Q1
Sometimes SCM manger lose connection with agent because the agent is dead.
A1
You should start the agent service.
$cd /etc/init.d
$./cloudera-scm-agent status
$./cloudera-scm-agent start
Cloudera distribution (CDH3 & CDH4) uses an agnet to control and monitor nodes. If the agent stop working, all services should 'Bad' health and it cannot be restarted thru Cloudera Manager.
Cloudera agent can be crushed, when /var/log directory is full.
Clean up /var/log to avoid this issue.
Q2
Hbase Shell Hanging
A2
First thing to check on cloudera manager if there is master and region server status are fine. In this case, there was two hbase master was running. I delete all instances of hbase and created the hbase master and RS instances again. NOw there was one master and 3 RS. Second, when you are accessing the cluster machine to run the hbase shell, ensure to " deploy client configuration" from the "Services" menu. If you are accessing the hbase from other server, ensure to download the configuration files and unzip it and set HBASE_CONF_DIR to that unzip directory. That will ensure that you are pointing to right hbase configuration..