systemd-poweroff.service - Man Page

systemd-poweroff​.service

systemd-halt​.service

systemd-reboot​.service

systemd-kexec​.service

/usr/lib/systemd/systemd-shutdown

/usr/lib/systemd/system-shutdown/

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​.

systemd(1), systemctl(1), systemd.special(7), reboot(2), systemd-suspend.service(8), systemd-soft-reboot.service(8), bootup(7)

bootup(7), systemd-analyze(1), systemd.directives(7), systemd.index(7), systemd-soft-reboot.service(8), systemd.special(7), systemd-suspend.service(8).

The man pages systemd-halt.service(8), systemd-kexec.service(8), systemd-reboot.service(8) and systemd-shutdown(8) are aliases of systemd-poweroff.service(8).