问题描述：登录mysql时报错ERROR 1524，如下所示：
数据库：mysql 5.7.21
1、异常重现
[root@leo-mysql5721 ~]# mysql -uroot -p
Enter password: 
ERROR 1524 (HY000): Plugin 'auth_socket' is not loaded

2、解决方案
mysql> select user,plugin from user;
+---------------+-----------------------+
| user          | plugin                |
+---------------+-----------------------+
| root          | auth_socket           |
| mysql.session | mysql_native_password |
| mysql.sys     | mysql_native_password |
| erika         | mysql_native_password |
| jeffrey       | mysql_native_password |
+---------------+-----------------------+
5 rows in set (0.00 sec)

mysql> update user set plugin='mysql_native_password' where user='root';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)

mysql> select user,plugin from user;
+---------------+-----------------------+
| user          | plugin                |
+---------------+-----------------------+
| root          | mysql_native_password |
| mysql.session | mysql_native_password |
| mysql.sys     | mysql_native_password |
| erika         | mysql_native_password |
| jeffrey       | mysql_native_password |
+---------------+-----------------------+
5 rows in set (0.00 sec)

[root@leo-mysql5721 ~]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 9
Server version: 5.7.21 MySQL Community Server (GPL)

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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> 

说明：如上所示，修改plugin后成功登录数据库.