[Bug 1901553] Re: Improve documentation around initrdless boot

[Launchpad Bug Tracker]

** Merge proposal linked:
   https://code.launchpad.net/~ubuntu-core-dev/grub/+git/ubuntu/+merge/412515

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https://bugs.launchpad.net/bugs/1901553

Title:
  Improve documentation around initrdless boot

Status in grub2 package in Ubuntu:
  Fix Released
Status in grub2 source package in Bionic:
  In Progress
Status in grub2 source package in Focal:
  Fix Released

Bug description:
  [Impact]
  (sort of prerequisite of bug 1929860 to avoid having to edit the patches and possibly introduce bugs that way, because these changes port the service to systemd unit)

   * 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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