Things to Do With 'kill'

kill is most often used without an argument or with -9, to kill a process off. But it can also be used to send various other signals to a process. Some are variations on process termination, but you can also get information about or out of processes.

Here are some you may find useful:

• kill -0 pid: This doesn't actually kill the process, just returns 0 (success) if the process exists and 1 (failure) if not. The command itself will not give you any output — you have to look at the exit code, using echo $? to get the information. So as a one-liner:

  kill -0 1685; echo $?

  will output 0 if process 1685 exists, and 1 if it doesn't. This can also be useful in shell scripts if you have a process number recorded and wish to check if it's still running.
• kill -9 pid: You probably already know that you can terminate the process WITH EXTREME PREJUDICE. kill -KILL does the same thing and has the advantage of looking more vicious. The downside is that it is an extra couple of characters to type.
• kill -HUP pid: Restarts the process.
• kill -INT pid: Another way of killing the process, this time by interrupting it. It is a useful halfway house between kill and kill -9.
• kill -ABRT pid: Stops your program and gets it to dump core if possible/appropriate. (kill -6 is a synonym.) This can be useful if a process is misbehaving, as it means that you may get debug information.