1. 修改mysqld.cnf配置文件，跳过验证

sudo vi /etc/mysql/mysql.conf.d/mysqld.cnf
#添加这行代码至文件：
skip-grant-tables
 29 [mysqld]
 30 skip-grant-tables
 31 pid-file        = /var/run/mysqld/mysqld.pid
 32 socket          = /var/run/mysqld/mysqld.sock
 33 datadir         = /var/lib/mysql
 34 log-error       = /var/log/mysql/error.log

2. 重启mysqld，登录修改密码

sudo service mysql restart

#连接mysql
mysql -u root

#更新mysql root用户密码为null
USE mysql;
UPDATE user SET plugin=‘mysql_native_password‘, authentication_string=null WHERE user=‘root‘;
FLUSH privileges;

3. 还原mysqld.cnf，重启mysqld，再使用ALTER修改密码

# 删除之前增加的`skip-grant-tables`选项
sudo vi /etc/mysql/mysql.conf.d/mysqld.cnf

#重启mysqld，现在可以在没有skip-grant-tables选项的情况下使用空密码登录
sudo service mysql restart

#
mysql -u root

# 真正地修改密码
ALTER USER ‘root‘@‘localhost‘ IDENTIFIED BY ‘password‘;

MySQL 重置密码

原文：https://www.cnblogs.com/develon/p/12718724.html