[gentoo-user] Re: OFF TOPIC Need Ubuntu network help

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2023-10-18, Michael <confabulate@kintzios.com> wrote:
>
>> The protective MBR and the BIOS boot partition are two different,
>> unrelated things. The BIOS boot partition is a real partition (usually
>> 1-2MB in size) that's present in the GPT parition table. It's used by
>> Grub as a place to store its files.
>
> Yes, this is needed on GPT disks when installed on BIOS MoBos.

There is a way to install Grub on GPT disks without it, but it takes
extra work and isn't worth it. You have to lock certain files in place
under /boot/grub so that block-lists can be embedded in sector 0.

All of the disk label utilities I've seen recently will, by default,
leave a sizable empty space between the primary GPT table and the
start of the first partition (which typically starts at a 1MB offset
from the start of the disk).  I've never understood why Grub won't use
that space they way it will use the empty space between an MBR and the
first partition.

>> It must be the first partition, and it doesn't have a real
>> filesystem (grub uses some sort of private filesystem):
>
> I'm not sure it uses any filesystem.  I understood it uses a raw sector jump 
> from the MBR to the GPT partition type 0xEE.

I've read a couple vague but differing descriptions of it. One
description specifically referred to "files" (plural) and some sort of
grub-private-internal filesystem.  However, it could be that it's
nothing but a single "file" starting at block 0 in that partition.
Whatever it is, it seems to be "opaque" in that Grub puts stuff in
that partition, Grub later uses that stuff, and nobody else needs to
know or care what it is or how it's organized. I haven't looked
through the Grub source code to try to see inside the black box...

--
Grant