1CONNECT(3P)                POSIX Programmer's Manual               CONNECT(3P)
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PROLOG

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.
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11

NAME

13       connect — connect a socket
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SYNOPSIS

16       #include <sys/socket.h>
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18       int connect(int socket, const struct sockaddr *address,
19           socklen_t address_len);
20

DESCRIPTION

22       The connect() function shall attempt to make a connection on a  connec‐
23       tion-mode  socket  or to set or reset the peer address of a connection‐
24       less-mode socket. The function takes the following arguments:
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26       socket      Specifies the file descriptor associated with the socket.
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28       address     Points to a sockaddr structure containing the peer address.
29                   The  length and format of the address depend on the address
30                   family of the socket.
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32       address_len Specifies the length of the sockaddr structure  pointed  to
33                   by the address argument.
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35       If  the socket has not already been bound to a local address, connect()
36       shall bind it to an address which, unless the socket's  address  family
37       is AF_UNIX, is an unused local address.
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39       If  the  initiating socket is not connection-mode, then connect() shall
40       set  the  socket's  peer  address,  and  no  connection  is  made.  For
41       SOCK_DGRAM sockets, the peer address identifies where all datagrams are
42       sent on subsequent send() functions, and limits the remote  sender  for
43       subsequent  recv()  functions.  If  the  sa_family member of address is
44       AF_UNSPEC, the socket's peer address shall be reset. Note that  despite
45       no  connection being made, the term ``connected'' is used to describe a
46       connectionless-mode socket for which a peer address has been set.
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48       If the initiating  socket  is  connection-mode,  then  connect()  shall
49       attempt  to  establish  a  connection  to  the address specified by the
50       address argument. If the connection cannot be  established  immediately
51       and  O_NONBLOCK is not set for the file descriptor for the socket, con‐
52       nect() shall block for up to an unspecified timeout interval until  the
53       connection  is  established. If the timeout interval expires before the
54       connection is established, connect()  shall  fail  and  the  connection
55       attempt  shall be aborted. If connect() is interrupted by a signal that
56       is caught while blocked waiting to establish  a  connection,  connect()
57       shall  fail  and set errno to [EINTR], but the connection request shall
58       not be aborted, and the connection shall be established asynchronously.
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60       If the connection cannot be established immediately and  O_NONBLOCK  is
61       set  for  the  file descriptor for the socket, connect() shall fail and
62       set errno to [EINPROGRESS], but the connection  request  shall  not  be
63       aborted, and the connection shall be established asynchronously. Subse‐
64       quent calls to connect() for the same socket, before the connection  is
65       established, shall fail and set errno to [EALREADY].
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67       When  the  connection  has  been established asynchronously, pselect(),
68       select(), and poll() shall indicate that the file  descriptor  for  the
69       socket is ready for writing.
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71       The  socket  in  use may require the process to have appropriate privi‐
72       leges to use the connect() function.
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RETURN VALUE

75       Upon successful completion, connect() shall  return  0;  otherwise,  −1
76       shall be returned and errno set to indicate the error.
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ERRORS

79       The connect() function shall fail if:
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81       EADDRNOTAVAIL
82              The specified address is not available from the local machine.
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84       EAFNOSUPPORT
85              The  specified  address  is  not a valid address for the address
86              family of the specified socket.
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88       EALREADY
89              A connection request is already in progress  for  the  specified
90              socket.
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92       EBADF  The socket argument is not a valid file descriptor.
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94       ECONNREFUSED
95              The  target address was not listening for connections or refused
96              the connection request.
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98       EINPROGRESS
99              O_NONBLOCK is set for the file descriptor for the socket and the
100              connection  cannot  be  immediately  established; the connection
101              shall be established asynchronously.
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103       EINTR  The attempt to establish a connection was interrupted by  deliv‐
104              ery  of a signal that was caught; the connection shall be estab‐
105              lished asynchronously.
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107       EISCONN
108              The specified socket is  connection-mode  and  is  already  con‐
109              nected.
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111       ENETUNREACH
112              No route to the network is present.
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114       ENOTSOCK
115              The socket argument does not refer to a socket.
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117       EPROTOTYPE
118              The specified address has a different type than the socket bound
119              to the specified peer address.
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121       ETIMEDOUT
122              The attempt to connect timed out before a connection was made.
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124       If the address family of the socket is AF_UNIX,  then  connect()  shall
125       fail if:
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127       EIO    An  I/O error occurred while reading from or writing to the file
128              system.
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130       ELOOP  A loop exists in symbolic links encountered during resolution of
131              the pathname in address.
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133       ENAMETOOLONG
134              The  length  of  a  component  of  a  pathname  is  longer  than
135              {NAME_MAX}.
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137       ENOENT A component of the pathname does not name an  existing  file  or
138              the pathname is an empty string.
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140       ENOTDIR
141              A  component of the path prefix of the pathname in address names
142              an existing file that is neither a directory nor a symbolic link
143              to a directory, or the pathname in address contains at least one
144              non-<slash> character and ends with one or more trailing <slash>
145              characters  and  the  last  pathname component names an existing
146              file that is neither a directory nor a symbolic link to a direc‐
147              tory.
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149       The connect() function may fail if:
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151       EACCES Search  permission is denied for a component of the path prefix;
152              or write access to the named socket is denied.
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154       EADDRINUSE
155              Attempt to establish a connection that uses addresses  that  are
156              already in use.
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158       ECONNRESET
159              Remote host reset the connection request.
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161       EHOSTUNREACH
162              The  destination  host  cannot  be reached (probably because the
163              host is down or a remote router cannot reach it).
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165       EINVAL The address_len argument is not a valid length for  the  address
166              family; or invalid address family in the sockaddr structure.
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168       ELOOP  More  than  {SYMLOOP_MAX} symbolic links were encountered during
169              resolution of the pathname in address.
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171       ENAMETOOLONG
172              The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
173              tion  of  a symbolic link produced an intermediate result with a
174              length that exceeds {PATH_MAX}.
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176       ENETDOWN
177              The local network interface used to  reach  the  destination  is
178              down.
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180       ENOBUFS
181              No buffer space is available.
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183       EOPNOTSUPP
184              The socket is listening and cannot be connected.
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186       The following sections are informative.
187

EXAMPLES

189       None.
190

APPLICATION USAGE

192       If  connect() fails, the state of the socket is unspecified. Conforming
193       applications should close the file descriptor and create a  new  socket
194       before attempting to reconnect.
195

RATIONALE

197       None.
198

FUTURE DIRECTIONS

200       None.
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SEE ALSO

203       accept(),  bind(),  close(),  getsockname(), poll(), pselect(), send(),
204       shutdown(), socket()
205
206       The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>
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209       Portions of this text are reprinted and reproduced in  electronic  form
210       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
211       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
212       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
213       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
214       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
215       event of any discrepancy between this version and the original IEEE and
216       The  Open Group Standard, the original IEEE and The Open Group Standard
217       is the referee document. The original Standard can be  obtained  online
218       at http://www.unix.org/online.html .
219
220       Any  typographical  or  formatting  errors that appear in this page are
221       most likely to have been introduced during the conversion of the source
222       files  to  man page format. To report such errors, see https://www.ker
223       nel.org/doc/man-pages/reporting_bugs.html .
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227IEEE/The Open Group                  2013                          CONNECT(3P)
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