I was using ProFTPD in standalone mode for a while and usually got a problem ProFTPD crash or shutdown occasionally.
So I switch to inetd mode and those problem gone.
However, I got new problem. After I restart my server, I will not able to connect to FTP. I have to switch ProFTPD to standalone and manually start ProFTPD once before switch back to inetd to get it work.
I’m using Ubuntu 14.04 32bit on DigitalOcean