FTP connection to the server cannot be established. FTP client returns the error ::

421 Service not available, remote server has closed connection

The following error message appears in the /var/log/messages log file ::

getaddrinfo 'Hostname_Is_Here' error: Name or service not known
warning: unable to determine IP address of 'host.domain.tld domain'



Cause ::

This problem happens because FTP server cannot determine IP address of the server by hostname. Try to PING Hostname

#ping hostname

For Example ::

#pign vps.example.com


Resolution

In this case you need to define the correct hostname in the configuration files below and restart network service.

/etc/hosts
/etc/sysconfig/network


The following example shows how to set up hostname "hostname.domain.tld" on RedHat systems.

/etc/hosts:
127.0.0.1 localhost localhost.localdomein
11.22.33.44 hostname.domain.tld hostname

/etc/sysconfig/network:
HOSTNAME=hostname.domain.tld

# /etc/init.d/network restart



Where "11.22.33.44" and "hostname.domain.tld" have to be replaced with the real server IP and hostname accordingly.

Also, in the latest Parallels Plesk Panel versions hostname can be set through Plesk CP on the Server->Preferences page.

Reference :: http://kb.parallels.com/en/929


Enjoy
James007