1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)listen.2 8.2 (Berkeley) 12/11/93 7.\" 8.Dd 9.Dt LISTEN 2 10.Os BSD 4.2 11.Sh NAME 12.Nm listen 13.Nd listen for connections on a socket 14.Sh SYNOPSIS 15.Fd #include <sys/socket.h> 16.Ft int 17.Fn listen "int s" "int backlog" 18.Sh DESCRIPTION 19To accept connections, a socket 20is first created with 21.Xr socket 2 , 22a willingness to accept incoming connections and 23a queue limit for incoming connections are specified with 24.Fn listen , 25and then the connections are 26accepted with 27.Xr accept 2 . 28The 29.Fn listen 30call applies only to sockets of type 31.Dv SOCK_STREAM 32or 33.Dv SOCK_SEQPACKET. 34.Pp 35The 36.Fa backlog 37parameter defines the maximum length the queue of 38pending connections may grow to. 39If a connection 40request arrives with the queue full the client may 41receive an error with an indication of 42.Er ECONNREFUSED , 43or, if the underlying protocol supports retransmission, 44the request may be ignored so that retries may succeed. 45.Sh RETURN VALUES 46A 0 return value indicates success; -1 indicates an error. 47.Sh ERRORS 48.Fn Listen 49will fail if: 50.Bl -tag -width [EOPNOTSUPP] 51.It Bq Er EBADF 52The argument 53.Fa s 54is not a valid descriptor. 55.It Bq Er ENOTSOCK 56The argument 57.Fa s 58is not a socket. 59.It Bq Er EOPNOTSUPP 60The socket is not of a type that supports the operation 61.Fn listen . 62.El 63.Sh SEE ALSO 64.Xr accept 2 , 65.Xr connect 2 , 66.Xr socket 2 67.Sh BUGS 68The 69.Fa backlog 70is currently limited (silently) to 5. 71.Sh HISTORY 72The 73.Nm 74function call appeared in 75.Bx 4.2 . 76