Re: Grub on BIOS/GPT

[David Ventura]

The machines I'll boot support this, so it's fine. (And they'll only
ever boot Linux, so no need for hybrid MBR).

Using grub-install also expects to read the device.map from my disk
and write to /boot/grub/i386-pc on my disk.
I understand how this makes sense for the use-case grub-install is
intended for, and how I'm fairly outside of it.

I'm trying to generate thousands of disk images for various tests on
real systems, and for each I know specifically what disk layout
they'll have, the address of the bios boot partition, path to grub
files, etc.

On Mon, 21 Feb 2022 at 11:17, Pascal Hambourg <pascal@plouf.fr.eu.org> wrote:
>
> Le 21/02/2022 à 10:11, David Ventura a écrit :
> >
> > I'm not sure how to do that; running grub-install with either a file
> > or a loop device as  target gets ignored and instead targets my
> > primary disk:
> >
> > $ grub-install -vvv /dev/loop13
> > grub-install: info: executing modprobe efivars 2>/dev/null.
> > grub-install: info: Looking for /sys/firmware/efi ...
> > grub-install: info: ...found.
> > Installing for x86_64-efi platform.
>
> The target device is ignored because grub-install detects an EFI
> platform and defaults to install for EFI boot. You must force BIOS
> platform with --target=i386-pc.
>
> > On top of that, I'm building a franken-disk that can boot both in
> > BIOS/GPT and UEFI/GPT with a bios boot partition and Grub in the ESP.
> > I'm not sure if grub-install would be confused by this, or just work.
> > Do you have any suggestions for this?
>
> I observed that some BIOS platforms won't boot if the boot flag is not
> set on a partition entry of the MBR ; conversely, some UEFI platforms
> won't boot if the boot flag is set on the GPT partition entry of the
> MBR. Workaround : create a hybrid/DOS MBR or set the boot flag on an
> empty partition entry of the MBR.



-- 
Stack is the new term for "I have no idea what I'm actually using".