1.\" Copyright (c) 1983, 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)accept.2 8.2 (Berkeley) 12/11/93 33.\" $FreeBSD$ 34.\" 35.Dd December 11, 1993 36.Dt ACCEPT 2 37.Os 38.Sh NAME 39.Nm accept 40.Nd accept a connection on a socket 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In sys/types.h 45.In sys/socket.h 46.Ft int 47.Fn accept "int s" "struct sockaddr *addr" "socklen_t *addrlen" 48.Sh DESCRIPTION 49The argument 50.Fa s 51is a socket that has been created with 52.Xr socket 2 , 53bound to an address with 54.Xr bind 2 , 55and is listening for connections after a 56.Xr listen 2 . 57The 58.Fn accept 59system call 60extracts the first connection request 61on the queue of pending connections, creates 62a new socket with the same properties as 63.Fa s , 64and allocates a new file descriptor 65for the socket. If no pending connections are 66present on the queue, and the socket is not marked 67as non-blocking, 68.Fn accept 69blocks the caller until a connection is present. 70If the socket is marked non-blocking and no pending 71connections are present on the queue, 72.Fn accept 73returns an error as described below. 74The accepted socket 75may not be used 76to accept more connections. The original socket 77.Fa s 78remains open. 79.Pp 80The argument 81.Fa addr 82is a result argument that is filled-in with 83the address of the connecting entity, 84as known to the communications layer. 85The exact format of the 86.Fa addr 87argument is determined by the domain in which the communication 88is occurring. 89The 90.Fa addrlen 91argument 92is a value-result argument; it should initially contain the 93amount of space pointed to by 94.Fa addr ; 95on return it will contain the actual length (in bytes) of the 96address returned. 97This call 98is used with connection-based socket types, currently with 99.Dv SOCK_STREAM . 100.Pp 101It is possible to 102.Xr select 2 103a socket for the purposes of doing an 104.Fn accept 105by selecting it for read. 106.Pp 107For certain protocols which require an explicit confirmation, 108such as 109.Tn ISO 110or 111.Tn DATAKIT , 112.Fn accept 113can be thought of 114as merely dequeueing the next connection 115request and not implying confirmation. 116Confirmation can be implied by a normal read or write on the new 117file descriptor, and rejection can be implied by closing the 118new socket. 119.Pp 120For some applications, performance may be enhanced by using an 121.Xr accept_filter 9 122to pre-process incoming connections. 123.Sh RETURN VALUES 124The call returns \-1 on error. If it succeeds, it returns a non-negative 125integer that is a descriptor for the accepted socket. 126.Sh ERRORS 127The 128.Fn accept 129system call will fail if: 130.Bl -tag -width Er 131.It Bq Er EBADF 132The descriptor is invalid. 133.It Bq Er EINTR 134The 135.Fn accept 136operation was interrupted. 137.It Bq Er EMFILE 138The per-process descriptor table is full. 139.It Bq Er ENFILE 140The system file table is full. 141.It Bq Er ENOTSOCK 142The descriptor references a file, not a socket. 143.It Bq Er EINVAL 144.Xr listen 2 145has not been called on the socket descriptor. 146.It Bq Er EFAULT 147The 148.Fa addr 149argument is not in a writable part of the 150user address space. 151.It Bq Er EWOULDBLOCK 152The socket is marked non-blocking and no connections 153are present to be accepted. 154.It Bq Er ECONNABORTED 155A connection arrived, but it was closed while waiting 156on the listen queue. 157.El 158.Sh SEE ALSO 159.Xr bind 2 , 160.Xr connect 2 , 161.Xr getpeername 2 , 162.Xr listen 2 , 163.Xr select 2 , 164.Xr socket 2 , 165.Xr accept_filter 9 166.Sh HISTORY 167The 168.Fn accept 169system call appeared in 170.Bx 4.2 . 171