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Re: Purpose of 'legacy_boot' attribute
From: |
Chris Murphy |
Subject: |
Re: Purpose of 'legacy_boot' attribute |
Date: |
Wed, 19 Oct 2011 14:53:29 -0600 |
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