I have installed Cloudera 5.9 on a single node cluster ( OS : RHEL 7.2).Cluster was functional and working fine. Suddenly while running a Spark job, it went into a bad health. If I run any hadoop command gives below error Ex: sudo -u hdfs hadoop fs -ls /tmp :8020 failed on connection exception: java.net.ConnectException: Connection refused; For more details see: http://wiki.apache.org/hadoop/ConnectionRefused   Tried to change the port from 8020 to 9000. Still returns the same error. jps command shows sudo jps 15649 Main 19394 Jps   Cloudera manager UI is running but all the components are in Unknown health. Below messages are seen Request to the Service Monitor failed. This may cause slow page responses. View the status of the Service Monitor. Request to the Host Monitor failed. This may cause slow page responses. View the status of the Host Monitor.   Please help.   Thanks Devendra ... View more