Shutdown (onmode -k) or override (onmode -O).
Cause
A dbspace has gone down during a checkpoint interval. The database server is configured to wait for an override when this situation occurs.
When the checkpoint actually happens, the following message appears: Checkpoint blocked by down space, waiting for override or shutdown.
Action
Either shut down the database server or issue an onmode -O command to override the down dbspace. For more information on the onmode utility, see The onmode utility.