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.TH LISTEN "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH PROLOG

This manual page is part of the POSIX Programmer's Manual.

The Linux implementation of this interface may differ (consult

the corresponding Linux manual page for details of Linux behavior),

or the interface may not be implemented on Linux.

.SH NAME

listen

\(em listen for socket connections and limit the queue of incoming

connections

.SH SYNOPSIS

.LP

.nf

#include <sys/socket.h>

.P

int listen(int \fIsocket\fP, int \fIbacklog\fP);

.fi

.SH DESCRIPTION

The

\fIlisten\fR()

function shall mark a connection-mode socket, specified by the

.IR socket

argument, as accepting connections.

.P

The

.IR backlog

argument provides a hint to the implementation which the implementation

shall use to limit the number of outstanding connections in the

socket's listen queue. Implementations may impose a limit on

.IR backlog

and silently reduce the specified value. Normally, a larger

.IR backlog

argument value shall result in a larger or equal length of the listen

queue. Implementations shall support values of

.IR backlog

up to SOMAXCONN, defined in

.IR <sys/socket.h> .

.P

The implementation may include incomplete connections in its listen

queue. The limits on the number of incomplete connections and completed

connections queued may be different.

.P

The implementation may have an upper limit on the length of the listen

queue\(emeither global or per accepting socket. If

.IR backlog

exceeds this limit, the length of the listen queue is set to the

limit.

.P

If

\fIlisten\fR()

is called with a

.IR backlog

argument value that is less than 0, the function behaves as if it had

been called with a

.IR backlog

argument value of 0.

.P

A

.IR backlog

argument of 0 may allow the socket to accept connections, in which case

the length of the listen queue may be set to an

implementation-defined minimum value.

.P

The socket in use may require the process to have appropriate

privileges to use the

\fIlisten\fR()

function.

.SH "RETURN VALUE"

Upon successful completions,

\fIlisten\fR()

shall return 0; otherwise, \(mi1 shall be returned and

.IR errno

set to indicate the error.

.SH ERRORS

The

\fIlisten\fR()

function shall fail if:

.TP

.BR EBADF

The

.IR socket

argument is not a valid file descriptor.

.TP

.BR EDESTADDRREQ

.br

The socket is not bound to a local address, and the protocol does not

support listening on an unbound socket.

.TP

.BR EINVAL

The

.IR socket

is already connected.

.TP

.BR ENOTSOCK

The

.IR socket

argument does not refer to a socket.

.TP

.BR EOPNOTSUPP

The socket protocol does not support

\fIlisten\fR().

.P

The

\fIlisten\fR()

function may fail if:

.TP

.BR EACCES

The calling process does not have appropriate privileges.

.TP

.BR EINVAL

The

.IR socket

has been shut down.

.TP

.BR ENOBUFS

Insufficient resources are available in the system to complete the

call.

.LP

.IR "The following sections are informative."

.SH "EXAMPLES"

None.

.SH "APPLICATION USAGE"

None.

.SH "RATIONALE"

None.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "\fIaccept\fR\^(\|)",

.IR "\fIconnect\fR\^(\|)",

.IR "\fIsocket\fR\^(\|)"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "\fB<sys_socket.h>\fP"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.unix.org/online.html .

Any typographical or formatting errors that appear

in this page are most likely

to have been introduced during the conversion of the source files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .