This property logically partitions a single physical host or virtual machine. In the context of installing the Machine Agent, the unique Host ID property is not required. However, if you do not define a unique Host ID, then the Machine Agent uses the Java API to retrieve the host ID. The results from the API can be inconsistent, and may cause the same JVM to return a different value for the same machine, each time the Machine Agent is restarted. To avoid these issues, AppDynamics recommends that you set the value of unique Host ID to the host ID that you want to see in the UI.