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ACCEPT(2)		    BSD	System Calls Manual		     ACCEPT(2)

     accept -- accept a	connection on a	socket

     Standard C	Library	(libc, -lc)

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

     accept(int	s, struct sockaddr * restrict addr,
	 socklen_t * restrict addrlen);

     The argument s is a socket	that has been created with socket(2), bound to
     an	address	with bind(2), and is listening for connections after a
     listen(2).	 The accept() system call extracts the first connection	re-
     quest on the queue	of pending connections,	creates	a new socket, and al-
     locates a new file	descriptor for the socket which	inherits the state of
     the O_NONBLOCK property from the original socket s.

     If	no pending connections are present on the queue, and the original
     socket is not marked as non-blocking, accept() blocks the caller until a
     connection	is present.  If	the original socket is marked non-blocking and
     no	pending	connections are	present	on the queue, accept() returns an er-
     ror as described below.  The accepted socket may not be used to accept
     more connections.	The original socket s remains open.

     The argument addr is a result argument that is filled-in with the address
     of	the connecting entity, as known	to the communications layer.  The ex-
     act format	of the addr argument is	determined by the domain in which the
     communication is occurring.  A null pointer may be	specified for addr if
     the address information is	not desired; in	this case, addrlen is not used
     and should	also be	null.  Otherwise, the addrlen argument is a value-re-
     sult argument; it should initially	contain	the amount of space pointed to
     by	addr; on return	it will	contain	the actual length (in bytes) of	the
     address returned.	This call is used with connection-based	socket types,
     currently with SOCK_STREAM.

     It	is possible to select(2) a socket for the purposes of doing an
     accept() by selecting it for read.

     For certain protocols which require an explicit confirmation, such	as ISO
     or	DATAKIT, accept() can be thought of as merely dequeueing the next con-
     nection request and not implying confirmation.  Confirmation can be im-
     plied by a	normal read or write on	the new	file descriptor, and rejection
     can be implied by closing the new socket.

     For some applications, performance	may be enhanced	by using an
     accept_filter(9) to pre-process incoming connections.

     The call returns -1 on error.  If it succeeds, it returns a non-negative
     integer that is a descriptor for the accepted socket.

     The accept() system call will fail	if:

     [EBADF]		The descriptor is invalid.

     [EINTR]		The accept() operation was interrupted.

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

     [ENFILE]		The system file	table is full.

     [ENOTSOCK]		The descriptor references a file, not a	socket.

     [EINVAL]		listen(2) has not been called on the socket descrip-

     [EINVAL]		The addrlen argument is	negative.

     [EFAULT]		The addr argument is not in a writable part of the
			user address space.

     [EWOULDBLOCK]	The socket is marked non-blocking and no connections
			are present to be accepted.

     [ECONNABORTED]	A connection arrived, but it was closed	while waiting
			on the listen queue.

     bind(2), connect(2), getpeername(2), listen(2), select(2),	socket(2),

     The accept() system call appeared in 4.2BSD.

BSD			       December	11, 1993			   BSD


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