1.无法查看mysql变量 

从mysql5.7.6开始information_schema.global_status已经开始被舍弃，为了兼容性，
此时需要打开 show_compatibility_56

2.修改参数文件 。

vi /etc/my.cnf 
[mysqld]
show_compatibility_56=ON

3.直接修改变量。

15:35:  [(none)]> show variables like '%log%';
ERROR 1682 (HY000): Native table 'performance_schema'.'session_variables' has the wrong structure
15:35:  [(none)]> set @@global.show_compatibility_56=ON;
Query OK, 0 rows affected (0.00 sec)

4.检查。

15:39:  [(none)]> select version();
+------------+
| version()  |
+------------+
| 5.7.43-log |
+------------+
1 row in set (0.00 sec)
15:36:  [(none)]> show variables like '%log%';
+--------------------------------------------+--------------------------------------------------------------+
| Variable_name                              | Value                                                        |
+--------------------------------------------+--------------------------------------------------------------+
| back_log                                   | 1024                                                         |
| binlog_cache_size                          | 4194304                                                      |
| binlog_checksum                            | CRC32                                                        |
| binlog_direct_non_transactional_updates    | OFF                                                          |
| binlog_error_action                        | ABORT_SERVER                                                 |

5.总结 
针对MySQL5.7,应该设置：
set @@global.show_compatibility_56=ON;