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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   (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.

       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

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       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.