Access denied for user 'root'@'IP地址' ,是因为相应的主机没有对应的访问权限

--开放权限如下
use mysql;
update user u set u.host = '%' where u.user = 'root' limit 1;
flush privileges;

--查看用户权限
show grants for current_user();

--mysql不推荐通过修改表的方式修改用户密码
INSERT or UPDATE statements for the mysql.user table that refer to literal passwords are logged as is,so you should avoid such statements
--通过客户端sql修改
MariaDB [mysql]>  UPDATE user SET Password = password('123456') WHERE User = 'root' ;
--此时可在binglog中可以看到明文的密码
[root@rudy_01 3306]# mysqlbinlog binlog.000006 --start-position=4224 >/tmp/test.sql
[root@rudy_01 3306]# cat /tmp/test.sql 
SET @@session.collation_database=DEFAULT/*!*/;
UPDATE user SET Password = password('123456') WHERE User = 'root'

--在 mysql 5.7 中 password 字段已经不存在了
mysql> UPDATE user SET Password = password('123456') WHERE User = 'root' ;
ERROR 1054 (42S22): Unknown column 'Password' in 'field list'

mysql> desc user;
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Field                  | Type                              | Null | Key | Default               | Extra |
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Host                   | char(60)                          | NO   | PRI |                       |       |
| User                   | char(32)                          | NO   | PRI |                       |       |
| Select_priv            | enum('N','Y')                     | NO   |     | N                     |       |

--注意出于安全考虑，alter user 时提示更新的是 0 条数据，但实际 password 已更新
mysql> select host,user,authentication_string,password_last_changed from user where user='root' and host='%';
+------+------+-------------------------------------------+-----------------------+
| host | user | authentication_string                     | password_last_changed |
+------+------+-------------------------------------------+-----------------------+
| %    | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 | 2016-01-08 15:38:13   |
+------+------+-------------------------------------------+-----------------------+
1 row in set (0.04 sec)

--提示更新0条，使用此方法不需要再 flush privileges
If you modify the grant tables indirectly using account-management statements such as GRANT, REVOKE,SET PASSWORD, or RENAME USER, 
the server notices these changes and loads the grant tables into memory again immediately.
mysql>  alter user 'root'@'%' identified by '12345678';
Query OK, 0 rows affected (0.00 sec)
--实际已更新
mysql>  select host,user,authentication_string,password_last_changed from user where user='root' and host='%';
+------+------+-------------------------------------------+-----------------------+
| host | user | authentication_string                     | password_last_changed |
+------+------+-------------------------------------------+-----------------------+
| %    | root | *84AAC12F54AB666ECFC2A83C676908C8BBC381B1 | 2016-01-08 15:53:09   |
+------+------+-------------------------------------------+-----------------------+
1 row in set (0.00 sec)

--在binlog中查出的sql如下
[root@rudy mysql]# cat /tmp/test.sql
SET @@session.collation_database=DEFAULT/*!*/;
ALTER USER 'root'@'%' IDENTIFIED WITH 'mysql_native_password' AS '*6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9'


--mysql对于密码有3种检验策略，默认validate_password_policy为MEDIUM
? LOW policy tests password length only. Passwords must be at least 8 characters long.
? MEDIUM policy adds the conditions that passwords must contain at least 1 numeric character, 1 lowercase and uppercase character, and 1 special (nonalphanumeric) character.
? STRONG policy adds the condition that password substrings of length 4 or longer must not match words

--注意validate_password默认是没有安装的
If the validate_password plugin is not installed, the validate_password_xxx system variables are not available, 
passwords in statements are not checked, and VALIDATE_PASSWORD_STRENGTH() always returns 0.
 
 
--检验密码复杂度 
mysql> select VALIDATE_PASSWORD_STRENGTH('abc1235jeme');
+-------------------------------------------+
| VALIDATE_PASSWORD_STRENGTH('abc1235jeme') |
+-------------------------------------------+
|                                         0 |
+-------------------------------------------+
1 row in set (0.00 sec)
--查找安装的插件，发现找不到validate_password
mysql> show plugins;
--手动安装
mysql> INSTALL PLUGIN validate_password SONAME 'validate_password.so';
mysql> show plugins;
+----------------------------+----------+--------------------+----------------------+---------+
| Name                       | Status   | Type               | Library              | License |
+----------------------------+----------+--------------------+----------------------+---------+
| validate_password          | ACTIVE   | VALIDATE PASSWORD  | validate_password.so | GPL     |
+----------------------------+----------+--------------------+----------------------+---------+
45 rows in set (0.04 sec)
--再次检验密码复杂度 
mysql> select VALIDATE_PASSWORD_STRENGTH('abc1235jeme');
+-------------------------------------------+
| VALIDATE_PASSWORD_STRENGTH('abc1235jeme') |
+-------------------------------------------+
|                                        50 |
+-------------------------------------------+

--安装validate_password插件后，就必需符合validate_password_policy的要求，否则语句执行出错
mysql> alter user 'root'@'%' identified by '123456';
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements