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
21 The listen() function shall mark a connection-mode socket, specified by
22 the socket argument, as accepting connections.
23 The backlog argument provides a hint to the implementation which the
25 implementation shall use to limit the number of outstanding connections
26 in the socket's listen queue. Implementations may impose a limit on
27 backlog and silently reduce the specified value. Normally, a larger
28 backlog argument value shall result in a larger or equal length of the
29 listen queue. Implementations shall support values of backlog up to
30 SOMAXCONN, defined in <sys/socket.h>.
31 The implementation may include incomplete connections in its listen
33 queue. The limits on the number of incomplete connections and completed
34 connections queued may be different.
35 The implementation may have an upper limit on the length of the listen
37 queue—either global or per accepting socket. If backlog exceeds this
38 limit, the length of the listen queue is set to the limit.
39 If listen() is called with a backlog argument value that is less than
41 0, the function behaves as if it had been called with a backlog argu‐
42 ment value of 0.
43 A backlog argument of 0 may allow the socket to accept connections, in
45 which case the length of the listen queue may be set to an implementa‐
46 tion-defined minimum value.
47 The socket in use may require the process to have appropriate privi‐
49 leges to use the listen() function.
50
52 Upon successful completions, listen() shall return 0; otherwise, -1
53 shall be returned and errno set to indicate the error.
54
56 The listen() function shall fail if:
57 EBADF The socket argument is not a valid file descriptor.
59 EDESTADDRREQ
61 The socket is not bound to a local address, and the protocol
62 does not support listening on an unbound socket.
63 EINVAL The socket is already connected.
65 ENOTSOCK
67 The socket argument does not refer to a socket.
68 EOPNOTSUPP
70 The socket protocol does not support listen().
71 The listen() function may fail if:
73 EACCES The calling process does not have appropriate privileges.
75 EINVAL The socket has been shut down.
77 ENOBUFS
79 Insufficient resources are available in the system to complete
80 the call.
81 The following sections are informative.
83
85 None.
86
88 None.
89
91 None.
92
94 None.
95
97 accept(), connect(), socket()
98 The Base Definitions volume of POSIX.1‐2017, <sys_socket.h>
100
102 Portions of this text are reprinted and reproduced in electronic form
103 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
104 table Operating System Interface (POSIX), The Open Group Base Specifi‐
105 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
106 Electrical and Electronics Engineers, Inc and The Open Group. In the
107 event of any discrepancy between this version and the original IEEE and
108 The Open Group Standard, the original IEEE and The Open Group Standard
109 is the referee document. The original Standard can be obtained online
110 at http://www.opengroup.org/unix/online.html .
111 Any typographical or formatting errors that appear in this page are
113 most likely to have been introduced during the conversion of the source
114 files to man page format. To report such errors, see https://www.ker‐
115 nel.org/doc/man-pages/reporting_bugs.html .
116IEEE/The Open Group 2017 LISTEN(3P)