在安装好的MySQL服务器上，配置了环境变量之后，发现用mysql无法登录，报如题的错误，实在没有办法，决定用安全模式对root用户修改密码：
首先关闭正在运行的MySQL;
在一个终端窗口运行命令：mysqld_safe --user=mysql --skip-grant-tables --skip-networking&
[root@MySQL ~]# mysqld_safe --user=mysql --skip-grant-tables --skip-networking&
运行之后新打开一个终端窗口：
[root@MySQL ~]# mysql -u root mysql
mysql> update mysql.user set authentication_string=password('mysql') where user = 'root';
Query OK, 1 row affected, 1 warning (0.02 sec)
Rows matched: 1 Changed: 1 Warnings: 1 mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec) mysql> exit
Bye
以上是5.7版本的修改密码方式，在5.7中存储密码的字段不再是password了，变成了authentication_string，在5.7之前采用以下命令：
mysql> UPDATE user SET Password=PASSWORD('newpassword') where USER='root';
修改之后登陆成功：
[root@MySQL ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is
Server version: 5.7.-log MySQL Community Server (GPL) Copyright (c) , , 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>