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. An environment variable called SYSTEMD_SLEEP_ACTION will be set and contain the sleep action that is processing. This is primarily helpful for suspend-then-hibernate where the value of the variable will be suspend, hibernate, or suspend-after-failed-hibernate in cases where hibernation has failed. 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 user.slice will be frozen while the executables are running, so they should not attempt to communicate with any user services expecting a reply. 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, systemd-hybrid-sleep.service, and systemd-suspend-then-hibernate.service should never be executed directly. Instead, trigger system sleep with a command such as systemctl suspend or systemctl hibernate. 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. Note that by default these services freeze user.slice while they run. This prevents the execution of any process in any of the user sessions while the system is entering into and resuming from sleep. Thus, this prevents the hooks in /usr/lib/systemd/system-sleep/, or any other process for that matter, from communicating with any user session process during sleep. systemd-sleep understands the following commands: suspend hibernate suspend-then-hibernate hybrid-sleep Suspend, hibernate, suspend then hibernate, or put the system to hybrid sleep. systemd-sleep.conf5 systemd1 systemctl1 systemd.special7 systemd-halt.service8