/sys$common/syshlp/helplib.hlb MOUNT, Qualifiers, /SUBSYSTEM  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /SUBSYSTEM
       /NOSUBSYSTEM

    Enables protected subsystems and the processing of subsystem
    ACEs. Requires the SECURITY privilege.

    By default, the disk from which you boot has /SUBSYSTEM enabled
    but other disks do not. For further details on subsystems, refer
    to the OpenVMS Guide to System Security.

    Example

    The following command mounts the volume labeled SLIP on DUA1 with
    mount messages disabled. Subsystems on the volume are accessible.
    MOUNT also assigns the logical name SACH.

    $ MOUNT/NOMESSAGE/SUBSYSTEM DUA1: SLIP SACH