Many thanks for this! So on next boot, the USB drive will be used as rootfs, just because of disk label being linux-root?
This is really an easy solution which we could implement into dietpi-drive_manager.
But needs testing on which devices these steps only work.
E.g. I am pretty sure on RPi the rootfs entry in /boot/cmdline.txt will be always respected. Ordoids have their boot.ini. I will try it on VM (x86_84).
Have you been able to get this to work on the pine64?
I have been unable to get older methods to work to transfer the rootFS from the SD card to the USB. There have been some changes in how DietPi seems to reading the sd card and I am not linux savvy enough to be able to figure it out on my own.