Adding Custom Packages It’s possible that a package you need is not available in NixOS. In that case, you can do two things. First, you can clone the Nixpkgs repository, add the package to your clone, and (optionally) submit a patch or pull request to have it accepted into the main Nixpkgs repository. This is described in detail in the Nixpkgs manual. In short, you clone Nixpkgs: $ git clone git://github.com/NixOS/nixpkgs.git $ cd nixpkgs Then you write and test the package as described in the Nixpkgs manual. Finally, you add it to environment.systemPackages, e.g. environment.systemPackages = [ pkgs.my-package ]; and you run nixos-rebuild, specifying your own Nixpkgs tree: # nixos-rebuild switch -I nixpkgs=/path/to/my/nixpkgs The second possibility is to add the package outside of the Nixpkgs tree. For instance, here is how you specify a build of the GNU Hello package directly in configuration.nix: environment.systemPackages = let my-hello = with pkgs; stdenv.mkDerivation rec { name = "hello-2.8"; src = fetchurl { url = "mirror://gnu/hello/${name}.tar.gz"; sha256 = "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6"; }; }; in [ my-hello ]; Of course, you can also move the definition of my-hello into a separate Nix expression, e.g. environment.systemPackages = [ (import ./my-hello.nix) ]; where my-hello.nix contains: with import <nixpkgs> {}; # bring all of Nixpkgs into scope stdenv.mkDerivation rec { name = "hello-2.8"; src = fetchurl { url = "mirror://gnu/hello/${name}.tar.gz"; sha256 = "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6"; }; } This allows testing the package easily: $ nix-build my-hello.nix $ ./result/bin/hello Hello, world!