It talks about mapping a port (and ip address, and protocol) to a process, but on Linux (and I think other unixes as well) that isn't quite accurate. It maps to

It talks about mapping a port (and ip address, and protocol) to a process, but on Linux (and I think other unixes as well) that isn't quite accurate. It maps to a file descriptor, and that file descriptor can potentially be share with other processes (for example by forking, or passing it over a unix domain socket). One common way this is used is to pass a socket file descriptor from the old process to the new process when restarting a service.