Re: Do I need to act on this warning from apt when installing grub?

[Pascal]

thank you for this feedback.

Le ven. 16 déc. 2022 à 12:47, Pascal Hambourg <pascal@plouf.fr.eu.org> a
écrit :

> On 16/12/2022 at 11:15, Pascal wrote:
> >
> > GRUB :
> >
> >               INTEL/MBR               GPT
> >              PARTITIONING         PARTITIONING
> >        +---------------------+---------------------+
> >        |MBR 1/3              |MBR 1/3              |
> >        |POST-MBR-GAP 2/3     |                     |
> >        |+-------------------+|+-------------------+|
> >        ||PART               |||PART BIOS-BOOT 2/3 ||
> >        ||/boot/grub/ 3/3    ||+-------------------+|
> >   BIOS ||...                ||+-------------------+|
> >   BOOT ||                   |||PART ESP (FAT)     ||
> >        ||                   |||/boot/grub/ 3/3    ||
> >        ||                   |||...                ||
> >        |+-------------------+|+-------------------+|
> >        +---------------------+---------------------+
> >        |                     |                     |
> >        |                     |                     |
> >        |+-------------------+|+-------------------+|
> >        ||PART ESP (FAT)     |||PART ESP (FAT)     ||
> >        ||/boot/efi/ 1/2     |||/boot/efi/ 1/2     ||
> >   UEFI ||/boot/grub/ 2/2    |||/boot/grub/ 2/2    ||
> >   BOOT ||...                |||...                ||
> >        ||                   |||                   ||
> >        ||                   |||                   ||
> >        |+-------------------+|+-------------------+|
> >        +---------------------+---------------------+
>
> 1) There is no need for an ESP for BIOS boot.
> 2) /boot/grub does not have to be in the ESP.
>
> > 3 steps for GRUB in BIOS mode and 2 steps in UEFI mode.
> >
> > in BIOS mode :
> > first, BIOS load MBC (Master Boot Code - step 1/3 of GRUB) from MBR to
> > memory and run it
> > - with INTEL/MBR partitioning, GRUB will be chained from MBR, then to
> > POST-MBR-GAP (step 2/3) and then to /boot/grub/... (step 3/3)
>
> "GRUB will be chained from MBR" makes no sense and does not fit between
> 1/3 and 2/3.
>
> > - with GPT partitioning, GRUB will be chained from MBR, then to a special
> > partition of type BIOS-BOOT (step 2/3 - can't use POST-MBR-GAP because
> used
> > by GPT) and then /boot/grub/... (step 3/3)
>
>  From the GRUB boot loader point of view, both are exactly the same. The
> GRUB boot image in the MBR does not read the partition table nor know
> anything about the BIOS boot partition. The GRUB core image start sector
> is embedded in the boot image in both cases. Only grub-install uses the
> BIOS boot partition.
>
> > in UEFI mode :
> > first, UEFI load an run a (GRUB) loader (step 1/2 of GRUB) located on ESP
> > (EFI system partition formated with FAT file system)
> > then the loader chain to /boot/grub/... (step 2/2)
>
> With secure boot, the UEFI firmware first loads shim which then loads GRUB.
>
>