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 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  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 connection shall be established asynchronously.

       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 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, 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
       Standard,  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 .