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By default, GNU tar drops a leading ‘/’ on
input or output, and complains about file names containing a ‘..’
component. There is an option that turns off this behavior:
Do not strip leading slashes from file names, and permit file names containing a ‘..’ file name component.
When tar extracts archive members from an archive, it strips any
leading slashes (‘/’) from the member name. This causes absolute
member names in the archive to be treated as relative file names. This
allows you to have such members extracted wherever you want, instead of
being restricted to extracting the member in the exact directory named
in the archive. For example, if the archive member has the name
‘/etc/passwd’, tar will extract it as if the name were
really ‘etc/passwd’.
File names containing ‘..’ can cause problems when extracting, so
tar normally warns you about such files when creating an
archive, and rejects attempts to extracts such files.
Other 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-GNU tar
program to use. Therefore, GNU tar also strips
leading slashes from member names when putting members into the
archive. For example, if you ask tar to add the file
‘/bin/ls’ to an archive, it will do so, but the member name will
be ‘bin/ls’(20).
Symbolic links containing ‘..’ or leading ‘/’ can also cause
problems when extracting, so tar normally extracts them last;
it may create empty files as placeholders during extraction.
If you use the ‘--absolute-names’ (‘-P’) option,
tar will do none of these transformations.
To archive or extract files relative to the root directory, specify the ‘--absolute-names’ (‘-P’) option.
Normally, tar acts on files relative to the working
directory—ignoring superior directory names when archiving, and
ignoring leading slashes when extracting.
When you specify ‘--absolute-names’ (‘-P’),
tar stores file names including all superior directory
names, and preserves leading slashes. If you only invoked
tar from the root directory you would never need the
‘--absolute-names’ option, but using this option
may be more convenient than switching to root.
Preserves full file names (including superior directory names) when archiving and extracting files.
tar prints out a message about removing the ‘/’ from
file names. This message appears once per GNU tar
invocation. It represents something which ought to be told; ignoring
what it means can cause very serious surprises, later.
Some people, nevertheless, do not want to see this message. Wanting to
play really dangerously, one may of course redirect tar standard
error to the sink. For example, under sh:
$ tar -c -f archive.tar /home 2> /dev/null
Another solution, both nicer and simpler, would be to change to the ‘/’ directory first, and then avoid absolute notation. For example:
$ tar -c -f archive.tar -C / home
See section Integrity, for some of the security-related implications of using this option.
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