Recovering super-user access

[Ricardo Lino Gonzalez]

Hi,

Following some security tips for MySQL, I ran the command:
rename user 'root'@'localhost' to 'newrootuser'@'localhost';

But for one of my faults I did not execute the command FLUSH PRIVILEGES;
Now I can not log in as root again nor as newrootuser, the result when trying to log in is as follows:

# mysql -u newrootuser -p'password'
ERROR 1698 (28000): Access denied for user 'newrootuser'@'localhost'

Is there any way to regain access?
Will I have to reinstall MYSQL?

I have already tried command like:
# /etc/init.d/mysql stop
# mysqld_safe --skip-grant-tables --skip-networking &

But I was not able to recover root access as expected.

I have access through other users but they are not super user.

Below is the MySQL version
+----------------------------------+
| VERSION() |
+----------------------------------+
| 10.0.29-MariaDB-0ubuntu0.16.04.1 |
+----------------------------------+

Thanks.