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MySQL错误日志 [Warning] IP address 'XX.XX.XX.XX' could not be resolved: Name or service not known 解决

编辑时间：2018-06-10 编辑：忘尘阅读：1097

##### 查看mysql错误日志目录
注意：默认情况下，所有日志创建于mysqld数据目录中,其中错误日志为 hostname.err 
```linux
mysql> show variables like 'log_error';       
+---------------+--------------------------------+
| Variable_name | Value                          |
+---------------+--------------------------------+
| log_error     | /var/log/mysql/mysql-error.log |
+---------------+--------------------------------+
1 row in set (0.00 sec)
```

在数据库的错误日志log中，会出现下面的警告:
```linux
190517  9:09:37 [Warning] IP address '47.95.28.143' could not be resolved: Name or service not known
190517 12:37:56 [Warning] IP address '47.52.221.59' could not be resolved: Name or service not known
190517 16:42:23 [Warning] IP address '119.23.138.247' could not be resolved: Name or service not known
190518  0:31:38 [Warning] IP address '47.97.16.76' could not be resolved: Name or service not known
190518  8:21:46 [Warning] IP address '47.100.64.9' could not be resolved: Name or service not known
190518  8:30:58 [Warning] IP address '47.100.64.86' could not be resolved: Name or service not known
190518 19:52:26 [Warning] IP address '61.140.237.118' could not be resolved: Name or service not known
190519  0:37:19 [Warning] IP address '106.15.52.246' could not be resolved: Name or service not known
190519  5:02:51 [Warning] IP address '47.94.52.159' could not be resolved: Name or service not known
190519  8:18:03 [Warning] IP address '106.14.104.214' could not be resolved: Name or service not known
190519  8:44:39 [Warning] IP address '47.96.254.10' could not be resolved: Name or service not known
190520  1:42:48 [Warning] IP address '120.78.225.124' could not be resolved: Name or service not known
190520  8:22:13 [Warning] IP address '118.31.244.58' could not be resolved: Name or service not known
190520  8:59:37 [Warning] IP address '47.100.130.114' could not be resolved: Name or service not known
```

##### 警告产生的原因:
出现错误的原因是MYSQL Server在本地内存中维护了一个非本地的Client TCP cache，这个cache中包含了远程Client的登录信息，比如IP地址，hostname等信息。

如果Client连接到服务器后，Mysql首先会在本地TCP池中根据IP地址解析客户端的hostname或者反解析，如果解析不到，就会去DNS中进行解析，如果还是解析失败，就是在errorlog中写入这样的警告信息。

##### 解决的办法
在mysql的配置文件my.cnf [mysqld]项中增加一项 skip-name-resolve 后重启mysql服务 (该参数的作用：不再进行反解析(ip不反解成域名)，这样也可以加快数据库的反应时间)
```linux
[mysqld]
skip-name-resolve
```

DNS解析是指，将 域名解析成ip地址；
DNS反解析是指，将IP地址反解析成域名；

来说两句吧