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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/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	   local (previously UNIX) domain protocols
	   PF_INET	   ARPA	Internet protocols
	   PF_INET6	   IPv6	(Internet Protocol version 6) protocols
	   PF_ISO	   ISO protocols
	   PF_NS	   Xerox Network Systems protocols
	   PF_IMPLINK	   IMP host at IMP link	layer
	   PF_APPLETALK	   AppleTalk protocols
	   PF_BLUETOOTH	   Bluetooth protocols

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


     The following flags can be	or'ed to the type to condition the returned
     file descriptor: The following flags are valid:

	   SOCK_CLOEXEC	Set the	close on exec property.
	   SOCK_NONBLOCK Sets non-blocking I/O.
	   SOCK_NOSIGPIPE Return EPIPE instead of raising SIGPIPE.

     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.	A stream
     socket must be in a connected state before	any data may be	sent or	re-
     ceived 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.
     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 recv(2).

     The communications	protocols used to implement a SOCK_STREAM ensure 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 an	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>.  The setsockopt(2)	and
     getsockopt(2) system calls	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:

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

     [EAFNOSUPPORT]	The address family (domain) is not supported or	the
			specified domain is not	supported by this protocol

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

     [ENFILE]		The system file	table is full.

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

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

     [EPROTOTYPE]	The socket type	is not supported by the	protocol.

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

     Stuart Sechrest, An Introductory 4.4BSD Interprocess Communication
     Tutorial.	(see /usr/share/doc/psd/20.ipctut)

     Samuel J. Leffler,	Robert S. Fabry, William N. Joy, Phil Lapsley, Steve
     Miller, and Chris Torek, Advanced 4.4BSD IPC Tutorial.  (see

     The socket() function call	appeared in 4.2BSD.

BSD			       January 23, 2012				   BSD


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