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 differ (con-
       sult 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 arguments:

       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  subsequent  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 speci-
       fied  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 estab-
       lished.  If  the  timeout  interval expires before the connection is established, connect() shall fail and the connection
       attempt shall be aborted. If connect() is interrupted by a signal 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 con-
       nection shall be established asynchronously.

       If the connection cannot be established immediately and O_NONBLOCK is set for the file descriptor for  the  socket,  con-
       nect()  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  estab-
       lished, 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 established; the
              connection shall be established asynchronously.

       EINTR  The attempt to establish a connection was interrupted by delivery of a signal  that  was  caught;  the  connection
              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,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (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 Standard, the original IEEE and The Open Group
       Standard  is  the  referee   document.   The   original   Standard   can   be   obtained   online   at   http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                   CONNECT(3P)