3.5 Recovering from a System Failure
  If the system fails during installation of an update or optional
  software product, VMSINSTAL.COM attempts to continue
  the installation upon rebooting. Depending on when the
  system failed, one of three conditions exists:

  .
        The system disk was not altered before the system failure.
        In this case, VMSINSTAL.COM instructs you to restart
        the installation.
  .
        The system disk or a library used by the installation was
        corrupted. In this case, VMSINSTAL.COM instructs you
        to restore either the system disk or the corrupted library
        from the backup copy and to restart the installation.
  .
        VMSINSTAL.COM continues the installation. In this
        case, the procedure performs most of the installation. In
        addition, VMSINSTAL.COM might tell you that you must
        perform some tasks manually to complete the installation.