Nagios is a free and open source computer-software application that monitors systems, networks and infrastructure. Nagios offers monitoring and alerting services for servers, switches, applications and services. It alerts users when things go wrong and alerts them a second time when the problem has been resolved.
Some times we may get a ping error in newly installed nagios.
This is simply a permission problem caused by the script /bin/ping.
So the problem can be solved by running the below command.
#chmod u+s /bin/ping