Ubuntu Core allsnaps initrd cannot mount sdb3 as rootfs if there is also one on sda3

[Gunther Laure]

Hi,

I tried to build a rescue USB stick for our embedded device running Ubuntu Core (xenial, amd64 allsnaps).
The rescue USB stick is also based on Ubuntu Core (xenial, amd64 allsnaps) and should allow to completely update the devices root filesystem.
(The idea is to be able to update from 15.04 to 16.04 later, just with this USB stick)

If I try to boot from the USB stick (BIOS or grub) the initrd mixes both systems. It looks for the partition called "writable" and the first found is always preferred.
In our case there would be 2 (one on sda, and one on sdb == usb).

I tried various kernel options to alter this behavior:

-          root=UUID=679....

-          root=LABEL='other_writable'  (I changed the name of the partition)

but with little success. sda (the internal flash)  is always mounted, though the kernel and initrd is loaded from sdb (the usb stick).

But as long as the internal flash  is mounted, a raw update (dd if= ...) is impossible.

I will move from Ubuntu Core to some other minimal Linux system (for the rescue system), but I wanted to tell this to the mailing list.


Best Regards,
Gunther
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