nichts/modules/system/system.mod.nix

{ config, ... }:
let
  machine-id = builtins.substring 0 32 (builtins.hashString "sha256" config.networking.hostName);
in
{
  system = {
    # My state version.
    stateVersion = "23.11";
  };
  environment.etc."machine-id".text = "${machine-id}\n";
}