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listen(2) [mojave man page]

LISTEN(2)						      BSD System Calls Manual							 LISTEN(2)

NAME
listen -- listen for connections on a socket SYNOPSIS
#include <sys/socket.h> int listen(int socket, int backlog); DESCRIPTION
Creation of socket-based connections requires several operations. First, a socket is created with socket(2). Next, a willingness to accept incoming connections and a queue limit for incoming connections are specified with listen(). Finally, the connections are accepted with accept(2). The listen() call applies only to sockets of type SOCK_STREAM. The backlog parameter defines the maximum length for the queue of pending connections. If a connection request arrives with the queue full, the client may receive an error with an indication of ECONNREFUSED. Alternatively, if the underlying protocol supports retransmission, the request may be ignored so that retries may succeed. RETURN VALUES
The listen() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS
listen() will fail if: [EACCES] The current process has insufficient privileges. [EBADF] The argument socket is not a valid file descriptor. [EDESTADDRREQ] The socket is not bound to a local address and the protocol does not support listening on an unbound socket. [EINVAL] socket is already connected. [ENOTSOCK] The argument socket does not reference a socket. [EOPNOTSUPP] The socket is not of a type that supports the operation listen(). SEE ALSO
accept(2), connect(2), connectx(2), socket(2) BUGS
The backlog is currently limited (silently) to 128. HISTORY
The listen() function call appeared in 4.2BSD. 4.2 Berkeley Distribution March 18, 2015 4.2 Berkeley Distribution

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listen(3SOCKET) 					     Sockets Library Functions						   listen(3SOCKET)

NAME
listen - listen for connections on a socket SYNOPSIS
cc [ flag ... ] file ... -lsocket -lnsl [ library ... ] #include <sys/types.h> #include <sys/socket.h> int listen(int s, int backlog); DESCRIPTION
To accept connections, a socket is first created with socket(3SOCKET), a backlog for incoming connections is specified with listen() and then the connections are accepted with accept(3SOCKET). 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 will receive an error with an indication of ECONNREFUSED for AF_UNIX sock- ets. If the underlying protocol supports retransmission, the connection request may be ignored so that retries may succeed. For AF_INET and AF_INET6sockets, the TCP will retry the connection. If the backlog is not cleared by the time the tcp times out, the connect will fail with ETIMEDOUT. RETURN VALUES
A 0 return value indicates success; -1 indicates an error. ERRORS
The call fails if: EBADF The argument s is not a valid file descriptor. ENOTSOCK The argument s is not a socket. EOPNOTSUPP The socket is not of a type that supports the operation listen(). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |MT-Level |Safe | +-----------------------------+-----------------------------+ SEE ALSO
accept(3SOCKET), connect(3SOCKET), socket(3SOCKET), attributes(5), socket.h(3HEAD) NOTES
There is currently no backlog limit. SunOS 5.11 8 Nov 1999 listen(3SOCKET)

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