1CONNECT(3P) POSIX Programmer's Manual CONNECT(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 connect — connect a socket
13
15 #include <sys/socket.h>
16 int connect(int socket, const struct sockaddr *address,
18 socklen_t address_len);
19
21 The connect() function shall attempt to make a connection on a connec‐
22 tion-mode socket or to set or reset the peer address of a connection‐
23 less-mode socket. The function takes the following arguments:
24 socket Specifies the file descriptor associated with the socket.
26 address Points to a sockaddr structure containing the peer address.
28 The length and format of the address depend on the address
29 family of the socket.
30 address_len Specifies the length of the sockaddr structure pointed to
32 by the address argument.
33 If the socket has not already been bound to a local address, connect()
35 shall bind it to an address which, unless the socket's address family
36 is AF_UNIX, is an unused local address.
37 If the initiating socket is not connection-mode, then connect() shall
39 set the socket's peer address, and no connection is made. For
40 SOCK_DGRAM sockets, the peer address identifies where all datagrams are
41 sent on subsequent send() functions, and limits the remote sender for
42 subsequent recv() functions. If the sa_family member of address is
43 AF_UNSPEC, the socket's peer address shall be reset. Note that despite
44 no connection being made, the term ``connected'' is used to describe a
45 connectionless-mode socket for which a peer address has been set.
46 If the initiating socket is connection-mode, then connect() shall
48 attempt to establish a connection to the address specified by the
49 address argument. If the connection cannot be established immediately
50 and O_NONBLOCK is not set for the file descriptor for the socket, con‐
51 nect() shall block for up to an unspecified timeout interval until the
52 connection is established. If the timeout interval expires before the
53 connection is established, connect() shall fail and the connection
54 attempt shall be aborted. If connect() is interrupted by a signal that
55 is caught while blocked waiting to establish a connection, connect()
56 shall fail and set errno to [EINTR], but the connection request shall
57 not be aborted, and the connection shall be established asynchronously.
58 If the connection cannot be established immediately and O_NONBLOCK is
60 set for the file descriptor for the socket, connect() shall fail and
61 set errno to [EINPROGRESS], but the connection request shall not be
62 aborted, and the connection shall be established asynchronously. Subse‐
63 quent calls to connect() for the same socket, before the connection is
64 established, shall fail and set errno to [EALREADY].
65 When the connection has been established asynchronously, pselect(),
67 select(), and poll() shall indicate that the file descriptor for the
68 socket is ready for writing.
69 The socket in use may require the process to have appropriate privi‐
71 leges to use the connect() function.
72
74 Upon successful completion, connect() shall return 0; otherwise, -1
75 shall be returned and errno set to indicate the error.
76
78 The connect() function shall fail if:
79 EADDRNOTAVAIL
81 The specified address is not available from the local machine.
82 EAFNOSUPPORT
84 The specified address is not a valid address for the address
85 family of the specified socket.
86 EALREADY
88 A connection request is already in progress for the specified
89 socket.
90 EBADF The socket argument is not a valid file descriptor.
92 ECONNREFUSED
94 The target address was not listening for connections or refused
95 the connection request.
96 EINPROGRESS
98 O_NONBLOCK is set for the file descriptor for the socket and the
99 connection cannot be immediately established; the connection
100 shall be established asynchronously.
101 EINTR The attempt to establish a connection was interrupted by deliv‐
103 ery of a signal that was caught; the connection shall be estab‐
104 lished asynchronously.
105 EISCONN
107 The specified socket is connection-mode and is already con‐
108 nected.
109 ENETUNREACH
111 No route to the network is present.
112 ENOTSOCK
114 The socket argument does not refer to a socket.
115 EPROTOTYPE
117 The specified address has a different type than the socket bound
118 to the specified peer address.
119 ETIMEDOUT
121 The attempt to connect timed out before a connection was made.
122 If the address family of the socket is AF_UNIX, then connect() shall
124 fail if:
125 EIO An I/O error occurred while reading from or writing to the file
127 system.
128 ELOOP A loop exists in symbolic links encountered during resolution of
130 the pathname in address.
131 ENAMETOOLONG
133 The length of a component of a pathname is longer than
134 {NAME_MAX}.
135 ENOENT A component of the pathname does not name an existing file or
137 the pathname is an empty string.
138 ENOTDIR
140 A component of the path prefix of the pathname in address names
141 an existing file that is neither a directory nor a symbolic link
142 to a directory, or the pathname in address contains at least one
143 non-<slash> character and ends with one or more trailing <slash>
144 characters and the last pathname component names an existing
145 file that is neither a directory nor a symbolic link to a direc‐
146 tory.
147 The connect() function may fail if:
149 EACCES Search permission is denied for a component of the path prefix;
151 or write access to the named socket is denied.
152 EADDRINUSE
154 Attempt to establish a connection that uses addresses that are
155 already in use.
156 ECONNRESET
158 Remote host reset the connection request.
159 EHOSTUNREACH
161 The destination host cannot be reached (probably because the
162 host is down or a remote router cannot reach it).
163 EINVAL The address_len argument is not a valid length for the address
165 family; or invalid address family in the sockaddr structure.
166 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
168 resolution of the pathname in address.
169 ENAMETOOLONG
171 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
172 tion of a symbolic link produced an intermediate result with a
173 length that exceeds {PATH_MAX}.
174 ENETDOWN
176 The local network interface used to reach the destination is
177 down.
178 ENOBUFS
180 No buffer space is available.
181 EOPNOTSUPP
183 The socket is listening and cannot be connected.
184 The following sections are informative.
186
188 None.
189
191 If connect() fails, the state of the socket is unspecified. Conforming
192 applications should close the file descriptor and create a new socket
193 before attempting to reconnect.
194
196 None.
197
199 None.
200
202 accept(), bind(), close(), getsockname(), poll(), pselect(), send(),
203 shutdown(), socket()
204 The Base Definitions volume of POSIX.1‐2017, <sys_socket.h>
206
208 Portions of this text are reprinted and reproduced in electronic form
209 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
210 table Operating System Interface (POSIX), The Open Group Base Specifi‐
211 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
212 Electrical and Electronics Engineers, Inc and The Open Group. In the
213 event of any discrepancy between this version and the original IEEE and
214 The Open Group Standard, the original IEEE and The Open Group Standard
215 is the referee document. The original Standard can be obtained online
216 at http://www.opengroup.org/unix/online.html .
217 Any typographical or formatting errors that appear in this page are
219 most likely to have been introduced during the conversion of the source
220 files to man page format. To report such errors, see https://www.ker‐
221 nel.org/doc/man-pages/reporting_bugs.html .
222IEEE/The Open Group 2017 CONNECT(3P)