Event handlers are commands that are triggered whenever the state of a host or service changes. They offer functionality similar to notifications. The main difference is that the event handlers are called for each type of change and even for each soft state change. This provides the ability to react to a problem before Nagios notifies it as a hard state and sends out notifications about it. Another difference is what the event handlers should do. Instead of notifying users that there is a problem, event handlers are meant to carry out actions automatically.
For example, if a service defined with
max_check_attempts is set to 4, the
retry_interval is set to 1, and
check_interval is set to 5, then the following example illustrates ...