@include value.texi
@defcodeindex op
+@defcodeindex kw
@c Put everything in one index (arbitrarily chosen to be the concept index).
@syncodeindex fn cp
@syncodeindex ky cp
@syncodeindex pg cp
@syncodeindex vr cp
+@syncodeindex kw cp
@copying
from archives.
Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
-2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
+2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.1 or
+under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
-Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
+Invariant Sections, with the Front-Cover Texts being ``A GNU Manual'',
and with the Back-Cover Texts as in (a) below. A copy of the license
-is included in the section entitled "GNU Free Documentation License".
+is included in the section entitled ``GNU Free Documentation
+License''.
(a) The FSF's Back-Cover Text is: ``You have the freedom to
copy and modify this GNU manual. Buying copies from the FSF
* Date input formats::
* Formats::
* Media::
+* Reliability and security::
Appendices
* Tar Internals::
* Genfile::
* Free Software Needs Free Documentation::
-* Copying This Manual::
+* GNU Free Documentation License::
* Index of Command Line Options::
* Index::
* defaults::
* verbose::
* checkpoints::
+* warnings::
* interactive::
The Three Option Styles
* gzip:: Creating and Reading Compressed Archives
* sparse:: Archiving Sparse Files
+Creating and Reading Compressed Archives
+
+* lbzip2:: Using lbzip2 with @GNUTAR{}.
+
Making @command{tar} Archives More Portable
* Portable Names:: Portable Names
The second chapter is a tutorial (@pxref{Tutorial}) which provides a
gentle introduction for people who are new to using @command{tar}. It is
-meant to be self contained, not requiring any reading from subsequent
+meant to be self-contained, not requiring any reading from subsequent
chapters to make sense. It moves from topic to topic in a logical,
progressive order, building on information already explained.
two frequently used options (@samp{file} and @samp{verbose}). The other
chapters do not refer to the tutorial frequently; however, if a section
discusses something which is a complex variant of a basic concept, there
-may be a cross reference to that basic concept. (The entire book,
+may be a cross-reference to that basic concept. (The entire book,
including the tutorial, assumes that the reader understands some basic
concepts of using a Unix-type operating system; @pxref{Tutorial}.)
When reporting a bug, please be sure to include as much detail as
possible, in order to reproduce it. @FIXME{Be more specific, I'd
like to make this node as detailed as 'Bug reporting' node in Emacs
-manual}.
+manual.}
@node Tutorial
@chapter Tutorial Introduction to @command{tar}
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. We will indicate those abbreviations
-appropriately to get you used to seeing them. (Note that the ``old
+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
If you don't specify this argument, then @command{tar} will examine
the environment variable @env{TAPE}. If it is set, its value will be
used as the archive name. Otherwise, @command{tar} will use the
-default archive, determined at the compile time. Usually it is
+default archive, determined at compile time. Usually it is
standard output or some physical tape drive attached to your machine
(you can verify what the default is by running @kbd{tar
--show-defaults}, @pxref{defaults}). If there is no tape drive
is now your @dfn{working directory}. (@emph{Please note}: Although
the full file name of this directory is
@file{/@var{homedir}/practice}, in our examples we will refer to
-this directory as @file{practice}; the @var{homedir} is presumed.
+this directory as @file{practice}; the @var{homedir} is presumed.)
In general, you should check that the files to be archived exist where
you think they do (in the working directory) by running @command{ls}.
@end smallexample
This example is just like the example we showed which did not use
-@option{--verbose}, except that @command{tar} generated the remaining lines
+@option{--verbose}, except that @command{tar} generated the remaining
@iftex
-(note the different font styles).
+lines (note the different font styles).
@end iftex
@ifinfo
-.
+lines.
@end ifinfo
In the rest of the examples in this chapter, we will frequently use
they will enter an infinite loop when this happens, so you should not
depend on this behavior unless you are certain you are running
@GNUTAR{}. In general, it is wise to always place the archive outside
-of the directory being dumped.
+of the directory being dumped.)
@node list
@section How to List Archives
@smallexample
@group
-$ @kbd{tar cfv archive /etc/mail}
+$ @kbd{tar --create --verbose --file archive /etc/mail}
tar: Removing leading `/' from member names
/etc/mail/
/etc/mail/sendmail.cf
/etc/mail/aliases
-$ @kbd{tar tf archive}
+$ @kbd{tar --test --file archive}
etc/mail/
etc/mail/sendmail.cf
etc/mail/aliases
@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
@smallexample
tar: folk: Not found in archive
tar: jazz: Not found in archive
-$
@end smallexample
@noindent
@smallexample
$ @kbd{tar -tvf music.tar}
+practice/blues
practice/folk
practice/jazz
-practice/rock
@end smallexample
@FIXME{make sure the above works when going through the examples in
@node tar invocation
@chapter Invoking @GNUTAR{}
-@UNREVISED
This chapter is about how one invokes the @GNUTAR{}
command, from the command synopsis (@pxref{Synopsis}). There are
* defaults::
* verbose::
* checkpoints::
+* warnings::
* interactive::
@end menu
@cindex return status
Besides successful exits, @GNUTAR{} may fail for
many reasons. Some reasons correspond to bad usage, that is, when the
-@command{tar} command 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.
+@command{tar} command line is improperly written. Errors may be
+encountered later, while processing the archive or the files. Some
+errors are recoverable, in which case the failure is delayed until
+@command{tar} has completed all its work. Some errors are such that
+it would be not meaningful, or at least risky, to continue processing:
+@command{tar} then aborts processing immediately. All abnormal exits,
+whether immediate or delayed, should always be clearly diagnosed on
+@code{stderr}, after a line stating the nature of the error.
Possible exit codes of @GNUTAR{} are summarized in the following
table:
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
+@command{tar} command (the corresponding options may be found
at @ref{frequent operations} and @ref{Operations}). Depending on
circumstances, you may also wish to customize how the chosen operating
mode behaves. For example, you may wish to change the way the output
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, @option{--file}
-(@option{-f})) takes the name of an archive file as an argument. If
+Some options must take an argument@footnote{For example, @option{--file}
+(@option{-f}) takes the name of an archive file as an argument. If
you do not supply an archive file name, @command{tar} will use a
default, but this can be confusing; thus, we recommend that you always
-supply a specific archive file name.) Where you @emph{place} the
+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
@node Long Options
@subsection Long Option Style
+@cindex long options
+@cindex options, long style
+@cindex options, GNU style
+@cindex options, mnemonic names
Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
dashes in a row, e.g., @option{--list}. The long names are more clear than
their corresponding short or old names. It sometimes happens that a
gives a fairly good set of hints about what the command does, even
for those not fully acquainted with @command{tar}.
+@cindex arguments to long options
+@cindex long options with mandatory arguments
Long options which require arguments take those arguments
immediately following the option name. There are two ways of
specifying a mandatory argument. It can be separated from the
@file{archive.tar} as argument by using any of the following notations:
@option{--file=archive.tar} or @option{--file archive.tar}.
+@cindex optional arguments to long options
+@cindex long options with optional arguments
In contrast, optional arguments must always be introduced using
an equal sign. For example, the @option{--backup} option takes
an optional argument specifying backup type. It must be used
@node Short Options
@subsection Short Option Style
+@cindex short options
+@cindex options, short style
+@cindex options, traditional
Most options also have a @dfn{short option} name. Short options start with
a single dash, and are followed by a single character, e.g., @option{-t}
(which is equivalent to @option{--list}). The forms are absolutely
The short option names are faster to type than long option names.
+@cindex arguments to short options
+@cindex short options with mandatory arguments
Short options which require arguments take their arguments immediately
following the option, usually separated by white space. It is also
possible to stick the argument right after the short option name, using
@w{@option{-f @var{archive-name}}} denote the option which indicates a
specific archive, here named @file{archive.tar}.
+@cindex optional arguments to short options
+@cindex short options with optional arguments
Short options which take optional arguments take their arguments
immediately following the option letter, @emph{without any intervening
white space characters}.
@node Old Options
@subsection Old Option Style
-@UNREVISED
+@cindex options, old style
+@cindex old option style
Like short options, @dfn{old options} are single letters. However, old options
must be written together as a single clumped set, without spaces separating
long option @option{--list}. So for example, the command @w{@samp{tar
cv}} specifies the option @option{-v} in addition to the operation @option{-c}.
+@cindex arguments to old options
+@cindex old options with mandatory arguments
When options that need arguments are given together with the command,
all the associated arguments follow, in the same order as the options.
Thus, the example given previously could also be written in the old
@node Mixing
@subsection Mixing Option Styles
+@cindex options, mixing different styles
All three styles may be intermixed in a single @command{tar} command,
so long as the rules for each style are fully
respected@footnote{Before @GNUTAR{} version 1.11.6,
@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.
+@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.
@opsummary{delete}
@item --delete
-Deletes members from the archive. Don't try this on a archive on a
+Deletes members from the archive. Don't try this on an archive on a
tape! @xref{delete}.
@opsummary{diff}
time, as the times of their accesses will be lost. On most platforms
restoring the access time also requires @command{tar} to restore the
data modification time too, so this option may also cause problems if
-other programs are writing the file at the same time. (Tar attempts
+other programs are writing the file at the same time (@command{tar} attempts
to detect this situation, but cannot do so reliably due to race
-conditions.) Worse, on most platforms restoring the access time also
+conditions). Worse, on most platforms restoring the access time also
updates the status change time, which means that this option is
incompatible with incremental backups.
@option{--atime-preserve=replace}, but this may change in the future
as support for @option{--atime-preserve=system} improves.
-If your operating system does not support
+If your operating or file system does not support
@option{--atime-preserve=@-system}, you might be able to preserve access
-times reliably by by using the @command{mount} command. For example,
+times reliably by using the @command{mount} command. For example,
you can mount the file system read-only, or access the file system via
a read-only loopback mount, or use the @samp{noatime} mount option
available on some systems. However, mounting typically requires
@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.
+for a detailed description.
@opsummary{checkpoint}
@item --checkpoint[=@var{number}]
want a visual indication that @command{tar} is still running, but
don't want to see @option{--verbose} output. You can also instruct
@command{tar} to execute a list of actions on each checkpoint, see
-@option{--checklist-action} below. For a detailed description, see
+@option{--checkpoint-action} below. For a detailed description, see
@ref{checkpoints}.
@opsummary{checkpoint-action}
When performing operations, @command{tar} will skip files that match
@var{pattern}. @xref{exclude}.
+@opsummary{exclude-backups}
+@item --exclude-backups
+Exclude backup and lock files. @xref{exclude,, exclude-backups}.
+
@opsummary{exclude-from}
@item --exclude-from=@var{file}
@itemx -X @var{file}
Exclude from dump any directory containing a valid cache directory
tag file, but still dump the directory node and the tag file itself.
-@xref{exclude}.
+@xref{exclude,, exclude-caches}.
@opsummary{exclude-caches-under}
@item --exclude-caches-under
@item --exclude-tag=@var{file}
Exclude from dump any directory containing file named @var{file}, but
-dump the directory node and @var{file} itself. @xref{exclude}.
+dump the directory node and @var{file} itself. @xref{exclude,, exclude-tag}.
@opsummary{exclude-tag-under}
@item --exclude-tag-under=@var{file}
Exclude from dump the contents of any directory containing file
-named @var{file}, but dump the directory node itself. @xref{exclude}.
+named @var{file}, but dump the directory node itself. @xref{exclude,,
+exclude-tag-under}.
@opsummary{exclude-tag-all}
@item --exclude-tag-all=@var{file}
Exclude from dump any directory containing file named @var{file}.
-@xref{exclude}.
+@xref{exclude,,exclude-tag-all}.
@opsummary{exclude-vcs}
@item --exclude-vcs
Exclude from dump directories and files, that are internal for some
widely used version control systems.
-@xref{exclude}.
+@xref{exclude,,exclude-vcs}.
@opsummary{file}
@item --file=@var{archive}
@xref{Formats}, for a detailed discussion of these formats.
+@opsummary{full-time}
+@item --full-time
+This option instructs @command{tar} to print file times to their full
+resolution. Usually this means 1-second resolution, but that depends
+on the underlying file system. The @option{--full-time} option takes
+effect only when detailed output (verbosity level 2 or higher) has
+been requested using the @option{--verbose} option, e.g., when listing
+or extracting archives:
+
+@smallexample
+$ @kbd{tar -t -v --full-time -f archive.tar}
+@end smallexample
+
+@noindent
+or, when creating an archive:
+
+@smallexample
+$ @kbd{tar -c -vv --full-time -f archive.tar .}
+@end smallexample
+
+Notice, thar when creating the archive you need to specify
+@option{--verbose} twice to get a detailed output (@pxref{verbose
+tutorial}).
+
@opsummary{group}
@item --group=@var{group}
@command{tar} will only operate on archives that have a label matching
the pattern specified in @var{name}. @xref{Tape Files}.
+@opsummary{level}
+@item --level=@var{n}
+Force incremental backup of level @var{n}. As of @GNUTAR version
+@value{VERSION}, the option @option{--level=0} truncates the snapshot
+file, thereby forcing the level 0 dump. Other values of @var{n} are
+effectively ignored. @xref{--level=0}, for details and examples.
+
+The use of this option is valid only in conjunction with the
+@option{--listed-incremental} option. @xref{Incremental Dumps},
+for a detailed description.
+
@opsummary{listed-incremental}
@item --listed-incremental=@var{snapshot-file}
@itemx -g @var{snapshot-file}
With other operations, informs @command{tar} that the archive is in
incremental format. @xref{Incremental Dumps}.
+@opsummary{lzip}
+@item --lzip
+
+This option tells @command{tar} to read or write archives through
+@command{lzip}. @xref{gzip}.
+
@opsummary{lzma}
@item --lzma
@opsummary{new-volume-script}
@item --new-volume-script
-(see --info-script)
+(see @option{--info-script})
@opsummary{newer}
@item --newer=@var{date}
@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.
+a detailed description.
@opsummary{no-delay-directory-restore}
@item --no-delay-directory-restore
the permissions specified in the archive. This is the default behavior
for ordinary users.
+@opsummary{no-seek}
+@item --no-seek
+
+The archive media does not support seeks to arbitrary
+locations. Usually @command{tar} determines automatically whether
+the archive can be seeked or not. Use this option to disable this
+mechanism.
+
@opsummary{no-unquote}
@item --no-unquote
Treat all input file or member names literally, do not interpret
@opsummary{pax-option}
@item --pax-option=@var{keyword-list}
-This option is meaningful only with @acronym{POSIX.1-2001} archives
-(@pxref{posix}). It modifies the way @command{tar} handles the
+This option enables creation of the archive in @acronym{POSIX.1-2001}
+format (@pxref{posix}) and modifies the way @command{tar} handles the
extended header keywords. @var{Keyword-list} is a comma-separated
list of keyword options. @xref{PAX keywords}, for a detailed
discussion.
from pipes on systems with buggy implementations. @xref{Reading}.
@opsummary{record-size}
-@item --record-size=@var{size}
+@item --record-size=@var{size}[@var{suf}]
Instructs @command{tar} to use @var{size} bytes per record when accessing the
-archive. @xref{Blocking Factor}.
+archive. The argument can be suffixed with a @dfn{size suffix}, e.g.
+@option{--record-size=10K} for 10 Kilobytes. @xref{size-suffixes},
+for a list of valid suffixes. @xref{Blocking Factor}, for a detailed
+description of this option.
@opsummary{recursion}
@item --recursion
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.
+in cases when such recognition fails. It takes effect only if the
+archive is open for reading (e.g. with @option{--list} or
+@option{--extract} options).
@opsummary{show-defaults}
@item --show-defaults
Here is an example of what you can see using this option:
@smallexample
-$ tar --show-defaults
---format=gnu -f- -b20 --quoting-style=escape \
+$ @kbd{tar --show-defaults}
+--format=gnu -f- -b20 --quoting-style=escape
--rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
@end smallexample
+@noindent
+Notice, that this option outputs only one line. The example output
+above has been split to fit page boundaries.
+
@opsummary{show-omitted-dirs}
@item --show-omitted-dirs
@noindent
would extract this file to file @file{name}.
-@opsummary{suffix}, summary
+@opsummary{suffix}
@item --suffix=@var{suffix}
Alters the suffix @command{tar} uses when backing up files from the default
@samp{~}. @xref{backup}.
@opsummary{tape-length}
-@item --tape-length=@var{num}
-@itemx -L @var{num}
+@item --tape-length=@var{num}[@var{suf}]
+@itemx -L @var{num}[@var{suf}]
Specifies the length of tapes that @command{tar} is writing as being
-@w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
+@w{@var{num} x 1024} bytes long. If optional @var{suf} is given, it
+specifies a multiplicative factor to be used instead of 1024. For
+example, @samp{-L2M} means 2 megabytes. @xref{size-suffixes}, for a
+list of allowed suffixes. @xref{Using Multiple Tapes}, for a detailed
+discussion of this option.
@opsummary{test-label}
@item --test-label
@opsummary{uncompress}
@item --uncompress
-(See @option{--compress}. @pxref{gzip})
+(See @option{--compress}, @pxref{gzip})
@opsummary{ungzip}
@item --ungzip
-(See @option{--gzip}. @pxref{gzip})
+(See @option{--gzip}, @pxref{gzip})
@opsummary{unlink-first}
@item --unlink-first
keep track of which volume of a multi-volume archive it is working in
@var{file}. @xref{volno-file}.
+@opsummary{warning}
+@item --warning=@var{keyword}
+
+Enable or disable warning messages identified by @var{keyword}. The
+messages are suppressed if @var{keyword} is prefixed with @samp{no-}.
+@xref{warnings}.
+
@opsummary{wildcards}
@item --wildcards
Use wildcards when matching member names with patterns.
@smallexample
tar (GNU tar) @value{VERSION}
-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>.
+Copyright (C) 2010 Free Software Foundation, Inc.
+Copyright (C) 2010 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
+This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Written by John Gilmore and Jay Fenlason.
@command{tar} packages into a single one which would be called
@code{paxutils}. So, who knows if, one of this days, the
@option{--version} would not output @w{@samp{tar (@acronym{GNU}
-paxutils) 3.2}}}.
+paxutils) 3.2}}.}.
@cindex Obtaining help
@cindex Listing all @command{tar} options
@opindex usage
If you only wish to check the spelling of an option, running @kbd{tar
--usage} may be a better choice. This will display a terse list of
-@command{tar} option without accompanying explanations.
+@command{tar} options without accompanying explanations.
The short help output is quite succinct, and you might have to get
back to the full documentation for precise points. If you are reading
@smallexample
@group
-@kbd{tar --show-defaults}
+$ @kbd{tar --show-defaults}
--format=gnu -f- -b20 --quoting-style=escape
--rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
@end group
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
+file on the archive. As of now, if the archive is 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
@option{--block-number} (@option{-R}) is used. Note that @GNUTAR{}
@option{--checkpoint}. In this case, the default checkpoint frequency
(at each 10th record) is assumed.
+@node warnings
+@section Controlling Warning Messages
+
+Sometimes, while performing the requested task, @GNUTAR{} notices
+some conditions that are not exactly errors, but which the user
+should be aware of. When this happens, @command{tar} issues a
+@dfn{warning message} describing the condition. Warning messages
+are output to the standard error and they do not affect the exit
+code of @command{tar} command.
+
+@xopindex{warning, explained}
+@GNUTAR{} allows the user to suppress some or all of its warning
+messages:
+
+@table @option
+@item --warning=@var{keyword}
+Control display of the warning messages identified by @var{keyword}.
+If @var{keyword} starts with the prefix @samp{no-}, such messages are
+suppressed. Otherwise, they are enabled.
+
+Multiple @option{--warning} messages accumulate.
+
+The tables below list allowed values for @var{keyword} along with the
+warning messages they control.
+@end table
+
+@subheading Keywords controlling @command{tar} operation
+@table @asis
+@kwindex all
+@item all
+Enable all warning messages. This is the default.
+@kwindex none
+@item none
+Disable all warning messages.
+@kwindex filename-with-nuls
+@cindex @samp{file name read contains nul character}, warning message
+@item filename-with-nuls
+@samp{%s: file name read contains nul character}
+@kwindex alone-zero-block
+@cindex @samp{A lone zero block at}, warning message
+@item alone-zero-block
+@samp{A lone zero block at %s}
+@end table
+
+@subheading Keywords applicable for @command{tar --create}
+@table @asis
+@kwindex cachedir
+@cindex @samp{contains a cache directory tag}, warning message
+@item cachedir
+@samp{%s: contains a cache directory tag %s; %s}
+@kwindex file-shrank
+@cindex @samp{File shrank by %s bytes}, warning message
+@item file-shrank
+@samp{%s: File shrank by %s bytes; padding with zeros}
+@kwindex xdev
+@cindex @samp{file is on a different filesystem}, warning message
+@item xdev
+@samp{%s: file is on a different filesystem; not dumped}
+@kwindex file-ignored
+@cindex @samp{Unknown file type; file ignored}, warning message
+@cindex @samp{socket ignored}, warning message
+@cindex @samp{door ignored}, warning message
+@item file-ignored
+@samp{%s: Unknown file type; file ignored}
+@*@samp{%s: socket ignored}
+@*@samp{%s: door ignored}
+@kwindex file-unchanged
+@cindex @samp{file is unchanged; not dumped}, warning message
+@item file-unchanged
+@samp{%s: file is unchanged; not dumped}
+@kwindex ignore-archive
+@cindex @samp{file is the archive; not dumped}, warning message
+@kwindex ignore-archive
+@cindex @samp{file is the archive; not dumped}, warning message
+@item ignore-archive
+@samp{%s: file is the archive; not dumped}
+@kwindex file-removed
+@cindex @samp{File removed before we read it}, warning message
+@item file-removed
+@samp{%s: File removed before we read it}
+@kwindex file-changed
+@cindex @samp{file changed as we read it}, warning message
+@item file-changed
+@samp{%s: file changed as we read it}
+@end table
+
+@subheading Keywords applicable for @command{tar --extract}
+@table @asis
+@kwindex timestamp
+@cindex @samp{implausibly old time stamp %s}, warning message
+@cindex @samp{time stamp %s is %s s in the future}, warning message
+@item timestamp
+@samp{%s: implausibly old time stamp %s}
+@*@samp{%s: time stamp %s is %s s in the future}
+@kwindex contiguous-cast
+@cindex @samp{Extracting contiguous files as regular files}, warning message
+@item contiguous-cast
+@samp{Extracting contiguous files as regular files}
+@kwindex symlink-cast
+@cindex @samp{Attempting extraction of symbolic links as hard links}, warning message
+@item symlink-cast
+@samp{Attempting extraction of symbolic links as hard links}
+@kwindex unknown-cast
+@cindex @samp{Unknown file type `%c', extracted as normal file}, warning message
+@item unknown-cast
+@samp{%s: Unknown file type `%c', extracted as normal file}
+@kwindex ignore-newer
+@cindex @samp{Current %s is newer or same age}, warning message
+@item ignore-newer
+@samp{Current %s is newer or same age}
+@kwindex unknown-keyword
+@cindex @samp{Ignoring unknown extended header keyword `%s'}, warning message
+@item unknown-keyword
+@samp{Ignoring unknown extended header keyword `%s'}
+@end table
+
+@subheading Keywords controlling incremental extraction:
+@table @asis
+@kwindex rename-directory
+@cindex @samp{%s: Directory has been renamed from %s}, warning message
+@cindex @samp{%s: Directory has been renamed}, warning message
+@item rename-directory
+@samp{%s: Directory has been renamed from %s}
+@*@samp{%s: Directory has been renamed}
+@kwindex new-directory
+@cindex @samp{%s: Directory is new}, warning message
+@item new-directory
+@samp{%s: Directory is new}
+@kwindex xdev
+@cindex @samp{%s: directory is on a different device: not purging}, warning message
+@item xdev
+@samp{%s: directory is on a different device: not purging}
+@kwindex bad-dumpdir
+@cindex @samp{Malformed dumpdir: 'X' never used}, warning message
+@item bad-dumpdir
+@samp{Malformed dumpdir: 'X' never used}
+@end table
+
@node interactive
@section Asking for Confirmation During Operations
@cindex Interactive operation
@node Operations
@subsection The Five Advanced @command{tar} Operations
-@UNREVISED
+@cindex basic operations
In the last chapter, you learned about the first three operations to
@command{tar}. This chapter presents the remaining five operations to
@command{tar}: @option{--append}, @option{--update}, @option{--concatenate},
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
+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
@node append
@subsection How to Add Files to Existing Archives: @option{--append}
-@UNREVISED
+@cindex appending files to existing archive
@opindex append
If you want to add files to an existing archive, you don't need to
create a new archive; you can use @option{--append} (@option{-r}).
Other operations don't deal with these members as perfectly as you might
prefer; if you were to use @option{--extract} to extract the archive,
-only the most recently added copy of a member with the same name as four
+only the most recently added copy of a member with the same name as
other members would end up in the working directory. This is because
@option{--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@footnote{Unless you give it
-@option{--keep-old-files} option, or the disk copy is newer than the
+@option{--keep-old-files} option, or the disk copy is newer than
the one in the archive and you invoke @command{tar} with
-@option{--keep-newer-files} option}. Thus, only the most recently archived
+@option{--keep-newer-files} option.}. Thus, only the most recently archived
member will end up being extracted, as it will replace the one
extracted before it, and so on.
+@cindex extracting @var{n}th copy of the file
+@xopindex{occurrence, described}
There exists a special option that allows you to get around this
behavior and extract (or list) only a particular copy of the file.
This is @option{--occurrence} option. If you run @command{tar} with
@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. (maybe xref Multiple Members
-with the Same Name.}
+There are a few ways to get around this. Xref to Multiple Members
+with the Same Name, maybe.}
@cindex Members, replacing with other members
@cindex Replacing members with other members
+@xopindex{delete, using before --append}
If you want to replace an archive member, use @option{--delete} to
-delete the member you want to remove from the archive, , and then use
+delete the member you want to remove from the archive, and then use
@option{--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
@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
+@opindex append
The simplest way to add a file to an already existing archive is the
@option{--append} (@option{-r}) operation, which writes specified
@node multiple
@subsubsection Multiple Members with the Same Name
+@cindex members, multiple
+@cindex multiple members
You can use @option{--append} (@option{-r}) to add copies of files
which have been updated since the archive was created. (However, we
@end smallexample
@xref{Writing}, for more information on @option{--extract} and
-@xref{Option Summary, --occurrence}, for the description of
+see @ref{Option Summary, --occurrence}, for a description of
@option{--occurrence} option.
@node update
@subsection Updating an Archive
-@UNREVISED
@cindex Updating an archive
-
@opindex update
+
In the previous section, you learned how to use @option{--append} to
add a file to an existing archive. A related operation is
@option{--update} (@option{-u}). The @option{--update} operation
@node how to update
@subsubsection How to Update an Archive Using @option{--update}
+@opindex update
You must use file name arguments with the @option{--update}
(@option{-u}) operation. If you don't specify any files,
@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 @option{--verbose} (@option{-v})
-option specified, using the names of all the files in the practice
+option specified, using the names of all the files in the @file{practice}
directory as file name arguments:
@smallexample
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
+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.
To use @option{--concatenate}, give the first archive with
@option{--file} option and name the rest of archives to be
concatenated on the command line. The members, and their member
-names, will be copied verbatim from those archives to the first one.
-@footnote{This can cause multiple members to have the same name, for
-information on how this affects reading the archive, @ref{multiple}.}
+names, will be copied verbatim from those archives to the first
+one@footnote{This can cause multiple members to have the same name. For
+information on how this affects reading the archive, see @ref{multiple}.}.
The new, concatenated archive will be called by the same name as the
one given with the @option{--file} option. As usual, if you omit
@option{--file}, @command{tar} will use the value of the environment
@node delete
@subsection Removing Archive Members Using @option{--delete}
-@UNREVISED
@cindex Deleting files from an archive
@cindex Removing files from an archive
folk
jazz
rock
-$
@end smallexample
@FIXME{Check if the above listing is actually produced after running
@node compare
@subsection Comparing Archive Members with the File System
@cindex Verifying the currency of an archive
-@UNREVISED
@opindex compare
The @option{--compare} (@option{-d}), or @option{--diff} operation compares
The spirit behind the @option{--compare} (@option{--diff},
@option{-d}) 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}.
+the archive media. For this latter goal, see @ref{verify}.
@node create options
@section Options Used by @option{--create}
the modification time of members when creating archives, instead of
their actual modification times. The argument @var{date} can be
either a textual date representation in almost arbitrary format
-(@pxref{Date input formats}) or a name of the existing file, starting
+(@pxref{Date input formats}) or a name of an existing file, starting
with @samp{/} or @samp{.}. In the latter case, the modification time
of that file will be used.
-The following example will set the modification date to 00:00:00 UTC,
+The following example will set the modification date to 00:00:00,
January 1, 1970:
@smallexample
archives. For example:
@smallexample
-@group
$ @kbd{tar -c -f archive.tar --owner=0 .}
-# @r{Or:}
+@end smallexample
+
+@noindent
+or:
+
+@smallexample
$ @kbd{tar -c -f archive.tar --owner=root .}
-@end group
@end smallexample
@item --group=@var{group}
@node extract options
@section Options Used by @option{--extract}
-@UNREVISED
+@cindex options for use with @option{--extract}
@xopindex{extract, additional options}
The previous chapter showed how to use @option{--extract} to extract
@node Reading
@subsection Options to Help Read Archives
@cindex Options when reading archives
-@UNREVISED
@cindex Reading incomplete records
@cindex Records, incomplete
directory timestamp will be offset again.
To correctly restore directory meta-information in such cases, use
-@option{delay-directory-restore} command line option:
+the @option{--delay-directory-restore} command line option:
@table @option
@opindex delay-directory-restore
Extract files and pipe their contents to the standard input of
@var{command}. When this option is used, instead of creating the
files specified, @command{tar} invokes @var{command} and pipes the
-contents of the files to its standard output. @var{Command} may
+contents of the files to its standard output. The @var{command} may
contain command line arguments. The program is executed via
@code{sh -c}. Notice, that @var{command} is executed once for each regular file
extracted. Non-regular files (directories, etc.) are ignored when this
@vrindex TAR_ATIME, to-command environment
@item TAR_ATIME
Time of last access. It is a decimal number, representing seconds
-since the epoch. If the archive provides times with nanosecond
+since the Epoch. If the archive provides times with nanosecond
precision, the nanoseconds are appended to the timestamp after a
decimal point.
GID of the file owner.
@end table
-In addition to these variables, @env{TAR_VERSION} contains the
+Additionally, the following variables contain information about
+tar mode and the archive being processed:
+
+@table @env
+@vrindex TAR_VERSION, to-command environment
+@item TAR_VERSION
@GNUTAR{} version number.
+@vrindex TAR_ARCHIVE, to-command environment
+@item TAR_ARCHIVE
+The name of the archive @command{tar} is processing.
+
+@vrindex TAR_BLOCKING_FACTOR, to-command environment
+@item TAR_BLOCKING_FACTOR
+Current blocking factor (@pxref{Blocking}).
+
+@vrindex TAR_VOLUME, to-command environment
+@item TAR_VOLUME
+Ordinal number of the volume @command{tar} is processing.
+
+@vrindex TAR_FORMAT, to-command environment
+@item TAR_FORMAT
+Format of the archive being processed. @xref{Formats}, for a complete
+list of archive format names.
+@end table
+
If @var{command} exits with a non-0 status, @command{tar} will print
an error message similar to the following:
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, @option{--starting-file} is not necessary.
-@xref{Incremental Dumps}, @xref{interactive}, and @ref{exclude}.)
+the file system, and then resume the same @command{tar} operation.
+In this case, @option{--starting-file} is not necessary.) See also
+@ref{interactive}, and @ref{exclude}.
@node Same Order
@unnumberedsubsubsec Same Order
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.)
+as having similar names through the side-effect of name truncation.
+@FIXME{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.
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:
+medium is a @dfn{pipe}:
@smallexample
$ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
@end smallexample
@noindent
-The command also works using short option forms:
+The command also works using long option forms:
@smallexample
+@group
$ @kbd{(cd sourcedir; tar --create --file=- . ) \
| (cd targetdir; tar --extract --file=-)}
-# Or:
-$ @kbd{tar --directory sourcedir --create --file=- . ) \
+@end group
+@end smallexample
+
+@noindent
+or
+
+@smallexample
+@group
+$ @kbd{tar --directory sourcedir --create --file=- . \
| tar --directory targetdir --extract --file=-}
+@end group
@end smallexample
@noindent
@node Backups
@chapter Performing Backups and Restoring Files
-@UNREVISED
+@cindex backups
-@GNUTAR{} 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
+@GNUTAR{} is distributed along with the scripts for performing backups
+and restores. 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:
-
-@smallexample
-http://www.cs.umd.edu/projects/amanda/amanda.html
-ftp://ftp.cs.umd.edu/pub/amanda
-@end smallexample
+This is free software, and it is available from @uref{http://www.amanda.org}.
@FIXME{
backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
@var{snapshot-file}}) and @option{--incremental} (@option{-G}).
-@opindex listed-incremental
+@xopindex{listed-incremental, described}
The option @option{--listed-incremental} instructs tar to operate on
an incremental archive with additional metadata stored in a standalone
file, called a @dfn{snapshot file}. The purpose of this file is to help
/usr}
@end smallexample
+@anchor{--level=0}
+@xopindex{level, described}
+You can force @samp{level 0} backups either by removing the snapshot
+file before running @command{tar}, or by supplying the
+@option{--level=0} option, e.g.:
+
+@smallexample
+$ @kbd{tar --create \
+ --file=archive.2.tar \
+ --listed-incremental=/var/log/usr.snar-0 \
+ --level=0 \
+ /usr}
+@end smallexample
+
Incremental dumps depend crucially on time stamps, so the results are
unreliable if you modify a file's time stamps during dumping (e.g.,
with the @option{--atime-preserve=replace} option), or if you set the clock
@anchor{device numbers}
@cindex Device numbers, using in incremental backups
Metadata stored in snapshot files include device numbers, which,
-obviously are supposed to be a non-volatile values. However, it turns
+obviously are supposed to be 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 @acronym{NFS} devices numbers over time. The solution implemented
-currently is to considers all @acronym{NFS} devices as being equal
+currently is to consider 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.
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}).
+(@pxref{TAR_OPTIONS}).
@end table
There is also another way to cope with changing device numbers. It is
Alternatively, you can use @option{--incremental}, which needs no
arguments. In general, @option{--incremental} (@option{-G}) can be
used as a shortcut for @option{--listed-incremental} when listing or
-extracting incremental backups (for more information, regarding this
+extracting incremental backups (for more information regarding this
option, @pxref{incremental-op}).
When extracting from the incremental backup @GNUTAR{} attempts to
@option{--incremental} or @option{--listed-incremental} option was
given, no matter what the verbosity level. This behavior, and,
especially, the binary output it produced were considered inconvenient
-and were changed in version 1.16}:
+and were changed in version 1.16.}:
@smallexample
@kbd{tar --list --incremental --verbose --verbose archive.tar}
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).
+more than once a day is usually not worth the trouble.)
@GNUTAR{} comes with scripts you can use to do full
and level-one (actually, even level-two and so on) dumps. Using
(for @code{restore}). These should be accessible from the machine on
which the backup script is run.
-If the list of file systems is very long you may wish to store it
+If the list of individual files is very long you may wish to store it
in a separate file. This file is usually named
@file{/etc/backup/files}, but this name may be overridden in
@file{backup-specs} using @code{FILELIST} variable.
@subsection Magnetic Tape Control
Backup scripts access tape device using special @dfn{hook functions}.
-These functions take a single argument -- the name of the tape
+These functions take a single argument --- the name of the tape
device. Their names are kept in the following variables:
@defvr {Backup variable} MT_BEGIN
@end table
@end deffn
-Following variables keep the names of user hook functions
+Following variables keep the names of user hook functions:
@defvr {Backup variable} DUMP_BEGIN
Dump begin function. It is executed before dumping the file system.
backup --level=@var{level} --time=@var{time}
@end smallexample
-The @option{level} option requests the dump level. Thus, to produce
+The @option{--level} option requests the dump level. Thus, to produce
a full dump, specify @code{--level=0} (this is the default, so
-@option{--level} may be omitted if its value is @code{0}).
-@footnote{For backward compatibility, the @code{backup} will also
+@option{--level} may be omitted if its value is
+@code{0})@footnote{For backward compatibility, the @code{backup} will also
try to deduce the requested dump level from the name of the
script itself. If the name consists of a string @samp{level-}
followed by a single decimal digit, that digit is taken as
the dump level number. Thus, you may create a link from @code{backup}
to @code{level-1} and then run @code{level-1} whenever you need to
-create a level one dump.}
+create a level one dump.}.
The @option{--time} option determines when should the backup be
run. @var{Time} may take three forms:
@item @var{hh}
-The dump must be run at @var{hh} hours
+The dump must be run at @var{hh} hours.
@item now
@file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
You may select the file systems (and/or files) to restore by
-giving @code{restore} list of @dfn{patterns} in its command
+giving @code{restore} a list of @dfn{patterns} in its command
line. For example, running
@smallexample
@table @option
@item -a
@itemx --all
-Restore all file systems and files specified in @file{backup-specs}
+Restore all file systems and files specified in @file{backup-specs}.
@item -l @var{level}
@itemx --level=@var{level}
@node Choosing
@chapter Choosing Files and Names for @command{tar}
-@UNREVISED
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
@node file
@section Choosing and Naming Archive Files
-@UNREVISED
@cindex Naming an archive
@cindex Archive Name
@cindex Choosing an archive file
@cindex Where is the archive?
+@opindex file
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}
@end smallexample
@noindent
-@command{tar} will complete the remote connection, if possible, and
+@command{tar} will set up the remote connection, if possible, and
prompt you for a username and password. If you use
@option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
-will complete the remote connection, if possible, using your username
+will attempt to set up the remote connection using your username
as the username on the remote machine.
@cindex Local and remote archives
(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{rmt} program installed (This command is included in
+have the @file{rmt} program installed (this command is included in
the @GNUTAR{} distribution and by default is installed under
-@file{@var{prefix}/libexec/rmt}, were @var{prefix} means your
+@file{@var{prefix}/libexec/rmt}, where @var{prefix} means your
installation prefix). If you need to use a file whose name includes a
colon, then the remote tape drive behavior
can be inhibited by using the @option{--force-local} option.
@cindex Reading file names from a file
@cindex Lists of file names
@cindex File Name arguments, alternatives
+@cindex @command{find}, using with @command{tar}
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
@option{--files-from=@var{file-of-names}} (@option{-T
more information.)
@smallexample
-$ @kbd{find . -size -400 -print > small-files}
+$ @kbd{find . -size -400 -print > small-files}
$ @kbd{tar -c -v -z -T small-files -f little.tgz}
@end smallexample
@noindent
In the file list given by @option{-T} option, any file name beginning
with @samp{-} character is considered a @command{tar} option and is
-processed accordingly.@footnote{Versions of @GNUTAR{} up to 1.15.1
+processed accordingly@footnote{Versions of @GNUTAR{} up to 1.15.1
recognized only @option{-C} option in file lists, and only if the
-option and its argument occupied two consecutive lines.} For example,
+option and its argument occupied two consecutive lines.}. For example,
the common use of this feature is to change to another directory by
specifying @option{-C} option:
@end menu
@node nul
-@subsection @code{NUL} Terminated File Names
+@subsection @code{NUL}-Terminated File Names
@cindex File names, terminated by @code{NUL}
-@cindex @code{NUL} terminated file names
+@cindex @code{NUL}-terminated file names
The @option{--null} option causes
@option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
to read file names terminated by a @code{NUL} instead of a newline, so
@table @option
@xopindex{null, described}
@item --null
-Only consider @code{NUL} terminated file names, instead of files that
+Only consider @code{NUL}-terminated file names, instead of files that
terminate in a newline.
@xopindex{no-null, described}
@file{long-files}. The @option{-print0} option to @command{find} is just
like @option{-print}, except that it separates files with a @code{NUL}
rather than with a newline. You can then run @command{tar} with both the
-@option{--null} and @option{-T} options to specify that @command{tar} get the
+@option{--null} and @option{-T} options to specify that @command{tar} gets the
files from that file, @file{long-files}, to create the archive
@file{big.tgz}. The @option{--null} option to @command{tar} will cause
@command{tar} to recognize the @code{NUL} separator between files.
@smallexample
-$ @kbd{find . -size +800 -print0 > long-files}
+$ @kbd{find . -size +800 -print0 > long-files}
$ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
@end smallexample
The @option{--no-null} option can be used if you need to read both
-zero-terminated and newline-terminated files on the same command line.
+@code{NUL}-terminated and newline-terminated files on the same command line.
For example, if @file{flist} is a newline-terminated file, then the
following command can be used to combine it with the above command:
@smallexample
@group
-$ @kbd{find . -size +800 -print0 |
+$ @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
+@GNUTAR is able to automatically detect @code{NUL}-terminated file lists, so
it is safe to use them even without the @option{--null} option. In
this case @command{tar} will print a warning and continue reading such
a file as if @option{--null} were actually given:
@smallexample
@group
-$ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
+$ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
tar: -: file name read contains nul character
@end group
@end smallexample
@node exclude
@section Excluding Some Files
-@UNREVISED
@cindex File names, excluding files by
@cindex Excluding files by name and pattern
@cindex Excluding files by file system
+@opindex exclude
+@opindex exclude-from
To avoid operating on files whose names match a particular pattern,
use the @option{--exclude} or @option{--exclude-from} options.
However, empty lines are OK.
+@table @option
@cindex version control system, excluding files
@cindex VCS, excluding files
@cindex SCCS, 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:
@item @file{_darcs}
@end itemize
+@opindex exclude-backups
+@item --exclude-backups
+Exclude backup and lock files. This option causes exclusion of files
+that match the following shell globbing patterns:
+
+@table @asis
+@item .#*
+@item *~
+@item #*#
+@end table
+
+@end table
+
@findex exclude-caches
When creating an archive, the @option{--exclude-caches} option family
causes @command{tar} to exclude all directories that contain a @dfn{cache
@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 it,
+storing a file to an archive, its file name is recorded in it,
along with the actual file contents. When restoring from an archive,
a file is created on disk with exactly the same name as that stored
in the archive. In the majority of cases this is the desired behavior
@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
+Any delimiter can be used in lieu of @samp{/}, the only requirement being
that it be used consistently throughout the expression. For example,
the following two expressions are equivalent:
just the first.
@item i
-Use case-insensitive matching
+Use case-insensitive matching.
@item x
@var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
@end smallexample
This is definitely not desired. To avoid this, the @samp{S} flag
-are used, which excludes symbolic link targets from filename
+is used, which excludes symbolic link targets from filename
transformations. The result is:
@smallexample
--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
+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
@node after
@section Operating Only on New Files
-@UNREVISED
@cindex Excluding file by age
@cindex Data Modification time, excluding files by
modification of the file's data (rather than status
changes), then use the @option{--newer-mtime=@var{date}} option.
+@cindex --after-date and --update compared
+@cindex --newer-mtime and --update compared
You may use these options with any operation. Note that these options
differ from the @option{--update} (@option{-u}) operation in that they
allow you to specify a particular date against which @command{tar} can
@node recurse
@section Descending into Directories
-@UNREVISED
@cindex Avoiding recursion in directories
@cindex Descending directories, avoiding
@cindex Directories, avoiding recursion
@cindex Recursion in directories, avoiding
-@FIXME{arrggh! this is still somewhat confusing to me. :-< }
-
Usually, @command{tar} will recursively explore all directories (either
those given on the command line or through the @option{--files-from}
option) for the various files they contain. However, you may not always
want @command{tar} to act this way.
@opindex no-recursion
+@cindex @command{find}, using with @command{tar}
The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
into specified directories. If you specify @option{--no-recursion}, you can
-use the @command{find} utility for hunting through levels of directories to
+use the @command{find} (@pxref{Top,, find, find, GNU Find Manual})
+utility for hunting through levels of directories to
construct a list of file names which you could then pass to @command{tar}.
@command{find} allows you to be more selective when choosing which files to
archive; see @ref{files}, for more information on using @command{find} with
-@command{tar}, or look.
+@command{tar}.
@table @option
@item --no-recursion
@node one
@section Crossing File System 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
which records the third file in the archive under the name
@file{red/cherry} so that, if the archive is extracted using
@samp{tar --extract}, the third file will be written in a subdirectory
-named @file{orange-colored}.
+named @file{red}.
You can use the @option{--directory} option to make the archive
independent of the original name of the directory holding the files.
@node absolute
@subsection Absolute File Names
-@UNREVISED
+@cindex absolute file names
+@cindex file names, absolute
+
+By default, @GNUTAR{} drops a leading @samp{/} on
+input or output, and complains about file names containing a @file{..}
+component. There is an option that turns off this behavior:
@table @option
@opindex absolute-names
containing a @file{..} file name component.
@end table
-By default, @GNUTAR{} drops a leading @samp{/} on
-input or output, and complains about file names containing a @file{..}
-component. This option turns off this behavior.
-
When @command{tar} extracts archive members from an archive, it strips any
leading slashes (@samp{/}) from the member name. This causes absolute
member names in the archive to be treated as relative file names. This
leading slashes from member names when putting members into the
archive. For example, if you ask @command{tar} to add the file
@file{/bin/ls} to an archive, it will do so, but the member name will
-be @file{bin/ls}.@footnote{A side effect of this is that when
+be @file{bin/ls}@footnote{A side effect of this is that when
@option{--create} is used with @option{--verbose} the resulting output
is not, generally speaking, the same as the one you'd get running
@kbd{tar --list} command. This may be important if you use some
scripts for comparing both outputs. @xref{listing member and file names},
-for the information on how to handle this case.}
+for the information on how to handle this case.}.
If you use the @option{--absolute-names} (@option{-P}) option,
@command{tar} will do none of these transformations.
@FIXME{Should be an example in the tutorial/wizardry section using this
to transfer files between systems.}
-@FIXME{Is write access an issue?}
-
@table @option
@item --absolute-names
Preserves full file names (including superior directory names) when
@end table
-@FIXME{this is still horrible; need to talk with dan on monday.}
-
@command{tar} prints out a message about removing the @samp{/} from
file names. This message appears once per @GNUTAR{}
invocation. It represents something which ought to be told; ignoring
$ @kbd{tar -c -f archive.tar -C / home}
@end smallexample
+@xref{Integrity}, for some of the security-related implications
+of using this option.
+
@include getdate.texi
@node Formats
@cindex gzip
@cindex bzip2
+@cindex lzip
@cindex lzma
@cindex lzop
@cindex compress
@GNUTAR{} is able to create and read compressed archives. It supports
-@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.}.
+a wide variety of compression programs, namely: @command{gzip},
+@command{bzip2}, @command{lzip}, @command{lzma}, @command{lzop},
+@command{xz} and traditional @command{compress}. The latter is
+supported mostly for backward compatibility, and we recommend
+against using it, because it is by far less effective than the other
+compression programs@footnote{It also had patent problems in the past.}.
Creating a compressed archive is simple: you just specify a
@dfn{compression option} along with the usual archive creation
commands. The compression option is @option{-z} (@option{--gzip}) to
create a @command{gzip} compressed archive, @option{-j}
(@option{--bzip2}) to create a @command{bzip2} compressed archive,
-@option{-J} (@option{--xz}) to create an @asis{XZ} archive,
+@option{--lzip} to create an @asis{lzip} compressed archive,
+@option{-J} (@option{--xz}) to create an @asis{XZ} archive,
@option{--lzma} to create an @asis{LZMA} compressed
archive, @option{--lzop} to create an @asis{LSOP} archive, and
@option{-Z} (@option{--compress}) to use @command{compress} program.
$ @kbd{tar cfz archive.tar.gz .}
@end smallexample
-You can also let @GNUTAR{} select the compression program basing on
+You can also let @GNUTAR{} select the compression program based on
the suffix of the archive file name. This is done using
@option{--auto-compress} (@option{-a}) command line option. For
example, the following invocation will use @command{bzip2} for
@end smallexample
For a complete list of file name suffixes recognized by @GNUTAR{},
-@ref{auto-compress}.
+see @ref{auto-compress}.
Reading compressed archive is even simpler: you don't need to specify
any additional options as @GNUTAR{} recognizes its format
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).
+(@pxref{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
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}))
+modified, i.e., you cannot update (@option{--update}, alias @option{-u})
them or delete (@option{--delete}) members from them or
-add (@option{--append} (@option{-r})) members to them. Likewise, you
+add (@option{--append}, alias @option{-r}) members to them. Likewise, you
cannot append another @command{tar} archive to a compressed archive using
-@option{--concatenate} (@option{-A})). Secondly, multi-volume
+@option{--concatenate} (@option{-A}). Secondly, multi-volume
archives cannot be compressed.
-The following table summarizes compression options used by @GNUTAR{}.
+The following options allow to select a particular compressor program:
@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}
-@item @samp{.xz} @tab @command{xz}
-@end multitable
-
@opindex gzip
@opindex ungzip
@item -z
@itemx --ungzip
Filter the archive through @command{gzip}.
-You can use @option{--gzip} and @option{--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, set @env{GZIP} environment variable, e.g.:
+@opindex xz
+@item -J
+@itemx --xz
+Filter the archive through @code{xz}.
+
+@item -j
+@itemx --bzip2
+Filter the archive through @code{bzip2}.
+
+@opindex lzip
+@item --lzip
+Filter the archive through @command{lzip}.
+
+@opindex lzma
+@item --lzma
+Filter the archive through @command{lzma}.
+
+@opindex lzop
+@item --lzop
+Filter the archive through @command{lzop}.
+
+@opindex compress
+@opindex uncompress
+@item -Z
+@itemx --compress
+@itemx --uncompress
+Filter the archive through @command{compress}.
+@end table
+
+When any of these options is given, @GNUTAR{} searches the compressor
+binary in the current path and invokes it. The name of the compressor
+program is specified at compilation time using a corresponding
+@option{--with-@var{compname}} option to @command{configure}, e.g.
+@option{--with-bzip2} to select a specific @command{bzip2} binary.
+@xref{lbzip2}, for a detailed discussion.
+
+The output produced by @command{tar --help} shows the actual
+compressor names along with each of these options.
+
+You can use any of these options on physical devices (tape drives,
+etc.) and remote files as well as on normal files; data to or from
+such devices or remote files is reblocked by another copy of the
+@command{tar} program to enforce the specified (or default) record
+size. The default compression parameters are used. Most compression
+programs allow to override these by setting a program-specific
+environment variable. For example, when using @command{gzip} you can
+use @env{GZIP} as in the example below:
@smallexample
$ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
@end smallexample
@noindent
-Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
-@command{gzip} explicitly:
+Another way would be to use the @option{-I} option instead (see
+below), e.g.:
+
+@smallexample
+$ @kbd{tar -cf archive.tar.gz -I 'gzip --best' subdir}
+@end smallexample
+
+@noindent
+Finally, the third, traditional, way to achieve the same result is to
+use pipe:
@smallexample
$ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
@end smallexample
@cindex corrupted archives
-About corrupted compressed archives: @command{gzip}'ed files have no
+About corrupted compressed archives: compressed files have no
redundancy, for maximum compression. The adaptive nature of the
compression scheme means that the compression tables are implicitly
spread all over the archive. If you lose a few blocks, the dynamic
construction of the compression tables becomes unsynchronized, and there
is little chance that you could recover later in the archive.
-There are pending suggestions for having a per-volume or per-file
-compression in @GNUTAR{}. This would allow for viewing the
-contents without decompression, and for resynchronizing decompression at
-every volume or file, in case of corrupted archives. Doing so, we might
-lose some compressibility. But this would have make recovering easier.
-So, there are pros and cons. We'll see!
+Another compression options provide a better control over creating
+compressed archives. These are:
-@opindex bzip2
-@item -J
-@itemx --xz
-Filter the archive through @code{xz}. Otherwise like
-@option{--gzip}.
-
-@item -j
-@itemx --bzip2
-Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
-
-@opindex lzma
-@item --lzma
-Filter the archive through @command{lzma}. Otherwise like @option{--gzip}.
-
-@opindex lzop
-@item --lzop
-Filter the archive through @command{lzop}. Otherwise like
-@option{--gzip}.
+@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:
-@opindex compress
-@opindex uncompress
-@item -Z
-@itemx --compress
-@itemx --uncompress
-Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
+@multitable @columnfractions 0.3 0.6
+@headitem Suffix @tab Compression program
+@item @samp{.gz} @tab @command{gzip}
+@item @samp{.tgz} @tab @command{gzip}
+@item @samp{.taz} @tab @command{gzip}
+@item @samp{.Z} @tab @command{compress}
+@item @samp{.taZ} @tab @command{compress}
+@item @samp{.bz2} @tab @command{bzip2}
+@item @samp{.tz2} @tab @command{bzip2}
+@item @samp{.tbz2} @tab @command{bzip2}
+@item @samp{.tbz} @tab @command{bzip2}
+@item @samp{.lz} @tab @command{lzip}
+@item @samp{.lzma} @tab @command{lzma}
+@item @samp{.tlz} @tab @command{lzma}
+@item @samp{.lzo} @tab @command{lzop}
+@item @samp{.xz} @tab @command{xz}
+@end multitable
@opindex use-compress-program
@item --use-compress-program=@var{prog}
@itemx -I=@var{prog}
Use external compression program @var{prog}. Use this option if you
-have a compression program that @GNUTAR{} does not support. There
-are two requirements to which @var{prog} should comply:
+are not happy with the compression program associated with the suffix
+at compile time or if you have a compression program that @GNUTAR{}
+does not support. There are two requirements to which @var{prog}
+should comply:
First, when called without options, it should read data from standard
input, compress it and output it on standard output.
#! /bin/sh
case $1 in
-d) gpg --decrypt - | gzip -d -c;;
-'') gzip -c | gpg -s ;;
+'') gzip -c | gpg -s;;
*) echo "Unknown option $1">&2; exit 1;;
esac
@end group
end up with less space on the tape.
@end ignore
+@menu
+* lbzip2:: Using lbzip2 with @GNUTAR{}.
+@end menu
+
+@node lbzip2
+@subsubsection Using lbzip2 with @GNUTAR{}.
+@cindex lbzip2
+@cindex Laszlo Ersek
+ @command{Lbzip2} is a multithreaded utility for handling
+@samp{bzip2} compression, written by Laszlo Ersek. It makes use of
+multiple processors to speed up its operation and in general works
+considerably faster than @command{bzip2}. For a detailed description
+of @command{lbzip2} see @uref{http://freshmeat.net/@/projects/@/lbzip2} and
+@uref{http://www.linuxinsight.com/@/lbzip2-parallel-bzip2-utility.html,
+lbzip2: parallel bzip2 utility}.
+
+ Recent versions of @command{lbzip2} are mostly command line compatible
+with @command{bzip2}, which makes it possible to automatically invoke
+it via the @option{--bzip2} @GNUTAR{} command line option. To do so,
+@GNUTAR{} must be configured with the @option{--with-bzip2} command
+line option, like this:
+
+@smallexample
+$ @kbd{./configure --with-bzip2=lbzip2 [@var{other-options}]}
+@end smallexample
+
+ Once configured and compiled this way, @command{tar --help} will show the
+following:
+
+@smallexample
+@group
+$ @kbd{tar --help | grep -- --bzip2}
+ -j, --bzip2 filter the archive through lbzip2
+@end group
+@end smallexample
+
+@noindent
+which means that running @command{tar --bzip2} will invoke @command{lbzip2}.
+
@node sparse
@subsection Archiving Sparse Files
@cindex Sparse Files
@node Attributes
@section Handling File Attributes
-@UNREVISED
+@cindex atrributes, files
+@cindex file attributes
When @command{tar} reads files, it updates their access times. To
avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
reset the access time retroactively or avoid changing it in the first
place.
-Handling of file attributes
-
@table @option
@opindex atime-preserve
@item --atime-preserve
The numeric ids are @emph{always} saved into @command{tar} archives.
The identifying names are added at create time when provided by the
-system, unless @option{--old-archive} (@option{-o}) is used. Numeric ids could be
+system, unless @option{--format=oldgnu} is used. Numeric ids could be
used when moving archives between a collection of machines using
a centralized management for attribution of numeric ids to users
and groups. This is often made through using the NIS capabilities.
symbolic links, and moreover, your distribution might be unusable if
it contains unresolved symbolic links.
+The @option{--dereference} option is not secure if an untrusted user
+can modify files during creation or extraction. @xref{Security}.
+
@node hard links
@subsection Hard Links
-@UNREVISED{}
@cindex File names, using hard links
@cindex hard links, dereferencing
@cindex dereferencing hard links
produces the following diagnostics:
@smallexample
-$ tar -c -f ../archive.tar jeden
+$ tar -c -f ../archive.tar -l jeden
tar: Missing links to `jeden'.
@end smallexample
@cindex ustar archive format
Archive format defined by @acronym{POSIX}.1-1988 specification is called
@code{ustar}. Although it is more flexible than the V7 format, it
-still has many restrictions (@xref{Formats,ustar}, for the detailed
+still has many restrictions (@pxref{Formats,ustar}, for the detailed
description of @code{ustar} format). Along with V7 format,
@code{ustar} format is a good choice for archives intended to be read
with other implementations of @command{tar}.
%d/PaxHeaders.%p/%f
@end smallexample
+@item exthdr.mtime=@var{value}
+
+This keyword defines the value of the @samp{mtime} field that
+is written into the ustar header blocks for the extended headers.
+By default, the @samp{mtime} field is set to the modification time
+of the archive member described by that extended headers.
+
@item globexthdr.name=@var{string}
This keyword allows user control over the name that is written into
the ustar header blocks for global extended header records. The name
environment variable. If @var{TMPDIR} is not set, @command{tar}
uses @samp{/tmp}.
+@item globexthdr.mtime=@var{value}
+
+This keyword defines the value of the @samp{mtime} field that
+is written into the ustar header blocks for the global extended headers.
+By default, the @samp{mtime} field is set to the time when
+@command{tar} was invoked.
+
@item @var{keyword}=@var{value}
When used with one of archive-creation commands, these keyword/value pairs
will be included at the beginning of the archive in a global extended
stored in the archive.
@end table
+In any of the forms described above, the @var{value} may be
+a string enclosed in curly braces. In that case, the string
+between the braces is understood either as a textual time
+representation, as described in @ref{Date input formats}, or a name of
+the existing file, starting with @samp{/} or @samp{.}. In the latter
+case, the modification time of that file is used.
+
+For example, to set all modification times to the current date, you
+use the following option:
+
+@smallexample
+--pax-option='mtime:=@{now@}'
+@end smallexample
+
+Note quoting of the option's argument.
+
+@cindex archives, binary equivalent
+@cindex binary equivalent archives, creating
+As another example, here is the option that ensures that any two
+archives created using it, will be binary equivalent if they have the
+same contents:
+
+@smallexample
+--pax-option=exthdr.name=%d/PaxHeaders/%f,atime:=0
+@end smallexample
+
@node Checksumming
@subsection Checksumming Problems
use signed checksums, while @GNUTAR{} uses unsigned
checksums while creating archives, as per @acronym{POSIX} standards. On
reading, @GNUTAR{} computes both checksums and
-accept any. It is somewhat worrying that a lot of people may go
+accepts 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.
-@GNUTAR{} compute checksums both ways, and accept
+@GNUTAR{} computes checksums both ways, and accept
any on read, so @acronym{GNU} tar can read Sun tapes even with their
wrong checksums. @GNUTAR{} produces the standard
checksum, however, raising incompatibilities with Sun. That is to
@cindex large values
@cindex future time stamps
@cindex negative time stamps
-@UNREVISED{}
+@UNREVISED
The above sections suggest to use @samp{oldest possible} archive
format if in doubt. However, sometimes it is not possible. If you
additional data will be needed to restore it. If the original file
name was @file{@var{dir}/@var{name}}, then the condensed file will be
named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
-@var{n} is a decimal number@footnote{technically speaking, @var{n} is a
+@var{n} is a decimal number@footnote{Technically speaking, @var{n} is a
@dfn{process @acronym{ID}} of the @command{tar} process which created the
archive (@pxref{PAX keywords}).}.
(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 @acronym{BSD} file system);
+file systems that support 32-bit i-numbers (e.g., the @acronym{BSD} file system);
@command{cpio}s way requires you to play some games (in its ``binary''
format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
they're 18 bits---it would have to play games with the "file system @acronym{ID}"
The exact path to this utility is determined when configuring the package.
It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for
your installation prefix. This location may also be overridden at
-runtime by using @option{rmt-command=@var{command}} option (@xref{Option Summary,
+runtime by using the @option{--rmt-command=@var{command}} option (@xref{Option Summary,
---rmt-command}, for detailed description of this option. @xref{Remote
Tape Server}, for the description of @command{rmt} command).
@xopindex{tape-length, short description}
@item -L @var{num}
-@itemx --tape-length=@var{num}
-Change tape after writing @var{num} x 1024 bytes.
+@itemx --tape-length=@var{size}[@var{suf}]
+Change tape after writing @var{size} units of data. Unless @var{suf} is
+given, @var{size} is treated as kilobytes, i.e. @samp{@var{size} x
+1024} bytes. The following suffixes alter this behavior:
+
+@float Table, size-suffixes
+@caption{Size Suffixes}
+@multitable @columnfractions 0.2 0.3 0.3
+@headitem Suffix @tab Units @tab Byte Equivalent
+@item b @tab Blocks @tab @var{size} x 512
+@item B @tab Kilobytes @tab @var{size} x 1024
+@item c @tab Bytes @tab @var{size}
+@item G @tab Gigabytes @tab @var{size} x 1024^3
+@item K @tab Kilobytes @tab @var{size} x 1024
+@item k @tab Kilobytes @tab @var{size} x 1024
+@item M @tab Megabytes @tab @var{size} x 1024^2
+@item P @tab Petabytes @tab @var{size} x 1024^5
+@item T @tab Terabytes @tab @var{size} x 1024^4
+@item w @tab Words @tab @var{size} x 2
+@end multitable
+@end float
This option might be useful when your tape drivers do not properly
detect end of physical tapes. By being slightly conservative on the
@end table
@node Remote Tape Server
-@section The Remote Tape Server
+@section Remote Tape Server
@cindex remote tape drive
@pindex rmt
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}.
+that can be backspaced with the @code{MTIOCTOP} @code{ioctl}).
This means that the @option{--append}, @option{--concatenate}, and
@option{--delete} commands will not work on any other kind of file.
@node Blocking
@section Blocking
-@UNREVISED
+@cindex block
+@cindex record
@dfn{Block} and @dfn{record} terminology is rather confused, and it
is also confusing to the expert reader. On the other hand, readers
blocking factor (particularly if you're not sure what the blocking factor
is), you can usually use the @option{--read-full-records} (@option{-B}) option while
specifying a blocking factor larger then the blocking factor of the archive
-(i.e., @samp{tar --extract --read-full-records --blocking-factor=300}.
+(i.e., @samp{tar --extract --read-full-records --blocking-factor=300}).
@xref{list}, for more information on the @option{--list} (@option{-t})
operation. @xref{Reading}, for a more detailed explanation of that option.
@table @option
@item -b @var{blocks}
@itemx --blocking-factor=@var{blocks}
-Set record size to @math{@var{blocks} * 512} bytes.
+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
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.
+tape motion without losing information.
@cindex Exabyte blocking
@cindex DAT blocking
Moves tape position back @var{number} files.
@item rewind
-Rewinds the tape. (Ignores @var{number}).
+Rewinds the tape. (Ignores @var{number}.)
@item offline
@itemx rewoff1
-Rewinds the tape and takes the tape device off-line. (Ignores @var{number}).
+Rewinds the tape and takes the tape device off-line. (Ignores @var{number}.)
@item status
Prints status information about the tape unit.
@end table
-@FIXME{Is there a better way to frob the spacing on the list?}
-
If you don't specify a @var{tapename}, @command{mt} uses the environment
variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
the default device specified in your @file{sys/mtio.h} file
the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
archive can be manipulated like any other archive (provided the
@option{--multi-volume} option is specified), but is stored on more
-than one tape or disk.
+than one tape or file.
When you specify @option{--multi-volume}, @command{tar} does not report an
error when it comes to the end of an archive volume (when reading), or
@anchor{tape-length}
@table @option
@opindex tape-length
-@item --tape-length=@var{size}
-@itemx -L @var{size}
-Set maximum length of a volume. The @var{size} argument should then
-be the usable size of the tape in units of 1024 bytes. This option
-selects @option{--multi-volume} automatically. For example:
+@item --tape-length=@var{size}[@var{suf}]
+@itemx -L @var{size}[@var{suf}]
+Set maximum length of a volume. The @var{suf}, if given, specifies
+units in which @var{size} is expressed, e.g. @samp{2M} mean 2
+megabytes (@pxref{size-suffixes}, for a list of allowed size
+suffixes). Without @var{suf}, units of 1024 bytes (kilobyte) are
+assumed.
+
+This option selects @option{--multi-volume} automatically. For example:
@smallexample
$ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}}
@end smallexample
+
+@noindent
+or, which is equivalent:
+
+@smallexample
+$ @kbd{tar --create --tape-length=4G --file=/dev/tape @var{files}}
+@end smallexample
@end table
@anchor{change volume prompt}
@table @kbd
@item ?
-Request @command{tar} to explain possible responses
+Request @command{tar} to explain possible responses.
@item q
Request @command{tar} to exit immediately.
@item n @var{file-name}
Request @command{tar} to run a subshell. This option can be disabled
by giving @option{--restrict} command line option to
@command{tar}@footnote{@xref{--restrict}, for more information about
-this option}.
+this option.}.
@item y
Request @command{tar} to begin writing the next volume.
@end table
@vrindex TAR_BLOCKING_FACTOR, info script environment variable
@item TAR_BLOCKING_FACTOR
-Current blocking factor (@pxref{Blocking}.
+Current blocking factor (@pxref{Blocking}).
@vrindex TAR_VOLUME, info script environment variable
@item TAR_VOLUME
@vrindex TAR_SUBCOMMAND, info script environment variable
@item TAR_SUBCOMMAND
-A 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
@node Tape Files
@subsection Tape Files
+@cindex labeling archives
+@opindex label
@UNREVISED
To give the archive a name which will be recorded in it, use the
@option{--multi-volume} (@pxref{Using Multiple Tapes}), then the
volume label will have @samp{Volume @var{nnn}} appended to the name
you give, where @var{nnn} is the number of the volume of the archive.
-(If you use the @option{--label=@var{volume-label}}) option when
+If you use the @option{--label=@var{volume-label}} option when
reading an archive, it checks to make sure the label on the tape
-matches the one you give. @xref{label}.
+matches the one you gave. @xref{label}.
When @command{tar} writes an archive to tape, it creates a single
tape file. If multiple archives are written to the same tape, one
@cindex Labeling an archive
@cindex Labels on the archive media
@cindex Labeling multi-volume archives
-@UNREVISED
@opindex label
To avoid problems caused by misplaced paper labels on the archive
-media, you can include a @dfn{label} entry---an archive member which
-contains the name of the archive---in the archive itself. Use the
+media, you can include a @dfn{label} entry --- an archive member which
+contains the name of the archive --- in the archive itself. Use the
@option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
-option in conjunction with the @option{--create} operation to include
-a label entry in the archive as it is being created.
+option@footnote{Until version 1.10, that option was called
+@option{--volume}, but is not available under that name anymore.} in
+conjunction with the @option{--create} operation to include a label
+entry in the archive as it is being created.
@table @option
@item --label=@var{archive-label}
the archive is being created, when used in conjunction with the
@option{--create} operation. Checks to make sure the archive label
matches the one specified (when used in conjunction with any other
-operation.
+operation).
@end table
If you create an archive using both
However, @option{--list} option will cause listing entire
contents of the archive, which may be undesirable (for example, if the
archive is stored on a tape). You can request checking only the volume
-by specifying @option{--test-label} option. This option reads only the
+label by specifying @option{--test-label} option. This option reads only the
first block of an archive, so it can be used with slow storage
devices. For example:
@end group
@end smallexample
- If @option{--test-label} is used with a single command line
-argument, @command{tar} compares the volume label with the
-argument. It exits with code 0 if the two strings match, and with code
-2 otherwise. In this case no output is displayed. For example:
+ If @option{--test-label} is used with one or more command line
+arguments, @command{tar} compares the volume label with each
+argument. It exits with code 0 if a match is found, and with code 1
+otherwise@footnote{Note that @GNUTAR{} versions up to 1.23 indicated
+mismatch with an exit code 2 and printed a spurious diagnostics on
+stderr.}. No output is displayed, unless you also used the
+@option{--verbose} option. For example:
@smallexample
@group
-$ @kbd{tar --test-label --file=iamanarchive 'iamalable'}
+$ @kbd{tar --test-label --file=iamanarchive 'iamalabel'}
@result{} 0
-$ @kbd{tar --test-label --file=iamanarchive 'iamalable' alabel}
+$ @kbd{tar --test-label --file=iamanarchive 'alabel'}
+@result{} 1
+@end group
+@end smallexample
+
+ When used with the @option{--verbose} option, @command{tar}
+prints the actual volume label (if any), and a verbose diagnostics in
+case of a mismatch:
+
+@smallexample
+@group
+$ @kbd{tar --test-label --verbose --file=iamanarchive 'iamalabel'}
+iamalabel
+@result{} 0
+$ @kbd{tar --test-label --verbose --file=iamanarchive 'alabel'}
+iamalabel
+tar: Archive label mismatch
@result{} 1
@end group
@end smallexample
creation time, it sounded logical to equally help the user taking care
of it when the archive is being read.
- The @option{--label} was once called @option{--volume}, but is not
-available under that name anymore.
-
You can also use @option{--label} to get a common information on
all tapes of a series. For having this information different in each
series created through a single script used on a regular basis, just
@group
$ @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`"}
+ --label="Daily backup for `date +%Y-%m-%d`"}
@end group
@end smallexample
- Also note that each label has its own date and time, which corresponds
-to when @GNUTAR{} initially attempted to write it,
+ Some more notes about volume labels:
+
+@itemize @bullet
+@item Each label has its own date and time, which corresponds
+to the time when @GNUTAR{} initially attempted to write it,
often soon after the operator launches @command{tar} or types the
-carriage return telling that the next tape is ready. 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.
+carriage return telling that the next tape is ready.
+
+@item Comparing date labels to get an idea of tape throughput is
+unreliable. It gives correct results only if the delays for rewinding
+tapes and the operator switching them were negligible, which is
+usually not the case.
+@end itemize
@node verify
@section Verifying Data as It is Stored
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).
+will not protect it from magnet fields or other physical hazards.)
The write protection device itself is usually an integral part of the
physical media, and can be a two position (write enabled/write
which can be removed from the center of a tape reel, or some other
changeable feature.
+@node Reliability and security
+@chapter Reliability and Security
+
+The @command{tar} command reads and writes files as any other
+application does, and is subject to the usual caveats about
+reliability and security. This section contains some commonsense
+advice on the topic.
+
+@menu
+* Reliability::
+* Security::
+@end menu
+
+@node Reliability
+@section Reliability
+
+Ideally, when @command{tar} is creating an archive, it reads from a
+file system that is not being modified, and encounters no errors or
+inconsistencies while reading and writing. If this is the case, the
+archive should faithfully reflect what was read. Similarly, when
+extracting from an archive, ideally @command{tar} ideally encounters
+no errors and the extracted files faithfully reflect what was in the
+archive.
+
+However, when reading or writing real-world file systems, several
+things can go wrong; these include permissions problems, corruption of
+data, and race conditions.
+
+@menu
+* Permissions problems::
+* Data corruption and repair::
+* Race conditions::
+@end menu
+
+@node Permissions problems
+@subsection Permissions Problems
+
+If @command{tar} encounters errors while reading or writing files, it
+normally reports an error and exits with nonzero status. The work it
+does may therefore be incomplete. For example, when creating an
+archive, if @command{tar} cannot read a file then it cannot copy the
+file into the archive.
+
+@node Data corruption and repair
+@subsection Data Corruption and Repair
+
+If an archive becomes corrupted by an I/O error, this may corrupt the
+data in an extracted file. Worse, it may corrupt the file's metadata,
+which may cause later parts of the archive to become misinterpreted.
+An tar-format archive contains a checksum that most likely will detect
+errors in the metadata, but it will not detect errors in the data.
+
+If data corruption is a concern, you can compute and check your own
+checksums of an archive by using other programs, such as
+@command{cksum}.
+
+When attempting to recover from a read error or data corruption in an
+archive, you may need to skip past the questionable data and read the
+rest of the archive. This requires some expertise in the archive
+format and in other software tools.
+
+@node Race conditions
+@subsection Race conditions
+
+If some other process is modifying the file system while @command{tar}
+is reading or writing files, the result may well be inconsistent due
+to race conditions. For example, if another process creates some
+files in a directory while @command{tar} is creating an archive
+containing the directory's files, @command{tar} may see some of the
+files but not others, or it may see a file that is in the process of
+being created. The resulting archive may not be a snapshot of the
+file system at any point in time. If an application such as a
+database system depends on an accurate snapshot, restoring from the
+@command{tar} archive of a live file system may therefore break that
+consistency and may break the application. The simplest way to avoid
+the consistency issues is to avoid making other changes to the file
+system while tar is reading it or writing it.
+
+When creating an archive, several options are available to avoid race
+conditions. Some hosts have a way of snapshotting a file system, or
+of temporarily suspending all changes to a file system, by (say)
+suspending the only virtual machine that can modify a file system; if
+you use these facilities and have @command{tar -c} read from a
+snapshot when creating an archive, you can avoid inconsistency
+problems. More drastically, before starting @command{tar} you could
+suspend or shut down all processes other than @command{tar} that have
+access to the file system, or you could unmount the file system and
+then mount it read-only.
+
+When extracting from an archive, one approach to avoid race conditions
+is to create a directory that no other process can write to, and
+extract into that.
+
+@node Security
+@section Security
+
+In some cases @command{tar} may be used in an adversarial situation,
+where an untrusted user is attempting to gain information about or
+modify otherwise-inaccessible files. Dealing with untrusted data
+(that is, data generated by an untrusted user) typically requires
+extra care, because even the smallest mistake in the use of
+@command{tar} is more likely to be exploited by an adversary than by a
+race condition.
+
+@menu
+* Privacy::
+* Integrity::
+* Live untrusted data::
+* Security rules of thumb::
+@end menu
+
+@node Privacy
+@subsection Privacy
+
+Standard privacy concerns apply when using @command{tar}. For
+example, suppose you are archiving your home directory into a file
+@file{/archive/myhome.tar}. Any secret information in your home
+directory, such as your SSH secret keys, are copied faithfully into
+the archive. Therefore, if your home directory contains any file that
+should not be read by some other user, the archive itself should be
+not be readable by that user. And even if the archive's data are
+inaccessible to untrusted users, its metadata (such as size or
+last-modified date) may reveal some information about your home
+directory; if the metadata are intended to be private, the archive's
+parent directory should also be inaccessible to untrusted users.
+
+One precaution is to create @file{/archive} so that it is not
+accessible to any user, unless that user also has permission to access
+all the files in your home directory.
+
+Similarly, when extracting from an archive, take care that the
+permissions of the extracted files are not more generous than what you
+want. Even if the archive itself is readable only to you, files
+extracted from it have their own permissions that may differ.
+
+@node Integrity
+@subsection Integrity
+
+When creating archives, take care that they are not writable by a
+untrusted user; otherwise, that user could modify the archive, and
+when you later extract from the archive you will get incorrect data.
+
+When @command{tar} extracts from an archive, by default it writes into
+files relative to the working directory. If the archive was generated
+by an untrusted user, that user therefore can write into any file
+under the working directory. If the working directory contains a
+symbolic link to another directory, the untrusted user can also write
+into any file under the referenced directory. When extracting from an
+untrusted archive, it is therefore good practice to create an empty
+directory and run @command{tar} in that directory.
+
+When extracting from two or more untrusted archives, each one should
+be extracted independently, into different empty directories.
+Otherwise, the first archive could create a symbolic link into an area
+outside the working directory, and the second one could follow the
+link and overwrite data that is not under the working directory. For
+example, when restoring from a series of incremental dumps, the
+archives should have been created by a trusted process, as otherwise
+the incremental restores might alter data outside the working
+directory.
+
+If you use the @option{--absolute-names} (@option{-P}) option when
+extracting, @command{tar} respects any file names in the archive, even
+file names that begin with @file{/} or contain @file{..}. As this
+lets the archive overwrite any file in your system that you can write,
+the @option{--absolute-names} (@option{-P}) option should be used only
+for trusted archives.
+
+Conversely, with the @option{--keep-old-files} (@option{-k}) option,
+@command{tar} refuses to replace existing files when extracting; and
+with the @option{--no-overwrite-dir} option, @command{tar} refuses to
+replace the permissions or ownership of already-existing directories.
+These options may help when extracting from untrusted archives.
+
+@node Live untrusted data
+@subsection Dealing with Live Untrusted Data
+
+Extra care is required when creating from or extracting into a file
+system that is accessible to untrusted users. For example, superusers
+who invoke @command{tar} must be wary about its actions being hijacked
+by an adversary who is reading or writing the file system at the same
+time that @command{tar} is operating.
+
+When creating an archive from a live file system, @command{tar} is
+vulnerable to denial-of-service attacks. For example, an adversarial
+user could create the illusion of an indefinitely-deep directory
+hierarchy @file{d/e/f/g/...} by creating directories one step ahead of
+@command{tar}, or the illusion of an indefinitely-long file by
+creating a sparse file but arranging for blocks to be allocated just
+before @command{tar} reads them. There is no easy way for
+@command{tar} to distinguish these scenarios from legitimate uses, so
+you may need to monitor @command{tar}, just as you'd need to monitor
+any other system service, to detect such attacks.
+
+While a superuser is extracting from an archive into a live file
+system, an untrusted user might replace a directory with a symbolic
+link, in hopes that @command{tar} will follow the symbolic link and
+extract data into files that the untrusted user does not have access
+to. Even if the archive was generated by the superuser, it may
+contain a file such as @file{d/etc/passwd} that the untrusted user
+earlier created in order to break in; if the untrusted user replaces
+the directory @file{d/etc} with a symbolic link to @file{/etc} while
+@command{tar} is running, @command{tar} will overwrite
+@file{/etc/passwd}. This attack can be prevented by extracting into a
+directory that is inaccessible to untrusted users.
+
+Similar attacks via symbolic links are also possible when creating an
+archive, if the untrusted user can modify an ancestor of a top-level
+argument of @command{tar}. For example, an untrusted user that can
+modify @file{/home/eve} can hijack a running instance of @samp{tar -cf
+- /home/eve/Documents/yesterday} by replacing
+@file{/home/eve/Documents} with a symbolic link to some other
+location. Attacks like these can be prevented by making sure that
+untrusted users cannot modify any files that are top-level arguments
+to @command{tar}, or any ancestor directories of these files.
+
+@node Security rules of thumb
+@subsection Security Rules of Thumb
+
+This section briefly summarizes rules of thumb for avoiding security
+pitfalls.
+
+@itemize @bullet
+
+@item
+Protect archives at least as much as you protect any of the files
+being archived.
+
+@item
+Extract from an untrusted archive only into an otherwise-empty
+directory. This directory and its parent should be accessible only to
+trusted users. For example:
+
+@example
+@group
+$ @kbd{chmod go-rwx .}
+$ @kbd{mkdir -m go-rwx dir}
+$ @kbd{cd dir}
+$ @kbd{tar -xvf /archives/got-it-off-the-net.tar.gz}
+@end group
+@end example
+
+As a corollary, do not do an incremental restore from an untrusted archive.
+
+@item
+Do not let untrusted users access files extracted from untrusted
+archives without checking first for problems such as setuid programs.
+
+@item
+Do not let untrusted users modify directories that are ancestors of
+top-level arguments of @command{tar}. For example, while you are
+executing @samp{tar -cf /archive/u-home.tar /u/home}, do not let an
+untrusted user modify @file{/}, @file{/archive}, or @file{/u}.
+
+@item
+Pay attention to the diagnostics and exit status of @command{tar}.
+
+@item
+When archiving live file systems, monitor running instances of
+@command{tar} to detect denial-of-service attacks.
+
+@item
+Avoid unusual options such as @option{--absolute-names} (@option{-P}),
+@option{--dereference} (@option{-h}), @option{--overwrite},
+@option{--recursive-unlink}, and @option{--remove-files} unless you
+understand their security implications.
+
+@end itemize
+
@node Changes
@appendix Changes
tar: Error exit delayed from previous errors
@end smallexample
-To treat member names as globbing patterns, use --wildcards option.
+To treat member names as globbing patterns, use the @option{--wildcards} option.
If you want to tar to mimic the behavior of versions prior to 1.15.91,
add this option to your @env{TAR_OPTIONS} variable.
distribution tarballs. @xref{Formats,v7}, for the detailed discussion
of this issue and its implications.
-@FIXME{Change the first argument to tar-formats when the new Automake is
-out. The proposition to add @anchor{} to the appropriate place of its
-docs was accepted by Automake people --Sergey 2006-05-25}.
-@xref{Options, tar-v7, Changing Automake's Behavior,
+@xref{Options, tar-formats, Changing Automake's Behavior,
automake, GNU Automake}, for a description on how to use various
archive formats with @command{automake}.
Earlier versions of @GNUTAR{} understood @option{-l} option as a
synonym for @option{--one-file-system}. Since such usage contradicted
to UNIX98 specification and harmed compatibility with other
-implementation, it was declared deprecated in version 1.14. However,
+implementations, it was declared deprecated in version 1.14. However,
to facilitate transition to its new semantics, it was supported by
versions 1.15 and 1.15.90. The present use of @option{-l} as a short
variant of @option{--check-links} was introduced in version 1.15.91.
@appendix Free Software Needs Free Documentation
@include freemanuals.texi
-@node Copying This Manual
-@appendix Copying This Manual
-
-@menu
-* GNU Free Documentation License:: License for copying this manual
-@end menu
+@node GNU Free Documentation License
+@appendix GNU Free Documentation License
@include fdl.texi
This appendix contains an index of all @GNUTAR{} long command line
options. The options are listed without the preceding double-dash.
-For a cross-reference of short command line options, @ref{Short Option Summary}.
+For a cross-reference of short command line options, see
+@ref{Short Option Summary}.
@printindex op