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From: rml@hpfcls.UUCP (rml)
Newsgroups: net.unix-wizards
Subject: Re: signal 0
Message-ID: <132000008@hpfcls.UUCP>
Date: Sat, 15-Dec-84 18:11:00 EST
Article-I.D.: hpfcls.132000008
Posted: Sat Dec 15 18:11:00 1984
Date-Received: Sun, 16-Dec-84 06:37:18 EST
References: <6192@brl-tgr.UUCP>
Organization: Hewlett-Packard - Fort Collins, CO
Lines: 17
Nf-ID: #R:brl-tgr:-619200:hpfcls:132000008:000:682
Nf-From: hpfcls!rml    Dec 10 15:11:00 1984

> I couldn't find the original message about using signal 0 to determine
> whether a child process has terminated without doing a wait for it.
> Since then, friends have researched the issue, with the following result:
> 
> 	signal 0 NOT SUPPORTED on 6th Edition UNIX, 7th Edition UNIX,
> 	nor 4.1BSD
> 
> 	signal 0 SUPPORTED on UNIX System III, UNIX System V, Research
>	Version 8, and 4.2BSD

Using signal 0 to determine whether a child process has terminated assumes
that, when sending a signal to a zombie process, kill(2) returns an error.
This is true in 4.2BSD, but not in System III or V (I have no idea about
Research Version 8).

			Bob Lenk
			{hplabs, ihnp4}!hpfcla!rml