Auto-switching power profiles when plugging in your charger using power-profiles-daemon on Linux

9 Dec 2021 2 minutes

The new power-profiles-daemon present in Ubuntu and Fedora is fantastic, I’ve been been able to squeeze out a lot of extra battery life and performance by switching the profiles. The only problem is the lack of support for auto-switching the profile based on whether or not your laptop is currently charging. Ideally, I wanted my laptop to go into performance mode when plugged in, and when it goes on battery it should switch back to balanced mode.

To do this I wrote a little script that monitors the charging state of your laptop, which then switches the power-profile whenever you plug or unplug it from your charger. The script is started automatically when you log in using a systemd user service. Before you’ll be able to use this script you need to install the inotify-tools package.

Copy the following script somewhere (I like using ~/.local/bin), and make sure that it is executable. You can adjust which power-profiles should be used for the charging, discharging and low battery states by changing the values in the AC_PROFILE, BAT_PROFILE and LOW_BAT_PROFILE variables, respectively.

Once you have the script stored somewhere and ready to execute, you can add the following service file in your local systemd config folder, i.e. ~/.config/systemd/user/power-monitor.service (you might need to create the folder). Be sure to update the ExecStart parameter to your script’s path. You can then enable and start the service using systemctl --user enable --now power-monitor.service.

That should be it. You can then monitor the script’s operation using systemctl --user status power-monitor.service, you should be getting log entries when it updates the power profile. The script will wait 30 seconds before starting up, I’ve found if I don’t add this delay the power-profiles daemon will throw an error when I log in (presumably because it is not yet ready).

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