wordhord
title::From Arch to NixOS
published::2022-07-18
time::5 mins
tags::[ Nix ]

I've found my Arch Linux installations tend to be an accumulation of packages, quick-fixes and hacks that weigh like a nightmare on my brain. This is normally not the world's biggest deal, except when I decide to try and trim down my installed packages and have to try and recall why I installed X specific package 4 years ago.

It becomes more of a problem when I move between jobs (or just machines within a job) and I'm suddenly confronted with a blank slate that I, yet again, have to hammer and quick-fix back into the idiosyncratic shape that I like.

A few years ago, I turned to tools like Ansible to help define what shape I want my machine to be in a declarative way. This works to some extent - except that I am lazy. If I have to use a quick-fix or install a package and the choice is either:

  1. Install the quick-fix/package
  2. Install the quick-fix/package to make sure it works, then encode it in an Ansible script

then I will tend to choose number 1, or more accurately just entirely forget about number 2. My Ansible definitions ended up being an outdated subset of the configuration of my machine, a kind of configuration drift familiar to anyone who has to work with IaC tooling without a regular CI/CD pipeline to enforce it.

A few years ago, on the back of learning Haskell more seriously, I encountered Nix. Frustrated with "works-on-my-machine" build processes at work with lots of hidden or implicit dependencies that I had to figure out in order to automate them, I was quite attracted to Nix's promise about reproducible builds. Nix is essentially is a language/toolset to define the packaging of a piece of software, which Nix calls a 'derivation'. Derivations are made up of the specific versioned inputs needed to build a piece of software - not just the source code, but build dependency tools, packages stuff like that. These derivations are then built with environments where the only things allowed into the build environments are the inputs you've specified (which is why these environments also have no network access).

When learning Nix you quickly come across NixOS, a Linux flavour based around the Nix package manager. It extends the declarative focus of Nix to the system itself, letting me define my system as a Nix expression:


  hardware.pulseaudio.enable = true;

  hardware.bluetooth = {
    enable = true;
    powerOnBoot = pkgs.lib.mkForce false;
  };

  networking.networkmanager.enable = true;

  time.timeZone = "Europe/Berlin";
  i18n.defaultLocale = "en_GB.UTF-8";

  services.xserver = {
    layout = "us";
    xkbVariant = "";
    enable = true;
    displayManager = {
      lightdm.enable = true;
      defaultSession = "none+i3";
    };
    windowManager.i3.enable = true;

    libinput.enable = true;
  };

  virtualisation.podman = {
    enable = true;
    dockerCompat = true;
  };

  users.users.mika = {
    isNormalUser = true;
    description = "Mika Naylor";
    extraGroups = [ "networkmanager" "wheel" "audio" "video" ];
    shell = pkgs.zsh;
  };

The crucial thing about this is that this isn't an extra layer of management on top of regular methods of changing my system - with NixOS you're more or less forced to define the system declaratively in order to induce change at all. I appreciate that this distinction forces me to actually document the changes I make to my system, the reasons I made it (in the git commit), and gives me the ability to rebuild the system again if I need to.

Using Home Manager has let me even bundle my previously ad-hoc dotfile management system into the same Nix expression format. For example, my zsh configuration now looks like:


{
  home.packages = with pkgs; [ pure-prompt ];

  programs.zsh = {
    enable = true;
    dotDir = ".config/zsh";
    enableSyntaxHighlighting = true;
    shellAliases = {
      ll = "ls -l";
      g = "git";
    };
    history = {
      size = 10000;
      path = "$HOME/.zsh_history";
      ignoreSpace = true;
    };
    initExtra = "
      autoload -U promptinit; promptinit
      PURE_PROMPT_SYMBOL="λ"
      prompt pure
    ";
    oh-my-zsh = {
      enable = true;
      plugins = [ "ssh-agent" "git" ];
    };
  };
}

Although I'm worried that converting all my dotfiles into this very specific language/form has a risk of lock-in, having everything defined the same way in the same language does tickle some part of my monkey brain.

A downside of Nix/NixOS is that learning it can be quite hard. The community points to the manuals as the resource for learning, but they often read like you need to already understand the thing they're talking about for them to make sense. If I wasn't already familiar with some FP concepts, I think I would have been totally lost. The way I've mostly learned Nix/NixOS has been from spelunking around people's Nix expressions on Github, which carries the risk of accidentally picking up bad practices or code smells.

I've only been using NixOS full time for a couple months but I'm already quite taken with it, especially for a work/development machine. The way NixOS works makes me feel like I have to be fairly principled about the definition of my machine - I don't do the same thing I did on Arch of installing a package to try it out and then forgetting that it's on my system for 3 years. With Nix I can try stuff out with nix-shell and if I don't decide to make it part of my system, the binaries get cleaned out on the next nix garbage collection. I'm still keeping Arch on my personal machine mostly out of pure inertia, but also because I'm a little scared about getting Steam and all the associated drivers working.

My new, fancy, enflakened NixOS files now live on the main branch of my Antimber repo. I've not run into any blocking problems with it yet as my daily driver, and picking it up has definitely helped give me the confidence to convert my projects' existing build processes to Nix Flakes. I'll check back in 6-12 months down the line to see if I still feel the same way.