Eight years ago. I get into my office [1] and I notice that pineal, the SGI (Silicon Graphics, Inc.) box I use, has crashed. Hard. The kernel crashed.
For a Unix system, that's bad.
Not knowing what happened, I bring the box back up and go about my business.
A few days later, it's crashed again.
This time though, I have a slight clue as to what might be going on. I had noticed one of the users of the box doing some odd things. Normally, I wouldn't care (seeing how this user was odd to begin with) but I couldn't help thinking that the odd thing this user was doing might have caused the machine to crash.
I, suspecting what happened, bring the box back up and go about my business.
A few days later, it's crashed again.
I bring it back up, get the odd user in question, and asked him to do what he was doing just prior to the crash, exactly.
I watch as the machine crashes.
Now, I still don't know why it crashed, but at least I knew what caused it to crash. It seems that the user in question logged in and ran a program called screen. screen is a program that allows you to have multiple command lines via a single login session (like a single terminal) and it would keep the session alive if you disconnected (heck, I used that program myself for those two reasons). Then, he would log into IRC (Internet Relay Chat) and have his IRC client log a channel to a file. He would then disconnect, leaving the IRC client running (because of screen) and logging a channel to a file. Doing both of those things would cause the system to crash.
Odd. Then again, he was an odd user.
So I basically banned the use of IRC on my box. He was the only user who used IRC and he had access to other systems with it, so it wasn't that big of a loss.
But it's odd the programs that can crash a Unix server. [2]