Modules

Module Structure

Standard module pattern:

{
  config,
  lib,
  pkgs,
  ...
}:
let
  inherit (lib) mkEnableOption mkOption mkIf types;
  cfg = config.services.myService;
in
{
  options.services.myService = {
    enable = mkEnableOption "my service";

    port = mkOption {
      type = types.port;
      default = 8080;
      description = "Port to listen on.";
    };
  };

  config = mkIf cfg.enable {
    # Configuration applied when enabled
  };
}

Creating a NixOS Module

1. •

   Create file at modules/nixos/<category>/<name>.nix

2. •

   Define options and config:

   nix

   {
     config,
     lib,
     pkgs,
     ...
   }:
   let
     cfg = config.services.myService;
   in
   {
     options.services.myService = {
       enable = lib.mkEnableOption "my service";
     };
   
     config = lib.mkIf cfg.enable {
       systemd.services.my-service = {
         wantedBy = [ "multi-user.target" ];
         serviceConfig.ExecStart = "${pkgs.myPackage}/bin/my-service";
       };
     };
   }
   

3. •

   Register in parent default.nix:

   nix

   # modules/nixos/services/default.nix
   _: {
     imports = [
       ./existing-service.nix
       ./my-service.nix  # Add this
     ];
   }
   

4. •

   Enable in host config:

   nix

   # hosts/server/myhost/default.nix
   { services.myService.enable = true; }
   

Creating a Home-Manager Module

1. •

   Create file at modules/home-manager/<category>/<name>.nix

2. •

   Define with optional osConfig access:

   nix

   {
     osConfig ? null,
     config,
     lib,
     pkgs,
     ...
   }:
   let
     cfg = config.purpose.myFeature;
   in
   {
     options.purpose.myFeature = {
       enable = lib.mkEnableOption "my feature";
     };
   
     config = lib.mkIf cfg.enable {
       home.packages = [ pkgs.myPackage ];
     };
   }
   

3. •

   Register in parent default.nix

4. •

   Enable in user config:

   nix

   # home/<user>/hm-config.nix
   { purpose.myFeature.enable = true; }
   

Common Namespaces

Directory Index Patterns

Export as attribute set (top-level)

# modules/nixos/default.nix
{
  boot = import ./boot;
  hardware = import ./hardware;
  services = import ./services;
}

Import list (subdirectories)

# modules/nixos/services/default.nix
_: {
  imports = [
    ./service-a.nix
    ./service-b.nix
  ];
}

Modifying Existing Modules

1. •Find the module using project-structure skill
2. •Understand existing options with nix eval
3. •Add new options or extend config
4. •Test affected configurations
5. •Run nix fmt on changed files