Default password of mysql in ubuntu server 16.04

I have installed ubuntu 16.04 server. Mysql server was installed by default in it. When I am trying to access the mysql with `mysql -u root -p`, I am unable to log in to mysql because I dont have the password. Is there any default password? I have also tried with `--skip-grant-tables`, even this does not work. Even trying to log in with just `mysql -u root` is a failure.