X-Git-Url: https://git.dogcows.com/gitweb?a=blobdiff_plain;f=doc%2Ftar.texi;h=43916e8d73d98b3677c71be5be928197998c89e9;hb=79dd2b901cd97f6510b142f0a513908efb62e58f;hp=f55ea78873097d3a31511bf1cd0ffc29ff2ac35e;hpb=3112b152e66ed563ecbcca763ccd458b529ec208;p=chaz%2Ftar diff --git a/doc/tar.texi b/doc/tar.texi index f55ea78..43916e8 100644 --- a/doc/tar.texi +++ b/doc/tar.texi @@ -1,3948 +1,8706 @@ -\input texinfo @c -*-texinfo-*- +\input texinfo @c %**start of header @setfilename tar.info -@settitle The Tar Manual: DRAFT -@setchapternewpage odd +@settitle GNU tar +@finalout +@smallbook @c %**end of header -@c Note: the edition number and date is listed in *two* places; please update. -@c subtitle and top node; search for !!set - -@c Search for comments marked with !! or <<< (or >>>) +@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{-I}) +@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{Writing} +@set xref-overwrite @xref{Writing} +@set pxref-overwrite @pxref{Writing} + +@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 -@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).>>> +@ifinfo +@direntry +* tar: (tar). Making tape (or disk) archives. +@end direntry -@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".>>> +This file documents @sc{gnu} @command{tar}, which creates and extracts +files from archives. -@c <<< @code{tar} is always lower case, in bold. >>> +Published by the Free Software Foundation, +59 Temple Place - Suite 330, +Boston, MA 02111-1307, USA -@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 +Copyright 1992, 1994, 1995, 1996, 1997, 1999 Free Software Foundation, Inc. -@c <<< (don't forget to comment these out in final draft) -ringo +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. -@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 +@ignore +Permission is granted to process this file through TeX and print the +results, provided the printed document carries copying permission +notice identical to this one except for the removal of this paragraph +(this paragraph not being relevant to the printed manual). -@iftex -@c finalout -@end iftex +@end ignore +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided that the entire +resulting derived work is distributed under the terms of a permission +notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions, +except that this permission notice may be stated in a translation approved +by the Foundation. +@end ifinfo -@ifinfo -This file documents @code{tar}, a utility used to store, backup, and -transport files. +@setchapternewpage odd -Copyright (C) 1992 Free Software Foundation, Inc. DRAFT! -@c Need to put distribution information here when ready. -@end ifinfo +@shorttitlepage @sc{gnu} @command{tar} -@c !!set edition number and date here @titlepage -@title @code{tar} -@subtitle The GNU Tape Archiver -@subtitle Edition 0.01, for @code{tar} Version 1.10 -@subtitle @today{} -@c remove preceding today line when ready -@sp 1 -@subtitle DRAFT -@c subtitle insert month here when ready - -@author Amy Gorin, Michael I. Bushnell, and Jay Fenlason -@c <<>>> +@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 @page @vskip 0pt plus 1filll -Copyright @copyright{} 1992 Free Software Foundation, Inc. - -@sp 2 -This draft is not yet ready for distribution. +Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999 Free Software +Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided that the entire +resulting derived work is distributed under the terms of a permission +notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions, +except that this permission notice may be stated in a translation approved +by the Foundation. @end titlepage -@ifinfo -@node Top, Introduction, (dir), (dir) -@top @code{tar} +@ifnottex +@node Top +@top Tar -This file documents @code{tar}, a utility used to store, backup, and -transport files. +@cindex file archival +@cindex archiving files -@c !!set edition number and date here -This is DRAFT Edition 0.01 of the @code{tar} documentation, @today{}, for @code{tar} -version 1.12. -@end ifinfo +@sc{gnu} @command{tar} creates and extracts files from archives. -@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 +This manual documents version @value{VERSION} of @sc{gnu} @command{tar}. + +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 -@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 +* Introduction:: +* Tutorial:: +* tar invocation:: +* operations:: +* Backups:: +* Choosing:: +* Date input formats:: +* Formats:: +* Media:: +* Index:: -@node Invoking @code{tar}, Tutorial, Introduction, Top -@chapter How To Invoke @code{tar} +@detailmenu -The usual way to invoke tar is + --- The Detailed Node Listing --- -@example -@code{tar} @var{options}... [@var{file-names}...] -@end example +Introduction -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. +* 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 -@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 +Tutorial Introduction to @command{tar} -@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}) +* 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:: -@item -Compare files in an archive with files in the file system -(@samp{--compare}, @samp{--diff} or @samp{-d}) +Two Frequently Used Options -@item -Add archives to another archive (@samp{--add-archive}, @samp{--catenate} -or @samp{-A}) -@c was --concatenate. -ringo +* file tutorial:: +* verbose tutorial:: +* help tutorial:: -@item -Create a new archive (@samp{--create} or @samp{-c}) +How to Create Archives -@item -Delete files from an archive (@samp{--delete}) +* prepare for examples:: +* Creating the archive:: +* create verbose:: +* short create:: +* create dir:: -@item -Extract files from an archive (@samp{--extract}, @samp{--get} or @samp{-x}) +How to List Archives -@item -List the files in an archive (@samp{--list} or @samp{-t}) +* list dir:: -@item -Update an archive by appending newer versions of already stored files -(@samp{--update} or @samp{-u}) -@end itemize +How to Extract Members from an Archive -@xref{Reading and Writing}, for more information about these -operations. +* extracting archives:: +* extracting files:: +* extract dir:: +* failing commands:: -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. +Invoking @sc{gnu} @command{tar} -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. +* Synopsis:: +* using tar options:: +* Styles:: +* All Options:: +* help:: +* verbose:: +* interactive:: -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. +The Three Option Styles -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. +* Mnemonic Options:: Mnemonic Option Style +* Short Options:: Short Option Style +* Old Options:: Old Option Style +* Mixing:: Mixing Option Styles -@node Old Syntax for Commands, , Argument Form, Invoking @code{tar} -@section An Old, but Still Supported, Syntax for @code{tar} Commands +All @command{tar} Options -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: +* Operation Summary:: +* Option Summary:: +* Short Option Summary:: -@example -@code{tar} @var{option-letters}... [@var{option-arguments}...] [@var{file-names}...]@refill -@end example +@sc{gnu} @command{tar} Operations -@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. +* Basic tar:: +* Advanced tar:: +* create options:: +* extract options:: +* backup:: +* Applications:: +* looking ahead:: -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}. +Advanced @sc{gnu} @command{tar} Operations -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. +* Operations:: +* current state:: +* append:: +* update:: +* concatenate:: +* delete:: +* compare:: -@node Tutorial, Wizardry, Invoking @code{tar}, Top -@chapter Getting Started With @code{tar} +How to Add Files to Existing Archives: @code{--append} -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. +* appending files:: Appending Files to an Archive +* multiple:: -@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 +Updating an Archive -@node Creating Archives, Listing Archive Contents, Tutorial, Tutorial -@section Creating Archives +* how to update:: -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. +Options used by @code{--create} -@menu -* Creating Example:: Creating Archives of Files -* Subdirectory:: Creating an Archive of a Subdirectory -@end menu +* Ignore Failed Read:: -@node Creating Example, Subdirectory, Creating Archives, Creating Archives -@subsection Creating Archives of Files +Options Used by @code{--extract} -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. +* Reading:: Options to Help Read Archives +* Writing:: Changing How @command{tar} Writes Files +* Scarce:: Coping with Scarce Resources -(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.) +Options to Help Read Archives -First, change into the directory containing the files you want to -archive: +* read full records:: +* Ignore Zeros:: -@example -% cd practice -@end example +Changing How @command{tar} Extracts Files Over Preexisting Files -@noindent -@file{~/practice} is now your working directory. +* Dealing with Old Files:: +* Overwrite Old Files:: +* Keep Old Files:: +* Unlink First:: +* Recursive Unlink:: -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. +Changing How @command{tar} Writes Files -To list the names of files in the working directory, type: +* Modification Times:: +* Setting Access Permissions:: +* Writing to Standard Output:: +* remove files:: -@example -% ls -@end example +Coping with Scarce Resources -The system responds: +* Starting File:: +* Same Order:: -@example -blues folk jazz -% -@end example +Performing Backups and Restoring Files -@noindent -Then, -@itemize @bullet -@item -Create a new archive (@samp{tar -c} or @samp{tar --create}) +* 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 -@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 +Setting Parameters for Backups and Restoration -@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}. +* backup-specs example:: An Example Text of @file{Backup-specs} +* Script Syntax:: Syntax for @file{Backup-specs} -@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 +Choosing Files and Names for @command{tar} -@noindent -Type: -@example -% tar --create --file=records blues folk jazz -@end example +* 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 -@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. +Reading Names from a File -@example -% ls -blues folk jazz records -% -@end example +* nul:: -@menu -* Listing Files:: Listing files in an archive -* Verbose:: Using @code{tar} in Verbose Mode -@end menu +Excluding Some Files -@node Listing Files, Verbose, Creating Example, Creating Example -@subsubsection Listing files in an archive +* problems with exclude:: -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: +Crossing Filesystem Boundaries -@example -% tar --list --file=records -@end example +* directory:: Changing Directory +* absolute:: Absolute File Names -@noindent -@code{tar} will respond: +Date input formats -@example -blues folk jazz -@end example +* General date syntax:: Common rules. +* Calendar date item:: 19 Dec 1994. +* Time of day item:: 9:20pm. +* Time zone item:: @sc{est}, @sc{gmt}, @sc{utc}, ... +* Day of week item:: Monday and others. +* Relative item in date strings:: next tuesday, 2 years ago. +* Pure numbers in date strings:: 19931219, 1440. +* Authors of getdate:: Bellovin, Berets, Eggert, Salz, et al. -@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. +Controlling the Archive Format -@node Verbose, , Listing Files, Creating Example -@subsubsection Using @code{tar} in Verbose Mode +* 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} -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) +Making @command{tar} Archives More Portable -@example -% tar --create --file=records --verbose blues folk jazz -blues -folk -jazz -@end example +* 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. -@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 +Using Less Space through Compression -To archive a directory, first move to its superior directory. If you -have been following the tutorial, you should type: +* gzip:: Creating and Reading Compressed Archives +* sparse:: Archiving Sparse Files -@example -% cd .. -% -@end example +Tapes and Other Archive Media -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: +* 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 -% tar --create --verbose --file=music practice -@end example +Blocking -@noindent -@code{tar} should respond: +* Format Variations:: Format Variations +* Blocking Factor:: The Blocking Factor of an Archive -@example -practice/ -practice/blues -practice/folk -practice/jazz -practice/records -@end example +Many Archives on One Tape -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. +* Tape Positioning:: Tape Positions and Tape Marks +* mt:: The @command{mt} Utility -@c >>> symbolic links and changing directories are now in main body, not in -@c >>> tutorial. -ringo +Using Multiple Tapes -@node Extracting Files -@section Extracting Files from an Archive +* Multi-Volume Archives:: Archives Longer than One Tape or Disk +* Tape Files:: Tape Files +@end detailmenu +@end menu -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. +@node Introduction +@chapter Introduction -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. +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. -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 - -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. - -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: - -@itemize @bullet -@item -Invoke @code{tar} and specify the @samp{--add-file} operation -(@samp{--add-file}, @samp{-r} or @samp{--append}) - -@item -Specify the archive to which the file will be added -(@samp{--file=@var{archive-name}} or @samp{-f @var{archive-name}}) - -@item -Specify the files to be added to the archive, using file-name -arguments -@end itemize +@node extracting archives +@subsection Extracting an Entire Archive -@noindent -For example: +To extract an entire archive, specify the archive file name only, with +no individual file names as arguments. For example, @example -% tar --add-file --file=records rock +$ @kbd{tar -xvf collection.tar} @end example @noindent -If you list the archive members in @file{records}, you will see that -@file{rock} has been added to the archive: +produces this: @example -% tar --list --file=records -blues -folk -jazz -rock +-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 -@c <<< this should be some kind of node. +@node extracting files +@subsection Extracting Specific Files + +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?} -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. +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. -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}: +You can now extract the member @file{blues} from the archive file +@file{collection.tar} like this: @example -% tar --add-file --verbose --file=records blues -blues +$ @kbd{tar --extract --file=collection.tar blues} @end example @noindent -If you now list the contents of the archive, you will obtain the following: +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 -f records -blues -folk -jazz -rock -blues +$ @kbd{tar -xvf music.tar practice/folk practice/jazz} @end example +@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 -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. +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. -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: +@FIXME{IMPORTANT! show the final structure, here. figure out what it +will be.} -@example -% tar --update --verbose --file=records blues folk rock classical -blues -classical -% -@end example +@node failing commands +@subsection Commands That Will Fail -@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: +Here are some sample commands you might try which will not work, and why +they won't work. -@itemize @bullet -@item -Invoke @code{tar}, and specify the @samp{--concatenate} operation -(@samp{-A} or @samp{--concatenate}) +If you try to use this command, -@item -Specify the archive file to be added to -(@samp{--file=@var{archive-name}} or @samp{-f @var{archive-name}}) +@example +$ @kbd{tar -xvf music.tar folk jazz} +@end example -@item -Specify the archives to be added, using file-name arguments. In this -case, the file-name arguments are, unusually, the names of archive -files. (Remember to include the path in the archive name, if the -archive file is not in your working directory.) -@end itemize +@noindent +you will get the following response: @example -% cd ~ -% tar --concatenate --file=music practice/records +tar: folk: Not found in archive +tar: jazz: Not found in archive +$ @end example -If you now list the contents of the @file{music}, you see it now -contains the archive members of @file{practice/records}: +@noindent +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 --list --file=music -blues -folk -jazz -rock -blues -practice/blues +$ @kbd{tar -tvf music.tar} practice/folk practice/jazz practice/rock -practice/blues -practice/classical @end example -@node Deleting Files, , , Tutorial -@comment node-name, next, previous, up -@section Deleting Files From an Archive +@FIXME{make sure the above works when going through the examples in +order...} -In some instances, you may want to remove some files from an archive -stored on disk +@noindent +Likewise, if you try to use this command, -@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 +@example +$ @kbd{tar -tvf music.tar folk jazz} +@end example -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. +@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}). -Execution of the @samp{--delete} operation can be very slow. +@menu +* Synopsis:: +* using tar options:: +* Styles:: +* All Options:: +* help:: +* verbose:: +* interactive:: +@end menu -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: +@node Synopsis +@section General Synopsis of @command{tar} -@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 @sc{gnu} @command{tar} program is invoked as either one of: -@item -Invoke @code{tar} and specify the @samp{--delete} operation -(@samp{--delete}). +@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 -@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}}) +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}.) + +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 -Specify the files to be deleted, using file-name arguments. +@menu +* Mnemonic Options:: Mnemonic Option Style +* Short Options:: Short Option Style +* Old Options:: Old Option Style +* Mixing:: Mixing Option Styles +@end menu -@item -List the contents of the archive file again---note that the files have -been removed. (this step is also optional) -@end itemize +@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: @example -% tar --list --file=records -blues -folk -jazz -% tar --delete --file=records blues -% tar --list --file=records -folk -jazz -% +$ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0} +@end example + +@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 +$ @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 --atime-preserve -@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. +Tells @command{tar} to preserve the access time field in a file's inode when +dumping 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. @FIXME-xref{} -@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 +@item --backup=@var{backup-type} -@node Compressed Archives, , Blocking Factor, Format Variations -@subsection Creating and Reading Compressed Archives -@cindex Compressed archives -@cindex Storing archives in compressed format +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{} -@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. +@item --block-number +@itemx -R -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. +With this option present, @command{tar} prints error messages for read errors +with the block number in the archive file. @FIXME-xref{} -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. +@item --blocking-factor=@var{blocking} +@itemx -b @var{blocking} -If there is no compress utility available, @code{tar} will report an -error. +Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per +record. @FIXME-xref{} -@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. +@item --bzip2 +@itemx -I -@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 +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-failed-read -@node Adding Files, Appending Archives, Modifying, Modifying -@subsection Adding Files to an Archive -@cindex Adding files to an archive -@cindex Updating an archive +Do not exit unsuccessfully merely because an unreadable file was encountered. +@xref{Reading}. -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}. +@item --ignore-zeros +@itemx -i -The following example adds the file @file{shemp} to the archive -@file{stooges} created above: +With this option, @command{tar} will ignore zeroed blocks in the archive, which +normally signals EOF. @xref{Reading}. -@example -tar --add-file --file=stooges shemp -@end example +@item --incremental +@itemx -G -You must specify the files to be added; there is no default. +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{} -@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. +@item --info-script=@var{script-file} +@itemx --new-volume-script=@var{script-file} +@itemx -F @var{script-file} -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. +When @command{tar} is performing multi-tape backups, @var{script-file} is run +at the end of each tape. @FIXME-xref{} -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. +@item --interactive +@itemx --confirmation +@itemx -w -@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 +Specifies that @command{tar} should ask the user for confirmation before +performing potentially destructive options, such as overwriting files. +@FIXME-xref{} -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. +@item --keep-old-files +@itemx -k -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): +Do not overwrite existing files when extracting files from an archive. +@xref{Writing}. -@example -tar --add-archive --file=stooges hail/hail/fredonia -@end example +@item --label=@var{name} +@itemx -V @var{name} -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}). +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{} -@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 +@item --listed-incremental=@var{snapshot-file} +@itemx -g @var{snapshot-file} -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. +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{} -The following example removes the file @file{curley} from the archive -@file{stooges}: +@item --mode=@var{permissions} -@example -tar --delete --file=stooges curley -@end example +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. -You can only use @samp{tar --delete} on an archive if the archive -device allows you to write to any point on the media. +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. -@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 +@item --multi-volume +@itemx -M -@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=-). +Informs @command{tar} that it should create or otherwise operate on a +multi-volume @command{tar} archive. @FIXME-xref{} -@node Matching Format Parameters, , Deleting Archive Files, Modifying -@subsection Matching the Format Parameters +@item --new-volume-script -Some format parameters must be taken into consideration when modifying -an archive: +(see --info-script) -Compressed archives cannot be modified. +@item --newer=@var{date} +@itemx --after-date=@var{date} +@itemx -N -You have to specify the block size of the archive when modifying an -archive with a non-default block size. +When creating an archive, @command{tar} will only add files that have changed +since @var{date}. @FIXME-xref{} -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 --newer-mtime -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 +In conjunction with @samp{--newer}, @command{tar} will only add files whose +contents have changed (as opposed to just @samp{--newer}, which will +also back up files for which any status information has changed). -@c <<< xref somewhere, for more information about format parameters. +@item --no-recursion -@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 +With this option, @command{tar} will not recurse into directories unless a +directory is explicitly named as an argument to @command{tar}. @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-same-owner -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. +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. -If the blocking factor of the archive differs from the default, -@code{tar} reports this. @xref{Blocking Factor}. +@item --no-same-permissions -@xref{Archive Reading Options} for a list of options which can be used -to modify @samp{--list}'s operation. +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. -This example prints a list of the archive members of the archive -@file{stooges}: +@item --null -@example -tar --list --file=stooges -@end example +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{} -@noindent -@code{tar} responds: +@item --numeric-owner -@example -larry -moe -shemp -marx/julius -marx/alexander -marx/karl -@end example +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{} -This example generates a verbose list of the archive members of the -archive file @file{dwarves}, which has a blocking factor of two: +@item --old-archive -@example -tar --list -v --file=blocks -@end example +(See @samp{--portability}.) @FIXME-pxref{} -@noindent -@code{tar} responds: +@item --one-file-system +@itemx -l -@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 +Used when creating an archive. Prevents @command{tar} from recursing into +directories that are on different file systems from the current +directory. @FIXME-xref{} -@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 +@item --overwrite -To read archive members from the archive and write them into the file -system, use @samp{tar --extract}. The archive itself is left -unchanged. +Overwrite existing files and directory metadata when extracting files +from an archive. @xref{Writing}. -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. +@item --owner=@var{user} -The following example shows the extraction of the archive -@file{stooges} into an empty directory: +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 -@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. -@noindent -Generating a listing of the directory (@samp{ls}) produces: +This option does not affect extraction from archives. -@example -larry -moe -shemp -marx -@end example +@item --portability +@itemx --old-archive +@itemx -o -@noindent -The subdirectory @file{marx} contains the files @file{julius}, -@file{alexander} and @file{karl}. +Tells @command{tar} to create an archive that is compatible with Unix V7 +@command{tar}. @FIXME-xref{} -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: +@item --posix -@example -tar --extract --file=stooges marx -@end example +Instructs @command{tar} to create a @sc{posix} compliant @command{tar} archive. @FIXME-xref{} -@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 +@item --preserve -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}). +Synonymous with specifying both @samp{--preserve-permissions} and +@samp{--same-order}. @FIXME-xref{} -@menu -* Archive Reading Options:: -* File Writing Options:: -* Scarce Disk Space:: Recovering From Scarce Disk Space -@end menu +@item --preserve-order -@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 +(See @samp{--same-order}; @pxref{Reading}.) -@c <<< each option wants its own node. summary after menu +@item --preserve-permissions +@itemx --same-permissions +@itemx -p -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}. +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{--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 --read-full-records +@itemx -B -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}. +Specifies that @command{tar} should reblock its input, for reading from pipes on +systems with buggy implementations. @xref{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 --record-size=@var{size} -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). +Instructs @command{tar} to use @var{size} bytes per record when accessing the +archive. @FIXME-xref{} -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 --recursive-unlink -@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 +Remove existing +directory hierarchies before extracting directories of the same name +from the archive. @xref{Writing}. -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 --remove-files -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. +Directs @command{tar} to remove the source file from the file system after +appending it to an archive. @FIXME-xref{} -This option is probably never needed on modern computer systems. +@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. +@samp{--to-stdout} -@c >>> is write access an issue? +@item -P -@table @samp -@item --absolute-paths -Preserves full file names (inclusing superior dirctory names) when -archiving files. Preserves leading slash when extracting files. -@end table +@samp{--absolute-names} -@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 +@item -R -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, +@samp{--block-number} -@example -tar --create iggy ziggy --directory=baz melvin -@end example +@item -S -@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. +@samp{--sparse} -Contrast this with the command +@item -T -@example -tar -c iggy ziggy bar/melvin -@end example +@samp{--files-from} -@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}. +@item -U -@table @samp -@item --directory=@file{directory} -@itemx -C @file{directory} -Changes the working directory. -@end table +@samp{--unlink-first} -@c <<>> +@item -o -@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} +@samp{--portability} -Once you have typed a @code{tar}command, it is usually performed -without any further information required of the user, or provided by -@code{tar}. The following options allow you to generate progress and -status information during an operation, or to confirm operations on -files as they are performed. +@item -p -@menu -* Additional Information:: -* Interactive Operation:: -@end menu +@samp{--preserve-permissions} -@node Additional Information, Interactive Operation, User Interaction, User Interaction -@section Progress and Status Information -@cindex Progress information -@cindex Status information -@cindex Information on progress and status of operations -@cindex Verbose operation -@cindex Record number where error occured -@cindex Error message, record number of -@cindex Version of the @code{tar} program - -Typically, @code{tar} performs most operations without reporting any -information to the user except error messages. If you have -encountered a problem when operating on an archive, however, you may -need more information than just an error message in order to solve the -problem. The following options can be helpful diagnostic tools. - -When used with most operations, @samp{--verbose} causes @code{tar} to -print the file names of the files or archive members it is operating -on. When used with @samp{tar --list}, the verbose option causes -@code{tar} to print out an @samp{ls -l} type listing of the files in -the archive. - -Verbose output appears on the standard output except when an archive -is being written to the standard output (as with @samp{tar --create ---file=- --verbose}). In that case @code{tar} writes verbose output to -the standard error stream. +@item -r -@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 +@samp{--append} -To find out where in an archive a message was triggered, use -@samp{--record-number}. @samp{--record-number} causes @code{tar} to -print, along with every message it produces, the record number within -the archive where the message was triggered. +@item -s -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 +@samp{--same-order} + +@item -t + +@samp{--list} + +@item -u + +@samp{--update} + +@item -v + +@samp{--verbose} + +@item -w + +@samp{--interactive} + +@item -x + +@samp{--extract} + +@item -z + +@samp{--gzip} -@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 -@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: +@node help +@section @sc{gnu} @command{tar} documentation + +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: @example -tar --version +tar (@sc{gnu} tar) @value{VERSION} @end example @noindent -might return: +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: @example -GNU tar version 1.09 +$ @kbd{tar --help | less} @end example -@c used to be an option. has been fixed. -@node Interactive Operation, , Additional Information, User Interaction -@section Asking for Confirmation During Operations -@cindex Interactive operation +@noindent +presuming, here, that you like using @command{less} for a pager. Other +popular pagers are @command{more} and @command{pg}. If you know about some +@var{keyword} which interests you and do not want to read all the +@value{op-help} output, another common idiom is doing: + +@example +tar --help | grep @var{keyword} +@end example + +@noindent +for getting only the pertinent lines. + +The perceptive reader would have noticed some contradiction in the +previous paragraphs. It is written that both @value{op-version} and +@value{op-help} print something, and have all other options ignored. In +fact, they cannot ignore each other, and one of them has to win. We do +not specify which is stronger, here; experiment if you really wonder! + +The short help output is quite succinct, and you might have to get back +to the full documentation for precise points. If you are reading this +paragraph, you already have the @command{tar} manual in some form. This +manual is available in printed form, as a kind of small book. It may +printed out of the @sc{gnu} @command{tar} distribution, provided you have @TeX{} +already installed somewhere, and a laser printer around. Just configure +the distribution, execute the command @w{@samp{make dvi}}, then print +@file{doc/tar.dvi} the usual way (contact your local guru to know how). +If @sc{gnu} @command{tar} has been conveniently installed at your place, this +manual is also available in interactive, hypertextual form as an Info +file. Just call @w{@samp{info tar}} or, if you do not have the +@command{info} program handy, use the Info reader provided within @sc{gnu} +Emacs, calling @samp{tar} from the main Info menu. + +There is currently no @code{man} page for @sc{gnu} @command{tar}. If you observe +such a @code{man} page on the system you are running, either it does not +long to @sc{gnu} @command{tar}, or it has not been produced by @sc{gnu}. Currently, +@sc{gnu} @command{tar} documentation is provided in Texinfo format only, if we +except, of course, the short result of @kbd{tar --help}. + +@node verbose +@section Checking @command{tar} progress + +@cindex Progress information +@cindex Status information +@cindex Information on progress and status of operations +@cindex Verbose operation +@cindex Block number where error occurred +@cindex Error message, block number of +@cindex Version of the @command{tar} program + +@cindex Getting more information during the operation +@cindex Information during operation +@cindex Feedback from @command{tar} + +Typically, @command{tar} performs most operations without reporting any +information to the user except error messages. When using @command{tar} +with many options, particularly ones with complicated or +difficult-to-predict behavior, it is possible to make serious mistakes. +@command{tar} provides several options that make observing @command{tar} +easier. These options cause @command{tar} to print information as it +progresses in its job, and you might want to use them just for being +more careful about what is going on, or merely for entertaining +yourself. 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. + +Normally, the @value{op-list} command to list an archive prints just +the file names (one per line) and the other commands are silent. +When used with most operations, the @value{op-verbose} option causes +@command{tar} to print the name of each file or archive member as it +is processed. This and the other options which make @command{tar} print +status information can be useful in monitoring @command{tar}. + +With @value{op-create} or @value{op-extract}, @value{op-verbose} used once +just prints the names of the files or members as they are processed. +Using it twice causes @command{tar} to print a longer listing (reminiscent +of @samp{ls -l}) for each member. Since @value{op-list} already prints +the names of the members, @value{op-verbose} used once with @value{op-list} +causes @command{tar} to print an @samp{ls -l} type listing of the files +in the archive. The following examples both extract members with +long list output: + +@example +$ @kbd{tar --extract --file=archive.tar --verbose --verbose} +$ @kbd{tar xvv archive.tar} +@end example + +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} (@samp{tar cfv -}, or even @samp{tar cv}---if the +installer let standard output be the default archive). In that case +@command{tar} writes verbose output to the standard error stream. + +The @value{op-totals} option---which is only meaningful when used with +@value{op-create}---causes @command{tar} to print the total +amount written to the archive, after it has been fully created. + +The @value{op-checkpoint} option prints an occasional message +as @command{tar} reads or writes the archive. In fact, it print +directory names while reading the archive. It is designed for +those who don't need the more detailed (and voluminous) output of +@value{op-block-number}, but do want visual confirmation that @command{tar} +is actually making forward progress. + +@FIXME{There is some confusion here. It seems that -R once wrote a +message at @samp{every} record read or written.} + +The @value{op-show-omitted-dirs} option, when reading an archive---with +@value{op-list} or @value{op-extract}, for example---causes a message +to be printed for each directory in the archive which is skipped. +This happens regardless of the reason for skipping: the directory might +not have been named on the command line (implicitly or explicitly), +it might be excluded by the use of the @value{op-exclude} option, or +some other reason. + +If @value{op-block-number} is used, @command{tar} prints, along with every +message it would normally produce, the block number within the archive +where the message was triggered. Also, supplementary messages are +triggered when reading blocks full of NULs, or when hitting end of file on +the archive. As of now, if the archive if properly terminated with a NUL +block, the reading of the file may stop before end of file is met, so the +position of end of file will not usually show when @value{op-block-number} +is used. Note that @sc{gnu} @command{tar} drains the archive before exiting when +reading the archive from a pipe. + +This option is especially useful when reading damaged archives, since +it helps pinpoint the damaged sections. It can also be used with +@value{op-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). @FIXME-xref{when the node name is set and the +backup section written.} + +@node interactive +@section Asking for Confirmation During Operations +@cindex Interactive operation + +Typically, @command{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{Choosing}), or by performing +an operation interactively, using the @value{op-interactive} option. +@command{tar} also accepts @samp{--confirmation} for this option. + +When the @value{op-interactive} option is specified, before +reading, writing, or deleting files, @command{tar} first prints a message +for each such file, telling what operation it intends to take, then asks +for confirmation on the terminal. The actions which require +confirmation include adding a file to the archive, extracting a file +from the archive, deleting a file from the archive, and deleting a file +from disk. 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}, @command{tar} skips that file. + +If @command{tar} is reading the archive from the standard input, +@command{tar} opens the file @file{/dev/tty} to support the interactive +communications. + +Verbose output is normally sent to standard output, separate from +other error messages. However, if the archive is produced directly +on standard output, then verbose output is mixed with errors on +@code{stderr}. Producing the archive on standard output may be used +as a way to avoid using disk space, when the archive is soon to be +consumed by another process reading it, say. Some people felt the need +of producing an archive on stdout, still willing to segregate between +verbose output and error output. A possible approach would be using a +named pipe to receive the archive, and having the consumer process to +read from that named pipe. This has the advantage of letting standard +output free to receive verbose output, all separate from errors. + +@node operations +@chapter @sc{gnu} @command{tar} Operations + +@menu +* Basic tar:: +* Advanced tar:: +* create options:: +* extract options:: +* backup:: +* Applications:: +* looking ahead:: +@end menu + +@node Basic tar +@section Basic @sc{gnu} @command{tar} Operations + +The basic @command{tar} operations, @value{op-create}, @value{op-list} and +@value{op-extract}, are currently presented and described in the tutorial +chapter of this manual. This section provides some complementary notes +for these operations. + +@table @asis +@item @value{op-create} + +Creating an empty archive would have some kind of elegance. One can +initialize an empty archive and later use @value{op-append} for adding +all members. Some applications would not welcome making an exception +in the way of adding the first archive member. On the other hand, +many people reported that it is dangerously too easy for @command{tar} +to destroy a magnetic tape with an empty archive@footnote{This is well +described in @cite{Unix-haters Handbook}, by Simson Garfinkel, Daniel +Weise & Steven Strassmann, IDG Books, ISBN 1-56884-203-1.}. The two most +common errors are: + +@enumerate +@item +Mistakingly using @code{create} instead of @code{extract}, when the +intent was to extract the full contents of an archive. This error +is likely: keys @kbd{c} and @kbd{x} are right next ot each other on +the QWERTY keyboard. Instead of being unpacked, the archive then +gets wholly destroyed. When users speak about @dfn{exploding} an +archive, they usually mean something else :-). + +@item +Forgetting the argument to @code{file}, when the intent was to create +an archive with a single file in it. This error is likely because a +tired user can easily add the @kbd{f} key to the cluster of option +letters, by the mere force of habit, without realizing the full +consequence of doing so. The usual consequence is that the single +file, which was meant to be saved, is rather destroyed. +@end enumerate + +So, recognizing the likelihood and the catastrophical nature of these +errors, @sc{gnu} @command{tar} now takes some distance from elegance, and +cowardly refuses to create an archive when @value{op-create} option is +given, there are no arguments besides options, and @value{op-files-from} +option is @emph{not} used. To get around the cautiousness of @sc{gnu} +@command{tar} and nevertheless create an archive with nothing in it, +one may still use, as the value for the @value{op-files-from} option, +a file with no names in it, as shown in the following commands: + +@example +@kbd{tar --create --file=empty-archive.tar --files-from=/dev/null} +@kbd{tar cfT empty-archive.tar /dev/null} +@end example + +@item @value{op-extract} + +A socket is stored, within a @sc{gnu} @command{tar} archive, as a pipe. + +@item @value{op-list} + +@sc{gnu} @command{tar} now shows dates as @samp{1996-11-09}, while it used to +show them as @samp{Nov 11 1996}. (One can revert to the old behavior by +defining @code{USE_OLD_CTIME} in @file{src/list.c} before reinstalling.) +But preferably, people should get used to ISO 8601 dates. Local +American dates should be made available again with full date localization +support, once ready. In the meantime, programs not being localizable +for dates should prefer international dates, that's really the way to go. + +Look up @url{http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html} if you +are curious, it contains a detailed explanation of the ISO 8601 standard. + +@end table + +@node Advanced tar +@section Advanced @sc{gnu} @command{tar} Operations + +Now that you have learned the basics of using @sc{gnu} @command{tar}, you may +want to learn about further ways in which @command{tar} can help you. + +This chapter presents five, more advanced operations which you probably +won't use on a daily basis, but which serve more specialized functions. +We also explain the different styles of options and why you might want +to use one or another, or a combination of them in your @command{tar} +commands. Additionally, this chapter includes options which allow you to +define the output from @command{tar} more carefully, and provide help and +error correction in special circumstances. + +@FIXME{check this after the chapter is actually revised to make sure +it still introduces the info in the chapter correctly : ).} + +@menu +* Operations:: +* current state:: +* append:: +* update:: +* concatenate:: +* delete:: +* compare:: +@end menu + +@node Operations +@subsection The Five Advanced @command{tar} Operations +@UNREVISED + +In the last chapter, you learned about the first three operations to +@command{tar}. This chapter presents the remaining five operations to +@command{tar}: @samp{--append}, @samp{--update}, @samp{--concatenate}, +@samp{--delete}, and @samp{--compare}. + +You are not likely to use these operations as frequently as those +covered in the last chapter; however, since they perform specialized +functions, they are quite useful when you do need to use them. We +will give examples using the same directory and files that you created +in the last chapter. As you may recall, the directory is called +@file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk}, +@samp{rock}, and the two archive files you created are +@samp{collection.tar} and @samp{music.tar}. + +We will also use the archive files @samp{afiles.tar} and +@samp{bfiles.tar}. @samp{afiles.tar} contains the members @samp{apple}, +@samp{angst}, and @samp{aspic}. @samp{bfiles.tar} contains the members +@samp{./birds}, @samp{baboon}, and @samp{./box}. + +Unless we state otherwise, all practicing you do and examples you follow +in this chapter will take place in the @file{practice} directory that +you created in the previous chapter; see @ref{prepare for examples}. +(Below in this section, we will remind you of the state of the examples +where the last chapter left them.) + +The five operations that we will cover in this chapter are: + +@table @kbd +@item --append +@itemx -r +Add new entries to an archive that already exists. +@item --update +@itemx -r +Add more recent copies of archive members to the end of an archive, if +they exist. +@item --concatenate +@itemx --catenate +@itemx -A +Add one or more pre-existing archives to the end of another archive. +@item --delete +Delete items from an archive (does not work on tapes). +@item --compare +@itemx --diff +@itemx -d +Compare archive members to their counterparts in the file system. +@end table + +@node current state +@subsection The Current State of the Practice Files + +Currently, the listing of the directory using @command{ls} is as follows: + +@example + +@end example + +@noindent +The archive file @samp{collection.tar} looks like this: + +@example +$ @kbd{tar -tvf collection.tar} + +@end example + +@noindent +The archive file @samp{music.tar} looks like this: + +@example +$ @kbd{tar -tvf music.tar} + +@end example + +@FIXME{need to fill in the above!!!} + +@node append +@subsection How to Add Files to Existing Archives: @code{--append} +@UNREVISED + +If you want to add files to an existing archive, you don't need to +create a new archive; you can use @value{op-append}. The archive must +already exist in order to use @samp{--append}. (A related operation +is the @samp{--update} operation; you can use this to add newer +versions of archive members to an existing archive. To learn how to +do this with @samp{--update}, @pxref{update}.) + +@FIXME{Explain in second paragraph whether you can get to the previous +version -- explain whole situation somewhat more clearly.} + +If you use @value{op-append} to add a file that has the same name as an +archive member to an archive containing that archive member, then the +old member is not deleted. What does happen, however, is somewhat +complex. @command{tar} @emph{allows} you to have infinite numbers of files +with the same name. Some operations treat these same-named members no +differently than any other set of archive members: for example, if you +view an archive with @value{op-list}, you will see all of those members +listed, with their modification times, owners, etc. + +Other operations don't deal with these members as perfectly as you might +prefer; if you were to use @value{op-extract} to extract the archive, +only the most recently added copy of a member with the same name as four +other members would end up in the working directory. This is because +@samp{--extract} extracts an archive in the order the members appeared +in the archive; the most recently archived members will be extracted +last. Additionally, an extracted member will @emph{replace} a file of +the same name which existed in the directory already, and @command{tar} +will not prompt you about this. Thus, only the most recently archived +member will end up being extracted, as it will replace the one +extracted before it, and so on. + +@FIXME{ hag -- you might want to incorporate some of the above into the +MMwtSN node; not sure. i didn't know how to make it simpler...} + +There are a few ways to get around this. @FIXME-xref{Multiple Members +with the Same Name.} + +@cindex Members, replacing with other members +@cindex Replacing members with other members +If you want to replace an archive member, use @value{op-delete} to +delete the member you want to remove from the archive, , and then use +@samp{--append} to add the member you want to be in the archive. Note +that you can not change the order of the archive; the most recently +added member will still appear last. In this sense, you cannot truly +``replace'' one member with another. (Replacing one member with another +will not work on certain types of media, such as tapes; see @ref{delete} +and @ref{Media}, for more information.) + +@menu +* appending files:: Appending Files to an Archive +* multiple:: +@end menu + +@node appending files +@subsubsection Appending Files to an Archive +@UNREVISED +@cindex Adding files to an Archive +@cindex Appending files to an Archive +@cindex Archives, Appending files to + +The simplest way to add a file to an already existing archive is the +@value{op-append} operation, which writes specified files into the +archive whether or not they are already among the archived files. +When you use @samp{--append}, you @emph{must} specify file name +arguments, as there is no default. If you specify a file that already +exists in the archive, another copy of the file will be added to the +end of the archive. As with other operations, the member names of the +newly added files will be exactly the same as their names given on the +command line. The @value{op-verbose} option will print out the names +of the files as they are written into the archive. + +@samp{--append} cannot be performed on some tape drives, unfortunately, +due to deficiencies in the formats those tape drives use. The archive +must be a valid @command{tar} archive, or else the results of using this +operation will be unpredictable. @xref{Media}. + +To demonstrate using @samp{--append} to add a file to an archive, +create a file called @file{rock} in the @file{practice} directory. +Make sure you are in the @file{practice} directory. Then, run the +following @command{tar} command to add @file{rock} to +@file{collection.tar}: + +@example +$ @kbd{tar --append --file=collection.tar rock} +@end example + +@noindent +If you now use the @value{op-list} operation, you will see that +@file{rock} has been added to the archive: + +@example +$ @kbd{tar --list --file=collection.tar} +-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 +-rw-rw-rw- me user 20 1996-09-23 16:44 rock +@end example + +@FIXME{in theory, dan will (soon) try to turn this node into what it's +title claims it will become...} + +@node multiple +@subsubsection Multiple Files with the Same Name + +You can use @value{op-append} to add copies of files which have been +updated since the archive was created. (However, we do not recommend +doing this since there is another @command{tar} option called +@samp{--update}; @pxref{update} for more information. We describe this +use of @samp{--append} here for the sake of completeness.) @FIXME{is +this really a good idea, to give this whole description for something +which i believe is basically a Stupid way of doing something? certain +aspects of it show ways in which tar is more broken than i'd personally +like to admit to, specifically the last sentence. On the other hand, i +don't think it's a good idea to be saying that re explicitly don't +recommend using something, but i can't see any better way to deal with +the situation.}When you extract the archive, the older version will be +effectively lost. This works because files are extracted from an +archive in the order in which they were archived. Thus, when the +archive is extracted, a file archived later in time will replace a +file of the same name which was archived earlier, even though the older +version of the file will remain in the archive unless you delete all +versions of the file. + +Supposing you change the file @file{blues} and then append the changed +version to @file{collection.tar}. As you saw above, the original +@file{blues} is in the archive @file{collection.tar}. If you change the +file and append the new version of the file to the archive, there will +be two copies in the archive. When you extract the archive, the older +version of the file will be extracted first, and then replaced by the +newer version when it is extracted. + +You can append the new, changed copy of the file @file{blues} to the +archive in this way: + +@example +$ @kbd{tar --append --verbose --file=collection.tar blues} +blues +@end example + +@noindent +Because you specified the @samp{--verbose} option, @command{tar} has +printed the name of the file being appended as it was acted on. Now +list the contents of the archive: + +@example +$ @kbd{tar --list --verbose --file=collection.tar} +-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 +-rw-rw-rw- me user 20 1996-09-23 16:44 rock +-rw-rw-rw- me user 58 1996-10-24 18:30 blues +@end example + +@noindent +The newest version of @file{blues} is now at the end of the archive +(note the different creation dates and file sizes). If you extract +the archive, the older version of the file @file{blues} will be +replaced by the newer version. You can confirm this by extracting +the archive and running @samp{ls} on the directory. @xref{Writing}, +for more information. (@emph{Please note:} This is the case unless +you employ the @value{op-backup} option. @FIXME-ref{Multiple Members +with the Same Name}.) + +@node update +@subsection Updating an Archive +@UNREVISED +@cindex Updating an archive + +In the previous section, you learned how to use @value{op-append} to add +a file to an existing archive. A related operation is +@value{op-update}. The @samp{--update} operation updates a @command{tar} +archive by comparing the date of the specified archive members against +the date of the file with the same name. If the file has been modified +more recently than the archive member, then the newer version of the +file is added to the archive (as with @value{op-append}). + +Unfortunately, you cannot use @samp{--update} with magnetic tape drives. +The operation will fail. + +@FIXME{other examples of media on which --update will fail? need to ask +charles and/or mib/thomas/dave shevett..} + +Both @samp{--update} and @samp{--append} 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, unless you use +the @value{op-backup} option. @FIXME-ref{Multiple Members with the +Same Name} + +@menu +* how to update:: +@end menu + +@node how to update +@subsubsection How to Update an Archive Using @code{--update} + +You must use file name arguments with the @value{op-update} operation. +If you don't specify any files, @command{tar} won't act on any files and +won't tell you that it didn't do anything (which may end up confusing +you). + +@FIXME{note: the above parenthetical added because in fact, this +behavior just confused the author. :-) } + +To see the @samp{--update} option at work, create a new file, +@file{classical}, in your practice directory, and some extra text to the +file @file{blues}, using any text editor. Then invoke @command{tar} with +the @samp{update} operation and the @value{op-verbose} option specified, +using the names of all the files in the practice directory as file name +arguments: + +@example +$ @kbd{tar --update -v -f collection.tar blues folk rock classical} +blues +classical +$ +@end example + +@noindent +Because we have specified verbose mode, @command{tar} prints out the names +of the files it is working on, which in this case are the names of the +files that needed to be updated. If you run @samp{tar --list} and look +at the archive, you will see @file{blues} and @file{classical} at its +end. There will be a total of two versions of the member @samp{blues}; +the one at the end will be newer and larger, since you added text before +updating it. + +(The reason @command{tar} does not overwrite the older file when updating +it is because writing to the middle of a section of tape is a difficult +process. Tapes are not designed to go backward. @xref{Media}, for more +information about tapes. + +@value{op-update} is not suitable for performing backups for two +reasons: it does not change directory content entries, and it lengthens +the archive every time it is used. The @sc{gnu} @command{tar} options intended +specifically for backups are more efficient. If you need to run +backups, please consult @ref{Backups}. + +@node concatenate +@subsection Combining Archives with @code{--concatenate} + +@cindex Adding archives to an archive +@cindex Concatenating Archives +Sometimes it may be convenient to add a second archive onto the end of +an archive rather than adding individual files to the archive. To add +one or more archives to the end of another archive, you should use the +@value{op-concatenate} operation. + +To use @samp{--concatenate}, name the archives to be concatenated on the +command line. (Nothing happens if you don't list any.) The members, +and their member names, will be copied verbatim from those archives. If +this causes multiple members to have the same name, it does not delete +any members; all the members with the same name coexist. @FIXME-ref{For +information on how this affects reading the archive, Multiple +Members with the Same Name.} + +To demonstrate how @samp{--concatenate} works, create two small archives +called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant +files from @file{practice}: + +@example +$ @kbd{tar -cvf bluesrock.tar blues rock} +blues +classical +$ @kbd{tar -cvf folkjazz.tar folk jazz} +folk +jazz +@end example + +@noindent +If you like, You can run @samp{tar --list} to make sure the archives +contain what they are supposed to: + +@example +$ @kbd{tar -tvf bluesrock.tar} +-rw-rw-rw- melissa user 105 1997-01-21 19:42 blues +-rw-rw-rw- melissa user 33 1997-01-20 15:34 rock +$ @kbd{tar -tvf folkjazz.tar} +-rw-rw-rw- melissa user 20 1996-09-23 16:44 folk +-rw-rw-rw- melissa user 65 1997-01-30 14:15 jazz +@end example + +We can concatenate these two archives with @command{tar}: + +@example +$ @kbd{cd ..} +$ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar} +@end example + +If you now list the contents of the @file{bluesclass.tar}, you will see +that now it also contains the archive members of @file{jazzfolk.tar}: + +@example +$ @kbd{tar --list --file=bluesrock.tar} +blues +rock +jazz +folk +@end example + +When you use @samp{--concatenate}, the source and target archives must +already exist and must have been created using compatible format +parameters. @FIXME-pxref{Matching Format Parameters}The new, +concatenated archive will be called by the same name as the first +archive listed on the command line. @FIXME{is there a way to specify a +new name?} + +Like @value{op-append}, this operation cannot be performed on some +tape drives, due to deficiencies in the formats those tape drives use. + +@cindex @code{concatenate} vs @command{cat} +@cindex @command{cat} vs @code{concatenate} +It may seem more intuitive to you to want or try to use @command{cat} to +concatenate two archives instead of using the @samp{--concatenate} +operation; after all, @command{cat} is the utility for combining files. + +However, @command{tar} archives incorporate an end-of-file marker which +must be removed if the concatenated archives are to be read properly as +one archive. @samp{--concatenate} removes the end-of-archive marker +from the target archive before each new archive is appended. If you use +@command{cat} to combine the archives, the result will not be a valid +@command{tar} format archive. If you need to retrieve files from an +archive that was added to using the @command{cat} utility, use the +@value{op-ignore-zeros} option. @xref{Ignore Zeros}, for further +information on dealing with archives improperly combined using the +@command{cat} shell utility. + +@FIXME{this shouldn't go here. where should it go?} You must specify +the source archives using @value{op-file} (@value{pxref-file}). If you +do not specify the target archive, @command{tar} uses the value of the +environment variable @env{TAPE}, or, if this has not been set, the +default archive name. + +@node delete +@subsection Removing Archive Members Using @samp{--delete} +@UNREVISED +@cindex Deleting files from an archive +@cindex Removing files from an archive + +You can remove members from an archive by using the @value{op-delete} +option. Specify the name of the archive with @value{op-file} and then +specify the names of the members to be deleted; if you list no member +names, nothing will be deleted. The @value{op-verbose} option will +cause @command{tar} to print the names of the members as they are deleted. +As with @value{op-extract}, you must give the exact member names when +using @samp{tar --delete}. @samp{--delete} will remove all versions of +the named file from the archive. The @samp{--delete} operation can run +very slowly. + +Unlike other operations, @samp{--delete} has no short form. + +@cindex Tapes, using @code{--delete} and +@cindex Deleting from tape archives +This operation will rewrite the archive. You can only use +@samp{--delete} on an archive if the archive device allows you to +write to any point on the media, such as a disk; because of this, it +does not work on magnetic tapes. Do not try to delete an archive member +from a magnetic tape; the action will not succeed, and you will be +likely to scramble the archive and damage your tape. There is no safe +way (except by completely re-writing the archive) to delete files from +most kinds of magnetic tape. @xref{Media}. + +To delete all versions of the file @file{blues} from the archive +@file{collection.tar} in the @file{practice} directory, make sure you +are in that directory, and then, + +@example +$ @kbd{tar --list --file=collection.tar} +blues +folk +jazz +rock +practice/blues +practice/folk +practice/jazz +practice/rock +practice/blues +$ @kbd{tar --delete --file=collection.tar blues} +$ @kbd{tar --list --file=collection.tar} +folk +jazz +rock +$ +@end example + +@FIXME{I changed the order of these nodes around and haven't had a chance +to fix the above example's results, yet. I have to play with this and +follow it and see what it actually does!} + +The @value{op-delete} option has been reported to work properly when +@command{tar} acts as a filter from @code{stdin} to @code{stdout}. + +@node compare +@subsection Comparing Archive Members with the File System +@cindex Verifying the currency of an archive +@UNREVISED + +The @samp{--compare} (@samp{-d}), or @samp{--diff} operation compares +specified archive members against files with the same names, and then +reports differences in file size, mode, owner, modification date and +contents. You should @emph{only} specify archive member names, not file +names. If you do not name any members, then @command{tar} will compare the +entire archive. If a file is represented in the archive but does not +exist in the file system, @command{tar} reports a difference. + +You have to specify the record size of the archive when modifying an +archive with a non-default record size. + +@command{tar} ignores files in the file system that do not have +corresponding members in the archive. + +The following example compares the archive members @file{rock}, +@file{blues} and @file{funk} in the archive @file{bluesrock.tar} with +files of the same name in the file system. (Note that there is no file, +@file{funk}; @command{tar} will report an error message.) + +@example +$ @kbd{tar --compare --file=bluesrock.tar rock blues funk} +rock +blues +tar: funk not found in archive +@end example + +@noindent +@FIXME{what does this actually depend on? i'm making a guess, +here.}Depending on the system where you are running @command{tar} and the +version you are running, @command{tar} may have a different error message, +such as: + +@example +funk: does not exist +@end example + +@FIXME-xref{somewhere, for more information about format parameters. +Melissa says: such as "format variations"? But why? Clearly I don't +get it yet; I'll deal when I get to that section.} + +The spirit behind the @value{op-compare} option is to check whether the +archive represents the current state of files on disk, more than validating +the integrity of the archive media. For this later goal, @xref{verify}. + +@node create options +@section Options Used by @code{--create} + +The previous chapter described the basics of how to use +@value{op-create} to create an archive from a set of files. +@xref{create}. This section described advanced options to be used with +@samp{--create}. + +@menu +* Ignore Failed Read:: +@end menu + +@node Ignore Failed Read +@subsection Ignore Fail Read + +@table @kbd +@item --ignore-failed-read +Do not exit with nonzero on unreadable files or directories. +@end table + +@node extract options +@section Options Used by @code{--extract} +@UNREVISED + +@FIXME{i need to get dan to go over these options with me and see if +there's a better way of organizing them.} + +The previous chapter showed how to use @value{op-extract} to extract +an archive into the filesystem. Various options cause @command{tar} to +extract more information than just file contents, such as the owner, +the permissions, the modification date, and so forth. This section +presents options to be used with @samp{--extract} when certain special +considerations arise. You may review the information presented in +@ref{extract} for more basic information about the +@samp{--extract} operation. + +@menu +* Reading:: Options to Help Read Archives +* Writing:: Changing How @command{tar} Writes Files +* Scarce:: Coping with Scarce Resources +@end menu + +@node Reading +@subsection Options to Help Read Archives +@cindex Options when reading archives +@cindex Reading incomplete records +@cindex Records, incomplete +@cindex End-of-archive entries, ignoring +@cindex Ignoring end-of-archive entries +@cindex Large lists of file names on small machines +@cindex Small memory +@cindex Running out of space +@UNREVISED + +Normally, @command{tar} will request data in full record increments from +an archive storage device. If the device cannot return a full record, +@command{tar} will report an error. However, some devices do not always +return full records, or do not require the last record of an archive to +be padded out to the next record boundary. To keep reading until you +obtain a full record, or to accept an incomplete record if it contains +an end-of-archive marker, specify the @value{op-read-full-records} option +in conjunction with the @value{op-extract} or @value{op-list} operations. +@value{xref-read-full-records}. + +The @value{op-read-full-records} option is turned on by default when +@command{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, @command{tar} +would fail as soon as it read an incomplete record from the pipe. + +If you're not sure of the blocking factor of an archive, you can +read the archive by specifying @value{op-read-full-records} and +@value{op-blocking-factor}, using a blocking factor larger than what the +archive uses. This lets you avoid having to determine the blocking factor +of an archive. @value{xref-blocking-factor}. + +@menu +* read full records:: +* Ignore Zeros:: +@end menu + +@node read full records +@unnumberedsubsubsec Reading Full Records + +@FIXME{need sentence or so of intro here} + +@table @kbd +@item --read-full-records +@item -B +Use in conjunction with @value{op-extract} to read an archive which +contains incomplete records, or one which has a blocking factor less +than the one specified. +@end table + +@node Ignore Zeros +@unnumberedsubsubsec Ignoring Blocks of Zeros + +Normally, @command{tar} stops reading when it encounters a block of zeros +between file entries (which usually indicates the end of the archive). +@value{op-ignore-zeros} allows @command{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 concatenating several archives +together). + +The @value{op-ignore-zeros} option is turned off by default because many +versions of @command{tar} write garbage after the end-of-archive entry, +since that part of the media is never supposed to be read. @sc{gnu} +@command{tar} does not write after the end of an archive, but seeks to +maintain compatiblity among archiving utilities. + +@table @kbd +@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 +@value{op-extract} or @value{op-list}. +@end table + +@node Writing +@subsection Changing How @command{tar} Writes Files +@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 +@UNREVISED + +@FIXME{need to mention the brand new option, --backup} + +@menu +* 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:: +@end menu + +@node Dealing with Old Files +@unnumberedsubsubsec Options Controlling the Overwriting of Existing Files + +When extracting files, if @command{tar} discovers that the extracted +file already exists, it normally replaces the file by removing it before +extracting it, to prevent confusion in the presence of hard or symbolic +links. However, if a directory cannot be removed because it is +nonempty, @command{tar} neither removes it nor modifies its ownership, +permissions, or time stamps. + +To be more cautious and prevent existing files from being replaced, use +the @value{op-keep-old-files} option. It causes @command{tar} to refuse +to replace or update a file that already exists, i.e., a file with the +same name as an archive member prevents extraction of that archive +member. + +To overwrite existing files, use the @value{op-overwrite} option. This +causes @command{tar} to write extracted files into the file system without +regard to the files already on the system; i.e., files with the same +names as archive members are overwritten when the archive is extracted. +It also causes @command{tar} to extract the ownership, permissions, +and time stamps onto any preexisting files or directories. +If the name of a corresponding file name is a symbolic link, the file +pointed to by the symbolic link will be overwritten instead of the +symbolic link itself (if this is possible). Moreover, special devices, +empty directories and even symbolic links are automatically removed if +they are in the way of extraction. + +Be careful when using the @value{op-overwrite} option, particularly when +combined with the @value{op-absolute-names} option, as this combination +can change the contents, ownership or permissions of any file on your +system. Also, many systems do not take kindly to overwriting files that +are currently being executed. + +@FIXME{these two P's have problems. i don't understand what they're +trying to talk about well enough to fix them; i may have just made them +worse (in particular the first of the two). waiting to talk with hag.} + +The @value{op-unlink-first} option causes @command{tar} to always +attempt to remove a file unconditionally before attempting to extract +it. This can make @command{tar} run a bit faster if you know in advance +that the extracted files all need to be removed. Normally this option +slows @command{tar} tar down slightly, so it is disabled by default. + +@FIXME{huh?} If you specify the @value{op-recursive-unlink} option, +@command{tar} removes @emph{anything} that keeps you from extracting a file +as far as current permissions will allow it. This could include removal +of the contents of a full directory hierarchy. For example, someone +using this feature may be very surprised at the results when extracting +a directory entry from the archive. This option can be dangerous; be +very aware of what you are doing if you choose to use it. + +@node Overwrite Old Files +@unnumberedsubsubsec Overwrite Old Files + +@table @kbd +@item --overwrite +Overwrite existing files and directory metadata when extracting files +from an archive. +@end table + +@node Keep Old Files +@unnumberedsubsubsec Keep Old Files + +@table @kbd +@item --keep-old-files +@itemx -k +Do not replace existing files from archive. The +@value{op-keep-old-files} option prevents @command{tar} from replacing +existing files with files with the same name from the archive. +The @value{op-keep-old-files} option is meaningless with @value{op-list}. +Prevents @command{tar} from replacing files in the file system during +extraction. +@end table + +@node Unlink First +@unnumberedsubsubsec Unlink First + +@table @kbd +@item --unlink-first +@itemx -U +Remove files before extracting over them. +@end table + +@node Recursive Unlink +@unnumberedsubsubsec Recursive Unlink + +@table @kbd +@item --recursive-unlink +When this option is specified, try removing files and directory hierarchies +before extracting over them. @emph{This is a dangerous option!} +@end table + +Some people argue that @sc{gnu} @command{tar} should not hesitate to overwrite +files with other files when extracting. When extracting a @command{tar} +archive, they expect to see a faithful copy of the state of the filesystem +when the archive was created. It is debatable that this would always +be a proper behavior. For example, suppose one has an archive in +which @file{usr/local} is a link to @file{usr/local2}. Since then, +maybe the site removed the link and renamed the whole hierarchy from +@file{/usr/local2} to @file{/usr/local}. Such things happen all the time. +I guess it would not be welcome at all that @sc{gnu} @command{tar} removes the +whole hierarchy just to make room for the link to be reinstated (unless it +@emph{also} simultaneously restores the full @file{/usr/local2}, of course! +@sc{gnu} @command{tar} is indeed able to remove a whole hierarchy to reestablish a +symbolic link, for example, but @emph{only if} @value{op-recursive-unlink} +is specified to allow this behavior. In any case, single files are +silently removed. + +@node Modification Times +@unnumberedsubsubsec Setting Modification Times + +Normally, @command{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. + +To set the modification times of extracted files to the time when +the files were extracted, use the @value{op-touch} option in +conjunction with @value{op-extract}. + +@table @kbd +@item --touch +@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 @value{op-extract}. +@end table + +@node Setting Access Permissions +@unnumberedsubsubsec Setting Access Permissions + +To set the modes (access permissions) of extracted files to those +recorded for those files in the archive, use @samp{--same-permissions} +in conjunction with the @value{op-extract} operation. @FIXME{Should be +aliased to ignore-umask.} + +@table @kbd +@item --preserve-permission +@itemx --same-permission +@itemx --ignore-umask +@itemx -p +Set modes of extracted archive members to those recorded in the +archive, instead of current umask settings. Use in conjunction with +@value{op-extract}. +@end table + +@FIXME{Following paragraph needs to be rewritten: why doesn't this cat +files together, why is this useful. is it really useful with +more than one file?} + +@node Writing to Standard Output +@unnumberedsubsubsec Writing to Standard Output + +To write the extracted files to the standard output, instead of +creating the files on the file system, use @value{op-to-stdout} in +conjunction with @value{op-extract}. This option is useful if you are +extracting files to send them through a pipe, and do not need to +preserve them in the file system. If you extract multiple members, +they appear on standard output concatenated, in the order they are +found in the archive. + +@table @kbd +@item --to-stdout +@itemx -O +Writes files to the standard output. Used in conjunction with +@value{op-extract}. Extract files to standard output. When this option +is used, instead of creating the files specified, @command{tar} writes +the contents of the files extracted to its standard output. This may +be useful if you are only extracting the files in order to send them +through a pipe. This option is meaningless with @value{op-list}. +@end table + +@FIXME{Why would you want to do such a thing, how are files separated on +the standard output? is this useful with more that one file? Are +pipes the real reason?} + +@node remove files +@unnumberedsubsubsec Removing Files + +@FIXME{the various macros in the front of the manual think that this +option goes in this section. i have no idea; i only know it's nowhere +else in the book...} + +@table @kbd +@item --remove-files +Remove files after adding them to the archive. +@end table + +@node Scarce +@subsection Coping with Scarce Resources +@cindex Middle of the archive, starting in the +@cindex Running out of space during extraction +@cindex Disk space, running out of +@cindex Space on the disk, recovering from lack of +@UNREVISED + +@menu +* Starting File:: +* Same Order:: +@end menu + +@node Starting File +@unnumberedsubsubsec Starting File + +@table @kbd +@item --starting-file=@var{name} +@itemx -K @var{name} +Starts an operation in the middle of an archive. Use in conjunction +with @value{op-extract} or @value{op-list}. +@end table + +If a previous attempt to extract files failed due to lack of disk +space, you can use @value{op-starting-file} to start extracting only +after member @var{name} of the archive. This assumes, of course, that +there is now free space, or that you are now extracting into a +different file system. (You could also choose to suspend @command{tar}, +remove unnecessary files from the file system, and then restart the +same @command{tar} operation. In this case, @value{op-starting-file} is +not necessary. @value{xref-incremental}, @value{xref-interactive}, +and @value{ref-exclude}.) + +@node Same Order +@unnumberedsubsubsec Same Order + +@table @kbd +@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 @value{op-compare}, +@value{op-list} +or @value{op-extract}. +@end table + +@FIXME{we don't need/want --preserve to exist any more (from melissa: +ie, don't want that *version* of the option to exist, or don't want +the option to exist in either version?} + +@FIXME{i think this explanation is lacking.} + +The @value{op-same-order} option tells @command{tar} that the list of file +names to be listed or extracted is sorted in the same order as the +files in the archive. This allows a large list of names to be used, +even on a small machine that would not otherwise be able to hold all +the names in memory at the same time. Such a sorted list can easily be +created by running @samp{tar -t} on the archive and editing its output. + +This option is probably never needed on modern computer systems. + +@node backup +@section Backup options + +@cindex backup options + +@sc{gnu} @command{tar} offers options for making backups of files before writing +new versions. These options control the details of these backups. +They may apply to the archive itself before it is created or rewritten, +as well as individual extracted members. Other @sc{gnu} programs (@command{cp}, +@command{install}, @command{ln}, and @command{mv}, for example) offer similar +options. + +Backup options may prove unexpectedly useful when extracting archives +containing many members having identical name, or when extracting archives +on systems having file name limitations, making different members appear +has having similar names through the side-effect of name truncation. +(This is true only if we have a good scheme for truncated backup names, +which I'm not sure at all: I suspect work is needed in this area.) +When any existing file is backed up before being overwritten by extraction, +then clashing files are automatically be renamed to be unique, and the +true name is kept for only the last file of a series of clashing files. +By using verbose mode, users may track exactly what happens. + +At the detail level, some decisions are still experimental, and may +change in the future, we are waiting comments from our users. So, please +do not learn to depend blindly on the details of the backup features. +For example, currently, directories themselves are never renamed through +using these options, so, extracting a file over a directory still has +good chances to fail. Also, backup options apply to created archives, +not only to extracted members. For created archives, backups will not +be attempted when the archive is a block or character device, or when it +refers to a remote file. + +For the sake of simplicity and efficiency, backups are made by renaming old +files prior to creation or extraction, and not by copying. The original +name is restored if the file creation fails. If a failure occurs after a +partial extraction of a file, both the backup and the partially extracted +file are kept. + +@table @samp + +@item --backup[=@var{method}] +@opindex --backup +@vindex VERSION_CONTROL +@cindex backups +Back up files that are about to be overwritten or removed. +Without this option, the original versions are destroyed. + +Use @var{method} to determine the type of backups made. +If @var{method} is not specified, use the value of the @env{VERSION_CONTROL} +environment variable. And if @env{VERSION_CONTROL} is not set, +use the @samp{existing} method. + +@vindex version-control @r{Emacs variable} +This option corresponds to the Emacs variable @samp{version-control}; +the same values for @var{method} are accepted as in Emacs. This option +also allows more descriptive names. The valid @var{method}s are: + +@table @samp +@item t +@itemx numbered +@opindex numbered @r{backup method} +Always make numbered backups. + +@item nil +@itemx existing +@opindex existing @r{backup method} +Make numbered backups of files that already have them, simple backups +of the others. + +@item never +@itemx simple +@opindex simple @r{backup method} +Always make simple backups. + +@end table + +@item --suffix=@var{suffix} +@opindex --suffix +@cindex backup suffix +@vindex SIMPLE_BACKUP_SUFFIX +Append @var{suffix} to each backup file made with @samp{--backup}. If this +option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX} +environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not +set, the default is @samp{~}, just as in Emacs. + +@end table + +Some people express the desire to @emph{always} use the @var{op-backup} +option, by defining some kind of alias or script. This is not as easy +as one may think, due to the fact that old style options should appear first +and consume arguments a bit unpredictably for an alias or script. But, +if you are ready to give up using old style options, you may resort to +using something like (a Bourne shell function here): + +@example +tar () @{ /usr/local/bin/tar --backup $*; @} +@end example + +@node Applications +@section Notable @command{tar} Usages +@UNREVISED + +@FIXME{Using Unix file linking capability to recreate directory +structures---linking files into one subdirectory and then +@command{tar}ring that directory.} + +@FIXME{Nice hairy example using absolute-names, newer, etc.} + +@findex uuencode +You can easily use archive files to transport a group of files from +one system to another: put all relevant files into an archive on one +computer system, transfer the archive to another system, and extract +the contents there. The basic transfer medium might be magnetic tape, +Internet FTP, or even electronic mail (though you must encode the +archive with @command{uuencode} in order to transport it properly by +mail). Both machines do not have to use the same operating system, as +long as they both support the @command{tar} program. + +For example, here is how you might copy a directory's contents from +one disk to another, while preserving the dates, modes, owners and +link-structure of all the files therein. In this case, the transfer +medium is a @dfn{pipe}, which is one a Unix redirection mechanism: + +@smallexample +$ @kbd{cd sourcedir; tar -cf - . | (cd targetdir; tar -xf -)} +@end smallexample + +@noindent +The command also works using short option forms: + +@FIXME{The following using standard input/output correct??} +@smallexample +$ @w{@kbd{cd sourcedir; tar --create --file=- . | (cd targetdir; tar --extract --file=-)}} +@end smallexample + +@noindent +This is one of the easiest methods to transfer a @command{tar} archive. + +@node looking ahead +@section Looking Ahead: The Rest of this Manual + +You have now seen how to use all eight of the operations available to +@command{tar}, and a number of the possible options. The next chapter +explains how to choose and change file and archive names, how to use +files to store names of other files which you can then call as +arguments to @command{tar} (this can help you save time if you expect to +archive the same list of files a number of times), and so forth. +@FIXME{in case it's not obvious, i'm making this up in some sense +based on my imited memory of what the next chapter *really* does. i +just wanted to flesh out this final section a little bit so i'd +remember to sitck it in here. :-)} + +If there are too many files to conveniently list on the command line, +you can list the names in a file, and @command{tar} will read that file. +@value{xref-files-from}. + +There are various ways of causing @command{tar} to skip over some files, +and not archive them. @xref{Choosing}. + +@node Backups +@chapter Performing Backups and Restoring Files +@UNREVISED + +@sc{gnu} @command{tar} is distributed along with the scripts which the Free +Software Foundation uses for performing backups. There is no corresponding +scripts available yet for doing restoration of files. Even if there is +a good chance those scripts may be satisfying to you, they are not the +only scripts or methods available for doing backups and restore. You may +well create your own, or use more sophisticated packages dedicated to +that purpose. + +Some users are enthusiastic about @code{Amanda} (The Advanced Maryland +Automatic Network Disk Archiver), a backup system developed by James +da Silva @file{jds@@cs.umd.edu} and available on many Unix systems. +This is free software, and it is available at these places: + +@example +http://www.cs.umd.edu/projects/amanda/amanda.html +ftp://ftp.cs.umd.edu/pub/amanda +@end example + +@ifclear PUBLISH + +Here is a possible plan for a future documentation about the backuping +scripts which are provided within the @sc{gnu} @command{tar} distribution. + +@example +.* dumps +. + what are dumps + +. + different levels of dumps +. - full dump = dump everything +. - level 1, level 2 dumps etc, - + A level n dump dumps everything changed since the last level + n-1 dump (?) + +. + how to use scripts for dumps (ie, the concept) +. - scripts to run after editing backup specs (details) + +. + Backup Specs, what is it. +. - how to customize +. - actual text of script [/sp/dump/backup-specs] + +. + Problems +. - rsh doesn't work +. - rtape isn't installed +. - (others?) + +. + the --incremental option of tar + +. + tapes +. - write protection +. - types of media +. : different sizes and types, useful for different things +. - files and tape marks + one tape mark between files, two at end. +. - positioning the tape + MT writes two at end of write, + backspaces over one when writing again. +@end example + +@end ifclear + +This chapter documents both the provided FSF scripts and @command{tar} +options which are more specific to usage as a backup tool. + +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 accidentally deleted). File system @dfn{backups} are also +called @dfn{dumps}. + +@menu +* 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 +@end menu + +@node Full Dumps +@section Using @command{tar} to Perform Full Dumps +@UNREVISED + +@cindex full dumps +@cindex dumps, full + +@cindex corrupted archives +Full dumps should only be made when no other people or programs +are modifying files in the filesystem. If files are modified while +@command{tar} is making the backup, they may not be stored properly in +the archive, in which case you won't be able to restore them if you +have to. (Files not being modified are written with no trouble, and do +not corrupt the entire archive.) + +You will want to use the @value{op-label} option to give the archive a +volume label, so you can tell what this archive is even if the label +falls off the tape, or anything like that. + +Unless the filesystem you are dumping is guaranteed to fit on +one volume, you will need to use the @value{op-multi-volume} option. +Make sure you have enough tapes on hand to complete the backup. + +If you want to dump each filesystem separately you will need to use +the @value{op-one-file-system} option to prevent @command{tar} from crossing +filesystem boundaries when storing (sub)directories. + +The @value{op-incremental} option is not needed, since this is a complete +copy of everything in the filesystem, and a full restore from this +backup would only be done onto a completely empty disk. + +Unless you are in a hurry, and trust the @command{tar} program (and your +tapes), it is a good idea to use the @value{op-verify} option, to make +sure your files really made it onto the dump properly. This will +also detect cases where the file was modified while (or just after) +it was being archived. Not all media (notably cartridge tapes) are +capable of being verified, unfortunately. + +@value{op-listed-incremental} 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. + +@value{op-incremental} @FIXME{look it up} + +@value{op-incremental} handle old @sc{gnu}-format incremental backup. + +This option should only be used when creating an incremental backup of +a filesystem. When the @value{op-incremental} option is used, @command{tar} +writes, at the beginning of the archive, an entry for each of the +directories that will be operated on. The entry for a directory +includes a list of all the files in the directory at the time the +dump was done, and a flag for each file indicating whether the file +is going to be put in the archive. This information is used when +doing a complete incremental restore. + +Note that this option causes @command{tar} to create a non-standard +archive that may not be readable by non-@sc{gnu} versions of the @command{tar} +program. + +The @value{op-incremental} option means the archive is an incremental +backup. Its meaning depends on the command that it modifies. + +If the @value{op-incremental} option is used with @value{op-list}, @command{tar} +will list, for each directory in the archive, the list of files in +that directory at the time the archive was created. This information +is put out in a format that is not easy for humans to read, but which +is unambiguous for a program: each file name is preceded by either a +@samp{Y} if the file is present in the archive, an @samp{N} if the +file is not included in the archive, or a @samp{D} if the file is +a directory (and is included in the archive). Each file name is +terminated by a null character. The last file is followed by an +additional null and a newline to indicate the end of the data. + +If the @value{op-incremental} option is used with @value{op-extract}, then +when the entry for a directory is found, all files that currently +exist in that directory but are not listed in the archive @emph{are +deleted from the directory}. + +This behavior is convenient when you are restoring a damaged file +system from a succession of incremental backups: it restores the +entire state of the file system to that which obtained when the backup +was made. If you don't use @value{op-incremental}, the file system will +probably fill up with files that shouldn't exist any more. + +@value{op-listed-incremental} handle new @sc{gnu}-format incremental backup. +This option handles new @sc{gnu}-format incremental backup. It has much the +same effect as @value{op-incremental}, but also the time when the dump +is done and the list of directories dumped is written to the given +@var{file}. When restoring, only files newer than the saved time are +restored, and the directory list is used to speed up operations. + +@value{op-listed-incremental} acts like @value{op-incremental}, but when +used in conjunction with @value{op-create} will also cause @command{tar} to +use the file @var{file}, which contains information about the state +of the filesystem at the time of the last backup, to decide which +files to include in the archive being created. That file will then +be updated by @command{tar}. If the file @var{file} does not exist when +this option is specified, @command{tar} will create it, and include all +appropriate files in the archive. + +The file, which is archive independent, contains the date it was last +modified and a list of devices, inode numbers and directory names. +@command{tar} will archive files with newer mod dates or inode change +times, and directories with an unchanged inode number and device but +a changed directory name. The file is updated after the files to +be archived are determined, but before the new archive is actually +created. + +@sc{gnu} @command{tar} actually writes the file twice: once before the data +and written, and once after. + +@node Inc Dumps +@section Using @command{tar} to Perform Incremental Dumps +@UNREVISED + +@cindex incremental dumps +@cindex dumps, incremental + +Performing incremental dumps is similar to performing full dumps, +although a few more options will usually be needed. + +A standard scheme is to do a @emph{monthly} (full) dump once a month, +a @emph{weekly} dump once a week of everything since the last monthly +and a @emph{daily} every day of everything since the last (weekly or +monthly) dump. + +Here is a sample script to dump the directory hierarchies @samp{/usr} +and @samp{/var}. + +@example +#! /bin/sh +tar --create \ + --blocking-factor=126 \ + --file=/dev/rmt/0 \ + --label="`hostname` /usr /var `date +%Y-%m-%d`" \ + --listed-incremental=/var/log/usr-var.snar \ + --verbose \ + /usr /var +@end example + +This script uses the file @file{/var/log/usr-var.snar} as a snapshot to +store information about the previous tar dump. + +The blocking factor 126 is an attempt to make the tape drive stream. +Some tape devices cannot handle 64 kB blocks or larger, and require the +block size to be a multiple of 1 kB; for these devices, 126 is the +largest blocking factor that can be used. + +@node incremental and listed-incremental +@section The Incremental Options +@UNREVISED + +@value{op-incremental} is used in conjunction with @value{op-create}, +@value{op-extract} or @value{op-list} when backing up and restoring file +systems. An archive cannot be extracted or listed with the +@value{op-incremental} option specified unless it was created with the +option specified. This option should only be used by a script, not by +the user, and is usually disregarded in favor of +@value{op-listed-incremental}, which is described below. + +@value{op-incremental} in conjunction with @value{op-create} causes +@command{tar} to write, at the beginning of the archive, an entry for +each of the directories that will be archived. The entry for a +directory includes a list of all the files in the directory at the +time the archive was created and a flag for each file indicating +whether or not the file is going to be put in the archive. + +Note that this option causes @command{tar} to create a non-standard +archive that may not be readable by non-@sc{gnu} versions of the @command{tar} +program. + +@value{op-incremental} in conjunction with @value{op-extract} causes +@command{tar} to read the lists of directory contents previously stored +in the archive, @emph{delete} files in the file system that did not +exist in their directories when the archive was created, and then +extract the files in the archive. + +This behavior is convenient when restoring a damaged file system from +a succession of incremental backups: it restores the entire state of +the file system to that which obtained when the backup was made. If +@value{op-incremental} isn't specified, the file system will probably +fill up with files that shouldn't exist any more. + +@value{op-incremental} in conjunction with @value{op-list} causes +@command{tar} to print, for each directory in the archive, the list of +files in that directory at the time the archive was created. This +information is put out in a format that is not easy for humans to +read, but which is unambiguous for a program: each file name is +preceded by either a @samp{Y} if the file is present in the archive, +an @samp{N} if the file is not included in the archive, or a @samp{D} +if the file is a directory (and is included in the archive). Each +file name is terminated by a null character. The last file is followed +by an additional null and a newline to indicate the end of the data. + +@value{op-listed-incremental} acts like @value{op-incremental}, but when +used in conjunction with @value{op-create} will also cause @command{tar} +to use the file @var{snapshot-file}, which contains information about +the state of the file system at the time of the last backup, to decide +which files to include in the archive being created. That file will +then be updated by @command{tar}. If the file @var{file} does not exist +when this option is specified, @command{tar} will create it, and include +all appropriate files in the archive. + +The file @var{file}, which is archive independent, contains the date +it was last modified and a list of devices, inode numbers and +directory names. @command{tar} will archive files with newer mod dates +or inode change times, and directories with an unchanged inode number +and device but a changed directory name. The file is updated after +the files to be archived are determined, but before the new archive is +actually created. + +Despite it should be obvious that a device has a non-volatile value, NFS +devices have non-dependable values when an automounter gets in the picture. +This led to a great deal of spurious redumping in incremental dumps, +so it is somewhat useless to compare two NFS devices numbers over time. +So @command{tar} now considers all NFS devices as being equal when it comes +to comparing directories; this is fairly gross, but there does not seem +to be a better way to go. + +@FIXME{this section needs to be written} + +@node Backup Levels +@section Levels of Backups +@UNREVISED + +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. + +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. + +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). + +@sc{gnu} @command{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 @command{tar} commands by hand. + +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. @FIXME{There is no such restore +script!}@FIXME-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}. @FIXME{There is +no such restore script!}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. @FIXME-xref{Scripted +Restoration, for more information on running the restoration script.} +@FIXME-xref{Scripted Backups, for more information on running the +backup scripts.} + +@emph{Please Note:} The backup scripts and the restoration scripts are +designed to be used together. While it is possible to restore files by +hand from an archive which was created using a backup script, and to create +an archive by hand which could then be extracted using the restore script, +it is easier to use the scripts.@FIXME{There is no such restore script!} +@value{xref-incremental}, and @value{xref-listed-incremental}, +before making such an attempt. + +@FIXME{shorten node names} + +@node Backup Parameters +@section Setting Parameters for Backups and Restoration +@UNREVISED + +The file @file{backup-specs} specifies backup parameters for the +backup and restoration scripts provided with @command{tar}. You must +edit @file{backup-specs} to fit your system configuration and schedule +before using these scripts. + +@FIXME{This about backup scripts needs to be written: BS is a shell +script .... thus ... @file{backup-specs} is in shell script syntax.} + +@FIXME-xref{Script Syntax, for an explanation of this syntax.} + +@FIXME{Whats a parameter .... looked at by the backup scripts +... which will be expecting to find ... now syntax ... value is linked +to lame ... @file{backup-specs} specifies the following parameters:} + +@table @samp +@item ADMINISTRATOR +The user name of the backup administrator. + +@item BACKUP_HOUR +The hour at which the backups are done. This can be a number from 0 +to 23, or the string @samp{now}. + +@item TAPE_FILE +The device @command{tar} writes the archive to. This device should be +attached to the host on which the dump scripts are run. + +@FIXME{examples for all ...} + +@item TAPE_STATUS +The command to use to obtain the status of the archive device, +including error count. On some tape drives there may not be such a +command; in that case, simply use `TAPE_STATUS=false'. + +@item BLOCKING +The blocking factor @command{tar} will use when writing the dump archive. +@value{xref-blocking-factor}. + +@item BACKUP_DIRS +A list of file systems to be dumped. You can include any directory +name in the list---subdirectories on that file system will be +included, regardless of how they may look to other networked machines. +Subdirectories on other file systems will be ignored. + +The host name specifies which host to run @command{tar} on, and should +normally be the host that actually contains the file system. However, +the host machine must have @sc{gnu} @command{tar} installed, and must be able +to access the directory containing the backup scripts and their +support files using the same file name that is used on the machine +where the scripts are run (ie. what @command{pwd} will print when in that +directory on that machine). If the host that contains the file system +does not have this capability, you can specify another host as long as +it can access the file system through NFS. + +@item BACKUP_FILES +A list of individual files to be dumped. These should be accessible +from the machine on which the backup script is run. + +@FIXME{Same file name, be specific. Through NFS ...} + +@end table + +@menu +* backup-specs example:: An Example Text of @file{Backup-specs} +* Script Syntax:: Syntax for @file{Backup-specs} +@end menu + +@node backup-specs example +@subsection An Example Text of @file{Backup-specs} +@UNREVISED + +The following is the text of @file{backup-specs} as it appears at FSF: + +@example +# site-specific parameters for file system backup. + +ADMINISTRATOR=friedman +BACKUP_HOUR=1 +TAPE_FILE=/dev/nrsmt0 +TAPE_STATUS="mts -t $TAPE_FILE" +BLOCKING=124 +BACKUP_DIRS=" + albert:/fs/fsf + apple-gunkies:/gd + albert:/fs/gd2 + albert:/fs/gp + geech:/usr/jla + churchy:/usr/roland + albert:/ + albert:/usr + apple-gunkies:/ + apple-gunkies:/usr + gnu:/hack + gnu:/u + apple-gunkies:/com/mailer/gnu + apple-gunkies:/com/archive/gnu" + +BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]" + +@end example + +@node Script Syntax +@subsection Syntax for @file{Backup-specs} +@UNREVISED + +@file{backup-specs} is in shell script syntax. The following +conventions should be considered when editing the script: +@FIXME{"conventions?"} + +A quoted string is considered to be contiguous, even if it is on more +than one line. Therefore, you cannot include commented-out lines +within a multi-line quoted string. BACKUP_FILES and BACKUP_DIRS are +the two most likely parameters to be multi-line. + +A quoted string typically cannot contain wildcards. In +@file{backup-specs}, however, the parameters BACKUP_DIRS and +BACKUP_FILES can contain wildcards. + +@node Scripted Backups +@section Using the Backup Scripts +@UNREVISED + +The syntax for running a backup script is: + +@example +@file{script-name} [@var{time-to-be-run}] +@end example + +where @var{time-to-be-run} can be a specific system time, or can be +@kbd{now}. If you do not specify a time, the script runs at the time +specified in @file{backup-specs}. @FIXME-pxref{Script Syntax} + +You should start a script with a tape or disk mounted. Once you +start a script, it prompts you for new tapes or disks as it +needs them. Media volumes don't have to correspond to archive +files---a multi-volume archive can be started in the middle of a +tape that already contains the end of another multi-volume archive. +The @code{restore} script prompts for media by its archive volume, +so to avoid an error message you should keep track of which tape +(or disk) contains which volume of the archive. @FIXME{There is +no such restore script!} @FIXME-xref{Scripted Restoration} +@FIXME{Have file names changed?} + +The backup scripts write two files on the file system. The first is a +record file in @file{/etc/tar-backup/}, which is used by the scripts +to store and retrieve information about which files were dumped. This +file is not meant to be read by humans, and should not be deleted by +them. @FIXME-xref{incremental and listed-incremental, for a more +detailed explanation of this file.} + +The second file is a log file containing the names of the file systems +and files dumped, what time the backup was made, and any error +messages that were generated, as well as how much space was left in +the media volume after the last volume of the archive was written. +You should check this log file after every backup. The file name is +@file{log-@var{mmm-ddd-yyyy}-level-1} or +@file{log-@var{mmm-ddd-yyyy}-full}. + +The script also prints the name of each system being dumped to the +standard output. + +@node Scripted Restoration +@section Using the Restore Script +@UNREVISED + +@ifset PUBLISH + +The @command{tar} distribution does not provide restoring scripts. + +@end ifset + +@ifclear PUBLISH + +@quotation +@strong{Warning:} The @sc{gnu} @command{tar} distribution does @emph{not} +provide any such @code{restore} script yet. This section is only +listed here for documentation maintenance purposes. In any case, +all contents is subject to change as things develop. +@end quotation + +@FIXME{A section on non-scripted restore may be a good idea.} + +To restore files that were archived using a scripted backup, use the +@code{restore} script. The syntax for the script is: + +where ***** are the file systems to restore from, and +***** is a regular expression which specifies which files to +restore. If you specify --all, the script restores all the files +in the file system. + +You should start the restore script with the media containing the +first volume of the archive mounted. The script will prompt for other +volumes as they are needed. If the archive is on tape, you don't need +to rewind the tape to to its beginning---if the tape head is +positioned past the beginning of the archive, the script will rewind +the tape as needed. @FIXME-xref{Media, for a discussion of tape +positioning.} + +If you specify @samp{--all} as the @var{files} argument, the +@code{restore} script extracts all the files in the archived file +system into the active file system. + +@quotation +@strong{Warning:} The script will delete files from the active file +system if they were not in the file system when the archive was made. +@end quotation + +@value{xref-incremental}, and @value{ref-listed-incremental}, +for an explanation of how the script makes that determination. + +@FIXME{this may be an option, not a given} + +@end ifclear + +@node Choosing +@chapter Choosing Files and Names for @command{tar} +@UNREVISED + +@FIXME{Melissa (still) Doesn't Really Like This ``Intro'' Paragraph!!!} + +Certain options to @command{tar} enable you to specify a name for your +archive. Other options let you decide which files to include or exclude +from the archive, based on when or whether files were modified, whether +the file names do or don't match specified patterns, or whether files +are in specified directories. + +@menu +* 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 +@end menu + +@node file +@section Choosing and Naming Archive Files +@cindex Naming an archive +@cindex Archive Name +@cindex Directing output +@cindex Choosing an archive file +@cindex Where is the archive? +@UNREVISED + +@FIXME{should the title of this section actually be, "naming an +archive"?} + +By default, @command{tar} uses an archive file name that was compiled when +it was built on the system; usually this name refers to some physical +tape drive on the machine. However, the person who installed @command{tar} +on the system may not set the default to a meaningful value as far as +most users are concerned. As a result, you will usually want to tell +@command{tar} where to find (or create) the archive. The @value{op-file} +option allows you to either specify or name a file to use as the archive +instead of the default archive file location. + +@table @kbd +@item --file=@var{archive-name} +@itemx -f @var{archive-name} +Name the archive to create or operate on. Use in conjunction with +any operation. +@end table + +For example, in this @command{tar} command, + +@example +$ @kbd{tar -cvf collection.tar blues folk jazz} +@end example + +@noindent +@file{collection.tar} is the name of the archive. It must directly +follow the @samp{-f} option, since whatever directly follows @samp{-f} +@emph{will} end up naming the archive. If you neglect to specify an +archive name, you may end up overwriting a file in the working directory +with the archive you create since @command{tar} will use this file's name +for the archive name. + +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, +floppy disk, or CD write drive. + +@cindex Writing new archives +@cindex Archive creation +If you do not name the archive, @command{tar} uses the value of the +environment variable @env{TAPE} as the file name for the archive. If +that is not available, @command{tar} uses a default, compiled-in archive +name, usually that for tape unit zero (ie. @file{/dev/tu00}). +@command{tar} always needs an archive name. + +If you use @file{-} as an @var{archive-name}, @command{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, +@command{tar} reads the original archive from its standard input and +writes the entire new archive to its standard output. + +@FIXME{might want a different example here; this is already used in +"notable tar usages".} + +@example +$ @kbd{cd sourcedir; tar -cf - . | (cd targetdir; tar -xf -)} +@end example + +@FIXME{help!} + +@cindex Standard input and output +@cindex tar to standard input and output +To specify an archive file on a device attached to a remote machine, +use the following: + +@example +@kbd{--file=@var{hostname}:/@var{dev}/@var{file name}} +@end example + +@noindent +@command{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}}, @command{tar} +will complete the remote connection, if possible, using your username +as the username on the remote machine. + +If the archive file name includes a colon (@samp{:}), then it is assumed +to be a file on another machine. If the archive file is +@samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the +host @var{host}. The remote host is accessed using the @command{rsh} +program, with a username of @var{user}. If the username is omitted +(along with the @samp{@@} sign), then your user name will be used. +(This is the normal @command{rsh} behavior.) It is necessary for the +remote machine, in addition to permitting your @command{rsh} access, to +have the @file{/usr/ucb/rmt} program installed. If you need to use a +file whose name includes a colon, then the remote tape drive behavior +can be inhibited by using the @value{op-force-local} option. + +@FIXME{i know we went over this yesterday, but bob (and now i do again, +too) thinks it's out of the middle of nowhere. it doesn't seem to tie +into what came before it well enough <>. 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 -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 +@FIXME{say anything else here to conclude the section?} -@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). +@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 -@node Backups and Restoration, Media, User Interaction, Top -@chapter Performing Backups and Restoring Files +@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}. + +A @var{pattern} containing @samp{/} excludes a name if an initial +subsequence of the name's components matches @var{pattern}; a +@var{pattern} without @samp{/} excludes a name if it matches any of its +name components. For example, the pattern @samp{*b/RCS} contains +@samp{/}, so it excludes @file{blob/RCS} and @file{.blob/RCS/f} but not +@file{blob/RCSit/RCS} or @file{/blob/RCS}, whereas the pattern +@samp{RCS} excludes all these names. Conversely, the pattern @samp{*.o} +lacks @samp{/}, so it excludes @file{.f.o}, @file{d/f.o}, and +@file{d.o/f}. + +Other than optionally stripping leading @samp{/} from names +(@pxref{absolute}), patterns and candidate names are used as-is. For +example, trailing @samp{/} is not trimmed from a user-specified name +before deciding whether to exclude it. + +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 -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}. +@findex exclude-from +Use the @samp{--exclude-from=@var{file-of-patterns}} option to read a +list of shell wildcards, one per line, from @var{file}; @command{tar} will +ignore files matching those regular expressions. 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 -* 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 +* problems with exclude:: @end menu -@node Backup Levels, Backup Scripts, Backups and Restoration, Backups and Restoration -@section Levels of Backups +@node problems with exclude +@unnumberedsubsec Problems with Using the @code{exclude} Options -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. +Some users find @samp{exclude} options confusing. Here are some common +pitfalls: -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. +@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. -A typical dump strategy would be to perform a full dump once a week, -and a level one dump once a day. This means some versions of files -will in fact be archived more than once, but this dump strategy makes -it possible to restore a file system to within one day of accuracy by -only extracting two archives---the last weekly (full) dump and the -last daily (level one) dump. The only information lost would be in -files changed or created since the last daily backup. (Doing dumps -more than once a day is usually not worth the trouble). +@item +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. -@node Backup Scripts, incremental and listed-incremental, Backup Levels, Backups and Restoration -@section Using Scripts to Perform Backups and Restoration +@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. -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. +For example, write: -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. +@example +$ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}} +@end example -@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. +@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 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. + +@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 + +To select files newer than the modification time of a file that already +exists, you can use the @samp{--reference} (@samp{-r}) option of @sc{gnu} +@command{date}, available in @sc{gnu} shell utilities 1.13 or later. It returns +the time stamp of the already-existing file; this time stamp expands to +become the referent date which @samp{--newer} uses to determine which +files to archive. For example, you could say, + +@example +$ @kbd{tar -cf @var{archive.tar} --newer="`date -r @var{file}`" /home} +@end example + +@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. +@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-file-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. + +@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. -@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 +* directory:: Changing Directory +* absolute:: Absolute File Names @end menu -@node Backup Parameters, Scripted Backups, Backup Scripts, Backup Scripts -@subsection Setting Parameters for Backups and Restoration +@node directory +@subsection Changing the Working Directory -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. +@FIXME{need to read over this node now for continuity; i've switched +things around some.} -@c <<< This about backup scripts needs to be written: -@c << /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 + +@node Date input formats +@chapter Date input formats + +@cindex date input formats +@findex getdate + +@quotation +Our units of temporal measurement, from seconds on up to months, are so +complicated, asymmetrical and disjunctive so as to make coherent mental +reckoning in time all but impossible. Indeed, had some tyrannical god +contrived to enslave our minds to time, to make it all but impossible +for us to escape subjection to sodden routines and unpleasant surprises, +he could hardly have done better than handing down our present system. +It is like a set of trapezoidal building blocks, with no vertical or +horizontal surfaces, like a language in which the simplest thought +demands ornate constructions, useless particles and lengthy +circumlocutions. Unlike the more successful patterns of language and +science, which enable us to face experience boldly or at least +level-headedly, our system of temporal calculation silently and +persistently encourages our terror of time. + +@dots{} It is as though architects had to measure length in feet, width +in meters and height in ells; as though basic instruction manuals +demanded a knowledge of five different languages. It is no wonder then +that we often look into our own immediate past or future, last Tuesday +or a week from Sunday, with feelings of helpless confusion. @dots{} + +--- Robert Grudin, @cite{Time and the Art of Living}. +@end quotation + +This section describes the textual date representations that @sc{gnu} +programs accept. These are the strings you, as a user, can supply as +arguments to the various programs. The C interface (via the +@code{getdate} function) is not described here. + +@cindex beginning of time, for Unix +@cindex epoch, for Unix +Although the date syntax here can represent any possible time since zero +A.D., computer integers are not big enough for such a (comparatively) +long time. The earliest date semantically allowed on Unix systems is +midnight, 1 January 1970 UCT. + @menu -* backup-specs example:: An Example Text of @file{Backup-specs} -* Script Syntax:: Syntax for @file{Backup-specs} +* General date syntax:: Common rules. +* Calendar date item:: 19 Dec 1994. +* Time of day item:: 9:20pm. +* Time zone item:: @sc{est}, @sc{gmt}, @sc{utc}, ... +* Day of week item:: Monday and others. +* Relative item in date strings:: next tuesday, 2 years ago. +* Pure numbers in date strings:: 19931219, 1440. +* Authors of getdate:: Bellovin, Berets, Eggert, Salz, et al. @end menu -@node backup-specs example, Script Syntax, Backup Parameters, Backup Parameters -@subsubsection An Example Text of @file{Backup-specs} -The following is the text of @file{backup-specs} as it appears at FSF: +@node General date syntax +@section General date syntax + +@cindex general date syntax + +@cindex items in date strings +A @dfn{date} is a string, possibly empty, containing many items +separated by white space. The white space may be omitted when no +ambiguity arises. The empty string means the beginning of today (i.e., +midnight). Order of the items is immaterial. A date string may contain +many flavors of items: + +@itemize @bullet +@item calendar date items +@item time of the day items +@item time zone items +@item day of the week items +@item relative items +@item pure numbers. +@end itemize + +@noindent We describe each of these item types in turn, below. + +@cindex numbers, written-out +@cindex ordinal numbers +@findex first @r{in date strings} +@findex next @r{in date strings} +@findex last @r{in date strings} +A few numbers may be written out in words in most contexts. This is +most useful for specifying day of the week items or relative items (see +below). Here is the list: @samp{first} for 1, @samp{next} for 2, +@samp{third} for 3, @samp{fourth} for 4, @samp{fifth} for 5, +@samp{sixth} for 6, @samp{seventh} for 7, @samp{eighth} for 8, +@samp{ninth} for 9, @samp{tenth} for 10, @samp{eleventh} for 11 and +@samp{twelfth} for 12. Also, @samp{last} means exactly @math{-1}. + +@cindex months, written-out +When a month is written this way, it is still considered to be written +numerically, instead of being ``spelled in full''; this changes the +allowed strings. + +@cindex case, ignored in dates +@cindex comments, in dates +Alphabetic case is completely ignored in dates. Comments may be introduced +between round parentheses, as long as included parentheses are properly +nested. Hyphens not followed by a digit are currently ignored. Leading +zeros on numbers are ignored. + + +@node Calendar date item +@section Calendar date item + +@cindex calendar date item + +A @dfn{calendar date item} specifies a day of the year. It is +specified differently, depending on whether the month is specified +numerically or literally. All these strings specify the same calendar date: @example -# site-specific parameters for file system backup. +1970-09-17 # ISO 8601. +70-9-17 # This century assumed by default. +70-09-17 # Leading zeros are ignored. +9/17/72 # Common U.S. writing. +24 September 1972 +24 Sept 72 # September has a special abbreviation. +24 Sep 72 # Three-letter abbreviations always allowed. +Sep 24, 1972 +24-sep-72 +24sep72 +@end example -ADMINISTRATOR=friedman -BACKUP_HOUR=1 -TAPE_FILE=/dev/nrsmt0 -TAPE_STATUS="mts -t $TAPE_FILE" -BLOCKING=124 -BACKUP_DIRS=" - albert:/fs/fsf - apple-gunkies:/gd - albert:/fs/gd2 - albert:/fs/gp - geech:/usr/jla - churchy:/usr/roland - albert:/ - albert:/usr - apple-gunkies:/ - apple-gunkies:/usr - gnu:/hack - gnu:/u - apple-gunkies:/com/mailer/gnu - apple-gunkies:/com/archive/gnu" +The year can also be omitted. In this case, the last specified year is +used, or the current year if none. For example: + +@example +9/17 +sep 17 +@end example + +Here are the rules. + +@cindex ISO 8601 date format +@cindex date format, ISO 8601 +For numeric months, the ISO 8601 format +@samp{@var{year}-@var{month}-@var{day}} is allowed, where @var{year} is +any positive number, @var{month} is a number between 01 and 12, and +@var{day} is a number between 01 and 31. A leading zero must be present +if a number is less than ten. If @var{year} is less than 100, then 1900 +is added to it to force a date in this century. The construct +@samp{@var{month}/@var{day}/@var{year}}, popular in the United States, +is accepted. Also @samp{@var{month}/@var{day}}, omitting the year. + +@cindex month names in date strings +@cindex abbreviations for months +Literal months may be spelled out in full: @samp{January}, +@samp{February}, @samp{March}, @samp{April}, @samp{May}, @samp{June}, +@samp{July}, @samp{August}, @samp{September}, @samp{October}, +@samp{November} or @samp{December}. Literal months may be abbreviated +to their first three letters, possibly followed by an abbreviating dot. +It is also permitted to write @samp{Sept} instead of @samp{September}. + +When months are written literally, the calendar date may be given as any +of the following: + +@example +@var{day} @var{month} @var{year} +@var{day} @var{month} +@var{month} @var{day} @var{year} +@var{day}-@var{month}-@var{year} +@end example + +Or, omitting the year: + +@example +@var{month} @var{day} +@end example + + +@node Time of day item +@section Time of day item + +@cindex time of day item + +A @dfn{time of day item} in date strings specifies the time on a given +day. Here are some examples, all of which represent the same time: + +@example +20:02:0 +20:02 +8:02pm +20:02-0500 # In @sc{est} (U.S. Eastern Standard Time). +@end example + +More generally, the time of the day may be given as +@samp{@var{hour}:@var{minute}:@var{second}}, where @var{hour} is +a number between 0 and 23, @var{minute} is a number between 0 and +59, and @var{second} is a number between 0 and 59. Alternatively, +@samp{:@var{second}} can be omitted, in which case it is taken to +be zero. + +@findex am @r{in date strings} +@findex pm @r{in date strings} +@findex midnight @r{in date strings} +@findex noon @r{in date strings} +If the time is followed by @samp{am} or @samp{pm} (or @samp{a.m.} +or @samp{p.m.}), @var{hour} is restricted to run from 1 to 12, and +@samp{:@var{minute}} may be omitted (taken to be zero). @samp{am} +indicates the first half of the day, @samp{pm} indicates the second +half of the day. In this notation, 12 is the predecessor of 1: +midnight is @samp{12am} while noon is @samp{12pm}. +(This is the zero-oriented interpretation of @samp{12am} and @samp{12pm}, +as opposed to the old tradition derived from Latin +which uses @samp{12m} for noon and @samp{12pm} for midnight.) + +@cindex time zone correction +@cindex minutes, time zone correction by +The time may be followed by a time zone correction, +expressed as @samp{@var{s}@var{hh}@var{mm}}, where @var{s} is @samp{+} +or @samp{-}, @var{hh} is a number of zone hours and @var{mm} is a number +of zone minutes. When a time zone correction is given this way, it +forces interpretation of the time in @sc{utc}, overriding any previous +specification for the time zone or the local time zone. The @var{minute} +part of the time of the day may not be elided when a time zone correction +is used. + +Either @samp{am}/@samp{pm} or a time zone correction may be specified, +but not both. + + +@node Time zone item +@section Time zone item + +@cindex time zone item + +A @dfn{time zone item} specifies an international time zone, indicated +by a small set of letters, e.g.@: @samp{UTC} for Coordinated Universal +Time. Any included period is ignored. By following a +non-daylight-saving time zone by the string @samp{DST} in a separate +word (that is, separated by some white space), the corresponding +daylight saving time zone may be specified. + +Time zone items are obsolescent and are not recommended, because they +are ambiguous; for example, @samp{EST} has a different meaning in +Australia than in the United States. Instead, it's better to use +unambiguous numeric time zone corrections like @samp{-0500}, as +described in the previous section. + +@node Day of week item +@section Day of week item + +@cindex day of week item + +The explicit mention of a day of the week will forward the date +(only if necessary) to reach that day of the week in the future. + +Days of the week may be spelled out in full: @samp{Sunday}, +@samp{Monday}, @samp{Tuesday}, @samp{Wednesday}, @samp{Thursday}, +@samp{Friday} or @samp{Saturday}. Days may be abbreviated to their +first three letters, optionally followed by a period. The special +abbreviations @samp{Tues} for @samp{Tuesday}, @samp{Wednes} for +@samp{Wednesday} and @samp{Thur} or @samp{Thurs} for @samp{Thursday} are +also allowed. + +@findex next @var{day} +@findex last @var{day} +A number may precede a day of the week item to move forward +supplementary weeks. It is best used in expression like @samp{third +monday}. In this context, @samp{last @var{day}} or @samp{next +@var{day}} is also acceptable; they move one week before or after +the day that @var{day} by itself would represent. + +A comma following a day of the week item is ignored. + + +@node Relative item in date strings +@section Relative item in date strings + +@cindex relative items in date strings +@cindex displacement of dates + +@dfn{Relative items} adjust a date (or the current date if none) forward +or backward. The effects of relative items accumulate. Here are some +examples: + +@example +1 year +1 year ago +3 years +2 days +@end example + +@findex year @r{in date strings} +@findex month @r{in date strings} +@findex fortnight @r{in date strings} +@findex week @r{in date strings} +@findex day @r{in date strings} +@findex hour @r{in date strings} +@findex minute @r{in date strings} +The unit of time displacement may be selected by the string @samp{year} +or @samp{month} for moving by whole years or months. These are fuzzy +units, as years and months are not all of equal duration. More precise +units are @samp{fortnight} which is worth 14 days, @samp{week} worth 7 +days, @samp{day} worth 24 hours, @samp{hour} worth 60 minutes, +@samp{minute} or @samp{min} worth 60 seconds, and @samp{second} or +@samp{sec} worth one second. An @samp{s} suffix on these units is +accepted and ignored. + +@findex ago @r{in date strings} +The unit of time may be preceded by a multiplier, given as an optionally +signed number. Unsigned numbers are taken as positively signed. No +number at all implies 1 for a multiplier. Following a relative item by +the string @samp{ago} is equivalent to preceding the unit by a +multiplier with value @math{-1}. + +@findex day @r{in date strings} +@findex tomorrow @r{in date strings} +@findex yesterday @r{in date strings} +The string @samp{tomorrow} is worth one day in the future (equivalent +to @samp{day}), the string @samp{yesterday} is worth +one day in the past (equivalent to @samp{day ago}). + +@findex now @r{in date strings} +@findex today @r{in date strings} +@findex this @r{in date strings} +The strings @samp{now} or @samp{today} are relative items corresponding +to zero-valued time displacement, these strings come from the fact +a zero-valued time displacement represents the current time when not +otherwise change by previous items. They may be used to stress other +items, like in @samp{12:00 today}. The string @samp{this} also has +the meaning of a zero-valued time displacement, but is preferred in +date strings like @samp{this thursday}. + + +@node Pure numbers in date strings +@section Pure numbers in date strings + +@cindex pure numbers in date strings + +The precise interpretation of a pure decimal number depends on +the context in the date string. + +If the decimal number is of the form @var{yyyy}@var{mm}@var{dd} and no +other calendar date item (@pxref{Calendar date item}) appears before it +in the date string, then @var{yyyy} is read as the year, @var{mm} as the +month number and @var{dd} as the day of the month, for the specified +calendar date. + +If the decimal number is of the form @var{hh}@var{mm} and no other time +of day item appears before it in the date string, then @var{hh} is read +as the hour of the day and @var{mm} as the minute of the hour, for the +specified time of the day. @var{mm} can also be omitted. + +If both a calendar date and a time of day appear to the left of a number +in the date string, but no relative item, then the number overrides the +year. + + +@node Authors of getdate +@section Authors of @code{getdate} + +@cindex authors of @code{getdate} + +@cindex Bellovin, Steven M. +@cindex Berets, Jim +@cindex Eggert, Paul +@cindex MacKenzie, David +@cindex Meyering, Jim +@cindex Salz, Rich +@code{getdate} was originally implemented by Steven M. Bellovin +(@samp{smb@@research.att.com}) while at the University of North Carolina +at Chapel Hill. The code was later tweaked by a couple of people on +Usenet, then completely overhauled by Rich $alz (@samp{rsalz@@bbn.com}) +and Jim Berets (@samp{jberets@@bbn.com}) in August, 1990. Various +revisions for the @sc{gnu} system were made by David MacKenzie, Jim Meyering, +and others. The code was rewritten again in August, 1999 by Paul Eggert, +to improve its support for daylight saving time. + +@cindex Pinard, F. +@cindex Berry, K. +This chapter was originally produced by Fran@,{c}ois Pinard +(@samp{pinard@@iro.umontreal.ca}) from the @file{getdate.y} source code, +and then edited by K.@: Berry (@samp{kb@@cs.umb.edu}). + +@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.) -BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]" +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. -@end example +@node old +@subsection Old V7 Archives +@cindex Format, old style +@cindex Old style format +@cindex Old style archives -@node Script Syntax, , backup-specs example, Backup Parameters -@subsubsection Syntax for @file{Backup-specs} +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 -@file{backup-specs} is in shell script syntax. The following -conventions should be considered when editing the script: -@c <<< "conventions?" +@menu +* gzip:: Creating and Reading Compressed Archives +* sparse:: Archiving Sparse Files +@end menu -A quoted string is considered to be contiguous, even if it is on more -than one line. Therefore, you cannot include commented-out lines -within a multi-line quoted string. BACKUP_FILES and BACKUP_DIRS are -the two most likely parameters to be multi-line. +@node gzip +@subsection Creating and Reading Compressed Archives +@cindex Compressed archives +@cindex Storing archives in compressed format +@UNREVISED -A quoted string typically cannot contain wildcards. In -@file{backup-specs}, however, the parameters BACKUP_DIRS and -BACKUP_FILES can contain wildcards. +@table @kbd +@item -z +@itemx --gzip +@itemx --ungzip +Filter the archive through @command{gzip}. +@end table -@node Scripted Backups, Scripted Restoration, Backup Parameters, Backup Scripts -@subsection Using the Backup Scripts +@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. -The syntax for running a backup script is: +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 -@file{script-name} [@var{time-to-be-run}] +$ @kbd{tar cfz archive.tar.gz subdir} @end example -where @var{time-to-be-run} can be a specific system time, or can be -@kbd{now}. If you do not specify a time, the script runs at the time -specified in @file{backup-specs} (@pxref{Script Syntax}). - -You should start a script with a tape or disk mounted. Once you start -a script, it prompts you for new tapes or disks as it needs them. -Media volumes don't have to correspond to archive files---a -multi-volume archive can be started in the middle of a tape that -already contains the end of another multi-volume archive. The -@code{restore} script prompts for media by its archive volume, so to -avoid an error message you should keep track of which tape (or disk) -contains which volume of the archive. @xref{Scripted Restoration}. - -@c <<}. + +@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 --version -Prints the version number of the @code{tar} program to the standard -error. +@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. This implies +@value{op-multi-volume}. @end table -@node Options, , Operations, Quick Reference -@appendixsec Table of Options +@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 -Options change the way @code{tar} performs an operation. +@ifclear PUBLISH -@table @samp -@item --absolute-paths -WILL BE INPUT WHEN QUESTION IS RESOLVED +@format +errors from system: +permission denied +no such file or directory +not owner -@item --after-date=@var{date} -Limit the operation to files changed after the given date. -@xref{File Exclusion}. +errors from @command{tar}: +directory checksum error +header format error -@item --block-size=@var{number} -Specify the blocking factor of an archive. @xref{Blocking Factor}. +errors from media/system: +i/o error +device busy +@end format -@item --compress -Specify a compressed archive. @xref{Compressed Archives}. +@end ifclear -@item --compress-block. -Create a whole block sized compressed archive. @xref{Compressed Archives}. +@node Blocking +@section Blocking +@UNREVISED -@item --confirmation -Solicit confirmation for each file. @xref{Interactive Operation} -<<< --selective should be a synonym. +@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. -@item --dereference -Treat a symbolic link as an alternate name for the file the link -points to. @xref{Symbolic Links}. +John Gilmore, the writer of the public domain @command{tar} from which +@sc{gnu} @command{tar} was originally derived, wrote (June 1995): -@item --directory=@file{directory} -Change the working directory. @xref{Changing Working Directory}. +@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 -@item --exclude=@var{pattern} -Exclude files which match the regular expression @var{pattern}. -@xref{File Exclusion}. +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. -@item --exclude-from=@file{file} -Exclude files which match any of the regular expressions listed in -the file @file{file}. @xref{File Exclusion}. +@menu +* Format Variations:: Format Variations +* Blocking Factor:: The Blocking Factor of an Archive +@end menu -@item --file=@var{archive-name} -Name the archive. @xref{Archive Name}). +@node Format Variations +@subsection Format Variations +@cindex Format Parameters +@cindex Format Options +@cindex Options, archive format specifying +@cindex Options, format specifying +@UNREVISED -@item --files-from=@file{file} -Read file-name arguments from a file on the file system. -@xref{File Name Lists}. +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. -@item --ignore-umask -Set modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. +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: -@item --ignore-zeros -Ignore end-of-archive entries. @xref{Archive Reading Options}. -<<< this should be changed to --ignore-end +@example +Cannot write to /dev/dlt: Invalid argument +@end example -@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. +@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 -@item --incremental (-G) -@c <<>> +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 -@item --tape-length=@var{n} (-L) -@c <<>> -@c <<< this needs to be written into main body as well -ringo +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: -@item --info-script=@var{program-file} -Create a multi-volume archive via a script. @xref{Multi-Volume Archives}. +@itemize @bullet -@item --interactive -Ask for confirmation before performing any operation on a file or -archive member. +@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 --keep-old-files -Prevent overwriting during extraction. @xref{File Writing Options}. +@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 --label=@var{archive-label} -Include an archive-label in the archive being created. @xref{Archive -Label}. +@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 --modification-time -Set the modification time of extracted files to the time they were -extracted. @xref{File Writing Options}. +@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 --multi-volume -Specify a multi-volume archive. @xref{Multi-Volume Archives}. +@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. -@item --newer=@var{date} -Limit the operation to files changed after the given date. -@xref{File Exclusion}. +@end table -@item --newer-mtime=@var{date} -Limit the operation to files modified after the given date. @xref{File -Exclusion}. +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: -@item --old -Create an old format archive. @xref{Old Style File Information}. -@c <<< did we agree this should go away as a synonym? +@example +$ @kbd{tar cf /dev/tape @var{directory}} +@end example -@item --old-archive -Create an old format archive. @xref{Old Style File Information}. +@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: -@item --one-file-system -Prevent @code{tar} from crossing file system boundaries when -archiving. @xref{File Exclusion}. +@example +$ @kbd{mt -f /dev/nrtape rewind} +$ @kbd{tar cf /dev/nrtape @var{directory-1}} +@end example -@item --portable -Create an old format archive. @xref{Old Style File Information}. -@c <<< was portability, may still need to be changed +@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: -@item --preserve-order -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. +@example +$ @kbd{tar cf /dev/nrtape @var{directory-2}} +@end example -@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}. +@noindent +and so on for all the archives you want to put on the same tape. -@item --same-order -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. +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: -@item --same-permission -Set the modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. +@example +$ @kbd{mt -f /dev/nrtape rewind} +$ @kbd{mt -f /dev/nrtape fsf 16} +$ @kbd{tar cf /dev/nrtape @var{directory-17}} +@end example -@item --sparse -Archive sparse files sparsely. @xref{Sparse Files}. +In all the previous examples, we put aside blocking considerations, but +you should do the proper things for that as well. @xref{Blocking}. -@item --starting-file=@var{file-name} -Begin reading in the middle of an archive. @xref{Scarce Disk Space}. +@menu +* Tape Positioning:: Tape Positions and Tape Marks +* mt:: The @command{mt} Utility +@end menu -@item --to-stdout -Write files to the standard output. @xref{File Writing Options}. +@node Tape Positioning +@subsection Tape Positions and Tape Marks +@UNREVISED -@item --uncompress -Specifdo a compressed archive. @xref{Compressed Archives}. +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 +archive files (or any other type of file stored on tape) begin and +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. -@item -V @var{archive-label} -Include an archive-label in the archive being created. @xref{Archive -Label}. -@c was --volume +If you think of data as a series of records "rrrr"'s, and tape marks as +"*"'s, a tape might look like the following: -@item --verbose -Print the names of files or archive members as they are being -operated on. @xref{Additional Information}. +@example +rrrr*rrrrrr*rrrrr*rr*rrrrr**------------------------- +@end example -@item --verify -Check for discrepancies in the archive immediately after it is -written. @xref{Write Verification}. +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 @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. @FIXME{There is no such +restore script!}@FIXME-xref{Scripted Restoration}@xref{mt}, for +an explanation of the tape moving utility. -@item -B -Read an archive with a smaller than specified block size or which -contains incomplete blocks. @xref{Archive Reading Options}). +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 +over the last tape mark, and write the new archive file. If you were +to add two archives to the example above, the tape might look like the +following: -@item -K @var{file-name} -Begin reading in the middle of an archive. @xref{Scarce Disk Space}. +@example +rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**---------------- +@end example -@item -M -Specify a multi-volume archive. @xref{Multi-Volume Archives}. +@node mt +@subsection The @command{mt} Utility +@UNREVISED -@item -N @var{date} -Limit operation to files changed after the given date. @xref{File Exclusion}. +@FIXME{Is it true that this only works on non-block devices? +should explain the difference, (fixed or variable).} +@value{xref-blocking-factor}. -@item -O -Write files to the standard output. @xref{File Writing Options}. +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"?} -@c <<<<- P is absolute paths, add when resolved. -ringo>>> +The syntax of the @command{mt} command is: -@item -R -Print the record number where a message is generated. -@xref{Additional Information}. +@example +@kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]} +@end example -@item -S -Archive sparse files sparsely. @xref{Sparse Files}. +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: -@item -T @var{file} -Read file-name arguments from a file on the file system. -@xref{File Name Lists}. +@FIXME{is there any use for record operations?} -@item -W -Check for discrepancies in the archive immediately after it is -written. @xref{Write Verification}. +@table @kbd +@item eof +@itemx weof +Writes @var{number} tape marks at the current position on the tape. -@item -Z -Specify a compressed archive. @xref{Compressed Archives}. +@item fsf +Moves tape position forward @var{number} files. -@item -b @var{number} -Specify the blocking factor of an archive. @xref{Blocking Factor}. +@item bsf +Moves tape position back @var{number} files. -@item -f @var{archive-name} -Name the archive. @xref{Archive Name}). +@item rewind +Rewinds the tape. (Ignores @var{number}). -@item -h -Treat a symbolic link as an alternate name for the file the link -points to. @xref{Symbolic Links}. +@item offline +@itemx rewoff1 +Rewinds the tape and takes the tape device off-line. (Ignores @var{number}). -@item -i -Ignore end-of-archive entries. @xref{Archive Reading Options}. +@item status +Prints status information about the tape unit. -@item -k -Prevent overwriting during extraction. @xref{File Writing Options}. +@end table -@item -l -Prevent @code{tar} from crossing file system boundaries when -archiving. @xref{File Exclusion}. +@FIXME{Is there a better way to frob the spacing on the list?} -@item -m -Set the modification time of extracted files to the time they were -extracted. @xref{File Writing Options}. +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}. -@item -o -Create an old format archive. @xref{Old Style File Information}. +@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. -@item -p -Set the modes of extracted files to those recorded in the archive. -@xref{File Writing Options}. +@FIXME{New node on how to find an archive?} -@item -s -Help process large lists of file-names on machines with small amounts of -memory. @xref{Archive Reading Options}. +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 -@item -v -Print the names of files or archive members they are being operated -on. @xref{Additional Information}. +(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. When the program finishes, @command{tar} will +immediately begin 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 -@item -w -@c <<>> +@menu +* Multi-Volume Archives:: Archives Longer than One Tape or Disk +* Tape Files:: Tape Files +@end menu -@item -z -Specify a compressed archive. @xref{Compressed Archives}. +@node Multi-Volume Archives +@subsection Archives Longer than One Tape or Disk +@cindex Multi-volume archives +@UNREVISED + +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 -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. +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 -C @file{directory} -Change the working directory. @xref{Changing Working Directory}. +You can read each individual volume of a multi-volume archive as if it +were an archive by itself. For example, to list the contents of one +volume, use @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 -F @var{program-file} -Create a multi-volume archive via a script. @xref{Multi-Volume Archives}. +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 -X @file{file} -Exclude files which match any of the regular expressions listed in -the file @file{file}. @xref{File Exclusion}. -@end table +@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. -@node Data Format Details, Concept Index, Quick Reference, Top -@appendix Details of the Archive Data Format +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. -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. +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. -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. +@cindex Labeling multi-volume archives +@FIXME{example} -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. +@FIXME{There should be a sample program here, including an exit +before end. Is the exit status even checked in tar? :-(} -@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 +@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 --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 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. +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: -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. +@example +@kbd{--label="@var{some-prefix} `date +@var{some-format}`"} +@end example -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. +or such, for pushing a common date in all volumes or an archive set. -The @code{longnames} field supports a feature that is not yet -implemented. This field should be empty. +@node label +@section Including a Label in the Archive +@cindex Labeling an archive +@cindex Labels on the archive media +@UNREVISED -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. +@table @kbd +@item -V @var{name} +@itemx --label=@var{name} +Create archive with volume name @var{name}. +@end table -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. +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. -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}. +@FIXME{Should the arg to --label be a quoted string?? No.} -@menu -* File Types:: File Types -* GNU File Types:: Additional File Types Supported by GNU -@end menu +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. -@node File Types, GNU File Types, Header Fields, Header Fields -@appendixsubsec File Types +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. -The following flags are used to describe file types: +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: -@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. +@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 -@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}. +@table @kbd +@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 +@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 -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. +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: -@node GNU File Types, , File Types, Header Fields -@appendixsubsec Additional File Types Supported by GNU +@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 -GNU @code{tar} uses additional file types to describe new types of -files in an archive. These are listed below. +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. -@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. +@FIXME{was --volume} -@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. +@node verify +@section Verifying Data as It is Stored +@cindex Verifying a write operation +@cindex Double-checking a write operation + +@table @kbd +@item -W +@itemx --verify +Attempt to verify the archive after writing. @end table -@node Sparse File Handling, , Header Fields, Data Format Details -@appendixsec Fields to Handle Sparse Files +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. + +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 following header information was added to deal with sparse files -(@pxref{Sparse Files}): +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. -@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. +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. In +multi-volume archives, each volume is verified after it is written, +before the next volume is written. -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. +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 @code{isextended} flag is only set for sparse files, and then only -if extended header records are needed when archiving the file. +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. + +@node Write Protection +@section Write Protection -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. +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). -@c so is @code{extended_header} the right way to write this? +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. -@node Concept Index, , Data Format Details, Top -@unnumbered Concept Index +@node Index +@unnumbered Index @printindex cp @@ -3950,4 +8708,6 @@ 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: