The service already has DefaultDeps disabled, so systemd should not try to stop
it. And if it *does* get stopped, we don't want the zombie process around.
KillMode=none does not change anything in the killall() phase, and we already
use argv[0][0] = '@' to protect against that anyway. KillMode=none should not
be useful in normal operation, so let's leave it out.
This is a different way to implement the fix proposed by commit
a4021390fe suggested by Lennart Poettering.
In this patch we instruct PID1 to not kill "systemctl switch-root" command
started by initrd-switch-root service using the "argv[0][0]='@'" trick.
See: https://www.freedesktop.org/wiki/Software/systemd/RootStorageDaemons/ for
more details.
We had to backup argv[0] because argv is modified by dispatch_verb().
Since commit 1f0958f640, systemd considers SIGTERM for short-running
services (aka Type=oneshot) as a failure.
This can be an issue with initrd-switch-root.service as the command run by this
service (in order to switch to the new rootfs) may still be running when
systemd does the switch.
However PID1 sends SIGTERM to all remaining processes right before
switching and initrd-switch-root.service can be one of those.
After systemd is reexecuted and its previous state is deserialized, systemd
notices that initrd-switch-root.service was killed with SIGTERM and considers
this as a failure which leads to the emergency shell.
To prevent this, this patch teaches systemd to consider a SIGTERM exit as a
clean one for this service.
It also removes "KillMode=none" since this is pretty useless as the service is
never stopped by systemd but it either exits normally or it's killed by a
SIGTERM as described previously.
Zbigniew Jędrzejewski-Szmek