ERROR 1698 (28000): Access denied for user 'mortega'@'localhost' code example

Example 1: 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;

Example 2: RROR 1698 (28000): Access denied for user 'root'@'localhost

sudo mysql -u root -p