E.g. to install "hello" from the latest Nixpkgs: $ nix-build '<nixpkgs>' -A hello -I nixpkgs=https://nixos.org/channels/nixpkgs-unstable/nixexprs.tar.xz Or to install a specific version of NixOS: $ nixos-rebuild switch -I nixpkgs=63def04891.tar.gz
63def04891