Add automatic gc

Author: jhh

nix/modules/nixos/server.nix

@@ -15,14 +15,22 @@ in
     mailutils
   ];
 
-  nix.settings = {
-    substituters = [
-      "https://strykeforce.cachix.org"
-    ];
+  nix = {
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 14d";
+      randomizedDelaySec = "1h";
+    };
+    settings = {
+      substituters = [
+        "https://strykeforce.cachix.org"
+      ];
 
-    trusted-public-keys = [
-      "strykeforce.cachix.org-1:+ux184cQfS4lruf/lIzs9WDMtOkJIZI2FQHfz5QEIrE="
-    ];
+      trusted-public-keys = [
+        "strykeforce.cachix.org-1:+ux184cQfS4lruf/lIzs9WDMtOkJIZI2FQHfz5QEIrE="
+      ];
+    };
   };
 
 }