[systemd-devel] What is the shutdown sequence with systemd and dracut?

[Lennart Poettering]

On Mo, 08.08.22 12:24, Patrick Schleizer (patrick-mailinglists at whonix.org) wrote:

> Hi!
>
> This is what I think but please correct me if I am wrong.
>
> 1. systemd runs systemd units for systemd shutdown.target
>
> 2. /lib/systemd/system-shutdown (shutdown.c) runs

I presume you mean /usr/lib/systemd/systemd-shutdown? (i.e. there's a
*d* in the file name; and the path outside of /usr/ is only done by
legacy distros, who still stick to spit /usr/ setups, which we do not
support anymore)

> 3. /lib/systemd/system-shutdown executes /run/initramfs/shutdown (which
> is dracut)

systemd-shutdown runs as PID 1 at this time, and it then chain loads
/run/initramfs/shutdown also as PID1 – if it exists. Thus, at that
moment no systemd code runs anymore, dracut is the only userspace code
remaining.

> 4. dracut shutdown.sh performs various cleanup tasks (such as kill all
> remaining processes and unmount root disk)

It should have been systemd-shutdown between steps 2 and 3 above which
should have already killed everything. But yeah, dracut is supposed to
detach the root fs.

> 5. /lib/systemd/system-shutdown runs scripts in the
> /usr/lib/systemd/system-shutdown/ folder

This is actually done before step 3 above.

> 6. /lib/systemd/system-shutdown performs further cleanup (similar to
> dracut, probably some functionality duplicated with dracut, includes
> kill all remaining processes, unmount the root risk) and eventually
> halt/reboot/poweroff/kexec.

Nah, the killing of processes it already did between steps 2 and
3. Also, as mentioned systemd-shutdown doesn't run at this time anymore.

Lennart

--
Lennart Poettering, Berlin