From owner-freebsd-questions@FreeBSD.ORG  Tue Dec  4 20:01:44 2012
Return-Path: <owner-freebsd-questions@FreeBSD.ORG>
Delivered-To: freebsd-questions@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52])
 by hub.freebsd.org (Postfix) with ESMTP id 8C1DAC74
 for <freebsd-questions@freebsd.org>; Tue,  4 Dec 2012 20:01:44 +0000 (UTC)
 (envelope-from martin@dc.cis.okstate.edu)
Received: from x.it.okstate.edu (x.it.okstate.edu [139.78.2.13])
 by mx1.freebsd.org (Postfix) with ESMTP id 567E88FC13
 for <freebsd-questions@freebsd.org>; Tue,  4 Dec 2012 20:01:44 +0000 (UTC)
Received: from dc.cis.okstate.edu (localhost [127.0.0.1])
 by x.it.okstate.edu (8.14.5/8.14.5) with ESMTP id qB4JdfGt085863
 for <freebsd-questions@freebsd.org>; Tue, 4 Dec 2012 13:39:41 -0600 (CST)
 (envelope-from martin@dc.cis.okstate.edu)
Message-Id: <201212041939.qB4JdfGt085863@x.it.okstate.edu>
To: freebsd-questions@freebsd.org
Subject: Safe Way to Tell if Process is Running
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <85861.1354649981.1@dc.cis.okstate.edu>
Date: Tue, 04 Dec 2012 13:39:41 -0600
From: Martin McCormick <martin@dc.cis.okstate.edu>
X-BeenThere: freebsd-questions@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: User questions <freebsd-questions.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-questions>, 
 <mailto:freebsd-questions-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-questions>
List-Post: <mailto:freebsd-questions@freebsd.org>
List-Help: <mailto:freebsd-questions-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>, 
 <mailto:freebsd-questions-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 04 Dec 2012 20:01:44 -0000

	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.

	Thank you.

Martin McCormick WB5AGZ  Stillwater, OK 
Systems Engineer
OSU Information Technology Department Telecommunications Services Group