现实中，难免会遇到忘记mysql数据库的root密码的时候
[root@oracle11g ~]# mysql -uroot -p
Enter password: 
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
[root@oracle11g ~]# 
如上，root密码忘记，现在已经无法登录了。

下面测试跳过密码登录，并重置root密码的过程。

查看当前版本：
[root@oracle11g ~]# rpm -qa | grep MySQL
MySQL-client-advanced-5.6.21-1.rhel5
MySQL-server-advanced-5.6.21-1.rhel5

停止mysql服务：
[root@oracle11g ~]# service mysql stop
Shutting down MySQL..                                      [  OK  ]
[root@oracle11g ~]# 

进入到skip-grant-tables模式：
[root@oracle11g ~]# mysqld_safe --skip-grant-tables
150223 23:07:05 mysqld_safe Logging to '/var/lib/mysql/oracle11g.err'.
150223 23:07:05 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

现在就不需要密码就可以进入mysql了：
[root@oracle11g ~]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.21-enterprise-commercial-advanced MySQL Enterprise Server - Advanced Edition (Commercial)

Copyright (c) 2000, 2014, 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> 

进入mysql系统数据库：
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
mysql>

修改root账户密码：
mysql> update user set password=password("root") where user="root";
Query OK, 4 rows affected (0.04 sec)
Rows matched: 4  Changed: 4  Warnings: 0

mysql>

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

mysql> exit
Bye
[root@oracle11g ~]# 
停止mysql进程：
[1]+  Stopped                 mysqld_safe --skip-grant-tables

启动mysql：
[root@oracle11g ~]# service mysql start
Starting MySQL                                             [  OK  ]
[root@oracle11g ~]#

使用刚才修改的密码进入mysql：
[root@oracle11g ~]# mysql -uroot -proot
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.6.21-enterprise-commercial-advanced MySQL Enterprise Server - Advanced Edition (Commercial)

Copyright (c) 2000, 2014, 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> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| kevin              |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.00 sec)

mysql>