man2/connect.2

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  61 .\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
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  63 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
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  65 .TH CONNECT 2 2007-12-28 "Linux" "Linux Programmer's Manual"
  66 .SH NAME
  67 connect \- initiate a connection on a socket
  68 .SH SYNOPSIS
  69 .nf
  70 .BR "#include <sys/types.h>" "          /* See NOTES */"
  71 .br
  72 .B #include <sys/socket.h>
  73 .sp
  74 .BI "int connect(int " sockfd ", const struct sockaddr *" serv_addr ,
  75 .BI "            socklen_t " addrlen );
  76 .fi
  77 .SH DESCRIPTION
  78 The
  79 .BR connect ()
  80 system call connects the socket referred to by the file descriptor
  81 .I sockfd
  82 to the address specified by
  83 .IR serv_addr .
  84 The
  85 .I addrlen
  86 argument specifies the size of
  87 .IR serv_addr .
  88 The format of the address in
  89 .I serv_addr
  90 is determined by the address space of the socket
  91 .IR sockfd ;
  92 see
  93 .BR socket (2)
  94 for further details.
  95
  96 If the socket
  97 .I sockfd
  98 is of type
  99 .B SOCK_DGRAM
 100 then
 101 .I serv_addr
 102 is the address to which datagrams are sent by default, and the only
 103 address from which datagrams are received.
 104 If the socket is of type
 105 .B SOCK_STREAM
 106 or
 107 .BR SOCK_SEQPACKET ,
 108 this call attempts to make a connection to the socket that is bound
 109 to the address specified by
 110 .IR serv_addr .
 111 .PP
 112 Generally, connection-based protocol sockets may successfully
 113 .BR connect ()
 114 only once; connectionless protocol sockets may use
 115 .BR connect ()
 116 multiple times to change their association.
 117 Connectionless sockets may
 118 dissolve the association by connecting to an address with the
 119 .I sa_family
 120 member of
 121 .I sockaddr
 122 set to
 123 .BR AF_UNSPEC
 124 (supported on Linux since kernel 2.2).
 125 .SH "RETURN VALUE"
 126 If the connection or binding succeeds, zero is returned.
 127 On error, \-1 is returned, and
 128 .I errno
 129 is set appropriately.
 130 .SH ERRORS
 131 The following are general socket errors only.
 132 There may be other domain-specific error codes.
 133 .TP
 134 .B EACCES
 135 For Unix domain sockets, which are identified by pathname:
 136 Write permission is denied on the socket file,
 137 or search permission is denied for one of the directories
 138 in the path prefix.
 139 (See also
 140 .BR path_resolution (7).)
 141 .TP
 142 .BR EACCES ", " EPERM
 143 The user tried to connect to a broadcast address without having the socket
 144 broadcast flag enabled or the connection request failed because of a local
 145 firewall rule.
 146 .TP
 147 .B EADDRINUSE
 148 Local address is already in use.
 149 .TP
 150 .B EAFNOSUPPORT
 151 The passed address didn't have the correct address family in its
 152 .I sa_family
 153 field.
 154 .TP
 155 .B EAGAIN
 156 No more free local ports or insufficient entries in the routing cache.
 157 For
 158 .B PF_INET
 159 see the
 160 .I net.ipv4.ip_local_port_range
 161 sysctl in
 162 .BR ip (7)
 163 on how to increase the number of local ports.
 164 .TP
 165 .B EALREADY
 166 The socket is non-blocking and a previous connection attempt has not yet
 167 been completed.
 168 .TP
 169 .B EBADF
 170 The file descriptor is not a valid index in the descriptor table.
 171 .TP
 172 .B ECONNREFUSED
 173 No-one listening on the remote address.
 174 .TP
 175 .B EFAULT
 176 The socket structure address is outside the user's address space.
 177 .TP
 178 .B EINPROGRESS
 179 The socket is non-blocking and the connection cannot be completed
 180 immediately.
 181 It is possible to
 182 .BR select (2)
 183 or
 184 .BR poll (2)
 185 for completion by selecting the socket for writing.
 186 After
 187 .BR select (2)
 188 indicates writability, use
 189 .BR getsockopt (2)
 190 to read the
 191 .B SO_ERROR
 192 option at level
 193 .B SOL_SOCKET
 194 to determine whether
 195 .BR connect ()
 196 completed successfully
 197 .RB ( SO_ERROR
 198 is zero) or unsuccessfully
 199 .RB ( SO_ERROR
 200 is one of the usual error codes listed here,
 201 explaining the reason for the failure).
 202 .TP
 203 .B EINTR
 204 The system call was interrupted by a signal that was caught; see
 205 .BR signal (7).
 206 .\" For TCP, the connection will complete asynchronously.
 207 .\" See http://lkml.org/lkml/2005/7/12/254
 208 .TP
 209 .B EISCONN
 210 The socket is already connected.
 211 .TP
 212 .B ENETUNREACH
 213 Network is unreachable.
 214 .TP
 215 .B ENOTSOCK
 216 The file descriptor is not associated with a socket.
 217 .TP
 218 .B ETIMEDOUT
 219 Timeout while attempting connection.
 220 The server may be too
 221 busy to accept new connections.
 222 Note that for IP sockets the timeout may
 223 be very long when syncookies are enabled on the server.
 224 .SH "CONFORMING TO"
 225 SVr4, 4.4BSD, (the
 226 .BR connect ()
 227 function first appeared in 4.2BSD), POSIX.1-2001.
 228 .\" SVr4 documents the additional
 229 .\" general error codes
 230 .\" .BR EADDRNOTAVAIL ,
 231 .\" .BR EINVAL ,
 232 .\" .BR EAFNOSUPPORT ,
 233 .\" .BR EALREADY ,
 234 .\" .BR EINTR ,
 235 .\" .BR EPROTOTYPE ,
 236 .\" and
 237 .\" .BR ENOSR .
 238 .\" It also
 239 .\" documents many additional error conditions not described here.
 240 .SH NOTES
 241 POSIX.1-2001 does not require the inclusion of
 242 .IR <sys/types.h> ,
 243 and this header file is not required on Linux.
 244 However, some historical (BSD) implementations required this header
 245 file, and portable applications are probably wise to include it.
 246
 247 The third argument of
 248 .BR connect ()
 249 is in reality an
 250 .I int
 251 (and this is what 4.x BSD and libc4 and libc5 have).
 252 Some POSIX confusion resulted in the present
 253 .IR socklen_t ,
 254 also used by glibc.
 255 See also
 256 .BR accept (2).
 257 .SH EXAMPLE
 258 An example of the use of
 259 .BR connect ()
 260 is shown in
 261 .BR getaddrinfo (3).
 262 .SH "SEE ALSO"
 263 .BR accept (2),
 264 .BR bind (2),
 265 .BR getsockname (2),
 266 .BR listen (2),
 267 .BR socket (2),
 268 .BR path_resolution (7)