Unified Nix Config for NixOS and macOS

1. Overview

The goal of this repository is to manage distinct systems using a single Git repository and Flake:

1. MacBook Pro 14 (macOS): Hostname mbp-14. Uses Home Manager (standalone) to manage user tools and dotfiles.
2. HP Z2 Mini G1a (NixOS): Hostname z2-mini. Uses NixOS for system configuration and Home Manager (as a module) for user configuration.

Key Philosophy: "Write once, run everywhere" for user tools (Neovim, Zsh, Git, etc.), while keeping system-specific configurations (disk mounts, networking, macOS settings) separate.

2. Directory Structure

This repository uses a modular structure to maximize code reuse:

.
├── .envrc                   # Direnv configuration (auto-loads dev shell)
├── .pre-commit-config.yaml  # Code formatting and linting rules
├── flake.nix                # Entry point for all systems
├── flake.lock
├── modules/
│   └── home/
│       ├── default.nix      # Imports all common modules
│       ├── core.nix         # Shells, Git, common packages
│       ├── neovim.nix       # Neovim config
│       └── gui.nix          # GUI tools (Ghostty, etc.)
├── hosts/
│   ├── mbp-14/              # macOS specific configs (MacBook Pro 14)
│   │   └── home.nix         # macOS-specific home overrides
│   └── z2-mini/             # NixOS specific configs (HP Z2 Mini G1a)
│       ├── configuration.nix# System-level config
│       ├── hardware-configuration.nix
│       └── home.nix         # NixOS-specific home overrides

3. Architecture & Implementation

The Flake (flake.nix)

The flake.nix produces two types of outputs:

• nixosConfigurations: For the z2-mini machine.
• homeConfigurations: For the mbp-14 machine.

Concept:

• Shared Inputs: Both systems share nixpkgs versions via flake.lock.
• NixOS (z2-mini): Implements Home Manager as a system module for atomic updates.
• macOS (mbp-14): Uses Home Manager in standalone mode.

Shared Configuration (modules/home/)

• modules/home/core.nix: Contains the bulk of user configuration (Packages, Shells, Git, etc.).
• Host Specifics: home.username and home.homeDirectory are defined in hosts/<machine>/home.nix to allow portability.

4. Workflow

Updating the MacBook (mbp-14)

You can run Home Manager using nix run without installing the home-manager CLI tool globally.

# From local source
$ nix run home-manager/master -- switch --flake .#wjkoh@mbp-14

# Directly from GitHub (useful for bootstrapping)
$ nix run home-manager/master -- switch --flake github:wjkoh/nix-config#wjkoh@mbp-14

Updating the HP Z2 (z2-mini)

# From local source
# nixos-rebuild switch --flake .#z2-mini

# Directly from GitHub
# nixos-rebuild switch --flake github:wjkoh/nix-config#z2-mini

5. Benefits

1. Single Source of Truth: Change configuration once, propagate to all machines.
2. Shared Lockfile: Ensures identical tool versions across macOS and Linux.
3. Atomic Updates: On NixOS, system and user configs update synchronously.

6. Post-Installation Steps

After applying the configuration, some manual steps are required:

Tailscale

• macOS (mbp-14): Install Tailscale manually via the Mac App Store or as a standalone app.
• NixOS (z2-mini): Tailscale is managed as a system service. Run sudo tailscale up to authenticate.

Google Cloud SDK

On both systems, you must authenticate manually to use gcloud and application default credentials:

$ gcloud auth login
$ gcloud auth application-default login