centos7 启动防火墙失败：Failed to start firewalld.service: Unit is masked.   ---- 刚yum安装了iptables

解决：

执行”systemctl start firewalld”启动，出现”Failed to start firewalld.service: Unit is masked.”错误。继续找解决方法，然后输入”systemctl unmask firewalld.service”。

解决CentOS7出现的”Failed to start firewalld.service”问题
然后再启动”systemctl start firewalld”即可解决问题没有报错。