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Re: Trouble making bootable USB from ISO image

Le 04/05/2019 à 18:41, deloptes a écrit :
Nicolas George wrote:

That is absolutely not true. Partition data, UEFI or not, bootable or
not, are just octets on a medium. They could be created with an Atari if
Atari had USB plugs, that would not make any difference.

The vague truth behind your statement is:

To edit UEFI variables, the computer need to have booted in UEFI mode.

The UEFI variables, the contents of the computer's non-volatile internal
memory. Not the contents of the drive. They contain, amongst other
things, the default boot options. They are not used when selecting the
boot option manually.

Yes, this is what I wanted to say - you are right. You can create the
partition with fdisk or alike, but grub refuses to install if it is not
booted in UEFI

Again, this is not true. GRUB will install, but it will just not be able to update EFI boot variables. Note that you do not need to update EFI boot variables if you install GRUB in the removable media path (--removable). At least with GRUB versions up to Stretch which relied on efibootmgr to update EFI boot variables. Maybe this has changed with Buster's GRUB version which does not rely on efibootmgr any more. Not tested yet.