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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 speci-
       fied by addr.  The addrlen argument specifies the size of addr.  The format of the address in  addr  is  deter-
       mined 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  appropri-
       ately.

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_res-
              olution(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.

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

       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  proba-
       bly 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
       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-12-03                        CONNECT(2)