To begin with the R-Pi gets it’s IP address via DHCP, so it can vary. Changing to fixed IP is very similar to the way it’s done in Ubuntu.

To change to static IP address:

sudo nano /etc/network/ interfaces

replace line “iface eth0 inet dhcp” with:

iface eth0 inet static
address 192.168.1.20
netmask 255.255.255.0
gateway 192.168.1.10

Check also that nameserver points to your gateway or ISP nameserver:

sudo nano /etc/resolv.conf
nameserver 192.168.1.10

You can restart the network interface but it’s easier just to reboot:

sudo reboot

Wait a bit for the reboot then log in and check the new config:

ifconfig

NOTE: nano is my preferred editor. I also use mc for quick simple file management.