Bug#1008294: grub: Grub doesn't detect another install

[Philip Ashmore]

Source: grub
Severity: important
X-Debbugs-Cc: contact at philipashmore.com

Dear Maintainer,

   * What led up to the situation?
I wanted to try Debian bookworm
   * What exactly did you do (or not do) that was effective (or
     ineffective)?
I installed Debian Bookworm onto a second SSD
   * What was the outcome of this action?
The install completed (from a netinst) but after rebooting, my original SSD install (buster) wasn't listed as a boot option in GRUB.
   * What outcome did you expect instead?
I expected that the original install would be listed.
I also expected that an "update-grub" from buster would list bookworm as a boot option - it didn't.
I tried changing the hostname in bullseye from "debian" to "bullseye" in bullseye before running "update-grub" - no cgange.

-- System Information:
Debian Release: 11.2
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.10.0-10-amd64 (SMP w/16 CPU threads)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE
Locale: LANG=en_IE.UTF-8, LC_CTYPE=en_IE.UTF-8 (charmap=UTF-8), LANGUAGE=en_IE:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled