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

       /WRITE (default)
       /NOWRITE

    Controls whether the volume can be written.

    By default, a volume is considered read/write when it is mounted.
    You can specify /NOWRITE to provide read-only access to protect
    files. This is equivalent to write-locking the device.

    Example

    The following command mounts a volume labeled BOOKS on NODE$DKA1
    and then proceeds to mount it on each node in the existing
    OpenVMS Cluster. The /NOWRITE qualifier makes the volume
    available for read-only access.

    $ MOUNT/CLUSTER/NOWRITE NODE$DKA1: BOOKS