As How to set multiple actions to button press in Energy Saving KCM? explains, I’ve configured my LINX 1010b (tablet)'s display to disable when its power button is pressed. However, this doesn’t work in SDDM. Any ideas of why and how to remediate this? I’ll file an issue with them if it’s out of the scope of here.
The short answer is that the PowerDevil service runs on the user session bus, so it only starts after you successfully log in. It also reads its configuration from your user’s config directory, so the solution isn’t simply to start it on the system bus.
SDDM would require better integration with the (system’s main) user session to replicate some of this functionality, and also other stuff like wifi network connections or input method integration. Unfortunately that stuff is hard, and the SDDM maintainer isn’t overly interested in tight integration with Plasma specifically. There has been a bit of discussion about how to move forward on this issue, and eventually the community will figure something out, but it’s not trivial and will take a good amount of engineering effort.
@jpetso, does an effort to broadly replicate most user configurations whilst viewing their entry in the SDDM GUI exist? That appears to be how Windows’s
winlogon.exe, AOSP, and (to my knowledge) macOS handle this.
Not sure what efforts are going on exactly, sorry! I’m not involved with SDDM work really, I’ve only infrequently seen a handful of high-level conversations here and there. Other people may have better insights.