depends what you mean by running an entire ubuntu os. It's not running systemd, its just running that one process you asked for. It be as if you booted ubuntu

depends what you mean by running an entire ubuntu os. It's not running systemd, its just running that one process you asked for. It be as if you booted ubuntu kernel and instead of running systemd to run all sorts of services, you run the single process you wanted. You're running on "ubuntu", but not really, i.e. the file system is provided by ubuntu, but you're not using the normal ubuntu environment with all the services that would start at boot. You can also have docker containers run systemd if you want, but that's a much more advanced use case.