It's the other direction. UML runs Linux kernel in ring 3. It emulates hardware protection mechanisms in order to make debugging easier and to run VMs when the

It's the other direction. UML runs Linux kernel in ring 3. It emulates hardware protection mechanisms in order to make debugging easier and to run VMs when there is no kernel access. UKL runs userspace apps in ring 0. It discards hardware protection mechanisms in order to make processes run faster, decrease boot time, and decrease management overhead.