Building a NixOS SD image for a Raspberry Pi Zero 2 w

1. Update zero2w.nix

In particular, don't forget:

• to configure your wifi
• to add an admin user able to connect through ssh

2. Build the image This builds a full linux kernel and can take multiple hours. Subsequent builds will be faster because the package artifacts will be cached. From an x86_64-linux host machine, run:

nix build -L .#nixosConfigurations.x86_64-linux.zero2w.config.system.build.sdImage

From an aarch64 host machine, run:

nix build -L .#nixosConfigurations.aarch64-linux.zero2w.config.system.build.sdImage

3. Copy the image in your sd card

DEVICE=/dev/disk5 # Whatever your sd card reader is
sudo dd if=result/sd-image/zero2.img of=$DEVICE bs=1M conv=fsync status=progress

4. Boot your Zero
5. Get your IP

ifconfig wlan0

6. From another machine, rebuild the system:

ZERO2_IP=<the-zero2-ip>
SSH_USER=<the-admin-user-in-the-pi>
nix run github:serokell/deploy-rs .#zero2w -- --ssh-user $SSH_USER --hostname $ZERO2_IP

Notes

• The Zero 2 doesn't have enough RAM to build itself. An initial lead was to create a swap partition, but it turns out it was a bad idea, as it would have decreased the sd card lifetime (sd cards don't like many write operations). A zram swap is not big enough to work. Hence the use of deploy-rs.
  • Note that nixos-rebuild --target-host would work instead of using deploy-rs. but as nixos-rebuild is not available on Darwin, I'm using deploy-rs that works both on NixOS and Darwin.
• I still couldn't find a way to use boot.kernelPackages = pkgs.linuxKernel.packages.linux_rpi3.
• the sdImage.extraFirmwareConfig option is not ideal as it cannot update config.txt after it is created in the sd image.
• An overlay in the hardware.deviceTree has activated the i2c bus. This means that the i2c-tools are now working!

See also

• this issue
• this gist