post(nixos): add `nix.gc` and update config style

source/_posts/caddy-nixos-part-2.md

@@ -225,11 +225,14 @@ Unattended upgrade can be enabled through the following config. Once enabled, Ni
 
 In the config, you can also specify the time that the server will reboot. I recommend to only enable it after everything is up and running, especially when setting a web server; you wouldn't want the server to reboot itself in the middle of your tinkering.
 
+(For more advanced usage of `dates`, see [`systemd.time`](https://jlk.fjfi.cvut.cz/arch/manpages/man/systemd.time.7#CALENDAR_EVENTS))
+
 ``` js
   system.autoUpgrade = {
     enable = true;
     allowReboot = true;
-    dates = "00:00";
+    # Daily 00:00
+    dates = "daily UTC";
   };
 ```
 
@@ -306,3 +309,16 @@ Kernel compiled with additional security-oriented patch set. [More details](http
 ```
   boot.kernelPackages = pkgs.linuxPackages_hardened;
 ```
+
+## Remove old, unreferenced packages
+
+Since my web server has limited disk space, it needs to run [garbage collector](https://nixos.org/nixos/manual/index.html#sec-nix-gc) from time to time.
+
+```
+  ## Garbage collector
+  nix.gc = {
+    automatic = true;
+    # Every Monday 00:00
+    dates = "weekly UTC";
+  };
+```

source/_posts/i2p-eepsite-nixos.md

@@ -40,15 +40,17 @@ To join the I2P network, I'm using [i2pd](https://i2pd.website/), an (unofficial
     enable = true;
     ifname = "ens3";
     address = "xxxx";
-    inTunnels.myEep = {
-      enable = true;
-      keys = "myEep-keys.dat";
-      inPort = 80;
-      address = "::1";
-      destination = "::1";
-      port = 8081;
-      # inbound.length = 1;
-      # outbound.length = 1;
+    inTunnels = {
+      myEep = {
+        enable = true;
+        keys = "myEep-keys.dat";
+        inPort = 80;
+        address = "::1";
+        destination = "::1";
+        port = 8081;
+        # inbound.length = 1;
+        # outbound.length = 1;
+      };
     };
     enableIPv4 = false;
     enableIPv6 = true;

source/_posts/tor-hidden-onion-nixos.md

@@ -37,15 +37,17 @@ The first step is to bring up a Tor hidden service to get an onion address. Add
   services.tor = {
     enable = true;
     enableGeoIP = false;
-    hiddenServices.myOnion = {
-      version = 3;
-      map = [
-        {
-          port = "80";
-          toHost = "[::1]";
-          toPort = "8080";
-        }
-      ];
+    hiddenServices = {
+      myOnion = {
+        version = 3;
+        map = [
+          {
+            port = "80";
+            toHost = "[::1]";
+            toPort = "8080";
+          }
+        ];
+      };
     };
     extraConfig = 
       ''