Re: Converted MBR to GPT and menu is gone, can't use grub-reboot either

[Pascal Hambourg]

On 16/02/2023 at 14:49, Chandler wrote:
> Hi all, I recently (like a month ago) upgraded one of our computers that
> hadn't received any upgrades for like 2 years.  Afterwards, it wouldn't
> boot.

What happened exactly at boot time ? Any error message ?

> I think it was because Grub2 got upgraded and no longer supported MBR?
> (it's now version 2.06-3~deb11u5)
> I read something along those lines, that I had to be using GPT now.  So

Nonsense. Of course GRUB still supports MBR/DOS.

> Except!  The boot menu is now gone and I actually just noticed now
> that I'm trying to run memtest86.  I tried holding Shift while it
> tries to boot, and also have tried tapping Esc, but neither of these
> bring up the menu.

What is in /etc/default/grub ?

> Then I remembered I could use grub-reboot to boot into memtest86, but
> not on this system apparently because when I tried that it told me this:
> WARNING: Detected GRUB environment block on diskfilter device
> Memory test (memtest86+, serial console 115200) will remain the default
> boot entry until manually cleared with:
>      grub-editenv /boot/grub/grubenv unset next_entry
>
> I guess, it's because /boot is on a md device?

See grub-reboot manual. GRUB cannot write on RAID or LVM devices at boot 
time to remove the next boot option in the GRUB environment block 
/boot/grub/grubenv, so the option will be persistent.