MySQL 忘记root密码的两种处理方法

【背景】

　　由于各个原因，我遇到过不只一次我服务的客户忘记了MySQL的root密码；如果是普通用户还好，我们可以用root用户去改它的密码，要命

　　的是把root给丢了！

　　对于MySQL来说如果你忘记了root密码，但是你又想通过改密码的方式把root密码找回来的话，你就要作好重启的准备了。

【方法一: skip_grant_tables + skip-networking 两次重启】

　　1): 第一步把MySQL给关掉

ps -ef | grep mysql
mysql                : ?        :: /usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf

kill - 

　　2): 以skip-grant-tables skip-networking 模式启动 mysqld

/usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf --skip-grant-tables --skip-networking &

　　3): 进入mysql

　　如果是mysql-5.7的话密码的hash值保存在了authentication_string这个列里面，5.7之前的版本保存在password列里面

select user,host,authentication_string from mysql.user;
+---------------+-----------+-------------------------------------------+
| user          | host      | authentication_string                     |
+---------------+-----------+-------------------------------------------+
| root          | localhost | *91B73478B18B04D13F6926FAB5A6178250EAB697 |
| mysql.session | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| mysql.sys     | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| monitor       | 127.0.0.1 | *DAD735712BB263A8DA12A091AABC625FE99DD344 |
| root          | 127.0.0.1 | *91B73478B18B04D13F6926FAB5A6178250EAB697 |
| backup        | 127.0.0.1 | *2139A3EF5FE5A0229BE550AD5ED2947B07F43B93 |
| backup        | localhost | *2139A3EF5FE5A0229BE550AD5ED2947B07F43B93 |
| appuser       | 127.0.0.1 | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+---------------+-----------+-------------------------------------------+
8 rows in set (0.01 sec)

　　采用直接更新密码hash值的方式来更新密码

update mysql.user set authentication_string = password('MTls0352') where user='root'; -- 更新密码为MTls0352
Query OK, 2 rows affected, 1 warning (1.01 sec)
Rows matched: 2  Changed: 2  Warnings: 1

select user,host,authentication_string from mysql.user;
+---------------+-----------+-------------------------------------------+
| user          | host      | authentication_string                     |
+---------------+-----------+-------------------------------------------+
| root          | localhost | *597B32612905C92ABC495354FC276D24D0A541C1 |
| mysql.session | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| mysql.sys     | localhost | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| monitor       | 127.0.0.1 | *DAD735712BB263A8DA12A091AABC625FE99DD344 |
| root          | 127.0.0.1 | *597B32612905C92ABC495354FC276D24D0A541C1 |
| backup        | 127.0.0.1 | *2139A3EF5FE5A0229BE550AD5ED2947B07F43B93 |
| backup        | localhost | *2139A3EF5FE5A0229BE550AD5ED2947B07F43B93 |
| appuser       | 127.0.0.1 | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+---------------+-----------+-------------------------------------------+
8 rows in set (0.00 sec)

　　4): 重启mysqld

pkill mysql

/usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf &

　　5): 用新的密码进入MySQL

mysql  -uroot -pMTls0352
mysql: [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: 5.7.23-log MySQL Community Server (GPL)

Copyright (c) 2000, 2018, 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 grants;
+---------------------------------------------------------------------+
| Grants for root@localhost                                           |
+---------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION        |
+---------------------------------------------------------------------+
2 rows in set (0.01 sec)

　　

【方法二：init-file + 一次重启】

　　1): 创建用于修改root密码的sql文件

touch /tmp/change_password.sql

　　内容如下

alter user root@'127.0.0.1' identified by 'mtls0352';
alter user root@'localhost' identified by 'mtls0352';

　　2): 关闭mysql服务

pkill mysqld # 我的主机上只有一个mysql服务所以用pkill mysqld 没有问题，如果你是单机多实例请用 kill $MYSQLPID

　　3): 代入修改密码的init-file来启动MySQL服务

/usr/local/mysql/bin/mysqld --init-file=/tmp/change_password.sql &

　　4): 用新密码登录MySQL

mysql -uroot -pmtls0352
mysql: [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
Server version: 5.7.-log MySQL Community Server (GPL)

Copyright (c) , , 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 grants;
+---------------------------------------------------------------------+
| Grants for root@localhost                                           |
+---------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION        |
+---------------------------------------------------------------------+
 rows in set (0.00 sec)

　　5): 删除修改密码的sql文件

rm /tmp/change_password.sql

【我的评介】

　　a: 第一种方法比较传统，第二种方法“角度刁钻” 但是两个都能解决问题；并且第二种方法看起来步骤又少一些，但是这并不只是问题的全部

　　通常一个线上的MySQL实例并不是以“/usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf &” 这样直接下命令的方式启动的，它们

　　通常和service ,systemctl 一起用的；所以这种情况下针对“方法二”还是要用service 或 systemctl把数据拉起来的，不然就不能用它们来管理

　　了，所以“方法二”最终也是要两次重启的。

　　b: 方法二能使用“alter user”语法，dba就可以不用care密码到底保存在mysql.user表中的那个列。

　　两种方法各有好处，所以重点还是要把一个方法搞的出神入画！

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