MySQL Error: : ‘Access denied for user ‘root’@’localhost’

sudo mysql

-- for MySQL
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'root';

-- for MariaDB
ALTER USER 'root'@'localhost' IDENTIFIED VIA mysql_native_password USING PASSWORD('root');

With a single query we are changing the auth_plugin to mysql_native_password and setting the root password to root and there isn’t any need to restart mysqld or start it with special privileges.

References
https://stackoverflow.com/questions/41645309/mysql-error-access-denied-for-user-rootlocalhost