ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

　　在安裝好的MySQL服務器上，配置了環境變量之后，發現用mysql無法登錄，報如題的錯誤，實在沒有辦法，決定用安全模式對root用戶修改密碼：

　　首先關閉正在運行的MySQL;

　　在一個終端窗口運行命令：mysqld_safe --user=mysql --skip-grant-tables --skip-networking&

[root@MySQL ~]# mysqld_safe --user=mysql --skip-grant-tables --skip-networking&

　　運行之后新打開一個終端窗口：

[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版本的修改密碼方式，在5.7中存儲密碼的字段不再是password了，變成了authentication_string，在5.7之前采用以下命令：

mysql> UPDATE user SET Password=PASSWORD('newpassword') where USER='root';

　　修改之后登陸成功：

[root@MySQL ~]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.7.9-log MySQL Community Server (GPL)

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