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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       connect - connect a socket

SYNOPSIS
       #include <sys/socket.h>

       int connect(int socket, const struct sockaddr *address,
              socklen_t address_len);


DESCRIPTION
       The  connect()  function shall attempt to make a connection on a socket. The function takes the following argu-
       ments:

       socket Specifies the file descriptor associated with the socket.

       address
              Points to a sockaddr structure containing the peer address.  The length and format of the address depend
              on the address family of the socket.

       address_len
              Specifies the length of the sockaddr structure pointed to by the address argument.


       If  the  socket  has  not  already  been bound to a local address, connect() shall bind it to an address which,
       unless the socket's address family is AF_UNIX, is an unused local address.

       If the initiating socket is not connection-mode, then connect() shall set the socket's  peer  address,  and  no
       connection  is made. For SOCK_DGRAM sockets, the peer address identifies where all datagrams are sent on subse-
       quent send() functions, and limits the remote sender for subsequent recv() functions.  If  address  is  a  null
       address for the protocol, the socket's peer address shall be reset.

       If  the  initiating  socket  is  connection-mode, then connect() shall attempt to establish a connection to the
       address specified by the address argument. If the connection cannot be established immediately  and  O_NONBLOCK
       is  not  set  for  the  file  descriptor for the socket, connect() shall block for up to an unspecified timeout
       interval until the connection is established. If the timeout interval expires before the connection  is  estab-
       lished, connect() shall fail and the connection attempt shall be aborted. If connect() is interrupted by a sig-
       nal that is caught while blocked waiting to establish a connection, connect()  shall  fail  and  set  errno  to
       [EINTR],  but  the  connection  request  shall  not  be  aborted, and the connection shall be established asyn-
       chronously.

       If the connection cannot be established immediately and O_NONBLOCK is set  for  the  file  descriptor  for  the
       socket,  connect()  shall fail and set errno to [EINPROGRESS], but the connection request shall not be aborted,
       and the connection shall be established asynchronously. Subsequent calls to  connect()  for  the  same  socket,
       before the connection is established, shall fail and set errno to [EALREADY].

       When  the  connection  has  been  established  asynchronously, select() and poll() shall indicate that the file
       descriptor for the socket is ready for writing.

       The socket in use may require the process to have appropriate privileges to use the connect() function.

RETURN VALUE
       Upon successful completion, connect() shall return 0; otherwise, -1 shall be returned and errno set to indicate
       the error.

ERRORS
       The connect() function shall fail if:

       EADDRNOTAVAIL
              The specified address is not available from the local machine.

       EAFNOSUPPORT
              The specified address is not a valid address for the address family of the specified socket.

       EALREADY
              A connection request is already in progress for the specified socket.

       EBADF  The socket argument is not a valid file descriptor.

       ECONNREFUSED
              The target address was not listening for connections or refused the connection request.

       EINPROGRESS
              O_NONBLOCK is set for the file descriptor for the socket and the connection cannot be immediately estab-
              lished; the connection shall be established asynchronously.

       EINTR  The attempt to establish a connection was interrupted by delivery of a signal that was caught; the  con-
              nection shall be established asynchronously.

       EISCONN
              The specified socket is connection-mode and is already connected.

       ENETUNREACH
              No route to the network is present.

       ENOTSOCK
              The socket argument does not refer to a socket.

       EPROTOTYPE
              The specified address has a different type than the socket bound to the specified peer address.

       ETIMEDOUT
              The attempt to connect timed out before a connection was made.


       If the address family of the socket is AF_UNIX, then connect() shall fail if:

       EIO    An I/O error occurred while reading from or writing to the file system.

       ELOOP  A loop exists in symbolic links encountered during resolution of the pathname in address.

       ENAMETOOLONG
              A  component  of  a  pathname  exceeded {NAME_MAX} characters, or an entire pathname exceeded {PATH_MAX}
              characters.

       ENOENT A component of the pathname does not name an existing file or the pathname is an empty string.

       ENOTDIR
              A component of the path prefix of the pathname in address is not a directory.


       The connect() function may fail if:

       EACCES Search permission is denied for a component of the path prefix; or write access to the named  socket  is
              denied.

       EADDRINUSE
              Attempt to establish a connection that uses addresses that are already in use.

       ECONNRESET
              Remote host reset the connection request.

       EHOSTUNREACH
              The  destination  host  cannot  be  reached (probably because the host is down or a remote router cannot
              reach it).

       EINVAL The address_len argument is not a valid length for the address family; or invalid address family in  the
              sockaddr structure.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the pathname in address.

       ENAMETOOLONG
              Pathname  resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.

       ENETDOWN
              The local network interface used to reach the destination is down.

       ENOBUFS
              No buffer space is available.

       EOPNOTSUPP
              The socket is listening and cannot be connected.


       The following sections are informative.

EXAMPLES
       None.

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

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       accept(),  bind(), close(), getsockname(), poll(), select(), send(), shutdown(), socket(), the Base Definitions
       volume of IEEE Std 1003.1-2001, <sys/socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,  Inc  and  The
       Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                          CONNECT(3P)