The purpose of this page is to provide general overview of power management in Arch Linux. As Arch Linux uses systemd as system manager, this article focuses on it.
There are multiple places where one can change power management settings:
There are also many power management tools:
- 1 Power management with systemd
- 2 See also
Power management with systemd
systemd handles some power-related ACPI events. They can be configured via the following options from
HandlePowerKey: specifies which action is invoked when the power key is pressed.
HandleSuspendKey: specifies which action is invoked when the suspend key is pressed.
HandleHibernateKey: specifies which action is invoked when the hibernate key is pressed.
HandleLidSwitch: specifies which action is invoked when the lid is closed.
The specified action can be one of
If these options are not configured, systemd will use its defaults:
- Restart the
systemd-loginddaemon for your changes to take effect (be warned: this will terminate all login sessions).
- systemd cannot handle AC and Battery ACPI events, so if you use Laptop Mode Tools or other similar tools acpid is still required.
- If more than one display is connected, the action specified by
In the current version of systemd, the
Handle* options will apply throughout the system unless they are "inhibited" (temporarily turned off) by a program, such as a power manager inside a desktop environment. If these inhibits are not taken, you can end up with a situation where systemd suspends your system, then when it wakes up the other power manager suspends it again.
Suspend and hibernate
systemd provides commands for suspend to RAM, hibernate and a hybrid suspend using the kernel's native suspend/resume functionality. There are also mechanisms to add hooks to customize pre- and post-suspend actions.
systemctl suspend should work out of the box, for
systemctl hibernate to work on your system you need to follow the instructions at Suspend and hibernate#Hibernation.
systemctl hybrid-sleep both hibernates and suspends at the same time. This combines some of the benefits and drawbacks of suspension and hibernation. This is useful in case a computer were to suddenly lose power (AC disconnection or battery depletion) since upon powerup it will resume from hibernation. If there is no power loss, then it will resume from suspension, which is much faster than resuming from hibernation. However, since "hybrid-sleep" has to dump memory to swap in order for hibernation to work, it is slower to enter sleep than a plain
systemctl suspend. An alternative is a delayed hibernation service file.
systemd does not use pm-utils to put the machine to sleep when using
systemctl hibernate or
systemctl hybrid-sleep; pm-utils hooks, including any custom hooks, will not be run. However, systemd provides two similar mechanisms to run custom scripts on these events.
Suspend/resume service files
Service files can be hooked into suspend.target, hibernate.target and sleep.target to execute actions before or after suspend/hibernate. Separate files should be created for user actions and root/system actions. Enable the
resume@user services to have them started at boot. Examples:
[Unit] Description=User suspend actions Before=sleep.target [Service] User=%I Type=forking Environment=DISPLAY=:0 ExecStartPre= -/usr/bin/pkill -u %u unison ; /usr/local/bin/music.sh stop ; /usr/bin/mysql -e 'slave stop' ExecStart=/usr/bin/sflock [Install] WantedBy=sleep.target
[Unit] Description=User resume actions After=suspend.target [Service] User=%I Type=simple ExecStartPre=/usr/local/bin/ssh-connect.sh ExecStart=/usr/bin/mysql -e 'slave start' [Install] WantedBy=suspend.target
For root/system actions (enable the
root-suspend services to have them started at boot):
[Unit] Description=Local system resume actions After=suspend.target [Service] Type=simple ExecStart=/usr/bin/systemctl restart mnt-media.automount [Install] WantedBy=suspend.target
[Unit] Description=Local system suspend actions Before=sleep.target [Service] Type=simple ExecStart=-/usr/bin/pkill sshfs [Install] WantedBy=sleep.target
A couple of handy hints about these service files (more in
Type=oneshotthen you can use multiple
ExecStart=lines. Otherwise only one
ExecStartline is allowed. You can add more commands with either
ExecStartPreor by separating commands with a semicolon (see the first example above; note the spaces before and after the semicolon, as they are required).
- A command prefixed with
-will cause a non-zero exit status to be ignored and treated as a successful command.
- The best place to find errors when troubleshooting these service files is of course with journalctl.
Combined Suspend/resume service file
With the combined suspend/resume service file, a single hook does all the work for different phases (sleep/resume) and for different targets (suspend/hibernate/hybrid-sleep).
Example and explanation:
[Unit] Description=Wicd sleep hook Before=sleep.target StopWhenUnneeded=yes [Service] Type=oneshot RemainAfterExit=yes ExecStart=-/usr/share/wicd/daemon/suspend.py ExecStop=-/usr/share/wicd/daemon/autoconnect.py [Install] WantedBy=sleep.target
RemainAfterExit=yes: After started, the service is considered active until it is explicitly stopped.
StopWhenUnneeded=yes: When active, the service will be stopped if no other active service requires it. In this specific example, it will be stopped after sleep.target is stopped.
- Because sleep.target is pulled in by suspend.target, hibernate.target and hybrid-sleep.target and sleep.target itself is a StopWhenUnneeded service, the hook is guaranteed to start/stop properly for different tasks.
Delayed hibernation service file
An alternative approach is delayed hibernation. This makes use of sleep hooks to suspend as usual but sets a timer to wake up later to perform hibernation. Here, entering sleep is faster than
systemctl hybrid-sleep since no hibernation is performed initially. However, unlike "hybrid-sleep", at this point there is no protection against power loss via hibernation while in suspension. This caveat makes this approach more suitable for laptops than desktops. Since hibernation is delayed, the laptop battery is only used during suspension and to trigger the eventual hibernation. This uses less power over the long-term than a "hybrid-sleep" which will remain suspended until the battery is drained. Note that if your laptop has a spinning hard disk, when it wakes up from suspend in order to hibernate, you may not want to be moving or carrying the laptop for these few seconds. Delayed hibernation may be desirable both to reduce power use as well as for security reasons (e.g. when using full disk encryption). An example script is located here. See also this post for an updated systemd sleep hook.
A slightly updated version of the service is:
[Unit] Description=Delayed hibernation trigger Documentation=https://bbs.archlinux.org/viewtopic.php?pid=1420279#p1420279 Documentation=https://wiki.archlinux.org/index.php/Power_management Before=suspend.target Conflicts=hibernate.target hybrid-suspend.target StopWhenUnneeded=true [Service] Type=oneshot RemainAfterExit=yes Environment="WAKEALARM=/sys/class/rtc/rtc0/wakealarm" Environment="SLEEPLENGTH=+2hour" ExecStart=-/usr/bin/sh -c 'echo -n "alarm set for "; date +%%s -d$SLEEPLENGTH | tee $WAKEALARM' ExecStop=-/usr/bin/sh -c '\ alarm=$(cat $WAKEALARM); \ now=$(date +%%s); \ if [ -z "$alarm" ] || [ "$now" -ge "$alarm" ]; then \ echo "hibernate triggered"; \ systemctl hibernate; \ else \ echo "normal wakeup"; \ fi; \ echo 0 > $WAKEALARM; \ ' [Install] WantedBy=sleep.target
Conflicts options ensure it only is run for suspension and not hibernation--otherwise the service will run twice if delayed hibernation is triggered. The
StopWhenUnneeded options are so it is started before sleep and stops upon resume. (Note that the
hibernate.target targets do not stop when unneeded, but
sleep.target does). Enable the service.
Hooks in /usr/lib/systemd/system-sleep
systemd runs all executables in
/usr/lib/systemd/system-sleep/, passing two arguments to each of them:
- Argument 1: either
post, depending on whether the machine is going to sleep or waking up
- Argument 2:
hybrid-sleep, depending on which is being invoked
In contrast to pm-utils, systemd will run these scripts concurrently and not one after another.
The output of any custom script will be logged by systemd-suspend.service, systemd-hibernate.service or systemd-hybrid-sleep.service. You can see its output in systemd's journal:
# journalctl -b -u systemd-suspend
An example of a custom sleep script:
#!/bin/sh case $1/$2 in pre/*) echo "Going to $2..." ;; post/*) echo "Waking up from $2..." ;; esac
Do not forget to make your script executable:
# chmod a+x /usr/lib/systemd/system-sleep/example.sh
man 7 systemd.special and
man 8 systemd-sleep for more details.