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一个朋友在领导要求他删除root@127.0.0.1，root@'%'等用户，只保留root@localhost时，
他写了一条类似delete from mysql.user where user='root'的命令……
注意，他并没有写 “and host=”的条件，导致悲剧发生，并且还flush了授权。

以下模拟误删操作，尝试做恢复：

MySQL版本：
MySQL 5.5.49

模拟误删操作：

1. mysql> DELETE FROM mysql.user WHERE user='root';

2. Query OK, 1 row affected (0.01 sec)

4. mysql> FLUSH PRIVILEGES;

5. Query OK, 0 rows affected (0.01 sec)

解决思路：
新安装或者初始化一个新的实例（与误删操作的MySQL版本最好一致）
初始化好后，启动实例，并以root@localhost用户登录，然后设置密码：

新实例上：

1. mysql> SELECT current_user();

2. +----------------+

3. | current_user() |

4. +----------------+

5. | root@localhost |

6. +----------------+

7. 1 row in set (0.00 sec)

9. mysql> SET PASSWORD=password('123456');

10. Query OK, 0 rows affected (0.00 sec)

12. mysql> FLUSH PRIVILEGES;

13. Query OK, 0 rows affected (0.00 sec)

将存放在mysql.user里的root@localhost用户信息查询出：

1. mysql> SELECT * FROM mysql.user WHERE user='root' AND host='localhost' INTO OUTFILE '/tmp/root.txt';

2. Query OK, 1 row affected (0.00 sec)

对于误删操作的实例：
首先将之前查询出的/tmp/root.txt文件传到该机上，此处传到同目录下，操作略。

然后要停掉mysqld，并绕过授权表启动：
可能无法通过mysqladmin shutdown来停止，此处直接kill掉mysqld_safe与mysqld，操作略。

然后启动：

1. [root@vm02 ~]# mysqld_safe --skip-grant-tables &

2. [1] 2957

3. [root@vm02 ~]# 160819 17:00:30 mysqld_safe Logging to '/data/mysql_log/err-log.err'.

4. 160819 17:00:30 mysqld_safe Starting mysqld daemon with databases from /data/mysql

进入mysql：

1. [root@vm02 ~]# mysql

2. Welcome to the MySQL monitor. Commands end with ; or \g.

3. Your MySQL connection id is 3

4. Server version: 5.5.49-log MySQL Community Server (GPL)

6. Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

8. Oracle is a registered trademark of Oracle Corporation and/or its

9. affiliates. Other names may be trademarks of their respective

10. owners.

12. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

14. mysql> SELECT user(),current_user();

15. +--------+----------------+

16. | user() | current_user()  |

17. +--------+----------------+

18. | root@  | @               |

19. +--------+----------------+

20. 1 row in set (0.00 sec)

可以查看一下mysql.user表，已经没有了误删的root用户，只剩下xxx@'ip1'，yyy@'ip2'，这样的业务用户：

1. mysql> SELECT user,host FROM mysql.user;

2. +------+---------------+

3. | user  | host          |

4. +------+---------------+

5. | xxx  | 192.168.1.185 |

6. | yyy  | 192.168.1.187 |

7. +------+---------------+

8. 2 rows in set (0.00 sec)

将之前的新实例的mysql.user表中的root@localhost信息导入mysql.user：

1. mysql> LOAD DATA INFILE '/tmp/root.txt' INTO TABLE mysql.user;

2. Query OK, 1 row affected (0.04 sec)

3. Records: 1 Deleted: 0 Skipped: 0 Warnings: 0

5. mysql> FLUSH PRIVILEGES;

6. Query OK, 0 rows affected (0.00 sec)

8. mysql> SELECT user,host FROM mysql.user WHERE user='root' AND host='localhost';

9. +------+---------------+

10. | user | host          |

11. +------+---------------+

12. | root | localhost     |

13. +------+---------------+

14. 1 rows in set (0.00 sec)

退出到shell环境，关闭以skip-grant-tables方式启动的mysqld：
此时已经可以用mysqladmin来关闭mysqld了：

1. [root@vm02 tmp]# mysqladmin -uroot -p123456 shutdown

2. 160819 17:08:08 mysqld_safe mysqld from pid file /data/mysql/mysql-pid ended

3. [1]+  Done                    mysqld_safe --skip-grant-tables  (wd: ~)

4. (wd now: /tmp)

5. [root@vm02 tmp]# ps -ef|grep mysql

6. root       3938   1973  0 17:08 pts/0    00:00:00 grep mysql

再重新启动mysqld：

1. [root@vm02 tmp]# mysqld_safe &

2. [1] 3939

3. [root@vm02 tmp]# 160819 17:08:53 mysqld_safe Logging to '/data/mysql_log/err-log.err'.

4. 160819 17:08:53 mysqld_safe Starting mysqld daemon with databases from /data/mysql

已经可以正常使用了，密码是之前在初始化的新实例设置的：

1. [root@vm02 tmp]# mysql -uroot -p123456

2. Welcome to the MySQL monitor. Commands end with ; or \g.

3. Your MySQL connection id is 2

4. Server version: 5.5.49-log MySQL Community Server (GPL)

6. Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

8. Oracle is a registered trademark of Oracle Corporation and/or its

9. affiliates. Other names may be trademarks of their respective

10. owners.

12. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

14. mysql> SELECT user(),current_user();

15. +----------------+----------------+

16. | user()            | current_user()  |

17. +----------------+----------------+

18. | root@localhost | root@localhost  |

19. +----------------+----------------+

20. 1 row in set (0.00 sec)

查看一下权限，可以对比一下，与之前的无异：

1. mysql> SHOW GRANTS;

2. +----------------------------------------------------------------------------------------------------------------------------------------+

3. | Grants for root@localhost                                                                                                              |

4. +----------------------------------------------------------------------------------------------------------------------------------------+

5. | GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY PASSWORD '*6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9' WITH GRANT OPTION |

6. | GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION                                                                           |

7. +----------------------------------------------------------------------------------------------------------------------------------------+

8. 2 rows in set (0.00 sec)

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