Meaning of killall -0

Question

I see from many place the follow command is used to check if a process exists, e.g.

killall -0 nginx

But from the documentation I can't see anything related to this argument, can anyone explain?

Solution

man 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.

killall kill processes by name instead of PID on Linux & BSD-based systems. In other Operating Systems (Solaris), the killall command is used to terminate all running processes.

Comments

[Philip]

Note: killall kills processes by name on Linux and BSD platforms. On other platforms (notable Solaris) is kills all processes (ie stops the server).