CentOS6關閉防火牆:

service iptables stop //臨時關閉
chkconfig iptables off //禁止開機啟動

注: Centos7使用同樣命令，會提示

stop iptables.service 
Failed to stop iptables.service: Unit iptables.service not loaded.

CentOS7關閉防火牆:

systemctl stop firewalld //臨時關閉

systemctl disable firewalld //禁止開機啟動

Removed symlink 
 
/etc/systemd/system/multi-user.target.wants/firewalld.service.

Removed symlink /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service.

也可以安裝iptables-services，使用下面的命令

yum install -y iptables-services //安裝iptables-services
service iptables stop //關閉防火牆
service iptables status //檢查防火牆狀態