I recently installed Ubuntu server on my server and I found out it had no gui by default. So I installed that with the help of this page
Everything seemed to be fine so I started copying some files to my server. When I checked it to see if it was done I saw the lock screen that asked for the root password. But I never set that password so I tried a the password I set for my user account. I also tried the following passwords: root, admin, (nothing) and (spacebar). I searched the internet and found out that there is no default password for root.
Am I stuck in this lock screen?
How should I shut the computer down? (there is no shutdown button in the lock screen)