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? I have booted in UEFI a bios-legacy OS (but not the other way round) and when booted showed it was booted in UEFI.
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. But thanks for this info.
