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.

       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  sockfd is not a valid open file descriptor.

       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 sockfd does not refer to 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
       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD, (the connect() function first
       appeared in 4.2BSD).

NOTES
       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.

       For background on the socklen_t type, see 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 4.10 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
       https://www.kernel.org/doc/man-pages/.



Linux				  2016-12-12			    CONNECT(2)