ubuntu18.04 mysql5.7/mariadb10.1 set root password

1. Login (use sudo to login without password)
sudo mysql -u root

2. Check
SELECT User,Host FROM mysql.user;

3. Delete out root user

DROP USER 'root'@'localhost';

4. Create new root user

CREATE USER 'root'@'%' IDENTIFIED BY 'your_password';

5. Grant permissions

GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' WITH GRANT OPTION;

6. FLUSH PRIVILEGES;