[anttiok]

Your statement "rump kernels do not have fork" is not entirely accurate in the context. Rump kernels do support fork. However, it is not conceptually a rump kernel's business to provide fork. So it's actually the Rumprun unikernel that does not provide fork here. It's a small but quite important distinction, because it means that if you wanted, you could take the upper part of the stack and bolt it on to some other simple bottom layer which does support fork. I certainly don't want to, but maybe someone else does.

Anyway, you are right, not everything is supported. It would be cool to know if a valid program will work on Rust+Rumprun without having to run it, but I can't imagine a simple solution to that problem. I guess if the problem of knowing if something will work without running it were solved, programs wouldn't have bugs ;)