tzupdate service: init

nixos/modules/module-list.nix

@@ -343,6 +343,7 @@
   ./services/misc/svnserve.nix
   ./services/misc/synergy.nix
   ./services/misc/taskserver
+  ./services/misc/tzupdate.nix
   ./services/misc/uhub.nix
   ./services/misc/zookeeper.nix
   ./services/monitoring/apcupsd.nix

nixos/modules/services/misc/tzupdate.nix

@@ -0,0 +1,45 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.tzupdate;
+in {
+  options.services.tzupdate = {
+    enable = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Enable the tzupdate timezone updating service. This provides
+        a one-shot service which can be activated with systemctl to 
+        update the timezone.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    # We need to have imperative time zone management for this to work.
+    # This will give users an error if they have set an explicit time
+    # zone, which is better than silently overriding it.
+    time.timeZone = null; 
+
+    # We provide a one-shot service which can be manually run. We could
+    # provide a service that runs on startup, but it's tricky to get
+    # a service to run after you have *internet* access.
+    systemd.services.tzupdate = {
+      description = "tzupdate timezone update service";
+      wants = [ "network-online.target" ];
+      after = [ "network-online.target" ];
+
+      serviceConfig = {
+        Type = "oneshot";
+        # We could link directly into pkgs.tzdata, but at least timedatectl seems
+        # to expect the symlink to point directly to a file in etc.
+        # Setting the "debian timezone file" to point at /dev/null stops it doing anything.
+        ExecStart = "${pkgs.tzupdate}/bin/tzupdate -z /etc/zoneinfo -d /dev/null";
+      };
+    };
+  };
+
+  meta.maintainers = [ maintainers.michaelpj ];
+}