$ sudo dpkg-reconfigure mysql-server-5.5

$ dpkg --get-selections | grep mysql-server-

mysql-server-5.5                                install
mysql-server-core-5.5                           install

sudo /etc/init.d/mysql stop

sudo /etc/init.d/mysqld stop

sudo mysqld_safe --skip-grant-tables &

mysql -uroot

use mysql;

update user set password=1234 where User='root';

flush privileges;

quit

sudo /etc/init.d/mysql stop
...
sudo /etc/init.d/mysql start

sudo /etc/init.d/mysqld stop
...
sudo /etc/init.d/mysqld start

mysql -u root -p 1234