LISTEN(P) POSIX Programmer's Manual LISTEN(P)NAMElisten - listen for socket connections and limit the queue of incoming
connections
SYNOPSIS
#include <sys/socket.h>
int listen(int socket, int backlog);
DESCRIPTION
The listen() function shall mark a connection-mode socket, specified by
the socket argument, as accepting connections.
The 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
backlog and silently reduce the specified value. Normally, a larger
backlog argument value shall result in a larger or equal length of the
listen queue. Implementations shall support values of backlog up to
SOMAXCONN, defined in <sys/socket.h>.
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.
The implementation may have an upper limit on the length of the listen
queue-either global or per accepting socket. If backlog exceeds this
limit, the length of the listen queue is set to the limit.
If listen() is called with a backlog argument value that is less than
0, the function behaves as if it had been called with a backlog argu‐
ment value of 0.
A 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 implementa‐
tion-defined minimum value.
The socket in use may require the process to have appropriate privi‐
leges to use the listen() function.
RETURN VALUE
Upon successful completions, listen() shall return 0; otherwise, -1
shall be returned and errno set to indicate the error.
ERRORS
The listen() function shall fail if:
EBADF The socket argument is not a valid file descriptor.
EDESTADDRREQ
The socket is not bound to a local address, and the protocol
does not support listening on an unbound socket.
EINVAL The socket is already connected.
ENOTSOCK
The socket argument does not refer to a socket.
EOPNOTSUPP
The socket protocol does not support listen().
The listen() function may fail if:
EACCES The calling process does not have the appropriate privileges.
EINVAL The socket has been shut down.
ENOBUFS
Insufficient resources are available in the system to complete
the call.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOaccept() , connect() , socket() , the Base Definitions volume of
IEEE Std 1003.1-2001, <sys/socket.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 LISTEN(P)
