signal 0

[rml]

> 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