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67 .TH CONNECT 2 2019-03-06 "Linux" "Linux Programmer's Manual"
69 connect \- initiate a connection on a socket
72 .BR "#include <sys/types.h>" " /* See NOTES */"
74 .B #include <sys/socket.h>
76 .BI "int connect(int " sockfd ", const struct sockaddr *" addr ,
77 .BI " socklen_t " addrlen );
82 system call connects the socket referred to by the file descriptor
84 to the address specified by
88 argument specifies the size of
90 The format of the address in
92 is determined by the address space of the socket
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
110 this call attempts to make a connection to the socket that is bound
111 to the address specified by
114 Generally, connection-based protocol sockets may successfully
116 only once; connectionless protocol sockets may use
118 multiple times to change their association.
119 Connectionless sockets may
120 dissolve the association by connecting to an address with the
126 (supported on Linux since kernel 2.2).
128 If the connection or binding succeeds, zero is returned.
129 On error, \-1 is returned, and
131 is set appropriately.
133 The following are general socket errors only.
134 There may be other domain-specific error codes.
137 For UNIX domain sockets, which are identified by pathname:
138 Write permission is denied on the socket file,
139 or search permission is denied for one of the directories
142 .BR path_resolution (7).)
144 .BR EACCES ", " EPERM
145 The user tried to connect to a broadcast address without having the socket
146 broadcast flag enabled or the connection request failed because of a local
150 Local address is already in use.
153 (Internet domain sockets)
154 The socket referred to by
156 had not previously been bound to an address and,
157 upon attempting to bind it to an ephemeral port,
158 it was determined that all port numbers in the ephemeral port range
159 are currently in use.
160 See the discussion of
161 .I /proc/sys/net/ipv4/ip_local_port_range
166 The passed address didn't have the correct address family in its
171 For nonblocking UNIX domain sockets, the socket is nonblocking, and the
172 connection cannot be completed immediately.
173 For other socket families, there are insufficient entries in the routing cache.
176 The socket is nonblocking and a previous connection attempt has not yet
181 is not a valid open file descriptor.
186 on a stream socket found no one listening on the remote address.
189 The socket structure address is outside the user's address space.
192 The socket is nonblocking and the connection cannot be completed immediately.
193 (UNIX domain sockets failed with
200 for completion by selecting the socket for writing.
203 indicates writability, use
211 completed successfully
213 is zero) or unsuccessfully
215 is one of the usual error codes listed here,
216 explaining the reason for the failure).
219 The system call was interrupted by a signal that was caught; see
221 .\" For TCP, the connection will complete asynchronously.
222 .\" See http://lkml.org/lkml/2005/7/12/254
225 The socket is already connected.
228 Network is unreachable.
233 does not refer to a socket.
236 The socket type does not support the requested communications protocol.
237 This error can occur, for example,
238 on an attempt to connect a UNIX domain datagram socket to a stream socket.
241 Timeout while attempting connection.
242 The server may be too
243 busy to accept new connections.
244 Note that for IP sockets the timeout may
245 be very long when syncookies are enabled on the server.
247 POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD,
249 first appeared in 4.2BSD).
250 .\" SVr4 documents the additional
251 .\" general error codes
252 .\" .BR EADDRNOTAVAIL ,
254 .\" .BR EAFNOSUPPORT ,
261 .\" documents many additional error conditions not described here.
263 POSIX.1 does not require the inclusion of
265 and this header file is not required on Linux.
266 However, some historical (BSD) implementations required this header
267 file, and portable applications are probably wise to include it.
269 For background on the
276 fails, consider the state of the socket as unspecified.
277 Portable applications should close the socket and create a new one for
280 An example of the use of
290 .BR path_resolution (7)