shutdown() call causes all or part of a full-duplex connection on the socket
sockfd to be shut down.
SHUT_RD, further receptions will be disallowed.
SHUT_WR, further transmissions will be disallowed.
SHUT_RDWR, further receptions and transmissions will be disallowed.
As currently implemented,
checks for the validity of
how are done in domain-specific code, and not all domains perform these checks.
Most notably, UNIX domain sockets simply ignore invalid values;
this may change in the future.