Thanks! Yes, Sysbox is using OS-virtualization techniques to augment the abstraction of the container, thereby enabling software that interacts deeply with the kernel (e.g., dockerd, k8s, etc) to run inside the container, and do so with proper isolation (no privileged containers). Now that you mention user-mode linux, it is one of the references we used as we built Sysbox, though they are very different things of course. I think my background as a VMware ESX kernel developer played a strong influence too ...