Re: [ale] systemd talk from July has slide deck online now

From: Guillermo <>
Date: Sun, 13 Sep 2015 15:57:02 -0300

2015-09-09 2:04 GMT-03:00 Steve Litt:
> If I want to use s6 as my init, what do I do, just put into my Grub
> kernel line init=/usr/bin/s6 or whatever the s6 executable is?

If you want to use the s6-linux-init package and minimum
customization, in addition to s6 and s6-linux-init, you'll need to
download and build two more packages, s6-linux-utils and
s6-portable-utils, and then you can follow the quickstart guide:

The described procedure however replaces /sbin/init, after backing it
up, with the saved output of s6-linux-init-maker, i.e. /tmp/init,
which is what the s6-linux-init documentation calls "the stage1
script". If you want to go the "new GRUB menu entry" route, it would
change to something like:

(As root)
rm -rf /tmp/s6-linux-init /tmp/s6-stage1-init
s6-linux-init-maker [options] /tmp/s6-linux-init > /tmp/s6-stage1-init
chmod 0700 /tmp/s6-stage1-init
mv /tmp/s6-linux-init /etc
mv /tmp/s6-stage1-init /sbin

The new GRUB menu entry can then pass an 'init=/sbin/s6-stage1-init'
option to the kernel. And you halt, reboot or poweroff the machine
with 's6-svscanctl -st /run/service', 's6-svscanctl -rt /run/service'
or 's6-svscanctl -pt /run/service', respectively. The
s6-linux-init-maker options you may additionally need or want are -d,
-u, -p and -e.

Note that you also need to write two scripts, /etc/rc.init and
/etc/rc.shutdown. These are what the s6-linux-init documentation calls
"the stage2 script" and "the stage3 script". But they serve the same
purpose as the ones in your Suckless Init document, so you already
know what goes in there. There are some notable differences, though:

 * The scan directory is /run/service, not /service, so it will be a
directory in a tmpfs, that is created and populated at boot time with
a (very small) initial set of services by the stage1 script. You then
have to copy or make symbolic links to the service directories you
want, which you would have in a non-volatile "service repository",
like /etc/sv, /var/service, /var/svc.d as OpenRC likes it, etc. and
then do an 's6-svscanctl -a /run/service'. All these actions can be
programmed inside /etc/rc.init.

 * /etc/rc.init will start executing when s6-svscan is already running
as process 1, so you don't need to call any svscanboot-like command at
the end of the script. You just let it finish and return when it's
done. It will be running as a child of s6-svscan and get reaped when
it returns.

 * /etc/rc.shutdown will be called with a single argument: 'halt',
'poweroff' or 'reboot', depending on the requested shutdown mode. And
will run as process 1 when the machine is shutting down, so if it
aborts or exits before executing the final halt, reboot or poweroff,
you'll get a kernel panic. Write it carefully.

 * Inside /etc/rc.shutdown, you can use s6-halt, s6-poweroff and
s6-reboot in place of sysvinit's counterparts. These programs come
with the s6-linux-utils package. And you can use 's6-nuke -t' and
's6-nuke -k' in place of 'killall5 -15' and 'killall5 -9',
respectively. The s6-nuke program comes with the s6-portable-utils
package. This will remove all dependencies on sysvinit-like binaries.
In particular, the ones that expect to talk to process 1 through
/dev/initctl won't even work.

Received on Sun Sep 13 2015 - 18:57:02 UTC

This archive was generated by hypermail 2.3.0 : Sun May 09 2021 - 19:44:19 UTC