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Old V7 Archives
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   Certain old versions of `tar' cannot handle additional information
recorded by newer `tar' programs.  To create an archive in V7 format
(not ANSI), which can be read by these old versions, specify the
`--old-archive' (`-o') option in conjunction with the `--create'
(`-c').  `tar' also accepts `--portability' for this option.  When you
specify it, `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 `--old-archive' (`-o') unless
the archive was created with using this option.

   In most cases, a _new_ format archive can be read by an _old_ `tar'
program without serious trouble, so this option should seldom be
needed.  On the other hand, most modern `tar's are able to read old
format archives, so it might be safer for you to always use
`--old-archive' (`-o') for your distributions.