Veiryfing ssh fingerprints of a system

When trying to connect to a system via ssh for the first time you will get a message that you need to trust the ssh fingerprint of that system.

How do you know if the fingerprint displayed is the correct one, or if there is a man in the middle attack going on?

If you have another terminal open on the system you have you can go to /etc/ssh and execute the following:

for file in *sa_key.pub
do   ssh-keygen -lf $file
done

This will diplay the ssh fingerprints valid for this system so you can double check them.