Nagios offers a very powerful mechanism for scheduling tests. However, there are many situations where you might want to perform tests on your own and just tell Nagios what the result is. One of the typical scenarios for using passive tests can be when performing the actual test takes very little time, but the startup overhead is large. This is usual for languages such as Java, whose runtime initialization requires a lot of resources.

Another reason might be that checks are done on different machines where the Nagios instance is running. In many cases, due to security issues, it is not possible to schedule checks directly from Nagios, as communications not initiated by those machines are blocked. In this case, it's often best to schedule checks on your own and simply submit the results back to Nagios. In cases where such tests are going to be written by you, it's wise to integrate them with a mechanism to send the results over NSCA directly.

Passive checks are responsible...