LISTEN(2) BSD System Calls Manual LISTEN(2)NAMElisten — listen for connections on a socket
SYNOPSIS
#include <sys/socket.h>
int
listen(int socket, int backlog);
DESCRIPTION
Creation of socket-based connections requires several operations. First,
a socket is created with socket(2). Next, a willingness to accept incom‐
ing connections and a queue limit for incoming connections are specified
with listen(). Finally, the connections are accepted with accept(2).
The listen() call applies only to sockets of type SOCK_STREAM or
SOCK_SEQPACKET.
The backlog parameter defines the maximum length for the queue of pending
connections. If a connection request arrives with the queue full, the
client may receive an error with an indication of ECONNREFUSED. Alterna‐
tively, if the underlying protocol supports retransmission, the request
may be ignored so that retries may succeed.
RETURN VALUES
The listen() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORSListen() will fail if:
[EACCES] The current process has insufficient privileges.
[EBADF] The argument socket 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] socket is already connected.
[ENOTSOCK] The argument socket does not reference a socket.
[EOPNOTSUPP] The socket is not of a type that supports the opera‐
tion listen().
SEE ALSOaccept(2), connect(2), socket(2)BUGS
The backlog is currently limited (silently) to 128.
HISTORY
The listen() function call appeared in 4.2BSD.
4.2 Berkeley Distribution December 11, 1993 4.2 Berkeley Distribution
