Section (2) listen
listen — listen for connections on a socket
#include <sys/types.h> /* See NOTES */ #include <sys/socket.h>
listen() marks the socket
referred to by
as a passive socket, that is, as a socket that will be used
to accept incoming connection requests using accept(2).
argument is a file descriptor that refers to a socket of type
argument defines the maximum length to which the queue of
pending connections for
sockfd may grow. If a
connection request arrives when the queue is full, the client
may receive an error with an indication of ECONNREFUSED or, if the underlying
protocol supports retransmission, the request may be ignored
so that a later reattempt at connection succeeds.
On success, zero is returned. On error, −1 is
errno is set
Another socket is already listening on the same port.
(Internet domain sockets) The socket referred to by
sockfdhad not previously been bound to an address and, upon attempting to bind it to an ephemeral port, it was determined that all port numbers in the ephemeral port range are currently in use. See the discussion of
sockfdis not a valid file descriptor.
The file descriptor
sockfddoes not refer to a socket.
The socket is not of a type that supports the
To accept connections, the following steps are performed:
POSIX.1 does not require the inclusion of
> and this header file is not required on
Linux. However, some historical (BSD) implementations
required this header file, and portable applications are
probably wise to include it.
The behavior of the
backlog argument on TCP sockets
changed with Linux 2.2. Now it specifies the queue length for
established sockets waiting to be accepted, instead of the
number of incomplete connection requests. The maximum length
of the queue for incomplete sockets can be set using
When syncookies are enabled there is no logical maximum
length and this setting is ignored. See tcp(7) for more
argument is greater than the value in
/proc/sys/net/core/somaxconn, then it is
silently truncated to that value; the default value in this
file is 128. In kernels before 2.4.25, this limit was a hard
the value 128.
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$Id: listen.2,v 1.6 1999/05/18 14:10:32 freitag Exp $
Modified Fri Jul 23 22:07:54 1993 by Rik Faith <faithcs.unc.edu>
Modified 950727 by aeb, following a suggestion by Urs Thuermann
Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esrthyrsus.com>
Modified 1998 by Andi Kleen
Modified 11 May 2001 by Sam Varshavchik <mrsamcourier-mta.com>