nixpkgs.flake.setFlakeRegistry

Whether to pin nixpkgs in the system-wide flake registry (/etc/nix/registry.json) to the store path of the sources of nixpkgs used to build the NixOS system.

This is on by default for NixOS configurations built with flakes.

This option makes nix run nixpkgs#hello reuse dependencies from the system, avoid refetching nixpkgs, and have a consistent result every time.

Note that this option makes the NixOS closure depend on the nixpkgs sources, which may add undesired closure size if the system will not have any nix commands run on it.