Impossibile Avviare proftpd server su Ubuntu 20

Se non riusciamo ad avviare “ProFtpd” su Ubuntu, utilizziamo il comando : systemctl status proftpd.service -l
per avere una diagnostica precisa.
Se l’errore è come questo : 

v systemd[1]: Starting LSB: Starts ProFTPD daemon…
Dec 04 10:17:02 AcWebDev proftpd[1231]: * Starting ftp server proftpd
Dec 04 10:17:02 AcWebDev proftpd[1241]: 2020-12-04 10:17:02,401 AcWebDev proftpd[1241]: processing configuration directory ‘/etc/proftpd/conf.d/’
Dec 04 10:17:02 AcWebDev proftpd[1241]: 2020-12-04 10:17:02,448 AcWebDev proftpd[1241]: warning: unable to determine IP address of ‘AcWebDev’
Dec 04 10:17:02 AcWebDev proftpd[1241]: 2020-12-04 10:17:02,448 AcWebDev proftpd[1241]: error: no valid servers configured
Dec 04 10:17:02 AcWebDev proftpd[1241]: 2020-12-04 10:17:02,448 AcWebDev proftpd[1241]: fatal: error processing configuration file ‘/etc/proftpd/proftpd.conf’
Dec 04 10:17:02 AcWebDev proftpd[1231]: …fail!
Dec 04 10:17:02 AcWebDev systemd[1]: proftpd.service: Control process exited, code=exited, status=1/FAILURE
Dec 04 10:17:02 AcWebDev systemd[1]: proftpd.service: Failed with result ‘exit-code’.
Dec 04 10:17:02 AcWebDev systemd[1]: Failed to start LSB: Starts ProFTPD daemon.

fare attenzione a quella riga : warning: unable to determine IP address of ‘AcWebDev’
Se vi è questo errore, proftpd non riesce a determinare l’indirizzo Ip del server, in questo caso “AcWebDev”
Controllare se il server risolve se stesso (ping AcWebDev) altrimenti inserire in /etc/hosts un associazione : IP -Nome (es 1.1.1.1.1 AcWebDev)

proftpd, errore proftpd, Failed to start LSB: Starts ProFTPD daemon,