I ran into a problem today when upgrading my vmhost to a new Linux version. Therefore, I had to move my vm clients to a different box to complete the upgrade, and minimize downtime. So, I copied the vdi files from my old server to my new server using the scp linux command. Fired up the VM’s on the new server, to discover that I did not have networking. After playing with the cards a bit (fiddling in the GUI) I still could not get eth0 to come up. Off to the Google I went. After reading through some forums, I was able to isolate the issue.
There is a rule in /etc/udev/rules.d/70-persistent-net.rules that defines the MAC address for the card. When coming up under the new VM hardware (new MAC for the virtual NIC) things freak out because the rule does not match the new MAC.
To resolve this, boot up your VM, and open /etc/udev/rules.d/70-persistent-net.rules with your favorite file editor, or for the lazy ones (like me) copy and paste the following:
sudo nano /etc/udev/rules.d/70-persistent-net.rules
Write down the MAC address of the adapter that isn’t working, shutdown your vm, and enter the mac in the virtualbox client settings as shown below:
fire up your VM, and you should be up and running again!
I originally found this fix in a forum here: https://forums.virtualbox.org/viewtopic.php?f=6&t=24383