System[.Posix].Process question

Hello. I am looking for something like System.Process.runInteractiveProcess (which gives me the in/out/err handles, which I like) but instead of ProcessHandle, I want a System.Posix.Types.ProcessID because I want to send a specific signal later. It seems that to a ProcessHandle I can only send SIGKILL (via System.Process.terminateProcess), and this is bad because the target process cannot intercept and handle it. In my case, it needs to cleanup (namely, kill its children). Thanks, J.W.