Re: UEFI/"BIOS" booting
- Date: Tue, 15 May 2018 08:51:29 +0200
- From: "Thomas Schmitt" <scdbackup@xxxxxxx>
- Subject: Re: UEFI/"BIOS" booting
> > And as said previously, BIOS does not expect any partitions.
Pascal Hambourg wrote:
> experience taught me that many BIOS implementations wrongly
> expect an MBR partition entry with the boot flag set in order to boot from
> the disk.
You are right (and those firmwares are wrong).
I had to introduce a special option in xorriso in order to cater for this:
with the final conclusion described in
- Boot flag on MBR partition of type 0xEE is bad on several EFI
- No MBR partition with boot flag is bad on some very few BIOS
- Compromise is to set the boot flag on a dummy partition of type 0x00.
This is barely UEFI-compliant because the specs say that a partition of
type 0x00 shall be regarded as non-existent.
Debian isohybrids for BIOS do not have this problem because MBR partition 1
has the boot flag set, anyway. But grub-mkrescue ISOs might be in need of
if the owner suffers from one of those rare BIOSes.
(It was decided that from the view of GRUB this is a workaround for a
specs violation by the firmware. iSo --mbr-force-bootable is not applied
Have a nice day :)