Invokes the VMS Debugger after program execution is interrupted  by
  CTRL/Y, but only if the /NOTRACEBACK qualifier was not specified
  with the LINK command when the program was linked.  For a complete
  description of the VMS Debugger, including more information about
  the DEBUG command, see the VMS Debugger Manual.

  Format:

    DEBUG

Additional information available:

Examples

  1.   $ FORTRAN/DEBUG/NOOPTIMIZE   WIDGET
       $ LINK/DEBUG  WIDGET
       $ RUN /NODEUG WIDGET

       ENTER NAME:
       ENTER NAME:
       ENTER NAME:
       ^Y
       $ DEBUG

          VAX DEBUG Version V5.4-00

       %DEBUG-I-INITIAL, language is FORTRAN, module set to WIDGET
       DBG>

  The FORTRAN and LINK commands both specify the /DEBUG qualifier to
  compile the program WIDGET.FOR with debugger symbol table
  information and to include the debugger in the image file. The
  RUN/NODEBUG command begins normal execution of the image
  WIDGET.EXE, without debugger control.  The image executes an
  infinite loop.  Pressing Ctrl/Y interrupts execution.  The DEBUG
  command gives control to the debugger, and you can now enter
  debugger commands at the DBG> prompt.