[Bug 2060624] Re: lubuntu/xubuntu reinstall (& install) on dual boot system, grub does appear & offer OS choice

[Mate Kukri]

I finally found the cause, the two big hints were:
- 2 fresh installs were in this order sda1, sda2
- only happens with install *without a reformat to sda1*

After the first install to sda1:
- MBR (and MBR gap) contains GRUB core pointing to sda1, sda1 contains modules and config, this config on sda1 contains no os-prober entries as this was a fresh install

After the second install to sda2:
- MBR (and MBR gap) contains GRUB core pointing to sda2, sda2 contains modules and config, this config on sda2 now has os-prober entries for the install on sda1
- everything seems normal
- sda1's grub config still doesnt contain os-prober entries, but it is dormant now

After the third install *without reformat to sda1*:
- MBR contains GRUB core again pointing to sda1, sda1 contains modules and config
- while the installer regenerates the GRUB config here, during this re-generation the old config *on sda1* (due to no format) is checked for the presence of os-prober entries, and these won't appear in the dormant config from step 1, thus no new os-prober entries for the install on sda2 will be generated

As a result sda1 was just a symptom and not the true cause, the true
cause is overwriting an install with a dormant grub config containing no
os-prober entries.

The reason a no reformat re-install to sda2 didn't trigger is due to the
existing grub config containing os-prober entries from step2. If the
initial installs were in a different order, e.g. sda2 then after it
sda1, then installing without reformat to sda2 will also trigger it.

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https://bugs.launchpad.net/bugs/2060624

Title:
  lubuntu/xubuntu reinstall (& install) on dual boot system, grub does
  appear & offer OS choice

Status in grub2 package in Ubuntu:
  New

Bug description:
  Warning: os-prober will not be executed to detect other bootable partitions.
  ----

  Lubuntu noble install to
  - hp dc7700 (c2d-e6320, 8gb, amd/ati rv610/radeon hd2400 pro/xt)

  System had two Lubuntu noble installs on box; original full disk install (sda1) + install alongside (sda2)
  This box is legacy (BIOS) or pre-uEFI (2005 HP Compaq) so no ESP was created at install time

  guiverc at dc7700-3:~$   blkid
  /dev/sda2: LABEL="lubuntu_2404" UUID="4b96ae36-ff60-46ff-888d-bab52f0664fc" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="b22c54df-02"
  /dev/sda1: LABEL="lubuntu_2404" UUID="24611116-48e0-47e3-af47-4cd692dcdbd6" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="b22c54df-01"

  ** expected result

  On reboot post-install (Lubuntu so calamares install) I grub did NOT
  appear, so I could boot into the untouched install & checked it worked
  (grub offered me two options correctly prior to install).

  ** actual result

  No grub menu appeared, so no dual boot option was offered??

  No problem, I'll just `update-grub` and that should fix it won't it?

  guiverc at dc7700-3:~$ sudo update-grub
  [sudo] password for guiverc:
  Sourcing file `/etc/default/grub'
  Sourcing file `/etc/default/grub.d/lubuntu-grub-theme.cfg'
  Generating grub configuration file ...
  Found theme: /usr/share/grub/themes/lubuntu-grub-theme/theme.txt
  Found linux image: /boot/vmlinuz-6.8.0-22-generic
  Found initrd image: /boot/initrd.img-6.8.0-22-generic
  Found memtest86+x64 image: /boot/memtest86+x64.bin
  Warning: os-prober will not be executed to detect other bootable partitions.
  Systems on them will not be added to the GRUB boot configuration.
  Check GRUB_DISABLE_OS_PROBER documentation entry.
  Adding boot menu entry for UEFI Firmware Settings ...
  done

  The issue is
  Warning: os-prober will not be executed to detect other bootable partitions.

  Prior releases of Ubuntu haven't done this (new grub 2.06 change) with
  a patch (ubuntu-os-prober-auto.patch) carried by Ubuntu that reverses
  this upstream change..

  If this is new behavior (for noble) we (Lubuntu at least) just need to
  document it, as its a change to mantic, lunar & prior releases (inc.
  kinetic, jammy which were 2.06 or later, it was default prior to jammy
  anyway).

  Maybe I'm missing something... I'll correct/add more as I can

  ProblemType: Bug
  DistroRelease: Ubuntu 24.04
  Package: grub2-common 2.12-1ubuntu7
  ProcVersionSignature: Ubuntu 6.8.0-22.22-generic 6.8.1
  Uname: Linux 6.8.0-22-generic x86_64
  ApportVersion: 2.28.0-0ubuntu1
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CurrentDesktop: LXQt
  Date: Tue Apr  9 16:21:14 2024
  InstallationDate: Installed on 2024-04-09 (0 days ago)
  InstallationMedia: Lubuntu 24.04 LTS "Noble Numbat" - Daily amd64 (20240408)
  SourcePackage: grub2
  UpgradeStatus: No upgrade log present (probably fresh install)

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