VMS Help DISMOUNT, Qualifiers, /ABORT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Requires volume ownership or the user privilege VOLPRO (volume
    protection) to use this qualifier with a volume that was mounted
    with neither the /GROUP nor the /SYSTEM qualifier. Additionally
    requires the user privilege SHARE if the volume is mounted
    privately by a process other than the process issuing the
    DISMOUNT command.

    Specifies that the volume is to be dismounted, regardless of who
    mounted it. The primary purpose of the /ABORT qualifier is to
    terminate mount verification. The DISMOUNT/ABORT command also
    cancels any outstanding I/O requests. If the volume was mounted
    with the /SHARE qualifier, the /ABORT qualifier causes the volume
    to be dismounted for all of the users who mounted it.