Re: Grub on BIOS/GPT

[Andrei Borzenkov]

On Mon, Feb 21, 2022 at 1:45 PM David Ventura <davidventura27@gmail.com> wrote:
>
> 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.
>

You could try grub-bios-setup which installs grub image onto the
device. grub-install does it as one of the steps it executes.

> 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".
>