Ubuntu carries a few things that Sysbox relies on: a couple that come to mind are the shiftfs module (which Sysbox uses to enable the user-namespace in containers without requiring Docker to be set in userns-remap mode) and a kernel patch that allows overlayfs mounts from within a user-namespace (since the Docker running inside the container uses overlayfs mounts for its inner images). Having said this, we are looking at ways of overcoming these requirements to extend Sysbox to more distros; it's one of the most asked features.