[systemd-devel] How to reboot from within a service

[Norbert Lange]

Am Mo., 19. Apr. 2021 um 16:02 Uhr schrieb Lennart Poettering
<lennart at poettering.net>:
>
> On So, 18.04.21 12:01, Norbert Lange (nolange79 at gmail.com) wrote:
>
> > Hello,
> >
> > My setup is some embedded system without logind, running a service
> > that should be able to poweroff, reboot or reboot-and-update.
> > Generally I guess this also includes triggering further services
> > programmatically fron another.
> >
> > 1) As I do currently: send SIGRTMIN+5 to PID1
> >     (not really the complete solution, would need to discern between
> > reboot/update).
> > 2) exec 'systemctl start reboot.target'
> >     basically a variant of 1).
> > 3) Same thing as 2), but do it with dbus or varlink.
> > 4) Some unknown and likely not existing configuration of unit files.
> >     doing something like "IfExitCode=121 then start reboot.target"
> > 5) Use the Watchdog and let it expire.
> >
> > While working, I would expect the first 3 options to be depended on
> > various level of rights to interfere with
> > PID1, aswell as being systemd specific (using dbus or systemd DSO).
> > Some sort of separation between
>
> If you want to reboot the system in a sysv compatible way you can only
> fork off "reboot" or "shutdown -r", or maybe send SIGINT to PID 1. The
> latter is pretty ugly though, since this will be treated as if people
> actually used Ctlr-Alt-Del on the console by PID 1, i.e. this is
> subject to misleading log messages and the reboot hard after hitting
> this 7x in 2s.

I wasn't particularly talking about sysv, but like not trying to
reboot the developers PC if he sent wrond command ;)

>
> > advertising the need for reboot and acting on it would be cleaner (ie.
> > hooking it up in service files).
> >
> > What are the best option(s) here?
>
> Use logind's D-Bus APIs. It's the cleanest way to reboot, as it
> honours inhibitors and stuff.

Yeah.. that makes sense once you got use sessions I guess.
I dont even have a dbus daemon running.

I ended up testing touching /run/custom/requestshutdown from the service,
and hooking up another service thats acts on it.
Seems to run fine so far, and if no reboot service is available,
nothing happens.

#custom.service
[Unit]
Description=Custom

[Service]
ExecStart=/opt/custom

ProtectSystem=strict
RuntimeDirectory=custom

#custom-reboot.path
[Unit]
Description=Custom Reboot Service
# think thats bad/not needed?
# PartOf=custom-reboot.service

[Path]
PathExists=/run/custom/requestshutdown
PathExists=/run/custom/requestupdate

#custom-reboot.service
[Unit]
Description=Custom Reboot Service

[Service]
ExecStart=/bin/systemctl start reboot.target --job-mode=replace-irreversibly
RemainAfterExit=yes

>
> Lennart

Thanks for your input.

regards, Norbert