@bgooley,    Thank you very much for your reply and advice. Now we know that CM is necessary to start the CDH because it is managed by CM. Unfortunately, our namenodes (2) and datanodes (4) hosts have been rebooted, so I cannot get back the processes managed by agents from “/var/run/cloudera-scm-agent/process”. Now I am trying to install a new CM, using a new set of hosts to simulate the situation about the existing CDH cluster, my plan (I read a post like this: https://community.cloudera.com/t5/Cloudera-Manager-Installation/cloudera-manager-database-lost/td-p/31989) is that after I install the new CM: 1. I extract the hosts and roles configuration as json file; 2. Update the json file host name as the existing CDH hosts; 3. Import the json file into CM; 4. Update all /etc/cloudera-scm-agent/config.ini server_host to the new CM;   One challenge for me is that we cannot remember all the roles in each host clearly, because we installed all services (include HDFS, Hbase, Hive, Impala, Zookeeper, Spark, Hue…etc.) before, but for HDFS and Hbase should be ok since our host name is like namenode01, namenode02, datanode01, datanode02, datanode03, datanode04… Would like to seek the help that: 1. In the new install CM, if some roles config are not match the exiting CDH, any impact? Especially to the data; 2. Can I install the new CM only and point the host into the existing CDH during the install process, I am afraid the new CM will re-install the CDH and have some impact the existing ones; BTW, it would be very appreciated if you can share the way to start HDFS without CM as your mentioned before.  Thanks again! ... View more