第一步：用帐号登录mysql
[root@CentOs5 ~]# mysql -u root

或 # mysql -uroot -p

第二步：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 -A

Database changed

第三步：修改密码，记得密码要用password()函数进行加密，一定不要忘记！！！
mysql> update user set password=password('qwe123') where user='root';
Query OK, 1 row affected (0.04 sec)
Rows matched: 1  Changed: 1  Warnings: 0

第四步：刷新权限表
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

第五步：退出mysql
mysql> quit
Bye