You should regularly back up any files you store on your local disk.
Howver, there are some things you should know before making backups of
your Linux system. First, do not attempt to back up remote file
systems, particularly not /afs. You also should not back up
/proc, as it is not a physical file system. There are two ways
to do this; either back up each partition separately (the -l
flag tells tar not to follow mount points; similar options may
exist for other backup software) or explicitly exclude /afs,
/proc, and other mount points.
Other things you probably don't want to backup are
/usr/vice/cache (your AFS cache, whose contents are simply copies
of files on AFS servers stored locally to save time) and directories
named tmp (which stands for temporary).
Also, if there is any chance that somebody else can read your backup,
and particularly if you are backing up over the network, you should be sure to exclude /etc/passwd* and
/etc/athena/srvtab. The contents of /etc/passwd.local tell
malicious people who can telnet to your machine. (The contents also
allow them to determine your root password, but only if you chose an
easily-guessed password, which you shouldn't have done anyway, or if
they have a lot of time or computational power.) If anybody
gets a copy of your srvtab, however, the consequences can be
dire. For instance, somebody with the contents of your srvtab
could monitor encrypted connections to your machine, pretend to be
your machine, and convince your machine that he has tickets as any
user.