二、不重启mysqld的方法
1、首先得有一个可以拥有修改权限的mysql数据库账号，当前的mysql实例账号（较低权限的账号，比如可以修改test数据库）或者其他相同版本实例的账号。把data/mysql目录下面的user表相关的文件复制到data/test目录下面。
[root@localhost mysql]# cp mysql/user.* cacti/
[root@localhost mysql]# chown mysql.mysql cacti/user.*
2、使用另一个较低权限的账号链接数据库，设置test数据库中的user存储的密码数据。
[root@localhost mysql]# mysql -ucacti -pcacti
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 17
Server version: 5.5.25a-log Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> use test
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
mysql> update user set password=password('kongzhong123') where user='root';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 5 Changed: 0 Warnings: 0
mysql>
3、把修改后的user.MYD和user.MYI复制到mysql目录下，记得备份之前的文件。
mv mysql/user.MYD mysql/user.MYD.bak
mv mysql/user.MYI mysql/user.MYI.bak
cp test/user.MY* mysql/
chown mysql.mysql mysql/user.*
4、查找mysql进程号，并且发送SIGHUP信号，重新加载权限表。
[root@localhost mysql]# pgrep -n mysql
2184
[root@localhost mysql]#
[root@localhost mysql]# kill -SIGHUP 2184
5、登陆测试
[root@localhost mysql]# mysql -uroot -pkongzhong123
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 20
Server version: 5.5.25a-log Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>