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From: csg@pyramid.UUCP (Carl S. Gutekunst)
Newsgroups: net.bugs.uucp
Subject: Re: uucico/uuxqt bugs...howcome?
Message-ID: <658@pyramid.UUCP>
Date: Mon, 29-Sep-86 22:19:36 EDT
Article-I.D.: pyramid.658
Posted: Mon Sep 29 22:19:36 1986
Date-Received: Wed, 1-Oct-86 04:24:37 EDT
References: <900@gilbbs.UUCP> <612@pyramid.UUCP> <728@ncc.UUCP> <579@rdin.UUCP>
Reply-To: csg@pyramid.UUCP (Carl S. Gutekunst)
Organization: Pyramid Technology Corp., Mountain View, CA
Lines: 24

In article <579@rdin.UUCP> perl@rdin.UUCP (Robert Perlberg) writes:
>Every hour, cron runs a program I call lckcheck....
>lckcheck searches for LCK. files in /usr/spool/uucp.  For each LCK.
>file, it opens the file and reads the PID from it.  It checks the
>existence of the process that created the LCK. file by sending a signal
>#0 with kill(2).  If the process does not exist, the file is removed.
>...  I don't
>know why all programs that use LCK. files don't do this.

Problem is that kill(0,pid) is a relatively new feature of UNIX. V7 and System
III do not have this capability. This is why I called the one-hour-lockfile-
removal an anachronism: early versions of UUCP had no choice; newer versions
could check the PID but rarely do. (Exceptions are 4.3BSD and HDB. I've been
told that Ultrix 1.2 UUCP checks the PID also.)

Since the system that raised the question is a Tandy 6000 running Xenix, they
have no choice either (even if they had sources).

>Why do programs that don't use the PID for verification put the PID there in
>the first place?

So humans can use ps(1) to find out if the process is still active.

<csg>