If the RMU Alter command includes a root-file-spec parameter, the
    database to which this root-file-spec refers is attached to as
    part of the RdbALTER startup. In this case, the ATTACH command is
    unnecessary. Otherwise, no commands changing database pages are
    allowed until an ATTACH command naming that database is issued.

    You can use the ATTACH command to attach to only one database at
    a time. Before invoking another database for altering, you must
    use the DETACH command to detach from the current database. See
    the help entry for the DETACH command for more information.