PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

CONNECT(3P)               POSIX Programmer's Manual              CONNECT(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       connect — connect a socket

SYNOPSIS         top

       #include <sys/socket.h>

       int connect(int socket, const struct sockaddr *address,
           socklen_t address_len);

DESCRIPTION         top

       The connect() function shall attempt to make a connection on a
       connection-mode socket or to set or reset the peer address of a
       connectionless-mode socket. The function takes the following
       arguments:

       socket      Specifies the file descriptor associated with the socket.

       address     Points to a sockaddr structure containing the peer
                   address. The length and format of the address depend on
                   the address family of the socket.

       address_len Specifies the length of the sockaddr structure pointed to
                   by the address argument.

       If the socket has not already been bound to a local address,
       connect() shall bind it to an address which, unless the socket's
       address family is AF_UNIX, is an unused local address.

       If the initiating socket is not connection-mode, then connect() shall
       set the socket's peer address, and no connection is made. For
       SOCK_DGRAM sockets, the peer address identifies where all datagrams
       are sent on subsequent send() functions, and limits the remote sender
       for subsequent recv() functions. If the sa_family member of address
       is AF_UNSPEC, the socket's peer address shall be reset. Note that
       despite no connection being made, the term ``connected'' is used to
       describe a connectionless-mode socket for which a peer address has
       been set.

       If the initiating socket is connection-mode, then connect() shall
       attempt to establish a connection to the address specified by the
       address argument. If the connection cannot be established immediately
       and O_NONBLOCK is not set for the file descriptor for the socket,
       connect() shall block for up to an unspecified timeout interval until
       the connection is established. If the timeout interval expires before
       the connection is established, connect() shall fail and the
       connection attempt shall be aborted. If connect() is interrupted by a
       signal that is caught while blocked waiting to establish a
       connection, connect() shall fail and set errno to [EINTR], but the
       connection request shall not be aborted, and the connection shall be
       established asynchronously.

       If the connection cannot be established immediately and O_NONBLOCK is
       set for the file descriptor for the socket, connect() shall fail and
       set errno to [EINPROGRESS], but the connection request shall not be
       aborted, and the connection shall be established asynchronously.
       Subsequent calls to connect() for the same socket, before the
       connection is established, shall fail and set errno to [EALREADY].

       When the connection has been established asynchronously, pselect(),
       select(), and poll() shall indicate that the file descriptor for the
       socket is ready for writing.

       The socket in use may require the process to have appropriate
       privileges to use the connect() function.

RETURN VALUE         top

       Upon successful completion, connect() shall return 0; otherwise, −1
       shall be returned and errno set to indicate the error.

ERRORS         top

       The connect() function shall fail if:

       EADDRNOTAVAIL
              The specified address is not available from the local machine.

       EAFNOSUPPORT
              The specified address is not a valid address for the address
              family of the specified socket.

       EALREADY
              A connection request is already in progress for the specified
              socket.

       EBADF  The socket argument is not a valid file descriptor.

       ECONNREFUSED
              The target address was not listening for connections or
              refused the connection request.

       EINPROGRESS
              O_NONBLOCK is set for the file descriptor for the socket and
              the connection cannot be immediately established; the
              connection shall be established asynchronously.

       EINTR  The attempt to establish a connection was interrupted by
              delivery of a signal that was caught; the connection shall be
              established asynchronously.

       EISCONN
              The specified socket is connection-mode and is already
              connected.

       ENETUNREACH
              No route to the network is present.

       ENOTSOCK
              The socket argument does not refer to a socket.

       EPROTOTYPE
              The specified address has a different type than the socket
              bound to the specified peer address.

       ETIMEDOUT
              The attempt to connect timed out before a connection was made.

       If the address family of the socket is AF_UNIX, then connect() shall
       fail if:

       EIO    An I/O error occurred while reading from or writing to the
              file system.

       ELOOP  A loop exists in symbolic links encountered during resolution
              of the pathname in address.

       ENAMETOOLONG
              The length of a component of a pathname is longer than
              {NAME_MAX}.

       ENOENT A component of the pathname does not name an existing file or
              the pathname is an empty string.

       ENOTDIR
              A component of the path prefix of the pathname in address
              names an existing file that is neither a directory nor a
              symbolic link to a directory, or the pathname in address
              contains at least one non-<slash> character and ends with one
              or more trailing <slash> characters and the last pathname
              component names an existing file that is neither a directory
              nor a symbolic link to a directory.

       The connect() function may fail if:

       EACCES Search permission is denied for a component of the path
              prefix; or write access to the named socket is denied.

       EADDRINUSE
              Attempt to establish a connection that uses addresses that are
              already in use.

       ECONNRESET
              Remote host reset the connection request.

       EHOSTUNREACH
              The destination host cannot be reached (probably because the
              host is down or a remote router cannot reach it).

       EINVAL The address_len argument is not a valid length for the address
              family; or invalid address family in the sockaddr structure.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during
              resolution of the pathname in address.

       ENAMETOOLONG
              The length of a pathname exceeds {PATH_MAX}, or pathname
              resolution of a symbolic link produced an intermediate result
              with a length that exceeds {PATH_MAX}.

       ENETDOWN
              The local network interface used to reach the destination is
              down.

       ENOBUFS
              No buffer space is available.

       EOPNOTSUPP
              The socket is listening and cannot be connected.

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       If connect() fails, the state of the socket is unspecified.
       Conforming applications should close the file descriptor and create a
       new socket before attempting to reconnect.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       accept(3p), bind(3p), close(3p), getsockname(3p), poll(3p),
       pselect(3p), send(3p), shutdown(3p), socket(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_socket.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                         CONNECT(3P)

Pages that refer to this page: netinet_in.h(0p)sys_socket.h(0p)accept(3p)bind(3p)freeaddrinfo(3p)listen(3p)pselect(3p)send(3p)socket(3p)