sudo gedit /etc/network/interfaces
Change the line iface eth0 inet dhcp to iface eth0 inet static and add the following just below it:
address 192.168.1.100 (IP address of what you want your Ubuntu machine to be)
netmask 255.255.255.0 (Default mask which in this case is the default class c subnet)
gateway 192.168.1.1 (Typically your router’s IP address)
network 192.168.1.0 (The network that this machine is running on)
broadcast 192.168.1.255 (A message that is sent to all out
network-attached hosts to essentially find a specific address. You
also receive them from other hosts)
dns-nameservers 192.168.1.1 (DNS or Domain Name Server used for responding to queries when you are searching for a website)
sudo /etc/init.d/networking stop sudo /etc/init.d/networking start