pid file handling issue

Michael Fischer mfischer at
Thu Oct 24 01:01:33 UTC 2013

On Wed, Oct 23, 2013 at 5:53 PM, Eric Wong <normalperson at> wrote:

> I read and stash the value of the pid file before issuing any USR2.
> Later, you can issue "kill -0 $old_pid" after sending SIGQUIT
> to ensure it's dead.

That's inherently racy; another process can claim the old PID in the interim.

> Checking the mtime of the pidfile is really bizarre...

Perhaps (though it's a normative criticism), but on the other hand, it
isn't subject to the race above.

> OTOH, there's times when users accidentally remove a pid
> file and regenerate by hand it from ps(1), too...

Sure, but (a) that's a corner case I'm not particularly concerned
about, and (b) it wouldn't cause any problems, assuming the user did
this before any reload attempt, and not in the middle or something.


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