Online monitoring in the upcoming Fermilab Tevatron runII

We describe the online event monitoring systems using ROOT for the CDF and DO collaborations in the upcoming Fermilab Tevatron runII. The CDF and DO experiments consist of many detector subsystems and will run in a high rate large bandwidth data transfer environment. In the experiments, it is crucial to monitor the performance of each subsystem and the integrity of the data, in real time with minimal interruption. ROOT is used as the main analysis tool for the monitoring systems and its GUI is used to browse the results via socket, allowing multiple GUI client connections.