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bashshellscriptingsignalskill

What does `kill -0 $pid` in a shell script do?

Basically, what signal does '0' represent, because here I see SIGNAL numbers starting from 1.

Solution

  • sending the signal 0 to a given PID just checks if any process with the given PID is running and you have the permission to send a signal to it.

    For more information see the following manpages:

    kill(1) 
    $ man 1 kill
...
If sig is 0, then no signal is sent, but error checking is still performed.
...
    kill(2) 
    $ man 2 kill
...
If sig is 0, then no signal is sent, but error checking is still performed; this 
can be used to check for the existence of a process ID or process group ID.
...