New Instalation

I just installed Perona XtraDB cluster on Centos 7, I am trying to login for the first time to mysql using the following command:
mysql -u root and I am getting this error ERROR 1045 (28000): Access denied for user ‘root’@‘localhost’ (using password: NO)
I also tried mysql -u root -p and I am getting ERROR 1045 (28000): Access denied for user ‘root’@‘localhost’ (using password: YES) I do not understand the problem

Check please if that helps: https://www.percona.com/blog/2016/05/18/where-is-the-mysql-5-7-root-password/