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This is only accidentally
true, but not in general. Whereas modification times are always
restored, in most cases, one has to be root for restoring the owner,
and use a special option for restoring permissions. Here, it just
happens that the restoring user is also the owner of the archived
members, and that the current
umask is compatible with original
For example, ‘--file’
(‘-f’) takes the name of an archive file as an argument. If
you do not supply an archive file name,
tar will use a
default, but this can be confusing; thus, we recommend that you always
supply a specific archive file name.
options, the last of which has an argument, is a rather opaque way to
write options. Some wonder if GNU
getopt should not
even be made helpful enough for considering such usages as invalid.
tar version 1.11.6,
a bug prevented intermixing old style options with long options in
Earlier versions of GNU
tar understood ‘-l’ as a
synonym for ‘--one-file-system’. The current semantics, which
complies to UNIX98, was introduced with version
1.15.91. See section Changes, for more information.
The ‘--recursion’ option is the default and is used here for clarity. The same example can be written as:
tar -cf a.tar /usr --no-recursion /var/*
There are plans to merge the
tar packages into a single one which would be called
paxutils. So, who knows if, one of this days, the
‘--version’ would not output ‘tar (GNU paxutils) 3.2’.
This is actually a shortcut for ‘--checkpoint=n --checkpoint-action=dot’. See section dot.
This is well described in Unix-haters Handbook, by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG Books, ISBN 1-56884-203-1.
Unless you give it
‘--keep-old-files’ (or ‘--skip-old-files’) option, or
the disk copy is newer than the one in the archive and you invoke
tar with ‘--keep-newer-files’ option.
This can cause multiple members to have the same name. For information on how this affects reading the archive, see Multiple Members with the Same Name.
Notice, that since both archives were created without ‘-P’ option (see section Absolute File Names), these commands should be run from the root file system.
Two ‘--verbose’ options were selected to avoid breaking usual verbose listing output (‘--list --verbose’) when using in scripts.
Versions of GNU
tar up to 1.15.1 used to dump verbatim binary
contents of the DUMPDIR header (with terminating nulls) when
‘--incremental’ or ‘--listed-incremental’ option was
given, no matter what the verbosity level. This behavior, and,
especially, the binary output it produced were considered inconvenient
and were changed in version 1.16.
For backward compatibility, the
backup will also
try to deduce the requested dump level from the name of the
script itself. If the name consists of a string ‘level-’
followed by a single decimal digit, that digit is taken as
the dump level number. Thus, you may create a link from
level-1 and then run
level-1 whenever you need to
create a level one dump.
Versions of GNU
tar up to 1.15.1
recognized only ‘-C’ option in file lists, and only if the
option and its argument occupied two consecutive lines.
According to the Bazaar docs,
globbing-patterns are Korn-shell style and regular expressions are
perl-style. As of GNU
tar version 1.34, these are
treated as shell-style globs and posix extended regexps. This will be
fixed in future releases.
Support for perl-style regexps will appear in future releases.
Notice that earlier GNU
tar versions used
globbing for inclusion members, which contradicted to UNIX98
specification and was not documented. See section Changes, for more
information on this and other changes.
A side effect of this is that when ‘--create’ is used with ‘--verbose’ the resulting output is not, generally speaking, the same as the one you’d get running tar --list command. This may be important if you use some scripts for comparing both outputs. See listing member and file names, for the information on how to handle this case.
It also had patent problems in the past.
To verbosely trace the decompressor selection, use the ‘--warning=decompress-program’ option (see section decompress-program).
There are plans to fix this in future releases.
See section PAX Format, Version 1.0.
Technically speaking, n is a
process ID of the
tar process which created the
archive (see section Controlling Extended Header Keywords).
If this message is not needed, you can turn it off using the ‘--warning=no-record-size’ option.
If you run GNU
tar under a different locale, the
translation to the locale’s language will be used.
See --restrict, for more information about this option.
Until version 1.10, that option was called ‘--volume’, but is not available under that name anymore.
Note that GNU
tar versions up to 1.23 indicated
mismatch with an exit code 2 and printed a spurious diagnostics on
Previous versions of
tar used full
regular expression matching, or before that, only exact string
matching, instead of wildcard matchers. We decided for the sake of
simplicity to use a uniform matching device through
The original version of the script can be seen at http://lists.gnu.org/archive/html/bug-tar/2016-11/msg00024.html
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