一：(停掉正在运行的mysql)
[root@NetDakVPS ~]# service mysql stop 
二：使用 “--skip-grant-tables”参数重新启动mysql
[root@NetDakVPS ~]# mysqld_safe --skip-grant-tables &

[1] 23810
Starting mysqld daemon with databases from /var/lib/mysql 
三：用root帐号登录mysql
[root@NetDakVPS ~]# mysql -u root
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.0.77 Source distributionType ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the buffer. 
四：改变用户数据库
mysql> use mysql
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -ADatabase changed 
五：修改密码，记得密码要用password()函数进行加密
mysql> update user set password=password(‘netdak‘) where user=‘root‘;
Query OK, 1 row affected (0.04 sec)
Rows matched: 1 Changed: 1 Warnings: 0 
六：刷新权限表
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec) 
七：退出mysql
mysql> quit
Bye 
八：对mysql进行重启
[root@NetDakVPS ~]# service mysql restart;
STOPPING server from pid file /var/run/mysqld/mysqld.pid
100421 13:44:03 mysqld endedStopping MySQL: [ OK ]
Starting MySQL: [ OK ]
[1]+ Done mysqld_safe --skip-grant-tables 
九：用更改过的密码重新登录即可。
[root@NetDakVPS ~]# mysql -u root -p
Enter password: netdak
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.0.77 Source distributionType ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the buffer.mysql> quit
Bye

十、重新执行修改密码

SET PASSWORD = PASSWORD(‘123456‘);

注：第十步不一定需要，但是 MySql5.6操作时可能会报错：You must SET PASSWORD before executing this statement.