ssh - I forgot my localhost root password

I installed Hadoop on my machine.
To start it, I was logging in as the user named hduser.

I connected to the ssh port using ssh localhost command.

Then I went to the bin folder of hadoop to start the namenode(sh start-all.sh) hduser's password was asked which I entered.

Now it entered a new prompt - root@localhost.
It asked for a password which I think I have forgotten.
Is it asking for the ssh public key password? If yes then how do I use it to log in. Of not how do I set my root password?