fix: nixConfig.extra-sbustituers https://github.com/ryan4yin/nixos-and-flakes-book/discussions/62#discussioncomment-7805510

modules/common.nix

@@ -0,0 +1,40 @@
+{
+  lib,
+  username,
+  ...
+}: {
+  nix.settings = {
+    # enable flakes globally
+    experimental-features = ["nix-command" "flakes"];
+
+    # given the users in this list the right to specify additional substituters via:
+    #    1. `nixConfig.substituers` in `flake.nix`
+    #    2. command line args `--options substituers http://xxx`
+    trusted-users = [username];
+
+    substituters = [
+      # cache mirror located in China
+      # status: https://mirror.sjtu.edu.cn/
+      "https://mirror.sjtu.edu.cn/nix-channels/store"
+      # status: https://mirrors.ustc.edu.cn/status/
+      # "https://mirrors.ustc.edu.cn/nix-channels/store"
+
+      "https://cache.nixos.org"
+    ];
+
+    trusted-public-keys = [
+      "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+    ];
+    builders-use-substitutes = true;
+  };
+
+  # do garbage collection weekly to keep disk usage low
+  nix.gc = {
+    automatic = lib.mkDefault true;
+    dates = lib.mkDefault "weekly";
+    options = lib.mkDefault "--delete-older-than 7d";
+  };
+
+  # Allow unfree packages
+  nixpkgs.config.allowUnfree = lib.mkDefault false;
+}

modules/darwin/default.nix

@@ -1,7 +1,9 @@
 {
   imports = [
-    ./apps.nix
+    ../common.nix
     ./nix-core.nix
+
+    ./apps.nix
     ./system.nix
   ];
 }

modules/darwin/nix-core.nix

@@ -12,9 +12,6 @@
   #
   ###################################################################################
 
-  # enable flakes globally
-  nix.settings.experimental-features = ["nix-command" "flakes"];
-
   # Allow unfree packages
   nixpkgs.config.allowUnfree = true;
 
@@ -28,13 +25,6 @@
 
   programs.nix-index.enable = true;
 
-  # boot.loader.grub.configurationLimit = 10;
-  # do garbage collection weekly to keep disk usage low
-  nix.gc = {
-    automatic = lib.mkDefault true;
-    options = lib.mkDefault "--delete-older-than 7d";
-  };
-
   # Disable auto-optimise-store because of this issue:
   #   https://github.com/NixOS/nix/issues/7273
   # "error: cannot link '/nix/store/.tmp-link-xxxxx-xxxxx' to '/nix/store/.links/xxxx': File exists"

modules/nixos/core-server.nix

@@ -9,27 +9,12 @@
   #
   ###################################################################################
 
+  imports = [
+    ../common.nix
+  ];
+
   # for nix server, we do not need to keep too much generations
   boot.loader.systemd-boot.configurationLimit = lib.mkDefault 10;
-  # boot.loader.grub.configurationLimit = 10;
-  # do garbage collection weekly to keep disk usage low
-  nix.gc = {
-    automatic = lib.mkDefault true;
-    dates = lib.mkDefault "weekly";
-    options = lib.mkDefault "--delete-older-than 7d";
-  };
-
-  nix.settings = {
-    # Manual optimise storage: nix-store --optimise
-    # https://nixos.org/manual/nix/stable/command-ref/conf-file.html#conf-auto-optimise-store
-    auto-optimise-store = true;
-    builders-use-substitutes = true;
-    # enable flakes globally
-    experimental-features = ["nix-command" "flakes"];
-  };
-
-  # Allow unfree packages
-  nixpkgs.config.allowUnfree = lib.mkDefault false;
 
   # Set your time zone.
   time.timeZone = "Asia/Shanghai";

modules/nixos/user-group.nix

@@ -1,8 +1,6 @@
 { username, ... }: 
 
 {
-  nix.settings.trusted-users = [username];
-
   # Don't allow mutation of users outside the config.
   users.mutableUsers = false;