Setting Static IP in Ubuntu Desktop: Using /etc/network/interfaces

To change IP to static using: /etc/network/interfaces

Step 1: Open /etc/network/interfaces /* Login as super user to execute this */
 / 

Step 2: Enter below details in file 
----------------------------------------------------------

auto eth0
iface eth0 inet static
address 192.168.1.1     /* Address u want */
netmask 255.255.255.0   /* Subnet mask */
gateway 192.168.1.1     /* Default mask */

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Step 3: 

Save above changes

Step 4: 
/etc/init.d/networking restart
to Restart service with static IP 

Note: To change this to Dynamic IP again please follow reverse process step4 to be run as it is.