listen(2)

NAME

listen − listen for connections on a socket

SYNOPSIS

int listen(int s, int backlog);

DESCRIPTION

To accept connections, a socket is first created using socket(), a queue for incoming connections is specified using listen(), and then connections are accepted using accept(). listen() applies only to unconnected sockets of type SOCK_STREAM. 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, the socket must be bound to an address by using bind() before connection establishment can continue, otherwise an EADDREQUIRED error is returned.

The listen queue is established for the socket specified by the s parameter, which is a socket descriptor.

backlog defines the maximum allowable length of the queue for pending connections. If a connection request arrives when the queue is full, the client receives an ETIMEDOUT error.

backlog is currently limited (silently) to be in the range of 1 to 20. If any other value is specified, the system automatically assigns the closest value within range.

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] The argument s is not a valid descriptor.

[EDESTADRREQ] No bind address was established.

[ENOTSOCK] The argument s is not a socket.

[EOPNOTSUPP] The socket is not of a type that supports the listen() operation.

[ENOBUFS] (Series 300/400 only) No buffer space is available. listen() cannot be started at this time.

[EINVAL] The socket has been shut down or is already connected (see socketx25(7)).

AUTHOR

listen() was developed by the University of California, Berkeley.

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