Things to Do With 'kill'

By Juliet Kemp (Send Email)
Posted Jan 5, 2009


Juliet Kemp
... other than what its name implies.

Tip of the Trade: 'kill' doesn't just kill processes dead, it also can send processes a variety of other signals.

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:

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  • 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.

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