SYSTEMD-POWEROFF.SERVICE(8) systemd-poweroff.serviceSYSTEMD-POWEROFF.SERVICE(8)
NAME
systemd-poweroff.service, systemd-halt.service, systemd-reboot.service,
systemd-kexec.service, systemd-shutdown - System shutdown logic
SYNOPSIS
systemd-poweroff.service
systemd-halt.service
systemd-reboot.service
systemd-kexec.service
/usr/lib/systemd/systemd-shutdown
/usr/lib/systemd/system-shutdown/
DESCRIPTION
systemd-poweroff.service is a system service that is pulled in by
poweroff.target and is responsible for the actual system power-off
operation. Similarly, systemd-halt.service is pulled in by halt.target,
systemd-reboot.service by reboot.target and systemd-kexec.service by
kexec.target to execute the respective actions.
When these services are run, they ensure that PID 1 is replaced by the
/usr/lib/systemd/systemd-shutdown binary which is then responsible for
the actual shutdown. Before shutting down, this binary will try to
unmount all remaining file systems (or at least remount them read-only),
disable all remaining swap devices, detach all remaining storage devices
and kill all remaining processes.
It is necessary to have this code in a separate binary because otherwise
rebooting after an upgrade might be broken — the running PID 1 could
still depend on libraries which are not available any more, thus keeping
the file system busy, which then cannot be re-mounted read-only.
Shortly before executing the actual system power-off/halt/reboot/kexec,
systemd-shutdown will run all executables in
/usr/lib/systemd/system-shutdown/. Those executables are called with one
argument: either "poweroff", "halt", "reboot", or "kexec", depending on
the chosen action. All executables in this directory are executed in
parallel, and execution of the action is not continued before all
executables finished. (A safety timeout of 90s is applied however.) Note
that these executables are run after all services have been shut down,
and after most mounts have been unmounted (the root file system as well
as /run/ and various API file systems are still around though). This
means any programs dropped into this directory must be prepared to run
in such a limited execution environment and not rely on external
services or hierarchies such as /var/ to be around (or writable).
Note that systemd-poweroff.service (and the related units) should never
be executed directly. Instead, trigger system shutdown with a command
such as "systemctl poweroff".
Another form of shutdown is provided by the systemd-soft-
reboot.service(8) functionality. It reboots only the OS userspace,
leaving the kernel, firmware, and hardware as it is.
SEE ALSO
systemd(1), systemctl(1), systemd.special(7), reboot(2), systemd-
suspend.service(8), systemd-soft-reboot.service(8), bootup(7)
systemd 257.9 SYSTEMD-POWEROFF.SERVICE(8)
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