Me, it was the time I rm r'ed the MySQL data directory for my company's customer service management system. Oops. Thankfully we had a backup from the month prior, but I learned two things that day: a) be really careful with rm and b) take it on yourself to make sure IT is backing up stuff that you're messing with.
You gotta hedge against your own stupid.
What about you, how'd you learn the hard way?
So, I did a simple /etc/init.d/clearcase stop (not sure that is the exact name) and:
# rm -rf /opt/clearcase
(hmm... that seems to be taking a little too long to run)
Panic - then ctrl-C - it was too late, /opt/clearcase/foo was NFS mounted 127.0.0.1:/ and it had already trashed /bin, /sbin, /etc, /var, and most of /usr.
Luckily I had good backups, but we did spend the rest of the day rebuilding the source repository while the developers couldn't check in any code.
So I merrily started mv-ing things to a scratch directory that we could wipe in 6 months if we didn't need anything from it.
Unfortunately, the zone file directory was NFS mounted from* $dedicated_dns_server. With pass root set.
I think I took all of A through to K of client zones offline before we noticed.
I'm just very very glad I decided to do it as an mv rather than an rm, since it meant all I needed to do was copy things back.
Not that I really learned my lesson that time; it took a couple more semi-disasters before I got sufficiently paranoid to be reasonably safe as root.
rm -rf ./*
I went
rm -rf . (can't get the wildcard thingamajig to show up)
It took me a second to understand why the command was taking so long to run, by the time I figured it out and killed the command, I had wiped out almost half of what was on the drive.
Biggest "oh. my. god" moment of my life. I think I had an actual panic attack for a bit even.
Luckily, media temple had a backup from just a few hours earlier (I was lucky, they only ran them periodically and it just so happened to fall on that day).
You are in .; The current directory listing include ..; Recursively deleting everything deletes everything on the drive.
Actually, I think the one time I saw someone do this, wildcards were involved. And I was going to explain, but the comment system is making my asterisks into bold markers.
rm -rf ./*
rm -rf *.*
sudo chown -R username:group $WEBAPP
I had the Linode backup service, so got away with restoring the whole VM from the previous night's backup.