NixOS on WSL

2023-01-22

I recently set up a new Windows machine for gaming, but I’m actually using it more to play around with Linux via WSL. I set up NixOS on WSL using the aptly named NixOS on WSL project, but ran into a few issues during setup that bricked my environment^{1-->. Below are the steps that ended up working for me in the end:}

Goals

Set up NixOS in WSL 2 on a new Windows 11 install (version 22H2.)
Reuse my flake-based configuration from my other NixOS 22.11 installations.
Take advantage of native systemd support in WSL.

Step 1: Install WSL 2

Per Microsoft’s documentation:

Open PowerShell as an admin by right-clicking on it and selecting “Run as administrator.”
Run wsl --install

Step 2: Install NixOS

Per NixOS-WSL’s documentation:

Download the installer listed in NixOS-WSL’s 22.05 release.
Move the file where you want your NixOS installation to live. I put it in C:\Users\<my username>\AppData\Local\NixOS, which I think follows Windows’s conventions.
Open PowerShell as a normal user, change to the directory you just made, and run wsl --import NixOS . nixos-wsl-installer.tar.gz --version 2
Run wsl -d NixOS to start NixOS. It’ll run through initial setup, then hang on “Starting systemd…” Press Ctrl + C to get back to PowerShell, and then run wsl --shutdown followed by wsl -d NixOS to get back into NixOS.

Step 3: Configure NixOS

At this point you should have a basic NixOS 22.05 installation! Let’s finish up by setting a username, switching over to flakes, updating to NixOS 22.11, and enabling native systemd:

Edit /etc/nixos/configuration.nix and make the following changes. Use sudo or some such to edit the file as root. You may want to nix-shell -p your favorite editor at this point – maybe Helix?
- Change wsl.defaultUser to your desired username, and add something like users.users.<your username>.isNormalUser = true;
- Remove references to ./nixos-wsl since we’ll set NixOS-WSL as a flake input:
```
  { lib, pkgs, config, modulesPath, ... }:
-
- with lib;
- let
-   nixos-wsl = import ./nixos-wsl;
- in
  {
    imports = [
      "${modulesPath}/profiles/minimal.nix"
-
-     nixos-wsl.nixosModules.wsl
    ];
```
- Add wsl.nativeSystemd = true;
- Add networking.hostName, and set it to your Windows 11 “Device name.” You can find this in the Windows Settings app under System > About.

Add /etc/nixos/flake.nix as root with contents like the following. Replace <host-name> with your actual host name from configuration.nix.

{

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-22.11";
    NixOS-WSL = {
      url = "github:nix-community/NixOS-WSL";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { self, nixpkgs, NixOS-WSL }: {
    nixosConfigurations."<host-name>" = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        { nix.registry.nixpkgs.flake = nixpkgs; }
        ./configuration.nix
        NixOS-WSL.nixosModules.wsl
      ];
    };
  };

}

Run sudo nixos-rebuild switch
exit out of NixOS, then run wsl --shutdown followed by wsl -d NixOS. You should be logged in as the new default user.
At this point you should have a stable base to make any configuration changes you’d like.

Step 4: Cleaning up

Rename wsl.automountPath to wsl.wslConf.automount.root in configuration.nix to match NixOS-WSL’s latest configuration.
Delete the now unused /etc/nixos/nixos-wsl directory.
Delete /home/nixos since you’ve changed your username.
You can run sudo nix-channel --remove nixos if you don’t want the channel hanging around now that we’re using flakes.

Addendum: Share `.ssh` directory with Windows

It turns out that file permissions set in WSL are preserved in NTFS^{2-->. You can store your SSH
configuration files in Windows, and still use them from WSL with no permissions issues:}

Set up your ~/.ssh in NixOS like normal.
Move your ~/.ssh directory to Windows with mv ~/.ssh /mnt/c/Users/<your Windows username>/.ssh
Soft link it back to your WSL VM with ln -s /mnt/c/Users/<your Windows username>/.ssh/ ~/.ssh

That’s it! You can verify that permissions carried over with ls -al ~/.ssh/

Addendum: Set up fish in NixOS the right way

I use fish as my shell, but when I set it up in WSL I started getting errors like this:

fish: Unknown command: ls
/nix/store/lkf5vmavnxa0s37imb03gv7hs6dh5pll-fish-3.5.1/share/fish/functions/ls.fish (line 64):
    command $__fish_ls_command $__fish_ls_color_opt $opt $argv
    ^
in function 'ls'

Uh oh. Obviously, there are important directories missing from my path. It turns out that I was missing some configuration^3-->:

programs.fish.enable = true;

I don’t know why this issue only appeared in WSL, but fish users should probably set programs.fish.enable in NixOS whether the issue appears or not.