Automated Ubuntu Installation

Ubuntu supports major version upgrades using the do-release-upgrade utility, but in my experience this is not a reliable means of updating the operating system. Automating installation facilitates testing and iterative design of systems configuration.

Although Ubuntu is a derivative of Debian, it doesn't follow the same conventions for an automated install.

x86_64 hardware and hypervisors usually don't provide a means of picking a one-time boot device. To force a reinstall wipe the first part of the disk.

# reinstall
# use with caution!
dd if=/dev/zero of=/dev/sda bs=1M count=100
reboot

BIOS PXE Boot

The initial ramdisk and kernel can be taken from the install ISO

mkdir -p /tftpboot/ubuntu22
cp casper/{vmlinuz,initrd} /tftpboot/ubuntu22/

# /tftpboot/pxelinux.cfg/01-00-0c-29-f9-6d-4e
DEFAULT menu.c32
PROMPT 0
TIMEOUT 10
MENU TITLE PXE Menu
LABEL Install Ubuntu 22 Server
  KERNEL ubuntu22/vmlinuz
  APPEND initrd=ubuntu22/initrd ip=dhcp cloud-config-url=/dev/null url=http://192.168.2.20/ubuntu-22.04.1-live-server-amd64.iso autoinstall ds=nocloud-net;s=http://192.168.2.20/ubuntu-srv/

Setting cloud-config-url is not required, but avoids a redundant fetch of the install image.

iPXE Loader

If the machine is booting with UEFI and iPXE the configuration is similar

#!ipxe
set base-url http://192.168.2.20/pub
kernel /ubuntu20/vmlinuz initrd=initrd ip=dhcp cloud-config-url=/dev/null url=http://192.168.2.20/ubuntu-20.04.5-live-server-amd64.iso autoinstall ds=nocloud-net;s=http://192.168.2.20/ubuntu-srv/
initrd /ubuntu20/initrd
boot

Server Config

Create two empty files

touch /var/www/htdocs/meta-data
touch /var/www/htdocs/vendor-data

As well as a file called user-data

#cloud-config
autoinstall:
  version: 1
  package_update: false
  package_upgrade: false
  identity:
    hostname: ubuntu-srv
    password: $crypted_pass
    username: ubuntu
  locale: en_US.UTF-8
  ssh:
    allow-pw: false
    authorized-keys: ['ssh-ed25519 ...']
    install-server: true
  packages:
    - net-tools
    - tmux
  user-data:
    timezone: America/New_York
  storage:
    layout:
      name: direct
      match:
        size: smallest
  late-commands:
    - |
      awk -F= '/HOSTNAME/ { print $2 }' /var/run/systemd/netif/leases/? > /target/etc/hostname
    - |
      echo 'eradman ALL=(ALL) NOPASSWD:ALL' > /target/etc/sudoers.d/ubuntu-nopw
      chmod 440 /target/etc/sudoers.d/ubuntu-nopw

Notes

#cloud-config is a YAML comment, but seems to be required! The installer will not report the cause of the failure if it is omitted.
hostname is required, and unfortunately cannot be set using DHCP option host-name. To work around this we use awk to find the hostname in the DHCP leases file at the end of the installation.
To break out of the installer and debug commands using a shell add false or return 1 at the end of early-commands: or late-commands.
Disable package updates to reduce install time. This is useful if the install needs to be repeated several times while debug the configuration.
Select the disk to install on. Selectors include model, vendor, path, id_path, devpath, serial, ssd, and size.

Minimal Workstation

#cloud-config
autoinstall:
  version: 1
  package_update: false
  package_upgrade: false
  identity:
    hostname: ubuntu-wks
    password: $crypted_pass
    username: ubuntu
  locale: en_US.UTF-8
  ssh:
    allow-pw: false
    authorized-keys: ['ssh-ed25519 ...']
    install-server: true
  user-data:
    timezone: America/New_York
  storage:
    layout:
      name: direct
      match:
        size: smallest
  packages:
    - adwaita-icon-theme-full
    - efibootmgr
    - gnome-control-center
    - gnome-session
    - gnome-shell-extension-ubuntu-dock
    - gnome-shell-extensions
    - gnome-terminal
    - nautilus
    - net-tools
  late-commands:
    - |
      awk -F= '/HOSTNAME/ { print $2 }' /var/run/systemd/netif/leases/? > /target/etc/hostname
    - |
      echo 'eradman ALL=(ALL) NOPASSWD:ALL' > /target/etc/sudoers.d/ubuntu-nopw
      chmod 440 /target/etc/sudoers.d/ubuntu-nopw
    - |
      /target/bin/efibootmgr | awk '/Boot.+ ubuntu/ { print substr($1, 5, 4) }' | xargs -n1 /target/bin/efibootmgr -o
      true

Notes

autoinstall will not set the boot order on UEFI systems. A manual workaround is to find the ubuntu label and make this item first in the boot list. Each item identifier is four hex digits.

Final Steps

After install, change critical: true to optional: true in /etc/netplan/50-cloud-init.yaml if the wired interface is no longer connected.

Ubuntu 20 may not use all available space. Expand the root volume using

lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv
resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv