/etc/network/interfaces

Define network interface on Ubuntu Linux systems. See /etc/sysconfig/network-scripts/ifcfg-eth0 for RedHat systems and /etc/conf.d/net for Gentoo.

Dynamic IP Address (DHCP):

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback


# The primary network interface
auto eth0
iface eth0 inet dhcp

Static IP Address:

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
        address 192.168.168.9
        netmask 255.255.255.0
        network 192.168.168.0
        broadcast 192.168.168.255
        gateway 192.168.168.1
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers 192.168.168.8
        dns-search example.com

Change from DHCP client to Static or resetting static IP Address:

Edit /etc/network/interfaces (shown above) as appropiate or run the following command:# ifconfig <dev> <ip> netmask <sub>
edit the following line in /etc/resolv.conf with your correct DNS server. name server xxx.xxx.xxx.xxx
Then remove the dhcp-client for the changes to stick. # apt-get remove dhcp-client
Run the following command for the changes to take effect: # /etc/init.d/networking restart
Finally, test your changes by running, say, "ping www.google.com".

From Gnome you can run System > Administration > Network > Devices.

Hostname

Incidently, you can change the hostname with the following:

# hostname myhostname
Edit /etc/hosts and /etc/hostname.
For a DHCP client edit the following line in /etc/dhcp3/dhclient.conf send host-name "myhostname";