Re: Double boot (Windows & Debian) with UEFI mode
On Thu 02 Dec 2021 at 09:50:06 (+0100), Thomas Schmitt wrote:
> Joe wrote:
> > I've never seen a legacy installation on GPT.
It might help if people pasted output into their posts, rather
than paraphrasing it so that we have to do the work to figure
out its meaning.
> It is suspicious that the partition table has both, a GRUB2 legacy BIOS
> partition and an EFI partition:
>
> > > dev / sda1 EFI system partition (fat32) 100 MiB
> > > dev / sda5 grub2 core.img 1.00 MiB
>
> The BIOS partition substitutes for the space between MBR and the start
> of the first MBR partition which once was used by GRUB code but in GPT
> is occupied by the GPT header and partition table entries.
> (The MBR itself can coexist with GPT. But its code size is restricted
> to 446 bytes. All further brain has to be loaded by this MBR code from
> some other place.)
>
> I understand that it indicates a GRUB2 installation which boots via
> legacy BIOS (or EFI's "CSM" mode).
> An EFI partition indicates that some system is prepared to boot via
> native EFI without CSM.
>
> The original poster, frantal@libero.it, indicated that the installed
> Debian is expected to boot via EFI. But i doubt that any MS-Windows
> would create a GRUB2 BIOS boot partition.
> So something is not as expected. Maybe that BIOS partition is just a
> piece of debris from earlier states. But for now it is suspicious.
I would agree: its presence here has to be explained.
I actually install one on every system disk. It wastes no space
because it sets the alignment to my preferred 4MB. Two of my
systems wouldn't without it as they're still BIOS-boot, on GPT.
Device Start End Sectors Size Type
/dev/sda1 2048 8191 6144 3M BIOS boot
/dev/sda2 8192 1023999 1015808 496M EFI System
[ … ]
I also had to add one to a dual-booting Lenovo as I booted
it in CSM to avoid touching the EFI boot configuration.
https://lists.debian.org/debian-user/2018/05/msg00454.html
So it's possible that the OP followed a well-written Howto
that didn't make assumptions, but it's also possible they
only /think/ they're booting Debian in EFI, seeing as they're
unable to boot linux at all at present.
I would've liked to have seen their ls /sys/firmware/efi
while they had a running linux system.
Cheers,
David.
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