Configuring/Changing/Updating DNS servers list on GNU/Linux System

Linux System Configuration:

login as: root
root@xxx.xxx.xxx.xxx’s password:
Last login: Fri Oct 25 07:04:21 2013 from xxx.xxx.xxx.xxx
Linux temp-sys 2.6.15-29-amd64-server #1 SMP Mon Sep 24 17:31:58 UTC 2007 x86_64                                                                                         GNU/Linux

The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.
root@temp-sys:~#

Checking the list of existing DNS servers configured on the DNS server:

root@temp-sys:/var/named# nslookup www.xenapp.testdom.net

;; connection timed out; no servers could be reached

root@temp-sys:/var/named#

root@temp-sys:/var/named# cat /etc/resolv.conf

#search site1.testdom.net

nameserver 203.54.1.20

search site1.testdom.net site2.testdom.net

root@temp-sys:/var/named#

Changing/Updating the DNS servers list:

root@temp-sys:/var/named#cp /etc/resolv.conf /etc/resolv.conf-25102013

root@temp-sys:/var/named# cat /etc/resolv.conf

#search site1.testdom.net

#nameserver 203.54.1.20

nameserver 203.54.1.10

search search site1.testdom.net site2.testdom.net

root@temp-sys:/var/named# nslookup www.xenapp.testdom.net

Server:         203.54.1.10

Address:        203.54.1.10#53

Name:   www.xenapp.testdom.net

Address: 656.299.305.207

root@temp-sys:/var/named#