Setting static IP in ubuntu

Login as sudo user or root user

$# sudo vi /etc/network/interfaces
replace following two lines

auto eth0
iface eth0 inet dhcp

With

auto eth0
iface eth0 inet static
address 192.168.100.109
netmask 255.255.255.0
gateway 192.168.100.1
write and quit(:wq) from the vi editor.

restart machine to take effect. If needed modify /etc/resolv.conf for dns servers information.