Comment 193 for bug 1886148

Hi,

> on the V14IIL Lenovo in
> all 3 modes- Legacy BIOS,UEFI,and UEFI+secure boot- success rate 100%.
> 2. mkusb cloning iso file
> 3. rufus in Windows 10 (dd mode)

So now it looks like valid GPT does the trick for Ubuntu ISOs on Lenovo.

There remain riddles:

Why does the grub-mkrescue ISO not boot on V14IIL ?
(I still wonder which other ISOs boot on that machine.)

Why did the old Ubuntu ISOs with their invalid GPT boot on sudodus' V130
whereas a similarly invalid GPT did not help with the 20201007.1 ISO ?

Maybe Canonical Ltd. should ask Lenovo Group Limited for enlightenment.

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The xorrisofs option to cause GPT during the production of an Ubuntu ISO
would be

  -appended_part_as_gpt

With GPT it is crucial for mountability of partition 1 (the ISO) to use
option

  -partition_offset 16

GPT partition 1 may start only after the GPT array. So it cannot start at
LBA 0. The best non-0 value for the partition start is ISO LBA 16 (GPT
LBA 64). Lower is not possible, higher is waste.

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Valid GPT is fewly tested with popular ISOs.

If Ubuntu ISOs switch from MBR partition table to GPT, then it will become
interesting to see whether there are any EFIs which hate it (and why they
do).

Have a nice day :)

Thomas