'\" te
.\"  Copyright 1989 AT&T  
.\" Copyright (C) 1999, Sun Microsystems, Inc. All Rights Reserved
.TH listen 3SOCKET "8 Nov 1999" "SunOS 5.11" "Sockets Library Functions"
.SH NAME
listen \- listen for connections on a socket
.SH SYNOPSIS
.LP
.nf
\fBcc\fR [ \fIflag\fR ... ] \fIfile\fR ... \fB-lsocket\fR \fB -lnsl \fR [ \fIlibrary\fR ... ]
#include <sys/types.h>
#include <sys/socket.h>

\fBint\fR \fBlisten\fR(\fBint\fR \fIs\fR, \fBint\fR \fIbacklog\fR);
.fi

.SH DESCRIPTION
.sp
.LP
To accept connections, a socket is first created with  \fBsocket\fR(3SOCKET), a backlog for incoming connections is specified with \fBlisten()\fR and then the connections are accepted with  \fBaccept\fR(3SOCKET). The \fBlisten()\fR call applies only to sockets of type \fBSOCK_STREAM\fR or \fBSOCK_SEQPACKET\fR.
.sp
.LP
The \fIbacklog\fR parameter defines the maximum length the queue of pending connections may grow to.
.sp
.LP
If a connection request arrives with the queue full, the client will receive an error with an indication of \fBECONNREFUSED\fR for  \fBAF_UNIX\fR sockets. If the underlying protocol supports retransmission,  the connection request may be ignored so that retries may succeed. For \fBAF_INET\fR and \fBAF_INET6\fRsockets, the \fBTCP\fR will retry the connection. If the  \fIbacklog\fR is not cleared by the time the tcp times out, the connect will fail with \fBETIMEDOUT\fR.
.SH RETURN VALUES
.sp
.LP
A \fB0\fR return value indicates success; \fB\(mi1\fR indicates an error.
.SH ERRORS
.sp
.LP
The call fails if:
.sp
.ne 2
.mk
.na
\fB\fBEBADF\fR\fR
.ad
.RS 14n
.rt  
The argument \fIs\fR is not a valid file descriptor.
.RE

.sp
.ne 2
.mk
.na
\fB\fBENOTSOCK\fR\fR
.ad
.RS 14n
.rt  
The argument \fIs\fR is not a socket.
.RE

.sp
.ne 2
.mk
.na
\fB\fBEOPNOTSUPP\fR\fR
.ad
.RS 14n
.rt  
The socket is not of a type that supports the operation \fBlisten()\fR.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
tab() box;
cw(2.75i) |cw(2.75i) 
lw(2.75i) |lw(2.75i) 
.
ATTRIBUTE TYPEATTRIBUTE VALUE
_
MT-LevelSafe
.TE

.SH SEE ALSO
.sp
.LP
\fBaccept\fR(3SOCKET), \fBconnect\fR(3SOCKET), \fBsocket\fR(3SOCKET), \fBattributes\fR(5), \fBsocket.h\fR(3HEAD)
.SH NOTES
.sp
.LP
There is currently no \fIbacklog\fR limit.