ResolutionMake sure that port 21 is opened on the server for incoming connections:
nmap -p21 -P0 SERVER_IP
Check the /var/log/messages file for any FTP related errors. If you are getting a PAM authentication error, you need to disable PAM in the /etc/proftpd.conf file (RPM-based Linux OS):
Make sure that the inetd/xinetd server is running. If it is not running you also may be experiencing problems with sending mail (SMTP), as soon as SMTP service usually works under the server control.
#ps -aux | grep inetd
#ps -aux | grep xinetd
If inetd/xinetd is not running it must be started.
for Linux servers:
for FreeBSD servers: