How Debian managed the systemd transition

> If someone implements a reboot-less upgrade from x.y to x.(y+1), and it actually works, I will personally buy them the beer or tasty non-alcoholic beverage of their choice*. Snapshotting the world and restoring using CRIU or similar tools doesn't count.

Hey, that's not fair: to go from n to n+1 you know the only way is to save and restore the kernel state in a version independent manner, so you're trying to define the only possible method out of your challenge. The problem with the method is the time it takes, but there are people working on it

https://sslab.gtisc.gatech.edu/pages/kup.html