man2/connect.2

   1 .\" Hey Emacs! This file is -*- nroff -*- source.
   2 .\"
   3 .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
   4 .\" Portions extracted from /usr/include/sys/socket.h, which does not have
   5 .\" any authorship information in it.  It is probably available under the GPL.
   6 .\"
   7 .\" Permission is granted to make and distribute verbatim copies of this
   8 .\" manual provided the copyright notice and this permission notice are
   9 .\" preserved on all copies.
  10 .\"
  11 .\" Permission is granted to copy and distribute modified versions of this
  12 .\" manual under the conditions for verbatim copying, provided that the
  13 .\" entire resulting derived work is distributed under the terms of a
  14 .\" permission notice identical to this one.
  15 .\"
  16 .\" Since the Linux kernel and libraries are constantly changing, this
  17 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  18 .\" responsibility for errors or omissions, or for damages resulting from
  19 .\" the use of the information contained herein.  The author(s) may not
  20 .\" have taken the same level of care in the production of this manual,
  21 .\" which is licensed free of charge, as they might when working
  22 .\" professionally.
  23 .\"
  24 .\" Formatted or processed versions of this manual, if unaccompanied by
  25 .\" the source, must acknowledge the copyright and authors of this work.
  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.
  32 .\"
  33 .\" Redistribution and use in source and binary forms, with or without
  34 .\" modification, are permitted provided that the following conditions
  35 .\" are met:
  36 .\" 1. Redistributions of source code must retain the above copyright
  37 .\"    notice, this list of conditions and the following disclaimer.
  38 .\" 2. Redistributions in binary form must reproduce the above copyright
  39 .\"    notice, this list of conditions and the following disclaimer in the
  40 .\"    documentation and/or other materials provided with the distribution.
  41 .\" 3. All advertising materials mentioning features or use of this software
  42 .\"    must display the following acknowledgement:
  43 .\"     This product includes software developed by the University of
  44 .\"     California, Berkeley and its contributors.
  45 .\" 4. Neither the name of the University nor the names of its contributors
  46 .\"    may be used to endorse or promote products derived from this software
  47 .\"    without specific prior written permission.
  48 .\"
  49 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  50 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  51 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  52 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  53 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  54 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  55 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  56 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  57 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  58 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  59 .\" SUCH DAMAGE.
  60 .\"
  61 .\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
  62 .\" Modified 1998, 1999 by Andi Kleen
  63 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
  64 .\"
  65 .TH CONNECT 2 2004-06-23 "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 .SH "RETURN VALUE"
 125 If the connection or binding succeeds, zero is returned.
 126 On error, \-1 is returned, and
 127 .I errno
 128 is set appropriately.
 129 .SH ERRORS
 130 The following are general socket errors only.
 131 There may be other domain-specific error codes.
 132 .TP
 133 .B EACCES
 134 For Unix domain sockets, which are identified by pathname:
 135 Write permission is denied on the socket file,
 136 or search permission is denied for one of the directories
 137 in the path prefix.
 138 (See also
 139 .BR path_resolution (7).)
 140 .TP
 141 .B EACCES, EPERM
 142 The user tried to connect to a broadcast address without having the socket
 143 broadcast flag enabled or the connection request failed because of a local
 144 firewall rule.
 145 .TP
 146 .B EADDRINUSE
 147 Local address is already in use.
 148 .TP
 149 .B EAFNOSUPPORT
 150 The passed address didn't have the correct address family in its
 151 .I sa_family
 152 field.
 153 .TP
 154 .B EAGAIN
 155 No more free local ports or insufficient entries in the routing cache.
 156 For
 157 .B PF_INET
 158 see the
 159 .I net.ipv4.ip_local_port_range
 160 sysctl in
 161 .BR ip (7)
 162 on how to increase the number of local ports.
 163 .TP
 164 .B EALREADY
 165 The socket is non-blocking and a previous connection attempt has not yet
 166 been completed.
 167 .TP
 168 .B EBADF
 169 The file descriptor is not a valid index in the descriptor table.
 170 .TP
 171 .B ECONNREFUSED
 172 No-one listening on the remote address.
 173 .TP
 174 .B EFAULT
 175 The socket structure address is outside the user's address space.
 176 .TP
 177 .B EINPROGRESS
 178 The socket is non-blocking and the connection cannot be completed
 179 immediately.
 180 It is possible to
 181 .BR select (2)
 182 or
 183 .BR poll (2)
 184 for completion by selecting the socket for writing.
 185 After
 186 .BR select (2)
 187 indicates writability, use
 188 .BR getsockopt (2)
 189 to read the
 190 .B SO_ERROR
 191 option at level
 192 .B SOL_SOCKET
 193 to determine whether
 194 .BR connect ()
 195 completed successfully
 196 .RB ( SO_ERROR
 197 is zero) or unsuccessfully
 198 .RB ( SO_ERROR
 199 is one of the usual error codes listed here,
 200 explaining the reason for the failure).
 201 .TP
 202 .B EINTR
 203 The system call was interrupted by a signal that was caught.
 204 .\" For TCP, the connection will complete asynchronously.
 205 .\" See http://lkml.org/lkml/2005/7/12/254
 206 .TP
 207 .B EISCONN
 208 The socket is already connected.
 209 .TP
 210 .B ENETUNREACH
 211 Network is unreachable.
 212 .TP
 213 .B ENOTSOCK
 214 The file descriptor is not associated with a socket.
 215 .TP
 216 .B ETIMEDOUT
 217 Timeout while attempting connection.
 218 The server may be too
 219 busy to accept new connections.
 220 Note that for IP sockets the timeout may
 221 be very long when syncookies are enabled on the server.
 222 .SH "CONFORMING TO"
 223 SVr4, 4.4BSD, (the
 224 .BR connect ()
 225 function first appeared in 4.2BSD), POSIX.1-2001.
 226 .\" SVr4 documents the additional
 227 .\" general error codes
 228 .\" .BR EADDRNOTAVAIL ,
 229 .\" .BR EINVAL ,
 230 .\" .BR EAFNOSUPPORT ,
 231 .\" .BR EALREADY ,
 232 .\" .BR EINTR ,
 233 .\" .BR EPROTOTYPE ,
 234 .\" and
 235 .\" .BR ENOSR .
 236 .\" It also
 237 .\" documents many additional error conditions not described here.
 238 .SH NOTES
 239 POSIX.1-2001 does not require the inclusion of
 240 .IR <sys/types.h> ,
 241 and this header file is not required on Linux.
 242 However, some historical (BSD) implementations required this header
 243 file, and portable applications are probably wise to include it.
 244
 245 The third argument of
 246 .BR connect ()
 247 is in reality an
 248 .I int
 249 (and this is what 4.x BSD and libc4 and libc5 have).
 250 Some POSIX confusion resulted in the present
 251 .IR socklen_t ,
 252 also used by glibc.
 253 See also
 254 .BR accept (2).
 255 .SH BUGS
 256 Unconnecting a socket by calling
 257 .BR connect ()
 258 with a
 259 .B AF_UNSPEC
 260 address is not yet implemented.
 261 .SH EXAMPLE
 262 An example of the use of
 263 .BR connect ()
 264 is shown in
 265 .BR getaddrinfo (3).
 266 .SH "SEE ALSO"
 267 .BR accept (2),
 268 .BR bind (2),
 269 .BR getsockname (2),
 270 .BR listen (2),
 271 .BR socket (2),
 272 .BR path_resolution (7)