How to netboot Ubuntu 24.04

The Ubuntu 24.04 (noble) images are not compatible with NBD boot out of the box due to some hilarious bureaucracy. However, thanks to changes in the image build procedure before 24.04’s release, it’s not particularly difficult to generate your own Ubuntu 24.04 image, complete with nbd-client pre-installed.

Pre-requisites

You will need to perform the following on a Raspberry Pi (or another machine with the arm64 architecture; image generation is not supported across architectures). You will need access to the root user on the image build system (building images requires the ability to mount file-systems).

Image generation requires quite a bit of space (at least double the uncompressed final image size), and involves a lot of I/O so a Raspberry Pi 5 with NVMe storage is ideal. The final Ubuntu Server 24.04 image is roughly 4GB in size, so you’ll need at least 8GB of space available (preferably quite a bit more). If you want to work on the Ubuntu Desktop image, this is roughly 9GB in size (so you’ll need at least 18GB of space available), but this guide will only cover the server image.

Install the ubuntu-image snap, with classic confinement.

$ sudo snap install ubuntu-image --classic

Clone the image definition repository, and switch to the noble (24.04) branch.

$ git clone https://git.launchpad.net/ubuntu-images
$ cd ubuntu-images
$ git checkout noble

Modifications

The definition for Ubuntu for Raspberry Pi images is a relatively simple YAML based format.

ubuntu-server-pi-arm64.yaml: The Ubuntu Server for Raspberry Pi defintion
ubuntu-pi-arm64.yaml: The Ubuntu Desktop for Raspberry Pi definition.

Open the ubuntu-server-pi-arm64.yaml file in your favourite text editor, and insert the highlighted lines below at the location shown:

name: ubuntu-server-raspi-arm64
display-name: Ubuntu Server Raspberry Pi arm64
revision: 2
architecture: arm64
series: noble
class: preinstalled
kernel: linux-image-raspi
gadget:
  url: "https://git.launchpad.net/snap-pi"
  branch: "classic"
  type: "git"
rootfs:
  archive: ubuntu
  components:
    - main
    - restricted
    - universe
    - multiverse
  mirror: "http://ports.ubuntu.com/ubuntu-ports/"
  sources-list-deb822: true
  pocket: updates
  seed:
    urls:
      - "git://git.launchpad.net/~ubuntu-core-dev/ubuntu-seeds/+git/"
    branch: noble
    names:
      - server
      - server-raspi
      - raspi-common
      - minimal
      - standard
      - cloud-image
      - supported-raspi-common
customization:
  extra-snaps:
    - name: snapd
  extra-packages:
    - name: nbd-client
  fstab:
    - label: "writable"
      mountpoint: "/"
      filesystem-type: "ext4"
      dump: false
      fsck-order: 1
    - label: "system-boot"
      mountpoint: "/boot/firmware"
      filesystem-type: "vfat"
      mount-options: "defaults"
      dump: false
      fsck-order: 1
artifacts:
  img:
    - name: ubuntu-24.04-preinstalled-server-arm64+raspi.img
  manifest:
    name: ubuntu-24.04-preinstalled-server-arm64+raspi.manifest

Note

If you wish to perform this procedure on the desktop image definition, the same lines need adding.

Build

After saving the modified YAML, exit your editor and run the build process:

$ mkdir build
$ sudo ubuntu-image classic -v --output-dir build/ ubuntu-server-pi-arm64.yaml

After some time, you should wind up with a couple of files under the “build” directory:

build/ubuntu-24.04-preinstalled-server-arm64+raspi.img: This is the uncompressed image which you use directly with your NBD setup
build/ubuntu-24.04-preinstalled-server-arm64+raspi.manifest: This is the manifest file containing a list of every package (and package version) included in the image