Re: BIOS_grub GUID signature within an EFI partition?

[Pascal Hambourg]

On 13/09/2023 at 11:47, Goh Lip wrote:
> On 9/13/23 15:15, Andrei Borzenkov wrote:
> > On Wed, Sep 13, 2023 at 9:53 AM Goh Lip <g.lip@gmx.com> wrote:
> > > You cannot mix efi and legacy install in the same disk
> >
> > You most certainly can as long as you have some way to select the boot
> > method.

Right.

> From a boot system of *another* disk or usb?

From the sams disk or media.

> Certainly not a boot system from that same disk, can it?
> A bios-grub and a efi-grub residing in the same disk? Possible?

Yes. BIOS-GRUB in the MBR and the BIOS boot partition, EFI-GRUB in the 
EFI system partition.

A caveat is that some broken BIOS/UEFI firmware require that a MBR 
partition entry has the boot flag set for BIOS boot, and/or the 
protective GPT partition entry does not have the boot flag set for EFI 
boot (so parted disk_flag pmbr_boot won't work). My usual workaround is 
to set the boot flag on an empty MBR partition entry with sfdisk, but it 
is ugly and fragile because partitioning tools often remove it.