Unikernels gained an increasing interest in the recent years because they provide efficient resource allocation and high performance for cloud services by bundling the application with a minimal set of OS services in a guest VM. Although a unikernel is by design small and lightweight, fleets of unikernels based on the same image are not necessarily more efficient than containers because the latter can rely upon OS primitives for sharing memory. Futhermore, porting POSIX applications on top of unikernels brings a new challenge: what does fork() mean in the world of unikernels where there is memory isolation within a VM? Lacking fork() support significantly reduces the applicability of unikernels in popular cloud applications.