Linux / UNIX set the DNS from the command line

Q. I just got Linux installed on my system. I'm able to connect to internet via IP address only. I'm not able to find out information about setting up new DNS sever ip under Linux. How do I configure primary and secondary DNS via terminal / shell prompt?

A. Under Linux / UNIX / BSD operating system, you need to edit the /etc/resolv.conf file and add the line:

nameserver {IP-OF-THE-DNS-1}
nameserver {IP-OF-THEISP-DNS-SERVER-2}

Login as the root, enter:
# vi /etc/resolv.conf
OR
$ sudo vi /etc/resolv.conf
Modify or enter nameserver as follows:
nameserver 208.67.222.222
nameserver 208.67.220.220

Save and close the file. To test DNS configuration type any one of the following command:
$ host google.com
$ dig google.com
$ ping google.com
$ nslookup your-domain.com
Output:

google.com has address 72.14.207.99
google.com has address 64.233.187.99
google.com has address 64.233.167.99
google.com mail is handled by 10 smtp4.google.com.
google.com mail is handled by 10 smtp1.google.com.
google.com mail is handled by 10 smtp2.google.com.
google.com mail is handled by 10 smtp3.google.com.

If you see valid output such as actual IP address or able to ping to remote server via hostname, it means that the dns is working for you. Also make sure you have valid default gateway setup, if you see the time out error.