With the new vSphere 4.1, the ESXi “hidden” tech support mode is no longer hidden. You can enable access the ESXi command line on the console and remotely via SSH easily in the new ESXi Tech Support Mode features, inside the Direct Console User Interface (DCUI). In the past, you had to press ALT+F1, type unsupported, and type the root password (all without any echo/response on the screen).
Now, to access the ESXi console locally or via SSH, just press F2, go to Troubleshooting Options, and enable local and/or remote tech support mode. From there, you can login just like an ESX server by pressing ALT+F1 and logging in as root.
Watch the video to see how it works, step by step: