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From: gwc@root.co.uk (Geoff Clare)
Newsgroups: comp.lang.c,comp.unix.questions
Subject: Re: logout
Message-ID: <2598@root44.co.uk>
Date: 7 Feb 91 15:03:38 GMT
References: <+W9+Y=A@irie.ais.org> <665707935@romeo.cs.duke.edu>
Followup-To: comp.unix.questions
Organization: UniSoft Ltd., London, England
Lines: 46

[I have cross-posted to comp.unix.questions and directed followups there
as this topic is UNIX specific, and not appropriate for comp.lang.c]

In article <+W9+Y=A@irie.ais.org> garath@ais.org (Belgarath) writes:
>
>	Hi.  I've created a generic menu program for new users on our system.
>I have everything working now except for a logout option.  Is there a way to
>have to program kill  all processes/jobs and then log the user out or do they
>need to quit the program and then exit?
>	Please respond via e-mail.  Thanks.
>P.S.  How could I have had this expire in, say 10 days?  I don't see expire at
>the top as one of the options I could fill in.

In <665707935@romeo.cs.duke.edu> drh@duke.cs.duke.edu (D. Richard Hipp) writes:

[stuff deleted]

>I`ve never tried it, but according to my man-pages, the following should
>do a more complete job of killing everyone off:

>  killpg(getpgrp(0),9)

This works, but killpg() is not very portable.  On all UNIX systems I'm
familiar with, the same effect can be obtained by using kill() with a
process ID of 0.  Also, signal 9 (SIGKILL) is not a good choice of
signal, because it cannot be caught and so the processes will not be
able to clean up.  As a rule SIGKILL should only be used as a last
resort to kill processes that otherwise refuse to die.  In the case
under discussion (simulating a logout), the appropriate signal is
SIGHUP, which is what the processes would receive when a user logs off
leaving background jobs running.

So the best solution is

   kill(0, SIGHUP);

or from a shell

   kill -1 0

If you want to kill processes which have been run with "nohup", use
SIGKILL instead of SIGHUP.

-- 
Geoff Clare <gwc@root.co.uk>  (Dumb American mailers: ...!uunet!root.co.uk!gwc)
UniSoft Limited, London, England.   Tel: +44 71 729 3773   Fax: +44 71 729 3273