Patching NixOS config

JanKaifer · March 5, 2021, 10:10pm

Hi, I am trying to add --ignore-default-control to thermald service:

[Service]
Type=dbus
SuccessExitStatus=1
BusName=org.freedesktop.thermald
ExecStart=/nix/store/sahg7c0lxzw28i3b6yz02024nwmnrdv0-thermald-2.2/sbin/thermald --no-daemon --dbus-enable

I looked at the source, and there is currently no way to do that. So my question is how can I patch it?

Sorry for the noobie question, I will be grateful for the correct keyword to google.
Stuff like “nixos patch XY” or “nix change nix expression” was not helpful.

jtojnar · March 5, 2021, 11:02pm

You can override systemd service lines using systemd.services.<name>.serviceConfig:

github.com

NixOS/nixpkgs/blob/c7c81dced8adc0278dbbaad7ecfc81895c18568b/nixos/modules/services/networking/dnsdist.nix#L49

    
      
          
          
    systemd.services.dnsdist = {
                wantedBy = [ "multi-user.target" ];
          
          
      startLimitIntervalSec = 0;
                serviceConfig = {
                  DynamicUser = true;
          
          
        # upstream overrides for better nixos compatibility
                  ExecStartPre = [ "" "${pkgs.dnsdist}/bin/dnsdist --check-config --config ${configFile}" ];
                  ExecStart = [ "" "${pkgs.dnsdist}/bin/dnsdist --supervised --disable-syslog --config ${configFile}" ];
                };
              };
            };
          }

Do not forget about the empty string, otherwise systemd will append your value to ExecStart instead of overriding it.