Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!mips!spool.mu.edu!cs.umn.edu!msi.umn.edu!math.fu-berlin.de!fauern!unido!mcshh!abqhh!tpki!oski!schlut
From: schlut@oski.toppoint.de (Olaf Schlueter)
Newsgroups: comp.os.minix
Subject: Re: (PC/AT) why not include 'sync' in keyboard.c (for rebooting?)
Message-ID: <33@oski.toppoint.de>
Date: 21 Apr 91 18:16:14 GMT
References: <3044@krafla.rhi.hi.is> <1991Apr16.111539.1287@syd.dit.CSIRO.AU> <792@philica.ica.philips.nl>
Lines: 39


adrie@philica.ica.philips.nl (Adrie Koolen) writes:

[about a safe way of shutting a minix system down by use of a daemon
process]

I think the best place for this daemon is init.  On the ST Version I can
stop every running process by hitting Ctrl-Alt-F10.  A kill(-1,9) call
is shot this way.  This will kill all user processes, even the shell or
program I am currently in.  cron, etc/update, my nnmaster and tostp
server are all gone then.

The only process which survives the kill(-1,9) is init. It does not
receive the signal, as it belongs to the OS itself like FS or MM.

The problem is that all what init is watching after kill(-1,9) are
login processes terminating. As conditioned it reponses by restarting
them. Also, betwen performing the sync and hitting cltrl-alt-F10
someone could issue a write operation.

So there has to be a way to tell even init that the system is about to
die and to put the things into proper order (first kill, then sync).  My
suggestion is to implement a keystroke which send a kill(1,SIGTERM)
(SIGTERM to init).  Init should then perform

kill(-1,9)	stops all user processes.
sync()		flushes the cache.

and should go idle waiting for the user to turn the system off
(by flipping the power switch or pressing ctrl-alt-del).

If you are running minix as an environment for more serious
things then personal education (no flames please :-)) and do not
want to place bodyguards to your console, you can even remove
all this PC like finger breaking keyboard stuff and write a
shutdown command:

main() { kill(1,15); }

executable for root only, of course.