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Nix on macOS: one flake, every machine

I run the same development environment on a MacBook Pro, inside WSL2 on a Windows machine, and on NixOS VMs. Not “similar” — identical. Same packages, same shell config, same editor plugins. One change propagates everywhere.

The tool that makes this possible is Nix, and the config lives at github.com/slimslenderslacks/nixos-config.

The problem Nix solves

Most approaches to environment management are per-platform: Homebrew on macOS, apt on Linux, something ad-hoc on WSL. Dotfiles help with shell config, but they don’t manage the tools themselves. The result is drift — the thing that works on your laptop doesn’t quite work on the server.

Nix takes a different approach. Every package is described as a pure function of its inputs, stored in an immutable path like /nix/store/abc123-ripgrep-14.1.0/. No global state, no install-time side effects. This means a Nix expression that builds ripgrep on macOS is the same expression that builds it on NixOS or inside WSL — the output is guaranteed to be identical.

One flake, three platforms

The entire config is driven from a single flake.nix. A central function called mksystem.nix takes a machine name and a few flags (darwin, wsl) and produces either a darwinSystem or nixosSystem. Critically, all three platform outputs share the same home-manager.nix — the file that defines my actual user environment: packages, dotfiles, shell config, neovim.

graph LR
    flake(["flake.nix\n— single source of truth —"])

    flake -->|"darwin=true"| darwin["macOS\nnix-darwin + home-manager"]
    flake -->|"wsl=true"| wsl["WSL2\nroot tarball + home-manager"]
    flake -->|"linux"| nixos["NixOS / Linux VM\nnixosSystem + home-manager"]

    hm["users/slim/home-manager.nix\npackages · dotfiles · shell · neovim"]

    hm -.->|shared| darwin
    hm -.->|shared| wsl
    hm -.->|shared| nixos

The platform-specific layers (darwin.nix, a machine .nix file) handle only what’s truly platform-specific: Homebrew casks on macOS, kernel settings on NixOS, WSL-specific tweaks. Everything else — the tools I actually use day to day — lives in home-manager.nix and is identical everywhere.

How macOS fits in

macOS doesn’t run NixOS, so there’s no NixOS init system or service manager to manage. Instead, nix-darwin fills that role. It provides a darwin-rebuild switch command analogous to nixos-rebuild switch, a module system for macOS system config, and integration with Homebrew for GUI apps and macOS-specific tools that work better as casks.

The Nix daemon itself is installed separately — I use the Determinate Systems nix-installer, which sets up /nix and enables flakes. After that, nix-darwin takes over and manages everything else declaratively.

Getting started

macOS

  1. Install Nix with flakes:

    curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install

  2. Clone the repo and run make:

    git clone https://github.com/slimslenderslacks/nixos-config
cd nixos-config
NIXNAME=macbook-pro-m1 make

    On first run, darwin-rebuild is bootstrapped directly from the build result — you don’t need it pre-installed.

WSL2

Build a WSL root tarball from any Linux machine (or from NixOS using cross-compilation):

make wsl
# copies ./result/tarball to Windows, then:
wsl --import nixos .\nixos .\path\to\tarball.tar.gz
wsl -d nixos

After wsl -d nixos you’re dropped directly into the Nix environment. No extra setup.

NixOS VM

Add a new machine entry to flake.nix pointing at mksystem.nix with darwin=false, add a machine .nix file under machines/, and run nixos-rebuild switch --flake .#your-machine.

What changes when you update

When I add a package to home-manager.nix and run make switch on the Mac, the same change is waiting for the WSL and NixOS environments the next time I rebuild them. The flake lock pins all inputs, so every machine builds against the same version of nixpkgs. No surprises.

The config is on GitHub. It’s a fork of Mitchell Hashimoto’s nixos-config, adapted for an Apple Silicon MacBook as the primary machine with WSL and NixOS VMs in the mix.

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