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



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

NAME
       connect -- connect a socket

SYNOPSIS
       #include <sys/socket.h>

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

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

ERRORS
       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
       None.

APPLICATION USAGE
       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
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       accept(), bind(), close(), getsockname(), poll(), pselect(), send(),
       shutdown(), socket()

       The Base Definitions volume of POSIX.1-2017, <sys_socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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                  2017                           CONNECT(3)
