Detecting Problems with Triggers

We have gained quite comprehensive knowledge of what kind of information we can gather using items. However, so far, we only have a single thing we are actively monitoring, so we have only created a single trigger (we did that in , Getting Your First Notification). Triggers can do way more. Let's recap what a trigger is.

A trigger defines when a condition is considered worthy of attention. It fires (that is, becomes active) when item data, or a lack of it, matches a particular condition, such as too high system load or too low free disk space.

Let's explore both of these concepts in more detail now. In this chapter, we will look at the following topics:

• Getting to know more about the trigger-and-item relationship
• Discovering trigger dependencies
• Constructing trigger expressions
• Preventing trigger flapping
• Checking for missing data
• Using event tags for correlation