在新安裝的linux系統中，防火牆默認是被禁掉的，一般也沒有配置過任何防火牆的策略，所有不存在/etc/sysconfig/iptables文件。
解決辦法：
1.鍵入以下命令，新建文件
2.復制以下代碼，此代碼默認開啟80,3306,22端口
# Firewall configuration written by system-config-firewall
# # Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 3306 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 21 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT
3.重啟防火牆
4.測試，搞定！