Dynamic Hostnames from DHCP in Autoinstall

In the user_data autoinstall I have being served via tftp, the hostname field is required. I'm using statically mapped dhcp entries to match machine to hostname, ip, etc.

How can I get the autoinstall hostname to accept the value from dhcp on pxe boot?

Thanks

I do not believe there is any way to make subiquity use the hostname in the DHCP offer. However, there are a number of ways that early-commands and late-commands could be used to do what you want.

My suggested solution is a user-data autoinstall file similar to this snippet. It will read the hostname in the DHCP offer from the DHCP lease file and overwrite /etc/hostname on the installed system.

#cloud-config
autoinstall:
  # NO identity section
  #identity:
  user-data:
    users:
    - name: ubuntu
      passwd: REDACTED
      shell: /bin/bash
      lock-passwd: false
      sudo: ALL=(ALL) NOPASSWD:ALL
      groups: users
  late-commands:
    - |
      bash <<'EOF'
        source <(cat /run/systemd/netif/leases/* | grep ^HOSTNAME=)
        [[ -n "${HOSTNAME}" ]] && echo "${HOSTNAME}" > /target/etc/hostname
      EOF
      true

These are some gotchas to watch out for no matter what approach you try.

• The autoinstall identity and user-data sections do not co-exist well. My preference is to use a user-data section and to not include an identity section. Because the only provided way to configure the hostname is the identity section another method must be used to configure the hostname (e.g. late-commands).
• If there is no identity section then subiquity changes behavior. The generated cloud-init configuration (in /target/etc/cloud/cloud.cfg.d/99-installer.cfg) will be different. There will be no /target/etc/hosts content generated and the file will be left empty. There are potentially other differences.
• Conversely, if there is an identity section then the provided hostname will be configured in multiple files. In /target/etc/hosts and potentially others.

see also

• Cloud-config-auto install (late comands random hostname + netwrok config)
• How can I run complex piped commands in Autoinstall / Cloud-Init?
• Ubuntu Server 20.04 cloud-config adding user does nothing

notes

• I tested using Ubuntu 22.04 (subiquity 22.04.2).