On 13.06.2022 16:54, Simon Becherer wrote:
Am 13.06.22 um 14:09 schrieb Andrei Borzenkov:
On 13.06.2022 12:43, Simon Becherer wrote:
If you want to install grub in GPT MBR, you will need BIOS boot partition. It better be located in the beginning to avoid any possible issues with BIOS access disk size limits.
here i do also not understand. actually i was thinking somewhere in mbr or gpt (the firts 2048 sectors) is the grub part which only says: "read /boot...."
Correct for MBR, wrong for GPT.
sorry still very unclear in my mind. so its not possible to boot from gpt-ext4 partition without having an additional uefi boot partition?
It is possible.
And I said nothing about UEFI boot partition which is called ESP (EFI System Partition). BIOS boot partition is used to reserve space for bootloader when using legacy BIOS boot.
Correct for MBR, wrong for GPT. could you please explain this for me?
i understand: in mbr there is a grub part somewhere in the first 2048 sectors who say -> load /boot/.... in gpt in the first 2048 sectors this is not the case.
There never was any formal specification for MBR, de-facto standard set by Microsoft fdisk was always to have some unused space before the first partition. This was traditionally used to store bootloader. GPT does have formal specification which does not define any unused space. To make sure there is space to install bootloader, grub2 is using partition with specific type (BIOS boot) to store bootloader. This is relevant only if you install grub2 in MBR (iow on the whole disk). If you install grub2 in PBR (i.e. in partition) bootloader goes somewhere inside of this partition and neither post MBR gap nor reserved partition is needed.
so if i convert a mbr to gpt then it will fail to boot ?
If you convert MBR into GPT in place, your system will likely fail to boot because grub2 first stage code will not include GPT support and will not find /boot/grub2. You need to reinstall grub2 to build the correct first stage code and if you want to install it in MBR you need BIOS grub partition in this case.
but you say later:
It is possible. this reverted (inside my brain) your statement.
simoN