• NAME
  
  connect - initiate a connection on a socket
• SYNOPSIS
  

  
   "#include <sys/types.h>" "          /* See NOTES */"
  
   #include <sys/socket.h>
  
   int connect(int  sockfd , const struct sockaddr * addr ,
                socklen_t  addrlen ); 

• DESCRIPTION
  
  The
  connect ()
  system call connects the socket referred to by the file descriptor
  sockfd
  to the address specified by
  addr .
  The
  addrlen
  argument specifies the size of
  addr .
  The format of the address in
  addr
  is determined by the address space of the socket
  sockfd ;
  see
  socket(2)
  for further details.
  
  If the socket
  sockfd
  is of type
  SOCK_DGRAM then
  addr
  is the address to which datagrams are sent by default, and the only
  address from which datagrams are received.
  If the socket is of type
  SOCK_STREAM or
  SOCK_SEQPACKET ,
  this call attempts to make a connection to the socket that is bound
  to the address specified by
  addr .
  
  
  
  Generally, connection-based protocol sockets may successfully
  connect ()
  only once; connectionless protocol sockets may use
  connect ()
  multiple times to change their association.
  Connectionless sockets may
  dissolve the association by connecting to an address with the
  sa_family
  member of
  sockaddr
  set to
  AF_UNSPEC
  (supported on Linux since kernel 2.2).
  
• RETURN VALUE
  
  If the connection or binding succeeds, zero is returned.
  On error, -1 is returned, and
  errno
  is set appropriately.
  
• ERRORS
  
  The following are general socket errors only.
  There may be other domain-specific error codes.
  

  EACCES

  For Unix domain sockets, which are identified by pathname:
  Write permission is denied on the socket file,
  or search permission is denied for one of the directories
  in the path prefix.
  (See also
  path_resolution(7) .)
  

  EACCES ", " EPERM
  

  The user tried to connect to a broadcast address without having the socket
  broadcast flag enabled or the connection request failed because of a local
  firewall rule.
  

  EADDRINUSE

  Local address is already in use.
  

  EAFNOSUPPORT

  The passed address didn't have the correct address family in its
  sa_family
  field.
  

  EAGAIN

  No more free local ports or insufficient entries in the routing cache.
  For
  AF_INET see the description of
  /proc/sys/net/ipv4/ip_local_port_range
  ip(7)
  for information on how to increase the number of local ports.
  

  EALREADY

  The socket is non-blocking and a previous connection attempt has not yet
  been completed.
  

  EBADF

  The file descriptor is not a valid index in the descriptor table.
  

  ECONNREFUSED

  No-one listening on the remote address.
  

  EFAULT

  The socket structure address is outside the user's address space.
  

  EINPROGRESS

  The socket is non-blocking and the connection cannot be completed
  immediately.
  It is possible to
  select(2)
  or
  poll(2)
  for completion by selecting the socket for writing.
  After
  select(2)
  indicates writability, use
  getsockopt(2)
  to read the
  SO_ERROR option at level
  SOL_SOCKET to determine whether
  connect ()
  completed successfully
  is zero) or unsuccessfully
  is one of the usual error codes listed here,
  explaining the reason for the failure).
  

  EINTR

  The system call was interrupted by a signal that was caught; see
  signal(7) .
  
  
  

  EISCONN

  The socket is already connected.
  

  ENETUNREACH

  Network is unreachable.
  

  ENOTSOCK

  The file descriptor is not associated with a socket.
  

  ETIMEDOUT

  Timeout while attempting connection.
  The server may be too
  busy to accept new connections.
  Note that for IP sockets the timeout may
  be very long when syncookies are enabled on the server.
  

• CONFORMING TO
  
  SVr4, 4.4BSD, (the
  connect ()
  function first appeared in 4.2BSD), POSIX.1-2001.
  
  
  
  
  
  
  
  
  
  
  
  
  
• NOTES
  
  POSIX.1-2001 does not require the inclusion of
  <sys/types.h> ,
  and this header file is not required on Linux.
  However, some historical (BSD) implementations required this header
  file, and portable applications are probably wise to include it.
  
  The third argument of
  connect ()
  is in reality an
  int
  (and this is what 4.x BSD and libc4 and libc5 have).
  Some POSIX confusion resulted in the present
  socklen_t ,
  also used by glibc.
  See also
  accept(2) .
  
• EXAMPLE
  
  An example of the use of
  connect ()
  is shown in
  getaddrinfo(3) .
  
• SEE ALSO
  
  accept(2) ,
  bind(2) ,
  getsockname(2) ,
  listen(2) ,
  socket(2) ,
  path_resolution(7)
  
• COLOPHON
  
  This page is part of release 3.19 of the Linux
  man-pages
  project.
  A description of the project,
  and information about reporting bugs,
  can be found at
  http://www.kernel.org/doc/man-pages/.
  

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