In Unix system like Debian, Ubuntu or Red Hat, It is possible to set a static IP address with ifconfig command.

My current Debian system IP address is 10.70.0.61


mkyong:~# ifconfig
eth0    Link encap:Ethernet  HWaddr 00:15:17:1D:CE:2F  
          inet addr:10.70.0.61  Bcast:10.70.3.255  Mask:255.255.252.0

I want change it to 10.70.0.66, just issue following command to set a static IP address in unix


ifconfig eth0 10.70.0.66 netmask 255.255.252.0

mkyong:~# ifconfig eth0 10.70.0.66 netmask 255.255.252.0
mkyong:~# ifconfig
eth0    Link encap:Ethernet  HWaddr 00:15:17:1D:CE:2F  
          inet addr:10.70.0.66  Bcast:10.70.3.255  Mask:255.255.252.0

Done.

P.S eth0 is your system network card.