Let's make our units more robust to being added to an initrd:
1. systemd-boot-update only makes sense if sd-boot is available in /usr/
to copy into the ESP. This is generally not the case in initrds, and
even if it was, we shouldn't update the ESP from the initrd, but from
the host instead.
2. The rfkill services save/restore rfkill state, but that information
is only available once /var/ is mounted, which generally happens
after the initrd transition.
3. utmp management is partly in /var/, and legacy anyway, hence don't
bother with it in the initrd.
No functional change, just a cleanup to make the subsequent changes easier to
see. This is a continuation of 9810e41942
> The block is reordered and split to have:
> 1. description + documentation
> 2. (optionally) conditions
> 3. all the dependencies
The dependencies for shutdown.target are listed separately because they are the
other deps are for startup, and shutdown.target only matter much later.
Otherwise we might install the socket unit early, but the service
backing it late, and then end up in strange loops when we enter rescue
mode, because we saw an event on /dev/rfkill but really can't dispatch
it nor flush it.
Fixes: #9171
With this rework we introduce systemd-rfkill.service as singleton that
is activated via systemd-rfkill.socket that listens on /dev/rfkill. That
way, we get notified each time a new rfkill device shows up or changes
state, in which case we restore and save its current setting to disk.
This is nicer than the previous logic, as this means we save/restore
state even of rfkill devices that are around only intermittently, and
save/restore the state even if the system is shutdown abruptly instead
of cleanly.
This implements what I suggested in #1019 and obsoletes it.
