Tuesday, January 31, 2023

Things to Do With ‘kill’

… other than what its name implies.

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 ofcharacters 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.

This article was first published on ServerWatch.com.

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