слушать подключения к сокету (listen for connections on a socket)
Имя (Name)
listen - listen for connections on a socket
Синопсис (Synopsis)
#include <sys/socket.h>
int listen(int sockfd, int backlog);
Описание (Description)
listen() marks the socket referred to by sockfd as a passive
socket, that is, as a socket that will be used to accept incoming
connection requests using accept(2).
The sockfd argument is a file descriptor that refers to a socket
of type SOCK_STREAM or SOCK_SEQPACKET.
The backlog argument defines the maximum length to which the
queue of pending connections for sockfd may grow. If a
connection request arrives when the queue is 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 a later reattempt at connection succeeds.
Возвращаемое значение (Return value)
On success, zero is returned. On error, -1 is returned, and
errno is set to indicate the error.
Ошибки (Error)
EADDRINUSE
Another socket is already listening on the same port.
EADDRINUSE
(Internet domain sockets) The socket referred to by sockfd
had not previously been bound to an address and, upon
attempting to bind it to an ephemeral port, it was
determined that all port numbers in the ephemeral port
range are currently in use. See the discussion of
/proc/sys/net/ipv4/ip_local_port_range in ip(7).
EBADF The argument sockfd is not a valid file descriptor.
ENOTSOCK
The file descriptor sockfd does not refer to a socket.
EOPNOTSUPP
The socket is not of a type that supports the listen()
operation.
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, 4.4BSD (listen() first appeared in
4.2BSD).
Примечание (Note)
To accept connections, the following steps are performed:
1. A socket is created with socket(2).
2. The socket is bound to a local address using bind(2), so
that other sockets may be connect(2)ed to it.
3. A willingness to accept incoming connections and a queue
limit for incoming connections are specified with
listen().
4. Connections are accepted with accept(2).
The behavior of the backlog argument 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
/proc/sys/net/ipv4/tcp_max_syn_backlog. When syncookies are
enabled there is no logical maximum length and this setting is
ignored. See tcp(7) for more information.
If the backlog argument is greater than the value in
/proc/sys/net/core/somaxconn, then it is silently capped to that
value. Since Linux 5.4, the default in this file is 4096; in
earlier kernels, the default value is 128. In kernels before
2.4.25, this limit was a hard coded value, SOMAXCONN, with the
value 128.
Примеры (Examples)
See bind(2).
Смотри также (See also)
accept(2), bind(2), connect(2), socket(2), socket(7)
