When you successfully install vSphere, the first yellow screen that you see is called the vSphere DCUI. DCUI is a frontend management system that helps perform some basic system administration tasks. It also offers the best way to troubleshoot some problems that may be difficult to troubleshoot through vMA, vCLI, or PowerCLI. Further, it is very useful when your host becomes irresponsive from the vCenter or is not accessible from any of the management tools.
Some useful tasks that can be performed using the DCUI are as follows:
Configuring the Lockdown mode
Checking connectivity of the Management Network by Ping
Configuring and restarting network settings
Restarting management agents
Viewing logs
Resetting vSphere configuration
Changing the root password