$ nix-build -A extra-utils /nix/store/8prawwsnvkjmfgwmc9diyxmhncpf79ks-extra-utils
extra-utils is a derivation packaging busybox, dhcpd, and their required libraries. They are modified using
patchelf so the content of the derivation is self-sufficient.
It is packaged with the stage-1 init script to create the initrd; it is everything the stage-1 init script can use to do its job.