3306端口巨坑，没有开启防火墙，可是防火墙规则仍是起效了！

今天远程访问Ubuntu上的MySQL时出现错误： 
ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.1.49' (60)

因此先登陆服务器，用命令netstat -tuln查看一下：

Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:139 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN tcp 0 0 127.0.1.1:53 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:445 0.0.0.0:* LISTEN ...

能够看出，MySQL配置应该没问题的，固然也确保MySQL用户密码等都是对的。

查了半天，怀疑是否是iptables问题（但记不得以前曾经配置过iptables，因此一直没想这块）： 
sudo iptables -L

Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all -- anywhere anywhere ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp dpt:http ACCEPT tcp -- localhost anywhere tcp dpt:mysql DROP tcp -- anywhere anywhere tcp dpt:mysql ACCEPT tcp -- anywhere anywhere tcp dpt:mysql ACCEPT tcp -- 192.168.1.0/24 anywhere tcp dpt:mysql Chain FORWARD (policy ACCEPT) target prot opt source destination DOCKER all -- anywhere anywhere ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere Chain OUTPUT (policy ACCEPT) target prot opt source destination Chain DOCKER (1 references) target prot opt source destination 

很奇怪这边怎么会有一个对mysql访问的DROP规则，但仍是先删为敬！ 
此次再iptables命令多加个参数： 
sudo iptables -L -n --line-number

Chain INPUT (policy ACCEPT) num target prot opt source destination 1 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 2 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 3 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 4 ACCEPT tcp -- 127.0.0.1 0.0.0.0/0 tcp dpt:3306 5 DROP tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:3306 6 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:3306 7 ACCEPT tcp -- 192.168.1.0/24 0.0.0.0/0 tcp dpt:3306 Chain FORWARD (policy ACCEPT) num target prot opt source destination 1 DOCKER all -- 0.0.0.0/0 0.0.0.0/0 2 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED 3 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 4 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 

这下每条规则前都有了序号，因此能够根据序号直接来修改或删除：

sudo optables -D INPUT 5 
把INPUT的第五条规则删除，而后去客户端再次登陆MySQL，成功！

虽然这个命令没有效果

我使用了

iptables -F
注意！清除规则是恢复到默认规则，若是默认规则为ACCEPT那就全是ACCEPT，若是默认规则是DROP的话，那就是全DROP了。