Per-Host Overrides

Every host can customize the global configuration without editing shared modules. Nix’s module system merges lists and attribute sets, so per-host files simply add to what’s already defined.

What Can Be Overridden

System-level (in default.nix or system.nix)

# Add Homebrew packages (macOS)
homebrew.brews = [ "mosquitto" ];
homebrew.casks = [ "slack" ];
homebrew.masApps = { "Xcode" = 497799835; };

# Add nix system packages
environment.systemPackages = with pkgs; [ terraform ];

# Change macOS defaults
system.defaults.dock.autohide = false;

# Enable the Apple container Linux builder
services.container-builder = {
  enable = true;
  cpus = 4;
  memory = "8G";
  maxJobs = 4;
  bridge.enable = true;
};

User-level (in home.nix)

{ pkgs, ... }:
{
  # Add user packages
  home.packages = with pkgs; [ spotify-player ];

  # Add shell aliases
  home.shellAliases = {
    work = "cd ~/workspace/work";
    personal = "cd ~/workspace/personal";
  };

  # Create files in $HOME
  home.file."workspace/personal/.gitconfig".text = ''
    [user]
      email = personal@example.com
  '';
}

How It Works

The host’s default.nix is imported as an additional module alongside the global modules. Nix merges all option definitions:

• Lists (homebrew.brews, home.packages): concatenated
• Attribute sets (home.shellAliases): merged (host values override on conflict)
• Scalars (system.defaults.dock.autohide): last definition wins (use lib.mkForce if the global module also sets it)

File Structure

hosts/aarch64-darwin/MYMACHINE/
├── default.nix     # System overrides (required)
├── user.nix        # Username, name, email, GitHub username (required)
└── home.nix        # Home-manager overrides (optional)

The home.nix is conditionally imported – if the file doesn’t exist, it’s skipped. No boilerplate needed.