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As described above, a tar
archive keeps, for each member it contains,
its metadata, such as modification time, mode and ownership of
the file. GNU tar
allows to replace these data with other values
when adding files to the archive. The options described in this
section affect creation of archives of any type. For POSIX archives,
see also Controlling Extended Header Keywords, for additional ways of controlling
metadata, stored in the archive.
When adding files to an archive, tar
will use
permissions for the archive members, rather than the permissions
from the files. permissions can be specified either as an octal
number or as symbolic permissions, like with
chmod
(See Permissions: (fileutils)File permissions section `File permissions' in GNU file utilities. This reference
also has useful information for those not being overly familiar with
the UNIX permission system). Using latter syntax allows for
more flexibility. For example, the value ‘a+rw’ adds read and write
permissions for everybody, while retaining executable bits on directories
or on any other file already marked as executable:
$ tar -c -f archive.tar --mode='a+rw' . |
When adding files to an archive, tar
will use date as
the modification time of members when creating archives, instead of
their actual modification times. The argument date can be
either a textual date representation in almost arbitrary format
(see section Date input formats) or a name of an existing file, starting
with ‘/’ or ‘.’. In the latter case, the modification time
of that file will be used.
The following example will set the modification date to 00:00:00, January 1, 1970:
$ tar -c -f archive.tar --mtime='1970-01-01' . |
When used with ‘--verbose’ (see section The ‘--verbose’ Option) GNU tar
will try to convert the specified date back to its textual
representation and compare it with the one given with
‘--mtime’ options. If the two dates differ, tar
will
print a warning saying what date it will use. This is to help user
ensure he is using the right date.
For example:
$ tar -c -f archive.tar -v --mtime=yesterday . tar: Option --mtime: Treating date `yesterday' as 2006-06-20 13:06:29.152478 … |
Specifies that tar
should use user as the owner of members
when creating archives, instead of the user associated with the source
file. The argument user can be either an existing user symbolic
name, or a decimal numeric user ID.
There is no value indicating a missing number, and ‘0’ usually means
root
. Some people like to force ‘0’ as the value to offer in
their distributions for the owner of files, because the root
user is
anonymous anyway, so that might as well be the owner of anonymous
archives. For example:
$ tar -c -f archive.tar --owner=0 . |
or:
$ tar -c -f archive.tar --owner=root . |
Files added to the tar
archive will have a group ID of group,
rather than the group from the source file. The argument group
can be either an existing group symbolic name, or a decimal numeric group ID.
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