Unfree software

Unfree software refers to software that has restrictive licensing on modification and/or redistribution. These types of software cannot be freely provided or distributed in an official capacity, which means that they are neither built by Hydra, nor as they cached on the official binary cache. Despite this, Nixpkgs offers a very large collection of unfree software as derivations, however they cannot be used by default without configuring Nixpkgs and opting in to unfree software usage.

Configuring

For NixOS

NixOS offers a module that can configure Nixpkgs, which will retroactively change the pkgs across your configuration to use the new settings, including allowing for unfree packages.

{ config, lib, pkgs, ... }: {
  nixpkgs.config.allowUnfree = true; # Allows all packages that are marked unfree to be built.

  environment.systemPackages = with pkgs; [
    steam # No error!
  ];
}

You may instead configure this on a per-package basis via allowUnfreePredicate.

Note: Please note that this function has awkward semantics and occasionally doesn't work as expected. Issues like this should be raised directly in Nixpkgs.

{ config, lib, pkgs, ... }: {
  # Add packages by their "derivation name" here.
  # Find the derivation name from https://search.nixos.org/
  nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
    "steam"
  ];
}

For Nix CLI

As you may have noticed, the above configuration does not apply globally to your NixOS system (and is not applicable for non-NixOS users). Instead, you can configure Nixpkgs at a user level by writing your configuration in ~/.config/nixpkgs/config.nix.

Note: This file is ignored using nix3 commands, leaving you with the environment variable technique as the easiest resort.

~/.config/nixpkgs/config.nix

{
  allowUnfree = true;
}

You can alternatively set the environment variable NIXPKGS_ALLOW_UNFREE=1, which is automatically picked up by the Nix CLI. For newer nix3 commands, you will need to additionally pass --impure, otherwise the environment variable is ignored.

$ export NIXPKGS_ALLOW_UNFREE=1
$ nix-shell -p vscode --command 'code' # nix-legacy
$ nix run --impure nixpkgs#vscode # nix3

See also

• Nixpkgs manual on allowing unfree packages