A nix configuration to build a custom NixOS image for aarch64 devices (Raspberry Pis, etc).
To build on NixOS, add boot.binfmt.emulatedSystems = [ "aarch64-linux" ]; to your host configuration and sudo nixos-rebuild test to enable building of aarch64 images on a non-aarch64 host.
Place the configuration for the system into the nixos directoy and then run the ./build_image.sh script. The nixos directory is used to setup the image and is included into the image as /etc/nixos/.
There is a flaw where the files in /etc/nixos are removed when nixos-rebuild is run on the built image. I worked around this by copying the config out and copying it back in after the rebuild.
sudo cp -rp /etc/nixos ~/nixos
sudo nixos-rebuild switch
sudo cp -rp ~/nixos /etc/nixos