Re: Shutdown/reboot script order?

From: Laurent Bercot <>
Date: Wed, 10 Jun 2015 20:14:24 +0200

On 10/06/2015 19:13, Steve Litt wrote:
> Does the preceding sentence mean that killall5 is available only when
> sysvinit is installed? That could be a problem.

  It all depends on how your distribution does things, but yes, killall5
comes with the sysvinit tarball, so it's most likely part of your
distribution's sysvinit package.
  Busybox comes with a killall5 utility, if you're dead-set on using
killall5, but all in all it's easier to just use kill.

> I think I could theoretically change Suckless-Init to
> run /bin/rc.shutdown with an exec so it *is* pid1. I think.

  It's very possible: change sigpoweroff() and sigreboot() so they
execvp(rcblahcmd[0], rcblahcmd) instead of spawn(rcblahcmd).

  Note that on Linux, you're likely to have bash, which includes
a kill builtin. If you don't mind depending on bash, or on any
other shell that runs kill as a builtin, you don't have to worry
about those process 1 shenanigans.

> How would one run a shutdown script as a PID higher than 1, then
> magically change back to PID1? Would you run 2 different shutdown
> scripts: one for the standard stuff, and one for the "killalls"?

  There needs to be support in init for that. Generally, to shut a
machine down, you send a signal to init, which then runs a
shutdown script.

  - sysvinit starts by killing all processes itself, before running
whatever's in /etc/inittab (usually /sbin/reboot). Since the nuke
has already been launched, the shutdown script doesn't need to run
as process 1. There are certainly subtleties with FUSE daemons,
though; I'm not sure how they're handled by sysvinit.
  - suckless init and runit just run the shutdown script in another
process. It works as long as you're lucky, but since most people
use Linux and bash, they're ok.
  - If you run s6-svscan as process 1, it execs into your shutdown
script, so your shutdown script runs as process 1. I paid attention
to that because I wanted it to work without depending on the
non-portable Linux behaviour where the process launching the nuke
is itself protected.

Received on Wed Jun 10 2015 - 18:14:24 UTC

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