From owner-freebsd-questions  Mon Mar 22 22:37:33 1999
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From: "Crist J. Clark" <cjc@cc942873-a.ewndsr1.nj.home.com>
Message-Id: <199903230637.BAA10035@cc942873-a.ewndsr1.nj.home.com>
Subject: Process Checking
To: freebsd-questions@FreeBSD.ORG (FreeBSD Questions)
Date: Tue, 23 Mar 1999 01:37:19 -0500 (EST)
Reply-To: cjclark@home.com
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I've got a question about monitoring a daemon. It's a server for a
game and not the most stable piece of software you have ever seen. I
want to run a cron job periodically to check if the process has not
died, and if it has, restart it.

This is the way I have it now after being slightly surprised by the
behavior of ps(1),

    svrpid=`cat $svr/.newstartd.pid`

    # check if its is running
    if ! ( ps -p $svrpid | grep $svrpid ); then
	echo "$0: $svr server not running"
	cd $svr
	./newstartd &
	cd ..
    fi

The file $svr/.newstartd.pid holds the last pid of the server. I 'ps'
that process and then 'grep' the return to make sure it is there. If it
is not, I restart it.

Now, I originally just had '! ps -p $svrpid' as the condition in the
if-statement until I realized ps(1) does _not_ return an error
(non-zero) when the pid it's asked to look up does not exist.

My question is:

Is there a more reliable and graceful way to check if a process,
identified by pid, is still alive? The '(ps | grep)' combo is somewhat
of an ugly kludge... but I can't think of when it would fail either.

Thanks.
-- 
Crist J. Clark                           cjclark@home.com


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