ERROR 1698 (28000): Access denied for user 'root'@'localhost' in mysql code example

Example: ERROR 1698 (28000): Access denied for user 'root'@'localhost'

>>> sudo mysql -u root -p

>>> USE mysql;

>>> UPDATE user SET plugin='mysql_native_password' WHERE User ='root';

>>> FLUSH PRIVILEGES;

>>> exit;

>>> service mysql restart;