The RMU Monitor Start command activates the Oracle Rdb monitor
    process (RDMS_MONITORnn, where nn represents the version Oracle
    Rdb), sets the priority of this process, and specifies a device,
    directory and file name in which to create the monitor log
    file. If the monitor process is active already, you receive the
    following error message:

    %RMU-F-MONMBXOPN, monitor is already running

    An Oracle Rdb monitor process must be running on a node for
    users logged in to that node to use any Oracle Rdb database.
    In a VMScluster environment, a monitor process must be running on
    each node in the cluster from which databases are accessed.

    The Oracle Rdb monitor process controls all database access and
    initiates the automatic database recovery procedure following a
    system failure or other abnormal termination of a database user
    process.

    See the Oracle Rdb Installation and Configuration Guide for
    information on support for multiple versions of Oracle Rdb.