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
       tool 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/ and pass one arguments to them: 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. 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)