NixOS

Declarative, reproducible, and fundamentally different.

Overview

Why NixOS?

• Declarative configuration - Your entire system is defined in one file. Rebuild it identically on any machine.
• Atomic upgrades and rollbacks - Updates either fully succeed or don't happen at all. Roll back to any previous state from the bootloader.
• Reproducible builds - Same inputs always produce the same outputs. Eliminates "works on my machine."
• 80,000+ packages - Nixpkgs is one of the largest and most up-to-date package repositories
• Dev environments - nix develop and nix shell create isolated, reproducible development environments
• No dependency conflicts - Every package version is stored in its own path in /nix/store/

How NixOS Works

Unlike traditional distros where you install packages imperatively, NixOS is configured declaratively. You edit /etc/nixos/configuration.nix to describe what your system should look like, then rebuild.

Example configuration.nix

{ config, pkgs, ... }:
{
  # Bootloader
  boot.loader.systemd-boot.enable = true;
  boot.loader.efi.canTouchEfiVariables = true;

  # Networking
  networking.hostName = "my-nixos";
  networking.networkmanager.enable = true;

  # Timezone and locale
  time.timeZone = "America/New_York";
  i18n.defaultLocale = "en_US.UTF-8";

  # Desktop environment
  services.xserver.enable = true;
  services.xserver.displayManager.gdm.enable = true;
  services.xserver.desktopManager.gnome.enable = true;

  # Audio
  services.pipewire = {
    enable = true;
    alsa.enable = true;
    pulse.enable = true;
  };

  # Users
  users.users.myuser = {
    isNormalUser = true;
    extraGroups = [ "wheel" "networkmanager" "docker" ];
  };

  # System packages
  environment.systemPackages = with pkgs; [
    vim
    neovim
    git
    curl
    wget
    firefox
    htop
    tmux
  ];

  # Enable Docker
  virtualisation.docker.enable = true;

  # Enable SSH
  services.openssh.enable = true;

  # Firewall
  networking.firewall.enable = true;
  networking.firewall.allowedTCPPorts = [ 22 80 443 ];

  system.stateVersion = "24.05";
}

Applying changes

# Edit your configuration
sudo nano /etc/nixos/configuration.nix

# Rebuild and switch to new configuration
sudo nixos-rebuild switch

# Rebuild but don't switch yet (test first)
sudo nixos-rebuild test

# Build and add to bootloader without switching
sudo nixos-rebuild boot

# Roll back to previous generation
sudo nixos-rebuild switch --rollback

# List all generations
nix-env --list-generations --profile /nix/var/nix/profiles/system

Nix Package Manager Commands

# Search for a package
nix search nixpkgs firefox

# Run a package without installing
nix run nixpkgs#cowsay -- "Hello"

# Open a shell with temporary packages
nix shell nixpkgs#python3 nixpkgs#nodejs

# Create a development environment (from a flake)
nix develop

# Garbage collect old generations
sudo nix-collect-garbage -d

# Optimize the Nix store
sudo nix store optimise

Flakes (Modern Nix)

Flakes are the modern way to manage Nix projects. They provide reproducible, hermetic builds with a lock file.

# Enable flakes (add to configuration.nix)
nix.settings.experimental-features = [ "nix-command" "flakes" ];

# Initialize a flake in a project
nix flake init

# A flake.nix for a dev environment:
{
  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";

  outputs = { self, nixpkgs }: {
    devShells.x86_64-linux.default =
      nixpkgs.legacyPackages.x86_64-linux.mkShell {
        packages = with nixpkgs.legacyPackages.x86_64-linux; [
          nodejs
          python3
          postgresql
        ];
      };
  };
}

# Enter the dev environment
nix develop

Home Manager

Home Manager lets you declaratively manage your user environment (dotfiles, user packages, shell config) with the same Nix approach.

# In your Home Manager config:
programs.git = {
  enable = true;
  userName = "Your Name";
  userEmail = "your@email.com";
};

programs.neovim = {
  enable = true;
  defaultEditor = true;
};

programs.zsh = {
  enable = true;
  shellAliases = {
    ll = "ls -la";
    update = "sudo nixos-rebuild switch";
  };
};

Tips

• Start with the NixOS manual and the Nix Pills tutorial series
• Use nixos-unstable channel if you want the latest packages
• Learn Flakes from the start - they're the future of Nix
• Use Home Manager to manage your dotfiles declaratively
• The learning curve is steep, but the payoff is enormous for reproducibility
• You can use Nix without NixOS - install the package manager on Ubuntu, Fedora, macOS, etc.
• Join the NixOS Discourse and Matrix channels - the community is helpful