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socket(3N)							    socket(3N)

NAME    [Toc]    [Back]

     socket - create an	endpoint for communication

SYNOPSIS    [Toc]    [Back]

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

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

DESCRIPTION    [Toc]    [Back]

     socket creates an endpoint	for communication and returns a	descriptor.

     The domain	parameter specifies a communications domain within which
     communication will	take place; this selects the protocol family which
     should be used.  The protocol family generally is the same	as the address
     family for	the addresses supplied in later	operations on the socket.
     These families are	defined	in the include file sys/socket.h.  There must
     be	an entry in the	netconfig(4) file for at least each protocol family
     and type required.	 If protocol has been specified, but no	exact match
     for the tuplet family, type, protocol is found, then the first entry
     containing	the specified family and type with zero	for protocol will be
     used.  The	currently understood formats are:

     PF_UNIX		 UNIX system internal protocols

     PF_INET		 ARPA Internet protocols

     The socket	has the	indicated type,	which specifies	the communication
     semantics.	 Currently defined types are:


     A SOCK_STREAM type	provides sequenced, reliable, two-way connection-based
     byte streams.  An out-of-band data	transmission mechanism may be
     supported.	 A SOCK_DGRAM socket supports datagrams	(connectionless,
     unreliable	messages of a fixed (typically small) maximum length).	A
     SOCK_SEQPACKET socket may provide a sequenced, reliable, two-way
     connection-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 not
     implemented for any protocol family.  SOCK_RAW sockets provide access to
     internal network interfaces.  The types SOCK_RAW, which is	available only
     to	a privileged user, and SOCK_RDM, for which no implementation currently
     exists, are not described here.

     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, multiple protocols may

									Page 1

socket(3N)							    socket(3N)

     exist, in which case a particular protocol	must be	specified in this
     manner.  The protocol number to use is particular to the "communication
     domain" in	which communication is to take place.  If a protocol is
     specified by the caller, then it will be packaged into a socket level
     option request and	sent to	the underlying protocol	layers.

     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(3N)	call.  Once connected, data may	be transferred using
     read(2) and write(2) calls	or some	variant	of the send(3N)	and recv(3N)
     calls.  When a session has	been completed,	a close(2) may be performed.
     Out-of-band data may also be transmitted as described on the send(3N)
     manual page and received as described on the recv(3N) manual page.

     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 (for
     instance 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	exit.

     SOCK_SEQPACKET sockets employ the same system calls as SOCK_STREAM
     sockets.  The only	difference is that read	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 datagrams to	be sent	to
     correspondents named in sendto calls.  Datagrams are generally received
     with recvfrom, 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 with SIGIO

     The operation of sockets is controlled by socket level options.  These
     options are defined in the	file /usr/include/sys/socket.h.

RETURN VALUE    [Toc]    [Back]

     A -1 is returned if an error occurs.  Otherwise the return	value is a
     descriptor	referencing the	socket.

									Page 2

socket(3N)							    socket(3N)

ERRORS    [Toc]    [Back]

     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.

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

     ENOMEM		 Insufficient user memory is available.

     ENOSR		 There were insufficient STREAMS resources available
			 to complete the operation.

SEE ALSO    [Toc]    [Back]

     close(2), fcntl(2), ioctl(2), read(2), write(2), accept(3N), bind(3N),
     connect(3N), getsockname(3N), getsockopt(3N), listen(3N), recv(3N),
     send(3N), shutdown(3N), socketpair(3N)

									PPPPaaaaggggeeee 3333
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