Server – Automated 20.04 Server Installation Using PXE and Live Server Image


How to do an fully automated Ubuntu 20.04 Server install using PXE and the live server image?


With the 20.04 release, it seems clear Ubuntu is further pushing the live server installer (subiquity) option. The debian-installer (d-i) image has been renamed legacy. So has the netboot installer I typically prefer. The 20.04 release also introduces a new automated installation option for the live server installer.

Best Answer

Fully Automated Ubuntu 20.04 server install using PXE

These are steps to do a fully automated Ubuntu 20.04 Server install using PXE with the live server image. I found the process to be lightly documented and filled with issues. In these steps I am installing 20.04 on a UEFI based server.

(edit: I adapted these steps for a BIOS based server at Deploy Ubuntu 20.04 on bare metal or virtualbox VM by pxelinux, cloud-init doesn't pick up user-data file )

There are many variations to these steps possible. They can be customized and tailored to suit one's needs. The goal is to provide one example of how to accomplish this and to help other users overcome the issues encountered.

links about the installer

config references

source code

Build a tftp server

All the following steps are run as root. These were tested on an Ubuntu 18.04 server.

Install the tftp server and a web server

apt-get -y install tftpd-hpa apache2

Configure apache to serve files from the tftp directory

cat > /etc/apache2/conf-available/tftp.conf <<EOF
<Directory /var/lib/tftpboot>
        Options +FollowSymLinks +Indexes
        Require all granted
Alias /tftp /var/lib/tftpboot
a2enconf tftp
systemctl restart apache2

Download the live server iso

wget -O /var/lib/tftpboot/ubuntu-20.04-live-server-amd64.iso

Extract the kernel and initramfs from the live server iso

mount /var/lib/tftpboot/ubuntu-20.04-live-server-amd64.iso /mnt/
cp /mnt/casper/vmlinuz /var/lib/tftpboot/
cp /mnt/casper/initrd /var/lib/tftpboot/
umount  /mnt

Download the grub image to load via PXE

wget -O /var/lib/tftpboot/pxelinux.0

Configure grub. This configuration will provide a fully automated boot option as well as a manual boot option

mkdir -p /var/lib/tftpboot/grub
cat > /var/lib/tftpboot/grub/grub.cfg <<'EOF'
menuentry "Focal Live Installer - automated" --id=autoinstall {
    echo "Loading Kernel..."
    # make sure to escape the ';' or surround argument in quotes
    linux /vmlinuz ip=dhcp url=http://${pxe_default_server}/tftp/ubuntu-20.04-live-server-amd64.iso autoinstall ds="nocloud-net;s=http://${pxe_default_server}/tftp/" root=/dev/ram0 cloud-config-url=/dev/null
    echo "Loading Ram Disk..."
    initrd /initrd
menuentry "Focal Live Installer" --id=install {
    echo "Loading Kernel..."
    linux /vmlinuz ip=dhcp url=http://${pxe_default_server}/tftp/ubuntu-20.04-live-server-amd64.iso root=/dev/ram0 cloud-config-url=/dev/null
    echo "Loading Ram Disk..."
    initrd /initrd

Configure cloud-init with the autoinstall configuration. I first ran the install manually to get the generated /var/log/installer/autoinstall-user-data file to use as the basis. I then made modifications based on my needs and errors encountered.

cat > /var/lib/tftpboot/meta-data <<EOF
instance-id: focal-autoinstall
cat > /var/lib/tftpboot/user-data <<'EOF'
  version: 1
  # use interactive-sections to avoid an automatic reboot
  #  - locale
    # even set to no/false, geoip lookup still happens
    #geoip: no
    preserve_sources_list: false
    - arches: [amd64, i386]
    - arches: [default]
  # r00tme
  identity: {hostname: focal-autoinstall, password: $6$.c38i4RIqZeF4RtR$hRu2RFep/.6DziHLnRqGOEImb15JT2i.K/F9ojBkK/79zqY30Ll2/xx6QClQfdelLe.ZjpeVYfE8xBBcyLspa/,
    username: ubuntu}
  keyboard: {layout: us, variant: ''}
  locale: en_US.UTF-8
  # interface name will probably be different
      version: 2
          critical: true
          dhcp-identifier: mac
          dhcp4: true
    allow-pw: true
    authorized-keys: []
    install-server: true
  # this creates an efi partition, /boot partition, and root(/) lvm volume
      reorder_uefi: False
      size: 0
    - {ptable: gpt, path: /dev/sda, preserve: false, name: '', grub_device: false,
      type: disk, id: disk-sda}
    - {device: disk-sda, size: 536870912, wipe: superblock, flag: boot, number: 1,
      preserve: false, grub_device: true, type: partition, id: partition-sda1}
    - {fstype: fat32, volume: partition-sda1, preserve: false, type: format, id: format-2}
    - {device: disk-sda, size: 1073741824, wipe: superblock, flag: linux, number: 2,
      preserve: false, grub_device: false, type: partition, id: partition-sda2}
    - {fstype: ext4, volume: partition-sda2, preserve: false, type: format, id: format-0}
    - {device: disk-sda, size: -1, flag: linux, number: 3, preserve: false,
      grub_device: false, type: partition, id: partition-sda3}
    - name: vg-0
      devices: [partition-sda3]
      preserve: false
      type: lvm_volgroup
      id: lvm-volgroup-vg-0
    - {name: lv-root, volgroup: lvm-volgroup-vg-0, size: 100%, preserve: false,
      type: lvm_partition, id: lvm-partition-lv-root}
    - {fstype: ext4, volume: lvm-partition-lv-root, preserve: false, type: format,
      id: format-1}
    - {device: format-1, path: /, type: mount, id: mount-2}
    - {device: format-0, path: /boot, type: mount, id: mount-1}
    - {device: format-2, path: /boot/efi, type: mount, id: mount-3}
  # override the kernel package
  - path: /run/kernel-meta-package
    content: |
    owner: root:root
    permissions: "0644"
  # attempt to also use an answers file by providing a file at the default path.  It did not seem to have any effect
  #- path: /subiquity_config/answers.yaml
  #  content: |
  #    InstallProgress:
  #      reboot: no
  #  owner: root:root
  #  permissions: "0644"

Configure DHCP

Set the DHCP Options 66,67 according to the documentation for your DHCP server.

Boot your server

At this point, you should be able to boot your UEFI based server and perform a completely automatic install.

Errors encountered

  • The server being installed requires over 2 GB of RAM. I ended up creating a VM with 3 GB for testing. EDIT Using the cloud-config-url=/dev/null kernel argument will prevent cloud-init from unnecessarily downloading the iso, which reduces the memory required, reduces network traffic, and speeds up boot time.
  • The generated /var/log/installer/autoinstall-user-data file was broken in the following ways
    • There is no version property, which caused a validation failure. I added the property
    • The network section required another level of nesting. This bug is mentioned in the config reference
    • The preserve property on each item in storage config needed to be set to false. Otherwise curtin would not install on a blank disk
    • The keyboard property toggle was set to null, which caused a validation failure. I simply removed the property
  • When curtin installs on a UEFI device, it reorders the boot order so the current boot option is first in the list. The result is that network boot becomes the first option the next reboot. So when the install is done and the reboot happens... you end up in the PXE environment again instead of booting from disk. I found an undocumented curtin option reorder_uefi. Luckily, subiquity happens to pass this configuration to curtin
  • The apt config option geoip doesn't seem to work. There were always logs for geoip requests
  • Using human readable values for partition sizes (e.g. size: 512M) resulted in the size being stored as a float, leading to errors when sizing LVM volumes as a percentage. Avoiding human readable values seems to fix this

Other missing features

I didn't dig into these as much. They are based on what my preseed files would do. Most of them could probably be fixed with clever use of early-commands, late-commands, and cloud-init. I may have also missed something

  • A way to set the timezone
  • A way to set the root password
  • A way to configure an apt only proxy. I like to use apt-cacher-ng for apt, but it does not work as a general proxy. The installer assumes any proxy you configure is for everything
  • A way to pause at the end of the install instead of automatically rebooting. The workaround is to add a value to interactive-sections, but that results in 3 pauses
  • Allow direct curtin configuration. You have to create yaml for cloud-init to provide yaml to subiquity, which then generates yaml for curtin. It would provide more configuration flexibility to be able to provide the curtin yaml directly
  • Allow direct cloud-init configuration. You have to create yaml for cloud-init to provide yaml to subiquity, which then generates yaml for cloud-init on the installed machine. These files should be easy to modify with late-commands, but I did not try it
  • Ability to choose the kernel package. I found that the kernel image installed is based on what is written to /run/kernel-meta-package. This is hardcoded to linux-generic in the initramfs. I prefer to use the linux-virtual package for VMs. I was able to use the cloud-init configuration to overwrite the file

Edit 1

The resulting /target/var/lib/cloud/seed/nocloud-net/user-data file used by cloud-init during first boot. The replies indicate the lock-passwd property has a typo and may affect some users

growpart: {mode: 'off'}
locale: en_US.UTF-8
preserve_hostname: true
resize_rootfs: false
ssh_pwauth: true
- gecos: ubuntu
  groups: [adm, cdrom, dip, plugdev, lxd, sudo]
  lock-passwd: false
  name: ubuntu
  passwd: $6$.c38i4RIqZeF4RtR$hRu2RFep/.6DziHLnRqGOEImb15JT2i.K/F9ojBkK/79zqY30Ll2/xx6QClQfdelLe.ZjpeVYfE8xBBcyLspa/
  shell: /bin/bash