Re: UEFI/"BIOS" booting
Hi,
i wrote:
> > 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:
https://savannah.gnu.org/bugs/?46716
http://lists.gnu.org/archive/html/bug-xorriso/2015-12/threads.html
with the final conclusion described in
https://lists.gnu.org/archive/html/bug-grub/2016-03/msg00087.html
Summary:
- Boot flag on MBR partition of type 0xEE is bad on several EFI
implementations.
- No MBR partition with boot flag is bad on some very few BIOS
implementations.
- 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
xorrisofs option
--mbr-force-bootable
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
by default.)
Have a nice day :)
Thomas
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