(tar)Special Options for Archiving

Archive Structure

Compression

Format Control

Special Options for Archiving
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     *(This message will disappear, once this node revised.)*

   To give the archive a name which will be recorded in it, use the
`--label=ARCHIVE-LABEL' (`-V ARCHIVE-LABEL') option.  This will write a
special record identifying VOLUME-LABEL as the name of the archive to
the front of the archive which will be displayed when the archive is
listed with `--list' (`-t').  If you are creating a multi-volume
archive with `--multi-volume' (`-M') (
FIXME: pxref Using Multiple Tapes
   ), then the volume label will have `Volume NNN' appended to the name
you give, where NNN is the number of the volume of the archive.  (If
you use the `--label=ARCHIVE-LABEL' (`-V ARCHIVE-LABEL') option when
reading an archive, it checks to make sure the label on the tape
matches the one you give.

FIXME: xref Special Options for Archiving
   .)

   Files in the filesystem occasionally have "holes."  A hole in a file
is a section of the file's contents which was never written.  The
contents of a hole read as all zeros.  On many operating systems,
actualdisk storage is not allocated for holes, but they are counted in
the length of the file.  If you archive such a file, `tar' could create
an archive longer than the original.  To have `tar' attempt to
recognize the holes in a file, use `--sparse' (`-S').  When you use the
`--sparse' (`-S') option, then, for any file using less disk space than
would be expected from its length, `tar' searches the file for
consecutive stretches of zeros.  It then records in the archive for the
file where the consecutive stretches of zeros are, and only archives the
"real contents" of the file.  On extraction (using `--sparse' (`-S') is
not needed on extraction) any such files have hols created wherever the
continuous stretches of zeros were found.  Thus, if you use `--sparse'
(`-S'), `tar' archives won't take more space than the original.

   When `tar' reads files, this causes them to have the access times
updated.  To have `tar' attempt to set the access times back to what
they were before they were read, use the `--atime-preserve' option.
This doesn't work for files that you don't own, unless you're root, and
it doesn't interact with incremental dumps nicely (
FIXME: pxref Making Backups
   ), but it is good enough for some purposes.