Bug#827956: grub: Doesn't apply default entry from /etc/default/grub

[Diederik de Haas]

On dinsdag 2 maart 2021 10:24:41 CET you wrote:
> I have a 'server' with no keyboard or monitor attached. I want to
> boot into a 5.9 kernel instead of a 5.10 kernel to see whether there's a
> NFS problem with 5.10.
> But regardless what I specify as GRUB_DEFAULT in /etc/default/grub, it
> always boots the top entry.
> 
> I've tried the following things:
> - Use the value following "$menuentry_id_option"
> - Placed single quotes around previous value
> - Placed double quotes around previous value
> - Replace "$menuentry_id_option" with "--id" in case it was incorrectly
>   not expanded/replaced in the grub entries
> - Use a numerical value
> 
> None of which resulted in grub booting anything other then the top
> entry.

There was one option that I hadn't tried: using the title.
When I did that and run 'update-grub' I got an interesting warning:

Warning: Please don't use old title `Debian GNU/Linux, with Linux 5.9.0-5-
amd64' for GRUB_DEFAULT, use `Advanced options for Debian GNU/Linux>Debian 
GNU/Linux, with Linux 5.9.0-5-amd64' (for versions before 2.00) or `gnulinux-
advanced-2f82ed85-9840-4338-a5b2-71c735333ed9>gnulinux-5.9.0-5-amd64-
advanced-2f82ed85-9840-4338-a5b2-71c735333ed9' (for 2.00 or later)

So I changed GRUB_DEFAULT to the (latter) value suggested by the warning ... 
and low-and-behold, that worked!

So my compliments for that excellent warning/error message.

> If this can't be fixed, can then at least the documentation be updated
> to say that grub only works interactively?

I would say that the documentation really does need to be updated as what's 
described in "info -f grub -n 'Simple configuration'" is not/no longer correct.
I would've expected an ID to be unique though ...

Cheers,
  Diederik
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