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CONNECT(2)		   Linux Programmer's Manual		    CONNECT(2)

       connect - initiate a connection on a socket

       #include <sys/types.h>	       /* See NOTES */
       #include <sys/socket.h>

       int connect(int sockfd, const struct sockaddr *addr,
		   socklen_t addrlen);

       The  connect()  system call connects the socket referred to by the file
       descriptor sockfd to the address specified by addr.  The addrlen	 argu-
       ment  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).

       If  the connection or binding succeeds, zero is returned.  On error, -1
       is returned, and errno is set appropriately.

       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

	      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.

	      Local address is already in use.

	      (Internet domain sockets) The socket referred to by  sockfd  had
	      not  previously been bound to an address and, upon attempting to
	      bind it to an ephemeral port, it was determined  that  all  port
	      numbers  in  the ephemeral port range are currently in use.  See
	      the  discussion  of  /proc/sys/net/ipv4/ip_local_port_range   in

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

       EAGAIN Insufficient entries in the routing cache.

	      The socket is nonblocking and a previous connection attempt  has
	      not yet been completed.

       EBADF  The  file	 descriptor is not a valid index in the descriptor ta-

	      No-one listening on the remote address.

       EFAULT The socket structure  address  is	 outside  the  user's  address

	      The socket is nonblocking and the connection cannot be completed
	      immediately.  It is possible to select(2) or poll(2) for comple-
	      tion by selecting the socket for writing.	 After select(2) indi-
	      cates writability, use getsockopt(2) to read the SO_ERROR option
	      at  level	 SOL_SOCKET  to	 determine whether connect() completed
	      successfully (SO_ERROR is zero) or unsuccessfully	 (SO_ERROR  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

	      The socket is already connected.

	      Network is unreachable.

	      The file descriptor sockfd does not refer to a socket.

	      The  socket  type	 does not support the requested communications
	      protocol.	 This error can occur, for example, on an  attempt  to
	      connect a UNIX domain datagram socket to a stream socket.

	      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.

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD, (the connect() function first
       appeared in 4.2BSD).

       POSIX.1 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).

       If  connect()  fails,  consider the state of the socket as unspecified.
       Portable applications should close the socket and create a new one  for

       An example of the use of connect() is shown in getaddrinfo(3).

       accept(2),  bind(2), getsockname(2), listen(2), socket(2), path_resolu-

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Linux				  2015-12-28			    CONNECT(2)