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listen() - Unix, Linux System Call
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NAME
listen - listen for connections on a socket
SYNOPSIS
#include <sys/socket.h>
int listen(int sockfd, int backlog); DESCRIPTION
To accept connections, a socket is first created with
socket(2),
a willingness to accept incoming connections and a queue limit for incoming
connections are specified with
listen(), and then 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 the queue of pending connections may
grow to. If a connection request arrives with the queue 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 retries succeed.
NOTES
The behaviour of the
backlog parameter on TCP sockets changed with Linux 2.2.
Now it specifies the queue length for
completely 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 the
tcp_max_syn_backlog sysctl.
When syncookies are enabled there is no logical maximum
length and this sysctl setting is ignored.
See
tcp(7)
for more information.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
ERRORS
Tag | Description |
EADDRINUSE | |
Another socket is already listening on the same port.
|
EBADF |
The argument
sockfd is not a valid descriptor.
|
ENOTSOCK | |
The argument
sockfd is not a socket.
|
EOPNOTSUPP | |
The socket is not of a type that supports the
listen() operation.
|
CONFORMING TO
4.4BSD, POSIX.1-2001.
The
listen() function call first appeared in 4.2BSD.
BUGS
If the socket is of type
AF_INET, and the
backlog argument is greater
than the constant
SOMAXCONN (128 in Linux 2.0 & 2.2), it is silently truncated
to
SOMAXCONN. SEE ALSO
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