I've found a couple of mistakes in the Chapter 2.1 material for DO180. Both are minor, but we should be paying attention to the details.
1: The command that is shown will not produce the output shown:
Change Hello! in the command to Hello world and you're good to go.
And, as I mentioned in another post, why is sudo being used?
2: Why use sudo when the currently logged in user is root?
Again, root (or sudo) is probably not needed because a mariadb uses port 3306 by default.