（1）登录到数据库所在服务器，手工kill掉MySQL进程：  

kill ' cat /mysql-data-directory/hostname.pid'

其中，/mysql-data-directory/hostname.pid指的是MySQL数据目录下的.pid文件，它记录了MySQL服务的进程号。

（2）使用--skip-grant-tables选项重启MySQL服务：

[root@iZ28dr6w0qvZ mysql]# ./bin/mysqld_safe --skip-grant-tables --user=root &[1] 17299[root@iZ28dr6w0qvZ mysql]# 151006 13:14:41 mysqld_safe Logging to '/alidata/log/mysql/error.log'.151006 13:14:41 mysqld_safe Starting mysqld daemon with databases from /alidata/server/mysql/data

其中--skip-grant-tables选项的意思是启动MySQL服务的时候跳过权限表认证。启动后，连接到MySQL的root将不需要命令。

（3）用空密码的root用户连接到MySQ，并且更新root口令：

[root@iZ28dr6w0qvZ ~]# mysql -urootWelcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 4Server version: 5.5.37-log MySQL Community Server (GPL)  Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.  Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.  Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.  mysql> set password = password('ysj123');ERROR 1290 (HY000): The MySQL server is running with the --skip-grant-tables option so it cannot execute this statementmysql> update mysql.user set password=password('123456') where user='root' and host='localhost';Query OK, 1 row affected (0.00 sec)Rows matched: 1 Changed: 1 Warnings: 0

 此时，由于使用了--skip-grant-tables选项启动，使用“set password”命令更改密码失败，直接更新user表的password字段后更改密码成功。

（4）刷新权限表，使得权限认证重新生效：

mysql> flush privileges;Query OK, 0 rows affected (0.00 sec)

（5）重新用root登录时，必须输入新口令：

[root@iZ28dr6w0qvZ ~]# mysql -urootERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)[root@iZ28dr6w0qvZ ~]# mysql -uroot -pEnter password:Welcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 8Server version: 5.5.37-log MySQL Community Server (GPL)  Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.  Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.  Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

注意：在MySQL中，密码丢失后无法找回，只能通过上述方式修改密码。

转自：http://www.cnblogs.com/chenqionghe/p/4863274.html