I just installed Ubuntu 12.04 Server 64-bit on a machine and when the prompt in the install came up to configure DHCP I didn't have an Internet connection so it failed. It gave my the option to configure it later so I chose it thinking it wouldn't be an issue to lookup how to configure it later. Now I can't even ping a DNS server and I'm at a loss of how to configure DHCP. I've found documentation on how to configure a DHCP server but little on how to actually just get client side DHCP configured, I have found some however.
dhclient.leases is completely empty and the routing table is empty. I tried, per the documentation here, adding the following lines to /etc/network/interfaces
auto eth0 iface eth0 inet dhcp
then running "sudo ifup eth0" as noted in the documentation. After ifup finally finished (took quite a few minutes) I was still unable to ping OpenDNS. It seems a file named dhclient.eth0.leases as added to /var/lib/dhcp but it is empty also.
I'm not really sure what to do or check at this point :/