[Bug 1887964] Re: VG unavailable after upgrade from 18.04 to 20.04 Cannot process volume group vg01 Volume group "vg01" not found

[Michel Bretschneider]

So I upgraded from 18.04 LTS to 20.04 LTS too and found that the
installed 5.4 kernel panics complaining something about volume group. I
booted the 4.15 kernel wich put in a volume group warning too but at
least runs. After adding 8.8.8.8 to the resolv.conf the machine is
almost ready to work with (yup, I run my own dns/dhcp/dovecot/postfix
which all need attention once that kernel/vg bug is no longer in the
way).

Since my /boot partition is small, I initially thought the ramdisk image
is missing/broken/corrupted (there were some warnings in the upgrade
process which got stuck between cannot upgrade and cannot restore to
initial state - which let me to reboot the machine, trying to fix that
on my own). So I uninstalled the 4.4 kernel so only 4.15 and 5.4 are
left. While grub was updating I noticed several

 WARNING: PV /dev/sda1 in VG nameOfVolumeGroup is using an old PV header, modify the VG to update.
 
So I ran sudo vgck --updatemetadata nameOfVolumeGroup to fix that, hoping it would suffice to make 5.4 boot. It didn't:

 Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-
block(0,0)

So I booted the 4.15 which complained

 Volume Group not found nameOfVolumeGroup
 Cannot process volume group nameOfVolumeGroup

but at least booted. Once the machine is booted the volume seems to be
accessible, not sure why. Not sure why that didn't work for 5.4.

I checked /etc/crypttab but as I don't have crypted drives it contains
only the comment header, hexdump -C shows it ends with 0a so no problem
there.

Now I'm a bit lost:

- why is grub still giving me the option to boot the 4.4 kernel, although it's uninstalled?
- why does 5.4 fail to process the volume group and panic?
- why does 4.15 complain about the vg but still manages to start? (the only good thing so far)
- what should I do to make 5.4 (and updated kernels in the future) work on this system?
- why does dns does not fall back to 8.8.8.8 or something if the local dns got broken by the update (yeah, that's another issue - point me in the right direction or I'll search for that once the kernel/vg foo is fixed)

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https://bugs.launchpad.net/bugs/1887964

Title:
  VG unavailable after upgrade from 18.04 to 20.04 Cannot process volume
  group vg01 Volume group "vg01" not found

Status in lvm2 package in Ubuntu:
  Confirmed
Status in lvm2 source package in Focal:
  Confirmed

Bug description:
  After upgrading a laptop configured with LVM from 18.04 to 20.04 the volume group is no longer found.
  During boot the console shows

  Volume group "vg01" not found
  Cannot process volume group vg01
  Gave up waiting for suspend/resume device
  ALERT! /dev/mapper/vg01-root does not exist. Dropping to a shell!

  Attached dist-upgrade logs and console output.

  Tried the "vgck --updatemetadata vg01" recommended on this bug report:
  https://bugs.launchpad.net/ubuntu-z-systems/+bug/1874381

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