Windows Core has no Start button, and obviously, there’s no logoff button. So, how does one logoff?
Well, it’s actually very easy. On the Windows Core command prompt just type logoff.
If, by some reason you’ve closed the command prompt and are feeling a bit lost, just open some other server, or even your own workstation command prompt and type logoff 1/server: W2K8Core, where the number 1 is the number of session, 0 (zero) is the console and remote are 1 and 2.
Now you can simply login again and open the command prompt.