Исправление MySQL\MariaDB Access denied for user 'root'@'localhost' (using password: YES) в Ubuntu

sudo mysql -u root -p

Для старых версий:

mysql.user SET plugin = 'mysql_native_password' WHERE user = 'root' AND plugin = 'unix_socket';

Для актуальных (без пароля - оставить пустые кавычки BY ''):

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'Pa$$W0rD';

FLUSH PRIVILEGES;

QUIT

sudo systemctl restart mysql