SDDM Background on Default Theme

Hi! I’m a new NixOS user. I’ve been trying to figure out how to set the background image for SDDM. From initial research, everyone says to package a custom theme and point services.displayManager.sddm.theme to that derivation.

However, I actually like the default (breeze?) theme for SDDM. Can I change the background image for this default theme? Arch Wiki says to put a file called theme.conf.user in the same theme directory (which my system tells me is /run/current-system/sw/share/sddm/themes/breeze, but I’m sure is in reality somewhere in the Nix store), but I can’t quite figure out how to do that.

I believe my question boils down to the following: Is a custom SDDM theme required to configure the background image in NixOS? And, as a bonus question, is it possible to modify the default breeze SDDM theme somehow?

Thanks for your time!

You can drop that theme.conf.user file in the right place by creating a package that contains that file at the right location. The easiest way is with pkgs.writeTextDir, which is what I do.

environment.systemPackages = [
  (pkgs.writeTextDir "share/sddm/themes/breeze/theme.conf.user" ''

Wow, super simple! Thanks a ton.

A note for anyone trying this at home: this method doesn’t like a raw path set for background (I tried /home/(user)/path/to/wallpaper.png) but all I got was a white screen.

If you want a custom file as your background, you can try what worked for me: create a derivation that just copies the wallpaper file to the Nix store.

Here’s my code:

  background-package = pkgs.stdenvNoCC.mkDerivation {
    name = "background-image";
    src = ./.;
    dontUnpack = true;
    installPhase = ''
      cp $src/wallpaper.png $out
  #services.xserver.enable = true;
  services.displayManager.sddm = {
    enable = lib.mkDefault true;
    theme = "breeze";
    wayland.enable = true;

  environment.systemPackages = [
      pkgs.writeTextDir "share/sddm/themes/breeze/theme.conf.user" ''
        background = ${background-package}