PowerDevil

PowerDevil is the internal name of the KDE power management service for Plasma. It is responsible for some (but not all) interactions with hardware functionality. The service will:

• Suspend or shut down sessions under certain conditions such as user inactivity, closing the laptop lid or pressing the power button.
• Adjust the brightness level of displays and keyboards, or turn display backlights off/on altogether.
• Change settings according to the current power state (plugged in, battery, low battery), which can be customized in System Settings.
• Monitor the current battery charge, and set charge thresholds for battery-powered devices that support it.
• Keep track of system state - e.g. suspend/idle/etc. inhibitors, activities, screen locking - to adjust power management behaviors accordingly.
• Communicate with underlying services such as UPower, power-profiles-daemon, ddcutil, and/or systemd to implement some of the above.
• Provide a D-Bus interface for other Plasma components such as the Power Management applet or the Brightness and Color applet.

Related components

Directly interacting with this service, but not located in this repository:

• The Power Management applet in plasma-workspace.
• The Brightness and Color applet, also part of plasma-workspace.
• Even KRunner commands for PowerDevil actions are part of plasma-workspace for some reason.
• In a Wayland session, KWin takes over certain functionality related to user activity tracking and turning displays on/off which in X11 is managed by PowerDevil directly.
• Plasma Mobile has its own UI for power management settings.

PowerDevil does not handle hardware interactions such as display configuration, turning wireless interfaces off/on ("airplane mode"), mounting/unmounting disks, or sound/audio configuration. Other Plasma components are responsible for these features.

Troubleshooting & reporting bugs

PowerDevil will be automatically started when logging into a Plasma session. When logging into different Plasma sessions with different users at the same time, each session will run its own instance of the service.

Similar to other KDE software, PowerDevil will only log warnings and errors by default. When troubleshooting or filing a bug report, it's a good idea to increase the verbosity of system log messages first.

If your system is based on systemd, like most Linux distributions nowadays, then the various Plasma components including PowerDevil are started as systemd service units after logging in. You can adjust the way that the service is run, by executing (in a terminal):

systemctl --user edit plasma-powerdevil.service

This will open an editor. Define an additional environment variable in the designated space to show all log messages in the PowerDevil log category, like this:

### Editing /home/$USER/.config/systemd/user/plasma-powerdevil.service.d/override.conf
### Anything between here and the comment below will become the contents of the drop-in file

[Service]
Environment="QT_LOGGING_RULES=org.kde.powerdevil=true"

### Edits below this comment will be discarded
### (...)

PowerDevil can be restarted inside an active Plasma session by executing:

systemctl --user restart plasma-powerdevil.service

After restarting the service, expanded logs will start appearing in your system log, which can be viewed with e.g. journalctl --boot. PowerDevil logs show up under the org_kde_powerdevil name.

Stopping the service is possible without closing or crashing the session, but a few expected desktop features will be absent until you restart it.

If the service crashes, coredumpctl should be able to retrieve stack traces that are useful for developers.

PowerDevil is split into two main components on the KDE bug tracker:

• Powerdevil, the background service (report bug after checking for duplicates)
• The kcm_powerdevil component in System Settings, referring to the Power Management settings UI (report bug after checking for duplicates)

Remember to include versions of relevant system software, and (if appropriate) system logs. The easier you make it for developers to reproduce bugs or find out why & where the code breaks, the more likely it is to get those issues fixed. Thanks for your help in making life better for other users and developers.

Troubleshooting DDC/CI monitor brightness controls

PowerDevil uses (lib)ddcutil to adjust brightness of external monitors. Log messages of ddcutil are included in the org_kde_powerdevil log output.

DDC/CI experiences can differ greatly among different monitor manufacturers and ddcutil is making the best of a complicated situation. Sometimes users can nonetheless run into issues with DDC/CI monitor support. If this happens and the power management service does not start correctly, Plasma as a whole will have trouble starting and functioning as intended.

Instead of disabling the PowerDevil service altogether, you can disable merely its use of ddcutil by defining POWERDEVIL_NO_DDCUTIL=1 as environment variable to your service configuration. Refer to the instructions for QT_LOGGING_RULES above for how to go about this. Aside from missing DDC/CI brightness controls, this will leave you with a working system until a fix can be found and deployed to your system.

Advanced users who want to dig into ddcutil can specify a ddcutil/ddcutilrc file in their config directory, to change selected ddcutil options (like these) and/or enable extremely detailed ddcutil tracing output. Chances are you'll need technical background knowledge and/or support from the ddcutil maintainer to get any useful fixes out of this. So let's just say that PowerDevil supports ddcutil config files, will apply the [global] and [libddcutil] config sections, and leave it at that.

Building & debugging

Set up a KDE development environment as described in the developer documentation, in particular the parts about setting up kdesrc-build and building KDE software including Plasma. PowerDevil is part of the workspace meta-target for kdesrc-build and will be built by following the standard instructions.

Restart using systemd (or your init system of choice) as mentioned earlier. Use system log messages and attach gdb to the running session for further debugging.

PowerDevil ships with KAuth helpers, which have to be configured on a system-wide basis. If you need to change these helpers, consult MRs !1715 and/or !3705 in plasma-workspace for possible ways to enable their development builds on your system.

DDC/CI brightness range experiments

PowerDevil verifies the monitor's VCP 0x10 maximum immediately before each write. For a monitor or compositor with an incorrect brightness scale, optional environment variables can remap it without rebuilding:

• POWERDEVIL_DDC_BRIGHTNESS_INPUT_MAX: input scale to expect.
• POWERDEVIL_DDC_BRIGHTNESS_OUTPUT_MAX: highest normal VCP 0x10 value to send.
• POWERDEVIL_DDC_BRIGHTNESS_WRAP_MIN and POWERDEVIL_DDC_BRIGHTNESS_WRAP_MAX: an optional dimmer wrapped segment following the normal range.
• POWERDEVIL_DDC_BRIGHTNESS_WRAP_GAMMA: optional curve for that combined sequence; 1 is linear by VCP step.
• POWERDEVIL_DDC_BRIGHTNESS_DELAY_MS: optional request debounce; 0 sends immediately, while 100 is a responsive starting point.

A global variable applies to every DDC/CI monitor. Prefer a per-display variable instead: append _EDID_<SHA256> to either name, where <SHA256> is the uppercase SHA-256 fingerprint of the display's first 128-byte EDID block. PowerDevil writes that suffix to the org_kde_powerdevil user journal when it detects the display. This lets a workaround apply only to the affected monitor, even if another monitor is attached later.

For example, a display whose logged suffix is EDID_ABCDEF... can be constrained to its stable 0..35 range while keeping a 0..100 laptop slider:

[Service]
Environment=POWERDEVIL_DDC_BRIGHTNESS_INPUT_MAX_EDID_ABCDEF...=100
Environment=POWERDEVIL_DDC_BRIGHTNESS_OUTPUT_MAX_EDID_ABCDEF...=35

If this monitor has an additional dim segment at 36..60, enable the per-display wrap sequence instead. A 0..100 slider then follows 36..60, 0..35: raw 36 is the slider minimum, raw 60 joins the normal zero point, and raw 35 remains the maximum.

[Service]
Environment=POWERDEVIL_DDC_BRIGHTNESS_INPUT_MAX_EDID_ABCDEF...=100
Environment=POWERDEVIL_DDC_BRIGHTNESS_OUTPUT_MAX_EDID_ABCDEF...=35
Environment=POWERDEVIL_DDC_BRIGHTNESS_WRAP_MIN_EDID_ABCDEF...=36
Environment=POWERDEVIL_DDC_BRIGHTNESS_WRAP_MAX_EDID_ABCDEF...=60
Environment=POWERDEVIL_DDC_BRIGHTNESS_WRAP_GAMMA_EDID_ABCDEF...=1

Add this to ~/.config/systemd/user/plasma-powerdevil.service.d/ddc-brightness.conf, then apply it with systemctl --user daemon-reload and systemctl --user restart plasma-powerdevil.service. If neither the per-display nor global input maximum is set, PowerDevil retains the monitor's native scale. Every remapped request is logged to the org_kde_powerdevil user journal.