add unattended upgrades

automatic-upgrades.nix

@@ -0,0 +1,17 @@
+{ config, pkgs, ... }:
+
+{
+  # Enable automatic garbage collection (prevents /boot or / filling up)
+  nix.gc.automatic     = true;
+  nix.gc.dates         = "03:00";           # run GC at 03:00 daily
+
+  # Enable automatic system upgrades
+  system.autoUpgrade = {
+    enable             = true;               # turn on unattended upgrades
+    dates              = "02:00";            # schedule upgrades at 02:00 each day
+    randomizedDelaySec = "45m";              # spread load by up to 45 minutes
+    allowReboot        = false;              # don't reboot if needed for new generation
+  };
+
+}
+

master.nix

@@ -11,6 +11,7 @@ in
 {
   imports = [
     ./hardware-configuration.nix
+    ./automatic-upgrades.nix
     ./bootloader.nix
     ./networking.nix
     ./misc.nix