The socket(3SOCKET) call creates a socket in the specified family and of the specified type.
s = socket(family, type, protocol);
If the protocol is unspecified (a value of 0), the system selects a protocol that supports the requested socket type. The socket handle (a file descriptor) is returned.
The family is specified by one of the constants defined in sys/socket.h. Constants named AF_suite specify the address format to use in interpreting names.
s = socket(AF_UNIX, SOCK_DGRAM, 0);
Set the protocol argument to 0, the default protocol, in most situations.