# nixos-rebuild switch
building Nix...
building the system configuration...
error: anonymous function at /nix/store/w631bj96k7pnxqpp3zf8hhi0wdgdxd8g-nixos-unstable-18.09pre147850.2428f5dda13/nixos-unstable/pkgs/top-level/default.nix:20:1 called with unexpected argument 'allowUnfree', at /nix/store/w631bj96k7pnxqpp3zf8hhi0wdgdxd8g-nixos-unstable-18.09pre147850.2428f5dda13/nixos-unstable/pkgs/top-level/impure.nix:82:1
(use '--show-trace' to show detailed location information)