Kill

kill -- surprise -- kills processes. You must supply a pid. If you want to kill a process by name, look at pkill or killall.

kill by itself will cause a process to try to finish what it's doing and save it's state before actually stopping the process, if you pass it the -9 option it will instead kill a process immediately and without waiting or saving any state/information. The HUP flag will cause the process to re-read it's configuration file (basically a restarting of the process).

Flags

-1 HUP; be careful with this, if used as root, this goes to ALL processes.
-HUP the same as -1
-6 abort, like doing a control-C
-9 uninterruptible kill -- stop the process NOW
-14 (or -ALRM) "alarm" - not supported by all processes, effect depends on the process
-15 kill politely (save changes, stop when done)

See also skill