[Letux-kernel] Subtle issue with U-Boot and kernel and SD card UUIDs

Matthijs van Duin matthijsvanduin at gmail.com
Tue May 23 15:48:29 CEST 2017

On 23 May 2017 at 15:31, H. Nikolaus Schaller <hns at goldelico.com> wrote:

> U-Boot only has some support for partition UUIDs.

I know it can also determine filesystem UUIDs, since Robert Nelson's images
use these for booting the system (provided an initramfs is present, since
the kernel doesn't support them)

I am not sure if the "MLO in FAT partition" approach works for GPT at all.

Not afaik. Of course when MLO at fixed offset is used you can use any
partition table format you want, but I don't know if older SoCs support

> By the way: this UUID thing is a strong argument against creating SD cards
> by dd-ing some .img to the raw disk. They will all share the UUIDs and are
> not
> uniquely identified any more.

Yes it's recommended to randomize various ids after flashing:
- disklabel (maybe, if you care)
- filesystem uuid
- machine id
- ssh host keys

I generally use a script which does all that after dd'ing the image and
expanding it to fit using resize2fs.

I also try to avoid using UUIDs anywhere in the first place.

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