nixos-config/system/desktop/suspend.nix

{ pkgs, config, ... }:

{
  systemd.services.screenlock = {
    before = [ "sleep.target" ];
    requiredBy = [ "sleep.target" ];
    environment = let
      display = if (config.services.xserver.display != null) then
        config.services.xserver.display
      else
        0;
    in { DISPLAY = ":${toString display}"; };
    script = ''
      ${pkgs.xlockmore}/bin/xlock -mode life1d -size 1 &
      sleep 1
    '';
    serviceConfig = {
      SyslogIdentifier = "screenlock";
      #Type = "simple";
      Type = "forking";
      User = config.users.users.mainUser.name;
    };
  };

  services.logind.lidSwitch = "ignore";

}