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：

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！