UNIX domain sockets are named with UNIX paths. For example, a socket might be named /tmp/foo. UNIX domain sockets communicate only between processes on a single host. Sockets in the UNIX domain are not considered part of the network protocols because they can be used to communicate only between processes on a single host.
Socket types define the communication properties visible to a user. The Internet domain sockets provide access to the TCP/IP transport protocols. The Internet domain is identified by the value AF_INET. Sockets exchange data only with sockets in the same domain.
The socket() 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. For more information, see the socket(3XNET) man page.
s = socket(AF_UNIX, SOCK_DGRAM, 0);
Set the protocol argument to 0, the default protocol, in most situations.