configuration.nix

TLDR

Edit system configuration

$ sudo nano /etc/nixos/configuration.nix

Rebuild system after changes

$ sudo nixos-rebuild switch

Test configuration without making it default

$ sudo nixos-rebuild test

Build but don't activate

$ sudo nixos-rebuild build

Rollback to previous generation

$ sudo nixos-rebuild switch --rollback

Check configuration syntax

$ nix-instantiate --parse /etc/nixos/configuration.nix

configuration.nix is the main system configuration file for NixOS, a Linux distribution built on the Nix package manager. It declaratively defines the entire system state: installed packages, enabled services, user accounts, and system settings.
The file uses the Nix expression language to describe system configuration. Changes are applied atomically via nixos-rebuild, which builds a new system generation that can be activated immediately or on next boot.
NixOS stores previous configurations as generations, enabling easy rollback to any prior state. This approach ensures reproducible system configurations that can be version-controlled and shared.

COMMON OPTIONS

boot.loader.systemd-boot.enable

Enable systemd-boot bootloader.

networking.hostName

Set system hostname.

time.timeZone

Set system timezone.

users.users.<name>

Define user accounts.

environment.systemPackages

List of system-wide packages.

services.<name>.enable

Enable system services.

programs.<name>.enable

Enable system programs.

nixpkgs.config.allowUnfree

Allow proprietary packages.

EXAMPLE

$ { config, pkgs, ... }:
{
  boot.loader.systemd-boot.enable = true;
  networking.hostName = "myhost";
  time.timeZone = "America/New_York";

  users.users.alice = {
    isNormalUser = true;
    extraGroups = [ "wheel" ];
  };

  environment.systemPackages = with pkgs; [
    vim git firefox
  ];

  services.openssh.enable = true;
}

CAVEATS

Syntax errors prevent system rebuild; always test with nixos-rebuild test first. The Nix language has a learning curve. Some proprietary software requires explicit allowUnfree setting. Large configuration changes may require significant download and build time.

HISTORY

NixOS was created by Eelco Dolstra based on his PhD research on the Nix package manager, with the first release in 2003. The declarative configuration model was revolutionary, treating system configuration as code that produces reproducible results. NixOS has gained popularity in DevOps and development environments where reproducibility is valued.

configuration.nix

TLDR

SYNOPSIS

DESCRIPTION

COMMON OPTIONS

EXAMPLE

CAVEATS

HISTORY

SEE ALSO