systemd-halt.service, systemd-poweroff.service, systemd-reboot.service,
   systemd-kexec.service, systemd-shutdown - System shutdown logic









   systemd-halt.service is a system service that is pulled in by and is responsible for the actual system halt. Similarly,
   systemd-poweroff.service is pulled in by,
   systemd-reboot.service by and systemd-kexec.service by to execute the respective actions.

   When these services are run, they ensure that PID 1 is replaced by the
   /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, 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

   Immediately before executing the actual system
   halt/poweroff/reboot/kexec systemd-shutdown will run all executables in
   /lib/systemd/system-shutdown/ and pass one arguments to them: either
   "halt", "poweroff", "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

   Note that systemd-halt.service (and the related units) should never be
   executed directly. Instead, trigger system shutdown with a command such
   as "systemctl halt" or suchlike.


   systemd(1), systemctl(1), systemd.special(7), reboot(2), systemd-


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