[Bug 1918265] Re: Random boot failure with Ubuntu 20.04 / grub 2.04 and Hyper-V 2012r2

[Paul Chilton]

I'm also getting the same problem. Across 3x Windows 2016 machines
running Hyper-V. Had this issue with Ubuntu 18.04 and now 20.04 but only
when they are connected to a VLAN. My vlan assignments are
10,40,100,110,120,200 - I'm going to test next with an odd numbered vlan
as that seems to be a pattern in all the above reports... I have tested
and I get the same behavior if the VLAN is assigned in Hyper-V UI, from
Powershell or even when using a default vlan on the network switch and
leaving hyper-v unaware of the vlan.

Sometimes you can get the machine to boot by hitting Enter on the Grub
boot screen (often 10+ attempts). A sure-fire way to get it to boot is
to go into Hyper-V VM settings, untag the vlan from the network
interface, hit Enter in the console to get it to boot and then re-add
the vlan assignment. This gets very boring very quickly when repeating
on multiple machines during maintenance and would love a fix or
workaround.

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https://bugs.launchpad.net/bugs/1918265

Title:
  Random boot failure with Ubuntu 20.04 / grub 2.04 and Hyper-V 2012r2

Status in grub2 package in Ubuntu:
  Confirmed

Bug description:
  Hi,

  We are experiencing some weird boot issues with Ubuntu 20.04 and
  Hyper-V 2012r2.

  In two cases the installation started successfully, as did the VM
  initial boot and then issues started to arise, where the boot process
  started to fail.

  grub start, the menu pop-up and then just after loading kernel and
  initrd (tried to put some echo(es) in the config the VM somehow reset
  and the menu pop-up back again.

  After a few of thoses either the VM shut-down or the boot is
  successfull, It seems completly random..

  Here it is captured on video:
    https://www.youtube.com/watch?v=5Bk3S-YGDZk

  If i setup a direct EFI-STUB boot of the kernel+initrd the boot
  process works every times.

  I suspected the "save_env/load_env" for a while but a stripped down
  grub.cfg give the same result..

  > insmod gzio
  > insmod part_gpt
  > insmod ext2
  > set root='hd0,gpt2'
  > if [ x$feature_platform_search_hint = xy ]; then
  >  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  94ebc17e-6aca-4e42-b489-b3eaa8a32d90
  > else
  >  search --no-floppy --fs-uuid --set=root 94ebc17e-6aca-4e42-b489-b3eaa8a32d90
  > fi
  > linux	/vmlinuz-5.8.0-44-generic root=/dev/mapper/ubuntu--vg-ubuntu--lv ro nosplash elevator=noop 
  > initrd	/initrd.img-5.8.0-44-generic
  > boot

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