UEFI vs BIOS I give up ( A Rant)

[jackdanielsesq]

MS introduced this artifical limitation of not allowing WinOS to install in MBR mode to boot from GPT. Well I have installed WInOS10 in BIOS mode on a this GPT disk, which I have running here ;=) It's a 4TB disk with multiple Linux all in MBR (NON-UEFI).
For GRUB to boot in BIOS/MBR from a GPT disk, one needs simply add an 1MB (unformatted) partition marked as bios_grub - preferable at the beginning of the disk, so BIOS can better find it....

Thank you for that ....

Regards

Jack

[Head_on_a_Stick]

I wanted to have this usb drive work on a friend's machine - on the off chance I was ever in a position with no laptop of my own. No luck.

To get the stick to work with both UEFI and non-UEFI you will need a GUID partition table with a BIOS boot partition[0] & an EFI system partition[1] and also the grub-pc-bin, grub-efi-ia32-bin & grub-efi-amd64-bin packages.

Then use these commands from the system on the USB stick:

Code: Select all

sudo -i
mount /dev/sdXY /mnt
grub-install --target=i386-pc /dev/sdX
grub-install --target=i386-efi --removable --efi-directory=/mnt
grub-install --target=x86_64-efi --removable --efi-directory=/mnt
umount /mnt
exit

Replace X with the letter assigned to the drive and replace Y with the number for the EFI system partition.

And remember to disable Secure Boot, MX does not support it.

[0] Type "ef02" in gdisk or "bios_grub" in gparted, *do not* format. It only needs to be ~0.5MiB so I use sectors 34-2047, they should be free in an optimally aligned disk.
[1] Needs to be FAT-formatted and of type "ef00" in gdsik or "boot,esp" in gparted.

EDIT: changed gparted's name for the BIOS boot partition, thanks fehlix.

[fehlix]

I wanted to have this usb drive work on a friend's machine - on the off chance I was ever in a position with no laptop of my own. No luck.

To get the stick to work with both UEFI and non-UEFI you will need a GUID partition table ...

GPT is not strictly required to boot from in UEFI mode. (That's about the confusen of GPT/DOS disks vs UEFI/BIOS boot)
MX Live USB can boot in both modes UEFI and BIOS from GPT or MBR(DOS) partition table layouts.
You can decide when you create with Live USB maker to choose either GPT or MBR partition table layout.

... with a BIOS boot partition[0] & an EFI system partition[1]

... the BIOS boot partition is recommended to have Grub boot reliable from GPT disks in BIOS mode.
But note, Grub can boot also using blocklists without this bios-boot partition - - not recommended , but working.

[0] Type "ef02" in gdisk or "bios_boot" in gparted, *do not* format. It only needs to be ~0.5MiB so I use sectors 34-2047, they should be free in an optimally aligned disk.

To make it simpler, just use Gparted and create 1 MB partition, and do stick to a alignment of 1MB boundary within Gparted.
Also, the bios-boot partition flag is called "bios_grub" within both Gparted and in gdisk.
In addtion for multi-boot installs, it might be worth to consider to install the efi-bootloader for each install
separately into the ESP using different bootloader-id's. So incase reEFInd might come handy and one can select between these efi-loaders as most UEFI-firmware will not scan for further efi-loader but only the fallback at /EFI/boot/bootx64.efi

[Head_on_a_Stick]

the bios-boot partition flag is called "bios_grub" within both Gparted and in gdisk.

D'oh! Thanks for the correction

I don't think gdisk uses that name though:

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   4              34            2047   1007.0 KiB  EF02

And yes, there's more than one way to skin this particular cat.

EDIT:

MX Live USB can boot in both modes UEFI and BIOS from GPT or MBR(DOS) partition table layouts.

Only if the firmware supports it. I've encountered machines that won't boot in UEFI mode from an msdos partition table.

[fehlix]

I don't think gdisk uses that name though:

Code: Select all

   4              34            2047   1007.0 KiB  EF02

correct: gdisk shows only the code ef02 not the flag-name