connect(3p) — Linux manual page

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.1‐2017, sys_socket.h(0p)

COPYRIGHT         top

       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(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)