A good backup system can help you recover from a lot of different kinds of situations: a botched upgrade (requiring re-installation), a hard drive crash, or even thumb-fingered users deleting the wrong file. In practice, though I've experienced all of these, it's the last sort of problem that causes me the most pain. Sometimes you just wish you could go back a few days in time and grab that file. What you want is something like the Internet Archive's "Wayback Machine", but for your own system. Here"s how to set one up using the rsnapshot package (included in the Debian and Ubuntu distributions).