[Bug 1870189] Re: initramfs does not get loaded

[Dexuan Cui]

So it looks this is considered as a feature rather than a bug for the
Ubuntu 20.04 VM image in Azure Marketplacet. To whoever uses such an
image on Azure: if you're installing a new kernel that doesn't have the
necessary drivers built-in (CONFIG_HYPERV=y, CONFIG_HYPERV_STORAGE=y),
you're supposed to comment out the GRUB_FORCE_PARTUUID line in
/etc/default/grub.d/40-force-partuuid.cfg and run 'sudo update-grub'.

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https://bugs.launchpad.net/bugs/1870189

Title:
  initramfs does not get loaded

Status in grub2 package in Ubuntu:
  Won't Fix
Status in linux-azure package in Ubuntu:
  Confirmed
Status in livecd-rootfs package in Ubuntu:
  Triaged

Bug description:
  A Gen-1 Ubuntu 19.10 VM on Azure was created and upgraded to Ubuntu
  20.04 by “do-release-upgrade –d”.

  Then the latest Ubuntu v5.6 kernel was installed from
  https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.6/. As soon as a
  reboot was performed, a panic with the v5.6 kernel occured because the
  rootfs can not be found.

  It turns out by default, initramfs does not get loaded:

  /boot/grub/grub.cfg:
  menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-3d2737e8-
  b95a-42bf-bac1-bb6fb4cda87f' {
  …
          if [ "${initrdfail}" = 1 ]; then
            linux /boot/vmlinuz-5.6.0-050600-generic root=PARTUUID=bc3d472f-401e-4774-affa-df1acba65a73 ro  console=tty1 console=ttyS0 earlyprintk=ttyS0 ignore_loglevel sysrq_always_enabled unknown_nmi_panic
            initrd        /boot/initrd.img-5.6.0-050600-generic
          else
            linux /boot/vmlinuz-5.6.0-050600-generic root=PARTUUID=bc3d472f-401e-4774-affa-df1acba65a73 ro  console=tty1 console=ttyS0 earlyprintk=ttyS0 ignore_loglevel sysrq_always_enabled unknown_nmi_panic panic=-1
            #Dexuan: here the initrd line is missing!
          fi
          initrdfail
  }

  
  As we can see, Ubuntu only uses the initrd.img if initrdfail=1. Normally, initrdfail = 0, so when we boot the v5.6 kernel for the first time, we must hit the “fail to mount rootfs” panic and the kernel will automatically reboot….   

  Also, the “initrdfail” here marks initrdfail=1, so when the kernel
  boots for the 2nd time, the kernel should successfully boot up.  Next,
  when the kernel boots for the 3rd time, it panics again since the
  userspace program resets initrdfail to 0, and next time when the
  kernel boots, it can boot up successfully -- this
  “panic/success/panic/success” pattern repeats forever…

  
  The linux-azure kernels are not affected since they have the vmbus driver and storage drivers built-in (i.e. “=y”):
  /boot/config-5.3.0-1013-azure:CONFIG_HYPERV_STORAGE=y
  /boot/config-5.3.0-1013-azure:CONFIG_HYPERV=y
  /boot/config-5.4.0-1006-azure:CONFIG_HYPERV_STORAGE=y
  /boot/config-5.4.0-1006-azure:CONFIG_HYPERV=y
  /boot/config-5.6.0-050600-generic:CONFIG_HYPERV_STORAGE=m
  /boot/config-5.6.0-050600-generic:CONFIG_HYPERV=m
  The v5.6 kernel uses =m rather than =y, so is affected here.

  
  It looks the setting may be intentional, but we should not assume a customer kernel must have the necessary vmbus/storage drivers built-in. 

  This issue only happens to the Ubuntu Marketplace image (19.10 and maybe 19.04 as well?) on Azure. 
  We installed a Ubuntu  20.04 VM from the .iso file from http://cdimage.ubuntu.com/daily-live/pending/ and don’t see the strange grub issue.

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