I was just setting up a new VPS when I hit this snag, the server threw the following error when I tried to start the LFD service
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.
When I dove down into it it would just give a standard error:
lfd.service: control process exited, code=killed status=9 Failed to start ConfigServer Firewall & Security - lfd.
Turns out I was going about the installation in the incorrect manner, I had not configured csf.conf yet and Testing Mode was still enabled.
Simple fix, configure your csf.conf however you want to and then disable Testing Mode and voila!