====== Change Ubuntu Server from DHCP to a Static IP Address ======
If the Ubuntu Server installer has set your server to use DHCP, you will want to change it to a static IP address so that people can actually use it.

Changing this setting without a GUI will require some text editing, but that's classic linux, right?

Let's open up the /etc/network/interfaces file. I'm going to use nano, but you can choose a different editor.

<code>sudo nano /etc/network/interfaces</code>
For the primary interface, which is usually eth0, you will see these lines:
<code>auto eth0
iface eth0 inet dhcp
</code>
As you can see, it's using DHCP right now. We are going to change dhcp to static, and then there are a number of options that should be added below it. Obviously you'd customize this to your network.
<code>auto eth0
iface eth0 inet static
        address 192.168.1.100
        netmask 255.255.255.0
        network 192.168.1.0
        broadcast 192.168.1.255
        gateway 192.168.1.1

</code>

Now we'll need to add in the DNS settings by editing the resolv.conf file:
<code>sudo nano /etc/resolv.conf</code>
On the line 'nameserver xxx.xxx.xxx.xxx' replace the x with the IP of your name server. (You can do ifconfig /all to find out what they are) 

You need to also remove the dhcp client for this to stick (thanks to Peter for noticing). You might need to remove dhcp-client3 instead.

<code>
sudo apt-get remove dhcp-client<br />
//OR_<br />
sudo apt-get remove isc-dhcp-client
</code>
Now we'll just need to restart the networking components:
<code>sudo /etc/init.d/networking restart

</code>
Ping www.google.com. If you get a response, name resolution is working(unless of course if google is in your hosts file).

===== Promiscuous Mode =====
To temporarily do this run:<br />
''ifconfig eth1 promisc''

If you want to make it permanent, edit ''/etc/network/interfaces''
<file>
auto eth1
 iface eth1 inet manual
       up ifconfig $IFACE 0.0.0.0 up
       up ip link set $IFACE promisc on
       down ip link set $IFACE promisc off
       down ifconfig $IFACE down
</file>

===== References =====
  * [[http://manpages.ubuntu.com/manpages/lucid/man5/interfaces.5.html|http://manpages.ubuntu.com/manpages/lucid/man5/interfaces.5.html]]
  * [[https://help.ubuntu.com/10.04/serverguide/network-configuration.html|https://help.ubuntu.com/10.04/serverguide/network-configuration.html]]
  * [[http://ubuntuforums.org/showthread.php?t''1225099|http://ubuntuforums.org/showthread.php?t''1225099]]

-- Main.FredPettis - 16 Mar 2010