How to access plasma-defined service?

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1

In order to fix some monitor brightness control related misbehavior I encountered after switching to Plasma 6, I am trying to apply the advice I got here. I have tried setting

  systemd.user.services.plasma-powerdevil = {
    environment = {
      POWERDEVIL_NO_DDCUTIL = "1";
    };
  };

in the hopes of just being able to extend a nix-defined systemd service, but that does not seem to be the way this service comes into existence and I just get

❯ systemctl --user status plasma-powerdevil
● plasma-powerdevil.service
     Loaded: bad-setting (Reason: Unit plasma-powerdevil.service has a bad unit file setting.)
     Active: active (running) since Sat 2025-06-14 11:07:39 CEST; 11min ago
 Invocation: 928c970dfeaf4e23a4d022b1d71e3675
   Main PID: 2823 (.org_kde_powerd)
      Tasks: 7 (limit: 37976)
     Memory: 13.5M (peak: 14.2M)
        CPU: 172ms
     CGroup: /user.slice/user-1000.slice/user@1000.service/background.slice/plasma-powerdevil.service
             └─2823 /nix/store/003sp6c3v67lplbr443qzfwngcpbjs16-powerdevil-6.3.5/libexec/org_kde_powerdevil

Jun 14 11:07:38 m-work systemd[2577]: Starting Powerdevil...
Jun 14 11:07:38 m-work org_kde_powerdevil[2823]: Starting libddcutil. library built Feb 17 2025 at 09:09:46. stdout_stderr_redirected=true
Jun 14 11:07:38 m-work org_kde_powerdevil[2823]: Initializing libddcutil.  ddcutil version: 2.2.0-dev, shared library: /nix/store/7ywk1r5az73cyk8>
Jun 14 11:07:38 m-work org_kde_powerdevil[2823]: [  2823] Options passed from client:
Jun 14 11:07:38 m-work org_kde_powerdevil[2823]: [  2823] Applying combined libddcutil options:
Jun 14 11:07:38 m-work org_kde_powerdevil[2823]: Library initialization complete.
Jun 14 11:07:38 m-work org_kde_powerdevil[2823]: org.kde.powerdevil: [DDCutilDetector]: Failed to initialize callback
Jun 14 11:07:39 m-work systemd[2577]: Started Powerdevil.
Jun 14 11:07:39 m-work org_kde_powerdevil[2823]: org.kde.powerdevil: Handle button events action could not check for screen configuration
Jun 14 11:19:12 m-work systemd[2577]: plasma-powerdevil.service: Service has no ExecStart=, ExecStop=, or SuccessAction=. Refusing.

I will now attempt to just set the variable globally

  environment.variables.POWERDEVIL_NO_DDCUTIL = "1";

but I do wonder if there is a better way?

2

Does the variable appear when you do systemctl cat --user plasma-powerdevil ?

3

Isn’t that kind of beside the point? The problem is that there seems to be no base NixOS config for this service to extend, leaving it incomplete, instead of just merging the env var into an existing definition. At least, that’s what I think is happening