How does systemctl schedule system shutdown?
When I type shutdown -h +30
, Linux somehow schedules runlevel's change within 30 minutes. On Debian, /sbin/shutdown
is symbolic link to /bin/systemctl
. My tests indicate that shutdown
does not use neither cron nor systemd timers.
How does system shutdown is implemented by systemd
?
Solution 1:
Good question. I tried what I now realise you must have tried- scheduling a shutdown and querying the systemd timers!
That showed that the shutdown was not in the systemd timers, as you noted. So then a quick perusal of the systemctl source gives us this call, as part of halt_main()
:
r = sd_bus_call_method(
b,
"org.freedesktop.login1",
"/org/freedesktop/login1",
"org.freedesktop.login1.Manager",
"ScheduleShutdown",
&error,
NULL,
"st",
arg_action == ACTION_HALT ? "halt" :
arg_action == ACTION_POWEROFF ? "poweroff" :
arg_action == ACTION_KEXEC ? "kexec" :
"reboot",
arg_when);
(systemctl.c line 7387)
So it would appear that shutdowns are handled by logind
. You can continue to pursue the details if you like- see login-dbus.c
. There are methods there for scheduling, cancelling, managing shutdowns. But for a deeper understanding, you may need to know more about logind/systemd than I do.
Long story short, the shutdown info is stored (at least) in a schedule file at /run/systemd/shutdown/scheduled
, the contents of mine as an example were:
USEC=1435715559055789
WARN_WALL=1
MODE=poweroff
Indicating time (in microseconds, presumably); whether to warn via wall
, and which mode (cf restart, kexec etc).
Hope this points you in the right direction at least!