This is an old one, but worthy of documentation…
By default root login over SSH is disabled in ESX 3.X and vSphere 4.X. While it is best practice for security to leave this disabled, from time to time a situation may warrant opening up this access.
To enable this on ESX 3.X and vSphere 4.X (w/service console), please refer to this KB Article posted by VMware.
To enable this on ESX4i (should also work for 3i), you must follow the procedure below. Please note that this is UNSUPPORTED and should only be done on ESX4i in a lab environment.
1. Press Alt + f1 to view the console, then type “unsupported” and press enter. Wait for “You have activated Tech Support Mode.”
2.You will see a password prompt. Enter he root password for the server. This will log you into the unsupported console.
3.Using vi, edit /etc/inetd.conf (vi /etc/inetd.conf) and look for a line beginning with #ssh. Remove the # and save the file. (Hit escape, type wq! and press enter).
4.Change to /sbin, and run ./services.sh restart
If you still have an issue accessing the server via SSH after doing this, restart the server.
This post comes at a perfect time. Just installed esx 3.0 on four 2650′s (just to play) in the lab and was looking for this info. Thanks!