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SOCKET(2)		    BSD	System Calls Manual		     SOCKET(2)

     socket -- create an endpoint for communication

     Standard C	Library	(libc, -lc)

     #include <sys/types.h>
     #include <sys/socket.h>

     socket(int	domain,	int type, int protocol);

     Socket() creates an endpoint for communication and	returns	a descriptor.

     The domain	parameter specifies a communications domain within which com-
     munication	will take place; this selects the protocol family which	should
     be	used.  These families are defined in the include file <sys/socket.h>.
     The currently understood formats are:

	   PF_LOCAL	   Host-internal protocols, formerly called PF_UNIX,
	   PF_UNIX	   Host-internal protocols, deprecated,	use PF_LOCAL,
	   PF_INET	   Internet version 4 protocols,
	   PF_IMPLINK	   ARPAnet IMP addresses,
	   PF_PUP	   PUP protocols, like BSP,
	   PF_CHAOS	   MIT CHAOS protocols,
	   PF_NS	   Xerox Network Systems protocols,
	   PF_ISO	   ISO protocols,
	   PF_OSI	   Open	Systems	Interconnection	protocols,
	   PF_ECMA	   European Computer Manufacturers,
	   PF_DATAKIT	   Datakit protocols,
	   PF_CCITT	   ITU-T protocols, like X.25,
	   PF_SNA	   IBM SNA,
	   PF_DECnet	   DECnet,
	   PF_DLI	   DEC Direct Data Link	Interface protocol,
	   PF_LAT	   LAT protocol,
	   PF_HYLINK	   NSC Hyperchannel,
	   PF_APPLETALK	   AppleTalk protocols,
	   PF_ROUTE	   Internal Routing protocol,
	   PF_LINK	   Link	layer interface,
	   PF_XTP	   eXpress Transfer Protocol,
	   PF_COIP	   Connection-Oriented IP, aka ST II,
	   PF_CNT	   Computer Network Technology,
	   PF_SIP	   Simple Internet Protocol,
	   PF_IPX	   Novell Internet Packet eXchange protocol,
	   PF_RTIP	   Help	Identify RTIP packets,
	   PF_PIP	   Help	Identify PIP packets,
	   PF_ISDN	   Integrated Services Digital Network,
	   PF_KEY	   Internal key-management function,
	   PF_INET6	   Internet version 6 protocols,
	   PF_NATM	   Native ATM access,
	   PF_ATM	   ATM,
	   PF_NETGRAPH	   Netgraph sockets

     The socket	has the	indicated type,	which specifies	the semantics of com-
     munication.  Currently defined types are:

	   SOCK_STREAM	   Stream socket,
	   SOCK_DGRAM	   Datagram socket,
	   SOCK_RAW	   Raw-protocol	interface,
	   SOCK_RDM	   Reliably-delivered packet,
	   SOCK_SEQPACKET  Sequenced packet stream

     A SOCK_STREAM type	provides sequenced, reliable, two-way connection based
     byte streams.  An out-of-band data	transmission mechanism may be sup-
     ported.  A	SOCK_DGRAM socket supports datagrams (connectionless, unreli-
     able messages of a	fixed (typically small)	maximum	length).  A
     SOCK_SEQPACKET socket may provide a sequenced, reliable, two-way connec-
     tion-based	data transmission path for datagrams of	fixed maximum length;
     a consumer	may be required	to read	an entire packet with each read	system
     call.  This facility is protocol specific,	and presently implemented only
     for PF_NS.	 SOCK_RAW sockets provide access to internal network protocols
     and interfaces.  The types	SOCK_RAW, which	is available only to the su-
     per-user, and SOCK_RDM, which is planned, but not yet implemented,	are
     not described here.

     The protocol specifies a particular protocol to be	used with the socket.
     Normally only a single protocol exists to support a particular socket
     type within a given protocol family.  However, it is possible that	many
     protocols may exist, in which case	a particular protocol must be speci-
     fied in this manner.  The protocol	number to use is particular to the
     "communication domain" in which communication is to take place; see

     Sockets of	type SOCK_STREAM are full-duplex byte streams, similar to
     pipes.  A stream socket must be in	a connected state before any data may
     be	sent or	received on it.	 A connection to another socket	is created
     with a connect(2) call.  Once connected, data may be transferred using
     read(2) and write(2) calls	or some	variant	of the send(2) and recv(2)
     calls.  (Some protocol families, such as the Internet family, support the
     notion of an "implied connect", which permits data	to be sent piggybacked
     onto a connect operation by using the sendto(2) call.)  When a session
     has been completed	a close(2) may be performed.  Out-of-band data may
     also be transmitted as described in send(2) and received as described in

     The communications	protocols used to implement a SOCK_STREAM insure that
     data is not lost or duplicated.  If a piece of data for which the peer
     protocol has buffer space cannot be successfully transmitted within a
     reasonable	length of time,	then the connection is considered broken and
     calls will	indicate an error with -1 returns and with ETIMEDOUT as	the
     specific code in the global variable errno.  The protocols	optionally
     keep sockets "warm" by forcing transmissions roughly every	minute in the
     absence of	other activity.	 An error is then indicated if no response can
     be	elicited on an otherwise idle connection for a extended	period (e.g. 5
     minutes).	A SIGPIPE signal is raised if a	process	sends on a broken
     stream; this causes naive processes, which	do not handle the signal, to

     SOCK_SEQPACKET sockets employ the same system calls as SOCK_STREAM	sock-
     ets.  The only difference is that read(2) calls will return only the
     amount of data requested, and any remaining in the	arriving packet	will
     be	discarded.

     SOCK_DGRAM	and SOCK_RAW sockets allow sending of datagrams	to correspon-
     dents named in send(2) calls.  Datagrams are generally received with
     recvfrom(2), which	returns	the next datagram with its return address.

     An	fcntl(2) call can be used to specify a process group to	receive	a
     SIGURG signal when	the out-of-band	data arrives.  It may also enable non-
     blocking I/O and asynchronous notification	of I/O events via SIGIO.

     The operation of sockets is controlled by socket level options.  These
     options are defined in the	file <sys/socket.h>.  Setsockopt(2) and
     getsockopt(2) are used to set and get options, respectively.

     A -1 is returned if an error occurs, otherwise the	return value is	a de-
     scriptor referencing the socket.

     The socket() call fails if:

     [EPROTONOSUPPORT]	The protocol type or the specified protocol is not
			supported within this domain.

     [EMFILE]		The per-process	descriptor table is full.

     [ENFILE]		The system file	table is full.

     [EACCES]		Permission to create a socket of the specified type
			and/or protocol	is denied.

     [ENOBUFS]		Insufficient buffer space is available.	 The socket
			cannot be created until	sufficient resources are

     accept(2),	bind(2), connect(2), getpeername(2), getsockname(2),
     getsockopt(2), ioctl(2), listen(2), read(2), recv(2), select(2), send(2),
     shutdown(2), socketpair(2), write(2), getprotoent(3), netgraph(4),

     "An Introductory 4.3 BSD Interprocess Communication Tutorial", PS1, 7.

     "BSD Interprocess Communication Tutorial",	PS1, 8.

     The socket() function call	appeared in 4.2BSD.

BSD			       November	24, 1997			   BSD


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