[Bug 1874147] Re: focal-server-cloudimg-amd64.img panics on first boot, cannot open root device

[David Baird]

Discussing here: https://bugs.launchpad.net/ubuntu/+source/linux-
azure/+bug/1870189

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https://bugs.launchpad.net/bugs/1874147

Title:
  focal-server-cloudimg-amd64.img panics on first boot, cannot open root
  device

Status in VMBuilder:
  New
Status in grub2 package in Ubuntu:
  New

Bug description:
  Various Focal cloudimg builds fail on first time ever booting (e.g.
  https://cloud-images.ubuntu.com/focal/20200418/focal-server-cloudimg-
  amd64.img). Here is the failed output:

  [    0.000000] Linux version 5.4.0-24-generic (buildd at lgw01-amd64-017) (gcc version 9.3.0 (Ubuntu 9.3.0-10ubuntu2)) #28-Ubuntu SMP Thu Apr 9 22:16:42 UTC 2020 (Ubuntu 5.4.0-24.28-generic 5.4.30)
  [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.4.0-24-generic root=PARTUUID=8a7c6798-57bf-4624-80a0-b896a73939f3 ro console=tty1 console=ttyS0 panic=-1
  ...
  [    1.043162] VFS: Cannot open root device "PARTUUID=8a7c6798-57bf-4624-80a0-b896a73939f3" or unknown-block(0,0): error -6
  [    1.045238] Please append a correct "root=" boot option; here are the available partitions:
  [    1.046921] 0b00         1048575 sr0
  [    1.046922]  driver: sr    
  [    1.048215] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
  [    1.049795] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.4.0-24-generic #28-Ubuntu
  [    1.051189] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
  [    1.052904] Call Trace:
  [    1.053459]  dump_stack+0x6d/0x9a
  [    1.054158]  panic+0x101/0x2e3
  [    1.054812]  mount_block_root+0x23f/0x2e8
  [    1.055645]  mount_root+0x38/0x3a 
  [    1.056319]  prepare_namespace+0x13f/0x194
  [    1.057236]  kernel_init_freeable+0x231/0x255
  [    1.058131]  ? rest_init+0xb0/0xb0
  [    1.058834]  kernel_init+0xe/0x100
  [    1.059535]  ret_from_fork+0x35/0x40
  [    1.060327] Kernel Offset: 0x1f800000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

  When booted, the second time, it works!

  The issue appears to be a bug in /boot/grub/grub.cfg, pertaining to
  "initrdfail." On first ever boot, grub will try to boot *without* an
  initrd, which (apparently) makes the kernel unable to mount root.

  Relevant section of /boot/grub/grub.cfg:

  menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-aca11948-bdc4-4726-9aca-ead9dcce6a5e' {
          recordfail
          load_video
          gfxmode $linux_gfx_mode
          insmod gzio
          if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
          insmod part_gpt
          insmod ext2
          if [ x$feature_platform_search_hint = xy ]; then
            search --no-floppy --fs-uuid --set=root  aca11948-bdc4-4726-9aca-ead9dcce6a5e
          else
            search --no-floppy --fs-uuid --set=root aca11948-bdc4-4726-9aca-ead9dcce6a5e
          fi
          if [ "${initrdfail}" = 1 ]; then
            linux /boot/vmlinuz-5.4.0-24-generic root=LABEL=cloudimg-rootfs ro  console=tty1 console=ttyS0
            initrd        /boot/initrd.img-5.4.0-24-generic
          else
            linux /boot/vmlinuz-5.4.0-24-generic root=LABEL=cloudimg-rootfs ro  console=tty1 console=ttyS0 panic=-1
          fi
          initrdfail
  }

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