If set, the pkgs argument to all NixOS modules is the value of this option, extended with nixpkgs.overlays, if that is also set. Either nixpkgs.crossSystem or nixpkgs.localSystem will be used in an assertion to check that the NixOS and Nixpkgs architectures match. Any other options in nixpkgs.*, notably config, will be ignored.
If unset, the pkgs argument to all NixOS modules is determined as shown in the default value for this option.
The default value imports the Nixpkgs source files relative to the location of this NixOS module, because NixOS and Nixpkgs are distributed together for consistency, so the nixos in the default value is in fact a relative path. The config, overlays, localSystem, and crossSystem come from this option's siblings.
This option can be used by applications like NixOps to increase the performance of evaluation, or to create packages that depend on a container that should be built with the exact same evaluation of Nixpkgs, for example. Applications like this should set their default value using lib.mkDefault, so user-provided configuration can override it without using lib.
Note that using a distinct version of Nixpkgs with NixOS may be an unexpected source of problems. Use this option with care.
An evaluation of Nixpkgs; the top level attribute set of packagesimport "${nixos}/.." {
inherit (cfg) config overlays localSystem crossSystem;
}
import <nixpkgs> {}</nixpkgs>