Often my ubuntu freezes up altogether(only able to move my cursor). So i try to reboot using the keys "ALT+PrntScrn+REISUB", but this is what happens >> Once i finish hitting the keys RE, my screen goes BLACK and it shows up a few lines of commands (or whatever) which I dont understand. I have no other choice other than manually force shut down (by pressing power button for 3-4 seconds)

Here is a screenshot of what my black screen displays as soon as I hit R,E

What do these lines mean? Is there anyway I can safely restart my PC?

(Since i was unable to use printscreen, i had to manually take a snap of my monitor using my camera. I had taken 3 pictures of the same screen, because I could not capture the entire text displayed on my screen in a single click)