from archives.
Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
-2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
+2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
and with the Back-Cover Texts as in (a) below. A copy of the license
is included in the section entitled "GNU Free Documentation License".
-(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
-this GNU Manual. Buying copies from GNU Press supports the FSF in
-developing GNU and promoting software freedom.''
+(a) The FSF's Back-Cover Text is: ``You have the freedom to
+copy and modify this GNU manual. Buying copies from the FSF
+supports it in developing GNU and promoting software freedom.''
@end quotation
@end copying
* Changes::
* Configuring Help Summary::
+* Fixing Snapshot Files::
* Tar Internals::
* Genfile::
* Free Software Needs Free Documentation::
* help::
* defaults::
* verbose::
+* checkpoints::
* interactive::
The Three Option Styles
Controlling the Archive Format
-* Portability:: Making @command{tar} Archives More Portable
* Compression:: Using Less Space through Compression
* Attributes:: Handling File Attributes
+* Portability:: Making @command{tar} Archives More Portable
* cpio:: Comparison of @command{tar} and @command{cpio}
+Using Less Space through Compression
+
+* gzip:: Creating and Reading Compressed Archives
+* sparse:: Archiving Sparse Files
+
Making @command{tar} Archives More Portable
* Portable Names:: Portable Names
* dereference:: Symbolic Links
+* hard links:: Hard Links
* old:: Old V7 Archives
* ustar:: Ustar Archives
* gnu:: GNU and old GNU format archives.
* Split Recovery:: Members Split Between Volumes
* Sparse Recovery:: Sparse Members
-Using Less Space through Compression
-
-* gzip:: Creating and Reading Compressed Archives
-* sparse:: Archiving Sparse Files
-
Tapes and Other Archive Media
* Device:: Device selection and switching
The third chapter presents the remaining five operations, and
information about using @command{tar} options and option syntax.
-@FIXME{this sounds more like a @acronym{GNU} Project Manuals Concept [tm] more
-than the reality. should think about whether this makes sense to say
-here, or not.} The other chapters are meant to be used as a
-reference. Each chapter presents everything that needs to be said
-about a specific topic.
+The other chapters are meant to be used as a reference. Each chapter
+presents everything that needs to be said about a specific topic.
One of the chapters (@pxref{Date input formats}) exists in its
entirety in other @acronym{GNU} manuals, and is mostly self-contained.
file system. You should have some basic understanding of directory
structure and how files are named according to which directory they are
in. You should understand concepts such as standard output and standard
-input, what various definitions of the term ``argument'' mean, and the
-differences between relative and absolute path names. @FIXME{and what
+input, what various definitions of the term @samp{argument} mean, and the
+differences between relative and absolute file names. @FIXME{and what
else?}
@item
This manual assumes that you are working from your own home directory
(unless we state otherwise). In this tutorial, you will create a
-directory to practice @command{tar} commands in. When we show path names,
-we will assume that those paths are relative to your home directory.
-For example, my home directory path is @file{/home/fsf/melissa}. All of
-my examples are in a subdirectory of the directory named by that path
+directory to practice @command{tar} commands in. When we show file names,
+we will assume that those names are relative to your home directory.
+For example, my home directory is @file{/home/fsf/melissa}. All of
+my examples are in a subdirectory of the directory named by that file
name; the subdirectory is called @file{practice}.
@item
of three forms: long (mnemonic) form, short form, and old style. Some
of the operations and options have no short or ``old'' forms; however,
the operations and options which we will cover in this tutorial have
-corresponding abbreviations. @FIXME{make sure this is still the case,
-at the end}We will indicate those abbreviations appropriately to get
-you used to seeing them. (Note that the ``old style'' option forms
-exist in @GNUTAR{} for compatibility with Unix
+corresponding abbreviations. We will indicate those abbreviations
+appropriately to get you used to seeing them. (Note that the ``old
+style'' option forms exist in @GNUTAR{} for compatibility with Unix
@command{tar}. In this book we present a full discussion of this way
of writing options and operations (@pxref{Old Options}), and we discuss
the other two styles of writing options (@xref{Long Options}, and
@item Owner name and group separated by a slash character.
If these data are not available (for example, when listing a @samp{v7} format
-archive), numeric ID values are printed instead.
+archive), numeric @acronym{ID} values are printed instead.
@item Size of the file, in bytes.
Now @command{cd} to the directory named @file{practice}; @file{practice}
is now your @dfn{working directory}. (@emph{Please note}: Although
-the full path name of this directory is
+the full file name of this directory is
@file{/@var{homedir}/practice}, in our examples we will refer to
this directory as @file{practice}; the @var{homedir} is presumed.
names of members you identify. For example, @w{@kbd{tar --list
--file=afiles.tar apple}} would only print @file{apple}.
-Because @command{tar} preserves paths, file names must be specified as
+Because @command{tar} preserves file names, these must be specified as
they appear in the archive (i.e., relative to the directory from which
the archive was created). Therefore, it is essential when specifying
member names to @command{tar} that you give the exact member names.
@node going further
@section Going Further Ahead in this Manual
+@UNREVISED
@FIXME{need to write up a node here about the things that are going to
be in the rest of the manual.}
* help::
* defaults::
* verbose::
+* checkpoints::
* interactive::
@end menu
available on some systems. However, mounting typically requires
superuser privileges and can be a pain to manage.
+@opsummary{auto-compress}
+@item --auto-compress
+@itemx -a
+
+During a @option{--create} operation, enables automatic compressed
+format recognition based on the archive suffix. The effect of this
+option is cancelled by @option{--no-auto-compress}. @xref{gzip}.
+
@opsummary{backup}
@item --backup=@var{backup-type}
This option tells @command{tar} to read or write archives through
@code{bzip2}. @xref{gzip}.
+@opsummary{check-device}
+@item --check-device
+Check device numbers when creating a list of modified files for
+incremental archiving. This is the default. @xref{device numbers},
+for a detailed description.
+
@opsummary{checkpoint}
@item --checkpoint[=@var{number}]
This option directs @command{tar} to print periodic checkpoint
messages as it reads through the archive. It is intended for when you
want a visual indication that @command{tar} is still running, but
-don't want to see @option{--verbose} output. For a detailed
-description, see @ref{Progress information}.
+don't want to see @option{--verbose} output. You can also instruct
+@command{tar} to execute a list of actions on each checkpoint, see
+@option{--checklist-action} below. For a detailed description, see
+@ref{checkpoints}.
+
+@opsummary{checkpoint-action}
+@item --checkpoint-action=@var{action}
+Instruct @command{tar} to execute an action upon hitting a
+breakpoint. Here we give only a brief outline. @xref{checkpoints},
+for a complete description.
+
+The @var{action} argument can be one of the following:
+
+@table @asis
+@item bell
+Produce an audible bell on the console.
+
+@item dot
+@itemx .
+Print a single dot on the standard listing stream.
+
+@item echo
+Display a textual message on the standard error, with the status and
+number of the checkpoint. This is the default.
+
+@item echo=@var{string}
+Display @var{string} on the standard error. Before output, the string
+is subject to meta-character expansion.
+
+@item exec=@var{command}
+Execute the given @var{command}.
+
+@item sleep=@var{time}
+Wait for @var{time} seconds.
+
+@item ttyout=@var{string}
+Output @var{string} on the current console (@file{/dev/tty}).
+@end table
+
+Several @option{--checkpoint-action} options can be specified. The
+supplied actions will be executed in order of their appearance in the
+command line.
+
+Using @option{--checkpoint-action} without @option{--checkpoint}
+assumes default checkpoint frequency of one checkpoint per 10 records.
@opsummary{check-links}
@item --check-links
complies to UNIX98, was introduced with version
1.15.91. @xref{Changes}, for more information.}.
+@xref{hard links}.
+
@opsummary{compress}
@opsummary{uncompress}
@item --compress
@item --exclude-tag-all=@var{file}
Exclude from dump any directory containing file named @var{file}.
-@xref{exclude}.
+@xref{exclude}.
+
+@opsummary{exclude-vcs}
+@item --exclude-vcs
+
+Exclude from dump directories and files, that are internal for some
+widely used version control systems.
+
+@xref{exclude}.
@opsummary{file}
@item --file=@var{archive}
@opsummary{force-local}
@item --force-local
-Forces @command{tar} to interpret the filename given to @option{--file}
+Forces @command{tar} to interpret the file name given to @option{--file}
as a local file, even if it looks like a remote tape drive name.
@xref{local and remote archives}.
@opsummary{group}
@item --group=@var{group}
-Files added to the @command{tar} archive will have a group id of @var{group},
+Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
rather than the group from the source file. @var{group} is first decoded
as a group symbolic name, but if this interpretation fails, it has to be
-a decimal numeric group ID. @xref{override}.
+a decimal numeric group @acronym{ID}. @xref{override}.
Also see the comments for the @option{--owner=@var{user}} option.
@command{gzip}, allowing @command{tar} to directly operate on several
kinds of compressed archives transparently. @xref{gzip}.
+@opsummary{hard-dereference}
+@item --hard-dereference
+When creating an archive, dereference hard links and store the files
+they refer to, instead of creating usual hard link members.
+
+@xref{hard links}.
+
@opsummary{help}
@item --help
@itemx -?
@item --incremental
@itemx -G
-Used to inform @command{tar} that it is working with an old
+Informs @command{tar} that it is working with an old
@acronym{GNU}-format incremental backup archive. It is intended
primarily for backwards compatibility only. @xref{Incremental Dumps},
for a detailed discussion of incremental archives.
With other operations, informs @command{tar} that the archive is in
incremental format. @xref{Incremental Dumps}.
+@opsummary{lzma}
+@item --lzma
+@itemx -J
+
+This option tells @command{tar} to read or write archives through
+@command{lzma}. @xref{gzip}.
+
+@item --lzop
+
+This option tells @command{tar} to read or write archives through
+@command{lzop}. @xref{gzip}.
+
@opsummary{mode}
@item --mode=@var{permissions}
(see --info-script)
-@opsummary{seek}
-@item --seek
-@itemx -n
-
-Assume that the archive media supports seeks to arbitrary
-locations. Usually @command{tar} determines automatically whether
-the archive can be seeked or not. This option is intended for use
-in cases when such recognition fails.
-
@opsummary{newer}
@item --newer=@var{date}
@itemx --after-date=@var{date}
An exclude pattern can match any subsequence of the name's components.
@xref{controlling pattern-matching}.
+@opsummary{no-auto-compress}
+@item --no-auto-compress
+
+Disables automatic compressed format recognition based on the archive
+suffix. @xref{--auto-compress}. @xref{gzip}.
+
+@opsummary{no-check-device}
+@item --no-check-device
+Do not check device numbers when creating a list of modified files
+for incremental archiving. @xref{device numbers}, for
+a detailed description.
+
@opsummary{no-delay-directory-restore}
@item --no-delay-directory-restore
-Setting modification times and permissions of extracted
-directories when all files from this directory has been
-extracted. This is the default. @xref{Directory Modification Times and Permissions}.
+Modification times and permissions of extracted
+directories are set when all files from this directory have been
+extracted. This is the default.
+@xref{Directory Modification Times and Permissions}.
@opsummary{no-ignore-case}
@item --no-ignore-case
@opsummary{no-ignore-command-error}
@item --no-ignore-command-error
-Print warnings about subprocesses terminated with a non-zero exit
+Print warnings about subprocesses that terminated with a nonzero exit
code. @xref{Writing to an External Program}.
+@opsummary{no-null}
+@item --no-null
+
+If the @option{--null} option was given previously, this option
+cancels its effect, so that any following @option{--files-from}
+options will expect their file lists to be newline-terminated.
+
@opsummary{no-overwrite-dir}
@item --no-overwrite-dir
@item --null
When @command{tar} is using the @option{--files-from} option, this option
-instructs @command{tar} to expect filenames terminated with @option{NUL}, so
+instructs @command{tar} to expect file names terminated with @acronym{NUL}, so
@command{tar} can correctly work with file names that contain newlines.
@xref{nul}.
When creating an archive, it is a synonym for
@option{--old-archive}. This behavior is for compatibility
with previous versions of @GNUTAR{}, and will be
-removed in the future releases.
+removed in future releases.
@xref{Changes}, for more information.
@item --one-file-system
Used when creating an archive. Prevents @command{tar} from recursing into
directories that are on different file systems from the current
-directory @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
-synonym for @option{--one-file-system}. This has changed in version
-1.15.91. @xref{Changes}, for more information.}.
+directory.
@opsummary{overwrite}
@item --overwrite
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.
+this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
@xref{override}.
This option does not affect extraction from archives.
-@opsummary{transform}
-@item --transform=@var{sed-expr}
-
-Transform file or member names using @command{sed} replacement expression
-@var{sed-expr}. For example,
-
-@smallexample
-$ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
-@end smallexample
-
-@noindent
-will add to @file{archive} files from the current working directory,
-replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
-discussion, @xref{transform}.
-
-To see transformed member names in verbose listings, use
-@option{--show-transformed-names} option
-(@pxref{show-transformed-names}).
-
-@opsummary{quote-chars}
-@item --quote-chars=@var{string}
-Always quote characters from @var{string}, even if the selected
-quoting style would not quote them (@pxref{quoting styles}).
-
-@opsummary{quoting-style}
-@item --quoting-style=@var{style}
-Set quoting style to use when printing member and file names
-(@pxref{quoting styles}). Valid @var{style} values are:
-@code{literal}, @code{shell}, @code{shell-always}, @code{c},
-@code{escape}, @code{locale}, and @code{clocale}. Default quoting
-style is @code{escape}, unless overridden while configuring the
-package.
-
@opsummary{pax-option}
@item --pax-option=@var{keyword-list}
This option is meaningful only with @acronym{POSIX.1-2001} archives
Specifying this option instructs @command{tar} that it should use the
permissions directly from the archive. @xref{Setting Access Permissions}.
+@opsummary{quote-chars}
+@item --quote-chars=@var{string}
+Always quote characters from @var{string}, even if the selected
+quoting style would not quote them (@pxref{quoting styles}).
+
+@opsummary{quoting-style}
+@item --quoting-style=@var{style}
+Set quoting style to use when printing member and file names
+(@pxref{quoting styles}). Valid @var{style} values are:
+@code{literal}, @code{shell}, @code{shell-always}, @code{c},
+@code{escape}, @code{locale}, and @code{clocale}. Default quoting
+style is @code{escape}, unless overridden while configuring the
+package.
+
@opsummary{read-full-records}
@item --read-full-records
@itemx -B
@opsummary{recursion}
@item --recursion
-With this option, @command{tar} recurses into directories.
+With this option, @command{tar} recurses into directories (default).
@xref{recurse}.
@opsummary{recursive-unlink}
(See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
+@opsummary{seek}
+@item --seek
+@itemx -n
+
+Assume that the archive media supports seeks to arbitrary
+locations. Usually @command{tar} determines automatically whether
+the archive can be seeked or not. This option is intended for use
+in cases when such recognition fails.
+
@opsummary{show-defaults}
@item --show-defaults
@opsummary{show-omitted-dirs}
@item --show-omitted-dirs
-Instructs @command{tar} to mention directories its skipping over when
+Instructs @command{tar} to mention the directories it is skipping when
operating on a @command{tar} archive. @xref{show-omitted-dirs}.
@opsummary{show-transformed-names}
Display file or member names after applying any transformations
(@pxref{transform}). In particular, when used in conjunction with one of
-archive creation operations it instructs tar to list the member names
-stored in the archive, as opposed to the actual file
+the archive creation operations it instructs @command{tar} to list the
+member names stored in the archive, as opposed to the actual file
names. @xref{listing member and file names}.
@opsummary{sparse}
@opsummary{sparse-version}
@item --sparse-version=@var{version}
-Specified the @dfn{format version} to use when archiving sparse
+Specifies the @dfn{format version} to use when archiving sparse
files. Implies @option{--sparse}. @xref{sparse}. For the description
of the supported sparse formats, @xref{Sparse Formats}.
@opsummary{strip-components}
@item --strip-components=@var{number}
Strip given @var{number} of leading components from file names before
-extraction.@footnote{This option was called @option{--strip-path} in
-version 1.14.} For example, if archive @file{archive.tar} contained
+extraction. For example, if archive @file{archive.tar} contained
@file{/some/file/name}, then running
@smallexample
rather than the data modification time stored in the archive.
@xref{Data Modification Times}.
+@opsummary{transform}
+@opsummary{xform}
+@item --transform=@var{sed-expr}
+@itemx --xform=@var{sed-expr}
+Transform file or member names using @command{sed} replacement expression
+@var{sed-expr}. For example,
+
+@smallexample
+$ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
+@end smallexample
+
+@noindent
+will add to @file{archive} files from the current working directory,
+replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
+discussion, @xref{transform}.
+
+To see transformed member names in verbose listings, use
+@option{--show-transformed-names} option
+(@pxref{show-transformed-names}).
+
@opsummary{uncompress}
@item --uncompress
@opsummary{use-compress-program}
@item --use-compress-program=@var{prog}
+@itemx -I=@var{prog}
Instructs @command{tar} to access the archive through @var{prog}, which is
presumed to be a compression program of some sort. @xref{gzip}.
@item --verbose
@itemx -v
-Specifies that @command{tar} should be more verbose about the operations its
-performing. This option can be specified multiple times for some
-operations to increase the amount of information displayed.
+Specifies that @command{tar} should be more verbose about the
+operations it is performing. This option can be specified multiple
+times for some operations to increase the amount of information displayed.
@xref{verbose}.
@opsummary{verify}
@item --volno-file=@var{file}
Used in conjunction with @option{--multi-volume}. @command{tar} will
-keep track of which volume of a multi-volume archive its working in
+keep track of which volume of a multi-volume archive it is working in
@var{file}. @xref{volno-file}.
@opsummary{wildcards}
@item -G @tab @ref{--incremental}.
+@item -J @tab @ref{--lzma}.
+
@item -K @tab @ref{--starting-file}.
@item -L @tab @ref{--tape-length}.
@item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
@ref{--portability}.
-The later usage is deprecated. It is retained for compatibility with
-the earlier versions of @GNUTAR{}. In the future releases
+The latter usage is deprecated. It is retained for compatibility with
+the earlier versions of @GNUTAR{}. In future releases
@option{-o} will be equivalent to @option{--no-same-owner} only.
@item -p @tab @ref{--preserve-permissions}.
@smallexample
tar (GNU tar) @value{VERSION}
-Copyright (C) 2006 Free Software Foundation, Inc.
+Copyright (C) 2008 Free Software Foundation, Inc.
This is free software. You may redistribute copies of it under the terms
of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.
@anchor{Progress information}
@cindex Progress information
-@opindex checkpoint
The @option{--checkpoint} option prints an occasional message
as @command{tar} reads or writes the archive. It is designed for
those who don't need the more detailed (and voluminous) output of
This example shows the default checkpoint message used by
@command{tar}. If you place a dot immediately after the equal
-sign, it will print a @samp{.} at each checkpoint. For example:
+sign, it will print a @samp{.} at each checkpoint@footnote{This is
+actually a shortcut for @option{--checkpoint=@var{n}
+--checkpoint-action=dot}. @xref{checkpoints, dot}.}. For example:
@smallexample
$ @kbd{tar -c --checkpoint=.1000} /var
...
@end smallexample
+The @option{--checkpoint} option provides a flexible mechanism for
+executing arbitrary actions upon hitting checkpoints, see the next
+section (@pxref{checkpoints}), for more information on it.
+
@opindex show-omitted-dirs
@anchor{show-omitted-dirs}
The @option{--show-omitted-dirs} option, when reading an archive---with
favor of the tape where the file appears earliest (closest to the
front of the tape). @xref{backup}.
+@node checkpoints
+@section Checkpoints
+@cindex checkpoints, defined
+@opindex checkpoint
+@opindex checkpoint-action
+
+A @dfn{checkpoint} is a moment of time before writing @var{n}th record to
+the archive (a @dfn{write checkpoint}), or before reading @var{n}th record
+from the archive (a @dfn{read checkpoint}). Checkpoints allow to
+periodically execute arbitrary actions.
+
+The checkpoint facility is enabled using the following option:
+
+@table @option
+@xopindex{checkpoint, defined}
+@item --checkpoint[=@var{n}]
+Schedule checkpoints before writing or reading each @var{n}th record.
+The default value for @var{n} is 10.
+@end table
+
+A list of arbitrary @dfn{actions} can be executed at each checkpoint.
+These actions include: pausing, displaying textual messages, and
+executing arbitrary external programs. Actions are defined using
+the @option{--checkpoint-action} option.
+
+@table @option
+@xopindex{checkpoint-action, defined}
+@item --checkpoint-action=@var{action}
+Execute an @var{action} at each checkpoint.
+@end table
+
+@cindex @code{echo}, checkpoint action
+The simplest value of @var{action} is @samp{echo}. It instructs
+@command{tar} to display the default message on the standard error
+stream upon arriving at each checkpoint. The default message is (in
+@acronym{POSIX} locale) @samp{Write checkpoint @var{n}}, for write
+checkpoints, and @samp{Read checkpoint @var{n}}, for read checkpoints.
+Here, @var{n} represents ordinal number of the checkpoint.
+
+In another locales, translated versions of this message are used.
+
+This is the default action, so running:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000 --checkpoint-action=echo} /var
+@end smallexample
+
+@noindent
+is equivalent to:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000} /var
+@end smallexample
+
+The @samp{echo} action also allows to supply a customized message.
+You do so by placing an equals sign and the message right after it,
+e.g.:
+
+@smallexample
+--checkpoint-action="echo=Hit %s checkpoint #%u"
+@end smallexample
+
+The @samp{%s} and @samp{%u} in the above example are
+@dfn{meta-characters}. The @samp{%s} meta-character is replaced with
+the @dfn{type} of the checkpoint: @samp{write} or
+@samp{read} (or a corresponding translated version in locales other
+than @acronym{POSIX}). The @samp{%u} meta-character is replaced with
+the ordinal number of the checkpoint. Thus, the above example could
+produce the following output when used with the @option{--create}
+option:
+
+@smallexample
+tar: Hit write checkpoint #10
+tar: Hit write checkpoint #20
+tar: Hit write checkpoint #30
+@end smallexample
+
+Aside from meta-character expansion, the message string is subject to
+@dfn{unquoting}, during which the backslash @dfn{escape sequences} are
+replaced with their corresponding @acronym{ASCII} characters
+(@pxref{escape sequences}). E.g. the following action will produce an
+audible bell and the message described above at each checkpoint:
+
+@smallexample
+--checkpoint-action='echo=\aHit %s checkpoint #%u'
+@end smallexample
+
+@cindex @code{bell}, checkpoint action
+There is also a special action which produces an audible signal:
+@samp{bell}. It is not equivalent to @samp{echo='\a'}, because
+@samp{bell} sends the bell directly to the console (@file{/dev/tty}),
+whereas @samp{echo='\a'} sends it to the standard error.
+
+@cindex @code{ttyout}, checkpoint action
+The @samp{ttyout=@var{string}} action outputs @var{string} to
+@file{/dev/tty}, so it can be used even if the standard output is
+redirected elsewhere. The @var{string} is subject to the same
+modifications as with @samp{echo} action. In contrast to the latter,
+@samp{ttyout} does not prepend @command{tar} executable name to the
+string, nor does it output a newline after it. For example, the
+following action will print the checkpoint message at the same screen
+line, overwriting any previous message:
+
+@smallexample
+--checkpoint-action="ttyout=\rHit %s checkpoint #%u"
+@end smallexample
+
+@cindex @code{dot}, checkpoint action
+Another available checkpoint action is @samp{dot} (or @samp{.}). It
+instructs @command{tar} to print a single dot on the standard listing
+stream, e.g.:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000 --checkpoint-action=dot} /var
+...
+@end smallexample
+
+For compatibility with previous @GNUTAR{} versions, this action can
+be abbreviated by placing a dot in front of the checkpoint frequency,
+as shown in the previous section.
+
+@cindex @code{sleep}, checkpoint action
+Yet another action, @samp{sleep}, pauses @command{tar} for a specified
+amount of seconds. The following example will stop for 30 seconds at each
+checkpoint:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000 --checkpoint-action=sleep=30}
+@end smallexample
+
+@cindex @code{exec}, checkpoint action
+Finally, the @code{exec} action executes a given external program.
+For example:
+
+@smallexample
+$ @kbd{tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint}
+@end smallexample
+
+This program is executed using @command{/bin/sh -c}, with no
+additional arguments. Its exit code is ignored. It gets a copy of
+@command{tar}'s environment plus the following variables:
+
+@table @env
+@vrindex TAR_VERSION, checkpoint script environment
+@item TAR_VERSION
+@GNUTAR{} version number.
+
+@vrindex TAR_ARCHIVE, checkpoint script environment
+@item TAR_ARCHIVE
+The name of the archive @command{tar} is processing.
+
+@vrindex TAR_BLOCKING_FACTOR, checkpoint script environment
+@item TAR_BLOCKING_FACTOR
+Current blocking factor (@pxref{Blocking}).
+
+@vrindex TAR_CHECKPOINT, checkpoint script environment
+@item TAR_CHECKPOINT
+Number of the checkpoint.
+
+@vrindex TAR_SUBCOMMAND, checkpoint script environment
+@item TAR_SUBCOMMAND
+A short option describing the operation @command{tar} is executing.
+@xref{Operations}, for a complete list of subcommand options.
+
+@vrindex TAR_FORMAT, checkpoint script environment
+@item TAR_FORMAT
+Format of the archive being processed. @xref{Formats}, for a complete
+list of archive format names.
+@end table
+
+Any number of actions can be defined, by supplying several
+@option{--checkpoint-action} options in the command line. For
+example, the command below displays two messages, pauses
+execution for 30 seconds and executes the @file{/sbin/cpoint} script:
+
+@example
+@group
+$ @kbd{tar -c -f arc.tar \
+ --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
+ --checkpoint-action='echo=Sleeping for 30 seconds' \
+ --checkpoint-action='sleep=30' \
+ --checkpoint-action='exec=/sbin/cpoint'}
+@end group
+@end example
+
+This example also illustrates the fact that
+@option{--checkpoint-action} can be used without
+@option{--checkpoint}. In this case, the default checkpoint frequency
+(at each 10th record) is assumed.
+
@node interactive
@section Asking for Confirmation During Operations
@cindex Interactive operation
Specifies that @command{tar} should use @var{user} as the owner of members
when creating archives, instead of the user associated with the source
file. The argument @var{user} can be either an existing user symbolic
-name, or a decimal numeric user ID.
+name, or a decimal numeric user @acronym{ID}.
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
@item --group=@var{group}
@opindex group
-Files added to the @command{tar} archive will have a group id of @var{group},
+Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
rather than the group from the source file. The argument @var{group}
-can be either an existing group symbolic name, or a decimal numeric group ID.
+can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
@end table
@node Ignore Failed Read
The @option{--read-full-records} (@option{-B}) 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
+machine. This is because on @acronym{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.
The command can obtain the information about the file it processes
from the following environment variables:
-@table @var
+@table @env
@vrindex TAR_FILETYPE, to-command environment
@item TAR_FILETYPE
Type of the file. It is a single letter with the following meaning:
with the @option{--atime-preserve=replace} option), or if you set the clock
backwards.
+@anchor{device numbers}
+@cindex Device numbers, using in incremental backups
Metadata stored in snapshot files include device numbers, which,
-obviously is supposed to be a non-volatile value. However, it turns
-out that NFS devices have undependable values when an automounter
+obviously are supposed to be a non-volatile values. However, it turns
+out that @acronym{NFS} devices have undependable values when an automounter
gets in the picture. This can lead to a great deal of spurious
redumping in incremental dumps, so it is somewhat useless to compare
-two NFS devices numbers over time. The solution implemented currently
-is to 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.
+two @acronym{NFS} devices numbers over time. The solution implemented
+currently is to considers all @acronym{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.
+
+Apart from using @acronym{NFS}, there are a number of cases where
+relying on device numbers can cause spurious redumping of unmodified
+files. For example, this occurs when archiving @acronym{LVM} snapshot
+volumes. To avoid this, use @option{--no-check-device} option:
+
+@table @option
+@xopindex{no-check-device, described}
+@item --no-check-device
+Do not rely on device numbers when preparing a list of changed files
+for an incremental dump.
+
+@xopindex{check-device, described}
+@item --check-device
+Use device numbers when preparing a list of changed files
+for an incremental dump. This is the default behavior. The purpose
+of this option is to undo the effect of the @option{--no-check-device}
+if it was given in @env{TAR_OPTIONS} environment variable
+(@pxref{TAR_OPTIONS}).
+@end table
+
+There is also another way to cope with changing device numbers. It is
+described in detail in @ref{Fixing Snapshot Files}.
Note that incremental archives use @command{tar} extensions and may
not be readable by non-@acronym{GNU} versions of the @command{tar} program.
machine where the scripts are run (i.e., 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.
+host as long as it can access the file system through @acronym{NFS}.
If the list of file systems is very long you may wish to put it
in a separate file. This file is usually named
@defvr {Backup variable} DIRLIST
-A path to the file containing the list of the file systems to backup
+The name of the file that contains a list of file systems to backup
or restore. By default it is @file{/etc/backup/dirs}.
@end defvr
@defvr {Backup variable} FILELIST
-A path to the file containing the list of the individual files to backup
+The name of the file that contains a list of individual files to backup
or restore. By default it is @file{/etc/backup/files}.
@end defvr
Name or IP address of the host machine being dumped or restored.
@item fs
-Full path name to the file system being dumped or restored.
+Full file name of the file system being dumped or restored.
@item fsname
File system name with directory separators replaced with colons. This
@multitable @columnfractions 0.20 0.60
@headitem Escape @tab Replaced with
-@item \a @tab Audible bell (ASCII 7)
-@item \b @tab Backspace (ASCII 8)
-@item \f @tab Form feed (ASCII 12)
-@item \n @tab New line (ASCII 10)
-@item \r @tab Carriage return (ASCII 13)
-@item \t @tab Horizontal tabulation (ASCII 9)
-@item \v @tab Vertical tabulation (ASCII 11)
-@item \? @tab ASCII 127
-@item \@var{n} @tab ASCII @var{n} (@var{n} should be an octal number
+@item \a @tab Audible bell (@acronym{ASCII} 7)
+@item \b @tab Backspace (@acronym{ASCII} 8)
+@item \f @tab Form feed (@acronym{ASCII} 12)
+@item \n @tab New line (@acronym{ASCII} 10)
+@item \r @tab Carriage return (@acronym{ASCII} 13)
+@item \t @tab Horizontal tabulation (@acronym{ASCII} 9)
+@item \v @tab Vertical tabulation (@acronym{ASCII} 11)
+@item \? @tab @acronym{ASCII} 127
+@item \@var{n} @tab @acronym{ASCII} @var{n} (@var{n} should be an octal number
of up to 3 digits)
@end multitable
@option{--files-from}.
@table @option
-@opindex null
+@xopindex{null, described}
@item --null
Only consider @code{NUL} terminated file names, instead of files that
terminate in a newline.
+
+@xopindex{no-null, described}
+@item --no-null
+Undo the effect of any previous @option{--null} option.
@end table
The @option{--null} option is just like the one in @acronym{GNU}
$ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
@end smallexample
-@FIXME{say anything else here to conclude the section?}
+The @option{--no-null} option can be used if you need to read both
+zero-terminated and newline-terminated files on the same command line.
+For example, if @file{flist} is a newline-terminated file, then the
+following command can be used to combine it with the above command:
+
+@smallexample
+@group
+$ @kbd{find . -size +800 -print0 |
+ tar -c -f big.tar --null -T - --no-null -T flist}
+@end group
+@end smallexample
+
+This example uses short options for typographic reasons, to avoid
+very long lines.
+
+@GNUTAR is able to automatically detect null-terminated file lists, so
+it is safe to use them even without the @option{--null} option. In
+this case @command{tar} will print a warning and continue reading such
+a file as if @option{--null} were actually given:
+
+@smallexample
+@group
+$ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
+tar: -: file name read contains nul character
+@end group
+@end smallexample
+
+The null terminator, however, remains in effect only for this
+particular file, any following @option{-T} options will assume
+newline termination. Of course, the null autodetection applies
+to these eventual surplus @option{-T} options as well.
@node exclude
@section Excluding Some Files
single line @file{*.o}, no files whose names end in @file{.o} will be
added to the archive.
+Notice, that lines from @var{file} are read verbatim. One of the
+frequent errors is leaving some extra whitespace after a file name,
+which is difficult to catch using text editors.
+
+However, empty lines are OK.
+
+@cindex version control system, excluding files
+@cindex VCS, excluding files
+@cindex SCCS, excluding files
+@cindex RCS, excluding files
+@cindex CVS, excluding files
+@cindex SVN, excluding files
+@cindex git, excluding files
+@cindex Bazaar, excluding files
+@cindex Arch, excluding files
+@cindex Mercurial, excluding files
+@cindex Darcs, excluding files
+@table @option
+@opindex exclude-vcs
+@item --exclude-vcs
+Exclude files and directories used by following version control
+systems: @samp{CVS}, @samp{RCS}, @samp{SCCS}, @samp{SVN}, @samp{Arch},
+@samp{Bazaar}, @samp{Mercurial}, and @samp{Darcs}.
+@end table
+
+As of version @value{VERSION}, the following files are excluded:
+
+@itemize @bullet
+@item @file{CVS/}, and everything under it
+@item @file{RCS/}, and everything under it
+@item @file{SCCS/}, and everything under it
+@item @file{.git/}, and everything under it
+@item @file{.gitignore}
+@item @file{.cvsignore}
+@item @file{.svn/}, and everything under it
+@item @file{.arch-ids/}, and everything under it
+@item @file{@{arch@}/}, and everything under it
+@item @file{=RELEASE-ID}
+@item @file{=meta-update}
+@item @file{=update}
+@item @file{.bzr}
+@item @file{.bzrignore}
+@item @file{.bzrtags}
+@item @file{.hg}
+@item @file{.hgignore}
+@item @file{.hgrags}
+@item @file{_darcs}
+@end itemize
+
@findex exclude-caches
When creating an archive, the @option{--exclude-caches} option family
causes @command{tar} to exclude all directories that contain a @dfn{cache
use to hold regenerable, non-precious data, so that such data can be
more easily excluded from backups.
-There are three @samp{exclude-caches} option, providing a different
+There are three @samp{exclude-caches} options, each providing a different
exclusion semantics:
@table @option
@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
+The main operating mode of @command{tar} does not act on a file name
+explicitly listed on the command line, if one of its file name
components is excluded. In the example above, if
you create an archive and exclude files that end with @samp{*.o}, but
explicitly name the file @samp{dir.o/foo} after all the options have been
@itemize @bullet
@item Non-printable control characters:
-
+@anchor{escape sequences}
@multitable @columnfractions 0.20 0.10 0.60
-@headitem Character @tab ASCII @tab Character name
+@headitem Character @tab @acronym{ASCII} @tab Character name
@item \a @tab 7 @tab Audible bell
@item \b @tab 8 @tab Backspace
@item \f @tab 12 @tab Form feed
@item \v @tab 11 @tab Vertical tabulation
@end multitable
-@item Space (ASCII 32)
+@item Space (@acronym{ASCII} 32)
@item Single and double quotes (@samp{'} and @samp{"})
./a'single'quote
./a"double"quote
./a\backslash
-./a tab
+./a tab
./a
newline
@end group
'./a'\''single'\''quote'
'./a"double"quote'
'./a\backslash'
-'./a tab'
+'./a tab'
'./a
newline'
@end group
'./a'\''single'\''quote'
'./a"double"quote'
'./a\backslash'
-'./a tab'
+'./a tab'
'./a
newline'
@end group
@command{Tar} archives contain detailed information about files stored
in them and full file names are part of that information. When
-storing file to an archive, its file name is recorded in the archive
+storing file to an archive, its file name is recorded in it,
along with the actual file contents. When restoring from an archive,
a file is created on disk with exactly the same name as that stored
in the archive. In the majority of cases this is the desired behavior
cases it is desirable to store files under differing names in the
archive.
-@GNUTAR{} provides two options for these needs.
+@GNUTAR{} provides several options for these needs.
@table @option
@opindex strip-components
two leading components (@file{usr/} and @file{include/}) off the file
name.
-If you add to the above invocation @option{--verbose} (@option{-v})
-option, you will note that the verbose listing still contains the
+If you add the @option{--verbose} (@option{-v}) option to the invocation
+above, you will note that the verbose listing still contains the
full file name, with the two removed components still in place. This
can be inconvenient, so @command{tar} provides a special option for
altering this behavior:
@end group
@end smallexample
-Notice that in both cases the file is @file{stdlib.h} extracted to the
+Notice that in both cases the file @file{stdlib.h} is extracted to the
current working directory, @option{--show-transformed-names} affects
only the way its name is displayed.
@table @option
@opindex transform
+@opindex xform
@item --transform=@var{expression}
+@itemx --xform=@var{expression}
Modify file names using supplied @var{expression}.
@end table
@var{regexp} and @var{replace} are described in detail in
@ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
+Any delimiter can be used in lieue of @samp{/}, the only requirement being
+that it be used consistently throughout the expression. For example,
+the following two expressions are equivalent:
+
+@smallexample
+@group
+s/one/two/
+s,one,two,
+@end group
+@end smallexample
+
+Changing delimiters is often useful when the @var{regex} contains
+slashes. For example, it is more convenient to write @code{s,/,-,} than
+@code{s/\//-/}.
+
+As in @command{sed}, you can give several replace expressions,
+separated by a semicolon.
+
Supported @var{flags} are:
@table @samp
@item @var{number}
Only replace the @var{number}th match of the @var{regexp}.
-Note: the @var{posix} standard does not specify what should happen
+Note: the @acronym{POSIX} standard does not specify what should happen
when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
follows the GNU @command{sed} implementation in this regard, so
the interaction is defined to be: ignore matches before the
@end table
-Any delimiter can be used in lieue of @samp{/}, the only requirement being
-that it be used consistently throughout the expression. For example,
-the following two expressions are equivalent:
+In addition, several @dfn{transformation scope} flags are supported,
+that control to what files transformations apply. These are:
+
+@table @samp
+@item r
+Apply transformation to regular archive members.
+
+@item R
+Do not apply transformation to regular archive members.
+
+@item s
+Apply transformation to symbolic link targets.
+
+@item S
+Do not apply transformation to symbolic link targets.
+
+@item h
+Apply transformation to hard link targets.
+
+@item H
+Do not apply transformation to hard link targets.
+@end table
+
+Default is @samp{rsh}, which means to apply tranformations to both archive
+members and targets of symbolic and hard links.
+
+Default scope flags can also be changed using @samp{flags=} statement
+in the transform expression. The flags set this way remain in force
+until next @samp{flags=} statement or end of expression, whichever
+occurs first. For example:
@smallexample
-@group
-s/one/two/
-s,one,two,
-@end group
+ --transform 'flags=S;s|^|/usr/local/|'
@end smallexample
-Changing delimiters is often useful when the @var{regex} contains
-slashes. For example, it is more convenient to write @code{s,/,-,} than
-@code{s/\//-/}.
-
Here are several examples of @option{--transform} usage:
@enumerate
$ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
@end smallexample
+@item Convert each file name to lower case:
+
+@smallexample
+$ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
+@end smallexample
+
@item Prepend @file{/prefix/} to each file name:
@smallexample
$ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
@end smallexample
-@item Convert each file name to lower case:
+@item Archive the @file{/lib} directory, prepending @samp{/usr/local}
+to each archive member:
@smallexample
-$ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
+$ @kbd{tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib}
@end smallexample
-
@end enumerate
+Notice the use of flags in the last example. The @file{/lib}
+directory often contains many symbolic links to files within it.
+It may look, for example, like this:
+
+@smallexample
+$ @kbd{ls -l}
+drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
+-rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
+lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
+...
+@end smallexample
+
+Using the expression @samp{s,^,/usr/local/,} would mean adding
+@samp{/usr/local} to both regular archive members and to link
+targets. In this case, @file{/lib/libc.so.6} would become:
+
+@smallexample
+ /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
+@end smallexample
+
+This is definitely not desired. To avoid this, the @samp{S} flag
+are used, which excludes symbolic link targets from filename
+transformations. The result is:
+
+@smallexample
+$ @kbd{tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
+ --show-transformed /lib}
+drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
+-rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
+lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 ->
+libc-2.3.2.so
+@end smallexample
+
Unlike @option{--strip-components}, @option{--transform} can be used
in any @GNUTAR{} operation mode. For example, the following command
adds files to the archive while replacing the leading @file{usr/}
together, then @option{--transform} is applied first, and the required
number of components is then stripped from its result.
+You can use as many @option{--transform} options in a single command
+line as you want. The specified expressions will then be applied in
+order of their appearance. For example, the following two invocations
+are equivalent:
+
+@smallexample
+$ @kbd{tar -cf arch.tar --transform='s,/usr/var,/var/' \
+ --transform='s,/usr/local,/usr/,'}
+$ @kbd{tar -cf arch.tar \
+ --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'}
+@end smallexample
+
@node after
@section Operating Only on New Files
@UNREVISED
For example:
@smallexample
-$ @kbd{(cd / && tar -c -f archive.tar home)}
-# @i{or}:
-$ @kbd{tar -c -f archive.tar -C / home}
+$ @kbd{tar -c -f archive.tar -C / home}
@end smallexample
@include getdate.texi
features were implemented in a way incompatible with other archive
formats.
-Archives in @samp{gnu} format are able to hold pathnames of unlimited
+Archives in @samp{gnu} format are able to hold file names of unlimited
length.
@item oldgnu
@item The maximum length of a symbolic link is limited to 99 characters.
@item It is impossible to store special files (block and character
devices, fifos etc.)
-@item Maximum value of user or group ID is limited to 2097151 (7777777
+@item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777
octal)
@item V7 archives do not contain symbolic ownership information (user
and group name of the file owner).
This format has traditionally been used by Automake when producing
Makefiles. This practice will change in the future, in the meantime,
-however this means that projects containing filenames more than 99
+however this means that projects containing file names more than 99
characters long will not be able to use @GNUTAR{} @value{VERSION} and
Automake prior to 1.9.
@enumerate
@item The maximum length of a file name is limited to 256 characters,
-provided that the filename can be split at directory separator in
+provided that the file name can be split at a directory separator in
two parts, first of them being at most 155 bytes long. So, in most
cases the maximum file name length will be shorter than 256
characters.
@item posix
Archive format defined by @acronym{POSIX.1-2001} specification. This is the
most flexible and feature-rich format. It does not impose any
-restrictions on file sizes or filename lengths. This format is quite
+restrictions on file sizes or file name lengths. This format is quite
recent, so not all tar implementations are able to handle it properly.
However, this format is designed in such a way that any tar
implementation able to read @samp{ustar} archives will be able to read
formats:
@multitable @columnfractions .10 .20 .20 .20 .20
-@headitem Format @tab UID @tab File Size @tab Path Name @tab Devn
+@headitem Format @tab UID @tab File Size @tab File Name @tab Devn
@item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
@item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
@item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
@cindex Compressed archives
@cindex Storing archives in compressed format
+@cindex gzip
+@cindex bzip2
+@cindex lzma
+@cindex lzop
+@cindex compress
@GNUTAR{} is able to create and read compressed archives. It supports
-@command{gzip} and @command{bzip2} compression programs. For backward
-compatibility, it also supports @command{compress} command, although
-we strongly recommend against using it, since there is a patent
-covering the algorithm it uses and you could be sued for patent
-infringement merely by running @command{compress}! Besides, it is less
-effective than @command{gzip} and @command{bzip2}.
+@command{gzip}, @command{bzip2}, @command{lzma} and @command{lzop} compression
+programs. For backward compatibility, it also supports
+@command{compress} command, although we strongly recommend against
+using it, because it is by far less effective than other compression
+programs@footnote{It also had patent problems in the past.}.
Creating a compressed archive is simple: you just specify a
@dfn{compression option} along with the usual archive creation
commands. The compression option is @option{-z} (@option{--gzip}) to
create a @command{gzip} compressed archive, @option{-j}
-(@option{--bzip2}) to create a @command{bzip2} compressed archive, and
+(@option{--bzip2}) to create a @command{bzip2} compressed archive,
+@option{-J} (@option{--lzma}) to create an @asis{LZMA} compressed
+archive, @option{--lzop} to create an @asis{LSOP} archive, and
@option{-Z} (@option{--compress}) to use @command{compress} program.
For example:
$ @kbd{tar cfz archive.tar.gz .}
@end smallexample
+You can also let @GNUTAR{} select the compression program basing on
+the suffix of the archive file name. This is done using
+@option{--auto-compress} (@option{-a}) command line option. For
+example, the following invocation will use @command{bzip2} for
+compression:
+
+@smallexample
+$ @kbd{tar cfa archive.tar.bz2 .}
+@end smallexample
+
+@noindent
+whereas the following one will use @command{lzma}:
+
+@smallexample
+$ @kbd{tar cfa archive.tar.lzma .}
+@end smallexample
+
+For a complete list of file name suffixes recognized by @GNUTAR{},
+@ref{auto-compress}.
+
Reading compressed archive is even simpler: you don't need to specify
any additional options as @GNUTAR{} recognizes its format
automatically. Thus, the following commands will list and extract the
$ @kbd{tar xf archive.tar.gz}
@end smallexample
+The format recognition algorithm is based on @dfn{signatures}, a
+special byte sequences in the beginning of file, that are specific for
+certain compression formats. If this approach fails, @command{tar}
+falls back to using archive name suffix to determine its format
+(@xref{auto-compress}, for a list of recognized suffixes).
+
The only case when you have to specify a decompression option while
reading the archive is when reading from a pipe or from a tape drive
that does not support random access. However, in this case @GNUTAR{}
Notice also, that there are several restrictions on operations on
compressed archives. First of all, compressed archives cannot be
-modified, i.e., you cannot update (@option{--update} (@option{-u})) them or delete
-(@option{--delete}) members from them. Likewise, you cannot append
-another @command{tar} archive to a compressed archive using
-@option{--append} (@option{-r})). Secondly, multi-volume archives cannot be
-compressed.
+modified, i.e., you cannot update (@option{--update} (@option{-u}))
+them or delete (@option{--delete}) members from them or
+add (@option{--append} (@option{-r})) members to them. Likewise, you
+cannot append another @command{tar} archive to a compressed archive using
+@option{--concatenate} (@option{-A})). Secondly, multi-volume
+archives cannot be compressed.
The following table summarizes compression options used by @GNUTAR{}.
@table @option
+@anchor{auto-compress}
+@opindex auto-compress
+@item --auto-compress
+@itemx -a
+Select a compression program to use by the archive file name
+suffix. The following suffixes are recognized:
+
+@multitable @columnfractions 0.3 0.6
+@headitem Suffix @tab Compression program
+@item @samp{.gz} @tab @command{gzip}
+@item @samp{.tgz} @tab @command{gzip}
+@item @samp{.taz} @tab @command{gzip}
+@item @samp{.Z} @tab @command{compress}
+@item @samp{.taZ} @tab @command{compress}
+@item @samp{.bz2} @tab @command{bzip2}
+@item @samp{.tz2} @tab @command{bzip2}
+@item @samp{.tbz2} @tab @command{bzip2}
+@item @samp{.tbz} @tab @command{bzip2}
+@item @samp{.lzma} @tab @command{lzma}
+@item @samp{.tlz} @tab @command{lzma}
+@item @samp{.lzo} @tab @command{lzop}
+@end multitable
+
@opindex gzip
@opindex ungzip
@item -z
@itemx --bzip2
Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
+@opindex lzma
+@item --lzma
+@itemx -J
+Filter the archive through @command{lzma}. Otherwise like @option{--gzip}.
+
+@opindex lzop
+@item --lzop
+Filter the archive through @command{lzop}. Otherwise like
+@option{--gzip}.
+
@opindex compress
@opindex uncompress
@item -Z
@itemx --uncompress
Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
-The @acronym{GNU} Project recommends you not use
-@command{compress}, because there is a patent covering the algorithm it
-uses. You could be sued for patent infringement merely by running
-@command{compress}.
-
@opindex use-compress-program
@item --use-compress-program=@var{prog}
+@itemx -I=@var{prog}
Use external compression program @var{prog}. Use this option if you
have a compression program that @GNUTAR{} does not support. There
are two requirements to which @var{prog} should comply:
archive signed with your private key:
@smallexample
-$ @kbd{tar -cf foo.tar.gpgz --use-compress=gpgz .}
+$ @kbd{tar -cf foo.tar.gpgz -Igpgz .}
@end smallexample
@noindent
-Likewise, the following command will list its contents:
+Likewise, the command below will list its contents:
@smallexample
-$ @kbd{tar -tf foo.tar.gpgz --use-compress=gpgz .}
+$ @kbd{tar -tf foo.tar.gpgz -Igpgz .}
@end smallexample
@ignore
they occupy. Also, the @code{suid} or @code{sgid} attributes of
files are easily and silently lost when files are given away.
-When writing an archive, @command{tar} writes the user id and user name
-separately. If it can't find a user name (because the user id is not
+When writing an archive, @command{tar} writes the user @acronym{ID} and user name
+separately. If it can't find a user name (because the user @acronym{ID} is not
in @file{/etc/passwd}), then it does not write one. When restoring,
it tries to look the name (if one was written) up in
-@file{/etc/passwd}. If it fails, then it uses the user id stored in
+@file{/etc/passwd}. If it fails, then it uses the user @acronym{ID} stored in
the archive instead.
@opindex no-same-owner
@menu
* Portable Names:: Portable Names
* dereference:: Symbolic Links
+* hard links:: Hard Links
* old:: Old V7 Archives
* ustar:: Ustar Archives
* gnu:: GNU and old GNU format archives.
@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
+only @acronym{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
symbolic links, and moreover, your distribution might be unusable if
it contains unresolved symbolic links.
+@node hard links
+@subsection Hard Links
+@UNREVISED{}
+@cindex File names, using hard links
+@cindex hard links, dereferencing
+@cindex dereferencing hard links
+
+Normally, when @command{tar} archives a hard link, it writes a
+block to the archive naming the target of the link (a @samp{1} type
+block). In that way, the actual file contents is stored in file only
+once. For example, consider the following two files:
+
+@smallexample
+@group
+$ ls
+-rw-r--r-- 2 gray staff 4 2007-10-30 15:11 one
+-rw-r--r-- 2 gray staff 4 2007-10-30 15:11 jeden
+@end group
+@end smallexample
+
+Here, @file{jeden} is a link to @file{one}. When archiving this
+directory with a verbose level 2, you will get an output similar to
+the following:
+
+@smallexample
+$ tar cfvv ../archive.tar .
+drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
+-rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
+hrw-r--r-- gray/staff 0 2007-10-30 15:11 ./one link to ./jeden
+@end smallexample
+
+The last line shows that, instead of storing two copies of the file,
+@command{tar} stored it only once, under the name @file{jeden}, and
+stored file @file{one} as a hard link to this file.
+
+It may be important to know that all hard links to the given file are
+stored in the archive. For example, this may be necessary for exact
+reproduction of the file system. The following option does that:
+
+@table @option
+@xopindex{check-links, described}
+@item --check-links
+@itemx -l
+Check the number of links dumped for each processed file. If this
+number does not match the total number of hard links for the file, print
+a warning message.
+@end table
+
+For example, trying to archive only file @file{jeden} with this option
+produces the following diagnostics:
+
+@smallexample
+$ tar -c -f ../archive.tar jeden
+tar: Missing links to `jeden'.
+@end smallexample
+
+Although creating special records for hard links helps keep a faithful
+record of the file system contents and makes archives more compact, it
+may present some difficulties when extracting individual members from
+the archive. For example, trying to extract file @file{one} from the
+archive created in previous examples produces, in the absense of file
+@file{jeden}:
+
+@smallexample
+$ tar xf archive.tar ./one
+tar: ./one: Cannot hard link to `./jeden': No such file or directory
+tar: Error exit delayed from previous errors
+@end smallexample
+
+The reason for this behavior is that @command{tar} cannot seek back in
+the archive to the previous member (in this case, @file{one}), to
+extract it@footnote{There are plans to fix this in future releases.}.
+If you wish to avoid such problems at the cost of a bigger archive,
+use the following option:
+
+@table @option
+@xopindex{hard-dereference, described}
+@item --hard-dereference
+Dereference hard links and store the files they refer to.
+@end table
+
+For example, trying this option on our two sample files, we get two
+copies in the archive, each of which can then be extracted
+independently of the other:
+
+@smallexample
+@group
+$ tar -c -vv -f ../archive.tar --hard-dereference .
+drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
+-rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
+-rw-r--r-- gray/staff 4 2007-10-30 15:11 ./one
+@end group
+@end smallexample
+
@node old
@subsection Old V7 Archives
@cindex Format, old style
@command{tar} programs that follow it.
In the majority of cases, @command{tar} will be configured to create
-this format by default. This will change in the future releases, since
+this format by default. This will change in future releases, since
we plan to make @samp{POSIX} format the default.
To force creation a @GNUTAR{} archive, use option
to ignore any keywords matching the given @var{pattern} in the extended
header records. In both cases, matching is performed using the pattern
matching notation described in @acronym{POSIX 1003.2}, 3.13
-(@pxref{wildcards}). For example:
+(@pxref{wildcards}). For example:
@smallexample
--pax-option delete=security.*
@multitable @columnfractions .25 .55
@headitem Meta-character @tab Replaced By
@item %d @tab The directory name of the file, equivalent to the
-result of the @command{dirname} utility on the translated pathname.
-@item %f @tab The filename of the file, equivalent to the result
-of the @command{basename} utility on the translated pathname.
-@item %p @tab The process ID of the @command{tar} process.
+result of the @command{dirname} utility on the translated file name.
+@item %f @tab The name of the file with the directory information
+stripped, equivalent to the result of the @command{basename} utility
+on the translated file name.
+@item %p @tab The process @acronym{ID} of the @command{tar} process.
@item %% @tab A @samp{%} character.
@end multitable
@item %n @tab An integer that represents the
sequence number of the global extended header record in the archive,
starting at 1.
-@item %p @tab The process ID of the @command{tar} process.
+@item %p @tab The process @acronym{ID} of the @command{tar} process.
@item %% @tab A @samp{%} character.
@end multitable
@subsection Checksumming Problems
SunOS and HP-UX @command{tar} fail to accept archives created using
-@GNUTAR{} and containing non-ASCII file names, that
+@GNUTAR{} and containing non-@acronym{ASCII} file names, that
is, file names having characters with the eight bit set, because they
use signed checksums, while @GNUTAR{} uses unsigned
checksums while creating archives, as per @acronym{POSIX} standards. On
two's-complement base-256 notation to store values that do not fit
into standard @acronym{ustar} range. Such archives can generally be
read only by a @GNUTAR{} implementation. Moreover, they sometimes
-cannot be correctly restored on another hosts even by @GNUTAR{}. For
+cannot be correctly restored on another hosts even by @GNUTAR{}. For
example, using two's complement representation for negative time
stamps that assumes a signed 32-bit @code{time_t} generates archives
that are not portable to hosts with differing @code{time_t}
result of the @command{dirname} utility on its full name.
@item %f @tab The file name of the file, equivalent to the result
of the @command{basename} utility on its full name.
-@item %p @tab The process ID of the @command{tar} process that
+@item %p @tab The process @acronym{ID} of the @command{tar} process that
created the archive.
@item %n @tab Ordinal number of this particular part.
@end multitable
For example, if the file @file{var/longfile} was split during archive
creation between three volumes, and the creator @command{tar} process
-had process ID @samp{27962}, then the member names will be:
+had process @acronym{ID} @samp{27962}, then the member names will be:
@smallexample
var/longfile
name was @file{@var{dir}/@var{name}}, then the condensed file will be
named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
@var{n} is a decimal number@footnote{technically speaking, @var{n} is a
-@dfn{process ID} of the @command{tar} process which created the
+@dfn{process @acronym{ID}} of the @command{tar} process which created the
archive (@pxref{PAX keywords}).}.
To expand a version 1.0 file, run @command{xsparse} as follows:
@FIXME{Reorganize the following material}
The @command{cpio} archive formats, like @command{tar}, do have maximum
-pathname lengths. The binary and old ASCII formats have a max path
-length of 256, and the new ASCII and CRC ASCII formats have a max
-path length of 1024. @acronym{GNU} @command{cpio} can read and write archives
-with arbitrary pathname lengths, but other @command{cpio} implementations
+file name lengths. The binary and old @acronym{ASCII} formats have a maximum file
+length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max
+file length of 1024. @acronym{GNU} @command{cpio} can read and write archives
+with arbitrary file name lengths, but other @command{cpio} implementations
may crash unexplainedly trying to read them.
-@command{tar} handles symbolic links in the form in which it comes in BSD;
+@command{tar} handles symbolic links in the form in which it comes in @acronym{BSD};
@command{cpio} doesn't handle symbolic links in the form in which it comes
in System V prior to SVR4, and some vendors may have added symlinks
to their system without enhancing @command{cpio} to know about them.
Others may have enhanced it in a way other than the way I did it
at Sun, and which was adopted by AT&T (and which is, I think, also
present in the @command{cpio} that Berkeley picked up from AT&T and put
-into a later BSD release---I think I gave them my changes).
+into a later @acronym{BSD} release---I think I gave them my changes).
(SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
can handle @command{tar} format input, and write it on output, and it
@command{cpio} handles special files; traditional @command{tar} doesn't.
-@command{tar} comes with V7, System III, System V, and BSD source;
-@command{cpio} comes only with System III, System V, and later BSD
+@command{tar} comes with V7, System III, System V, and @acronym{BSD} source;
+@command{cpio} comes only with System III, System V, and later @acronym{BSD}
(4.3-tahoe and later).
@command{tar}'s way of handling multiple hard links to a file can handle
-file systems that support 32-bit inumbers (e.g., the BSD file system);
-@command{cpio}s way requires you to play some games (in its "binary"
-format, i-numbers are only 16 bits, and in its "portable ASCII" format,
-they're 18 bits---it would have to play games with the "file system ID"
-field of the header to make sure that the file system ID/i-number pairs
+file systems that support 32-bit inumbers (e.g., the @acronym{BSD} file system);
+@command{cpio}s way requires you to play some games (in its ``binary''
+format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
+they're 18 bits---it would have to play games with the "file system @acronym{ID}"
+field of the header to make sure that the file system @acronym{ID}/i-number pairs
of different files were always different), and I don't know which
@command{cpio}s, if any, play those games. Those that don't might get
confused and think two files are the same file when they're not, and
This means that the @option{--append}, @option{--concatenate}, and
@option{--delete} commands will not work on any other kind of file.
Some media simply cannot be backspaced, which means these commands and
-options will never be able to work on them. These non-backspacing
+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
@xopindex{read-full-records, short description}
@item -B
@itemx --read-full-records
-Reblock as we read (for reading 4.2BSD pipes).
+Reblock as we read (for reading 4.2@acronym{BSD} pipes).
If @option{--read-full-records} is used, @command{tar}
will not panic if an attempt to read a record from the archive does
-not return a full record. Instead, @command{tar} will keep reading
+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
+because on @acronym{BSD} Unix systems, a read of a pipe will return however
much happens to be in the pipe, even if it is less than @command{tar}
requested. If this option was not used, @command{tar} would fail as
soon as it read an incomplete record from the pipe.
@item TAR_ARCHIVE
The name of the archive @command{tar} is processing.
+@vrindex TAR_BLOCKING_FACTOR, info script environment variable
+@item TAR_BLOCKING_FACTOR
+Current blocking factor (@pxref{Blocking}.
+
@vrindex TAR_VOLUME, info script environment variable
@item TAR_VOLUME
Ordinal number of the volume @command{tar} is about to start.
@vrindex TAR_SUBCOMMAND, info script environment variable
@item TAR_SUBCOMMAND
-Short option describing the operation @command{tar} is executing
+A short option describing the operation @command{tar} is executing
@xref{Operations}, for a complete list of subcommand options.
@vrindex TAR_FORMAT, info script environment variable
case $TAR_SUBCOMMAND in
-c) ;;
-d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
- ;;
+ ;;
*) exit 1
esac
@end group
@end smallexample
-The same script cant be used while listing, comparing or extracting
+The same script can be used while listing, comparing or extracting
from the created archive. For example:
@smallexample
Right margin of the text output. Used for wrapping.
@end deftypevr
+@node Fixing Snapshot Files
+@appendix Fixing Snapshot Files
+@include tar-snapshot-edit.texi
+
@node Tar Internals
@appendix Tar Internals
@include intern.texi
projects / chaz / tar / blobdiff