listen.2 (2010 09)

l
listen(2) listen(2)
NAME
listen - listen for connections on a socket
SYNOPSIS
#include <sys/socket.h>
int listen(int s, int backlog);
DESCRIPTION
To accept connections, a socket is first created using
socket(), a queue for incoming connections is
activated using
listen(), and then connections are accepted using
accept(). listen() applies
only to unconnected sockets of type SOCK_STREAM. Except for AF_VME_LINK, if the socket has not
been bound to a local port before
listen()
is invoked, the system automatically binds a local port for
the socket to listen on (see inet (7F)). For sockets in the address family AF_CCITT and AF_VME_LINK,
the socket must be bound to an address by using
bind() before connection establishment can continue,
otherwise an [EADDREQUIRED] error is returned.
A listen queue is established for the socket specified by the s parameter, which is a socket descriptor.
backlog defines the desirable queue length for pending connections. The actual queue length may be
greater than the specified backlog . If a connection request arrives when the queue is full, the client will
receive an [ETIMEDOUT] error.
backlog is limited to the range of 0 to
SOMAXCONN, which is defined in
<sys/socket.h>. SOMAXCONN
is currently set to 4096. If any other value is specified, the system automatically assigns the closest value
within the range. Note that for HP-UX BSD Sockets,abacklog of 0 specifies only 1 pending connection
is allowed at any given time. For X/Open Sockets,abacklog of 0 specifies no further connection is
allowed.
X/Open Sockets Compilation Environment
See xopen_networking(7).
DEPENDENCIES
AF_CCITT
Call-acceptance can be controlled by the
X25_CALL_ACPT_APPROVAL ioctl() call described in
RETURN VALUE. Upon successful completion,
listen() returns 0; otherwise, it returns −1 and sets
errno to indicate the error.
ERRORS
listen() fails if any of the following conditions are encountered:
[EBADF] s is not a valid file descriptor.
[EDESTADDRREQ] The socket s has not been bound to an address by using
bind().
[ENOTSOCK] s is a valid file descriptor but it is not a socket.
[EOPNOTSUPP] The socket referenced by s does not support
listen().
[EINVAL] The socket has been shut down or is already connected.
WARNINGS
Linking binary objects compiled to X/Open Sockets specification and binary objects compiled to HP-UX
BSD Sockets specification to the same executable may result in unexpected behavior, including applica-
tion abnormal termination and unexpected socket errors. See xopen_networking(7) for details and
remedy.
FUTURE DIRECTION
Currently, the default behavior is the HP-UX BSD Sockets; however, it might be changed to X/Open
Sockets in a future release. At that time, any HP-UX BSD Sockets behavior that is incompatible with
X/Open Sockets might be obsoleted. Applications that conform to the X/Open specification now will
avoid migration problems (see xopen_networking(7)).
AUTHOR
listen() was developed by HP and the University of California, Berkeley.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1