NAME
listen —
listen for connections on a
socket
SYNOPSIS
#include
<sys/socket.h>
int
listen(int
s, 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 withlisten(),
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
may succeed.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ERRORS
listen() will fail if:
- [
EBADF] - The argument s is not a valid descriptor.
- [
ENOTSOCK] - The argument s is not a socket.
- [
EOPNOTSUPP] - The socket is not of a type that supports the operation
listen(). - [
EINVAL] - The socket is already connected.
SEE ALSO
STANDARDS
The listen() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
HISTORY
The listen() system call first appeared in
4.1cBSD.
BUGS
The backlog is currently limited (silently) to the value of the kern.somaxconn sysctl, which defaults to 128.