What's the worst sysadmin mistake you ever made? Confess here.

We've all done it - a keystroke, a mouse click, a button push and you get that sick feeling...

One of mine - at a very large bank I was administering an extremely important piece of enterprise software used to send work to thousands of servers globally. In order to apply a patch, I simply had to backup a binary, stop the system for 30 seconds replace the binary (on unix), and restart. Yes, our change control processes were terrible.

Instead of typing 'cp <filename>' (copy) to back it up, I typed 'mv <filename>' (move). The system went loopy and began spawning thousands of rogue processes, filled up the server, all ground to a halt. Production system was in the toilet in the middle of a business day, you get the idea.

I still cringe at the memory, even though it was 20+ years ago.

EDIT: Over 500 replies, amazing. If you mess up you are not alone!