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listen() - Unix, Linux System Call
listen - listen for connections on a socket
int listen(int sockfd, int backlog);
To accept connections, a socket is first created with
a willingness to accept incoming connections and a queue limit for incoming
connections are specified with
listen(), and then the connections are
listen() call applies only to sockets of type
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.
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
When syncookies are enabled there is no logical maximum
length and this sysctl setting is ignored.
for more information.
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
Another socket is already listening on the same port.
sockfd is not a valid descriptor.
sockfd is not a socket.
The socket is not of a type that supports the
listen() function call first appeared in 4.2BSD.
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