@Mark Thanks to the Q&A for kindly complimenting my contribution. I try my best to learn and share. From a distance it is hard to know how helpful that is. I'll keep on learning, sharing and appreciating the support I get from the community.
PS I need to make my questions shorter and clearer π
Though I'm not quite sure about this ubuntu.img in data being mounted as root partition. Is it really like that? Can't imagine it (or did I misunderstood you).
Yes. That provides the rootfs for UT. This is part of the reason why bootloader cannot be locked again after flashing, as doing so will erase /data partition, and thus delete the UT rootfs image.