systemd systemd-suspend.service 8 systemd-suspend.service systemd-hibernate.service systemd-hybrid-sleep.service systemd-suspend-then-hibernate.service systemd-sleep System sleep state logic systemd-suspend.service systemd-hibernate.service systemd-hybrid-sleep.service systemd-suspend-then-hibernate.service /usr/lib/systemd/system-sleep systemd-suspend.service is a system service that is pulled in by suspend.target and is responsible for the actual system suspend. Similarly, systemd-hibernate.service is pulled in by hibernate.target to execute the actual hibernation. Finally, systemd-hybrid-sleep.service is pulled in by hybrid-sleep.target to execute hybrid hibernation with system suspend and pulled in by suspend-then-hibernate.target to execute system suspend with a timeout that will activate hibernate later. Immediately before entering system suspend and/or hibernation systemd-suspend.service (and the other mentioned units, respectively) will run all executables in /usr/lib/systemd/system-sleep/ and pass two arguments to them. The first argument will be pre, the second either suspend, hibernate, hybrid-sleep, or suspend-then-hibernate 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 /usr/lib/systemd/system-sleep/ are intended for local use only and should be considered hacks. If applications want to react to system suspend/hibernation and resume, they should rather use the Inhibitor interface. Note that systemd-suspend.service, systemd-hibernate.service, and systemd-hybrid-sleep.service systemd-suspend-then-hibernate.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-sleep.conf5. systemd-sleep understands the following commands: suspend hibernate hybrid-sleep suspend-then-hibernate Suspend, hibernate, suspend then hibernate, or put the system to hybrid sleep. systemd-sleep.conf5, systemd1, systemctl1, systemd.special7, systemd-halt.service8