[Bug 2060695] [NEW] 24.04 grub-pc cannot upgrade on mirrored software RAID root disk

[Chris Siebenmann]

Public bug reported:

I am testing the 24.04 pre-beta in a libvirt virtual machine with two
/dev/vd* disks set up as a single mirrored software RAID device,
/dev/md0, that is used for the root filesystem. Since this is a libvirt
install, it is using BIOS booting, not UEFI (maybe someday libvirt will
support snapshots of UEFI based VMs). When I attempt to install Ubuntu
updates, the grub-pc install fails with:

grub-pc: Running grub-install ...
Installing for i386-pc platform.
grub-install: warning: File system `ext2' doesn't support embedding.
grub-install: warning: Embedding is not possible.  GRUB can only be installed in this setup by using blocklists.  However, blocklists are UNRELIABLE and their use is discouraged..
grub-install: error: diskfilter writes are not supported.
  grub-install failure for /dev/md0
You must correct your GRUB install devices before proceeding:

  DEBIAN_FRONTEND=dialog dpkg --configure grub-pc
  dpkg --configure -a
dpkg: error processing package grub-pc (--configure):
 installed grub-pc package post-installation script subprocess returned error exit status 1

'debconf-show' reports (changed) settings as:
* grub-efi/cloud_style_installation: false
* grub-pc/install_devices: /dev/disk/by-id/md-name-ubuntu-server:0
* grub-pc/install_devices_empty: false

The same mirrored root filesystem configuration works on 22.04 LTS.

** Affects: grub2 (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2060695

Title:
  24.04 grub-pc cannot upgrade on mirrored software RAID root disk

Status in grub2 package in Ubuntu:
  New

Bug description:
  I am testing the 24.04 pre-beta in a libvirt virtual machine with two
  /dev/vd* disks set up as a single mirrored software RAID device,
  /dev/md0, that is used for the root filesystem. Since this is a
  libvirt install, it is using BIOS booting, not UEFI (maybe someday
  libvirt will support snapshots of UEFI based VMs). When I attempt to
  install Ubuntu updates, the grub-pc install fails with:

  grub-pc: Running grub-install ...
  Installing for i386-pc platform.
  grub-install: warning: File system `ext2' doesn't support embedding.
  grub-install: warning: Embedding is not possible.  GRUB can only be installed in this setup by using blocklists.  However, blocklists are UNRELIABLE and their use is discouraged..
  grub-install: error: diskfilter writes are not supported.
    grub-install failure for /dev/md0
  You must correct your GRUB install devices before proceeding:

    DEBIAN_FRONTEND=dialog dpkg --configure grub-pc
    dpkg --configure -a
  dpkg: error processing package grub-pc (--configure):
   installed grub-pc package post-installation script subprocess returned error exit status 1

  'debconf-show' reports (changed) settings as:
  * grub-efi/cloud_style_installation: false
  * grub-pc/install_devices: /dev/disk/by-id/md-name-ubuntu-server:0
  * grub-pc/install_devices_empty: false

  The same mirrored root filesystem configuration works on 22.04 LTS.

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