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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 argument specifies the size of addr.  The for-
       mat  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; connec-
       tionless 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

       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 directo-
              ries in the path prefix.  (See also path_resolution(7).)

              The user tried to connect to a broadcast address without having the  socket  broad-
              cast  flag  enabled  or  the  connection request failed because of a local firewall

              Local address is already in use.

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

              Non-existent interface was requested or the requested address was not local.

              The socket is nonblocking and a previous connection attempt has not yet  been  com-

       EBADF  The file descriptor is not a valid index in the descriptor table.

              No-one listening on the remote address.

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

              The  socket  is nonblocking 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  suc-
              cessfully  (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).

              The socket is already connected.

              Network is unreachable.

              The file descriptor is not associated with a socket.

              Timeout while attempting connection.  The server may be too busy to accept new con-
              nections.   Note  that  for IP sockets the timeout may be very long when syncookies
              are enabled on the server.

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

       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).

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

       accept(2), bind(2), getsockname(2), listen(2), socket(2), path_resolution(7)

       This page is part of release 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information    about    reporting    bugs,    can    be    found    at

Linux                                       2008-12-03                                 CONNECT(2)

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