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Re: Simultaneous EFI and Legacy bootloader installation


On 2016-03-29, Mario Limonciello wrote:
> On 03/29/2016 07:50 PM, Limonciello, Mario wrote:
> > I'd like to propose changing this and by default install both legacy 
> > and UEFI bootloaders on architectures that support both regardless of 
> > which mode the system is running in at installation. Making this 
> > change has a few obvious implications:
> > * The installation disk would always be formatted GPT.
> > * An ESP would always be created.
> > * If the user is in legacy at installation time, it's not possible to 
> > create an EFI boot entry since EFI runtime services aren't present.  
> > The removable media fallback path (\efi\boot\boot$ARCH.efi) will need 
> > to be used to boot the system at this point and at some point create 
> > a "debian" NVRAM boot entry
> >
> > I'm not aware of any modern systems that are unable to boot a GPT 
> > partitioned disk.  If there are systems like this in the wild, it 
> > would be worthwhile to leave support to install in MBR mode when 
> > doing an expert install so that people can still use them.

At least well into 2009/ 2010 era systems (most of those are early UEFI 
based underneath, but only expose a mandatory BIOS CSM to the user), 
you can sometimes find mainboards which refuse booting from a disk 
that doesn't have a MBR partition with the bootflag set. On these 
systems it is often possible to trick them into booting by setting the 
bootflag on the protective MBR around the GPT partitions, although this
is a blatant violation of the UEFI specification (and might break more 
modern systems).

Of course, most of the affected systems won't be detected as UEFI
capable in the first place (because they will only allow booting
via the BIOS CSM), but it's still something to be aware of. 

I'd very much appreciate BIOS and UEFI variants of grub to be 
co-installable (including their maintainer script orchestration), 
also to make moving installed systems between different mainboards 
easier (I am using a custom /etc/grub.d/ hook using grub-pc and 
grub-efi-amd64-bin for semi-portable installations on USB sticks
myself, usually without any particular problems besides the one
mentioned above).

	Stefan Lippers-Hollmann

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