当我们忘记mysql的密码的时候，通过修改配置文件，进行免密登录；

1. 修改配置文件/etc/my.cnf，添加以下内容

[mysqld]
skip-grant-tables

2. 重启mysql

systemctl restart mysqld

3. 免密登录

mysql -uroot

4. 重新设置密码(mysql8版本)

# 在线重新启动权限系统
FLUSH PRIVILEGES;
# 查看当前的密码策略
show variables like 'validate_password%';
+-------------------------------------------------+--------+
| Variable_name                                   | Value  |
+-------------------------------------------------+--------+
| validate_password.changed_characters_percentage | 0      |
| validate_password.check_user_name               | ON     |
| validate_password.dictionary_file               |        |
| validate_password.length                        | 8      |
| validate_password.mixed_case_count              | 1      |
| validate_password.number_count                  | 1      |
| validate_password.policy                        | MEDIUM |
| validate_password.special_char_count            | 1      |
+-------------------------------------------------+--------+
# 密码策略调整到最低
set global validate_password.policy =LOW;
# 修改密码程度为4
set global validate_password.length =4;
# 查询用户和用户对应的地址
select host,user from mysql.user;
ALTER USER 'root'@'%' IDENTIFIED BY 'root1@';
FLUSH PRIVILEGES;

5. 注释免密登录的配置，重新登录