Pressing Ctrl/Y at DCL level enables you to interrupt an image
    that is running without debugger control, so that you can then
    start the debugger with the DCL command DEBUG.

    You can bring an image under debugger control only if, as a
    minimum, that image was linked with the /TRACEBACK qualifier
    (/TRACEBACK is the default for the LINK command).

    When you press Ctrl/Y to interrupt the image's execution, control
    is passed to DCL. If you then enter the DCL command DEBUG, the
    interrupted image is brought under control of the debugger. The
    debugger sets its language-dependent parameters to the source
    language of the module in which execution was interrupted and
    displays its prompt. You can then determine where execution was
    suspended by entering a SHOW CALLS command.

    The Ctrl/Y-DEBUG sequence is not supported in the kept debugger
    configuration.

    The Ctrl/Y-DEBUG sequence is not supported in the VSI DECwindows
    Motif for OpenVMS user interface to the debugger. Instead, use
    the STOP button.

    Within a debugging session, you can use the CONNECT command to
    connect an image that is running without debugger control in
    another process (of the same job) to that debugging session.

    Related commands:

       CONNECT
       Ctrl/C
       DEBUG (DCL command)
       RUN (DCL command)