[Bug 1901553] Re: Improve documentation around initrdless boot

[Dimitri John Ledkov]

GNU GRUB  version 2.04

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 │ Ubuntu 20.10 (20.10) (on /dev/sda1)                                        │
 │ Advanced options for Ubuntu 20.10 (20.10) (on /dev/sda1)                   │
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      Use the ↑ and ↓ keys to select which entry is highlighted.          
      Press enter to boot the selected OS, `e' to edit the commands       
      before booting or `c' for a command-line.                           
   The highlighted entry will be executed automatically in 0s.    





GRUB_FORCE_PARTUUID set, attempting initrdless boot.
Linux version 5.8.0-1008-kvm (buildd at lcy01-amd64-016) (gcc (Ubuntu 10.2.0-13ubuntu1) 10.2.0, GNU ld (GNU)
Command line: BOOT_IMAGE=/boot/vmlinuz-5.8.0-1008-kvm root=PARTUUID=f6bea054-a6e1-4734-91e2-eb6425be905b1
x86/fpu: x87 FPU will use FXSAVE
BIOS-provided physical RAM map:
BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
BIOS-e820: [mem 0x0000000000100000-0x000000007ffdffff] usable


So it is not obvious if grub output will be visible in the console log,
because GRUB_TERMINAL=console might not be set.

Also, previously the first message from the boot was from kernel. But my
patch introduced 'GRUB_FORCE_PARTUUID' option.

Also, somehow on the minimal cloud image 'Ubuntu 20.10' was detected on
/dev/sda1 - aka the only Ubuntu that there is..... and somehow I'm
getting 10s grub menu prompt.

It almost feels like maybe kernel should be emitting dmesg message that
it performing initrdless boot. rather that just:

EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
VFS: Mounted root (ext4 filesystem) readonly on device 8:1.
Run /sbin/init as init process

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

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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