Each node sends sensor data and other information such as swap usage, fill level of file systems and S.M.A.R.T. data of the hard disks to a multicast address where the head-node can collect them. The way each node collects the sensor data depends on the hardware type. The Qlustar Cluster Suite detects the type that is suitable for a specific compute node. You can list the current metrics by running ganglia --help. The package ganglia-webfrontend allows to view the state of your cluster and each node from within a web-browser. It suffices to visit the Link http://<head-node>/ganglia.