kbd{--unlink-first} (@kbd{-U}) +@set ref-unlink-first @ref{Writing} +@set xref-unlink-first @xref{Writing} +@set pxref-unlink-first @pxref{Writing} + +@set op-update @kbd{--update} (@kbd{-u}) +@set ref-update @ref{update} +@set xref-update @xref{update} +@set pxref-update @pxref{update} + +@set op-use-compress-prog @kbd{--use-compress-prog=@var{program}} +@set ref-use-compress-prog @ref{gzip} +@set xref-use-compress-prog @xref{gzip} +@set pxref-use-compress-prog @pxref{gzip} + +@set op-verbose @kbd{--verbose} (@kbd{-v}) +@set ref-verbose @ref{verbose} +@set xref-verbose @xref{verbose} +@set pxref-verbose @pxref{verbose} + +@set op-verify @kbd{--verify} (@kbd{-W}) +@set ref-verify @ref{verify} +@set xref-verify @xref{verify} +@set pxref-verify @pxref{verify} + +@set op-version @kbd{--version} +@set ref-version @ref{help} +@set xref-version @xref{help} +@set pxref-version @pxref{help} + +@set op-volno-file @kbd{--volno-file=@var{file-of-number}} +@set ref-volno-file @ref{Using Multiple Tapes} +@set xref-volno-file @xref{Using Multiple Tapes} +@set pxref-volno-file @pxref{Using Multiple Tapes} + +@include version.texi + +@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 + +@defindex op +@syncodeindex op cp + +@dircategory GNU Packages +@direntry +* Tar: (tar). Making tape (or disk) archives. +@end direntry + +@dircategory Individual utilities +@direntry +* tar: (tar)tar invocation. Invoking @sc{gnu} @command{tar} +@end direntry -@c Search for comments marked with !! or <<< (or >>>) +@ifinfo +This file documents @sc{gnu} @command{tar}, which creates and extracts +files from archives. -@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).>>> +Copyright 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001 Free Software +Foundation, Inc. -@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".>>> +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 +or any later version published by the Free Software Foundation; +with no Invariant Sections, with no +Front-Cover Texts, and with no Back-Cover Texts. +A copy of the license is included in the section entitled ``GNU +Free Documentation License''. -@c <<< @code{tar} is always lower case, in bold. >>> +@end ifinfo -@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 +@shorttitlepage @sc{gnu} @command{tar} -@c <<< (don't forget to comment these out in final draft) -ringo +@titlepage +@title @sc{gnu} tar: an archiver tool +@subtitle @value{RENDITION} @value{VERSION}, @value{UPDATED} +@author Melissa Weisshaus, Jay Fenlason, +@author Thomas Bushnell, n/BSG, Amy Gorin +@c he said to remove it: Fran@,{c}ois Pinard +@c i'm thinking about how the author page *should* look. -mew 2may96 -@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 +@page +@vskip 0pt plus 1filll +Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001 +Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 +or any later version published by the Free Software Foundation; +with no Invariant Sections, with no +Front-Cover Texts, and with no Back-Cover Texts. +A copy of the license is included in the section entitled ``GNU +Free Documentation License''. +@end titlepage -@iftex -@c finalout -@end iftex +@ifnottex +@node Top +@top @sc{gnu} tar: an archiver tool -@ifinfo -This file documents @code{tar}, a utility used to store, backup, and -transport files. +@cindex file archival +@cindex archiving files -Copyright (C) 1992 Free Software Foundation, Inc. DRAFT! -@c Need to put distribution information here when ready. -@end ifinfo +@sc{gnu} @command{tar} creates and extracts files from archives. -@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, Michael I. Bushnell, and Jay Fenlason -@c <<>>> +This manual documents version @value{VERSION} of @sc{gnu} @command{tar}. -@page -@vskip 0pt plus 1filll -Copyright @copyright{} 1992 Free Software Foundation, Inc. +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 -@sp 2 -This draft is not yet ready for distribution. -@end titlepage +@c The master menu, created with texinfo-master-menu, goes here. +@c (However, getdate.texi's menu is interpolated by hand.) -@ifinfo -@node Top, Introduction, (dir), (dir) -@top @code{tar} +@menu +* Introduction:: +* Tutorial:: +* tar invocation:: +* operations:: +* Backups:: +* Choosing:: +* Date input formats:: +* Formats:: +* Media:: +* Free Software Needs Free Documentation:: +* Copying This Manual:: +* Index:: + +@detailmenu + --- The Detailed Node Listing --- + +Introduction -This file documents @code{tar}, a utility used to store, backup, and -transport files. +* 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 +* posix compliance:: +* Authors:: @sc{gnu} @command{tar} Authors +* Reports:: Reporting bugs or suggestions -@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 +Tutorial Introduction to @command{tar} -@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 +* 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:: -@node Introduction, Invoking @code{tar}, Top, Top -@chapter @code{tar}: The GNU Tape Archiver - -You can use @code{tar} to create an @dfn{archive}---a single file -which contains other files' 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 name @code{tar} comes from the words ``Tape ARchiver'', but -@code{tar} can actually process archives wherever they are stored; on -tapes and disk files, for example. In addition, tar can read archives -from standard input or write them to standard output. (This is often -useful if redirected another program with a pipe.) - -@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 +Two Frequently Used Options -@node Invoking @code{tar}, Tutorial, Introduction, Top -@chapter How To Invoke @code{tar} +* file tutorial:: +* verbose tutorial:: +* help tutorial:: -The usual way to invoke tar is +How to Create Archives -@example -@code{tar} @var{options}... [@var{file-names}...] -@end example +* prepare for examples:: +* Creating the archive:: +* create verbose:: +* short create:: +* create dir:: -All the options start with @samp{-}. The arguments which do not start -with @samp{-} are taken to be file-name arguments. (But -@xref{Argument Form}.) You can actually type in arguments in any -order. In this manual the options always precede the file-name -arguments, to make examples easier to understand. +How to List Archives -@menu -* Option Form:: The Forms of Arguments -* Argument Functions:: The Functions of Arguments -* Old Syntax for Commands:: An Old, but Still Supported, Syntax - for @code{tar} Commands -@end menu +* list dir:: -@node Option Form, Old Syntax for Commands, Argument Functions, Invoking @code{tar} -@section The Forms of Arguments - -Most options of @code{tar} have a single letter form (a single letter -preceded by @samp{-}), and at least one mnemonic form (a word or -abbreviation preceded by @samp{--}). The forms are absolutely -identical in function. For example, you can use either @samp{tar -t} -or @samp{tar --list} to list the contents of an archive. In addition, -mnemonic names can be given unique abbreviations. For example, -@samp{--cre} can be used in place of @samp{--create} because there is -no other option which begins with @samp{cre}. - -Some options require an additional argument. Single letter options -which require arguments use the immediately following argument. (This -is an exception to the rule that @code{tar} arguments which are not -options are file-name arguments.) 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. In fact, @samp{-C} requires a further argument (the name -of the directory which to change to). In this case, tar would think -it needs to change to a directory named @samp{--file=george}, and -wouldn't interpret @samp{--file-george} as an option at all! - -@node Argument Functions, Argument Form, Invoking @code{tar}, Invoking @code{tar} -@section The Functions of Arguments - -You must give exactly one option from the following list to tar. This -option specifies the basic operation for tar to perform. - -@itemize -@item -Add files to an existing archive (@samp{--add-file}, @samp{--append} or -@samp{-r}) +How to Extract Members from an Archive -@item -Compare files in an archive with files in the file system -(@samp{--compare}, @samp{--diff} or @samp{-d}) +* extracting archives:: +* extracting files:: +* extract dir:: +* failing commands:: -@item -Add archives to another archive (@samp{--add-archive}, @samp{--catenate} -or @samp{-A}) -@c was --concatenate. -ringo +Invoking @sc{gnu} @command{tar} -@item -Create a new archive (@samp{--create} or @samp{-c}) +* Synopsis:: +* using tar options:: +* Styles:: +* All Options:: +* help:: +* verbose:: +* interactive:: -@item -Delete files from an archive (@samp{--delete}) +The Three Option Styles -@item -Extract files from an archive (@samp{--extract}, @samp{--get} or @samp{-x}) +* Mnemonic Options:: Mnemonic Option Style +* Short Options:: Short Option Style +* Old Options:: Old Option Style +* Mixing:: Mixing Option Styles -@item -List the files in an archive (@samp{--list} or @samp{-t}) +All @command{tar} Options -@item -Update an archive by appending newer versions of already stored files -(@samp{--update} or @samp{-u}) -@end itemize +* Operation Summary:: +* Option Summary:: +* Short Option Summary:: -@xref{Reading and Writing}, for more information about these -operations. +@sc{gnu} @command{tar} Operations -The remaining options 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. +* Basic tar:: +* Advanced tar:: +* create options:: +* extract options:: +* backup:: +* Applications:: +* looking ahead:: -The remaining arguments are file-name arguments. For --add-file and ---create these arguments specify the names of files (which must -already exist) to place in the archive. For the remaining operation -types, the file-name arguments specify archive members to compare, -delete, extract, list, or update. When naming archive members, you -must give the exact name of the member in the archive. When naming -files, the normal file name rules apply. +Advanced @sc{gnu} @command{tar} Operations -If you don't use any file-name arguments, @samp{--add-file}, -@samp{--update} and @samp{--delete} will do nothing. Naturally, -@samp{--create} will make an empty archive if given no file-name -arguments. The other operations of @code{tar} will act on defaults. +* Operations:: +* current state:: +* append:: +* update:: +* concatenate:: +* delete:: +* compare:: -Anytime you use a file-name argument to specify a directory file, -@code{tar} acts recursively on all the files and directories beneath -that directory. +How to Add Files to Existing Archives: @code{--append} -@node Old Syntax for Commands, , Argument Form, Invoking @code{tar} -@section An Old, but Still Supported, Syntax for @code{tar} Commands +* appending files:: Appending Files to an Archive +* multiple:: -For historical reasons, GNU @code{tar} also accepts a syntax for -commands which splits options that require additional arguments into -two parts. That syntax is of the form: +Updating an Archive -@example -@code{tar} @var{option-letters}... [@var{option-arguments}...] [@var{file-names}...]@refill -@end example +* how to update:: -@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. +Options Used by @code{--create} -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}. +* Ignore Failed Read:: -On the other hand, 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. +Options Used by @code{--extract} -@node Tutorial, Wizardry, Invoking @code{tar}, Top -@chapter Getting Started With @code{tar} +* Reading:: Options to Help Read Archives +* Writing:: Changing How @command{tar} Writes Files +* Scarce:: Coping with Scarce Resources -This chapter guides you through some basic examples of @code{tar} -operations. If you already know how to use some other version of tar, -then you probably don't need to read this chapter. In the examples, -the lines you should type are preceded by a @samp{%}, which is a -typical shell prompt. +Options to Help Read Archives -@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 +* read full records:: +* Ignore Zeros:: -@node Creating Archives, Listing Archive Contents, Tutorial, Tutorial -@section Creating Archives +Changing How @command{tar} Writes Files -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. +* Dealing with Old Files:: +* Overwrite Old Files:: +* Keep Old Files:: +* Unlink First:: +* Recursive Unlink:: +* Modification Times:: +* Setting Access Permissions:: +* Writing to Standard Output:: +* remove files:: -@menu -* Creating Example:: Creating Archives of Files -* Subdirectory:: Creating an Archive of a Subdirectory -@end menu +Coping with Scarce Resources -@node Creating Example, Subdirectory, Creating Archives, Creating Archives -@subsection Creating Archives of Files +* Starting File:: +* Same Order:: -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. +Performing Backups and Restoring 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.) +* Full Dumps:: Using @command{tar} to Perform Full Dumps +* Inc Dumps:: Using @command{tar} to Perform Incremental Dumps +* incremental and listed-incremental:: The Incremental Options +* 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 -First, change into the directory containing the files you want to -archive: +Setting Parameters for Backups and Restoration -@example -% cd practice -@end example +* backup-specs example:: An Example Text of @file{Backup-specs} +* Script Syntax:: Syntax for @file{Backup-specs} -@noindent -@file{~/practice} is now your working directory. +Choosing Files and Names for @command{tar} -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. +* file:: Choosing the Archive's Name +* Selecting Archive Members:: +* files:: Reading Names from a File +* exclude:: Excluding Some Files +* Wildcards:: +* after:: Operating Only on New Files +* recurse:: Descending into Directories +* one:: Crossing Filesystem Boundaries -To list the names of files in the working directory, type: +Reading Names from a File -@example -% ls -@end example +* nul:: -The system responds: +Excluding Some Files -@example -blues folk jazz -% -@end example +* controlling pattern-patching with exclude:: +* problems with exclude:: -@noindent -Then, -@itemize @bullet -@item -Create a new archive (@samp{tar -c} or @samp{tar --create}) +Crossing Filesystem Boundaries -@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 +* directory:: Changing Directory +* absolute:: Absolute File Names -@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}. +Date input formats -@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 +* 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. +* Authors of getdate:: Bellovin, Eggert, Salz, Berets, et al. -@noindent -Type: -@example -% tar --create --file=records blues folk jazz -@end example +Controlling the Archive Format -@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. +* Portability:: Making @command{tar} Archives More Portable +* Compression:: Using Less Space through Compression +* Attributes:: Handling File Attributes +* Standard:: The Standard Format +* Extensions:: @sc{gnu} Extensions to the Archive Format +* cpio:: Comparison of @command{tar} and @command{cpio} -@example -% ls -blues folk jazz records -% -@end example +Making @command{tar} Archives More Portable -@menu -* Listing Files:: Listing files in an archive -* Verbose:: Using @code{tar} in Verbose Mode -@end menu +* Portable Names:: Portable Names +* dereference:: Symbolic Links +* old:: Old V7 Archives +* posix:: @sc{posix} archives +* Checksumming:: Checksumming Problems +* Large or Negative Values:: Large files, negative time stamps, etc. -@node Listing Files, Verbose, Creating Example, Creating Example -@subsubsection Listing files in an archive +Using Less Space through Compression -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: +* gzip:: Creating and Reading Compressed Archives +* sparse:: Archiving Sparse Files -@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. - -@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 +* Multi-Volume Archives:: Archives Longer than One Tape or Disk +* Tape Files:: Tape Files -To archive a directory, first move to its superior directory. If you -have been following the tutorial, you should type: +Copying This Manual -@example -% cd .. -% -@end example +* GNU Free Documentation License:: License for copying this manual -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: +@end detailmenu +@end menu -@example -% tar --create --verbose --file=music practice -@end example +@node Introduction +@chapter Introduction -@noindent -@code{tar} should respond: +Welcome to the @sc{gnu} @command{tar} manual. @sc{gnu} @command{tar} 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. -@example -practice/ -practice/blues -practice/folk -practice/jazz -practice/records -@end example +@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 +* posix compliance:: +* Authors:: @sc{gnu} @command{tar} Authors +* Reports:: Reporting bugs or suggestions +@end menu -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. +@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 @sc{gnu} +@command{tar} 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. + +@FIXME{this sounds more like a @sc{gnu} Project Manuals Concept [tm] more +than the reality. should think about whether this makes sense to say +here, or not.} 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 @sc{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 the 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 last 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 filesystem, +and a @dfn{member name} is the name of an archive member within the +archive. -@c >>> symbolic links and changing directories are now in main body, not in -@c >>> tutorial. -ringo +@cindex extraction +@cindex unpacking +The term @dfn{extraction} refers to the process of copying an archive +member (or multiple members) into a file in the filesystem. Extracting +all the members of an archive is often called @dfn{extracting the +archive}. The term @dfn{unpack} can also be used to refer to the +extraction of many or all the members of an archive. Extracting an +archive does not destroy the archive's structure, just as creating an +archive does not destroy the copies of the files that exist outside of +the archive. You may also @dfn{list} the members in a given archive +(this is often thought of as ``printing'' them to the standard output, +or the command line), or @dfn{append} members to a pre-existing archive. +All of these operations can be performed using @command{tar}. + +@node What tar Does +@section What @command{tar} Does + +@cindex tar +The @command{tar} program provides the ability to create @command{tar} +archives, as well as various other kinds of manipulation. For example, +you can use @command{tar} on previously created archives to extract files, +to store additional files, or to update or list files which were already +stored. + +Initially, @command{tar} archives were used to store files conveniently on +magnetic tape. The name @command{tar} comes from this use; it stands for +@code{t}ape @code{ar}chiver. Despite the utility's name, @command{tar} can +direct its output to available devices, files, or other programs (using +pipes). @command{tar} may even access remote devices or files (as archives). + +@FIXME{the following table entries need a bit of work..} + +You can use @command{tar} archives in many ways. We want to stress a few +of them: storage, backup, and transportation. + +@table @asis +@item Storage +Often, @command{tar} archives are used to store related files for +convenient file transfer over a network. For example, the @sc{gnu} Project +distributes its software bundled into @command{tar} archives, so that +all the files relating to a particular program (or set of related +programs) can be transferred as a single unit. + +A magnetic tape can store several files in sequence. However, the tape +has no names for these files; it only knows their relative position on +the tape. One way to store several files on one tape and retain their +names is by creating a @command{tar} archive. Even when the basic transfer +mechanism can keep track of names, as FTP can, the nuisance of handling +multiple files, directories, and multiple links makes @command{tar} +archives useful. + +Archive files are also used for long-term storage. You can think of +this as transportation from the present into the future. (It is a +science-fiction idiom that you can move through time as well as in +space; the idea here is that @command{tar} can be used to move archives in +all dimensions, even time!) + +@item Backup +Because the archive created by @command{tar} is capable of preserving file +information and directory structure, @command{tar} is commonly used for +performing full and incremental backups of disks. A backup puts a +collection of files (possibly pertaining to many users and +projects) together on a disk or a tape. This guards against accidental +destruction of the information in those files. @sc{gnu} @command{tar} has +special features that allow it to be used to make incremental and full +dumps of all the files in a filesystem. + +@item Transportation +You can create an archive on one system, transfer it to another system, +and extract the contents there. This allows you to transport a group of +files from one system to another. +@end table -@node Extracting Files -@section Extracting Files from an Archive +@node Naming tar Archives +@section How @command{tar} Archives are Named -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. +Conventionally, @command{tar} archives are given names ending with +@samp{.tar}. This is not necessary for @command{tar} to operate properly, +but this manual follows that convention in order to accustom readers to +it and to make examples more clear. -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. +@cindex tar file +@cindex entry +@cindex tar entry +Often, people refer to @command{tar} archives as ``@command{tar} files,'' and +archive members as ``files'' or ``entries''. For people familiar with +the operation of @command{tar}, this causes no difficulty. However, in +this manual, we consistently refer to ``archives'' and ``archive +members'' to make learning to use @command{tar} easier for novice users. -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 <<>> 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 +@node extract +@section How to Extract Members from an Archive +@UNREVISED +@cindex Extraction +@cindex Retrieving files from an archive +@cindex Resurrecting files from an archive -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. +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 @value{op-extract} operation. As with +@value{op-create}, specify the name of the archive with @value{op-file}. +Extracting an archive does not modify the archive in any way; you can +extract it multiple times if you want or need to. -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. +Using @samp{--extract}, you can extract an entire archive, or specific +files. The files can be directories containing other files, or not. As +with @value{op-create} and @value{op-list}, 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:: +* 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: +@example +$ @kbd{tar -xvf collection.tar} +@end example -@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}}) +@example +-rw-rw-rw- me user 28 1996-10-18 16:31 jazz +-rw-rw-rw- me user 21 1996-09-23 16:44 blues +-rw-rw-rw- me user 20 1996-09-23 16:44 folk +@end example -@item -Specify the files to be added to the archive, using file-name -arguments -@end itemize +@node extracting files +@subsection Extracting Specific Files -@noindent -For example: +To extract specific archive members, give their exact member names as +arguments, as printed by @value{op-list}. 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. It will be identical to the original +file @file{blues} that you deleted. @FIXME{check this; will the times, +permissions, owner, etc be the same, also?} + +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: @example -% tar --add-file --file=records rock +$ @kbd{tar --extract --file=collection.tar blues} @end example @noindent -If you list the archive members in @file{records}, you will see that -@file{rock} has been added to the archive: +If you list the files in the directory again, you will see that the file +@file{blues} has been restored, with its original permissions, creation +times, and owner.@FIXME{This is only accidentally true, but not in +general. 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 +@value{op-list}. + +@FIXME{we hope this will change:}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}}. To find the +exact member names of the members of an archive, use @value{op-list} +(@pxref{list}). + +If you give the @value{op-verbose} option, then @value{op-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. + +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 @samp{--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: @example -% tar --list --file=records -blues -folk -jazz -rock +$ @kbd{tar -xvf music.tar practice/folk practice/jazz} @end example -@c <<< this should be some kind of node. +@FIXME{need to show tar's response; used verbose above. also, here's a +good place to demonstrate the -v -v thing. have to write that up +(should be trivial, but i'm too tired!).} + +@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. + +@FIXME{IMPORTANT! show the final structure, here. figure out what it +will be.} -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 failing commands +@subsection Commands That Will Fail -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}: +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, @example -% tar --add-file --verbose --file=records blues -blues +$ @kbd{tar -xvf music.tar folk jazz} @end example @noindent -If you now list the contents of the archive, you will obtain the following: +you will get the following response: @example -% tar --list -f records -blues -folk -jazz -rock -blues +tar: folk: Not found in archive +tar: jazz: Not found in archive +$ @end example @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: +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: @example -% tar --update --verbose --file=records blues folk rock classical -blues -classical -% +$ @kbd{tar -tvf music.tar} +practice/folk +practice/jazz +practice/rock @end example -@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: - -@itemize @bullet -@item -Invoke @code{tar}, and specify the @samp{--concatenate} operation -(@samp{-A} or @samp{--concatenate}) - -@item -Specify the archive file to be added to -(@samp{--file=@var{archive-name}} or @samp{-f @var{archive-name}}) - -@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 - -@example -% cd ~ -% tar --concatenate --file=music practice/records -@end example +@FIXME{make sure the above works when going through the examples in +order...} -If you now list the contents of the @file{music}, you see it now -contains the archive members of @file{practice/records}: +@noindent +Likewise, if you try to use this command, @example -%tar --list --file=music -blues -folk -jazz -rock -blues -practice/blues -practice/folk -practice/jazz -practice/rock -practice/blues -practice/classical +$ @kbd{tar -tvf music.tar folk jazz} @end example -@node Deleting Files, , , Tutorial -@comment node-name, next, previous, up -@section Deleting Files From an Archive - -In some instances, you may want to remove some files from an archive -stored on disk +@noindent +you would get a similar response. Members with those names are not in the +archive. You must use the correct member names 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 + +@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 @sc{gnu} @command{tar} +@UNREVISED + +This chapter is about how one invokes the @sc{gnu} @command{tar} 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 @value{op-help} and +@value{op-version} (@pxref{help}), @value{op-verbose} (@pxref{verbose}) +and @value{op-interactive} options (@pxref{interactive}). -@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 +* Synopsis:: +* using tar options:: +* Styles:: +* All Options:: +* help:: +* verbose:: +* interactive:: +@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 Synopsis +@section General Synopsis of @command{tar} -Execution of the @samp{--delete} operation can be very slow. +The @sc{gnu} @command{tar} program is invoked as either one of: -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: +@example +@kbd{tar @var{option}@dots{} [@var{name}]@dots{}} +@kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}} +@end example -@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) +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 @value{op-compare}, @value{op-delete}, +@value{op-extract}, @value{op-list} or @value{op-update}. When naming +archive members, you must give the exact name of the member in the +archive, as it is printed by @value{op-list}. For @value{op-append} +and @value{op-create}, 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 @value{op-absolute-names} +option). @value{xref-absolute-names}, for more information about +@value{op-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 filesystem 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 +@value{op-files-from} option. + +If you don't use any file name arguments, @value{op-append}, +@value{op-delete} and @value{op-concatenate} will do nothing, while +@value{op-create} will usually yield a diagnostic and inhibit @command{tar} +execution. The other operations of @command{tar} (@value{op-list}, +@value{op-extract}, @value{op-compare}, and @value{op-update}) will act +on the entire contents of the archive. + +@cindex exit status +@cindex return status +Besides successful exits, @sc{gnu} @command{tar} may fail for many reasons. +Some reasons correspond to bad usage, that is, when the @command{tar} +command is improperly written. +Errors may be encountered later, while encountering an error +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 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. + +@sc{gnu} @command{tar} returns only a few exit statuses. I'm really +aiming simplicity in that area, for now. If you are not using the +@value{op-compare} option, zero means that everything went well, besides +maybe innocuous warnings. Nonzero means that something went wrong. +Right now, as of today, ``nonzero'' is almost always 2, except for +remote operations, where it may be 128. + +@node using tar options +@section Using @command{tar} Options + +@sc{gnu} @command{tar} 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 (two lists +of four operations each 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 @value{op-verbose}, 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}.) + +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 @samp{-T} and @samp{-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 @value{op-list}. + +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 chap. 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. (For example, @value{op-file} 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. + +@FIXME{hag to write a brief paragraph on the option(s) which can +optionally take an argument} -@item -Invoke @code{tar} and specify the @samp{--delete} operation -(@samp{--delete}). +@menu +* Mnemonic Options:: Mnemonic Option Style +* Short Options:: Short Option Style +* Old Options:: Old Option Style +* Mixing:: Mixing Option Styles +@end menu -@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}}) +@node Mnemonic Options +@subsection Mnemonic Option Style + +@FIXME{have to decide whether or ot to replace other occurrences of +"mnemonic" with "long", or *ugh* vice versa.} + +Each option has at least one long (or mnemonic) name starting with two +dashes in a row, e.g.@: @samp{--list}. The long names are more clear than +their corresponding short or old names. It sometimes happens that a +single mnemonic option has many different different names which are +synonymous, such as @samp{--compare} and @samp{--diff}. In addition, +long option names can be given unique abbreviations. For example, +@samp{--cre} can be used in place of @samp{--create} because there is no +other mnemonic 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.) + +Mnemonic 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: -@item -Specify the files to be deleted, using file-name arguments. +@example +$ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0} +@end example -@item -List the contents of the archive file again---note that the files have -been removed. (this step is also optional) -@end itemize +@noindent +gives a fairly good set of hints about what the command does, even +for those not fully acquainted with @command{tar}. + +Mnemonic options which require arguments take those arguments +immediately following the option name; they are introduced by an equal +sign. For example, the @samp{--file} option (which tells the name +of the @command{tar} archive) is given a file such as @file{archive.tar} +as argument by using the notation @samp{--file=archive.tar} for the +mnemonic option. + +@node Short Options +@subsection Short Option Style + +Most options also have a short option name. Short options start with +a single dash, and are followed by a single character, e.g.@: @samp{-t} +(which is equivalent to @samp{--list}). The forms are absolutely +identical in function; they are interchangeable. + +The short option names are faster to type than long option names. + +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{@samp{-f +archive.tar}} or @samp{-farchive.tar} instead of using +@samp{--file=archive.tar}. Both @samp{--file=@var{archive-name}} and +@w{@samp{-f @var{archive-name}}} denote the option which indicates a +specific archive, here named @file{archive.tar}. + +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 +@sc{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: @example -% tar --list --file=records -blues -folk -jazz -% tar --delete --file=records blues -% tar --list --file=records -folk -jazz -% +$ @kbd{tar -c -v -b 20 -f /dev/rmt0} @end example -@node Wizardry, Archive Structure, Tutorial, Top -@chapter Wizardry +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 +@UNREVISED + +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@footnote{Beware that if you precede options +with a dash, you are announcing the short option style instead of the +old option style; short options are decoded differently.}. 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 @samp{-t}, and consequently, the same as the +mnemonic option @samp{--list}. So for example, the command @w{@samp{tar +cv}} specifies the option @samp{-v} in addition to the operation @samp{-c}. + +@FIXME{bob suggests having an uglier example. :-) } + +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: -<<>>>> +@node Mixing +@subsection Mixing Option Styles -@node Archive Structure, Reading and Writing, Wizardry, Top -@chapter The Structure of an Archive +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 @sc{gnu} +@command{tar} version 1.11.6, a bug prevented intermixing old style options +with mnemonic 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. -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. +For example, all the following commands are wholly equivalent, and +illustrate the many combinations and orderings of option styles. +@example +@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 example -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. +On the other hand, the following commands are @emph{not} equivalent to +the previous set: -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}. +@example +@kbd{tar -f -c archive.tar} +@kbd{tar -fc archive.tar} +@kbd{tar -fcarchive.tar} +@kbd{tar -farchive.tarc} +@kbd{tar cfarchive.tar} +@end example -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. +@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 +@samp{-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. @menu -* Old Style File Information:: Old Style File Information -* Archive Label:: -* Format Variations:: +* Operation Summary:: +* Option Summary:: +* Short Option Summary:: @end menu -@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 +@node Operation Summary +@subsection Operations -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. +@table @kbd -@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 +@item --append +@itemx -r -@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 +Appends files to the end of the archive. @xref{append}. -@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. +@item --catenate +@itemx -A -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. +Same as @samp{--concatenate}. @xref{concatenate}. -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 +@item --compare +@itemx -d -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: +Compares archive members with their counterparts in the file +system, and reports differences in file size, mode, owner, +modification date and contents. @xref{compare}. -@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 +@item --concatenate +@itemx -A -@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 +Appends other @command{tar} archives to the end of the archive. +@xref{concatenate}. -@node Format Variations, , Archive Label, Archive Structure -@section Format Variations -@cindex Format Parameters -@cindex Format Options -@cindex Options to specify archive format. +@item --create +@itemx -c -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. +Creates a new @command{tar} archive. @xref{create}. -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. +@item --delete +Deletes members from the archive. Don't try this on a archive on a +tape! @xref{delete}. -@menu -* Multi-Volume Archives:: -* Sparse Files:: -* Blocking Factor:: -* Compressed Archives:: -@end menu +@item --diff +@itemx -d -@node Multi-Volume Archives, Sparse Files, Format Variations, Format Variations -@subsection Archives Longer than One Tape or Disk -@cindex Multi-volume archives +Same @samp{--compare}. @xref{compare}. -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. +@item --extract +@itemx -x -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. +Extracts members from the archive into the file system. @xref{extract}. -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}. +@item --get +@itemx -x -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. +Same as @samp{--extract}. @xref{extract}. -@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. +@item --list +@itemx -t +Lists the members in an archive. @xref{list}. -<<< There should be a sample program here, including an exit before -<<< end. +@item --update +@itemx -u -@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. +@FIXME{It was: A combination of the @samp{--compare} and @samp{--append} operations. +This is not true and rather misleading, as @value{op-compare} +does a lot more than @value{op-update} for ensuring files are identical.} +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}. -@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 -@node Sparse Files, Blocking Factor, Multi-Volume Archives, Format Variations -@subsection Archiving Sparse Files -@cindex Sparse Files +@node Option Summary +@subsection @command{tar} Options -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. +@table @kbd -@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. +@item --absolute-names +@itemx -P -@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 +Normally when creating an archive, @command{tar} strips an initial @samp{/} from +member names. This option disables that behavior. @FIXME-xref{} -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 +@item --after-date -@code{tar} ignores the @samp{--sparse} option when reading an archive. +(See @samp{--newer}.) @FIXME-pxref{} -@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 +@item --anchored +An exclude pattern must match an initial subsequence of the name's components. +@FIXME-xref{} -@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. +@item --atime-preserve -@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 +Tells @command{tar} to preserve the access time field in a file's inode when +reading it. Due to limitations in the @code{utimes} system call, the +modification time field is also preserved, which may cause problems if +the file is simultaneously being modified by another program. +This option is incompatible with incremental backups, because +preserving the access time involves updating the last-changed time. +Also, this option does not work on files that you do not own, +unless you're root. +@FIXME-xref{} -@node Compressed Archives, , Blocking Factor, Format Variations -@subsection Creating and Reading Compressed Archives -@cindex Compressed archives -@cindex Storing archives in compressed format +@item --backup=@var{backup-type} -@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. +Rather than deleting files from the file system, @command{tar} will back them up +using simple or numbered backups, depending upon @var{backup-type}. +@FIXME-xref{} -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. +@item --block-number +@itemx -R -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. +With this option present, @command{tar} prints error messages for read errors +with the block number in the archive file. @FIXME-xref{} -If there is no compress utility available, @code{tar} will report an -error. +@item --blocking-factor=@var{blocking} +@itemx -b @var{blocking} -@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. +Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per +record. @FIXME-xref{} -@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 +@item --bzip2 +@itemx -j + +This option tells @command{tar} to read or write archives through @code{bzip2}. +@FIXME-xref{} + +@item --checkpoint + +This option directs @command{tar} to print periodic checkpoint messages as it +reads through the archive. Its intended for when you want a visual +indication that @command{tar} is still running, but don't want to see +@samp{--verbose} output. @FIXME-xref{} -@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. - -@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 -@c >>> MIB -- why not use -Z instead of -z -z ? -ringo +@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. @FIXME-xref{} -@node Reading and Writing, Insuring Accuracy, Archive Structure, Top -@chapter Reading and Writing Archives +@item --confirmation -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. +(See @samp{--interactive}.) @FIXME-pxref{} -@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 +@item --dereference +@itemx -h -@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? +When creating a @command{tar} archive, @command{tar} will archive the file that a symbolic +link points to, rather than archiving the symlink. @FIXME-xref{} -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. +@item --directory=@var{dir} +@itemx -C @var{dir} -@c >>> MIB--does standard input and output redirection work with all -@c >>> operations? -@c >>> need example for standard input and output (screen and keyboard?) +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. @FIXME-xref{} -@cindex Standard input and output -@cindex tar to standard input and output +@item --exclude=@var{pattern} -To specify an archive file on a device attached to a remote machine, -use the following: +When performing operations, @command{tar} will skip files that match +@var{pattern}. @FIXME-xref{} -@example ---file=@var{hostname}:/@var{dev}/@var{file name} -@end example +@item --exclude-from=@var{file} +@itemx -X @var{file} -@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. +Similar to @samp{--exclude}, except @command{tar} will use the list of patterns +in the file @var{file}. @FIXME-xref{} -@c >>>MIB --- is this clear? +@item --file=@var{archive} +@itemx -f @var{archive} -@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. -@end table +@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. @FIXME-xref{} -@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 +@item --files-from=@var{file} +@itemx -T @var{file} -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. +@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. @FIXME-xref{} -The following example creates an archive named @file{stooges}, -containing the files @file{larry}, @file{moe} and @file{curley}: +@item --force-local -@example -tar --create --file=stooges larry moe curley -@end example +Forces @command{tar} to interpret the filename given to @samp{--file} as a local +file, even if it looks like a remote tape drive name. @FIXME-xref{} -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}: +@item --group=@var{group} -@example -tar --create --file=hail/hail/fredonia marx -@end example +Files added to the @command{tar} archive will have a group id of @var{group}, +rather than the group from the source file. @var{group} is first decoded +as a group symbolic name, but if this interpretation fails, it has to be +a decimal numeric group ID. @FIXME-xref{} -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: +Also see the comments for the @value{op-owner} option. -@example -tar --create --file=home -@end example +@item --gunzip -@xref{File Name Lists}, for other ways to specify files to archive. +(See @samp{--gzip}.) @FIXME-pxref{} -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. +@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. @FIXME-xref{} -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. +@item --help -To find out what files are already stored in an archive, use @samp{tar ---list --file=@var{archive-name}}. @xref{Listing Contents}. +@command{tar} will print out a short message summarizing the operations and +options to @command{tar} and exit. @FIXME-xref{} -@menu -* Adding Files:: -* Appending Archives:: -* Deleting Archive Files:: Deleting Files From an Archive -* Matching Format Parameters:: -@end menu +@item --ignore-case +Ignore case when excluding files. +@FIXME-xref{} -@node Adding Files, Appending Archives, Modifying, Modifying -@subsection Adding Files to an Archive -@cindex Adding files to an archive -@cindex Updating an archive +@item --ignore-failed-read -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}. +Do not exit unsuccessfully merely because an unreadable file was encountered. +@xref{Reading}. -The following example adds the file @file{shemp} to the archive -@file{stooges} created above: +@item --ignore-zeros +@itemx -i -@example -tar --add-file --file=stooges shemp -@end example +With this option, @command{tar} will ignore zeroed blocks in the archive, which +normally signals EOF. @xref{Reading}. -You must specify the files to be added; there is no default. +@item --incremental +@itemx -G -@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. +Used to inform @command{tar} that it is working with an old @sc{gnu}-format +incremental backup archive. It is intended primarily for backwards +compatibility only. @FIXME-xref{} -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. +@item --info-script=@var{script-file} +@itemx --new-volume-script=@var{script-file} +@itemx -F @var{script-file} -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. +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. @FIXME-xref{} -@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 +@item --interactive +@itemx --confirmation +@itemx -w -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}). - -@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 - -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. +Specifies that @command{tar} should ask the user for confirmation before +performing potentially destructive options, such as overwriting files. +@FIXME-xref{} -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): +@item --keep-old-files +@itemx -k -@example -tar --add-archive --file=stooges hail/hail/fredonia -@end example +Do not overwrite existing files when extracting files from an archive. +@xref{Writing}. -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}). +@item --label=@var{name} +@itemx -V @var{name} -@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 +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}. @FIXME-xref{} -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. +@item --listed-incremental=@var{snapshot-file} +@itemx -g @var{snapshot-file} -The following example removes the file @file{curley} from the archive -@file{stooges}: +During a @samp{--create} operation, specifies that the archive that +@command{tar} creates is a new @sc{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. @FIXME-xref{} -@example -tar --delete --file=stooges curley -@end example +@item --mode=@var{permissions} -You can only use @samp{tar --delete} on an archive if the archive -device allows you to write to any point on the media. +When adding files to an archive, @command{tar} will use @var{permissions} +for the archive members, rather than the permissions from the files. +The program @command{chmod} and this @command{tar} option share the same syntax +for what @var{permissions} might be. @xref{File permissions, Permissions, +File permissions, fileutils, @sc{gnu} file utilities}. This reference also +has useful information for those not being overly familiar with the Unix +permission system. -@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 +Of course, @var{permissions} might be plainly specified as an octal number. +However, by using generic symbolic modifications to mode bits, this allows +more flexibility. For example, the value @samp{a+rw} adds read and write +permissions for everybody, while retaining executable bits on directories +or on any other file already marked as executable. -@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=-). +@item --multi-volume +@itemx -M -@node Matching Format Parameters, , Deleting Archive Files, Modifying -@subsection Matching the Format Parameters +Informs @command{tar} that it should create or otherwise operate on a +multi-volume @command{tar} archive. @FIXME-xref{} -Some format parameters must be taken into consideration when modifying -an archive: +@item --new-volume-script -Compressed archives cannot be modified. +(see --info-script) -You have to specify the block size of the archive when modifying an -archive with a non-default block size. +@item --newer=@var{date} +@itemx --after-date=@var{date} +@itemx -N -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. +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 last-modified time specifies +the date. @FIXME-xref{} -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 +@item --newer-mtime=@var{date} -@c <<< xref somewhere, for more information about format parameters. +Like @samp{--newer}, but add only files whose +contents have changed (as opposed to just @samp{--newer}, which will +also back up files for which any status information has changed). -@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 +@item --no-anchored +An exclude pattern can match any subsequence of the name's components. +@FIXME-xref{} -@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 --no-ignore-case +Use case-sensitive matching when excluding files. +@FIXME-xref{} -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. +@item --no-recursion -If the blocking factor of the archive differs from the default, -@code{tar} reports this. @xref{Blocking Factor}. +With this option, @command{tar} will not recurse into directories. +@FIXME-xref{} -@xref{Archive Reading Options} for a list of options which can be used -to modify @samp{--list}'s operation. +@item --no-same-owner -This example prints a list of the archive members of the archive -@file{stooges}: +When extracting an archive, do not attempt to preserve the owner +specified in the @command{tar} archive. This the default behavior +for ordinary users; this option has an effect only for the superuser. -@example -tar --list --file=stooges -@end example +@item --no-same-permissions -@noindent -@code{tar} responds: +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; this option has an effect only for the superuser. -@example -larry -moe -shemp -marx/julius -marx/alexander -marx/karl -@end example +@item --no-wildcards +Do not use wildcards when excluding files. +@FIXME-xref{} -This example generates a verbose list of the archive members of the -archive file @file{dwarves}, which has a blocking factor of two: +@item --no-wildcards-match-slash +Wildcards do not match @samp{/} when excluding files. +@FIXME-xref{} -@example -tar --list -v --file=blocks -@end example +@item --null -@noindent -@code{tar} responds: +When @command{tar} is using the @samp{--files-from} option, this option +instructs @command{tar} to expect filenames terminated with @kbd{NUL}, so +@command{tar} can correctly work with file names that contain newlines. +@FIXME-xref{} -@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 +@item --numeric-owner -@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 +This option will notify @command{tar} that it should use numeric user and group +IDs when creating a @command{tar} file, rather than names. @FIXME-xref{} -To read archive members from the archive and write them into the file -system, use @samp{tar --extract}. The archive itself is left -unchanged. +@item --old-archive -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. +(See @samp{--portability}.) @FIXME-pxref{} -The following example shows the extraction of the archive -@file{stooges} into an empty directory: +@item --one-file-system +@itemx -l -@example -tar --extract --file=stooges -@end example +Used when creating an archive. Prevents @command{tar} from recursing into +directories that are on different file systems from the current +directory. @FIXME-xref{} -@noindent -Generating a listing of the directory (@samp{ls}) produces: +@item --overwrite -@example -larry -moe -shemp -marx -@end example +Overwrite existing files and directory metadata when extracting files +from an archive. @xref{Overwrite Old Files}. -@noindent -The subdirectory @file{marx} contains the files @file{julius}, -@file{alexander} and @file{karl}. +@item --owner=@var{user} -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: +Specifies that @command{tar} should use @var{user} as the owner of members +when creating archives, instead of the user associated with the source +file. @var{user} is first decoded as a user symbolic name, but if +this interpretation fails, it has to be a decimal numeric user ID. +@FIXME-xref{} -@example -tar --extract --file=stooges marx -@end example +There is no value indicating a missing number, and @samp{0} usually means +@code{root}. Some people like to force @samp{0} as the value to offer in +their distributions for the owner of files, because the @code{root} user is +anonymous anyway, so that might as well be the owner of anonymous archives. -@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 +This option does not affect extraction from archives. + +@item --portability +@itemx --old-archive +@itemx -o -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}). +Tells @command{tar} to create an archive that is compatible with Unix V7 +@command{tar}. @FIXME-xref{} -@menu -* Archive Reading Options:: -* File Writing Options:: -* Scarce Disk Space:: Recovering From Scarce Disk Space -@end menu +@item --posix -@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 +Instructs @command{tar} to create a @sc{posix} compliant @command{tar} archive. @FIXME-xref{} -@c <<< each option wants its own node. summary after menu +@item --preserve -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}. +Synonymous with specifying both @samp{--preserve-permissions} and +@samp{--same-order}. @FIXME-xref{} -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. +@item --preserve-order -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}. +(See @samp{--same-order}; @pxref{Reading}.) -@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 +@item --preserve-permissions +@itemx --same-permissions +@itemx -p -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). +When @command{tar} is extracting an archive, it normally subtracts the users' +umask from the permissions specified in the archive and uses that +number as the permissions to create the destination file. Specifying +this option instructs @command{tar} that it should use the permissions directly +from the archive. @xref{Writing}. -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. +@item --read-full-records +@itemx -B -@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 +Specifies that @command{tar} should reblock its input, for reading from pipes on +systems with buggy implementations. @xref{Reading}. -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. +@item --record-size=@var{size} -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. +Instructs @command{tar} to use @var{size} bytes per record when accessing the +archive. @FIXME-xref{} -This option is probably never needed on modern computer systems. +@item --recursion + +With this option, @command{tar} recurses into directories. +@FIXME-xref{} + +@item --recursive-unlink + +Remove existing +directory hierarchies before extracting directories of the same name +from the archive. @xref{Writing}. + +@item --remove-files + +Directs @command{tar} to remove the source file from the file system after +appending it to an archive. @FIXME-xref{} + +@item --rsh-command=@var{cmd} + +Notifies @command{tar} that is should use @var{cmd} to communicate with remote +devices. @FIXME-xref{} -@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 -@c we don't need/want --preserve to exist any more +This option is an optimization for @command{tar} when running on machines with +small amounts of memory. It informs @command{tar} that the list of file +arguments has already been sorted to match the order of files in the +archive. @xref{Reading}. -@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 +@item --same-owner -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. +When extracting an archive, @command{tar} will attempt to preserve the owner +specified in the @command{tar} archive with this option present. +This is the default behavior for the superuser; this option has an +effect only for ordinary users. @FIXME-xref{} -@table @samp -@item --keep-old files -@itemx -k -Prevents @code{tar} from overwriting files in the file system during -extraction. -@end table +@item --same-permissions -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. +(See @samp{--preserve-permissions}; @pxref{Writing}.) -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}. +@item --show-omitted-dirs -@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 +Instructs @command{tar} to mention directories its skipping over when operating +on a @command{tar} archive. @FIXME-xref{} -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. +@item -M -@c >>> is write access an issue? +@samp{--multi-volume} -@table @samp -@item --absolute-paths -Preserves full file names (inclusing superior dirctory names) when -archiving files. Preserves leading slash when extracting files. -@end table +@item -N -@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 +@samp{--newer} -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, +@item -O -@example -tar --create iggy ziggy --directory=baz melvin -@end example +@samp{--to-stdout} -@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. - -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. +@item -P -Contrast this with the command +@samp{--absolute-names} -@example -tar -c iggy ziggy bar/melvin -@end example +@item -R -@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}. +@samp{--block-number} -@table @samp -@item --directory=@file{directory} -@itemx -C @file{directory} -Changes the working directory. -@end table +@item -S -@c <<>> +@samp{--keep-old-files} -@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 -l -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. +@samp{--one-file-system} -@menu -* Additional Information:: -* Interactive Operation:: -@end menu +@item -m -@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. +@samp{--touch} -@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 -o -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. +@samp{--portability} -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 -p -@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 +@samp{--preserve-permissions} -@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 -r -@example -tar --version -@end example +@samp{--append} -@noindent -might return: +@item -s -@example -GNU tar version 1.09 -@end example -@c used to be an option. has been fixed. +@samp{--same-order} -@node Interactive Operation, , Additional Information, User Interaction -@section Asking for Confirmation During Operations -@cindex Interactive operation +@item -t -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 +@samp{--list} -@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 -u -@node Backups and Restoration, Media, User Interaction, Top -@chapter Performing Backups and Restoring Files +@samp{--update} -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 -v -@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 +@samp{--verbose} -@node Backup Levels, Backup Scripts, Backups and Restoration, Backups and Restoration -@section Levels of Backups +@item -w -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. +@samp{--interactive} -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 -x -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). +@samp{--extract} -@node Backup Scripts, incremental and listed-incremental, Backup Levels, Backups and Restoration -@section Using Scripts to Perform Backups and Restoration +@item -z -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. +@samp{--gzip} -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. +@end table -@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. +@node help +@section @sc{gnu} @command{tar} documentation -@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 +Being careful, the first thing is really checking that you are using @sc{gnu} +@command{tar}, indeed. The @value{op-version} option will generate a message +giving confirmation that you are using @sc{gnu} @command{tar}, with the precise +version of @sc{gnu} @command{tar} you are using. @command{tar} identifies itself +and prints the version number to the standard output, then immediately +exits successfully, without doing anything else, ignoring all other +options. For example, @w{@samp{tar --version}} might return: -@node Backup Parameters, Scripted Backups, Backup Scripts, Backup Scripts -@subsection Setting Parameters for Backups and Restoration +@example +tar (@sc{gnu} tar) @value{VERSION} +@end example -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. +@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 @value{op-version} would not yield @w{@samp{tar (@sc{gnu} paxutils) 3.2}}}. + +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. @sc{gnu} @command{tar} has a short help +feature, triggerable through the @value{op-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: -@c <<< This about backup scripts needs to be written: -@c <<>. bob also comments that if Amanda isn't free software, we +shouldn't mention it..} + +When the archive is being created to @file{/dev/null}, @sc{gnu} @command{tar} +tries to minimize input and output operations. The Amanda backup +system, when used with @sc{gnu} @command{tar}, has an initial sizing pass which +uses this feature. + +@node Selecting Archive Members +@section Selecting Archive Members +@cindex Specifying files to act on +@cindex Specifying archive members + +@dfn{File Name arguments} specify which files in the file system +@command{tar} operates on, when creating or adding to an archive, or which +archive members @command{tar} operates on, when reading or deleting from +an archive. @xref{Operations}. + +To specify file names, you can include them as the last arguments on +the command line, as follows: +@smallexample +@kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}] +@end smallexample + +If you specify a directory name as a file name argument, all the files +in that directory are operated on by @command{tar}. + +If you do not specify files when @command{tar} is invoked with +@value{op-create}, @command{tar} operates on all the non-directory files in +the working directory. If you specify either @value{op-list} or +@value{op-extract}, @command{tar} operates on all the archive members in the +archive. If you specify any operation other than one of these three, +@command{tar} does nothing. + +By default, @command{tar} takes file names from the command line. However, +there are other ways to specify file or member names, or to modify the +manner in which @command{tar} selects the files or members upon which to +operate. @FIXME{add xref here}In general, these methods work both for +specifying the names of files and archive members. + +@node files +@section Reading Names from a File +@UNREVISED + +@cindex Reading file names from a file +@cindex Lists of file names +@cindex File Name arguments, alternatives +Instead of giving the names of files or archive members on the command +line, you can put the names into a file, and then use the +@value{op-files-from} option to @command{tar}. Give the name of the file +which contains the list of files to include as the argument to +@samp{--files-from}. In the list, the file names should be separated by +newlines. You will frequently use this option when you have generated +the list of files to archive with the @command{find} utility. + +@table @kbd +@item --files-from=@var{file name} +@itemx -T @var{file name} +Get names to extract or create from file @var{file name}. +@end table + +If you give a single dash as a file name for @samp{--files-from}, (i.e., +you specify either @samp{--files-from=-} or @samp{-T -}), then the file +names are read from standard input. + +Unless you are running @command{tar} with @samp{--create}, you can not use +both @samp{--files-from=-} and @samp{--file=-} (@samp{-f -}) in the same +command. + +@FIXME{add bob's example, from his message on 2-10-97} + +The following example shows how to use @command{find} to generate a list of +files smaller than 400K in length and put that list into a file +called @file{small-files}. You can then use the @samp{-T} option to +@command{tar} to specify the files from that file, @file{small-files}, to +create the archive @file{little.tgz}. (The @samp{-z} option to +@command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for +more information.) + +@example +$ @kbd{find . -size -400 -print > small-files} +$ @kbd{tar -c -v -z -T small-files -f little.tgz} +@end example + +@noindent +@FIXME{say more here to conclude the example/section?} + +@menu +* nul:: +@end menu + +@node nul +@subsection @kbd{NUL} Terminated File Names + +@cindex File names, terminated by @kbd{NUL} +@cindex @kbd{NUL} terminated file names +The @value{op-null} option causes @value{op-files-from} to read file +names terminated by a @code{NUL} instead of a newline, so files whose +names contain newlines can be archived using @samp{--files-from}. + +@table @kbd +@item --null +Only consider @kbd{NUL} terminated file names, instead of files that +terminate in a newline. +@end table + +The @samp{--null} option is just like the one in @sc{gnu} @command{xargs} and +@command{cpio}, and is useful with the @samp{-print0} predicate of @sc{gnu} +@command{find}. In @command{tar}, @samp{--null} also causes +@value{op-directory} options to be treated as file names to archive, in +case there are any files out there called @file{-C}. + +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 @samp{-print0} option to @command{find} just just +like @samp{-print}, except that it separates files with a @kbd{NUL} +rather than with a newline. You can then run @command{tar} with both the +@samp{--null} and @samp{-T} options to specify that @command{tar} get the +files from that file, @file{long-files}, to create the archive +@file{big.tgz}. The @samp{--null} option to @command{tar} will cause +@command{tar} to recognize the @kbd{NUL} separator between files. + +@example +$ @kbd{find . -size +800 -print0 > long-files} +$ @kbd{tar -c -v --null --files-from=long-files --file=big.tar} +@end example + +@FIXME{say anything else here to conclude the section?} + +@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 +@UNREVISED + +To avoid operating on files whose names match a particular pattern, +use the @value{op-exclude} or @value{op-exclude-from} options. + +@table @kbd +@item --exclude=@var{pattern} +Causes @command{tar} to ignore files that match the @var{pattern}. +@end table + +@findex exclude +The @value{op-exclude} 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 @samp{--exclude} options. + +@table @kbd +@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 @samp{--exclude-from=@var{file-of-patterns}} 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. + +@FIXME{do the exclude options files need to have stuff separated by +newlines the same as the files-from option does?} + +@menu +* controlling pattern-patching with exclude:: +* problems with exclude:: +@end menu + +@node controlling pattern-patching with exclude +@unnumberedsubsec Controlling Pattern-Matching with the @code{exclude} Options + +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: + +@example +--ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme' +@end example + +ignores case when excluding @samp{makefile}, but not when excluding +@samp{readme}. + +@table @option +@item --anchored +@itemx --no-anchored +If anchored (the default), a pattern must match an initial subsequence +of the name's components. Otherwise, the pattern can match any subsequence. + +@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. + +@item --wildcards +@itemx --no-wildcards +When using wildcards (the default), @samp{*}, @samp{?}, and @samp{[...]} +are the usual shell wildcards, and @samp{\} escapes wildcards. +Otherwise, none of these characters are special, and patterns must match +names literally. + +@item --wildcards-match-slash +@itemx --no-wildcards-match-slash +When wildcards match slash (the default), 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 exclude patterns are interpreted. If +recursion is in effect, a pattern excludes a name if it matches any of +the name's parent directories. + +@node problems with exclude +@unnumberedsubsec Problems with Using the @code{exclude} Options + +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 path 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 @value{op-exclude} and +@value{op-exclude-from}. Be careful: use @value{op-exclude} when files +to be excluded are given as a pattern on the command line. Use +@samp{--exclude-from=@var{file-of-patterns}} 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 @value{op-exclude}, be sure to quote the @var{pattern} +parameter, so @sc{gnu} @command{tar} 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: + +@example +$ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}} +@end example + +@noindent +rather than: + +@example +$ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}} +@end example + +@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 +In earlier versions of @command{tar}, what is now the +@samp{--exclude-from=@var{file-of-patterns}} option was called +@samp{--exclude=@var{pattern}} instead. Now, +@samp{--exclude=@var{pattern}} applies to patterns listed on the command +line and @samp{--exclude-from=@var{file-of-patterns}} 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. However, @command{tar} often +uses wildcard patterns for matching (or globbing) archive members instead +of actual files in the filesystem. 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: excluding a directory also excludes all the files beneath it. + +There are some discussions floating in the air and asking for modifications +in the way @sc{gnu} @command{tar} accomplishes wildcard matches. We perceive +any change of semantics in this area as a delicate thing to impose on +@sc{gnu} @command{tar} users. On the other hand, the @sc{gnu} project should be +progressive enough to correct any ill design: compatibility at all price +is not always a good attitude. In conclusion, it is @emph{possible} +that slight amendments be later brought to the previous description. +Your opinions on the matter are welcome. + +@node after +@section Operating Only on New Files +@cindex Excluding file by age +@cindex Modification time, excluding files by +@cindex Age, excluding files by +@UNREVISED + +The @value{op-after-date} option causes @command{tar} to only work on files +whose modification or inode-changed 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 last-modified 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 @samp{--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 actual contents of the file (rather than inode +changes), then use the @value{op-newer-mtime} option. + +You may use these options with any operation. Note that these options +differ from the @value{op-update} 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 @kbd +@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 modification or inode-changed 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 last-modified time of that file is used as the date. + +@item --newer-mtime=@var{date} +Acts like @value{op-after-date}, but only looks at modification times. +@end table + +These options limit @command{tar} to only operating on files which have +been modified after the date specified. A file is considered to have +changed if the contents have been modified, or if the 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 @value{op-after-date} tests both the @code{mtime} +(time the contents of the file were last modified) and @code{ctime} +(time the file's status was last changed: owner, permissions, etc) +fields, while @value{op-newer-mtime} tests only @code{mtime} field. + +To be precise, @value{op-after-date} checks @emph{both} @code{mtime} and +@code{ctime} and processes the file if either one is more recent than +@var{date}, while @value{op-newer-mtime} only checks @code{mtime} and +disregards @code{ctime}. Neither uses @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. + +@FIXME{Need example of --newer-mtime with quoted argument.} + +@quotation +@strong{Please Note:} @value{op-after-date} and @value{op-newer-mtime} +should not be used for incremental backups. Some files (such as those +in renamed directories) are not selected properly by these options. +@xref{incremental and listed-incremental}. +@end quotation + +@noindent +@FIXME{which tells -- need to fill this in!} + +@node recurse +@section Descending into Directories +@cindex Avoiding recursion in directories +@cindex Descending directories, avoiding +@cindex Directories, avoiding recursion +@cindex Recursion in directories, avoiding +@UNREVISED + +@FIXME{arrggh! this is still somewhat confusing to me. :-< } + +@FIXME{show dan bob's comments, from 2-10-97} + +Usually, @command{tar} will recursively explore all directories (either +those given on the command line or through the @value{op-files-from} +option) for the various files they contain. However, you may not always +want @command{tar} to act this way. + +The @value{op-no-recursion} option inhibits @command{tar}'s recursive descent +into specified directories. If you specify @samp{--no-recursion}, you can +use the @command{find} 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}, or look. + +@table @kbd +@item --no-recursion +Prevents @command{tar} from recursively descending directories. + +@item --recursion +Requires @command{tar} to recursively descend directories. +This is the default. +@end table + +When you use @samp{--no-recursion}, @sc{gnu} @command{tar} 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{! -d}} option to @command{find} @FIXME{needs more +explanation or a cite to another info file}as they usually do not want +all the files in a directory. They then use the @value{op-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 +@value{op-same-permissions} option does not affect them---while users +might really like it to. Specifying @value{op-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. + +The @value{op-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 @value{op-no-recursion} option also affects how exclude patterns +are interpreted (@pxref{controlling pattern-patching with exclude}). + +@FIXME{example here} + +@node one +@section Crossing Filesystem Boundaries +@cindex File system boundaries, not crossing +@UNREVISED + +@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 +@value{op-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 @value{op-files-from}, regardless of where they reside. + +@table @kbd +@item --one-file-system +@itemx -l +Prevents @command{tar} from crossing file system boundaries when +archiving. Use in conjunction with any write operation. +@end table + +The @samp{--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 filesystem 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. + +It is reported that using this option, the mount point is is archived, +but nothing under it. + +This option is useful for making full or incremental archival backups of +a file system. If this option is used in conjunction with +@value{op-verbose}, 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 +@UNREVISED + +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 +@value{op-files-from}, use @value{op-directory}. This will change the +working directory to the directory @var{directory} after that point in +the list. + +@table @kbd +@item --directory=@var{directory} +@itemx -C @var{directory} +Changes the working directory in the middle of a command line. +@end table + +For example, + +@example +$ @kbd{tar -c -f jams.tar grape prune -C food cherry} +@end example + +@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, + +@example +$ @kbd{tar -c -f jams.tar grape prune -C food red/cherry} +@end example + +@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{orange-colored}. + +You can use the @samp{--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}: + +@example +$ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a} +@end example + +@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 @samp{--directory} options are interpreted consecutively. If +@samp{--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 +@samp{--directory} option. + +@FIXME{dan: does this mean that you *can* use the short option form, but +you can *not* use the long option form with --files-from? or is this +totally screwed?} + +When using @samp{--files-from} (@pxref{files}), you can put @samp{-C} +options in the file list. Unfortunately, you cannot put +@samp{--directory} options in the file list. (This interpretation can +be disabled by using the @value{op-null} option.) + +@node absolute +@subsection Absolute File Names +@UNREVISED + +@table @kbd +@item -P +@itemx --absolute-names +Do not strip leading slashes from file names, and permit file names +containing a @file{..} file name component. +@end table + +By default, @sc{gnu} @command{tar} drops a leading @samp{/} on input or output, +and complains about file names containing a @file{..} component. +This option turns off this behavior. + +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-@sc{gnu} @command{tar} program to use. Therefore, +@sc{gnu} @command{tar} 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}. + +If you use the @value{op-absolute-names} option, @command{tar} will do +none of these transformations. + +To archive or extract files relative to the root directory, specify +the @value{op-absolute-names} 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 @value{op-absolute-names}, @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 @value{op-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.} + +@FIXME{Is write access an issue?} + +@table @kbd +@item --absolute-names +Preserves full file names (including superior directory names) when +archiving files. Preserves leading slash when extracting files. + +@end table + +@FIXME{this is still horrible; need to talk with dan on monday.} + +@command{tar} prints out a message about removing the @samp{/} from file +names. This message appears once per @sc{gnu} @command{tar} 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}: + +@example +$ @kbd{tar -c -f archive.tar /home 2> /dev/null} +@end example + +@noindent +Another solution, both nicer and simpler, would be to change to +the @file{/} directory first, and then avoid absolute notation. +For example: + +@example +$ @kbd{(cd / && tar -c -f archive.tar home)} +$ @kbd{tar -c -f archive.tar -C / home} +@end example + +@include getdate.texi + +@node Formats +@chapter Controlling the Archive Format + +@FIXME{need an intro here} + +@menu +* Portability:: Making @command{tar} Archives More Portable +* Compression:: Using Less Space through Compression +* Attributes:: Handling File Attributes +* Standard:: The Standard Format +* Extensions:: @sc{gnu} Extensions to the Archive Format +* cpio:: Comparison of @command{tar} and @command{cpio} +@end menu + +@node Portability +@section Making @command{tar} Archives More Portable + +Creating a @command{tar} archive on a particular system that is meant to be +useful later on many other machines and with other versions of @command{tar} +is more challenging than you might think. @command{tar} archive formats +have been evolving since the first versions of Unix. Many such formats +are around, and are not always compatible with each other. This section +discusses a few problems, and gives some advice about making @command{tar} +archives more portable. + +One golden rule is simplicity. For example, limit your @command{tar} +archives to contain only regular files and directories, avoiding +other kind of special files. Do not attempt to save sparse files or +contiguous files as such. Let's discuss a few more problems, in turn. + +@menu +* Portable Names:: Portable Names +* dereference:: Symbolic Links +* old:: Old V7 Archives +* posix:: @sc{posix} archives +* Checksumming:: Checksumming Problems +* Large or Negative Values:: Large files, negative time stamps, etc. +@end menu + +@node Portable Names +@subsection Portable Names + +Use portable file and member names. A name is portable if it contains +only ASCII letters and digits, @samp{/}, @samp{.}, @samp{_}, and +@samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or +contain @samp{/-}. Avoid deep directory nesting. For portability to +old Unix hosts, limit your file name components to 14 characters or +less. + +If you intend to have your @command{tar} archives to be read under MSDOS, +you should not rely on case distinction for file names, and you might +use the @sc{gnu} @command{doschk} program for helping you further diagnosing +illegal MSDOS names, which are even more limited than System V's. + +@node dereference +@subsection Symbolic Links +@cindex File names, using symbolic links +@cindex Symbolic link as file name + +Normally, when @command{tar} archives a symbolic link, it writes a +block to the archive naming the target of the link. In that way, the +@command{tar} archive is a faithful record of the filesystem contents. +@value{op-dereference} is used with @value{op-create}, and causes @command{tar} +to archive the files symbolic links point to, instead of the links +themselves. When this option is used, when @command{tar} encounters a +symbolic link, it will archive the linked-to file, instead of simply +recording the presence of a symbolic link. + +The name under which the file is stored in the file system is not +recorded in the archive. To record both the symbolic link name and +the file name in the system, archive the file under both names. If +all links were recorded automatically by @command{tar}, an extracted file +might be linked to a file name that no longer exists in the file +system. + +If a linked-to file is encountered again by @command{tar} while creating +the same archive, an entire second copy of it will be stored. (This +@emph{might} be considered a bug.) + +So, for portable archives, do not archive symbolic links as such, +and use @value{op-dereference}: many systems do not support +symbolic links, and moreover, your distribution might be unusable if +it contains unresolved symbolic links. + +@node old +@subsection Old V7 Archives +@cindex Format, old style +@cindex Old style format +@cindex Old style archives + +Certain old versions of @command{tar} cannot handle additional +information recorded by newer @command{tar} programs. To create an +archive in V7 format (not ANSI), which can be read by these old +versions, specify the @value{op-old-archive} option in +conjunction with the @value{op-create}. @command{tar} also +accepts @samp{--portability} for this option. When you specify it, +@command{tar} leaves out information about directories, pipes, fifos, +contiguous files, and device files, and specifies file ownership by +group and user IDs instead of group and user names. + +When updating an archive, do not use @value{op-old-archive} +unless the archive was created with using this option. + +In most cases, a @emph{new} format archive can be read by an @emph{old} +@command{tar} program without serious trouble, so this option should +seldom be needed. On the other hand, most modern @command{tar}s are +able to read old format archives, so it might be safer for you to +always use @value{op-old-archive} for your distributions. + +@node posix +@subsection @sc{gnu} @command{tar} and @sc{posix} @command{tar} + +@sc{gnu} @command{tar} was based on an early draft of the @sc{posix} 1003.1 +@code{ustar} standard. @sc{gnu} extensions to @command{tar}, such as the +support for file names longer than 100 characters, use portions of the +@command{tar} header record which were specified in that @sc{posix} draft as +unused. Subsequent changes in @sc{posix} have allocated the same parts of +the header record for other purposes. As a result, @sc{gnu} @command{tar} is +incompatible with the current @sc{posix} spec, and with @command{tar} programs +that follow it. + +We plan to reimplement these @sc{gnu} extensions in a new way which is +upward compatible with the latest @sc{posix} @command{tar} format, but we +don't know when this will be done. + +In the mean time, there is simply no telling what might happen if you +read a @sc{gnu} @command{tar} archive, which uses the @sc{gnu} extensions, using +some other @command{tar} program. So if you want to read the archive +with another @command{tar} program, be sure to write it using the +@samp{--old-archive} option (@samp{-o}). + +@FIXME{is there a way to tell which flavor of tar was used to write a +particular archive before you try to read it?} + +Traditionally, old @command{tar}s have a limit of 100 characters. @sc{gnu} +@command{tar} attempted two different approaches to overcome this limit, +using and extending a format specified by a draft of some P1003.1. +The first way was not that successful, and involved @file{@@MaNgLeD@@} +file names, or such; while a second approach used @file{././@@LongLink} +and other tricks, yielding better success. In theory, @sc{gnu} @command{tar} +should be able to handle file names of practically unlimited length. +So, if @sc{gnu} @command{tar} fails to dump and retrieve files having more +than 100 characters, then there is a bug in @sc{gnu} @command{tar}, indeed. + +But, being strictly @sc{posix}, the limit was still 100 characters. +For various other purposes, @sc{gnu} @command{tar} used areas left unassigned +in the @sc{posix} draft. @sc{posix} later revised P1003.1 @code{ustar} format by +assigning previously unused header fields, in such a way that the upper +limit for file name length was raised to 256 characters. However, the +actual @sc{posix} limit oscillates between 100 and 256, depending on the +precise location of slashes in full file name (this is rather ugly). +Since @sc{gnu} @command{tar} use the same fields for quite other purposes, +it became incompatible with the latest @sc{posix} standards. + +For longer or non-fitting file names, we plan to use yet another set +of @sc{gnu} extensions, but this time, complying with the provisions @sc{posix} +offers for extending the format, rather than conflicting with it. +Whenever an archive uses old @sc{gnu} @command{tar} extension format or @sc{posix} +extensions, would it be for very long file names or other specialities, +this archive becomes non-portable to other @command{tar} implementations. +In fact, anything can happen. The most forgiving @command{tar}s will +merely unpack the file using a wrong name, and maybe create another +file named something like @file{@@LongName}, with the true file name +in it. @command{tar}s not protecting themselves may segment violate! + +Compatibility concerns make all this thing more difficult, as we +will have to support @emph{all} these things together, for a while. +@sc{gnu} @command{tar} should be able to produce and read true @sc{posix} format +files, while being able to detect old @sc{gnu} @command{tar} formats, besides +old V7 format, and process them conveniently. It would take years +before this whole area stabilizes@dots{} + +There are plans to raise this 100 limit to 256, and yet produce @sc{posix} +conforming archives. Past 256, I do not know yet if @sc{gnu} @command{tar} +will go non-@sc{posix} again, or merely refuse to archive the file. + +There are plans so @sc{gnu} @command{tar} support more fully the latest @sc{posix} +format, while being able to read old V7 format, @sc{gnu} (semi-@sc{posix} plus +extension), as well as full @sc{posix}. One may ask if there is part of +the @sc{posix} format that we still cannot support. This simple question +has a complex answer. Maybe that, on intimate look, some strong +limitations will pop up, but until now, nothing sounds too difficult +(but see below). I only have these few pages of @sc{posix} telling about +``Extended tar Format'' (P1003.1-1990 -- section 10.1.1), and there are +references to other parts of the standard I do not have, which should +normally enforce limitations on stored file names (I suspect things +like fixing what @kbd{/} and @kbd{@key{NUL}} means). There are also +some points which the standard does not make clear, Existing practice +will then drive what I should do. + +@sc{posix} mandates that, when a file name cannot fit within 100 to +256 characters (the variance comes from the fact a @kbd{/} is +ideally needed as the 156'th character), or a link name cannot +fit within 100 characters, a warning should be issued and the file +@emph{not} be stored. Unless some @value{op-posix} option is given +(or @env{POSIXLY_CORRECT} is set), I suspect that @sc{gnu} @command{tar} +should disobey this specification, and automatically switch to using +@sc{gnu} extensions to overcome file name or link name length limitations. + +There is a problem, however, which I did not intimately studied yet. +Given a truly @sc{posix} archive with names having more than 100 characters, +I guess that @sc{gnu} @command{tar} up to 1.11.8 will process it as if it were an +old V7 archive, and be fooled by some fields which are coded differently. +So, the question is to decide if the next generation of @sc{gnu} @command{tar} +should produce @sc{posix} format by default, whenever possible, producing +archives older versions of @sc{gnu} @command{tar} might not be able to read +correctly. I fear that we will have to suffer such a choice one of these +days, if we want @sc{gnu} @command{tar} to go closer to @sc{posix}. We can rush it. +Another possibility is to produce the current @sc{gnu} @command{tar} format +by default for a few years, but have @sc{gnu} @command{tar} versions from some +1.@var{POSIX} and up able to recognize all three formats, and let older +@sc{gnu} @command{tar} fade out slowly. Then, we could switch to producing @sc{posix} +format by default, with not much harm to those still having (very old at +that time) @sc{gnu} @command{tar} versions prior to 1.@var{POSIX}. + +@sc{posix} format cannot represent very long names, volume headers, +splitting of files in multi-volumes, sparse files, and incremental +dumps; these would be all disallowed if @value{op-posix} or +@env{POSIXLY_CORRECT}. Otherwise, if @command{tar} is given long +names, or @samp{-[VMSgG]}, then it should automatically go non-@sc{posix}. +I think this is easily granted without much discussion. + +Another point is that only @code{mtime} is stored in @sc{posix} +archives, while @sc{gnu} @command{tar} currently also store @code{atime} +and @code{ctime}. If we want @sc{gnu} @command{tar} to go closer to @sc{posix}, +my choice would be to drop @code{atime} and @code{ctime} support on +average. On the other hand, I perceive that full dumps or incremental +dumps need @code{atime} and @code{ctime} support, so for those special +applications, @sc{posix} has to be avoided altogether. + +A few users requested that @value{op-sparse} be always active by +default, I think that before replying to them, we have to decide +if we want @sc{gnu} @command{tar} to go closer to @sc{posix} on average, while +producing files. My choice would be to go closer to @sc{posix} in the +long run. Besides possible double reading, I do not see any point +of not trying to save files as sparse when creating archives which +are neither @sc{posix} nor old-V7, so the actual @value{op-sparse} would +become selected by default when producing such archives, whatever +the reason is. So, @value{op-sparse} alone might be redefined to force +@sc{gnu}-format archives, and recover its previous meaning from this fact. + +@sc{gnu}-format as it exists now can easily fool other @sc{posix} @command{tar}, +as it uses fields which @sc{posix} considers to be part of the file name +prefix. I wonder if it would not be a good idea, in the long run, +to try changing @sc{gnu}-format so any added field (like @code{ctime}, +@code{atime}, file offset in subsequent volumes, or sparse file +descriptions) be wholly and always pushed into an extension block, +instead of using space in the @sc{posix} header block. I could manage +to do that portably between future @sc{gnu} @command{tar}s. So other @sc{posix} +@command{tar}s might be at least able to provide kind of correct listings +for the archives produced by @sc{gnu} @command{tar}, if not able to process +them otherwise. + +Using these projected extensions might induce older @command{tar}s to fail. +We would use the same approach as for @sc{posix}. I'll put out a @command{tar} +capable of reading @sc{posix}ier, yet extended archives, but will not produce +this format by default, in @sc{gnu} mode. In a few years, when newer @sc{gnu} +@command{tar}s will have flooded out @command{tar} 1.11.X and previous, we +could switch to producing @sc{posix}ier extended archives, with no real harm +to users, as almost all existing @sc{gnu} @command{tar}s will be ready to read +@sc{posix}ier format. In fact, I'll do both changes at the same time, in a +few years, and just prepare @command{tar} for both changes, without effecting +them, from 1.@var{POSIX}. (Both changes: 1---using @sc{posix} convention for +getting over 100 characters; 2---avoiding mangling @sc{posix} headers for @sc{gnu} +extensions, using only @sc{posix} mandated extension techniques). + +So, a future @command{tar} will have a @value{op-posix} +flag forcing the usage of truly @sc{posix} headers, and so, producing +archives previous @sc{gnu} @command{tar} will not be able to read. +So, @emph{once} pretest will announce that feature, it would be +particularly useful that users test how exchangeable will be archives +between @sc{gnu} @command{tar} with @value{op-posix} and other @sc{posix} @command{tar}. + +In a few years, when @sc{gnu} @command{tar} will produce @sc{posix} headers by +default, @value{op-posix} will have a strong meaning and will disallow +@sc{gnu} extensions. But in the meantime, for a long while, @value{op-posix} +in @sc{gnu} tar will not disallow @sc{gnu} extensions like @value{op-label}, +@value{op-multi-volume}, @value{op-sparse}, or very long file or link names. +However, @value{op-posix} with @sc{gnu} extensions will use @sc{posix} +headers with reserved-for-users extensions to headers, and I will be +curious to know how well or bad @sc{posix} @command{tar}s will react to these. + +@sc{gnu} @command{tar} prior to 1.@var{POSIX}, and after 1.@var{POSIX} without +@value{op-posix}, generates and checks @samp{ustar@w{ }@w{ }}, with two +suffixed spaces. This is sufficient for older @sc{gnu} @command{tar} not to +recognize @sc{posix} archives, and consequently, wrongly decide those archives +are in old V7 format. It is a useful bug for me, because @sc{gnu} @command{tar} +has other @sc{posix} incompatibilities, and I need to segregate @sc{gnu} @command{tar} +semi-@sc{posix} archives from truly @sc{posix} archives, for @sc{gnu} @command{tar} should +be somewhat compatible with itself, while migrating closer to latest +@sc{posix} standards. So, I'll be very careful about how and when I will do +the correction. + +@node Checksumming +@subsection Checksumming Problems + +SunOS and HP-UX @command{tar} fail to accept archives created using @sc{gnu} +@command{tar} and containing non-ASCII file names, that is, file names +having characters with the eight bit set, because they use signed +checksums, while @sc{gnu} @command{tar} uses unsigned checksums while creating +archives, as per @sc{posix} standards. On reading, @sc{gnu} @command{tar} computes +both checksums and accept any. It is somewhat worrying that a lot of +people may go around doing backup of their files using faulty (or at +least non-standard) software, not learning about it until it's time +to restore their missing files with an incompatible file extractor, +or vice versa. + +@sc{gnu} @command{tar} compute checksums both ways, and accept any on read, +so @sc{gnu} tar can read Sun tapes even with their wrong checksums. +@sc{gnu} @command{tar} produces the standard checksum, however, raising +incompatibilities with Sun. That is to say, @sc{gnu} @command{tar} has not +been modified to @emph{produce} incorrect archives to be read by buggy +@command{tar}'s. I've been told that more recent Sun @command{tar} now +read standard archives, so maybe Sun did a similar patch, after all? + +The story seems to be that when Sun first imported @command{tar} +sources on their system, they recompiled it without realizing that +the checksums were computed differently, because of a change in +the default signing of @code{char}'s in their compiler. So they +started computing checksums wrongly. When they later realized their +mistake, they merely decided to stay compatible with it, and with +themselves afterwards. Presumably, but I do not really know, HP-UX +has chosen that their @command{tar} archives to be compatible with Sun's. +The current standards do not favor Sun @command{tar} format. In any +case, it now falls on the shoulders of SunOS and HP-UX users to get +a @command{tar} able to read the good archives they receive. + +@node Large or Negative Values +@subsection Large or Negative Values +@cindex large values +@cindex future time stamps +@cindex negative time stamps + +@sc{posix} @command{tar} format uses fixed-sized unsigned octal strings +to represent numeric values. User and group IDs and device major and +minor numbers have unsigned 21-bit representations, and file sizes and +times have unsigned 33-bit representations. @sc{gnu} @command{tar} +generates @sc{posix} representations when possible, but for values +outside the @sc{posix} range it generates two's-complement base-256 +strings: uids, gids, and device numbers have signed 57-bit +representations, and file sizes and times have signed 89-bit +representations. These representations are an extension to @sc{posix} +@command{tar} format, so they are not universally portable. + +The most common portability problems with out-of-range numeric values +are large files and future or negative time stamps. + +Portable archives should avoid members of 8 GB or larger, as @sc{posix} +@command{tar} format cannot represent them. + +Portable archives should avoid time stamps from the future. @sc{posix} +@command{tar} format can represent time stamps in the range 1970-01-01 +00:00:00 through 2242-03-16 12:56:31 @sc{utc}. However, many current +hosts use a signed 32-bit @code{time_t}, or internal time stamp format, +and cannot represent time stamps after 2038-01-19 03:14:07 @sc{utc}; so +portable archives must avoid these time stamps for many years to come. + +Portable archives should also avoid time stamps before 1970. These time +stamps are a common @sc{posix} extension but their @code{time_t} +representations are negative. Many traditional @command{tar} +implementations generate a two's complement representation for negative +time stamps that assumes a signed 32-bit @code{time_t}; hence they +generate archives that are not portable to hosts with differing +@code{time_t} representations. @sc{gnu} @command{tar} recognizes this +situation when it is run on host with a signed 32-bit @code{time_t}, but +it issues a warning, as these time stamps are nonstandard and unportable. + +@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 +@UNREVISED + +@table @kbd +@item -z +@itemx --gzip +@itemx --ungzip +Filter the archive through @command{gzip}. +@end table + +@FIXME{ach; these two bits orig from "compare" (?). where to put?} Some +format parameters must be taken into consideration when modifying an +archive.@FIXME{???} Compressed archives cannot be modified. + +You can use @samp{--gzip} and @samp{--gunzip} 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; if you need to +override them, avoid the @value{op-gzip} option and run @command{gzip} +explicitly. (Or set the @env{GZIP} environment variable.) + +The @value{op-gzip} option does not work with the @value{op-multi-volume} +option, or with the @value{op-update}, @value{op-append}, +@value{op-concatenate}, or @value{op-delete} operations. + +It is not exact to say that @sc{gnu} @command{tar} is to work in concert +with @command{gzip} in a way similar to @command{zip}, say. Surely, it is +possible that @command{tar} and @command{gzip} be done with a single call, +like in: + +@example +$ @kbd{tar cfz archive.tar.gz subdir} +@end example + +@noindent +to save all of @samp{subdir} into a @code{gzip}'ed archive. Later you +can do: + +@example +$ @kbd{tar xfz archive.tar.gz} +@end example + +@noindent +to explode and unpack. + +The difference is that the whole archive is compressed. With +@command{zip}, archive members are archived individually. @command{tar}'s +method yields better compression. On the other hand, one can view the +contents of a @command{zip} archive without having to decompress it. As +for the @command{tar} and @command{gzip} tandem, you need to decompress the +archive to see its contents. However, this may be done without needing +disk space, by using pipes internally: + +@example +$ @kbd{tar tfz archive.tar.gz} +@end example + +@cindex corrupted archives +About corrupted compressed archives: @command{gzip}'ed files have no +redundancy, for maximum compression. 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. + +There are pending suggestions for having a per-volume or per-file +compression in @sc{gnu} @command{tar}. This would allow for viewing the +contents without decompression, and for resynchronizing decompression at +every volume or file, in case of corrupted archives. Doing so, we might +lose some compressibility. But this would have make recovering easier. +So, there are pros and cons. We'll see! + +@table @kbd +@item -j +@itemx --bzip2 +Filter the archive through @code{bzip2}. Otherwise like @value{op-gzip}. + +@item -Z +@itemx --compress +@itemx --uncompress +Filter the archive through @command{compress}. Otherwise like @value{op-gzip}. + +@item --use-compress-program=@var{prog} +Filter through @var{prog} (must accept @samp{-d}). +@end table + +@value{op-compress} stores an archive in compressed format. This +option is useful in saving time over networks and space in pipes, and +when storage space is at a premium. @value{op-compress} causes +@command{tar} to compress when writing the archive, or to uncompress when +reading the archive. + +To perform compression and uncompression on the archive, @command{tar} +runs the @command{compress} utility. @command{tar} uses the default +compression parameters; if you need to override them, avoid the +@value{op-compress} option and run the @command{compress} utility +explicitly. It is useful to be able to call the @command{compress} +utility from within @command{tar} because the @command{compress} utility by +itself cannot access remote tape drives. + +The @value{op-compress} option will not work in conjunction with the +@value{op-multi-volume} option or the @value{op-append}, @value{op-update} +and @value{op-delete} operations. @xref{Operations}, for +more information on these operations. + +If there is no compress utility available, @command{tar} will report an error. +@strong{Please note} that the @command{compress} program may be covered by +a patent, and therefore we recommend you stop using it. + +@value{op-bzip2} acts like @value{op-compress}, except that it uses +the @code{bzip2} utility. + +@table @kbd +@item --compress +@itemx --uncompress +@itemx -z +@itemx -Z +When this option is specified, @command{tar} will compress (when writing +an archive), or uncompress (when reading an archive). Used in +conjunction with the @value{op-create}, @value{op-extract}, @value{op-list} and +@value{op-compare} operations. +@end table + +You can have archives be compressed by using the @value{op-gzip} option. +This will arrange for @command{tar} to use the @command{gzip} program to be +used to compress or uncompress the archive wren writing or reading it. + +To use the older, obsolete, @command{compress} program, use the +@value{op-compress} option. The @sc{gnu} Project recommends you not use +@command{compress}, because there is a patent covering the algorithm it +uses. You could be sued for patent infringement merely by running +@command{compress}. + +I have one question, or maybe it's a suggestion if there isn't a way +to do it now. I would like to use @value{op-gzip}, but I'd also like the +output to be fed through a program like @sc{gnu} @command{ecc} (actually, right +now that's @samp{exactly} what I'd like to use :-)), basically adding +ECC protection on top of compression. It seems as if this should be +quite easy to do, but I can't work out exactly how to go about it. +Of course, I can pipe the standard output of @command{tar} through +@command{ecc}, but then I lose (though I haven't started using it yet, +I confess) the ability to have @command{tar} use @command{rmt} for it's I/O +(I think). + +I think the most straightforward thing would be to let me specify a +general set of filters outboard of compression (preferably ordered, +so the order can be automatically reversed on input operations, and +with the options they require specifiable), but beggars shouldn't be +choosers and anything you decide on would be fine with me. + +By the way, I like @command{ecc} but if (as the comments say) it can't +deal with loss of block sync, I'm tempted to throw some time at adding +that capability. Supposing I were to actually do such a thing and +get it (apparently) working, do you accept contributed changes to +utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995). + +Isn't that exactly the role of the @value{op-use-compress-prog} option? +I never tried it myself, but I suspect you may want to write a +@var{prog} script or program able to filter stdin to stdout to +way you want. It should recognize the @samp{-d} option, for when +extraction is needed rather than creation. + +It has been reported that if one writes compressed data (through the +@value{op-gzip} or @value{op-compress} options) to a DLT and tries to use +the DLT compression mode, the data will actually get bigger and one will +end up with less space on the tape. + +@node sparse +@subsection Archiving Sparse Files +@cindex Sparse Files +@UNREVISED + +@table @kbd +@item -S +@itemx --sparse +Handle sparse files efficiently. +@end table + +This option causes all files to be put in the archive to be tested for +sparseness, and handled specially if they are. The @value{op-sparse} +option is useful when many @code{dbm} files, for example, are being +backed up. Using this option dramatically decreases the amount of +space needed to store such a file. + +In later versions, this option may be removed, and the testing and +treatment of sparse files may be done automatically with any special +@sc{gnu} options. For now, it is an option needing to be specified on +the command line with the creation or updating of an archive. + +Files in the filesystem occasionally have ``holes.'' A hole in a file +is a section of the file's contents which was never written. The +contents of a hole read as all zeros. On many operating systems, +actual disk storage is not allocated for holes, but they are counted +in the length of the file. If you archive such a file, @command{tar} +could create an archive longer than the original. To have @command{tar} +attempt to recognize the holes in a file, use @value{op-sparse}. When +you use the @value{op-sparse} option, then, for any file using less +disk space than would be expected from its length, @command{tar} searches +the file for consecutive stretches of zeros. It then records in the +archive for the file where the consecutive stretches of zeros are, and +only archives the ``real contents'' of the file. On extraction (using +@value{op-sparse} is not needed on extraction) any such files have +hols created wherever the continuous stretches of zeros were found. +Thus, if you use @value{op-sparse}, @command{tar} archives won't take +more space than the original. + +A file is sparse if it contains blocks of zeros whose existence is +recorded, but that have no space allocated on disk. When you specify +the @value{op-sparse} option in conjunction with the @value{op-create} +operation, @command{tar} tests all files for sparseness while archiving. +If @command{tar} finds a file to be sparse, it uses a sparse representation of +the file in the archive. @value{xref-create}, for more information +about creating archives. + +@value{op-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. + +@quotation +@strong{Please Note:} Always use @value{op-sparse} when performing file +system backups, to avoid archiving the expanded forms of files stored +sparsely in the system. + +Even if your system has no sparse files currently, some may be +created in the future. If you use @value{op-sparse} while making file +system backups as a matter of course, you can be assured the archive +will never take more space on the media than the files take on disk +(otherwise, archiving a disk filled with sparse files might take +hundreds of tapes). @FIXME-xref{incremental when node name is set.} +@end quotation + +@command{tar} ignores the @value{op-sparse} option when reading an archive. + +@table @kbd +@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 + +However, users should be well aware that at archive creation time, @sc{gnu} +@command{tar} still has to read whole disk file to locate the @dfn{holes}, and +so, even if sparse files use little space on disk and in the archive, they +may sometimes require inordinate amount of time for reading and examining +all-zero blocks of a file. Although it works, it's painfully slow for a +large (sparse) file, even though the resulting tar archive may be small. +(One user reports that dumping a @file{core} file of over 400 megabytes, +but with only about 3 megabytes of actual data, took about 9 minutes on +a Sun Sparcstation ELC, with full CPU utilization.) + +This reading is required in all cases and is not related to the fact +the @value{op-sparse} option is used or not, so by merely @emph{not} +using the option, you are not saving time@footnote{Well! We should say +the whole truth, here. When @value{op-sparse} is selected while creating +an archive, the current @command{tar} algorithm requires sparse files to be +read twice, not once. We hope to develop a new archive format for saving +sparse files in which one pass will be sufficient.}. + +Programs like @command{dump} do not have to read the entire file; by examining +the file system directly, they can determine in advance exactly where the +holes are and thus avoid reading through them. The only data it need read +are the actual allocated data blocks. @sc{gnu} @command{tar} uses a more portable +and straightforward archiving approach, it would be fairly difficult that +it does otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, +on 1990-12-10: + +@quotation +What I did say is that you cannot tell the difference between a hole and an +equivalent number of nulls without reading raw blocks. @code{st_blocks} at +best tells you how many holes there are; it doesn't tell you @emph{where}. +Just as programs may, conceivably, care what @code{st_blocks} is (care +to name one that does?), they may also care where the holes are (I have +no examples of this one either, but it's equally imaginable). + +I conclude from this that good archivers are not portable. One can +arguably conclude that if you want a portable program, you can in good +conscience restore files with as many holes as possible, since you can't +get it right. +@end quotation + +@node Attributes +@section Handling File Attributes +@UNREVISED + +When @command{tar} reads files, this causes them to have the access +times updated. To have @command{tar} attempt to set the access times +back to what they were before they were read, use the +@value{op-atime-preserve} option. + +Handling of file attributes + +@table @kbd +@item --atime-preserve +Preserve access times on files that are read. +This doesn't work for files that +you don't own, unless you're root, and it doesn't interact with +incremental dumps nicely (@pxref{Backups}), and it can set access or +modification times incorrectly if other programs access the file while +@command{tar} is running; but it is good enough for some purposes. + +@item -m +@itemx --touch +Do not extract file modified time. + +When this option is used, @command{tar} leaves the modification times +of the files it extracts as the time when the files were extracted, +instead of setting it to the time recorded in the archive. + +This option is meaningless with @value{op-list}. + +@item --same-owner +Create extracted files with the same ownership they have in the +archive. + +This is the default behavior for the superuser, +so this option is meaningful only for non-root users, when @command{tar} +is executed on those systems able to give files away. This is +considered as a security flaw by many people, at least because it +makes quite difficult to correctly account users for the disk space +they occupy. Also, the @code{suid} or @code{sgid} attributes of +files are easily and silently lost when files are given away. + +When writing an archive, @command{tar} writes the user id and user name +separately. If it can't find a user name (because the user id is not +in @file{/etc/passwd}), then it does not write one. When restoring, +and doing a @code{chmod} like when you use @value{op-same-permissions}, +@FIXME{same-owner?}it tries to look the name (if one was written) +up in @file{/etc/passwd}. If it fails, then it uses the user id +stored in the archive instead. + +@item --no-same-owner +Do not attempt to restore ownership when extracting. This is the +default behavior for ordinary users, so this option has an effect +only for the superuser. + +@item --numeric-owner +The @value{op-numeric-owner} option allows (ANSI) archives to be written +without user/group name information or such information to be ignored +when extracting. It effectively disables the generation and/or use +of user/group name information. This option forces extraction using +the numeric ids from the archive, ignoring the names. + +This is useful in certain circumstances, when restoring a backup from +an emergency floppy with different passwd/group files for example. +It is otherwise impossible to extract files with the right ownerships +if the password file in use during the extraction does not match the +one belonging to the filesystem(s) being extracted. This occurs, +for example, if you are restoring your files after a major crash and +had booted from an emergency floppy with no password file or put your +disk into another machine to do the restore. + +The numeric ids are @emph{always} saved into @command{tar} archives. +The identifying names are added at create time when provided by the +system, unless @value{op-old-archive} is used. Numeric ids could be +used when moving archives between a collection of machines using +a centralized management for attribution of numeric ids to users +and groups. This is often made through using the NIS capabilities. + +When making a @command{tar} file for distribution to other sites, it +is sometimes cleaner to use a single owner for all files in the +distribution, and nicer to specify the write permission bits of the +files as stored in the archive independently of their actual value on +the file system. The way to prepare a clean distribution is usually +to have some Makefile rule creating a directory, copying all needed +files in that directory, then setting ownership and permissions as +wanted (there are a lot of possible schemes), and only then making a +@command{tar} archive out of this directory, before cleaning everything +out. Of course, we could add a lot of options to @sc{gnu} @command{tar} for +fine tuning permissions and ownership. This is not the good way, +I think. @sc{gnu} @command{tar} is already crowded with options and moreover, +the approach just explained gives you a great deal of control already. + +@item -p +@itemx --same-permissions +@itemx --preserve-permissions +Extract all protection information. + +This option causes @command{tar} to set the modes (access permissions) of +extracted files exactly as recorded in the archive. If this option +is not used, the current @code{umask} setting limits the permissions +on extracted files. + +This option is meaningless with @value{op-list}. + +@item --preserve +Same as both @value{op-same-permissions} and @value{op-same-order}. + +The @value{op-preserve} option has no equivalent short option name. +It is equivalent to @value{op-same-permissions} plus @value{op-same-order}. + +@FIXME{I do not see the purpose of such an option. (Neither I. FP.)} + +@end table + +@node Standard +@section The Standard Format +@UNREVISED + +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 @command{tar} utility or Tar mode in @sc{gnu} +Emacs. + +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 @command{tar} uses to detect file corruption, and +information about file types. + +Archives are permitted to have more than one member with the same +member 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, see @ref{update}. +@FIXME-xref{To learn more about having more than one archive member with the +same name, see -backup node, when it's written.} + +In addition to entries describing archive members, an archive may +contain entries which @command{tar} itself uses to store information. +@value{xref-label}, for an example of such an archive entry. + +A @command{tar} archive file contains a series of blocks. Each block +contains @code{BLOCKSIZE} bytes. Although this format may be thought +of as being on magnetic tape, other media are often used. + +Each file archived is represented by a header block which describes +the file, followed by zero or more blocks which give the contents +of the file. At the end of the archive file there may be a block +filled with binary zeros as an end-of-file marker. A reasonable system +should write a block of zeros at the end, but must not assume that +such a block exists when reading an archive. + +The blocks may be @dfn{blocked} for physical I/O operations. +Each record of @var{n} blocks (where @var{n} is set by the +@value{op-blocking-factor} option to @command{tar}) is written with a single +@w{@samp{write ()}} operation. On magnetic tapes, the result of +such a write is a single record. When writing an archive, +the last record of blocks should be written at the full size, with +blocks after the zero block containing all zeros. When reading +an archive, a reasonable system should properly handle an archive +whose last record is shorter than the rest, or which contains garbage +records after a zero block. + +The header block is defined in C as follows. In the @sc{gnu} @command{tar} +distribution, this is part of file @file{src/tar.h}: + +@example +@include header.texi +@end example + +All characters in header blocks are represented by using 8-bit +characters in the local variant of ASCII. Each field within the +structure is contiguous; that is, there is no padding used within +the structure. Each character on the archive medium is stored +contiguously. + +Bytes representing the contents of files (after the header block +of each file) are not translated in any way and are not constrained +to represent characters in any character set. The @command{tar} format +does not distinguish text files from binary files, and no translation +of file contents is performed. + +The @code{name}, @code{linkname}, @code{magic}, @code{uname}, and +@code{gname} are null-terminated character strings. All other fields +are 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. + +The @code{name} field is the file name of the file, with directory names +(if any) preceding the file name, separated by slashes. + +@FIXME{how big a name before field overflows?} + +The @code{mode} field provides nine bits specifying file permissions +and three bits to specify the Set UID, Set GID, and Save Text +(@dfn{sticky}) modes. Values for these bits are defined above. +When special permissions are required to create a file with a given +mode, and the user restoring files from the archive does not hold such +permissions, the mode bit(s) specifying those special permissions +are ignored. Modes which are not supported by the operating system +restoring files from the archive will be ignored. Unsupported modes +should be faked up when creating or updating an archive; e.g.@: the +group permission could be copied from the @emph{other} permission. + +The @code{uid} and @code{gid} fields are the numeric user and group +ID of the file owners, respectively. If the operating system does +not support numeric user or group IDs, these fields should be ignored. + +The @code{size} field is the size of the file in bytes; linked files +are archived with this field specified as zero. @FIXME-xref{Modifiers, in +particular the @value{op-incremental} option.} + +The @code{mtime} field is the modification time of the file at the time +it was archived. It 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. + +The @code{chksum} field is the ASCII representation of the octal value +of the simple sum of all bytes in the header block. Each 8-bit +byte in the header is added to an unsigned integer, initialized to +zero, the precision of which shall be no less than seventeen bits. +When calculating the checksum, the @code{chksum} field is treated as +if it were all blanks. + +The @code{typeflag} field specifies the type of file archived. If a +particular implementation does not recognize or permit the specified +type, the file will be extracted as if it were a regular file. As this +action occurs, @command{tar} issues a warning to the standard error. + +The @code{atime} and @code{ctime} fields are used in making incremental +backups; they store, respectively, the particular file's access time +and last inode-change time. + +The @code{offset} is used by the @value{op-multi-volume} option, when +making a multi-volume archive. The offset is number of bytes into +the file that we need to restart at to continue the file on the next +tape, i.e., where we store the location that a continued file is +continued at. + +The following fields were added to deal with sparse files. A file +is @dfn{sparse} if it takes in unallocated blocks which end up being +represented as zeros, i.e., no useful data. A test to see if a file +is sparse is to look at the number blocks allocated for it versus the +number of characters in the file; if there are fewer blocks allocated +for the file than would normally be allocated for a file of that +size, then the file is sparse. This is the method @command{tar} uses to +detect a sparse file, and once such a file is detected, it is treated +differently from non-sparse files. + +Sparse files are often @code{dbm} files, or other database-type files +which have data at some points and emptiness in the greater part of +the file. Such files can appear to be very large when an @samp{ls +-l} is done on them, when in truth, there may be a very small amount +of important data contained in the file. It is thus undesirable +to have @command{tar} think that it must back up this entire file, as +great quantities of room are wasted on empty blocks, which can lead +to running out of room on a tape far earlier than is necessary. +Thus, sparse files are dealt with so that these empty blocks are +not written to the tape. Instead, what is written to the tape is a +description, of sorts, of the sparse file: where the holes are, how +big the holes are, and how much data is found at the end of the hole. +This way, the file takes up potentially far less room on the tape, +and when the file is extracted later on, it will look exactly the way +it looked beforehand. The following is a description of the fields +used to handle a sparse file: + +The @code{sp} is an array of @code{struct sparse}. Each @code{struct +sparse} contains two 12-character strings which represent an offset +into the file and a number of bytes to be written at that offset. +The offset is absolute, and not relative to the offset in preceding +array element. + +The header can hold four of these @code{struct sparse} at the moment; +if more are needed, they are not stored in the header. + +The @code{isextended} flag is set when an @code{extended_header} +is needed to deal with a file. Note that this means that this flag +can only be set when dealing with a sparse file, and it is only set +in the event that the description of the file will not fit in the +allotted room for sparse structures in the header. In other words, +an extended_header is needed. + +The @code{extended_header} structure is used for sparse files which +need more sparse structures than can fit in the header. The header can +fit 4 such structures; if more are needed, the flag @code{isextended} +gets set and the next block is an @code{extended_header}. + +Each @code{extended_header} structure contains an array of 21 +sparse structures, along with a similar @code{isextended} flag +that the header had. There can be an indeterminate number of such +@code{extended_header}s to describe a sparse file. + +@table @asis + +@item @code{REGTYPE} +@itemx @code{AREGTYPE} +These flags represent a regular file. In order to be compatible +with older versions of @command{tar}, a @code{typeflag} value of +@code{AREGTYPE} should be silently recognized as a regular file. +New archives should be created using @code{REGTYPE}. Also, for +backward compatibility, @command{tar} treats a regular file whose name +ends with a slash as a directory. + +@item @code{LNKTYPE} +This flag represents a file linked to another file, of any type, +previously archived. Such files are identified in Unix by each +file having the same device and inode number. The linked-to name is +specified in the @code{linkname} field with a trailing null. + +@item @code{SYMTYPE} +This represents a symbolic link to another file. The linked-to name +is specified in the @code{linkname} field with a trailing null. + +@item @code{CHRTYPE} +@itemx @code{BLKTYPE} +These represent 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 respectively. +Operating systems may map the device specifications to their own +local specification, or may ignore the entry. + +@item @code{DIRTYPE} +This flag specifies 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) which the directory may +hold. A @code{size} field of zero indicates no such limiting. Systems +which do not support limiting in this manner should ignore the +@code{size} field. + +@item @code{FIFOTYPE} +This specifies a FIFO special file. Note that the archiving of a +FIFO file archives the existence of this file and not its contents. + +@item @code{CONTTYPE} +This specifies a contiguous file, which is the same as a normal +file except that, in operating systems which support it, all its +space is allocated contiguously on the disk. Operating systems +which do not allow contiguous allocation should silently treat this +type as a normal file. + +@item @code{A} @dots{} @code{Z} +These are reserved for custom implementations. Some of these are +used in the @sc{gnu} modified format, as described below. + +@end table + +Other values are reserved for specification in future revisions of +the P1003 standard, and should not be used by any @command{tar} program. + +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. + +For references, see ISO/IEC 9945-1:1990 or IEEE Std 1003.1-1990, pages +169-173 (section 10.1) for @cite{Archive/Interchange File Format}; and +IEEE Std 1003.2-1992, pages 380-388 (section 4.48) and pages 936-940 +(section E.4.48) for @cite{pax - Portable archive interchange}. + +@node Extensions +@section @sc{gnu} Extensions to the Archive Format +@UNREVISED + +The @sc{gnu} format uses additional file types to describe new types of +files in an archive. These are listed below. + +@table @code +@item GNUTYPE_DUMPDIR +@itemx 'D' +This represents a directory and a list of files created by the +@value{op-incremental} option. The @code{size} field gives the total +size of the associated list of files. Each file name is preceded by +either a @samp{Y} (the file should be in this archive) or an @samp{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 GNUTYPE_MULTIVOL +@itemx 'M' +This represents a file continued from another volume of a multi-volume +archive created with the @value{op-multi-volume} option. 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. + +@item GNUTYPE_SPARSE +@itemx 'S' +This flag indicates that we are dealing with a sparse file. Note +that archiving a sparse file requires special operations to find +holes in the file, which mark the positions of these holes, along +with the number of bytes of data to be found after the hole. + +@item GNUTYPE_VOLHDR +@itemx 'V' +This file type is used to mark the volume header that was given with +the @value{op-label} option when the archive was created. The @code{name} +field contains the @code{name} given after the @value{op-label} option. +The @code{size} field is zero. Only the first file in each volume +of an archive should have this type. + +@end table + +You may have trouble reading a @sc{gnu} format archive on a non-@sc{gnu} +system if the options @value{op-incremental}, @value{op-multi-volume}, +@value{op-sparse}, or @value{op-label} were used when writing the archive. +In general, if @command{tar} does not use the @sc{gnu}-added fields of the +header, other versions of @command{tar} should be able to read the +archive. Otherwise, the @command{tar} program will give an error, the +most likely one being a checksum error. + +@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 +pathname lengths. The binary and old ASCII formats have a max path +length of 256, and the new ASCII and CRC ASCII formats have a max +path length of 1024. @sc{gnu} @command{cpio} can read and write archives +with arbitrary pathname 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 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 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 BSD source; +@command{cpio} comes only with System III, System V, and later 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 inumbers (e.g., the 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 ASCII" format, +they're 18 bits---it would have to play games with the "file system ID" +field of the header to make sure that the file system 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}, @sc{gnu} @command{tar}, 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 @sc{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. + +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. + +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. + +@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 + +@node Device +@section Device Selection and Switching +@UNREVISED + +@table @kbd +@item -f [@var{hostname}:]@var{file} +@itemx --file=[@var{hostname}:]@var{file} +Use archive file or device @var{file} on @var{hostname}. +@end table + +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 (@kbd{@@}), 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 @file{/etc/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 @file{/etc/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. + +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, @sc{gnu} @command{tar} 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. + +@sc{gnu} @command{tar} 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 @kbd +@item --force-local +Archive file is local even if it contains a colon. + +@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. + +@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}. + +@item -L @var{num} +@itemx --tape-length=@var{num} +Change tape after writing @var{num} x 1024 bytes. + +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. + +@item -F @var{file} +@itemx --info-script=@var{file} +@itemx --new-volume-script=@var{file} +Execute @file{file} at end of each tape. If @file{file} exits with +nonzero status, exit. This implies @value{op-multi-volume}. +@end table + +@node Remote Tape Server +@section The 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{/etc/rmt} +on any machine whose tape drive you want to use. @command{tar} calls +@file{/etc/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. It is +Copyright @copyright{} 1983 by the Regents of the University of +California, but can be freely distributed. Instructions for compiling +and installing it are included in the @file{Makefile}. + +@cindex absolute file names +Unless you use the @value{op-absolute-names} option, @sc{gnu} @command{tar} 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, @sc{gnu} @command{tar} 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 @sc{gnu} @command{tar}, 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}, +@sc{gnu} @command{tar} 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 @value{op-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 know 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 @value{op-append}, @value{op-update}, +@value{op-concatenate}, and @value{op-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 @value{op-multi-volume}, @value{op-label}, and +@value{op-incremental} 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 @value{op-incremental} 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 @command{tar}: +directory checksum error +header format error + +errors from media/system: +i/o error +device busy +@end format + +@end ifclear + +@node Blocking +@section Blocking +@UNREVISED + +@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. + +John Gilmore, the writer of the public domain @command{tar} from which +@sc{gnu} @command{tar} was originally derived, wrote (June 1995): + +@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 @sc{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 @sc{gnu} @command{tar}. + +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 @sc{gnu} @command{tar}. + +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 @value{op-blocking-factor} 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 +@value{op-blocking-factor}) larger than the actual blocking factor, and then use +the @value{op-read-full-records} option. (If you specify a blocking factor +with @value{op-blocking-factor} and don't use the @value{op-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 @value{op-blocking-factor} when reading, because @command{tar} cannot +figure it out. In any case, use @value{op-list} 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 +@value{op-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. @sc{gnu} @command{tar}, however, will support arbitrarily +large record sizes, limited only by the amount of virtual memory or the +physical characteristics of the tape device. + +@menu +* Format Variations:: Format Variations +* Blocking Factor:: The Blocking Factor of an Archive +@end menu + +@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. + +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 @value{op-blocking-factor} option +specified (@value{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 + +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 (ie. the size of a +record in units of 512 bytes) is called the @dfn{blocking factor}. +The @value{op-blocking-factor} 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. + +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 @sc{gnu} @command{tar}, 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: + +@example +Cannot write to /dev/dlt: Invalid argument +@end example + +@noindent +In such cases, it sometimes happen that the @command{tar} bundled by the +system is aware of block size idiosyncrasies, while @sc{gnu} @command{tar} requires +an explicit specification for the block size, which it cannot guess. +This yields some people to consider @sc{gnu} @command{tar} 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 @value{op-list} 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 @value{op-read-full-records} option while +specifying a blocking factor larger then the blocking factor of the archive +(ie. @samp{tar --extract --read-full-records --blocking-factor=300}. +@xref{list}, for more information on the @value{op-list} +operation. @xref{Reading}, for a more detailed explanation of that option. + +@table @kbd +@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 @value{op-list}. +@end table + +Device blocking + +@table @kbd +@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 dissapper. Id est, we are using block size of 112 right +now, and we haven't had the problem since we switched@dots{} + +With @sc{gnu} @command{tar} 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 +@value{op-blocking-factor} is not explicitly specified on the @command{tar} +invocation. +@end itemize + +In previous versions of @sc{gnu} @command{tar}, the @samp{--compress-block} +option (or even older: @samp{--block-compress}) was necessary to +reblock compressed archives. It is now a dummy option just asking +not to be used, and otherwise ignored. 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 + +@item -i +@itemx --ignore-zeros +Ignore blocks of zeros in archive (means EOF). + +The @value{op-ignore-zeros} 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. + +@item -B +@itemx --read-full-records +Reblock as we read (for reading 4.2BSD pipes). + +If @value{op-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 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 loosing 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 @samp{--number-blocks} instead of +@samp{--block-number}, so @samp{--block} will then expand to +@samp{--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: + +@example +$ @kbd{tar cf /dev/tape @var{directory}} +@end example + +@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: + +@example +$ @kbd{mt -f /dev/nrtape rewind} +$ @kbd{tar cf /dev/nrtape @var{directory-1}} +@end example + +@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: + +@example +$ @kbd{tar cf /dev/nrtape @var{directory-2}} +@end example + +@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: + +@example +$ @kbd{mt -f /dev/nrtape rewind} +$ @kbd{mt -f /dev/nrtape fsf 16} +$ @kbd{tar cf /dev/nrtape @var{directory-17}} +@end example -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). +In all the previous examples, we put aside blocking considerations, but +you should do the proper things for that as well. @xref{Blocking}. -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. +@menu +* Tape Positioning:: Tape Positions and Tape Marks +* mt:: The @command{mt} Utility +@end menu -@node Tape Positioning, , Write Protection, Media -@section Tape Positions and Tape Marks +@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 @@ -3109,26 +7914,26 @@ 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------------------------- +rrrr*rrrrrr*rrrrr*rr*rrrrr**------------------------- @end example 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. +script will find the archive automatically. @FIXME{There is no such +restore script!}@FIXME-xref{Scripted Restoration}@xref{mt}, for +an explanation of the tape moving utility. 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 @@ -3137,812 +7942,501 @@ to add two archives to the example above, the tape might look like the following: @example -0000x000000x00000x00x00000x000x0000xx---------------- +rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**---------------- @end example -@menu -* mt:: The @code{mt} Utility -@end menu +@node mt +@subsection The @command{mt} Utility +@UNREVISED -@node mt, , Tape Positioning, Tape Positioning -@subsection The @code{mt} Utility +@FIXME{Is it true that this only works on non-block devices? +should explain the difference, (fixed or variable).} +@value{xref-blocking-factor}. -<<< is it true that this only works on non-block devices? should -<<< explain the difference, xref to block-size (fixed or variable). +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"?} -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"? - -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}] +@kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]} @end example 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 @kbd @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}). - @item offline @itemx rewoff1 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 +@FIXME{Is there a better way to frob the spacing on the list?} + +If you don't specify a @var{tapename}, @command{mt} uses the environment +variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} uses the device @file{/dev/rmt12}. -@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. +@FIXME{New node on how to find an archive?} -@c <<< MIB -- program to list all the labels on a tape? +If you use @value{op-extract} with the @value{op-label} option specified, +@command{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, @command{tar} extracts the archive. +@value{xref-label}. +@FIXME-xref{Matching Format Parameters}@FIXME{fix cross +references}@samp{tar --list --label} will cause @command{tar} to print the +label. + +@FIXME{Program to list all the labels on a tape?} + +@node Using Multiple Tapes +@section Using Multiple Tapes +@UNREVISED + +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 @value{op-exclude} or dumping entire filesystems. +Therefore, @command{tar} supports multiple tapes automatically. + +Use @value{op-multi-volume} on the command line, and then @command{tar} will, +when it reaches the end of the tape, prompt for another tape, and +continue the archive. Each tape will have an independent archive, and +can be read without needing the other. (As an exception to this, the +file that @command{tar} was archiving when it ran out of tape will usually +be split between the two archives; in this case you need to extract from +the first archive, using @value{op-multi-volume}, and then put in the +second tape when prompted, so @command{tar} can restore both halves of the +file.) + +@sc{gnu} @command{tar} multi-volume archives do not use a truly portable format. +You need @sc{gnu} @command{tar} at both end to process them properly. + +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. +@item y +Request @command{tar} to begin writing the next volume. +@end table -@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?) +(You should only type @samp{y} after you have changed the tape; +otherwise @command{tar} will write over the volume it just finished.) + +If you want more elaborate behavior than this, give @command{tar} the +@value{op-info-script} option. The file @var{script-name} is expected +to be a program (or shell script) to be run instead of the normal +prompting procedure. If the program fails, @command{tar} exits; +otherwise, @command{tar} begins writing the next volume. The behavior +of the +@samp{n} response to the normal tape-change prompt is not available +if you use @value{op-info-script}. + +The method @command{tar} uses to detect end of tape is not perfect, and +fails on some operating systems or on some devices. You can use the +@value{op-tape-length} option if @command{tar} can't detect the end of the +tape itself. This option selects @value{op-multi-volume} automatically. +The @var{size} argument should then be the usable size of the tape. +But for many devices, and floppy disks in particular, this option is +never required for real, as far as we know. + +The volume number used by @command{tar} in its tape-change prompt +can be changed; if you give the @value{op-volno-file} option, then +@var{file-of-number} should be an unexisting 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 @value{ref-label}, it @emph{only} affects the number used in +the prompt.) + +If you want @command{tar} to cycle through a series of tape drives, then +you can use the @samp{n} response to the tape-change prompt. This is +error prone, however, and doesn't work at all with @value{op-info-script}. +Therefore, if you give @command{tar} multiple @value{op-file} options, then +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). + +Multi-volume archives + +With @value{op-multi-volume}, @command{tar} will not abort when it cannot +read or write any more data. Instead, it will ask you to prepare a new +volume. If the archive is on a magnetic tape, you should change tapes +now; if the archive is on a floppy disk, you should change disks, etc. + +Each volume of a multi-volume archive is an independent @command{tar} +archive, complete in itself. For example, you can list or extract any +volume alone; just don't specify @value{op-multi-volume}. However, if one +file in the archive is split across volumes, the only way to extract +it successfully is with a multi-volume extract command @samp{--extract +--multi-volume} (@samp{-xM}) starting on or before the volume where +the file begins. + +For example, let's presume someone has two tape drives on a system +named @file{/dev/tape0} and @file{/dev/tape1}. For having @sc{gnu} +@command{tar} 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 cMff /dev/tape0 /dev/tape1 @var{files}} +@end smallexample @menu -* Operations:: A Table of Operations -* Options:: Table of Options +* Multi-Volume Archives:: Archives Longer than One Tape or Disk +* Tape Files:: Tape Files @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. - -@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. +@node Multi-Volume Archives +@subsection Archives Longer than One Tape or Disk +@cindex Multi-volume archives +@UNREVISED -@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. +To create an archive that is larger than will fit on a single unit of +the media, use the @value{op-multi-volume} option in conjunction with +the @value{op-create} option (@pxref{create}). A +@dfn{multi-volume} archive can be manipulated like any other archive +(provided the @value{op-multi-volume} option is specified), but is +stored on more than one tape or disk. -@item --concatenate -Adds copies of an archive or archives to the end of another archive. +When you specify @value{op-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 --create -Creates a new archive. +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 @value{op-list}, without @value{op-multi-volume} specified. +To extract an archive member from one volume (assuming it is described +that volume), use @value{op-extract}, again without +@value{op-multi-volume}. -@item --delete -Deletes files from the archive. All versions of the files are deleted. +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 +@value{op-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 --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. +@value{op-info-script} is like @value{op-multi-volume}, except that +@command{tar} does not prompt you directly to change media volumes when +a volume is full---instead, @command{tar} runs commands you have stored +in @var{script-name}. For example, this option can be used to eject +cassettes, or to broadcast messages such as @samp{Someone please come +change my tape} when performing unattended backups. When @var{script-name} +is done, @command{tar} will assume that the media has been changed. -@item --extract -Reads files from the archive and writes them into the active file -system. +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. -@item --get -Reads files from the archive and writes them into the active file -system. +If a multi-volume archive was labeled using @value{op-label} +(@value{pxref-label}) when it was created, @command{tar} will not +automatically label volumes which are added later. To label subsequent +volumes, specify @value{op-label} again in conjunction with the +@value{op-append}, @value{op-update} or @value{op-concatenate} operation. -@item --help -Prints a list of @code{tar} operations and options. +@cindex Labeling multi-volume archives +@FIXME{example} -@item --list -Prints a list of the contents of the archive. +@FIXME{There should be a sample program here, including an exit +before end. Is the exit status even checked in tar? :-(} -@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. +@table @kbd +@item --multi-volume +@itemx -M +Creates a multi-volume archive, when used in conjunction with +@value{op-create}. To perform any other operation on a multi-volume +archive, specify @value{op-multi-volume} in conjunction with that +operation. -@item --version -Prints the version number of the @code{tar} program to the standard -error. +@item --info-script=@var{program-file} +@itemx -F @var{program-file} +Creates a multi-volume archive via a script. Used in conjunction with +@value{op-create}. @end table -@node Options, , Operations, Quick Reference -@appendixsec Table of Options - -Options change the way @code{tar} performs an operation. - -@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}. - -@item --block-size=@var{number} -Specify the blocking factor of an archive. @xref{Blocking Factor}. - -@item --compress -Specify a compressed archive. @xref{Compressed Archives}. - -@item --compress-block. -Create a whole block sized compressed archive. @xref{Compressed Archives}. - -@item --confirmation -Solicit confirmation for each file. @xref{Interactive Operation} -<<< --selective should be a synonym. - -@item --dereference -Treat a symbolic link as an alternate name for the file the link -points to. @xref{Symbolic Links}. - -@item --directory=@file{directory} -Change the working directory. @xref{Changing Working Directory}. +Beware that there is @emph{no} real standard about the proper way, for a +@command{tar} archive, to span volume boundaries. If you have a multi-volume +created by some vendor's @command{tar}, there is almost no chance you could +read all the volumes with @sc{gnu} @command{tar}. The converse is also true: +you may not expect multi-volume archives created by @sc{gnu} @command{tar} to +be fully recovered by vendor's @command{tar}. Since there is little chance +that, in mixed system configurations, some vendor's @command{tar} will work on +another vendor's machine, and there is a great chance that @sc{gnu} @command{tar} +will work on most of them, your best bet is to install @sc{gnu} @command{tar} +on all machines between which you know exchange of files is possible. + +@node Tape Files +@subsection Tape Files +@UNREVISED + +To give the archive a name which will be recorded in it, use the +@value{op-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 @value{op-list}. +If you are creating a multi-volume archive with +@value{op-multi-volume}@FIXME-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 @value{op-label} +option when reading an archive, it checks to make sure the label on the +tape matches the one you give. @value{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: -@item --exclude=@var{pattern} -Exclude files which match the regular expression @var{pattern}. -@xref{File Exclusion}. - -@item --exclude-from=@file{file} -Exclude files which match any of the regular expressions listed in -the file @file{file}. @xref{File Exclusion}. - -@item --file=@var{archive-name} -Name the archive. @xref{Archive Name}). +@example +@kbd{--label="@var{some-prefix} `date +@var{some-format}`"} +@end example -@item --files-from=@file{file} -Read file-name arguments from a file on the file system. -@xref{File Name Lists}. +or such, for pushing a common date in all volumes or an archive set. -@item --ignore-umask -Set modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. +@node label +@section Including a Label in the Archive +@cindex Labeling an archive +@cindex Labels on the archive media +@UNREVISED -@item --ignore-zeros -Ignore end-of-archive entries. @xref{Archive Reading Options}. -<<< this should be changed to --ignore-end +@table @kbd +@item -V @var{name} +@itemx --label=@var{name} +Create archive with volume name @var{name}. +@end table -@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. +This option causes @command{tar} to write out a @dfn{volume header} at +the beginning of the archive. If @value{op-multi-volume} is used, each +volume of the archive will have a volume header of @samp{@var{name} +Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the +next, and so on. -@item --incremental (-G) -@c <<>> +@FIXME{Should the arg to --label be a quoted string?? No.} -@item --tape-length=@var{n} (-L) -@c <<>> -@c <<< this needs to be written into main body as well -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 +@value{op-label} option in conjunction with the @value{op-create} operation +to include a label entry in the archive as it is being created. -@item --info-script=@var{program-file} -Create a multi-volume archive via a script. @xref{Multi-Volume Archives}. +If you create an archive using both @value{op-label} and +@value{op-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. +@FIXME-xref{Multi-Volume Archives, for information on creating multiple +volume archives.} + +If you list or extract an archive using @value{op-label}, @command{tar} will +print an error if the archive label doesn't match the @var{archive-label} +specified, and will then not list nor extract the archive. 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 @value{op-multi-volume} 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. + +The @value{op-label} was once called @samp{--volume}, but is not available +under that name anymore. -@item --interactive -Ask for confirmation before performing any operation on a file or -archive member. +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}. @command{tar} will print the +label first, and then print archive member information, as in the +example below: -@item --keep-old-files -Prevent overwriting during extraction. @xref{File Writing Options}. +@example +$ @kbd{tar --verbose --list --file=iamanarchive} +V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header-- +-rw-rw-rw- ringo user 40 1990-05-21 13:30 iamafilename +@end example +@table @kbd @item --label=@var{archive-label} -Include an archive-label in the archive being created. @xref{Archive -Label}. - -@item --modification-time -Set the modification time of extracted files to the time they were -extracted. @xref{File Writing Options}. - -@item --multi-volume -Specify a multi-volume archive. @xref{Multi-Volume Archives}. - -@item --newer=@var{date} -Limit the operation to files changed after the given date. -@xref{File Exclusion}. - -@item --newer-mtime=@var{date} -Limit the operation to files modified after the given date. @xref{File -Exclusion}. - -@item --old -Create an old format archive. @xref{Old Style File Information}. -@c <<< did we agree this should go away as a synonym? - -@item --old-archive -Create an old format archive. @xref{Old Style File Information}. - -@item --one-file-system -Prevent @code{tar} from crossing file system boundaries when -archiving. @xref{File Exclusion}. - -@item --portable -Create an old format archive. @xref{Old Style File Information}. -@c <<< was portability, may still need to be changed - -@item --preserve-order -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. - -@item --preserve-permission -Set modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. - -@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}. - -@item --same-order -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. - -@item --same-permission -Set the modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. - -@item --sparse -Archive sparse files sparsely. @xref{Sparse Files}. - -@item --starting-file=@var{file-name} -Begin reading in the middle of an archive. @xref{Scarce Disk Space}. - -@item --to-stdout -Write files to the standard output. @xref{File Writing Options}. - -@item --uncompress -Specifdo a compressed archive. @xref{Compressed Archives}. - -@item -V @var{archive-label} -Include an archive-label in the archive being created. @xref{Archive -Label}. -@c was --volume - -@item --verbose -Print the names of files or archive members as they are being -operated on. @xref{Additional Information}. - -@item --verify -Check for discrepancies in the archive immediately after it is -written. @xref{Write Verification}. - -@item -B -Read an archive with a smaller than specified block size or which -contains incomplete blocks. @xref{Archive Reading Options}). - -@item -K @var{file-name} -Begin reading in the middle of an archive. @xref{Scarce Disk Space}. - -@item -M -Specify a multi-volume archive. @xref{Multi-Volume Archives}. - -@item -N @var{date} -Limit operation to files changed after the given date. @xref{File Exclusion}. +@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 +@value{op-create} option. Checks to make sure the archive label +matches the one specified (when used in conjunction with the +@value{op-extract} option. +@end table -@item -O -Write files to the standard output. @xref{File Writing Options}. +To get a common information on all tapes of a series, use the +@value{op-label} option. 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: -@c <<<<- P is absolute paths, add when resolved. -ringo>>> +@example +$ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"} +$ @kbd{tar --create --file=/dev/tape --multi-volume \ + --volume="Daily backup for `date +%Y-%m-%d`"} +@end example -@item -R -Print the record number where a message is generated. -@xref{Additional Information}. +Also note that each label has its own date and time, which corresponds +to when @sc{gnu} @command{tar} 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. Comparing date labels does give +an idea of tape throughput only if the delays for rewinding tapes +and the operator switching them were negligible, which is usually +not the case. -@item -S -Archive sparse files sparsely. @xref{Sparse Files}. +@FIXME{was --volume} -@item -T @var{file} -Read file-name arguments from a file on the file system. -@xref{File Name Lists}. +@node verify +@section Verifying Data as It is Stored +@cindex Verifying a write operation +@cindex Double-checking a write operation +@table @kbd @item -W -Check for discrepancies in the archive immediately after it is -written. @xref{Write Verification}. - -@item -Z -Specify a compressed archive. @xref{Compressed Archives}. - -@item -b @var{number} -Specify the blocking factor of an archive. @xref{Blocking Factor}. - -@item -f @var{archive-name} -Name the archive. @xref{Archive Name}). - -@item -h -Treat a symbolic link as an alternate name for the file the link -points to. @xref{Symbolic Links}. - -@item -i -Ignore end-of-archive entries. @xref{Archive Reading Options}. - -@item -k -Prevent overwriting during extraction. @xref{File Writing Options}. - -@item -l -Prevent @code{tar} from crossing file system boundaries when -archiving. @xref{File Exclusion}. - -@item -m -Set the modification time of extracted files to the time they were -extracted. @xref{File Writing Options}. - -@item -o -Create an old format archive. @xref{Old Style File Information}. - -@item -p -Set the modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. - -@item -s -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. - -@item -v -Print the names of files or archive members they are being operated -on. @xref{Additional Information}. - -@item -w -@c <<>> - -@item -z -Specify a compressed archive. @xref{Compressed Archives}. - -@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 -C @file{directory} -Change the working directory. @xref{Changing Working Directory}. - -@item -F @var{program-file} -Create a multi-volume archive via a script. @xref{Multi-Volume Archives}. - -@item -X @file{file} -Exclude files which match any of the regular expressions listed in -the file @file{file}. @xref{File Exclusion}. +@itemx --verify +Attempt to verify the archive after writing. @end table -@node Data Format Details, Concept Index, Quick Reference, Top -@appendix Details of the Archive Data Format +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. -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. +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. -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. - -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. - -@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 +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. -@node Header Data, Header Fields, Data Format Details, Data Format Details -@appendixsec The Distribution of Data in the Header - -The header record is defined in C as follows: -@c I am taking the following code on faith. - -@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 - - -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. +To check for discrepancies in an archive immediately after it is +written, use the @value{op-verify} option in conjunction with +the @value{op-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. -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. +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. -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. +One can explicitly compare an already made archive with the file system +by using the @value{op-compare} option, instead of using the more automatic +@value{op-verify} option. @value{xref-compare}. + +Note that these two options have a slightly different intent. The +@value{op-compare} option how identical are the logical contents of some +archive with what is on your disks, while the @value{op-verify} option is +really for checking if the physical contents agree and if the recording +media itself is of dependable quality. So, for the @value{op-verify} +operation, @command{tar} tries to defeat all in-memory cache pertaining to +the archive, while it lets the speed optimization undisturbed for the +@value{op-compare} option. If you nevertheless use @value{op-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 @value{op-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 @value{op-verify} option will not work in conjunction with the +@value{op-multi-volume} option or the @value{op-append}, +@value{op-update} and @value{op-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 -The @code{longnames} field supports a feature that is not yet -implemented. This field should be empty. +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). -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 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. -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. +@node Free Software Needs Free Documentation +@appendix Free Software Needs Free Documentation +@include freemanuals.texi -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}. +@node Copying This Manual +@appendix Copying This Manual @menu -* File Types:: File Types -* GNU File Types:: Additional File Types Supported by GNU +* GNU Free Documentation License:: License for copying this manual @end menu -@node File Types, GNU File Types, Header Fields, Header Fields -@appendixsubsec File Types - -The following flags are used to describe file types: - -@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. - -@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. - -@item LF_SPARSE -@itemx 'S' -Indicates a sparse file. @xref{Sparse Files}. @xref{Sparse File -Handling}. - -@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 Sparse File Handling, , Header Fields, Data Format Details -@appendixsec Fields to Handle Sparse Files - -The following header information was added to deal with sparse files -(@pxref{Sparse Files}): - -@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. - -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. - -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. - -@c so is @code{extended_header} the right way to write this? - -@node Concept Index, , Data Format Details, Top -@unnumbered Concept Index +@node Index +@appendix Index @printindex cp @@ -3950,4 +8444,6 @@ 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: