systemd-suspend.service is a system service that is pulled in by and is responsible for the actual system suspend.
       Similarly, systemd-hibernate.service is pulled in by
       to execute the actual hibernation. Finally,
       systemd-hybrid-sleep.service is pulled in by to
       execute hybrid hibernation with system suspend.

       Immediately before entering system suspend and/or hibernation
       systemd-suspend.service (and the other mentioned units, respectively)
       will run all executables in /lib/systemd/system-sleep/ and pass two
       arguments to them. The first argument will be "pre", the second either
       "suspend", "hibernate", or "hybrid-sleep" depending on the chosen
       action. Immediately after leaving system suspend and/or hibernation the
       same executables are run, but the first argument is now "post". All
       executables in this directory are executed in parallel, and execution
       of the action is not continued until all executables have finished.

       Note that scripts or binaries dropped in /lib/systemd/system-sleep/ are
       intended for local use only and should be considered hacks. If
       applications want to be notified of system suspend/hibernation and
       resume, there are much nicer interfaces available.

       Note that systemd-suspend.service, systemd-hibernate.service, and
       systemd-hybrid-sleep.service should never be executed directly.
       Instead, trigger system sleep states with a command such as "systemctl
       suspend" or similar.

       Internally, this service will echo a string like "mem" into
       /sys/power/state, to trigger the actual system suspend. What exactly is
       written where can be configured in the "[Sleep]" section of
       /etc/systemd/sleep.conf or a sleep.conf.d file. See systemd-

       systemd-sleep understands the following commands:

       -h, --help
           Print a short help text and exit.

           Print a short version string and exit.

       suspend, hibernate, hybrid-sleep
           Suspend, hibernate, or put the system to hybrid sleep.
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