shutdown —
shut down part of a full-duplex connection
Standard C Library (libc, -lc)
The shutdown() call causes all or part of a full-duplex
  connection on the socket associated with s to be shut
  down. The how argument specifies which part of the
  connection will be shut down. Permissible values are:
  - SHUT_RD
- further receives will be disallowed.
- SHUT_WR
- further sends will be disallowed.
- SHUT_RDWR
- further sends and receives will be disallowed.
 
A 0 is returned if the call succeeds, -1 if it fails.
The call succeeds unless:
  - [EBADF]
- s is not a valid descriptor.
- [EINVAL]
- The how argument is invalid.
- [ENOTCONN]
- The specified socket is not connected.
- [ENOTSOCK]
- s is a file, not a socket.
Theshutdown() function call appeared in
  4.2BSD. The how arguments used
  to be simply 0, 1, and 2, but now have named values as specified by
  X/Open Portability Guide Issue 4
  (“XPG4”).