treewide: Switch to system users (#71055)

treewide: Switch to system users

nixos/modules/services/databases/redis.nix

@@ -194,7 +194,10 @@ in
       allowedTCPPorts = [ cfg.port ];
     };
 
-    users.users.redis.description = "Redis database user";
+    users.users.redis = {
+      description = "Redis database user";
+      isSystemUser = true;
+    };
 
     environment.systemPackages = [ cfg.package ];
 

nixos/modules/services/databases/rethinkdb.nix

@@ -99,6 +99,7 @@ in
     users.users.rethinkdb = mkIf (cfg.user == "rethinkdb")
       { name = "rethinkdb";
         description = "RethinkDB server user";
+        isSystemUser = true;
       };
 
     users.groups = optionalAttrs (cfg.group == "rethinkdb") (singleton