Web lists-archives.com

Re: Unable to boot BIOS/GPT system.


Pascal Hambourg wrote:
> If the EFI firmware can boot in legacy BIOS compatibility mode, it may
> require to set the boot flag on the protective GPT partition entry in the
> protective MBR.

According to user reports on grub-devel mailing list about grub-mkrescue
ISOs, the boot flag must not be set on the protective MBR partition.
But some BIOS implementations wont't regard the medium as bootable if there
is no boot flag set at all.

The compromise that finally worked for those who tested, was to create an
MBR partition of type 0x00 starting at LBA 0, having only one block, and
bearing the boot flag.
The tested EFIs and operating systems still recognized GPT if an additional
partiton of type 0x00 was present. But doubts remain. YMMV.

The decision with grub-mkrescue was to omit the boot flag by default
and to leave it to the user whether add-on xorrisofs option
--mbr-force-bootable shall cause the boot flag to be set on a dummy

Have a nice day :)