Safe Way to Tell if Process is Running

Robert Bonomi bonomi at
Tue Dec 4 20:08:14 UTC 2012

> Subject: Safe Way to Tell if Process is Running
> Date: Tue, 04 Dec 2012 13:39:41 -0600
> From: Martin McCormick <martin at>
> 	About 20 years ago, I saw some code in which you
> verified whether or not a process was running by giving it a
> kill -0 command. If the process was running, nothing happened to
> it but your kill -0 command exited with a 0 status. If there was
> no process with that PID, the kill command exited non-zero.
> 	I use this in a system(command); in a C program I wrote
> some years ago and I think this is now causing a segmentation
> fault when the process number being signalled doesn't exist. Is
> there a better way to determine if process number 12345 is
> running without bothering it?
> 	None of the documentation on kill (1) shows a signal 0
> nor does kill -l.
> 	Something tells me this is a bad idea these days, but I
> still need an easy way to see if XYZ process is still alive.

'man 2  kill' tells all.

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