@Zhaojie    The errors to focus here are the below ones which are causing unknown health alerts. This is being caused because CM agent is not able to connect to Host Monitor.   Please ensure the hosts generating the alerts have space available and are not overloaded in terms of COU and memory. You can also try to hard restart the CM agents if this is feasible option since hard restart will stop the services running on the host and clear any thread deadlocks in cluster services.   The health test result for HOST_SCM_HEALTH has become bad: This host is in contact with the Cloudera Manager Server. This host is not in contact with the Host Monitor. The health test result for HOST_AGENT_LOG_DIRECTORY_FREE_SPACE has become unknown: Not enough data to test: Test of whether the Cloudera Manager Agent's log directory has enough free space.   Hope this helps, Paras Was your question answered? Make sure to mark the answer as the accepted solution. If you find a reply useful, say thanks by clicking on the thumbs up button.   ... View more