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1 | .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu) |
2 | .\" Portions extracted from /usr/include/sys/socket.h, which does not have | |
3 | .\" any authorship information in it. It is probably available under the GPL. | |
4 | .\" | |
93015253 | 5 | .\" %%%LICENSE_START(VERBATIM) |
77117f4f MK |
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4b72fb64 | 25 | .\" %%%LICENSE_END |
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26 | .\" |
27 | .\" | |
28 | .\" Other portions are from the 6.9 (Berkeley) 3/10/91 man page: | |
29 | .\" | |
30 | .\" Copyright (c) 1983 The Regents of the University of California. | |
31 | .\" All rights reserved. | |
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a9cd9cb7 | 33 | .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB) |
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34 | .\" Redistribution and use in source and binary forms, with or without |
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8c9302dc | 61 | .\" %%%LICENSE_END |
77117f4f MK |
62 | .\" |
63 | .\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com> | |
64 | .\" Modified 1998, 1999 by Andi Kleen | |
65 | .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com> | |
66 | .\" | |
e8426ca2 | 67 | .TH CONNECT 2 2020-04-11 "Linux" "Linux Programmer's Manual" |
77117f4f MK |
68 | .SH NAME |
69 | connect \- initiate a connection on a socket | |
70 | .SH SYNOPSIS | |
71 | .nf | |
72 | .BR "#include <sys/types.h>" " /* See NOTES */" | |
73 | .br | |
74 | .B #include <sys/socket.h> | |
68e4db0a | 75 | .PP |
a2b8b6d6 | 76 | .BI "int connect(int " sockfd ", const struct sockaddr *" addr , |
77117f4f MK |
77 | .BI " socklen_t " addrlen ); |
78 | .fi | |
79 | .SH DESCRIPTION | |
80 | The | |
81 | .BR connect () | |
82 | system call connects the socket referred to by the file descriptor | |
83 | .I sockfd | |
84 | to the address specified by | |
a2b8b6d6 | 85 | .IR addr . |
77117f4f MK |
86 | The |
87 | .I addrlen | |
88 | argument specifies the size of | |
a2b8b6d6 | 89 | .IR addr . |
77117f4f | 90 | The format of the address in |
a2b8b6d6 | 91 | .I addr |
77117f4f MK |
92 | is determined by the address space of the socket |
93 | .IR sockfd ; | |
94 | see | |
95 | .BR socket (2) | |
96 | for further details. | |
efeece04 | 97 | .PP |
77117f4f MK |
98 | If the socket |
99 | .I sockfd | |
100 | is of type | |
45d522a8 | 101 | .BR SOCK_DGRAM , |
77117f4f | 102 | then |
a2b8b6d6 | 103 | .I addr |
77117f4f MK |
104 | is the address to which datagrams are sent by default, and the only |
105 | address from which datagrams are received. | |
106 | If the socket is of type | |
107 | .B SOCK_STREAM | |
108 | or | |
109 | .BR SOCK_SEQPACKET , | |
110 | this call attempts to make a connection to the socket that is bound | |
111 | to the address specified by | |
a2b8b6d6 | 112 | .IR addr . |
77117f4f | 113 | .PP |
f4ba6a21 MK |
114 | Some protocol sockets (e.g., UNIX domain stream sockets) |
115 | may successfully | |
77117f4f | 116 | .BR connect () |
f4ba6a21 MK |
117 | only once. |
118 | .PP | |
119 | Some protocol sockets | |
120 | (e.g., datagram sockets in the UNIX and Internet domains) | |
121 | may use | |
77117f4f MK |
122 | .BR connect () |
123 | multiple times to change their association. | |
f4ba6a21 MK |
124 | .PP |
125 | Some protocol sockets | |
126 | (e.g., TCP sockets as well as datagram sockets in the UNIX and | |
127 | Internet domains) | |
128 | may dissolve the association by connecting to an address with the | |
77117f4f MK |
129 | .I sa_family |
130 | member of | |
131 | .I sockaddr | |
132 | set to | |
f4ba6a21 MK |
133 | .BR AF_UNSPEC; |
134 | thereafter, the socket can be connected to another address. | |
135 | .RB ( AF_UNSPEC | |
136 | is supported on Linux since kernel 2.2.) | |
47297adb | 137 | .SH RETURN VALUE |
77117f4f MK |
138 | If the connection or binding succeeds, zero is returned. |
139 | On error, \-1 is returned, and | |
140 | .I errno | |
141 | is set appropriately. | |
142 | .SH ERRORS | |
143 | The following are general socket errors only. | |
144 | There may be other domain-specific error codes. | |
145 | .TP | |
146 | .B EACCES | |
008f1ecc | 147 | For UNIX domain sockets, which are identified by pathname: |
77117f4f MK |
148 | Write permission is denied on the socket file, |
149 | or search permission is denied for one of the directories | |
150 | in the path prefix. | |
151 | (See also | |
152 | .BR path_resolution (7).) | |
153 | .TP | |
154 | .BR EACCES ", " EPERM | |
155 | The user tried to connect to a broadcast address without having the socket | |
156 | broadcast flag enabled or the connection request failed because of a local | |
157 | firewall rule. | |
158 | .TP | |
159 | .B EADDRINUSE | |
160 | Local address is already in use. | |
161 | .TP | |
ac7477eb MK |
162 | .B EADDRNOTAVAIL |
163 | (Internet domain sockets) | |
164 | The socket referred to by | |
165 | .I sockfd | |
166 | had not previously been bound to an address and, | |
167 | upon attempting to bind it to an ephemeral port, | |
168 | it was determined that all port numbers in the ephemeral port range | |
169 | are currently in use. | |
170 | See the discussion of | |
171 | .I /proc/sys/net/ipv4/ip_local_port_range | |
172 | in | |
173 | .BR ip (7). | |
174 | .TP | |
77117f4f MK |
175 | .B EAFNOSUPPORT |
176 | The passed address didn't have the correct address family in its | |
177 | .I sa_family | |
178 | field. | |
179 | .TP | |
180 | .B EAGAIN | |
14662577 | 181 | For nonblocking UNIX domain sockets, the socket is nonblocking, and the |
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182 | connection cannot be completed immediately. |
183 | For other socket families, there are insufficient entries in the routing cache. | |
77117f4f MK |
184 | .TP |
185 | .B EALREADY | |
ff40dbb3 | 186 | The socket is nonblocking and a previous connection attempt has not yet |
77117f4f MK |
187 | been completed. |
188 | .TP | |
189 | .B EBADF | |
d60d564d MK |
190 | .I sockfd |
191 | is not a valid open file descriptor. | |
77117f4f MK |
192 | .TP |
193 | .B ECONNREFUSED | |
96a35a83 MK |
194 | A |
195 | .BR connect () | |
196 | on a stream socket found no one listening on the remote address. | |
77117f4f MK |
197 | .TP |
198 | .B EFAULT | |
199 | The socket structure address is outside the user's address space. | |
200 | .TP | |
201 | .B EINPROGRESS | |
55dc41dc | 202 | The socket is nonblocking and the connection cannot be completed immediately. |
85bb10df | 203 | (UNIX domain sockets failed with |
14662577 BP |
204 | .BR EAGAIN |
205 | instead.) | |
77117f4f MK |
206 | It is possible to |
207 | .BR select (2) | |
208 | or | |
209 | .BR poll (2) | |
210 | for completion by selecting the socket for writing. | |
211 | After | |
212 | .BR select (2) | |
213 | indicates writability, use | |
214 | .BR getsockopt (2) | |
215 | to read the | |
216 | .B SO_ERROR | |
217 | option at level | |
218 | .B SOL_SOCKET | |
219 | to determine whether | |
220 | .BR connect () | |
221 | completed successfully | |
222 | .RB ( SO_ERROR | |
223 | is zero) or unsuccessfully | |
224 | .RB ( SO_ERROR | |
225 | is one of the usual error codes listed here, | |
226 | explaining the reason for the failure). | |
227 | .TP | |
228 | .B EINTR | |
229 | The system call was interrupted by a signal that was caught; see | |
230 | .BR signal (7). | |
231 | .\" For TCP, the connection will complete asynchronously. | |
232 | .\" See http://lkml.org/lkml/2005/7/12/254 | |
233 | .TP | |
234 | .B EISCONN | |
235 | The socket is already connected. | |
236 | .TP | |
237 | .B ENETUNREACH | |
238 | Network is unreachable. | |
239 | .TP | |
240 | .B ENOTSOCK | |
deedfd97 MK |
241 | The file descriptor |
242 | .I sockfd | |
243 | does not refer to a socket. | |
77117f4f | 244 | .TP |
65558bed MK |
245 | .B EPROTOTYPE |
246 | The socket type does not support the requested communications protocol. | |
247 | This error can occur, for example, | |
248 | on an attempt to connect a UNIX domain datagram socket to a stream socket. | |
249 | .TP | |
77117f4f MK |
250 | .B ETIMEDOUT |
251 | Timeout while attempting connection. | |
252 | The server may be too | |
253 | busy to accept new connections. | |
254 | Note that for IP sockets the timeout may | |
255 | be very long when syncookies are enabled on the server. | |
47297adb | 256 | .SH CONFORMING TO |
d5bc35a7 MK |
257 | POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD, |
258 | .RB (connect () | |
259 | first appeared in 4.2BSD). | |
77117f4f MK |
260 | .\" SVr4 documents the additional |
261 | .\" general error codes | |
262 | .\" .BR EADDRNOTAVAIL , | |
263 | .\" .BR EINVAL , | |
264 | .\" .BR EAFNOSUPPORT , | |
265 | .\" .BR EALREADY , | |
266 | .\" .BR EINTR , | |
267 | .\" .BR EPROTOTYPE , | |
268 | .\" and | |
269 | .\" .BR ENOSR . | |
270 | .\" It also | |
271 | .\" documents many additional error conditions not described here. | |
272 | .SH NOTES | |
d1969970 | 273 | POSIX.1 does not require the inclusion of |
77117f4f MK |
274 | .IR <sys/types.h> , |
275 | and this header file is not required on Linux. | |
276 | However, some historical (BSD) implementations required this header | |
277 | file, and portable applications are probably wise to include it. | |
efeece04 | 278 | .PP |
ec5df7af MK |
279 | For background on the |
280 | .I socklen_t | |
281 | type, see | |
77117f4f | 282 | .BR accept (2). |
efeece04 | 283 | .PP |
977e3384 | 284 | If |
536f641b | 285 | .BR connect () |
977e3384 MH |
286 | fails, consider the state of the socket as unspecified. |
287 | Portable applications should close the socket and create a new one for | |
288 | reconnecting. | |
77117f4f MK |
289 | .SH EXAMPLE |
290 | An example of the use of | |
291 | .BR connect () | |
292 | is shown in | |
293 | .BR getaddrinfo (3). | |
47297adb | 294 | .SH SEE ALSO |
77117f4f MK |
295 | .BR accept (2), |
296 | .BR bind (2), | |
297 | .BR getsockname (2), | |
298 | .BR listen (2), | |
299 | .BR socket (2), | |
300 | .BR path_resolution (7) |