Our FTP service xinetd has suddenly stopped working - tried to restart xinetd but didn't fix the issue.

We get the following error in ftpzilla:
Status: Connection established, waiting for welcome message...
Error: Could not connect to server

Our /etc/hosts contains:
127.0.0.1 localhost.localdomain localhost
::1 localhost6.localdomain6 localhost6

Also if we ping the 'hostname' from the server... it pings from different domains on our host.

Try to connect to FTP from ssh, get the following:
421 Service not available, remote server has closed connection

We are running Plesk 10.4.4 and Centos 5.7

If anyone could help that would be really great. Thanks.

Do you have firewall rules configured for FTP?

iptables -L -n | grep 21

Do you have the FTP firewall modules loaded?

lsmod | grep ftp

Whats listening on port 21:

netstat -anp | grep 21 | grep LISTEN

Are there any errors in your logs for the FTP service? (Try /var/log/messages to start, but depending on what FTP server you are using it might use a different log)

Is the client negotiating with the server? Do you see it trying to connect?

tethereal -i eth0 host your_ip and port 21

Replace eth0 with your network interface and your_ip with the client. Do you see it connecting?

If you do not have tethereal installed, run this command as root:

yum install wireshark

Thanks for your help! Will keep that in my notes for future.

The problem was caused by a missing ClamAV integration library for ProFTP server.
proftpd[12598]: Fatal: unknown configuration directive 'ClamAV' on line 2 of '/etc/proftp-asl.conf'