Re: Purpose of 'legacy_boot' attribute

[Chris Murphy]

On Oct 19, 2011, at 9:16 AM, Brian C. Lane wrote:

> On Tue, Oct 18, 2011 at 11:15:28PM -0600, Chris Murphy wrote:
>> Is it correct that the parted 'legacy_boot' flag sets the partition 
>> attribute "Legacy BIOS Bootable" bit? And is there any case where it would 
>> be appropriate for it to be set for an EFI System partition?
>> 
>> I ask because I'm seeing Fedora 16 beta InstallDVD set this parted 
>> 'legacy_boot' flag on an EFI System partition. But the LiveCD does not. That 
>> discrepancy is a likely bug. However, I'm wondering which one is incorrect. 
>> It doesn't seem like the EFI System partition should have this attribute 
>> set, if indeed the flag sets the Legacy BIOS Bootable bit.
> 
> The primary use for legacy_boot is with the gptmbr bootloader, so yes it
> doesn't really make sense to set it on an EFI system. I used it in
> livecd-iso-to-disk when creating hybrid EFI/BIOS bootable USB sticks.

Should I file a bug on the F16b InstallDVD setting 'legacy_boot' on EFI System 
partitions?

F16b Install DVD method also sets the 'hidden' flag which the F16b LiveCD does 
not do. I'd expect linux and Mac OS X to ignore this flag in favor of fstab, so 
it's probably only meaningful for Windows systems.

> I was also just wondering if we (Fedora) should be setting legacy_boot
> on /boot partitions instead of the boot flag, since the latter writes an EFI
> system GUID to the partition type. 


Neither Install DVD or LiveCD installations to conventional disks are setting 
linux boot partitions with a 'legacy_boot' flag, and both installations 
function as expected. So I don't see that the flag is either useful or 
detrimental. Someone would need alter their boot strategy after the fact to end 
up with a dependency on this flag I think.  In the case of gptmbr or syslinux, 
it seems they look for 'legacy_boot' to know where to jump to next in the boot 
process.

Chris Murphy