Our NRPE configuration should now be complete and working as expected. However, in some cases, for example, if there is a firewall issue or an issue of invalid configuration, the NRPE based checks may not work correctly. There are some steps that you can take to determine the root cause of the problem.

The first thing that should be checked is whether Nagios server can connect to the NRPE process on the remote machine. Assuming that we want to use NRPE on 192.168.2.1, we can check if NRPE accepts connections by using check_tcp from the Nagios plugins. By default, NRPE uses port 5666, which we'll also use in the following example, which shows how to check this:

$ /opt/nagios/plugins/check_tcp -H 192.168.2.1 -p 5666

TCP OK - 0.009 second response time on port 5666|time=0.008794s;;;0.000000;10.000000

If NRPE is not set up on the remote host, the plugin will return Connection refused. If the connection could not be established, the result will be No route to host. In these...