This section describes some simple uses of
You can use `
cpio', and `
will need to use `
mt' to get the full potential of your tapes and
ftape driver. For a start I'd recommend using `
it can archive lots of directories and let you pick out separate files
from an archive.
cpio creates smaller archives and is more
generally more flexible than
tar, but is missing some features
like volume labels. `
afio' creates backups where each file is
compressed individually and then concatenated. This will allow you to
access the files ``after'' the point of the error. If you use
tar files, all data after the point of the error is
lost! (to me, this is a pretty good reason for NOT using compression
on backups). The choice of which is most appropriate depends on the
situation and the features and malfeatures of each of the packages. I
recommend taking a look at each package at reviewing the options that
each provides. It's possible that this HOWTO may provide more detail
on this subject at some point in the future.
To make a backup of your kernel source tree using
tar, do this
(assuming you have the sources in
# cd /usr/src # tar cf /dev/ftape linux
This will not compress the files, but gives you a smoother tape run.
If you want the compression (and you've got
tar 1.11.2), you
just include the
-z flag(*), eg: `
tar czf /dev/ftape
For further instructions on how to use
mt look at the man pages and the texinfo files that comes
with the respective distributions.
tar assumes that the first argument is options, so the
-' is not necessary, i.e. these two commands are the same:
tar xzf /dev/ftape' and `
tar -xzf /dev/ftape'
OK, let us restore the backup of the kernel source you made in section Writing an archive to a tape above. To do this you simply say
tar xf /dev/ftape
If you used compression, you will have to say
tar xzf /dev/ftape
When you use compression,
gzip will complain about trailing
garbage after the very end of the archive (and this will lead to a
`broken pipe' message). This can be safely ignored.
For the other utilities, please read the man page.
tar has an option (
-d) for detecting differences between two
archives. To test your backup of the kernel source say
tar df /dev/ftape
If you do not have the man page for
tar, you are not lost (yet);
tar has a built-in option list: try `
tar --help 2>&1 | less'
To put more than one backup on a tape you must have the
utility. You will probably have it already, if you got one of the
mainline distributions (eg. Slackware or Debian).
cpio generate a single Tape ARchive
and know nothing about multiple files or positioning of a tape, it
just reads or writes from/to a device.
mt knows everything about
moving the tape back and forth, but nothing about reading the data off
the tape. As you might have guessed, combining
mt does the trick.
By using the
nftape) device, you can use
mt' to position the tape the correct place (`
/dev/nftape fsf 2' means step over two ``file marks'', i.e.
tar files) and then use
cpio to read or write
the relevant data.
The most common use of the non-rewinding device is to append another backup to an existing tape. Here are the specific steps with a little explanation thrown in for good measure.
The tape should now be positioned at the End-of-Tape (EOT), which is actually between to End-of-File (EOF) marks. The tape won't move unless a program opens the device, closes the rewinding device, removes the device driver from kernel memory (rmmod) or ejects the tape. Using `
mt -f /dev/n???? eof
mt eof' may be faster on QIC tapes.
zftapecache some information that belongs in the header segments on the tape and update those header segments only when the tape is rewound. This caching is necessary because rewinding the tape and updating the header segments takes a conspicious amount of time. The drawback of this caching is that you will lose information if you have written to the tape and not rewound the device.
``Is there a way to extend an archive -- put a file on the tape, then later, add more to the tape?''
tar documentation will tell you to use `
but it does not work. This is a limitation of the current
Since a tape does not have a ``filesystem'' on it, you do not mount /
unmount the tape. To backup, you just insert the tape and run your
tar' command (or whatever you use to access the tape with).