1LISTEN(3P) POSIX Programmer's Manual LISTEN(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 listen - listen for socket connections and limit the queue of incoming
13 connections
14
16 #include <sys/socket.h>
17 int listen(int socket, int backlog);
19
22 The listen() function shall mark a connection-mode socket, specified by
23 the socket argument, as accepting connections.
24 The backlog argument provides a hint to the implementation which the
26 implementation shall use to limit the number of outstanding connections
27 in the socket's listen queue. Implementations may impose a limit on
28 backlog and silently reduce the specified value. Normally, a larger
29 backlog argument value shall result in a larger or equal length of the
30 listen queue. Implementations shall support values of backlog up to
31 SOMAXCONN, defined in <sys/socket.h>.
32 The implementation may include incomplete connections in its listen
34 queue. The limits on the number of incomplete connections and completed
35 connections queued may be different.
36 The implementation may have an upper limit on the length of the listen
38 queue-either global or per accepting socket. If backlog exceeds this
39 limit, the length of the listen queue is set to the limit.
40 If listen() is called with a backlog argument value that is less than
42 0, the function behaves as if it had been called with a backlog argu‐
43 ment value of 0.
44 A backlog argument of 0 may allow the socket to accept connections, in
46 which case the length of the listen queue may be set to an implementa‐
47 tion-defined minimum value.
48 The socket in use may require the process to have appropriate privi‐
50 leges to use the listen() function.
51
53 Upon successful completions, listen() shall return 0; otherwise, -1
54 shall be returned and errno set to indicate the error.
55
57 The listen() function shall fail if:
58 EBADF The socket argument is not a valid file descriptor.
60 EDESTADDRREQ
62 The socket is not bound to a local address, and the protocol
64 does not support listening on an unbound socket.
65 EINVAL The socket is already connected.
67 ENOTSOCK
69 The socket argument does not refer to a socket.
70 EOPNOTSUPP
72 The socket protocol does not support listen().
73 The listen() function may fail if:
76 EACCES The calling process does not have the appropriate privileges.
78 EINVAL The socket has been shut down.
80 ENOBUFS
82 Insufficient resources are available in the system to complete
83 the call.
84 The following sections are informative.
87
89 None.
90
92 None.
93
95 None.
96
98 None.
99
101 accept(), connect(), socket(), the Base Definitions volume of
102 IEEE Std 1003.1-2001, <sys/socket.h>
103
105 Portions of this text are reprinted and reproduced in electronic form
106 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
107 -- Portable Operating System Interface (POSIX), The Open Group Base
108 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
109 Electrical and Electronics Engineers, Inc and The Open Group. In the
110 event of any discrepancy between this version and the original IEEE and
111 The Open Group Standard, the original IEEE and The Open Group Standard
112 is the referee document. The original Standard can be obtained online
113 at http://www.opengroup.org/unix/online.html .
114IEEE/The Open Group 2003 LISTEN(3P)