Ubuntu 22.04 server installer doesn't boot on Xen server as domU in PVH mode

[Neil du Preez]

The Xen server I am working on has Debian 12 as dom0. As mentioned in the summary I am trying to install Ubuntu 22.04 server as a domU in PVH mode.

I tested using ubuntu-22.04.4-live-server-amd64.iso.

This is the domU configuration I used. It attempts to use PVHGRUB:

  name = "ubuntu-2204"
  memory = 1024
  maxmem = 1024
  vcpus = 1
  vif = [ 'bridge=xenbr0' ]
  disk = [ '/root/ubuntu-22.04.4-live-server-amd64.iso,raw,xvdg,r,cdrom', '/dev/myvg/ubuntu-2204-root,raw,xvda,rw', '/dev/myvg/ubuntu-2204-swap,raw,xvdb,rw' ]
  type = "pvh"
  kernel = "/usr/lib/grub-xen/grub-i386-xen_pvh.bin"

I can see the grub menu, and I edit the first entry (Try or install Ubuntu) by appending "console=hvc0 nosplash" to the end of the kernel commandline.

I can then see console output scrolling past, until this point:

  Begin: Running /scripts/init-premount ... done.
  Begin: Mounting root file system ... Begin: Running /scripts/nfs-top ... done.
  Begin: Running /scripts/nfs-premount ... done.
  Begin: Running /scripts/casper-premount ... done.
  done.
  Unable to find a medium containing a live file system
  Attempt interactive netboot from a URL?
  yes no (default yes): no

  BusyBox v1.30.1 (Ubuntu 1:1.30.1-7ubuntu3) built-in shell (ash)
  Enter 'help' for a list of built-in commands.

  (initramfs) Unable to find a medium containing a live file system

I then destroyed the domU and tried the following domU config in PV mode instead. The kernel and ramdisk were extracted from the ISO:

  name = "ubuntu-2204"
  memory = 1024
  maxmem = 1024
  vcpus = 1
  vif = [ 'bridge=xenbr0' ]
  disk = [ '/root/ubuntu-22.04.4-live-server-amd64.iso,raw,xvdg,r,cdrom', '/dev/myvg/ubuntu-2204-root,raw,xvda,rw', '/dev/myvg/ubuntu-2204-swap,raw,xvdb,rw' ]
  type = "pv"
  kernel = "/root/ubuntu-2204-vmlinuz"
  ramdisk = "/root/ubuntu-2204-initrd"
  extra = "console=hvc0 nosplash"

The above config allows me to install the OS successfully over the serial console using the standard server installer. After installation is complete, I can boot the newly installed VM with PVHGRUB in PVH mode using this config:

  name = "ubuntu-2204"
  memory = 1024
  maxmem = 1024
  vcpus = 1
  vif = [ 'bridge=xenbr0' ]
  disk = [ '/dev/myvg/ubuntu-2204-root,raw,xvda,rw', '/dev/myvg/ubuntu-2204-swap,raw,xvdb,rw' ]
  type = "pvh"
  kernel = "/usr/lib/grub-xen/grub-i386-xen_pvh.bin"

I expected to be able to install the Ubuntu 22.04 domU in PVH mode with PVHGRUB.

Instead I had to install the Ubuntu 22.04 domU in PV mode as described above. It was only after successful installation in PV mode, that I could boot the installed domU in PVH mode.

[Robie Basak (racb)]

Thank you for taking the time to report this bug and helping to make Ubuntu better.

It isn't obvious to me what Ubuntu might be "doing wrong", if anything, that is causing this issue. Xen in Ubuntu is in our universe component and community-supported only. Therefore I don't expect this bug to make progress unless/until someone can volunteer an investigation and describe what exactly Ubuntu needs to change. If you could help with that, please do!

[Neil du Preez (technopunk)]

Thank you for your reply.

My main goal was to raise awareness since it wasn't clear to me whether anyone was aware of this issue. As I mentioned previously, it would be great to be able to install in PVH mode since it is "the best" mode currently available as I understand it based on this page:

https://wiki.xenproject.org/wiki/Understanding_the_Virtualization_Spectrum

I have (subsequently to submitting this report) encountered similar behaviour with a Debian 12 installer, so it is not Ubuntu-specific.

Unfortunately I don't have time to dig much deeper into this, and the workaround I mentioned works well. I have / will mention it again on Debian channels as well.