hi,
the table has been slightly modified and some explanations have been added.
please let me know if there are any errors or gaps in this summary.
regards, lacsaP.
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 ||... |||... ||
|| ||| ||
|| ||| ||
|+-------------------+|+-------------------+|
+---------------------+---------------------+
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)
- 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)
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)
Le jeu. 15 déc. 2022 à 11:31, Pascal <[email protected]> a écrit :
> INTEL/MBR GPT
> PARTITIONING PARTITIONING
> +----------------+----------------+
> |MBR |MBR |
> |POST-MBR-GAP |GPT |
> |+--------------+|+--------------+|
> ||PART |||PART BIOS-BOOT||
> ||/boot/grub/ ||+--------------+|
> BIOS ||... ||+--------------+|
> BOOT || |||PART ESP (FAT)||
> || |||/boot/grub/ ||
> || |||... ||
> |+--------------+|+--------------+|
> +----------------+----------------+
> | | |
> | |GPT |
> |+--------------+|+--------------+|
> ||PART ESP (FAT)|||PART ESP (FAT)||
> ||/boot/grub/ |||/boot/grub/ ||
> UEFI ||... |||... ||
> BOOT || ||| ||
> || ||| ||
> || ||| ||
> |+--------------+|+--------------+|
> +----------------+----------------+
>
> Le mer. 14 déc. 2022 à 12:36, Goh Lip <[email protected]> a écrit :
>
>>
>>
>> On 12/14/22 17:15, Chris Green wrote:
>> > On Wed, Dec 14, 2022 at 10:31:40AM +0800, Goh Lip wrote:
>> >>
>> >>
>> >> On 13/12/2022 18:55, Chris Green wrote:
>>
>> >>
>> >> Is your partition table GPT, not msdos?
>> >>
>> > Yes, it's GPT:-
>> >
>> > Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
>>
>> > Disklabel type: gpt
>>
>> >
>> > Device Start End Sectors Size Type
>> > /dev/sda1 2048 4095 2048 1M BIOS boot
>> > /dev/sda2 4096 1054719 1050624 513M EFI System
>> > /dev/sda3 1054720 1953523711 1952468992 931G Linux filesystem
>> >
>> >
>> > (There's an 8Tb USB drive as well, this is my backup system which
>> > lives in the garage, quite a way away from the house)
>> >
>>
>>
>> See
>> https://www.gnu.org/software/grub/manual/grub/grub.html#BIOS-installation
>>
>> To set up bios-legacy boot on gpt partitioning properly, you will need a
>> small partition labelled "bios_grub".
>> And yes, without it, as you found out, it will still install and boot.
>> But it will not be reliable and will, in time, likely to fail again. And
>> you can still make it work again the way you have done (and will likely
>> fail again).
>>
>> Personally, I would suggest that for gpt partitioning, boot in uefi. And
>> in msdos partitioning, boot in bios-legacy (though that too can be
>> booted in uefi boot - with unreliable performance).
>>
>> Hope this explains. Regards.
>>
>> ps: best when issuing grub-install command, use "--target=i386-pc" in
>> that command for boot-legacy boots and "--target=x86_64-efi" for uefi
>> boots, especially when installing legacy in gpt or uefi in msdos (latter
>> always not recommended, but I've done it)
>>
>>
>>
>>
