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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  do-
       main-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.

       EADDRNOTAVAIL
	      (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
	      ip(7).

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

       EAGAIN Insufficient entries in the routing cache.

       EALREADY
	      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-
	      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 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
	      signal(7).

       EISCONN
	      The socket is already connected.

       ENETUNREACH
	      Network is unreachable.

       ENOTSOCK
	      The file descriptor is not associated with a socket.

       EPROTOTYPE
	      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.

       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).

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

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 3.74 of the	Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       http://www.kernel.org/doc/man-pages/.

Linux				  2014-09-06			    CONNECT(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

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