I posted a tweet tonight.

Love it that you access the DCUI from a putty session pic.twitter.com/ODZuFaYMmL

— Maish Saidel-Keesing (@maishsk) August 8, 2013

I needed to restart the management agent on a ESXi host (it would not reconnect to vCenter)

Restarting the Management agents on an ESXi or ESX host (1003490) is the correct KB for information on how to do it.

If you are at the console - you go in through the DCUI.

There is a not well known fact that you can also invoke the Direct Console User Interface (DCUI) from a remote SSH session as well.

Accessing Direct Console User Interface (DCUI) from an SSH session(2039638)

Very simple, just type dcui from the shell prompt. When you are done, Ctrl+C.

Before..

After

Just have to read the KB's…