[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
this.


> 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.

Matthijs
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