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ACCEPT(2)		  FreeBSD System Calls Manual		     ACCEPT(2)

     accept, accept4 --	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);

     accept4(int s, struct sockaddr * restrict addr,
	 socklen_t * restrict addrlen, int flags);

     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
     request on	the queue of pending connections, creates a new	socket,	and
     allocates a new file descriptor for the socket which inherits the state
     of	the O_NONBLOCK and O_ASYNC properties and the destination of SIGIO and
     SIGURG signals from the original socket s.

     The accept4() system call is similar, but the O_NONBLOCK property of the
     new socket	is instead determined by the SOCK_NONBLOCK flag	in the flags
     argument, the O_ASYNC property is cleared,	the signal destination is
     cleared and the close-on-exec flag	on the new file	descriptor can be set
     via the SOCK_CLOEXEC flag in the flags argument.

     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
     error 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
     exact 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-result 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
     implied by	a normal read or write on the new file descriptor, and rejec-
     tion 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.

     When using	accept(), portable programs should not rely on the O_NONBLOCK
     and O_ASYNC properties and	the signal destination being inherited,	but
     should set	them explicitly	using fcntl(2);	accept4() sets these proper-
     ties consistently,	but may	not be fully portable across UNIX platforms.

     These calls return	-1 on error.  If they succeed, they return a non-nega-
     tive integer that is a descriptor for the accepted	socket.

     The accept() and accept4()	system calls 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-

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

			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.

     The accept4() system call will also fail if:

     [EINVAL]		The flags argument is invalid.

     bind(2), connect(2), getpeername(2), getsockname(2), listen(2),
     select(2),	socket(2), accept_filter(9)

     The accept() system call appeared in 4.2BSD.

     The accept4() system call appeared	in FreeBSD 10.0.

FreeBSD	Ports 11.2		October	9, 2014		    FreeBSD Ports 11.2


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