Centos Mysql忘记密码，修改密码，MySQL数据库user表为空的问题

Centos Mysql忘记密码，修改密码

1．修改MySQL的登录设置：
vim /etc/my.cnf
在[mysqld]的段中加上一句：skip-grant-tables

2．重新启动mysql
service mysql restart

3．登录并修改MySQL的root密码

 mysql> use mysql; 
 Database changed 
 mysql> update user set password = password ('new-password') where user = 'root'; 
 Query OK, 0 rows affected (0.00 sec) 
 Rows matched: 5 Changed: 0 Warnings: 0 
 mysql> flush privileges; 
 Query OK, 0 rows affected (0.01 sec) 
 mysql> quit

4．将MySQL的登录设置修改回来
vim /etc/my.cnf
将刚才在[mysqld]的段中加上的skip-grant-tables注释
保存并且退出vim

5．重新启动mysql
service mysql restart

注意：如果依旧密码错误，有可能mysql.user表被清空了。解决步骤如下：

MySQL数据库user表为空的问题

一、用户表有用户，直接修改密码

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
修改mysql配置文件my.cnf(如果找不到my.cnf，可以使用 sudo find / -name my.cnf 查找文件位置)：

vim /etc/my.cnf
在[mysqld]中添加

skip-grant-tables

重启mysql服务，用空密码直接登录，查询用户表，有结果则按如下步骤修改，结果为空直接看最后的解决办法

mysql> select Host,User,authentication_string from mysql.user;
+-----------+---------------+-------------------------------------------+
| Host      | User          | authentication_string                     |
+-----------+---------------+-------------------------------------------+
| localhost | root          | *6A7A490FB9DC8C33C2B025A91737077A7E9CC5E5 |
| localhost | mysql.session | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| localhost | mysql.sys     | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| %         | root          | *6A7A490FB9DC8C33C2B025A91737077A7E9CC5E5 |
+-----------+---------------+-------------------------------------------+
4 rows in set (0.00 sec)

修改对应用户的密码
重置密码为 123456

mysql> update mysql.user set authentication_string=password('123456') where user='root' 
Query OK, 2 rows affected, 1 warning (0.00 sec)
Rows matched: 2  Changed: 2  Warnings: 1

刷新权限，使配置生效

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

退出

mysql> quit
Bye

取消或注释掉my.cnf配置文件添加的选项 skip-grant-tables，重启mysql服务，搞定收工。

二、用户表没有数据，则需要插入用户数据

mysql> select Host,User,authentication_string from mysql.user;
Empty set (0.00 sec)

退出登陆

mysql> exit
Bye

编辑my.cnf配置文件，添加或修改下面两项（我这没有sql_mode项）：

sql_mode=NO_ENGINE_SUBSTITUTION
skip-grant-tables

停止mysql服务，启动数据库的安全模式：mysqld_safe &
使用root 空密码连接数据库： mysql -uroot -p
插入root用户数据

mysql> insert into mysql.user(Host,User,authentication_string) values("%","root",password("123456")); 
Query OK, 1 row affected, 4 warnings (0.00 sec)

再次查询mysql.user表，会报错

mysql> select Host,User,authentication_string from mysql.user;
ERROR 1194 (HY000): Table 'user' is marked as crashed and should be repaired

需要修复mysql.user表

mysql> REPAIR TABLE mysql.user;
+------------+--------+----------+-------------------------------------------------+
| Table      | Op     | Msg_type | Msg_text                                        |
+------------+--------+----------+-------------------------------------------------+
| mysql.user | repair | info     | Wrong bytesec: 113-108- 95 at 396; Skipped      |
| mysql.user | repair | info     | Found block that points outside data file at 32 |
| mysql.user | repair | info     | Found block that points outside data file at 36 |
| mysql.user | repair | info     | Found block that points outside data file at 40 |
| mysql.user | repair | info     | Found block that points outside data file at 44 |
| mysql.user | repair | info     | Found block that points outside data file at 48 |
| mysql.user | repair | info     | Found block that points outside data file at 52 |
| mysql.user | repair | info     | Found block that points outside data file at 56 |
| mysql.user | repair | info     | Found block that points outside data file at 60 |
| mysql.user | repair | warning  | Number of rows changed from 4 to 3              |
| mysql.user | repair | status   | OK                                              |
+------------+--------+----------+-------------------------------------------------+
11 rows in set (0.64 sec)

再次查询user表

mysql> select Host,User,authentication_string from mysql.user;
+-----------+---------------+-------------------------------------------+
| Host      | User          | authentication_string                     |
+-----------+---------------+-------------------------------------------+
| localhost | mysql.session | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| localhost | mysql.sys     | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| %         | root          | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+-----------+---------------+-------------------------------------------+
3 rows in set (0.00 sec)
修改root用户的权限：

  update mysql.user set
     `Select_priv` = 'Y',
   `Insert_priv` = 'Y',
   `Update_priv` = 'Y',
   `Delete_priv` = 'Y',
   `Create_priv` = 'Y',
   `Drop_priv` = 'Y',
   `Reload_priv` = 'Y',
   `Shutdown_priv` = 'Y',
   `Process_priv` = 'Y',
   `File_priv` = 'Y',
   `Grant_priv` = 'Y',
   `References_priv` = 'Y',
   `Index_priv` = 'Y',
   `Alter_priv` = 'Y',
   `Show_db_priv` = 'Y',
   `Super_priv` = 'Y',
   `Create_tmp_table_priv` = 'Y',
   `Lock_tables_priv` = 'Y',
   `Execute_priv` = 'Y',
   `Repl_slave_priv` = 'Y',
   `Repl_client_priv` = 'Y',
   `Create_view_priv` = 'Y',
   `Show_view_priv` = 'Y',
   `Create_routine_priv` = 'Y',
   `Alter_routine_priv` = 'Y',
   `Create_user_priv` = 'Y',
   `Event_priv` = 'Y',
   `Trigger_priv` = 'Y',
   `Create_tablespace_priv` = 'Y'
   where user='root';

更新权限

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

退出登陆

mysql> exit
Bye

退出mysql，将my.cnf配置文件的修改恢复
结束mysqld_safe 进程：pkill mysql
启动mysql服务: systemctl start mysql
问题解决！

参考： https://blog.csdn.net/m0_67391377/article/details/124167854
https://www.qycn.com/xzx/article/7071.html