.\" $OpenBSD: listen.2,v 1.2 1996/03/19 23:15:16 niklas Exp $ .\" $NetBSD: listen.2,v 1.7 1996/02/16 20:38:45 phil Exp $ .\" .\" Copyright (c) 1983, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)listen.2 8.2 (Berkeley) 12/11/93 .\" .Dd December 11, 1993 .Dt LISTEN 2 .Os BSD 4.2 .Sh NAME .Nm listen .Nd listen for connections on a socket .Sh SYNOPSIS .Fd #include <sys/socket.h> .Ft int .Fo listen .Fa "int socket" .Fa "int backlog" .Fc .Sh DESCRIPTION Creation of socket-based connections requires several operations. First, a socket is created with .Xr socket 2 . Next, a willingness to accept incoming connections and a queue limit for incoming connections are specified with .Fn listen . Finally, the connections are accepted with .Xr accept 2 . The .Fn listen call applies only to sockets of type .Dv SOCK_STREAM or .Dv SOCK_SEQPACKET. .Pp The .Fa backlog parameter defines the maximum length for the queue of pending connections. If a connection request arrives with the queue full, the client may receive an error with an indication of .Er ECONNREFUSED . Alternatively, if the underlying protocol supports retransmission, the request may be ignored so that retries may succeed. .Sh RETURN VALUES .Rv -std listen .Sh ERRORS .Fn Listen will fail if: .Bl -tag -width Er .\" ========== .It Bq Er EACCES The current process has insufficient privileges. .\" ========== .It Bq Er EBADF The argument .Fa socket is not a valid file descriptor. .\" ========== .It Bq Er EDESTADDRREQ The socket is not bound to a local address and the protocol does not support listening on an unbound socket. .\" ========== .It Bq Er EINVAL .Fa socket is already connected. .\" ========== .It Bq Er ENOTSOCK The argument .Fa socket does not reference a socket. .\" ========== .It Bq Er EOPNOTSUPP The socket is not of a type that supports the operation .Fn listen . .El .Sh SEE ALSO .Xr accept 2 , .Xr connect 2 , .Xr socket 2 .Sh BUGS The .Fa backlog is currently limited (silently) to 128. .Sh HISTORY The .Fn listen function call appeared in .Bx 4.2 .