[Bug 1901553] Re: Improve documentation around initrdless boot

[Dimitri John Ledkov]

GRUB_FORCE_PARTUUID set, attempting initrdless boot.
[    0.000000] Linux version 5.8.0-25-generic (buildd at lcy01-amd64-022) (gcc (Ubuntu 10.2.0-13ubuntu1) 10)
[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.8.0-25-generic root=PARTUUID=f6bea054-a6e1-4734-1
[    0.000000] KERNEL supported cpus:

(panic)

(grub again)

GRUB_FORCE_PARTUUID set, initrdless boot failed. Attempting with initrd.
[    0.000000] Linux version 5.8.0-25-generic (buildd at lcy01-amd64-022) (gcc (Ubuntu 10.2.0-13ubuntu1) 10)
[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.8.0-25-generic root=PARTUUID=f6bea054-a6e1-4734-0
[    0.000000] KERNEL supported cpus:

second boot

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Title:
  Improve documentation around initrdless boot

Status in grub2 package in Ubuntu:
  New

Bug description:
  [Impact]

   * Sometimes it is not obvious why initrdless boot is generated; when
  is it attempted; and when it fails and boots with initrd.

   * Improve UX by leaving breadcrumbs and emit messages about
  initrdless boot, in more places

  [Test Case]

   * Boot system with initrdless boot
     - for example minimal cloud image from https://cloud-images.ubuntu.com/minimal/releases/
     - boot without graphical terminal, i.e. -nographics qemu option
   * Upgrade to new grub package
   * Uncomment GRUB_TERMINAL=console in /etc/default/grub

  
   1. Call `sudo update-grub`, a message should be emitted that initrdless boot will be attempted.

   2. Inspecting /boot/grub/grub.cfg, there are comments that initrdless
  boot will be attempted

   * Reboot

   * Observe the following:

   3. Inspecting console log, there are echo message from grub about
  attempting initrdless boot.

   * Install linux-generic kernel flavour; and remove kvm kernel
  flavour, reboot.

   * Observe in the console log

   1. There should be message about attempting initrdless boot
   2. kernel panic
   3. message about initrdless boot failing and attempting to boot with initrd

  [Regression Potential]

   * This change adds a few more user visible message, without
  translations. The actual behaviour that is happening is unchanged.
  This simply better notifies users about what is happening, and can be
  inspected interactively, statically, and from boot logs.

  [Other Info]

   * CPC requested these UX improvements, as there have been concerns
  that users are failing to discover why initrdless boot is happening;
  or failing; and how to effect it.

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