Re: BIOS_grub GUID signature within an EFI partition?

[Pascal Hambourg]

On 13/09/2023 at 14:22, Goh Lip wrote:
> On 13/09/2023 18:01, Pascal Hambourg wrote:
>
> > Yes. BIOS-GRUB in the MBR and the BIOS boot partition, EFI-GRUB in the
> > EFI system partition.
>
> Yes, this can be done. But how do we boot in one instance in UEFI and
> then in another in bios-legacy?
>
> Do we need to go to computer bios-setup each time to boot?

Or use the computer boot menu.

> > 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.
>
> In my previous system, I set boot flags in *all* my efi partitions. Now
> I set flag to just my own dedicated (grub) efi partition that sort of
> chainload into say my systemd-boot or refind boots.

What "boot flag" are you talking about ?
The boot flag in DOS/MBR partition entries (meaning you don't use GPT) ?
The legacy_boot flag in GPT partition entries ?
Parted's "boot" flag which represents the ESP type in GPT partition 
entries ?

The first two are irrelevant for EFI boot.
AFAIK, legacy_boot is used only by syslinux gptmbr boot loader.