Update dns name server entry in ubuntu using command line

Introduction

Traditionally /etc/resolv.conf is modified to change the DNS server IP address. However, if resolvconf utility is installed (and it comes as default in ubuntu), then its not make sense to modify /etc/resolv.conf. Note that resolvconf utility overrides it whenever interface is restarted or whole machine is rebooted. Warning is mentioned in the file itself.

warning msg in resolv.conf

ubuntu:~$ cat /etc/resolv.conf

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)

# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

nameserver 10.140.50.5

How to change DNS nameserver entry

update the dns-nameservers line in /etc/network/interfaces

Updating /etc/network/interfaces

ubuntu:~$ cat /etc/network/interfaces

# This file describes the network interfaces available on your system

# and how to activate them. For more information, see interfaces(5).

# The loopback network interface

auto lo

iface lo inet loopback

# The primary network interface

auto eth0

iface eth0 inet static

address 10.102.38.121

netmask 255.255.255.0

network 10.102.38.0

broadcast 10.102.38.255

gateway 10.102.38.1

# dns-* options are implemented by the resolvconf package, if installed

#dns-nameservers 10.102.38.1

dns-nameservers 10.140.40.5

Restart the interface

# ifdown eth01; ifup eth01

Now check /etc/resolv.conf entry. It should have updated entry

/etc/resolve.conf

ubuntu:~$ cat /etc/resolv.conf

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)

# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

nameserver 10.140.40.5

Additional note

Above steps can be used to modify interface ip address as well. So, in /etc/network/interfaces, IP address should be modified and then interface should be restarted.

Reference

http://askubuntu.com/questions/224966/how-do-i-get-resolvconf-to-regenerate-resolv-conf-after-i-change-etc-network-in