modules/shared: add nix-daemon

modules/nixos/common/default.nix

@@ -2,7 +2,7 @@
 {
   imports = [
     ./auto-upgrade.nix
-    ./nix-daemon.nix
+    ../../shared/nix-daemon.nix
     ./reboot.nix
     ./security.nix
     ./sops-nix.nix
@@ -12,6 +12,17 @@
     inputs.srvos.nixosModules.server
   ];
 
+  # users in trusted group are trusted by the nix-daemon
+  nix.settings.trusted-users = [ "@trusted" ];
+
+  users.groups.trusted = { };
+
+  # Sometimes it fails if a store path is still in use.
+  # This should fix intermediate issues.
+  systemd.services.nix-gc.serviceConfig = {
+    Restart = "on-failure";
+  };
+
   networking.firewall.allowedTCPPorts = [ 9273 ];
 
   srvos.flake = inputs.self;