Linux box occasionally locks at 100% usage
I'm running RH9 on a P3-650. It's my little everything box - web, mail, ftp, ssh, etc.
About once every two weeks, I will wake up, or return home to find that my Linux box is hitting the hard drive like crazy, and slamming the processor. I can't seem to get enough cycles to log in (even to one of the text-based virtual consoles) to run top and see what's wrong.
I'm using Sendmail on this machine and I'm a total newbie at setting it up, so I was thinking maybe someone was using me to send spam, but I have no way to know this. All my sendmail logs give me are these little lines saying it's refusing additional connections because the load level is too high.
Is it possible to "nice" a service so that if it is sendmail that's doing this, I could still have some resources left over to examine what's going on? Is there another common culprit besides sendmail that might be causing this behavior? Any logs I could check to see what's happening?