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#### 4.3.1 Overriding File Metadata

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 PAX keywords, for additional ways of controlling metadata, stored in the archive.

`--mode=permissions`

  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 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' .

`--mtime=date`

  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 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 verbose tutorial) 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
      …

  When used with `--clamp-mtime` GNU `tar` will only set the modification date to date on files whose actual modification date is later than date. This is to make it easy to build reproducible archives given a common timestamp for generated files while still retaining the original timestamps of untouched files.

      $ tar -c -f archive.tar --clamp-mtime --mtime=@$SOURCE_DATE_EPOCH .

`--owner=user`

  Specifies that `tar` should use user as the owner of members when creating archives, instead of the user associated with the source file.

  If user contains a colon, it is taken to be of the form name:id where a nonempty name specifies the user name and a nonempty id specifies the decimal numeric user ID. If user does not contain a colon, it is taken to be a user number if it is one or more decimal digits; otherwise it is taken to be a user name.

  If a name is given but no number, the number is inferred from the current host’s user database if possible, and the file’s user number is used otherwise. If a number is given but no name, the name is inferred from the number if possible, and an empty name is used otherwise. If both name and number are given, the user database is not consulted, and the name and number need not be valid on the current host.

  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 .

`--group=group`

  Files added to the `tar` archive will have a group ID of group, rather than the group from the source file. As with `--owner`, the argument group can be an existing group symbolic name, or a decimal numeric group ID, or name:id.

The `--owner` and `--group` options affect all files added to the archive. GNU `tar` provides also two options that allow for more detailed control over owner translation:

`--owner-map=file`

  Read UID translation map from file.

  When reading, empty lines are ignored. The ‘`#`’ sign, unless quoted, introduces a comment, which extends to the end of the line. Each nonempty line defines mapping for a single UID. It must consist of two fields separated by any amount of whitespace. The first field defines original username and UID. It can be a valid user name or a valid UID prefixed with a plus sign. In both cases the corresponding UID or user name is inferred from the current host’s user database.

  The second field defines the UID and username to map the original one to. Its format can be the same as described above. Otherwise, it can have the form newname:newuid, in which case neither newname nor newuid are required to be valid as per the user database.

  For example, consider the following file:

      +10     bin
      smith   root:0

  Given this file, each input file that is owner by UID 10 will be stored in archive with owner name ‘`bin`’ and owner UID corresponding to ‘`bin`’. Each file owned by user ‘`smith`’ will be stored with owner name ‘`root`’ and owner ID 0. Other files will remain unchanged.

  When used together with `--owner-map`, the `--owner` option affects only files whose owner is not listed in the map file.

`--group-map=file`

  Read GID translation map from file.

  The format of file is the same as for `--owner-map` option:

  Each nonempty line defines mapping for a single GID. It must consist of two fields separated by any amount of whitespace. The first field defines original group name and GID. It can be a valid group name or a valid GID prefixed with a plus sign. In both cases the corresponding GID or user name is inferred from the current host’s group database.

  The second field defines the GID and group name to map the original one to. Its format can be the same as described above. Otherwise, it can have the form newname:newgid, in which case neither newname nor newgid are required to be valid as per the group database.

  When used together with `--group-map`, the `--group` option affects only files whose owner group is not rewritten using the map file.

Next: Extended File Attributes, Up: create options [Contents][Index]