按照教程在centos7上安装csf，出现了Job for lfd.service failed

Question

教程地址：1，https://www.vultr.com/docs/se...
2，https://www.vpsserver.com/com...
执行到systemctl start lfd
这一步出现了错误：Job for lfd.service failed because a fatal signal was delivered to the control process. See "systemctl status lfd.service" and "journalctl -xe" for details.
然后我输入：systemctl status lfd.service
出现的错误提示：`lfd.service - ConfigServer Firewall & Security - lfd
Loaded: loaded (/usr/lib/systemd/system/lfd.service; enabled; vendor preset: disabled)
Active: failed (Result: signal) since Wed 2017-02-22 14:26:35 CST; 29s ago
Process: 29291 ExecStart=/usr/sbin/lfd (code=killed, signal=KILL)

Starting ConfigServer Firewall & Security - lfd...
lfd.service: control process exited, code=killed status=9
Failed to start ConfigServer Firewall & Security - lfd.
Unit lfd.service entered failed state.
lfd.service failed. `
怎么会这样呢？求解决具体方法。