Debian offers the swupdate package in a stable release now. I'm currently building a complete debian image using FAI. The system has a GRUB bootloader and a single partition for the root filesystem with a permanent partition for persistent data.
I can't find any good explanation how to use swupdate for replacing the complete root filesystem. with a new generated one. Is that even possible while running the system or does swupdate boot into an updating image for that. The documentation does not explain how to do that.
My use case for that is to have an atomic update of the system without using APT for that because the system is not able to connect to a network nor is it possible to ship a complete APT mirror.