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

NAME
     socket -- create an endpoint for communication

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

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

DESCRIPTION
     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.  These families are defined in
     the include file <sys/socket.h>.  The currently understood formats are

	   AF_UNIX	   (UNIX internal protocols),
	   AF_INET	   (ARPA Internet protocols),
	   AF_ISO	   (ISO protocols),
	   AF_NS	   (Xerox Network Systems protocols), and
	   AF_IMPLINK	   (IMP host at IMP link layer).

     The socket has the indicated type, which specifies the semantics of communication.  Cur-
     rently defined types are:

	   SOCK_STREAM
	   SOCK_DGRAM
	   SOCK_RAW
	   SOCK_SEQPACKET
	   SOCK_RDM

     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 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 super-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 specified in this manner.	The protocol number to use is particular to the communi-
     cation domain in which communication is to take place; see protocols(5).

     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.  When a
     session has been completed a close(2) may be performed.  Out-of-band data may also be trans-
     mitted as described in send(2) and received as described in recv(2).

     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 suc-
     cessfully 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 forc-
     ing 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 exit.

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

     SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams to correspondents 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.

RETURN VALUES
     A -1 is returned if an error occurs, otherwise the return value is a descriptor referencing
     the socket.

ERRORS
     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 freed.

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

     An Introductory 4.3 BSD Interprocess Communication Tutorial, reprinted in UNIX Programmer's
     Supplementary Documents Volume 1.

     BSD Interprocess Communication Tutorial, reprinted in UNIX Programmer's Supplementary
     Documents Volume 1.

HISTORY
     The socket() function call appeared in 4.2BSD.

4.2 Berkeley Distribution		   June 4, 1993 		4.2 Berkeley Distribution
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