I think the explanation is that you are supposed to replace <username>
with an actual username, such as root
. However, in the example you give, I see the #
sign at your prompt, and the name 'root@host' in your prompt, which means (usually) that you are already
the root user, and should probably put some other username there instead.
As Anish implied, when asking questions, the more information you provide, the better!
At the very very least, it helps to know what Linux you are running, in case the suggestions to help you might vary from one OS to another.