切换到root用户，然后进入mysql 的bin目录后，
root@cps-desktop:/usr/local/mysql/bin# /etc/init.d/mysql stop 
root@cps-desktop:/usr/local/mysql/bin# ./mysqld_safe --user=mysql --skip-grant-tables --skip-networking & 
root@cps-desktop:/usr/local/mysql/bin# ./mysql -u root mysql 
mysql> UPDATE user SET Password=PASSWORD('newpassword') where USER='root';
mysql> FLUSH PRIVILEGES;
mysql> quit;

最后重启数据库：
root@cps-desktop:/usr/local/mysql/bin# /etc/init.d/mysql restart 
root@cps-desktop:/usr/local/mysql/bin# mysql -u root -p 
Enter password: <输入新设的密码newpassword>