How to backup data on CentOS without username&password

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http://stackoverflow.com – My tutor just gave me a server, which had been installed CentOS. He told me to learn Linux with, but first of all, I should enter it and back up data without username and password! (Because he forgot all of them). Now I am running this noisy server, there are only 4 items I can choose: Language, Session, Restart or Shut Down. Also, a field to enter user's info. Could you please tell me how to do? (The first thing I wanna do is to backup all data on this server) (HowTos)