Ctrl+C ( Stop Processing Command )

Imagine you just typed in a command and hit the Enter-key . . . and
suddenly you realized it was the wrong command and it is copying the full
hda8 partition into a plugins directory . . . how do we stop the command
from processing ??

Crtl+C

And the command will stop its insane work instantly . . . . sure a bunch
of files will already have been copied, but you do not have to wait the
full 15 minutes until it has finished.

Any command given in the terminal can be stopped like this, a search for
rootkits, a virus scan, updatedb . .you name it, all things that take
long enough to give you time to think . . and say "Ouch ! I did it
wrong, I have to stop this !"