MySQL無法登錄問題-"ERROR 1045 (28000): Access denied for user 'root'@'localhost'"-之解決方法-密碼重置

筆者在CentOS7上安裝MySQL 5.7版本，安裝完成後，登錄的時候，提示登錄被拒絕：

[root@cdh1 ~]# mysql -uroot -p
Enter password: 
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

以前安裝5.6版本的時候，root用戶的默認密碼爲空， 提示輸入密碼時，敲回車即能登錄。但是此次安裝的5.7版本按默認密碼爲空的方式登錄，卻不能登錄。原因是5.7版本中，系統會隨機爲root用戶設置一個密碼。此時，若想進入mysql命令行模式，需先進行root用戶的密碼重置操作。

root用戶密碼重置非常簡單：

1、修改文件：/etc/my.cnf ：

 找到 mysql配置的代碼塊，添加一行配置 skip-grant-tables ， 繞過密碼驗證，如下圖：

修改完，保存退出，並重啓mysql

[root@cdh1 etc]# systemctl restart mysqld.service

2、進入mysql命令行， 修改root用戶的密碼：

[root@cdh1 etc]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.21 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, 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> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

mysql> update user set authentication_string = password('123'), password_expired = 'N', password_last_changed = now() where user = 'root';
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 1

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql> quit;
Bye

此處需要注意，在5.6版本中，密碼字段是 password ， 在5.7版本中，密碼字段是 authentication_string 。

3、將/etc/my.cnf 文件恢復原狀，即刪除第一步中添加的配置：skip-grant-tables ， 保存退出。

4、重啓mysql服務，即可使用新密碼進行登錄：

[root@cdh1 etc]# systemctl restart mysqld.service
[root@cdh1 etc]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.21 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, 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>

至此，MySQL 的root用戶默認密碼修改完成！