How to set static IP linux

1. Open /etc/network/interfaces

there will be written something like this

auto lo
iface lo inet loopback

Change text like this

auto lo eth0
iface lo inet loopback
iface eth0 inet static
        address xxx.xxx.xxx.xxx(this is your ip)
        netmask xxx.xxx.xxx.xxx(this is your mask)
        gateway xxx.xxx.xxx.xxx(this is your gateway)