MySQL误删root用户怎么恢复
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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：
mysql> DELETE FROM mysql.user WHERE user='root';
Query OK, 1 row affected (0.01 sec)
mysql> FLUSH PRIVILEGES;
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：
mysql> SELECT current_user();
+----------------+
| current_user() |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.00 sec)
mysql> SET PASSWORD=password('123456');
Query OK, 0 rows affected (0.00 sec)
mysql> FLUSH PRIVILEGES;
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：
mysql> SELECT * FROM mysql.user WHERE user='root' AND host='localhost' INTO OUTFILE '/tmp/root.txt';
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：
[root@vm02 ~]# mysqld_safe --skip-grant-tables &
[1] 2957
[root@vm02 ~]# 160819 17:00:30 mysqld_safe Logging to '/data/mysql_log/err-log.err'.
160819 17:00:30 mysqld_safe Starting mysqld daemon with databases from /data/mysql
进入mysql：
[root@vm02 ~]# mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.5.49-log MySQL Community Server (GPL)
Copyright (c) 2000, 2016, 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> SELECT user(),current_user();
+--------+----------------+
| user()| current_user() |
+--------+----------------+
| root@ | @ |
+--------+----------------+
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：
mysql> SELECT user,host FROM mysql.user;
+------+---------------+
| user| host |
+------+---------------+
| xxx | 192.168.1.185 |
| yyy| 192.168.1.187 |
+------+---------------+
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：
mysql> LOAD DATA INFILE '/tmp/root.txt' INTO TABLE mysql.user;
Query OK, 1 row affected (0.04 sec)
Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT user,host FROM mysql.user WHERE user='root' AND host='localhost';
+------+---------------+
| user | host|
+------+---------------+
| root | localhost |
+------+---------------+
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：
[root@vm02 tmp]# mysqladmin -uroot -p123456 shutdown
160819 17:08:08 mysqld_safe mysqld from pid file /data/mysql/mysql-pid ended
[1]+ Done mysqld_safe --skip-grant-tables (wd: ~)
(wd now: /tmp)
[root@vm02 tmp]# ps -ef|grep mysql
root 3938 1973 0 17:08 pts/0 00:00:00 grep mysql
再重新启动mysqld：
[root@vm02 tmp]# mysqld_safe &
[1] 3939
[root@vm02 tmp]# 160819 17:08:53 mysqld_safe Logging to '/data/mysql_log/err-log.err'.
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：
[root@vm02 tmp]# mysql -uroot -p123456
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.5.49-log MySQL Community Server (GPL)
Copyright (c) 2000, 2016, 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> SELECT user(),current_user();
+----------------+----------------+
| user() | current_user()|
+----------------+----------------+
| root@localhost | root@localhost |
+----------------+----------------+
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：
mysql> SHOW GRANTS;
+----------------------------------------------------------------------------------------------------------------------------------------+
| Grants for root@localhost |
+----------------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY PASSWORD '*6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION |
+----------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
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