Virtual machines are playing an important role in today's IT infrastructure. They help lower the cost of hardware by allowing multiple systems to reside and re-use resources from a single physical machine. It also allows migration from a large number of physical hardware to a small number of high-end servers with a large number of processors.

For Intel based platforms, VMware virtualization (http://www.vmware.com/) is one of the most advanced technologies. This spans from desktop solutions to server products. VMware also offers a free virtualization platform called VMware Server (http://www.vmware.com/products/server/).

Although Nagios does not offer a large variety of plugins to monitor VMware systems, VMware offers a Perl API that can easily be used to query virtual machines, along with a few of their parameters. On Windows operating systems, there is also the VmCOM API that allows interaction with VMware server product.

These functions allow querying of the virtual machine...