The Nagios server is not started after a cluster install and you are unable to manage it from Ambari Web.
Log into the Nagios server host.
Confirm that the Nagios server is not running. From a shell:
ps -ef | grep nagios
You should not see a Nagios process running.
Start the Nagios process manuallly. From a shell:
service nagios start
The server starts. You should be able to see that started state reflected in Ambari Web. You can now manage (start/stop) Nagios from Ambari Web.
