Nagios 4 provides a query handler, which can be used for two-way communications with Nagios. It is used internally by Nagios worker processes. It can also be used by external applications for getting and setting data

In this chapter, we learned what the query handler is and how to communicate with it using the Unix domain sockets. We also learned about the services that the query handler provides in Nagios 4.

We learned how to query the Nagios scheduled tasks queues and load control settings. We also found out how to change the load control settings, although we do not recommend that you do so, as they are internal settings.

We also learned how to use NERD to receive notifications about changes in the host and/or service status. We created a sample application that shows the changes in real time. In addition, we connected Nagios and the NERD notifications with the Gource application that can be used to show animated, real-time visualization of the changes in status.

This chapter concludes...