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

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	 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).

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 ta‐
	      ble.

       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 com‐
	      pleted 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() com‐
	      pleted  successfully  (SO_ERROR  is  zero)   or	unsuccessfully
	      (SO_ERROR	 is one of the usual error codes listed here, explain‐
	      ing 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_resolu‐
       tion(7)

COLOPHON
       This page is part of release 3.15 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/.

Linux				  2008-12-03			    CONNECT(2)

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