@c do not alter them inconsiderately. Much work is needed for GNU tar
@c internals (the sources, the programs themselves). Revising the
@c adequacy of the manual while revising the sources, and cleaning them
-@c both at the same time, seems to him like a good way to proceed.
+@c both at the same time, is a good way to proceed.
@c ---------------------------------------------------------------------
@c Output marks for nodes needing revision, but not in PUBLISH rendition.
@c @value{\entry\}
@c @end macro
+@macro GNUTAR
+@acronym{GNU} @command{tar}
+@end macro
+
@set op-absolute-names @kbd{--absolute-names} (@kbd{-P})
@set ref-absolute-names @ref{absolute}
@set xref-absolute-names @xref{absolute}
@set xref-bzip2 @xref{gzip}
@set pxref-bzip2 @pxref{gzip}
+@set op-check-links @kbd{--check-links} (@kbd{-l})
+@set ref-check-links @ref{--check-links}
+@set xref-check-links @xref{--check-links}
+@set pxref-check-links @pxref{--check-links}
+
@set op-checkpoint @kbd{--checkpoint}
@set ref-checkpoint @ref{verbose}
@set xref-checkpoint @xref{verbose}
@set pxref-checkpoint @pxref{verbose}
+@set op-check-links @kbd{--check-links}
+
@set op-compare @kbd{--compare} (@kbd{--diff}, @kbd{-d})
@set ref-compare @ref{compare}
@set xref-compare @xref{compare}
@set pxref-interactive @pxref{interactive}
@set op-keep-old-files @kbd{--keep-old-files} (@kbd{-k})
-@set ref-keep-old-files @ref{Writing}
-@set xref-keep-old-files @xref{Writing}
-@set pxref-keep-old-files @pxref{Writing}
+@set ref-keep-old-files @ref{Keep Old Files}
+@set xref-keep-old-files @xref{Keep Old Files}
+@set pxref-keep-old-files @pxref{Keep Old Files}
+
+@set op-keep-newer-files @kbd{--keep-old-files}
+@set ref-keep-newer-files @ref{Keep Newer Files}
+@set xref-keep-newer-files @xref{Keep Newer Files}
+@set pxref-keep-newer-files @pxref{Keep Newer Files}
@set op-label @kbd{--label=@var{archive-label}} (@kbd{-V @var{archive-label}})
@set ref-label @ref{label}
@set xref-no-recursion @xref{recurse}
@set pxref-no-recursion @pxref{recurse}
-@set op-no-same-owner @kbd{--no-same-owner}
+@set op-no-same-owner @kbd{--no-same-owner} (@kbd{-o})
@set ref-no-same-owner @ref{Attributes}
@set xref-no-same-owner @xref{Attributes}
@set pxref-no-same-owner @pxref{Attributes}
@set xref-numeric-owner @xref{Attributes}
@set pxref-numeric-owner @pxref{Attributes}
+@set op-occurrence @kbd{--occurrence}
+@set ref-occurrence @ref{--occurrence}
+@set xref-occurrence @xref{--occurrence}
+@set pxref-occurrence @pxref{--occurrence}
+
@set op-old-archive @kbd{--old-archive} (@kbd{-o})
@set ref-old-archive @ref{old}
@set xref-old-archive @xref{old}
@set xref-owner @xref{Option Summary}
@set pxref-owner @pxref{Option Summary}
+@set op-format @kbd{--format}
+@set ref-format @ref{format}
+@set xref-format @xref{format}
+@set pxref-format @pxref{format}
+
+@set op-format-v7 @kbd{--format=v7}
+@set op-format-gnu @kbd{--format=gnu}
+@set op-format-oldgnu @kbd{--format=oldgnu}
+@set op-format-posix @kbd{--format=posix}
+@set op-format-ustar @kbd{--format=ustar}
+
@set op-posix @kbd{--posix}
@set ref-posix @ref{posix}
@set xref-posix @xref{posix}
@set xref-starting-file @xref{Scarce}
@set pxref-starting-file @pxref{Scarce}
+@set op-strip-path @kbd{--strip-path}
+@set ref-strip-path @ref{--strip-path}
+@set xref-strip-path @xref{--strip-path}
+@set pxref-strip-path @pxref{--strip-path}
+
@set op-suffix @kbd{--suffix=@var{suffix}}
@set ref-suffix @ref{Backup options}
@set xref-suffix @xref{Backup options}
from archives.
Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
-2003 Free Software Foundation, Inc.
+2003, 2004 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
@dircategory Individual utilities
@direntry
-* tar: (tar)tar invocation. Invoking @acronym{GNU} @command{tar}
+* tar: (tar)tar invocation. Invoking @GNUTAR{}.
@end direntry
@shorttitlepage @acronym{GNU} @command{tar}
* Definitions:: Some Definitions
* What tar Does:: What @command{tar} Does
* Naming tar Archives:: How @command{tar} Archives are Named
-* posix compliance::
-* Authors:: @acronym{GNU} @command{tar} Authors
+* Current status:: Current development status of @GNUTAR{}
+* Authors:: @GNUTAR{} Authors
* Reports:: Reporting bugs or suggestions
Tutorial Introduction to @command{tar}
* extract dir::
* failing commands::
-Invoking @acronym{GNU} @command{tar}
+Invoking @GNUTAR{}
* Synopsis::
* using tar options::
* Option Summary::
* Short Option Summary::
-@acronym{GNU} @command{tar} Operations
+@GNUTAR{} Operations
* Basic tar::
* Advanced tar::
* Applications::
* looking ahead::
-Advanced @acronym{GNU} @command{tar} Operations
+Advanced @GNUTAR{} Operations
* Operations::
* append::
* Dealing with Old Files::
* Overwrite Old Files::
* Keep Old Files::
+* Keep Newer Files::
* Unlink First::
* Recursive Unlink::
* Modification Times::
* Day of week items:: Monday and others.
* Relative items in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings:: 19931219, 1440.
-* Authors of getdate:: Bellovin, Eggert, Salz, Berets, et al.
+* Seconds since the Epoch:: @@1078100502.
+* Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
Controlling the Archive Format
@node Introduction
@chapter Introduction
-@acronym{GNU} @command{tar} creates
-and manipulates (@dfn{archives}) which are actually collections of
+@GNUTAR{} creates
+and manipulates @dfn{archives} which are actually collections of
many other files; the program provides users with an organized and
systematic method for controlling a large amount of data.
The name ``tar'' originally came from the phrase ``Tape ARchive'', but
* Definitions:: Some Definitions
* What tar Does:: What @command{tar} Does
* Naming tar Archives:: How @command{tar} Archives are Named
-* posix compliance::
-* Authors:: @acronym{GNU} @command{tar} Authors
+* Current status:: Current development status of @GNUTAR{}
+* Authors:: @GNUTAR{} Authors
* Reports:: Reporting bugs or suggestions
@end menu
@section What this Book Contains
The first part of this chapter introduces you to various terms that will
-recur throughout the book. It also tells you who has worked on @acronym{GNU}
-@command{tar} and its documentation, and where you should send bug reports
+recur throughout the book. It also tells you who has worked on @GNUTAR{}
+and its documentation, and where you should send bug reports
or comments.
The second chapter is a tutorial (@pxref{Tutorial}) which provides a
In addition, one section of this manual (@pxref{Standard}) contains a
big quote which is taken directly from @command{tar} sources.
-In general, we give both the long and short (abbreviated) option names
+In general, we give both long and short (abbreviated) option names
at least once in each section where the relevant option is covered, so
that novice readers will become familiar with both styles. (A few
options have no short versions, and the relevant sections will
puts a collection of files (possibly pertaining to many users and
projects) together on a disk or a tape. This guards against
accidental destruction of the information in those files.
-@acronym{GNU} @command{tar} has special features that allow it to be
+@GNUTAR{} has special features that allow it to be
used to make incremental and full dumps of all the files in a
filesystem.
this manual, we consistently refer to ``archives'' and ``archive
members'' to make learning to use @command{tar} easier for novice users.
-@node posix compliance
-@section @sc{posix} Compliance
+@node Current status
+@section Current development status of @GNUTAR{}
-@noindent
-@FIXME{must ask franc,ois about this. dan hagerty thinks this might
-be an issue, but we're not really sure at this time. dan just tried a
-test case of mixing up options' orders while the variable was set, and
-there was no problem...}
-
-We make some of our recommendations throughout this book for one
-reason in addition to what we think of as ``good sense''. The main
-additional reason for a recommendation is to be compliant with the
-@sc{posix} standards. If you set the shell environment variable
-@env{POSIXLY_CORRECT}, @acronym{GNU} @command{tar} will force you to
-adhere to these standards. Therefore, if this variable is set and you
-violate one of the @sc{posix} standards in the way you phrase a
-command, for example, @acronym{GNU} @command{tar} will not allow the
-command and will signal an error message. You would then have to
-reorder the options or rephrase the command to comply with the
-@sc{posix} standards.
-
-There is a chance in the future that, if you set this environment
-variable, your archives will be forced to comply with @sc{posix} standards,
-also. No @acronym{GNU} @command{tar} extensions will be allowed.
+@GNUTAR{} is currently in the process of active development, whose
+primary aims are:
+
+@itemize @bullet
+@item Improve compatibility between @GNUTAR{} and other @command{tar}
+implementations.
+@item Switch to using @acronym{POSIX} archives.
+@item Revise sparse file handling and multiple volume processing.
+@item Merge with the @acronym{GNU} @code{paxutils} project.
+@end itemize
+
+Some of these aims are already attained, while others are still
+being worked upon. From the point of view of an end user, the
+following issues need special mentioning:
+
+@table @asis
+@item Use of short option @option{-o}.
+
+Earlier versions of @GNUTAR{} understood @option{-o} command line
+option as a synonym for @option{--old-archive}.
+
+@GNUTAR{} starting from version 1.13.90 understands this option as
+a synonym for @option{--no-same-owner}. This is compatible with
+UNIX98 @command{tar} implementations.
+
+However, to facilitate transition, @option{-o} option retains its
+old semantics when it is used with one of archive-creation commands.
+Users are encouraged to use @value{op-format-oldgnu} instead.
+
+It is especially important, since versions of @acronym{GNU} Automake
+up to and including 1.8.4 invoke tar with this option to produce
+distribution tarballs. @xref{Formats,v7}, for the detailed discussion
+of this issue and its implications.
+
+Future versions of @GNUTAR{} will understand @option{-o} only as a
+synonym for @option{--no-same-owner}.
+
+@item Use of short option @option{-l}
+
+Earlier versions of @GNUTAR{} understood @option{-l} option as a
+synonym for @samp{--one-file-system}. Such usage is deprecated.
+For compatibility with other implementations future versions of
+@GNUTAR{} will understand this option as a synonym for
+@option{--check-links}.
+
+@item Use of options @option{--portability} and @option{--old-archive}
+
+These options are deprecated. Please use @option{--format=v7} instead.
+
+@item Use of option @option{--posix}
+
+This option is deprecated. Please use @option{--format=posix} instead.
+@end table
@node Authors
-@section @acronym{GNU} @command{tar} Authors
+@section @GNUTAR{} Authors
-@acronym{GNU} @command{tar} was originally written by John Gilmore,
+@GNUTAR{} was originally written by John Gilmore,
and modified by many people. The @acronym{GNU} enhancements were
written by Jay Fenlason, then Joy Kendall, and the whole package has
-been further maintained by Thomas Bushnell, n/BSG, and finally
-Fran@,{c}ois Pinard, with the help of numerous and kind users.
+been further maintained by Thomas Bushnell, n/BSG, Fran@,{c}ois
+Pinard, Paul Eggert, and finally Sergey Poznyakoff with the help of
+numerous and kind users.
We wish to stress that @command{tar} is a collective work, and owes much to
all those people who reported problems, offered solutions and other
insights, or shared their thoughts and suggestions. An impressive, yet
partial list of those contributors can be found in the @file{THANKS}
-file from the @acronym{GNU} @command{tar} distribution.
+file from the @GNUTAR{} distribution.
@FIXME{i want all of these names mentioned, Absolutely. BUT, i'm not
sure i want to spell out the history in this detail, at least not for
@FIXME{History is more important, and surely more interesting, than
actual names. Quoting names without history would be meaningless. FP}
-Jay Fenlason put together a draft of a @acronym{GNU} @command{tar}
+Jay Fenlason put together a draft of a @GNUTAR{}
manual, borrowing notes from the original man page from John Gilmore.
This was withdrawn in version 1.11. Thomas Bushnell, n/BSG and Amy
-Gorin worked on a tutorial and manual for @acronym{GNU} @command{tar}.
+Gorin worked on a tutorial and manual for @GNUTAR{}.
Fran@,{c}ois Pinard put version 1.11.8 of the manual together by
taking information from all these sources and merging them. Melissa
Weisshaus finally edited and redesigned the book to create version
For version 1.12, Daniel Hagerty contributed a great deal of technical
consulting. In particular, he is the primary author of @ref{Backups}.
+In July, 2003 @GNUTAR{} was put on CVS at @url{savannah.gnu.org}, and
+an active development and maintenance work has started
+again. Currently @GNUTAR{} is being maintained by Paul Eggert, Sergey
+Poznyakoff and Jeff Bailey.
+
+Support for @acronym{POSIX} archives was added by Sergey Poznyakoff.
+
@node Reports
@section Reporting bugs or suggestions
If you find problems or have suggestions about this program or manual,
please report them to @file{bug-tar@@gnu.org}.
+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}.
+
@node Tutorial
@chapter Tutorial Introduction to @command{tar}
precedes lines you should type; to make this more clear, those lines are
shown in @kbd{this font}, as opposed to lines which represent the
computer's response; those lines are shown in @code{this font}, or
-sometimes @samp{like this}. When we have lines which are too long to be
-displayed in any other way, we will show them like this:
-
-@smallexample
-This is an example of a line which would otherwise not fit in this space.
-@end smallexample
+sometimes @samp{like this}.
-@FIXME{how often do we use smallexample?}
+@c When we have lines which are too long to be
+@c displayed in any other way, we will show them like this:
@node basic tar options
@section Basic @command{tar} Operations and Options
corresponding abbreviations. @FIXME{make sure this is still the case,
at the end}We will indicate those abbreviations appropriately to get
you used to seeing them. (Note that the ``old style'' option forms
-exist in @acronym{GNU} @command{tar} for compatibility with Unix
+exist in @GNUTAR{} for compatibility with Unix
@command{tar}. We present a full discussion of this way of writing
options and operations appears in @ref{Old Options}, and we discuss
-the other two styles of writing options in @ref{Mnemonic Options} and
+the other two styles of writing options in @ref{Mnemonic Options}, and
@ref{Short Options}.)
In the examples and in the text of this tutorial, we usually use the
the same result and can make typing long @command{tar} commands easier.
For example, instead of typing
-@example
+@smallexample
@kbd{tar --create --verbose --file=afiles.tar apple angst aspic}
-@end example
+@end smallexample
@noindent
you can type
-@example
+@smallexample
@kbd{tar -c -v -f afiles.tar apple angst aspic}
-@end example
+@end smallexample
@noindent
or even
-@example
+@smallexample
@kbd{tar -cvf afiles.tar apple angst aspic}
-@end example
+@end smallexample
@noindent
For more information on option syntax, see @ref{Advanced tar}. In
then @command{tar} will print an error message. The error message might
look roughly like one of the following:
-@example
+@smallexample
tar: can't open /dev/rmt8 : No such device or address
tar: can't open /dev/rsmt0 : I/O error
-@end example
+@end smallexample
@noindent
To avoid confusion, we recommend that you always specify an archive file
use @samp{--verbose} twice in a command to get a listing such as that
in the former case. For example, instead of saying
-@example
+@smallexample
@kbd{tar -cvf afiles.tar apple angst aspic}
-@end example
+@end smallexample
@noindent
above, you might say
-@example
+@smallexample
@kbd{tar -cvvf afiles.tar apple angst aspic}
-@end example
+@end smallexample
@noindent
This works equally well using short or long forms of options. Using
long forms, you would simply write out the mnemonic form of the option
twice, like this:
-@example
+@smallexample
$ @kbd{tar --create --verbose --verbose @dots{}}
-@end example
+@end smallexample
@noindent
Note that you must double the hyphens properly each time.
To place the files @file{blues}, @file{folk}, and @file{jazz} into an
archive named @file{collection.tar}, use the following command:
-@example
+@smallexample
$ @kbd{tar --create --file=collection.tar blues folk jazz}
-@end example
+@end smallexample
The order of the arguments is not very important, @emph{when using long
option forms}. You could also say:
-@example
+@smallexample
$ @kbd{tar blues --create folk --file=collection.tar jazz}
-@end example
+@end smallexample
@noindent
However, you can see that this order is harder to understand; this is
(they are @dfn{file name arguments} to the @samp{--create} operation).
@FIXME{xref here to the discussion of file name args?}Now that they are
in the archive, they are called @emph{archive members}, not files.
-@FIXME{xref to definitions?}
+(@pxref{Definitions,members}).
When you create an archive, you @emph{must} specify which files you
want placed in the archive. If you do not specify any archive
-members, @acronym{GNU} @command{tar} will complain.
+members, @GNUTAR{} will complain.
If you now list the contents of the working directory (@kbd{ls}), you will
find the archive file listed as well as the files you saw previously:
-@example
+@smallexample
blues folk jazz collection.tar
-@end example
+@end smallexample
@noindent
Creating the archive @samp{collection.tar} did not destroy the copies of
@command{tar} will list the files it is acting on as it is working. In
verbose mode, the @code{create} example above would appear as:
-@example
+@smallexample
$ @kbd{tar --create --verbose --file=collection.tar blues folk jazz}
blues
folk
jazz
-@end example
+@end smallexample
This example is just like the example we showed which did not use
@samp{--verbose}, except that @command{tar} generated the remaining lines
previous example (including the @value{op-verbose} option) looks like
using short option forms:
-@example
+@smallexample
$ @kbd{tar -cvf collection.tar blues folk jazz}
blues
folk
jazz
-@end example
+@end smallexample
@noindent
As you can see, the system responds the same no matter whether you use
forms. For example, suppose you attempted the above example in the
following way:
-@example
+@smallexample
$ @kbd{tar -cfv collection.tar blues folk jazz}
-@end example
+@end smallexample
@noindent
In this case, @command{tar} will make an archive file called @file{v},
This example,
-@example
+@smallexample
$ @kbd{tar blues --create folk --file=collection.tar jazz}
-@end example
+@end smallexample
@noindent
is confusing as it is. When shown using short forms, however, it
becomes much more so:
-@example
+@smallexample
$ @kbd{tar blues -c folk -f collection.tar jazz}
-@end example
+@end smallexample
@noindent
It would be very easy to put the wrong string of characters
does what, and therefore where different names have to be placed.
(Placing options in an unusual order can also cause @command{tar} to
report an error if you have set the shell environment variable
-@env{POSIXLY_CORRECT}; @pxref{posix compliance} for more information
-on this.)
+@env{POSIXLY_CORRECT}.)
@node create dir
@subsection Archiving Directories
have followed the previous instructions in this tutorial, you should
type:
-@example
+@smallexample
$ @kbd{cd ..}
$
-@end example
+@end smallexample
@noindent
This will put you into the directory which contains @file{practice},
specify the subdirectory, @file{practice}, as a file name argument. To
store @file{practice} in the new archive file @file{music.tar}, type:
-@example
+@smallexample
$ @kbd{tar --create --verbose --file=music.tar practice}
-@end example
+@end smallexample
@noindent
@command{tar} should output:
-@example
+@smallexample
practice/
practice/blues
practice/folk
practice/jazz
practice/collection.tar
-@end example
+@end smallexample
Note that the archive thus created is not in the subdirectory
@file{practice}, but rather in the current working directory---the
If you give @command{tar} a command such as
-@example
+@smallexample
$ @kbd{tar --create --file=foo.tar .}
-@end example
+@end smallexample
@noindent
@command{tar} will report @samp{tar: ./foo.tar is the archive; not
it. Then, when @command{tar} attempts to add all the files in the
directory @file{.} to the archive, it notices that the file
@file{./foo.tar} is the same as the archive @file{foo.tar}, and skips
-it. (It makes no sense to put an archive into itself.) @acronym{GNU}
-@command{tar} will continue in this case, and create the archive
+it. (It makes no sense to put an archive into itself.) @GNUTAR{}
+will continue in this case, and create the archive
normally, except for the exclusion of that one file. (@emph{Please
note:} Other versions of @command{tar} are not so clever; they will
enter an infinite loop when this happens, so you should not depend on
-this behavior unless you are certain you are running @acronym{GNU}
-@command{tar}.) @FIXME{bob doesn't like this sentence, since he does
+this behavior unless you are certain you are running @GNUTAR{}.)
+ @FIXME{bob doesn't like this sentence, since he does
it all the time, and we've been doing it in the editing passes for
this manual: In general, make sure that the archive is not inside a
directory being dumped.}
example, you can examine the archive @file{collection.tar} that you
created in the last section with the command,
-@example
+@smallexample
$ @kbd{tar --list --file=collection.tar}
-@end example
+@end smallexample
@noindent
The output of @command{tar} would then be:
-@example
+@smallexample
blues
folk
jazz
-@end example
+@end smallexample
@FIXME{we hope this will change. if it doesn't, need to show the
creation of bfiles somewhere above!!! : }
@noindent
The archive @file{bfiles.tar} would list as follows:
-@example
+@smallexample
./birds
baboon
./box
-@end example
+@end smallexample
@noindent
Be sure to use a @value{op-file} option just as with @value{op-create}
If you had used @value{op-verbose} mode, the example above would look
like:
-@example
+@smallexample
$ @kbd{tar --list --verbose --file=collection.tar folk}
-rw-rw-rw- myself user 62 1990-05-23 10:55 folk
-@end example
+@end smallexample
@cindex File name arguments, using @code{--list} with
@cindex @code{--list} with file name arguments
@node list dir
@unnumberedsubsec Listing the Contents of a Stored Directory
-@UNREVISED
-
-@FIXME{i changed the order of these nodes around and haven't had a
-chance to play around with this node's example, yet. i have to play
-with it and see what it actually does for my own satisfaction, even if
-what it says *is* correct..}
To get information about the contents of an archived directory,
use the directory name as a file name argument in conjunction with
For example, to find out about files in the directory @file{practice}, in
the archive file @file{music.tar}, type:
-@example
+@smallexample
$ @kbd{tar --list --verbose --file=music.tar practice}
-@end example
+@end smallexample
@command{tar} responds:
-@example
+@smallexample
drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
-rw-rw-rw- myself user 42 1990-05-21 13:29 practice/blues
-rw-rw-rw- myself user 62 1990-05-23 10:55 practice/folk
-rw-rw-rw- myself user 40 1990-05-21 13:30 practice/jazz
-rw-rw-rw- myself user 10240 1990-05-31 21:49 practice/collection.tar
-@end example
+@end smallexample
When you use a directory name as a file name argument, @command{tar} acts on
all the files (including sub-directories) in that directory.
* extracting archives::
* extracting files::
* extract dir::
+* extracting untrusted archives::
* failing commands::
@end menu
To extract an entire archive, specify the archive file name only, with
no individual file names as arguments. For example,
-@example
+@smallexample
$ @kbd{tar -xvf collection.tar}
-@end example
+@end smallexample
@noindent
produces this:
-@example
+@smallexample
-rw-rw-rw- me user 28 1996-10-18 16:31 jazz
-rw-rw-rw- me user 21 1996-09-23 16:44 blues
-rw-rw-rw- me user 20 1996-09-23 16:44 folk
-@end example
+@end smallexample
@node extracting files
@subsection Extracting Specific Files
one of the files you had placed in the archive @file{collection.tar}
earlier (say, @file{blues}), you can extract it from the archive without
changing the archive's structure. It will be identical to the original
-file @file{blues} that you deleted. @FIXME{check this; will the times,
-permissions, owner, etc be the same, also?}
+file @file{blues} that you deleted. @FIXME{At the time of this
+writing, atime and ctime are not restored. Since this is a tutorial
+for a beginnig user, it should hardly be mentioned here. Maybe in
+a footnote? --gray}.
First, make sure you are in the @file{practice} directory, and list the
files in the directory. Now, delete the file, @samp{blues}, and list
You can now extract the member @file{blues} from the archive file
@file{collection.tar} like this:
-@example
+@smallexample
$ @kbd{tar --extract --file=collection.tar blues}
-@end example
+@end smallexample
@noindent
If you list the files in the directory again, you will see that the file
(@pxref{list}).
You can extract a file to standard output by combining the above options
-with the @option{--to-stdout} option (@pxref{Writing to Standard
+with the @value{op-to-stdout} option (@pxref{Writing to Standard
Output}).
If you give the @value{op-verbose} option, then @value{op-extract} will
which you extract, the files from the extracted archive will replace
the files already in the working directory (and possible
subdirectories). This will happen regardless of whether or not the
-files in the working directory were more recent than those extracted.
+files in the working directory were more recent than those extracted
+(there exist, however, special options that alter this behavior
+@pxref{Writing}).
However, if a file was stored with a directory name as part of its file
name, and that directory does not exist under the working directory when
@file{music.tar}. To extract only the files you deleted, use the
following command:
-@example
+@smallexample
$ @kbd{tar -xvf music.tar practice/folk practice/jazz}
-@end example
+practice/folk
+practice/jazz
+@end smallexample
+
+@noindent
+If you were to specify two @value{op-verbose} options, @command{tar}
+would have displayed more detail about the extracted files, as shown
+in the example below:
-@FIXME{need to show tar's response; used verbose above. also, here's a
-good place to demonstrate the -v -v thing. have to write that up
-(should be trivial, but i'm too tired!).}
+@smallexample
+$ @kbd{tar -xvvf music.tar practice/folk practice/jazz}
+-rw-rw-rw- me user 28 1996-10-18 16:31 practice/jazz
+-rw-rw-rw- me user 20 1996-09-23 16:44 practice/folk
+@end smallexample
@noindent
Because you created the directory with @file{practice} as part of the
@FIXME{IMPORTANT! show the final structure, here. figure out what it
will be.}
+@node extracting untrusted archives
+@subsection Extracting Archives from Untrusted Sources
+
+Extracting files from archives can overwrite files that already exist.
+If you receive an archive from an untrusted source, you should make a
+new directory and extract into that directory, so that you don't have
+to worry about the extraction overwriting one of your existing files.
+For example, if @file{untrusted.tar} came from somewhere else on the
+Internet, and you don't necessarily trust its contents, you can
+extract it as follows:
+
+@smallexample
+$ @kbd{mkdir newdir}
+$ @kbd{cd newdir}
+$ @kbd{tar -xvf ../untrusted.tar}
+@end smallexample
+
+It is also a good practice to examine contents of the archive
+before extracting it, using @option{op-list} option, possibly combined
+with @option{op-verbose}.
+
@node failing commands
@subsection Commands That Will Fail
If you try to use this command,
-@example
+@smallexample
$ @kbd{tar -xvf music.tar folk jazz}
-@end example
+@end smallexample
@noindent
you will get the following response:
-@example
+@smallexample
tar: folk: Not found in archive
tar: jazz: Not found in archive
$
-@end example
+@end smallexample
@noindent
This is because these files were not originally @emph{in} the parent
directory @file{..}, where the archive is located; they were in the
@file{practice} directory, and their file names reflect this:
-@example
+@smallexample
$ @kbd{tar -tvf music.tar}
practice/folk
practice/jazz
practice/rock
-@end example
+@end smallexample
@FIXME{make sure the above works when going through the examples in
order...}
@noindent
Likewise, if you try to use this command,
-@example
+@smallexample
$ @kbd{tar -tvf music.tar folk jazz}
-@end example
+@end smallexample
@noindent
you would get a similar response. Members with those names are not in the
be in the rest of the manual.}
@node tar invocation
-@chapter Invoking @acronym{GNU} @command{tar}
+@chapter Invoking @GNUTAR{}
@UNREVISED
-This chapter is about how one invokes the @acronym{GNU} @command{tar}
+This chapter is about how one invokes the @GNUTAR{}
command, from the command synopsis (@pxref{Synopsis}). There are
numerous options, and many styles for writing them. One mandatory
option specifies the operation @command{tar} should perform
@node Synopsis
@section General Synopsis of @command{tar}
-The @acronym{GNU} @command{tar} program is invoked as either one of:
+The @GNUTAR{} program is invoked as either one of:
-@example
+@smallexample
@kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
@kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
-@end example
+@end smallexample
The second form is for when old options are being used.
@cindex exit status
@cindex return status
-Besides successful exits, @acronym{GNU} @command{tar} may fail for
+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
clearly diagnosed on @code{stderr}, after a line stating the nature of
the error.
-@acronym{GNU} @command{tar} returns only a few exit statuses. I'm really
+@GNUTAR{} returns only a few exit statuses. I'm really
aiming simplicity in that area, for now. If you are not using the
@value{op-compare} option, zero means that everything went well, besides
maybe innocuous warnings. Nonzero means that something went wrong.
@node using tar options
@section Using @command{tar} Options
-@acronym{GNU} @command{tar} has a total of eight operating modes which
+@GNUTAR{} has a total of eight operating modes which
allow you to perform a variety of tasks. You are required to choose
one operating mode each time you employ the @command{tar} program by
specifying one, and only one operation as an argument to the
only use the option style(s) which makes the most sense to you until you
feel comfortable with the others.
-@FIXME{hag to write a brief paragraph on the option(s) which can
-optionally take an argument}
+Some options @emph{may} take an argument (currently, there are
+two such options: @value{op-backup} and @value{op-occurrence}). Such
+options may have at most long and short forms, they do not have old style
+equivalent. The rules for specifying an argument for such options
+are stricter than those for specifying mandatory arguments. Please,
+pay special attention to them.
@menu
* Mnemonic Options:: Mnemonic Option Style
@node Mnemonic Options
@subsection Mnemonic Option Style
-@FIXME{have to decide whether or ot to replace other occurrences of
+@FIXME{have to decide whether or not to replace other occurrences of
"mnemonic" with "long", or *ugh* vice versa.}
Each option has at least one long (or mnemonic) name starting with two
meanings are generally easier to discern than those of their
corresponding short options (see below). For example:
-@example
+@smallexample
$ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
-@end example
+@end smallexample
@noindent
gives a fairly good set of hints about what the command does, even
for those not fully acquainted with @command{tar}.
Mnemonic options which require arguments take those arguments
-immediately following the option name; they are introduced by an equal
-sign. For example, the @samp{--file} option (which tells the name
-of the @command{tar} archive) is given a file such as @file{archive.tar}
-as argument by using the notation @samp{--file=archive.tar} for the
-mnemonic option.
+immediately following the option name. There are two ways of
+specifying a mandatory argument. It can be separated from the
+option name either by an equal sign, or by any amount of
+white space characters. For example, the @samp{--file} option (which
+tells the name of the @command{tar} archive) is given a file such as
+@file{archive.tar} as argument by using any of the following notations:
+@samp{--file=archive.tar} or @samp{--file archive.tar}.
+
+In contrast, optional arguments must always be introduced using
+an equal sign. For example, the @samp{--backup} option takes
+an optional argument specifying backup type. It must be used
+as @samp{--backup=@var{backup-type}}.
@node Short Options
@subsection Short Option Style
@w{@samp{-f @var{archive-name}}} denote the option which indicates a
specific archive, here named @file{archive.tar}.
+Short options which take optional arguments take their arguments
+immediately following the option letter, @emph{without any intervening
+white space characters}.
+
Short options' letters may be clumped together, but you are not
required to do this (as compared to old options; see below). When
short options are clumped as a set, use one (single) dash for them
an argument directly follows that option, as is usual for Unix programs.
For example:
-@example
+@smallexample
$ @kbd{tar -c -v -b 20 -f /dev/rmt0}
-@end example
+@end smallexample
If you reorder short options' locations, be sure to move any arguments
that belong to them. If you do not move the arguments properly, you may
Thus, the example given previously could also be written in the old
style as follows:
-@example
+@smallexample
$ @kbd{tar cvbf 20 /dev/rmt0}
-@end example
+@end smallexample
@noindent
Here, @samp{20} is the argument of @samp{-b} and @samp{/dev/rmt0} is
This old way of writing @command{tar} options can surprise even experienced
users. For example, the two commands:
-@example
+@smallexample
@kbd{tar cfz archive.tar.gz file}
@kbd{tar -cfz archive.tar.gz file}
-@end example
+@end smallexample
@noindent
are quite different. The first example uses @file{archive.tar.gz} as
the value for option @samp{f} and recognizes the option @samp{z}. The
second example, however, uses @file{z} as the value for option
-@samp{f}---probably not what was intended.
+@samp{f} --- probably not what was intended.
Old options are kept for compatibility with old versions of @command{tar}.
This second example could be corrected in many ways, among which the
following are equivalent:
-@example
+@smallexample
@kbd{tar -czf archive.tar.gz file}
@kbd{tar -cf archive.tar.gz -z file}
@kbd{tar cf archive.tar.gz -z file}
-@end example
+@end smallexample
@FIXME{still could explain this better; it's redundant:}
@cindex option syntax, traditional
As far as we know, all @command{tar} programs, @acronym{GNU} and
-non-@acronym{GNU}, support old options. @acronym{GNU} @command{tar}
+non-@acronym{GNU}, support old options. @GNUTAR{}
supports them not only for historical reasons, but also because many
people are used to them. For compatibility with Unix @command{tar},
the first argument is always treated as containing command and option
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 @acronym{GNU} @command{tar} version 1.11.6,
+respected@footnote{Before @GNUTAR{} version 1.11.6,
a bug prevented intermixing old style options with mnemonic options in
some cases.}. Old style options and either of the modern styles of
options may be mixed within a single @command{tar} command. However,
For example, all the following commands are wholly equivalent, and
illustrate the many combinations and orderings of option styles.
-@example
+@smallexample
@kbd{tar --create --file=archive.tar}
@kbd{tar --create -f archive.tar}
@kbd{tar --create -farchive.tar}
@kbd{tar f archive.tar --create}
@kbd{tar f archive.tar -c}
@kbd{tar fc archive.tar}
-@end example
+@end smallexample
On the other hand, the following commands are @emph{not} equivalent to
the previous set:
-@example
+@smallexample
@kbd{tar -f -c archive.tar}
@kbd{tar -fc archive.tar}
@kbd{tar -fcarchive.tar}
@kbd{tar -farchive.tarc}
@kbd{tar cfarchive.tar}
-@end example
+@end smallexample
@noindent
These last examples mean something completely different from what the
indication that @command{tar} is still running, but don't want to see
@samp{--verbose} output. @FIXME-xref{}
+@item --check-links
+@itemx -l
+If this option was given, @command{tar} will check the number of links
+dumped for each processed file. If this number does not match the
+total number of hard links for the file, a warning message will be
+output.
+
+Future versions will take @option{-l} as a short version of
+@option{--check-links}. However, current release still retains the old
+semantics for @option{-l}.
+
+@xref{Current status}, for more information.
+
@item --compress
@itemx --uncompress
@itemx -Z
as a local file, even if it looks like a remote tape drive name.
@FIXME-xref{}
+@item --format=@var{format}
+
+Selects output archive format. @var{Format} may be one of the
+following:
+
+@table @samp
+@item v7
+Creates an archive that is compatible with Unix V7 @command{tar}.
+
+@item oldgnu
+Creates an archive that is compatible with GNU @command{tar} version
+1.12 or earlier.
+
+@item gnu
+Creates archive in GNU tar 1.13 format. Basically it is the same as
+@samp{oldgnu} with the only difference in the way it handles long
+numeric fields.
+
+@item ustar
+Creates a POSIX.1-1988 compatible archive.
+
+@item posix
+Creates a POSIX.1-2001 archive.
+
+@end table
+
+@xref{Formats}, for a detailed discussion of these formats.
+
@item --group=@var{group}
Files added to the @command{tar} archive will have a group id of @var{group},
Also see the comments for the @value{op-owner} option.
-@item --gunzip
-
-(See @samp{--gzip}.) @FIXME-pxref{}
-
@item --gzip
@itemx --gunzip
@itemx --ungzip
performing potentially destructive options, such as overwriting files.
@FIXME-xref{}
+@item --keep-newer-files
+
+Do not replace existing files that are newer than their archive copies
+when extracting files from an archive.
+
@item --keep-old-files
@itemx -k
@FIXME-xref{}
@item --no-same-owner
+@itemx -o
When extracting an archive, do not attempt to preserve the owner
specified in the @command{tar} archive. This the default behavior
and group IDs when creating a @command{tar} file, rather than names.
@FIXME-xref{}
-@item --old-archive
+@item -o
+When extracting files, this option is a synonym for
+@option{--no-same-owner}, i.e. it prevents @command{tar} from
+restoring ownership of files being extracted.
+
+When creating an archive, @option{-o} is a synonym for
+@option{--old-archive}. This behavior is for compatibility
+with previous versions of @GNUTAR{}, and will be
+removed in the future releases.
+
+@xref{Current status}, for more information.
+
+@item --occurrence[=@var{number}]
+
+This option can be used in conjunction with one of the subcommands
+@option{--delete}, @option{--diff}, @option{--extract} or
+@option{--list} when a list of files is given either on the command
+line or via @option{-T} option.
+
+This option instructs @command{tar} to process only the @var{number}th
+occurrence of each named file. @var{Number} defaults to 1, so
+
+@smallexample
+tar -x -f archive.tar --occurrence filename
+@end smallexample
+
+@noindent
+will extract the first occurrence of @file{filename} from @file{archive.tar}
+and will terminate without scanning to the end of the archive.
-(See @samp{--portability}.) @FIXME-pxref{}
+@item --old-archive
+Synonym for @option{--format=v7}.
@item --one-file-system
@itemx -l
-
Used when creating an archive. Prevents @command{tar} from recursing into
directories that are on different file systems from the current
-directory. @FIXME-xref{}
+directory.
+
+Earlier versions of @GNUTAR{} understood @option{-l} as a
+synonym for @option{--one-file-system}. Although such usage is still
+allowed in the present version, it is @emph{strongly discouraged}.
+The future versions of @GNUTAR{} will use @option{-l} as
+a synonym for @option{--check-links}.
+
+@xref{Current status}, for more information.
@item --overwrite
This option does not affect extraction from archives.
+@item --pax-option=@var{keyword-list}
+
+This option is meaningful only with POSIX.1-2001 archives
+(@FIXME-xref{}). It modifies the way @command{tar} handles the
+extended header keywords. @var{Keyword-list} is a comma-separated
+list of keyword options, each keyword option taking one of
+the following forms:
+
+@table @asis
+@item delete=@var{pattern}
+When used with one of archive-creation command (@FIXME-xref{}),
+this option instructs @command{tar} to omit from extended header records
+that it produces any keywords matching the string @var{pattern}.
+
+When used in extract or list mode, this option instructs tar
+to ignore any keywords matching the given @var{pattern} in the extended
+header records. In both cases, matching is performed using the pattern
+matching notation described in POSIX 1003.2, 3.13 (@FIXME-xref{}, see
+man 7 glob). For example:
+
+@smallexample
+--pax-option delete=security.*
+@end smallexample
+
+would suppress security-related information.
+
+@item exthdr.name=@var{string}
+
+This keyword allows user control over the name that is written into the
+ustar header blocks for the extended headers. The name is obtained
+from @var{string} after substituting the following meta-characters:
+
+@multitable @columnfractions .30 .70
+@item Meta-character @tab Replaced By
+@item %d @tab The directory name of the file, equivalent to the
+result of the @command{dirname} utility on the translated pathname.
+@item %f @tab The filename of the file, equivalent to the result
+of the @command{basename} utility on the translated pathname.
+@item %p @tab The process ID of the @command{tar} process.
+@item %% @tab A @samp{%} character.
+@end multitable
+
+Any other @samp{%} characters in @var{string} produce undefined
+results.
+
+If no option @samp{exthdr.name=string} is specified, @command{tar}
+will use the following default value:
+
+@smallexample
+%d/PaxHeaders.%p/%f
+@end smallexample
+
+@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
+shall will be obtained from the contents of @var{string}, after the
+following character substitutions have been made:
+
+@multitable @columnfractions .30 .70
+@item Meta-character @tab Replaced By
+@item %n @tab An integer that represents the
+sequence number of the global extended header record in the archive,
+starting at 1.
+@item %p @tab The process ID of the @command{tar} process.
+@item %% @tab A @samp{%} character.
+@end multitable
+
+Any other @samp{%} characters in string produce undefined results.
+
+If no option @samp{globexthdr.name=string} is specified, @command{tar}
+will use the following default value:
+
+@smallexample
+$TMPDIR/GlobalHead.%p.%n
+@end smallexample
+
+@noindent
+where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
+environment variable. If @var{TMPDIR} is not set, @command{tar}
+uses @samp{/tmp}.
+
+@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
+header record. When used with one of archive-reading commands,
+@command{tar} will behave as if it has encountered these keyword/value
+pairs at the beginning of the archive in a global extended header
+record.
+
+@item @var{keyword}:=@var{value}
+When used with one of archive-creation commands, these keyword/value pairs
+will be included as records at the beginning of an extended header for
+each file. This is effectively equivalent to @var{keyword}=@var{value}
+form except that it creates no global extended header records.
+
+When used with one of archive-reading commands, @command{tar} will
+behave as if these keyword/value pairs were included as records at the
+end of each extended header; thus, they will override any global or
+file-specific extended header record keywords of the same names.
+For example, in the command:
+
+@smallexample
+tar --format=posix --create \
+ --file archive --pax-option gname:=user .
+@end smallexample
+
+the group name will be forced to a new value for all files
+stored in the archive.
+@end table
+
@item --portability
@itemx --old-archive
-@itemx -o
-
-Tells @command{tar} to create an archive that is compatible with Unix V7
-@command{tar}. @FIXME-xref{}
+Synonym for @option{--format=v7}.
@item --posix
-
-Instructs @command{tar} to create a @sc{posix} compliant @command{tar}
-archive. @FIXME-xref{}
+Same as @option{--format=posix}.
@item --preserve
(See @samp{--preserve-permissions}; @pxref{Writing}.)
+@item --show-defaults
+
+Displays the default options used by @command{tar} and exits
+successfully. This option is intended for use in shell scripts.
+Here is an example of what you can see using this option:
+
+@smallexample
+$ tar --show-defaults
+--format=gnu -f- -b20
+@end smallexample
+
@item --show-omitted-dirs
Instructs @command{tar} to mention directories its skipping over when
files in the archive until it finds one that matches @var{name}.
@xref{Scarce}.
+@item --strip-path=@var{number}
+Strip given @var{number} of leading components from file names before
+extraction. For example, if archive @file{archive.tar} contained
+@file{/some/file/name}, then running
+
+@smallexample
+tar --extract --file archive.tar --strip-path=2
+@end smallexample
+
+@noindent
+would extracted this file to file @file{name}.
+
@item --suffix=@var{suffix}
Alters the suffix @command{tar} uses when backing up files from the default
Instructs @command{tar} to access the archive through @var{prog}, which is
presumed to be a compression program of some sort. @FIXME-xref{}
+@item --utc
+
+Display file modification dates in @acronym{UTC}. This option implies
+@samp{--verbose}.
+
@item --verbose
@itemx -v
@item -l
-@samp{--one-file-system}
+@samp{--one-file-system}. Use of this short option is deprecated. It
+is retained for compatibility with the earlier versions of GNU
+@command{tar}, and will be changed in future releases.
+
+@xref{Current status}, for more information.
@item -m
@item -o
-@samp{--portability}
+When creating --- @samp{--no-same-owner}, when extracting ---
+@samp{--portability}.
+
+The later usage is deprecated. It is retained for compatibility with
+the earlier versions of @GNUTAR{}. In the future releases
+@option{-o} will be equivalent to @samp{--no-same-owner} only.
@item -p
@end table
@node help
-@section @acronym{GNU} @command{tar} documentation
+@section @GNUTAR{} documentation
Being careful, the first thing is really checking that you are using
-@acronym{GNU} @command{tar}, indeed. The @value{op-version} option
+@GNUTAR{}, indeed. The @value{op-version} option
will generate a message giving confirmation that you are using
-@acronym{GNU} @command{tar}, with the precise version of @acronym{GNU}
-@command{tar} you are using. @command{tar} identifies itself and
+@GNUTAR{}, with the precise version of @GNUTAR{}
+you are using. @command{tar} identifies itself and
prints the version number to the standard output, then immediately
exits successfully, without doing anything else, ignoring all other
options. For example, @w{@samp{tar --version}} might return:
-@example
+@smallexample
tar (@acronym{GNU} tar) @value{VERSION}
-@end example
+@end smallexample
@noindent
The first occurrence of @samp{tar} in the result above is the program
Another thing you might want to do is checking the spelling or meaning
of some particular @command{tar} option, without resorting to this
-manual, for once you have carefully read it. @acronym{GNU}
-@command{tar} has a short help feature, triggerable through the
+manual, for once you have carefully read it. @GNUTAR{}
+has a short help feature, triggerable through the
@value{op-help} option. By using this option, @command{tar} will
print a usage message listing all available options on standard
output, then exit successfully, without doing anything else and
may be several screens long. So, if you are not using some kind of
scrollable window, you might prefer to use something like:
-@example
+@smallexample
$ @kbd{tar --help | less}
-@end example
+@end smallexample
@noindent
presuming, here, that you like using @command{less} for a pager. Other
@var{keyword} which interests you and do not want to read all the
@value{op-help} output, another common idiom is doing:
-@example
+@smallexample
tar --help | grep @var{keyword}
-@end example
+@end smallexample
@noindent
for getting only the pertinent lines.
back to the full documentation for precise points. If you are reading
this paragraph, you already have the @command{tar} manual in some
form. This manual is available in printed form, as a kind of small
-book. It may printed out of the @acronym{GNU} @command{tar}
+book. It may printed out of the @GNUTAR{}
distribution, provided you have @TeX{} already installed somewhere,
and a laser printer around. Just configure the distribution, execute
the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the
-usual way (contact your local guru to know how). If @acronym{GNU}
-@command{tar} has been conveniently installed at your place, this
+usual way (contact your local guru to know how). If @GNUTAR{}
+has been conveniently installed at your place, this
manual is also available in interactive, hypertextual form as an Info
file. Just call @w{@samp{info tar}} or, if you do not have the
@command{info} program handy, use the Info reader provided within
@acronym{GNU} Emacs, calling @samp{tar} from the main Info menu.
-There is currently no @code{man} page for @acronym{GNU} @command{tar}.
+There is currently no @code{man} page for @GNUTAR{}.
If you observe such a @code{man} page on the system you are running,
-either it does not long to @acronym{GNU} @command{tar}, or it has not
-been produced by @acronym{GNU}. Currently, @acronym{GNU}
-@command{tar} documentation is provided in Texinfo format only, if we
+either it does not long to @GNUTAR{}, or it has not
+been produced by @acronym{GNU}. Currently, @GNUTAR{}
+documentation is provided in Texinfo format only, if we
except, of course, the short result of @kbd{tar --help}.
@node verbose
in the archive. The following examples both extract members with
long list output:
-@example
+@smallexample
$ @kbd{tar --extract --file=archive.tar --verbose --verbose}
-$ @kbd{tar xvv archive.tar}
-@end example
+$ @kbd{tar xvvf archive.tar}
+@end smallexample
Verbose output appears on the standard output except when an archive is
being written to the standard output, as with @samp{tar --create
file on the archive. As of now, if the archive if properly terminated
with a NUL block, the reading of the file may stop before end of file
is met, so the position of end of file will not usually show when
-@value{op-block-number} is used. Note that @acronym{GNU}
-@command{tar} drains the archive before exiting when reading the
+@value{op-block-number} is used. Note that @GNUTAR{}
+drains the archive before exiting when reading the
archive from a pipe.
This option is especially useful when reading damaged archives, since
output free to receive verbose output, all separate from errors.
@node operations
-@chapter @acronym{GNU} @command{tar} Operations
+@chapter @GNUTAR{} Operations
@menu
* Basic tar::
@end menu
@node Basic tar
-@section Basic @acronym{GNU} @command{tar} Operations
+@section Basic @GNUTAR{} Operations
The basic @command{tar} operations, @value{op-create}, @value{op-list} and
@value{op-extract}, are currently presented and described in the tutorial
@item
Mistakingly using @code{create} instead of @code{extract}, when the
intent was to extract the full contents of an archive. This error
-is likely: keys @kbd{c} and @kbd{x} are right next ot each other on
+is likely: keys @kbd{c} and @kbd{x} are right next to each other on
the QWERTY keyboard. Instead of being unpacked, the archive then
gets wholly destroyed. When users speak about @dfn{exploding} an
archive, they usually mean something else :-).
@end enumerate
So, recognizing the likelihood and the catastrophical nature of these
-errors, @acronym{GNU} @command{tar} now takes some distance from elegance, and
+errors, @GNUTAR{} now takes some distance from elegance, and
cowardly refuses to create an archive when @value{op-create} option is
given, there are no arguments besides options, and @value{op-files-from}
-option is @emph{not} used. To get around the cautiousness of @acronym{GNU}
-@command{tar} and nevertheless create an archive with nothing in it,
+option is @emph{not} used. To get around the cautiousness of @GNUTAR{}
+and nevertheless create an archive with nothing in it,
one may still use, as the value for the @value{op-files-from} option,
a file with no names in it, as shown in the following commands:
-@example
+@smallexample
@kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
@kbd{tar cfT empty-archive.tar /dev/null}
-@end example
+@end smallexample
@item @value{op-extract}
-A socket is stored, within a @acronym{GNU} @command{tar} archive, as a pipe.
+A socket is stored, within a @GNUTAR{} archive, as a pipe.
@item @value{op-list}
-@acronym{GNU} @command{tar} now shows dates as @samp{1996-08-30},
+@GNUTAR{} now shows dates as @samp{1996-08-30},
while it used to show them as @samp{Aug 30 1996}. (One can revert to
the old behavior by defining @code{USE_OLD_CTIME} in @file{src/list.c}
before reinstalling.) But preferably, people should get used to ISO
@end table
@node Advanced tar
-@section Advanced @acronym{GNU} @command{tar} Operations
+@section Advanced @GNUTAR{} Operations
-Now that you have learned the basics of using @acronym{GNU}
-@command{tar}, you may want to learn about further ways in which
-@command{tar} can help you.
+Now that you have learned the basics of using @GNUTAR{}, you may want
+to learn about further ways in which @command{tar} can help you.
This chapter presents five, more advanced operations which you probably
won't use on a daily basis, but which serve more specialized functions.
following @command{tar} command to add @file{rock} to
@file{collection.tar}:
-@example
+@smallexample
$ @kbd{tar --append --file=collection.tar rock}
-@end example
+@end smallexample
@noindent
If you now use the @value{op-list} operation, you will see that
@file{rock} has been added to the archive:
-@example
+@smallexample
$ @kbd{tar --list --file=collection.tar}
-rw-rw-rw- me user 28 1996-10-18 16:31 jazz
-rw-rw-rw- me user 21 1996-09-23 16:44 blues
-rw-rw-rw- me user 20 1996-09-23 16:44 folk
-rw-rw-rw- me user 20 1996-09-23 16:44 rock
-@end example
+@end smallexample
@FIXME{in theory, dan will (soon) try to turn this node into what it's
title claims it will become...}
which i believe is basically a Stupid way of doing something? certain
aspects of it show ways in which tar is more broken than i'd personally
like to admit to, specifically the last sentence. On the other hand, i
-don't think it's a good idea to be saying that re explicitly don't
+don't think it's a good idea to be saying that we explicitly don't
recommend using something, but i can't see any better way to deal with
the situation.}When you extract the archive, the older version will be
effectively lost. This works because files are extracted from an
You can append the new, changed copy of the file @file{blues} to the
archive in this way:
-@example
+@smallexample
$ @kbd{tar --append --verbose --file=collection.tar blues}
blues
-@end example
+@end smallexample
@noindent
Because you specified the @samp{--verbose} option, @command{tar} has
printed the name of the file being appended as it was acted on. Now
list the contents of the archive:
-@example
+@smallexample
$ @kbd{tar --list --verbose --file=collection.tar}
-rw-rw-rw- me user 28 1996-10-18 16:31 jazz
-rw-rw-rw- me user 21 1996-09-23 16:44 blues
-rw-rw-rw- me user 20 1996-09-23 16:44 folk
-rw-rw-rw- me user 20 1996-09-23 16:44 rock
-rw-rw-rw- me user 58 1996-10-24 18:30 blues
-@end example
+@end smallexample
@noindent
The newest version of @file{blues} is now at the end of the archive
using the names of all the files in the practice directory as file name
arguments:
-@example
+@smallexample
$ @kbd{tar --update -v -f collection.tar blues folk rock classical}
blues
classical
$
-@end example
+@end smallexample
@noindent
Because we have specified verbose mode, @command{tar} prints out the names
@value{op-update} is not suitable for performing backups for two
reasons: it does not change directory content entries, and it
-lengthens the archive every time it is used. The @acronym{GNU}
-@command{tar} options intended specifically for backups are more
+lengthens the archive every time it is used. The @GNUTAR{}
+options intended specifically for backups are more
efficient. If you need to run backups, please consult @ref{Backups}.
@node concatenate
called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
files from @file{practice}:
-@example
+@smallexample
$ @kbd{tar -cvf bluesrock.tar blues rock}
blues
classical
$ @kbd{tar -cvf folkjazz.tar folk jazz}
folk
jazz
-@end example
+@end smallexample
@noindent
If you like, You can run @samp{tar --list} to make sure the archives
contain what they are supposed to:
-@example
+@smallexample
$ @kbd{tar -tvf bluesrock.tar}
-rw-rw-rw- melissa user 105 1997-01-21 19:42 blues
-rw-rw-rw- melissa user 33 1997-01-20 15:34 rock
$ @kbd{tar -tvf folkjazz.tar}
-rw-rw-rw- melissa user 20 1996-09-23 16:44 folk
-rw-rw-rw- melissa user 65 1997-01-30 14:15 jazz
-@end example
+@end smallexample
We can concatenate these two archives with @command{tar}:
-@example
+@smallexample
$ @kbd{cd ..}
$ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
-@end example
+@end smallexample
If you now list the contents of the @file{bluesclass.tar}, you will see
that now it also contains the archive members of @file{jazzfolk.tar}:
-@example
+@smallexample
$ @kbd{tar --list --file=bluesrock.tar}
blues
rock
jazz
folk
-@end example
+@end smallexample
When you use @samp{--concatenate}, the source and target archives must
already exist and must have been created using compatible format
@file{collection.tar} in the @file{practice} directory, make sure you
are in that directory, and then,
-@example
+@smallexample
$ @kbd{tar --list --file=collection.tar}
blues
folk
jazz
rock
$
-@end example
+@end smallexample
@FIXME{I changed the order of these nodes around and haven't had a chance
to fix the above example's results, yet. I have to play with this and
files of the same name in the file system. (Note that there is no file,
@file{funk}; @command{tar} will report an error message.)
-@example
+@smallexample
$ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
rock
blues
tar: funk not found in archive
-@end example
+@end smallexample
@noindent
@FIXME{what does this actually depend on? i'm making a guess,
version you are running, @command{tar} may have a different error message,
such as:
-@example
+@smallexample
funk: does not exist
-@end example
+@end smallexample
@FIXME-xref{somewhere, for more information about format parameters.
Melissa says: such as "format variations"? But why? Clearly I don't
The @value{op-ignore-zeros} option is turned off by default because many
versions of @command{tar} write garbage after the end-of-archive entry,
-since that part of the media is never supposed to be read. @acronym{GNU}
-@command{tar} does not write after the end of an archive, but seeks to
+since that part of the media is never supposed to be read. @GNUTAR{}
+does not write after the end of an archive, but seeks to
maintain compatiblity among archiving utilities.
@table @kbd
* Dealing with Old Files::
* Overwrite Old Files::
* Keep Old Files::
+* Keep Newer Files::
* Unlink First::
* Recursive Unlink::
* Modification Times::
@value{op-overwrite} option. It causes @command{tar} to overwrite
existing files and to follow existing symbolic links when extracting.
-Some people argue that @acronym{GNU} @command{tar} should not hesitate
+Some people argue that @GNUTAR{} should not hesitate
to overwrite files with other files when extracting. When extracting
a @command{tar} archive, they expect to see a faithful copy of the
state of the filesystem when the archive was created. It is debatable
@file{usr/local2}. Since then, maybe the site removed the link and
renamed the whole hierarchy from @file{/usr/local2} to
@file{/usr/local}. Such things happen all the time. I guess it would
-not be welcome at all that @acronym{GNU} @command{tar} removes the
+not be welcome at all that @GNUTAR{} removes the
whole hierarchy just to make room for the link to be reinstated
(unless it @emph{also} simultaneously restores the full
-@file{/usr/local2}, of course! @acronym{GNU} @command{tar} is indeed
+@file{/usr/local2}, of course! @GNUTAR{} is indeed
able to remove a whole hierarchy to reestablish a symbolic link, for
example, but @emph{only if} @value{op-recursive-unlink} is specified
to allow this behavior. In any case, single files are silently
extraction.
@end table
+@node Keep Newer Files
+@unnumberedsubsubsec Keep Newer Files
+
+@table @kbd
+@item --keep-newer-files
+Do not replace existing files that are newer than their archive
+copies. This option is meaningless with @value{op-list}.
+@end table
+
@node Unlink First
@unnumberedsubsubsec Unlink First
a big file and don't want to store the file on disk before processing
it. You can use a command like this:
-@example
+@smallexample
tar -xOzf foo.tgz bigfile | process
-@end example
+@end smallexample
or even like this if you want to process the concatenation of the files:
-@example
+@smallexample
tar -xOzf foo.tgz bigfile1 bigfile2 | process
-@end example
+@end smallexample
@node remove files
@unnumberedsubsubsec Removing Files
@cindex backup options
-@acronym{GNU} @command{tar} offers options for making backups of files
+@GNUTAR{} offers options for making backups of files
before writing new versions. These options control the details of
these backups. They may apply to the archive itself before it is
created or rewritten, as well as individual extracted members. Other
if you are ready to give up using old style options, you may resort to
using something like (a Bourne shell function here):
-@example
+@smallexample
tar () @{ /usr/local/bin/tar --backup $*; @}
-@end example
+@end smallexample
@node Applications
@section Notable @command{tar} Usages
@noindent
The command also works using short option forms:
-@FIXME{The following using standard input/output correct??}
@smallexample
$ @w{@kbd{cd sourcedir; tar --create --file=- . | (cd targetdir; tar --extract --file=-)}}
@end smallexample
arguments to @command{tar} (this can help you save time if you expect to
archive the same list of files a number of times), and so forth.
@FIXME{in case it's not obvious, i'm making this up in some sense
-based on my imited memory of what the next chapter *really* does. i
+based on my limited memory of what the next chapter *really* does. i
just wanted to flesh out this final section a little bit so i'd
-remember to sitck it in here. :-)}
+remember to stick it in here. :-)}
If there are too many files to conveniently list on the command line,
you can list the names in a file, and @command{tar} will read that file.
@chapter Performing Backups and Restoring Files
@UNREVISED
-@acronym{GNU} @command{tar} is distributed along with the scripts
+@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
da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
This is free software, and it is available at these places:
-@example
+@smallexample
http://www.cs.umd.edu/projects/amanda/amanda.html
ftp://ftp.cs.umd.edu/pub/amanda
-@end example
+@end smallexample
@ifclear PUBLISH
Here is a possible plan for a future documentation about the backuping
-scripts which are provided within the @acronym{GNU} @command{tar}
+scripts which are provided within the @GNUTAR{}
distribution.
-@example
+@smallexample
.* dumps
. + what are dumps
. - positioning the tape
MT writes two at end of write,
backspaces over one when writing again.
-@end example
+@end smallexample
@end ifclear
Here is a sample script to dump the directory hierarchies @samp{/usr}
and @samp{/var}.
-@example
+@smallexample
#! /bin/sh
tar --create \
--blocking-factor=126 \
--listed-incremental=/var/log/usr-var.snar \
--verbose \
/usr /var
-@end example
+@end smallexample
This script uses the file @file{/var/log/usr-var.snar} as a snapshot to
store information about the previous tar dump.
files changed or created since the last daily backup. (Doing dumps
more than once a day is usually not worth the trouble).
-@acronym{GNU} @command{tar} comes with scripts you can use to do full
+@GNUTAR{} comes with scripts you can use to do full
and level-one dumps. Using scripts (shell programs) to perform
backups and restoration is a convenient and reliable alternative to
typing out file name lists and @command{tar} commands by hand.
The host name specifies which host to run @command{tar} on, and should
normally be the host that actually contains the file system. However,
-the host machine must have @acronym{GNU} @command{tar} installed, and
+the host machine must have @GNUTAR{} installed, and
must be able to access the directory containing the backup scripts and
their support files using the same file name that is used on the
machine where the scripts are run (ie. what @command{pwd} will print
The following is the text of @file{backup-specs} as it appears at FSF:
-@example
+@smallexample
# site-specific parameters for file system backup.
ADMINISTRATOR=friedman
BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
-@end example
+@end smallexample
@node Script Syntax
@subsection Syntax for @file{Backup-specs}
The syntax for running a backup script is:
-@example
+@smallexample
@file{script-name} [@var{time-to-be-run}]
-@end example
+@end smallexample
where @var{time-to-be-run} can be a specific system time, or can be
@kbd{now}. If you do not specify a time, the script runs at the time
@ifclear PUBLISH
@quotation
-@strong{Warning:} The @acronym{GNU} @command{tar} distribution does @emph{not}
+@strong{Warning:} The @GNUTAR{} distribution does @emph{not}
provide any such @code{restore} script yet. This section is only
listed here for documentation maintenance purposes. In any case,
all contents is subject to change as things develop.
For example, in this @command{tar} command,
-@example
+@smallexample
$ @kbd{tar -cvf collection.tar blues folk jazz}
-@end example
+@end smallexample
@noindent
@file{collection.tar} is the name of the archive. It must directly
@FIXME{might want a different example here; this is already used in
"notable tar usages".}
-@example
+@smallexample
$ @kbd{cd sourcedir; tar -cf - . | (cd targetdir; tar -xf -)}
-@end example
+@end smallexample
@FIXME{help!}
To specify an archive file on a device attached to a remote machine,
use the following:
-@example
+@smallexample
@kbd{--file=@var{hostname}:/@var{dev}/@var{file name}}
-@end example
+@end smallexample
@noindent
@command{tar} will complete the remote connection, if possible, and
here?>>. bob also comments that if Amanda isn't free software, we
shouldn't mention it..}
-When the archive is being created to @file{/dev/null}, @acronym{GNU}
-@command{tar} tries to minimize input and output operations. The
-Amanda backup system, when used with @acronym{GNU} @command{tar}, has
+When the archive is being created to @file{/dev/null}, @GNUTAR{}
+tries to minimize input and output operations. The
+Amanda backup system, when used with @GNUTAR{}, has
an initial sizing pass which uses this feature.
@node Selecting Archive Members
@command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for
more information.)
-@example
+@smallexample
$ @kbd{find . -size -400 -print > small-files}
$ @kbd{tar -c -v -z -T small-files -f little.tgz}
-@end example
+@end smallexample
@noindent
@FIXME{say more here to conclude the example/section?}
@file{big.tgz}. The @samp{--null} option to @command{tar} will cause
@command{tar} to recognize the @kbd{NUL} separator between files.
-@example
+@smallexample
$ @kbd{find . -size +800 -print0 > long-files}
$ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
-@end example
+@end smallexample
@FIXME{say anything else here to conclude the section?}
However, this matching procedure can be altered by the options listed
below. These options accumulate. For example:
-@example
+@smallexample
--ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
-@end example
+@end smallexample
ignores case when excluding @samp{makefile}, but not when excluding
@samp{readme}.
@item
When you use @value{op-exclude}, be sure to quote the @var{pattern}
-parameter, so @acronym{GNU} @command{tar} sees wildcard characters
+parameter, so @GNUTAR{} sees wildcard characters
like @samp{*}. If you do not do this, the shell might expand the
@samp{*} itself using files at hand, so @command{tar} might receive a
list of files instead of one pattern, or none at all, making the
For example, write:
-@example
+@smallexample
$ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}}
-@end example
+@end smallexample
@noindent
rather than:
-@example
+@smallexample
$ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
-@end example
+@end smallexample
@item
You must use use shell syntax, or globbing, rather than @code{regexp}
This is the default.
@end table
-When you use @samp{--no-recursion}, @acronym{GNU} @command{tar} grabs
+When you use @samp{--no-recursion}, @GNUTAR{} grabs
directory entries themselves, but does not descend on them
recursively. Many people use @command{find} for locating files they
want to back up, and since @command{tar} @emph{usually} recursively
later options and operands, and can be overridden by later occurrences
of @option{--no-recursion} and @option{--recursion}. For example:
-@example
+@smallexample
$ @kbd{tar -cf jams.tar --norecursion grape --recursion grape/concord}
-@end example
+@end smallexample
@noindent
creates an archive with one entry for @file{grape}, and the recursive
For example,
-@example
+@smallexample
$ @kbd{tar -c -f jams.tar grape prune -C food cherry}
-@end example
+@end smallexample
@noindent
will place the files @file{grape} and @file{prune} from the current
Contrast this with the command,
-@example
+@smallexample
$ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
-@end example
+@end smallexample
@noindent
which records the third file in the archive under the name
@file{/etc/hosts}, and @file{/lib/libc.a} into the archive
@file{foo.tar}:
-@example
+@smallexample
$ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
-@end example
+@end smallexample
@noindent
However, the names of the archive members will be exactly what they were
containing a @file{..} file name component.
@end table
-By default, @acronym{GNU} @command{tar} drops a leading @samp{/} on
+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.
Other @command{tar} programs do not do this. As a result, if you
create an archive whose member names start with a slash, they will be
-difficult for other people with a non-@acronym{GNU} @command{tar}
-program to use. Therefore, @acronym{GNU} @command{tar} also strips
+difficult for other people with a non-@GNUTAR{}
+program to use. Therefore, @GNUTAR{} also strips
leading slashes from member names when putting members into the
archive. For example, if you ask @command{tar} to add the file
@file{/bin/ls} to an archive, it will do so, but the member name will
@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 @acronym{GNU} @command{tar}
+file names. This message appears once per @GNUTAR{}
invocation. It represents something which ought to be told; ignoring
what it means can cause very serious surprises, later.
play really dangerously, one may of course redirect @command{tar} standard
error to the sink. For example, under @command{sh}:
-@example
+@smallexample
$ @kbd{tar -c -f archive.tar /home 2> /dev/null}
-@end example
+@end smallexample
@noindent
Another solution, both nicer and simpler, would be to change to
the @file{/} directory first, and then avoid absolute notation.
For example:
-@example
+@smallexample
$ @kbd{(cd / && tar -c -f archive.tar home)}
$ @kbd{tar -c -f archive.tar -C / home}
-@end example
+@end smallexample
@include getdate.texi
@node Formats
@chapter Controlling the Archive Format
-@FIXME{need an intro here}
+Due to historical reasons, there are several formats of tar archives.
+All of them are based on the same principles, but have some subtle
+differences that often make them incompatible with each other.
+
+GNU tar is able to create and handle archives in a variety of formats.
+The most frequently used formats are (in alphabetical order):
+
+@table @asis
+@item gnu
+Format used by @GNUTAR{} versions up to 1.13.25. This format derived
+from an early POSIX standard, adding some improvements such as
+sparse file handling and incremental archives. Unfortunately these
+features were implemented in a way incompatible with other archive
+formats.
+
+Archives in @samp{gnu} format are able to hold pathnames of unlimited
+length.
+
+@item oldgnu
+Format used by @GNUTAR{} of versions prior to 1.12.
+
+@item v7
+Archive format, compatible with the V7 implementation of tar. This
+format imposes a number of limitations. The most important of them
+are:
+
+@enumerate
+@item The maximum length of a file name is limited to 99 characters.
+@item The maximum length of a symbolic link is limited to 99 characters.
+@item It is impossible to store special files (block and character
+devices, fifos etc.)
+@item Maximum value of user or group ID is limited to 2097151 (7777777
+octal)
+@item V7 archives do not contain symbolic ownership information (user
+and group name of the file owner).
+@end enumerate
+
+This format has traditionally been used by Automake when producing
+Makefiles. This practice will change in the future, in the meantime,
+however this means that projects containing filenames more than 99
+characters long will not be able to use @GNUTAR{} @value{VERSION} and
+Automake prior to 1.9.
+
+@item ustar
+Archive format defined by POSIX.1-1988 specification. It stores
+symbolic ownership information. It is also able to store
+special files. However, it imposes several restrictions as well:
+
+@enumerate
+@item The maximum length of a file name is limited to 256 characters,
+provided that the filename can be split at directory separator in
+two parts, first of them being at most 155 bytes long. So, in most
+cases the maximum file name length will be shorter than 256
+characters.
+@item The maximum length of a symbolic link name is limited to
+100 characters.
+@item Maximum size of a file the archive is able to accomodate
+is 8GB
+@item Maximum value of UID/GID is 2097151.
+@item Maximum number of bits in device major and minor numbers is 21.
+@end enumerate
+
+@item star
+Format used by J@"org Schilling @command{star}
+implementation. @GNUTAR{} is able to read @samp{star} archives but
+currently does not produce them.
+
+@item posix
+Archive format defined by POSIX.1-2001 specification. This is the
+most flexible and feature-rich format. It does not impose any
+restrictions on file sizes or filename lengths. This format is quite
+recent, so not all tar implementations are able to handle it properly.
+However, this format is designed in such a way that any tar
+implementation able to read @samp{ustar} archives will be able to read
+most @samp{posix} archives as well, with the only exception that any
+additional information (such as long file names etc.) will in such
+case be extracted as plain text files along with the files it refers to.
+
+This archive format will be the default format for future versions
+of @GNUTAR{}.
+
+@end table
+
+The following table summarizes the limitations of each of these
+formats:
+
+@multitable @columnfractions .10 .20 .20 .20 .20
+@item Format @tab UID @tab File Size @tab Path Name @tab Devn
+@item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
+@item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
+@item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
+@item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
+@item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
+@end multitable
+
+The default format for @GNUTAR{} is defined at compilation
+time. You may check it by running @command{tar --help}, and examining
+the last lines of its output. Usually, @GNUTAR{} is configured
+to create archives in @samp{gnu} format, however, future version will
+switch to @samp{posix}.
@menu
* Portability:: Making @command{tar} Archives More Portable
* Portable Names:: Portable Names
* dereference:: Symbolic Links
* old:: Old V7 Archives
+* gnu:: GNU and old GNU format archives.
* posix:: @sc{posix} archives
* Checksumming:: Checksumming Problems
* Large or Negative Values:: Large files, negative time stamps, etc.
Certain old versions of @command{tar} cannot handle additional
information recorded by newer @command{tar} programs. To create an
archive in V7 format (not ANSI), which can be read by these old
-versions, specify the @value{op-old-archive} option in
-conjunction with the @value{op-create}. @command{tar} also
-accepts @samp{--portability} for this option. When you specify it,
+versions, specify the @value{op-format-v7} option in
+conjunction with the @value{op-create} (@command{tar} also
+accepts @samp{--portability} or @samp{op-old-archive} for this
+option). When you specify it,
@command{tar} leaves out information about directories, pipes, fifos,
contiguous files, and device files, and specifies file ownership by
group and user IDs instead of group and user names.
-When updating an archive, do not use @value{op-old-archive}
+When updating an archive, do not use @value{op-format-v7}
unless the archive was created with using this option.
In most cases, a @emph{new} format archive can be read by an @emph{old}
@command{tar} program without serious trouble, so this option should
seldom be needed. On the other hand, most modern @command{tar}s are
able to read old format archives, so it might be safer for you to
-always use @value{op-old-archive} for your distributions.
+always use @value{op-format-v7} for your distributions.
-@node posix
-@subsection @acronym{GNU} @command{tar} and @sc{posix} @command{tar}
+@node gnu
+@subsection @acronym{GNU} and old @GNUTAR{} format
-@acronym{GNU} @command{tar} was based on an early draft of the
+@GNUTAR{} was based on an early draft of the
@sc{posix} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
@command{tar}, such as the support for file names longer than 100
characters, use portions of the @command{tar} header record which were
specified in that @sc{posix} draft as unused. Subsequent changes in
@sc{posix} have allocated the same parts of the header record for
-other purposes. As a result, @acronym{GNU} @command{tar} is
-incompatible with the current @sc{posix} spec, and with @command{tar}
-programs that follow it.
-
-We plan to reimplement these @acronym{GNU} extensions in a new way which is
-upward compatible with the latest @sc{posix} @command{tar} format, but we
-don't know when this will be done.
-
-In the mean time, there is simply no telling what might happen if you
-read a @acronym{GNU} @command{tar} archive, which uses the
-@acronym{GNU} extensions, using some other @command{tar} program. So
-if you want to read the archive with another @command{tar} program, be
-sure to write it using the @samp{--old-archive} option (@samp{-o}).
-
-@FIXME{is there a way to tell which flavor of tar was used to write a
-particular archive before you try to read it?}
-
-Traditionally, old @command{tar}s have a limit of 100 characters.
-@acronym{GNU} @command{tar} attempted two different approaches to
-overcome this limit, using and extending a format specified by a draft
-of some P1003.1. The first way was not that successful, and involved
-@file{@@MaNgLeD@@} file names, or such; while a second approach used
-@file{././@@LongLink} and other tricks, yielding better success. In
-theory, @acronym{GNU} @command{tar} should be able to handle file
-names of practically unlimited length. So, if @acronym{GNU}
-@command{tar} fails to dump and retrieve files having more than 100
-characters, then there is a bug in @acronym{GNU} @command{tar},
-indeed.
-
-But, being strictly @sc{posix}, the limit was still 100 characters.
-For various other purposes, @acronym{GNU} @command{tar} used areas
-left unassigned in the @sc{posix} draft. @sc{posix} later revised
-P1003.1 @code{ustar} format by assigning previously unused header
-fields, in such a way that the upper limit for file name length was
-raised to 256 characters. However, the actual @sc{posix} limit
-oscillates between 100 and 256, depending on the precise location of
-slashes in full file name (this is rather ugly). Since @acronym{GNU}
-@command{tar} use the same fields for quite other purposes, it became
-incompatible with the latest @sc{posix} standards.
-
-For longer or non-fitting file names, we plan to use yet another set
-of @acronym{GNU} extensions, but this time, complying with the
-provisions @sc{posix} offers for extending the format, rather than
-conflicting with it. Whenever an archive uses old @acronym{GNU}
-@command{tar} extension format or @sc{posix} extensions, would it be
-for very long file names or other specialities, this archive becomes
-non-portable to other @command{tar} implementations. In fact,
-anything can happen. The most forgiving @command{tar}s will merely
-unpack the file using a wrong name, and maybe create another file
-named something like @file{@@LongName}, with the true file name in it.
-@command{tar}s not protecting themselves may segment violate!
-
-Compatibility concerns make all this thing more difficult, as we will
-have to support @emph{all} these things together, for a while.
-@acronym{GNU} @command{tar} should be able to produce and read true
-@sc{posix} format files, while being able to detect old @acronym{GNU}
-@command{tar} formats, besides old V7 format, and process them
-conveniently. It would take years before this whole area
-stabilizes@dots{}
-
-There are plans to raise this 100 limit to 256, and yet produce
-@sc{posix} conforming archives. Past 256, I do not know yet if
-@acronym{GNU} @command{tar} will go non-@sc{posix} again, or merely
-refuse to archive the file.
-
-There are plans so @acronym{GNU} @command{tar} support more fully the
-latest @sc{posix} format, while being able to read old V7 format,
-@acronym{GNU} (semi-@sc{posix} plus extension), as well as full
-@sc{posix}. One may ask if there is part of the @sc{posix} format
-that we still cannot support. This simple question has a complex
-answer. Maybe that, on intimate look, some strong limitations will
-pop up, but until now, nothing sounds too difficult (but see below).
-I only have these few pages of @sc{posix} telling about ``Extended tar
-Format'' (P1003.1-1990 -- section 10.1.1), and there are references to
-other parts of the standard I do not have, which should normally
-enforce limitations on stored file names (I suspect things like fixing
-what @kbd{/} and @kbd{@key{NUL}} means). There are also some points
-which the standard does not make clear, Existing practice will then
-drive what I should do.
-
-@sc{posix} mandates that, when a file name cannot fit within 100 to
-256 characters (the variance comes from the fact a @kbd{/} is ideally
-needed as the 156'th character), or a link name cannot fit within 100
-characters, a warning should be issued and the file @emph{not} be
-stored. Unless some @value{op-posix} option is given (or
-@env{POSIXLY_CORRECT} is set), I suspect that @acronym{GNU}
-@command{tar} should disobey this specification, and automatically
-switch to using @acronym{GNU} extensions to overcome file name or link
-name length limitations.
-
-There is a problem, however, which I did not intimately studied yet.
-Given a truly @sc{posix} archive with names having more than 100
-characters, I guess that @acronym{GNU} @command{tar} up to 1.11.8 will
-process it as if it were an old V7 archive, and be fooled by some
-fields which are coded differently. So, the question is to decide if
-the next generation of @acronym{GNU} @command{tar} should produce
-@sc{posix} format by default, whenever possible, producing archives
-older versions of @acronym{GNU} @command{tar} might not be able to
-read correctly. I fear that we will have to suffer such a choice one
-of these days, if we want @acronym{GNU} @command{tar} to go closer to
-@sc{posix}. We can rush it. Another possibility is to produce the
-current @acronym{GNU} @command{tar} format by default for a few years,
-but have @acronym{GNU} @command{tar} versions from some 1.@var{POSIX}
-and up able to recognize all three formats, and let older
-@acronym{GNU} @command{tar} fade out slowly. Then, we could switch to
-producing @sc{posix} format by default, with not much harm to those
-still having (very old at that time) @acronym{GNU} @command{tar}
-versions prior to 1.@var{POSIX}.
-
-@sc{posix} format cannot represent very long names, volume headers,
-splitting of files in multi-volumes, sparse files, and incremental
-dumps; these would be all disallowed if @value{op-posix} or
-@env{POSIXLY_CORRECT}. Otherwise, if @command{tar} is given long
-names, or @samp{-[VMSgG]}, then it should automatically go non-@sc{posix}.
-I think this is easily granted without much discussion.
-
-Another point is that only @code{mtime} is stored in @sc{posix}
-archives, while @acronym{GNU} @command{tar} currently also store
-@code{atime} and @code{ctime}. If we want @acronym{GNU} @command{tar}
-to go closer to @sc{posix}, my choice would be to drop @code{atime}
-and @code{ctime} support on average. On the other hand, I perceive
-that full dumps or incremental dumps need @code{atime} and
-@code{ctime} support, so for those special applications, @sc{posix}
-has to be avoided altogether.
-
-A few users requested that @value{op-sparse} be always active by
-default, I think that before replying to them, we have to decide if we
-want @acronym{GNU} @command{tar} to go closer to @sc{posix} on
-average, while producing files. My choice would be to go closer to
-@sc{posix} in the long run. Besides possible double reading, I do not
-see any point of not trying to save files as sparse when creating
-archives which are neither @sc{posix} nor old-V7, so the actual
-@value{op-sparse} would become selected by default when producing such
-archives, whatever the reason is. So, @value{op-sparse} alone might
-be redefined to force @acronym{GNU}-format archives, and recover its
-previous meaning from this fact.
-
-@acronym{GNU}-format as it exists now can easily fool other @sc{posix}
-@command{tar}, as it uses fields which @sc{posix} considers to be part
-of the file name prefix. I wonder if it would not be a good idea, in
-the long run, to try changing @acronym{GNU}-format so any added field
-(like @code{ctime}, @code{atime}, file offset in subsequent volumes,
-or sparse file descriptions) be wholly and always pushed into an
-extension block, instead of using space in the @sc{posix} header
-block. I could manage to do that portably between future
-@acronym{GNU} @command{tar}s. So other @sc{posix} @command{tar}s
-might be at least able to provide kind of correct listings for the
-archives produced by @acronym{GNU} @command{tar}, if not able to
-process them otherwise.
-
-Using these projected extensions might induce older @command{tar}s to
-fail. We would use the same approach as for @sc{posix}. I'll put out
-a @command{tar} capable of reading @sc{posix}ier, yet extended
-archives, but will not produce this format by default, in
-@acronym{GNU} mode. In a few years, when newer @acronym{GNU}
-@command{tar}s will have flooded out @command{tar} 1.11.X and
-previous, we could switch to producing @sc{posix}ier extended
-archives, with no real harm to users, as almost all existing
-@acronym{GNU} @command{tar}s will be ready to read @sc{posix}ier
-format. In fact, I'll do both changes at the same time, in a few
-years, and just prepare @command{tar} for both changes, without
-effecting them, from 1.@var{POSIX}. (Both changes: 1---using
-@sc{posix} convention for getting over 100 characters; 2---avoiding
-mangling @sc{posix} headers for @acronym{GNU} extensions, using only
-@sc{posix} mandated extension techniques).
-
-So, a future @command{tar} will have a @value{op-posix} flag forcing
-the usage of truly @sc{posix} headers, and so, producing archives
-previous @acronym{GNU} @command{tar} will not be able to read. So,
-@emph{once} pretest will announce that feature, it would be
-particularly useful that users test how exchangeable will be archives
-between @acronym{GNU} @command{tar} with @value{op-posix} and other
-@sc{posix} @command{tar}.
-
-In a few years, when @acronym{GNU} @command{tar} will produce
-@sc{posix} headers by default, @value{op-posix} will have a strong
-meaning and will disallow @acronym{GNU} extensions. But in the
-meantime, for a long while, @value{op-posix} in @acronym{GNU} tar will
-not disallow @acronym{GNU} extensions like @value{op-label},
-@value{op-multi-volume}, @value{op-sparse}, or very long file or link
-names. However, @value{op-posix} with @acronym{GNU} extensions will
-use @sc{posix} headers with reserved-for-users extensions to headers,
-and I will be curious to know how well or bad @sc{posix}
-@command{tar}s will react to these.
-
-@acronym{GNU} @command{tar} prior to 1.@var{POSIX}, and after
-1.@var{POSIX} without @value{op-posix}, generates and checks
-@samp{ustar@w{ }@w{ }}, with two suffixed spaces. This is sufficient
-for older @acronym{GNU} @command{tar} not to recognize @sc{posix}
-archives, and consequently, wrongly decide those archives are in old
-V7 format. It is a useful bug for me, because @acronym{GNU}
-@command{tar} has other @sc{posix} incompatibilities, and I need to
-segregate @acronym{GNU} @command{tar} semi-@sc{posix} archives from
-truly @sc{posix} archives, for @acronym{GNU} @command{tar} should be
-somewhat compatible with itself, while migrating closer to latest
-@sc{posix} standards. So, I'll be very careful about how and when I
-will do the correction.
+other purposes. As a result, @GNUTAR{} format is
+incompatible with the current @sc{posix} specification, and with
+@command{tar} programs that follow it.
+
+In the majority of cases, @command{tar} will be configured to create
+this format by default. This may change in the future, since we plan
+to make @samp{posix} format the default.
+
+To force creation a @GNUTAR{} archive, use option
+@value{op-format-gnu}.
+
+Some @command{tar} options are currently basing on @GNUTAR{}
+format, and can therefore be used only with @samp{gnu}
+or @samp{oldgnu} archive formats. The list of such options follows:
+
+@itemize @bullet
+@item @value{op-label}, when used with @value{op-create}.
+@item @value{op-incremental}
+@item @value{op-multi-volume}
+@item @value{op-sparse}
+@end itemize
+
+These options will be re-implemented for the @samp{posix} archive
+format in the future.
+
+@node posix
+@subsection @GNUTAR{} and @sc{posix} @command{tar}
+
+The version @value{VERSION} of @GNUTAR{} is able
+to read and create archives conforming to @sc{posix.1-2001} standard.
+
+A @sc{posix} conformant archive will be created if @command{tar}
+was given @value{op-format-posix} option.
+Notice, that currently @acronym{GNU} extensions are not
+allowed with this format. Following is the list of options that
+cannot be used with @value{op-format-posix}:
+
+@itemize @bullet
+@item @value{op-label}, when used with @value{op-create}.
+@item @value{op-incremental}
+@item @value{op-multi-volume}
+@item @value{op-sparse}
+@end itemize
+
+This restriction will disappear in the future versions.
@node Checksumming
@subsection Checksumming Problems
SunOS and HP-UX @command{tar} fail to accept archives created using
-@acronym{GNU} @command{tar} and containing non-ASCII file names, that
+@GNUTAR{} and containing non-ASCII file names, that
is, file names having characters with the eight bit set, because they
-use signed checksums, while @acronym{GNU} @command{tar} uses unsigned
+use signed checksums, while @GNUTAR{} uses unsigned
checksums while creating archives, as per @sc{posix} standards. On
-reading, @acronym{GNU} @command{tar} computes both checksums and
+reading, @GNUTAR{} computes both checksums and
accept any. It is somewhat worrying that a lot of people may go
around doing backup of their files using faulty (or at least
non-standard) software, not learning about it until it's time to
restore their missing files with an incompatible file extractor, or
vice versa.
-@acronym{GNU} @command{tar} compute checksums both ways, and accept
+@GNUTAR{} compute checksums both ways, and accept
any on read, so @acronym{GNU} tar can read Sun tapes even with their
-wrong checksums. @acronym{GNU} @command{tar} produces the standard
+wrong checksums. @GNUTAR{} produces the standard
checksum, however, raising incompatibilities with Sun. That is to
-say, @acronym{GNU} @command{tar} has not been modified to
+say, @GNUTAR{} has not been modified to
@emph{produce} incorrect archives to be read by buggy @command{tar}'s.
I've been told that more recent Sun @command{tar} now read standard
archives, so maybe Sun did a similar patch, after all?
@sc{posix} @command{tar} format uses fixed-sized unsigned octal strings
to represent numeric values. User and group IDs and device major and
minor numbers have unsigned 21-bit representations, and file sizes and
-times have unsigned 33-bit representations. @acronym{GNU} @command{tar}
+times have unsigned 33-bit representations. @GNUTAR{}
generates @sc{posix} representations when possible, but for values
outside the @sc{posix} range it generates two's-complement base-256
strings: uids, gids, and device numbers have signed 57-bit
implementations generate a two's complement representation for negative
time stamps that assumes a signed 32-bit @code{time_t}; hence they
generate archives that are not portable to hosts with differing
-@code{time_t} representations. @acronym{GNU} @command{tar} recognizes this
+@code{time_t} representations. @GNUTAR{} recognizes this
situation when it is run on host with a signed 32-bit @code{time_t}, but
it issues a warning, as these time stamps are nonstandard and unportable.
option, or with the @value{op-update}, @value{op-append},
@value{op-concatenate}, or @value{op-delete} operations.
-It is not exact to say that @acronym{GNU} @command{tar} is to work in concert
+It is not exact to say that @GNUTAR{} is to work in concert
with @command{gzip} in a way similar to @command{zip}, say. Surely, it is
possible that @command{tar} and @command{gzip} be done with a single call,
like in:
-@example
+@smallexample
$ @kbd{tar cfz archive.tar.gz subdir}
-@end example
+@end smallexample
@noindent
to save all of @samp{subdir} into a @code{gzip}'ed archive. Later you
can do:
-@example
+@smallexample
$ @kbd{tar xfz archive.tar.gz}
-@end example
+@end smallexample
@noindent
to explode and unpack.
archive to see its contents. However, this may be done without needing
disk space, by using pipes internally:
-@example
+@smallexample
$ @kbd{tar tfz archive.tar.gz}
-@end example
+@end smallexample
@cindex corrupted archives
About corrupted compressed archives: @command{gzip}'ed files have no
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 @acronym{GNU} @command{tar}. This would allow for viewing the
+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.
archive for the file where the consecutive stretches of zeros are, and
only archives the ``real contents'' of the file. On extraction (using
@value{op-sparse} is not needed on extraction) any such files have
-hols created wherever the continuous stretches of zeros were found.
+holes created wherever the continuous stretches of zeros were found.
Thus, if you use @value{op-sparse}, @command{tar} archives won't take
more space than the original.
@end table
However, users should be well aware that at archive creation time,
-@acronym{GNU} @command{tar} still has to read whole disk file to
+@GNUTAR{} still has to read whole disk file to
locate the @dfn{holes}, and so, even if sparse files use little space
on disk and in the archive, they may sometimes require inordinate
amount of time for reading and examining all-zero blocks of a file.
examining the file system directly, they can determine in advance
exactly where the holes are and thus avoid reading through them. The
only data it need read are the actual allocated data blocks.
-@acronym{GNU} @command{tar} uses a more portable and straightforward
+@GNUTAR{} uses a more portable and straightforward
archiving approach, it would be fairly difficult that it does
otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, on
1990-12-10:
stored in the archive instead.
@item --no-same-owner
+@itemx -o
Do not attempt to restore ownership when extracting. This is the
default behavior for ordinary users, so this option has an effect
only for the superuser.
wanted (there are a lot of possible schemes), and only then making a
@command{tar} archive out of this directory, before cleaning
everything out. Of course, we could add a lot of options to
-@acronym{GNU} @command{tar} for fine tuning permissions and ownership.
-This is not the good way, I think. @acronym{GNU} @command{tar} is
+@GNUTAR{} for fine tuning permissions and ownership.
+This is not the good way, I think. @GNUTAR{} is
already crowded with options and moreover, the approach just explained
gives you a great deal of control already.
@end table
@node Standard
-@section The Standard Format
+@section Basic Tar Format
@UNREVISED
While an archive may contain many files, the archive itself is a
@acronym{GNU} Emacs.
Physically, an archive consists of a series of file entries terminated
-by an end-of-archive entry, which consists of 512 zero bytes. A file
+by an end-of-archive entry, which consists of two 512 blocks of zero
+bytes. A file
entry usually describes one of the files in the archive (an
@dfn{archive member}), and consists of a file header and the contents
of the file. File headers contain file names and statistics, checksum
Each file archived is represented by a header block which describes
the file, followed by zero or more blocks which give the contents
-of the file. At the end of the archive file there may be a block
+of the file. At the end of the archive file there are two 512-byte blocks
filled with binary zeros as an end-of-file marker. A reasonable system
-should write a block of zeros at the end, but must not assume that
-such a block exists when reading an archive.
+should write such end-of-file marker at the end of an archive, but
+must not assume that such a block exists when reading an archive. In
+particular @GNUTAR{} always issues a warning if it does not encounter it.
The blocks may be @dfn{blocked} for physical I/O operations.
Each record of @var{n} blocks (where @var{n} is set by the
whose last record is shorter than the rest, or which contains garbage
records after a zero block.
-The header block is defined in C as follows. In the @acronym{GNU}
-@command{tar} distribution, this is part of file @file{src/tar.h}:
+The header block is defined in C as follows. In the @GNUTAR{}
+distribution, this is part of file @file{src/tar.h}:
-@example
+@smallexample
@include header.texi
-@end example
+@end smallexample
All characters in header blocks are represented by using 8-bit
characters in the local variant of ASCII. Each field within the
The @code{name}, @code{linkname}, @code{magic}, @code{uname}, and
@code{gname} are null-terminated character strings. All other fields
are zero-filled octal numbers in ASCII. Each numeric field of width
-@var{w} contains @var{w} minus 2 digits, a space, and a null, except
-@code{size}, and @code{mtime}, which do not contain the trailing null.
+@var{w} contains @var{w} minus 1 digits, and a null.
The @code{name} field is the file name of the file, with directory names
(if any) preceding the file name, separated by slashes.
special files.
You might want to look at the freely available alternatives. The
-major ones are @command{afio}, @acronym{GNU} @command{tar}, and
+major ones are @command{afio}, @GNUTAR{}, and
@command{pax}, each of which have their own extensions with some
backwards compatibility.
compiled). The default is normally set up to be the @dfn{first} tape
drive or other transportable I/O medium on the system.
-Starting with version 1.11.5, @acronym{GNU} @command{tar} uses
+Starting with version 1.11.5, @GNUTAR{} uses
standard input and standard output as the default device, and I will
not try anymore supporting automatic device detection at installation
time. This was failing really in too many cases, it was hopeless.
all this mess, using standard input and output as a default really
sounds like the only clean choice left, and a very useful one too.
-@acronym{GNU} @command{tar} reads and writes archive in records, I
+@GNUTAR{} reads and writes archive in records, I
suspect this is the main reason why block devices are preferred over
character devices. Most probably, block devices are more efficient
too. The installer could also check for @samp{DEFTAPE} in
and installing it are included in the @file{Makefile}.
@cindex absolute file names
-Unless you use the @value{op-absolute-names} option, @acronym{GNU}
-@command{tar} will not allow you to create an archive that contains
+Unless you use the @value{op-absolute-names} option, @GNUTAR{}
+will not allow you to create an archive that contains
absolute file names (a file name beginning with @samp{/}.) If you try,
@command{tar} will automatically remove the leading @samp{/} from the
file names it stores in the archive. It will also type a warning
message telling you what it is doing.
When reading an archive that was created with a different
-@command{tar} program, @acronym{GNU} @command{tar} automatically
+@command{tar} program, @GNUTAR{} automatically
extracts entries in the archive which have absolute file names as if
the file names were not absolute. This is an important feature. A
visitor here once gave a @command{tar} tape to an operator to restore;
-the operator used Sun @command{tar} instead of @acronym{GNU}
-@command{tar}, and the result was that it replaced large portions of
+the operator used Sun @command{tar} instead of @GNUTAR{},
+and the result was that it replaced large portions of
our @file{/bin} and friends with versions from the tape; needless to
say, we were unhappy about having to recover the file system from
backup tapes.
For example, if the archive contained a file @file{/usr/bin/computoy},
-@acronym{GNU} @command{tar} would extract the file to @file{usr/bin/computoy},
+@GNUTAR{} would extract the file to @file{usr/bin/computoy},
relative to the current directory. If you want to extract the files in
an archive to the same absolute names that they had when the archive
was created, you should do a @samp{cd /} before extracting the files
two terms in a quite consistent way.
John Gilmore, the writer of the public domain @command{tar} from which
-@acronym{GNU} @command{tar} was originally derived, wrote (June 1995):
+@GNUTAR{} was originally derived, wrote (June 1995):
@quotation
The nomenclature of tape drives comes from IBM, where I believe
The term @dfn{logical block} often represents the basic chunk of
allocation of many disk blocks as a single entity, which the operating
system treats somewhat atomically; this concept is only barely used
-in @acronym{GNU} @command{tar}.
+in @GNUTAR{}.
The term @dfn{physical record} is another way to speak of a physical
block, those two terms are somewhat interchangeable. In this manual,
to the application. The term @dfn{unit record} describes a small set
of characters which are transmitted whole to or by the application,
and often refers to a line of text. Those two last terms are unrelated
-to what we call a @dfn{record} in @acronym{GNU} @command{tar}.
+to what we call a @dfn{record} in @GNUTAR{}.
When writing to tapes, @command{tar} writes the contents of the archive
in chunks known as @dfn{records}. To change the default blocking
If you use a blocking factor larger than 20, older @command{tar}
programs might not be able to read the archive, so we recommend this
-as a limit to use in practice. @acronym{GNU} @command{tar}, however,
+as a limit to use in practice. @GNUTAR{}, however,
will support arbitrarily large record sizes, limited only by the
amount of virtual memory or the physical characteristics of the tape
device.
Archives with blocking factors larger than 20 cannot be read
by very old versions of @command{tar}, or by some newer versions
of @command{tar} running on old machines with small address spaces.
-With @acronym{GNU} @command{tar}, the blocking factor of an archive is limited
+With @GNUTAR{}, the blocking factor of an archive is limited
only by the maximum record size of the device containing the archive,
or by the amount of available virtual memory.
imposed by the device drivers, may yield unexpected diagnostics. For
example, this has been reported:
-@example
+@smallexample
Cannot write to /dev/dlt: Invalid argument
-@end example
+@end smallexample
@noindent
In such cases, it sometimes happen that the @command{tar} bundled by
-the system is aware of block size idiosyncrasies, while @acronym{GNU}
-@command{tar} requires an explicit specification for the block size,
+the system is aware of block size idiosyncrasies, while @GNUTAR{}
+requires an explicit specification for the block size,
which it cannot guess. This yields some people to consider
-@acronym{GNU} @command{tar} is misbehaving, because by comparison,
+@GNUTAR{} is misbehaving, because by comparison,
@cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}},
for example, might resolve the problem.
Apparently, Exabyte drives have a physical block size of 8K bytes.
If we choose our blocksize as a multiple of 8k bytes, then the problem
-seems to dissapper. Id est, we are using block size of 112 right
+seems to disappear. Id est, we are using block size of 112 right
now, and we haven't had the problem since we switched@dots{}
-With @acronym{GNU} @command{tar} the blocking factor is limited only
+With @GNUTAR{} the blocking factor is limited only
by the maximum record size of the device containing the archive, or by
the amount of available virtual memory.
invocation.
@end itemize
-In previous versions of @acronym{GNU} @command{tar}, the
-@samp{--compress-block} option (or even older:
-@samp{--block-compress}) was necessary to reblock compressed archives.
-It is now a dummy option just asking not to be used, and otherwise
-ignored. If the output goes directly to a local disk, and not through
+If the output goes directly to a local disk, and not through
stdout, then the last write is not extended to a full record size.
Otherwise, reblocking occurs. Here are a few other remarks on this
topic:
opens the archive file before using it and closes it afterwards, this
means that a simple:
-@example
+@smallexample
$ @kbd{tar cf /dev/tape @var{directory}}
-@end example
+@end smallexample
@noindent
will reposition the tape to its beginning both prior and after saving
To save @var{directory-1} as a first archive at the beginning of a
tape, and leave that tape ready for a second archive, you should use:
-@example
+@smallexample
$ @kbd{mt -f /dev/nrtape rewind}
$ @kbd{tar cf /dev/nrtape @var{directory-1}}
-@end example
+@end smallexample
@cindex tape marks
@dfn{Tape marks} are special magnetic patterns written on the tape
So, you may now save @var{directory-2} as a second archive after the
first on the same tape by issuing the command:
-@example
+@smallexample
$ @kbd{tar cf /dev/nrtape @var{directory-2}}
-@end example
+@end smallexample
@noindent
and so on for all the archives you want to put on the same tape.
the first 16 tape marks before saving @var{directory-17}, say, by using
these commands:
-@example
+@smallexample
$ @kbd{mt -f /dev/nrtape rewind}
$ @kbd{mt -f /dev/nrtape fsf 16}
$ @kbd{tar cf /dev/nrtape @var{directory-17}}
-@end example
+@end smallexample
In all the previous examples, we put aside blocking considerations, but
you should do the proper things for that as well. @xref{Blocking}.
If you think of data as a series of records "rrrr"'s, and tape marks as
"*"'s, a tape might look like the following:
-@example
+@smallexample
rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
-@end example
+@end smallexample
Tape devices read and write tapes using a read/write @dfn{tape
head}---a physical part of the device which can only access one
to add two archives to the example above, the tape might look like the
following:
-@example
+@smallexample
rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
-@end example
+@end smallexample
@node mt
@subsection The @command{mt} Utility
The syntax of the @command{mt} command is:
-@example
+@smallexample
@kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
-@end example
+@end smallexample
where @var{tapename} is the name of the tape device, @var{number} is
the number of times an operation is performed (with a default of one),
second tape when prompted, so @command{tar} can restore both halves of the
file.)
-@acronym{GNU} @command{tar} multi-volume archives do not use a truly
-portable format. You need @acronym{GNU} @command{tar} at both end to
+@GNUTAR{} multi-volume archives do not use a truly
+portable format. You need @GNUTAR{} at both end to
process them properly.
When prompting for a new tape, @command{tar} accepts any of the following
the file begins.
For example, let's presume someone has two tape drives on a system
-named @file{/dev/tape0} and @file{/dev/tape1}. For having @acronym{GNU}
-@command{tar} to switch to the second drive when it needs to write the
+named @file{/dev/tape0} and @file{/dev/tape1}. For having @GNUTAR{}
+to switch to the second drive when it needs to write the
second tape, and then back to the first tape, etc., just do either of:
@smallexample
Beware that there is @emph{no} real standard about the proper way, for
a @command{tar} archive, to span volume boundaries. If you have a
multi-volume created by some vendor's @command{tar}, there is almost
-no chance you could read all the volumes with @acronym{GNU}
-@command{tar}. The converse is also true: you may not expect
-multi-volume archives created by @acronym{GNU} @command{tar} to be
+no chance you could read all the volumes with @GNUTAR{}.
+The converse is also true: you may not expect
+multi-volume archives created by @GNUTAR{} to be
fully recovered by vendor's @command{tar}. Since there is little
chance that, in mixed system configurations, some vendor's
@command{tar} will work on another vendor's machine, and there is a
-great chance that @acronym{GNU} @command{tar} will work on most of
-them, your best bet is to install @acronym{GNU} @command{tar} on all
+great chance that @GNUTAR{} will work on most of
+them, your best bet is to install @GNUTAR{} on all
machines between which you know exchange of files is possible.
@node Tape Files
People seem to often do:
-@example
+@smallexample
@kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
-@end example
+@end smallexample
or such, for pushing a common date in all volumes or an archive set.
print the label first, and then print archive member information, as
in the example below:
-@example
+@smallexample
$ @kbd{tar --verbose --list --file=iamanarchive}
V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
-rw-rw-rw- ringo user 40 1990-05-21 13:30 iamafilename
-@end example
+@end smallexample
@table @kbd
@item --label=@var{archive-label}
series created through a single script used on a regular basis, just
manage to get some date string as part of the label. For example:
-@example
+@smallexample
$ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
$ @kbd{tar --create --file=/dev/tape --multi-volume \
--volume="Daily backup for `date +%Y-%m-%d`"}
-@end example
+@end smallexample
Also note that each label has its own date and time, which corresponds
-to when @acronym{GNU} @command{tar} initially attempted to write it,
+to 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
projects / chaz / tar / blobdiff