mysql的密码策略通过插件的方式进行检查，插件的名称是validate_password，可通过如下方式安装：
mysql> INSTALL PLUGIN validate_password SONAME 'validate_password.so';
Query OK, 0 rows affected (0.03 sec)
mysql> SELECT PLUGIN_NAME, PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS;
+-------------------------------+---------------+
| PLUGIN_NAME | PLUGIN_STATUS |
+-------------------------------+---------------+
| validate_password | ACTIVE |
+-------------------------------+---------------+
54 rows in set (0.00 sec)
mysql> exit
Bye
[root@localhost ~]# vi /etc/my.cnf
[mysqld]
plugin-load=validate_password.so
validate-password=FORCE_PLUS_PERMANENT ##可以让mysqld在密码验证插件未启用的情况下启动失败
重启Mysql服务，
mysql> show variables like '%pass%';
+--------------------------------------+-----------------+
| Variable_name | Value |
+--------------------------------------+-----------------+
| disconnect_on_expired_password | ON |
| old_passwords | 0 |
| report_password | |
| sha256_password_private_key_path | private_key.pem |
| sha256_password_public_key_path | public_key.pem |
| validate_password_dictionary_file | |
| validate_password_length | 8 |
| validate_password_mixed_case_count | 1 |
| validate_password_number_count | 1 |
| validate_password_policy | MEDIUM |
| validate_password_special_char_count | 1 |
+--------------------------------------+-----------------+
11 rows in set (0.00 sec)
可以看到，validate_password提供了一些额外的控制密码强度的参数控制。其完整含义可参考http://dev.mysql.com/doc/refman/5.6/en/validate-password-plugin.html和http://dev.mysql.com/doc/refman/5.6/en/validate-password-options-variables.html
mysql> set password = password('mysql');
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
mysql> set password = password('DFFEJd$:7'); -- $是特殊字符, 官方文档好像没有提及, @是可以的。
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'passwor'DushJd$:7')' at line 1
mysql> set password = password('DFFEJd:7');
Query OK, 0 rows affected (0.00 sec)
这样新建的账户就强行启用密码策略了，但是已存在的用户还是原来的密码，可以正常的登录。所以此时需要更改这些用户的密码。mysql有个参数，按官方解释，如果设置这些账户的密码过期，也是可以阻止他们登录的，但5.6中实际上好像这个选项没生效。
mysql> alter user root@'172.18.30.193' password expire;
Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
到30.193的服务登录，还是可以上去。5.7的时候，好像就没有这个问题了。