[Hackbraten]

ZFS lets you create copy-on-write clones of live filesystems. It also lets you re-define (via `zfs promote`) which one is the clone and which one is the original.

Two downsides of that approach would be that 1. you would have to have ZFS as your root filesystem (which comes with its very own layers of complexity and trouble), and 2. to roll back, you'd have to reboot the system and change a kernel cmdline parameter so it boots back into the previous filesystem in its original state.

No matter which technique you end up using (ZFS or anything else), I think as long as you're on a bare metal system, rebooting or at least `kexec`-ing will be unavoidable. A live kernel can't change its own state back to a saved previous version, except in a few select special situations.