I have a backup script that runs in the background daily on my linux (Fedora 9) computer. If the computer is shut down while the backup is in progress the backup may be dama
Another get-you-started solution: During shutdown, the system runs the scripts in /etc/init.d/ (or really, a script in /etc/rc.*/, but you get the idea.) You could create a script in that directory that checks the status of your backup, and delays shuts down until the backup completes. Or better yet, it gracefully interrupts your backup.
The super-user could workaround this script (with /sbin/halt for example,) but you can not prevent the super-user for doing anything if their mind is really set into doing it.