/usr/bin/mysql_secure_installation

mysql> UPDATE mysql.user SET Password=PASSWORD('password') WHERE User='root';
mysql> DELETE FROM mysql.user WHERE User='';
mysql> DELETE FROM mysql.user WHERE User='root' AND Host NOT IN ('localhost', '127.0.0.1', '::1');
mysql> DROP DATABASE test;
mysql> DELETE FROM mysql.db WHERE Db='test' OR Db='test\\_%';
mysql> FLUSH PRIVILEGES;