How to solve eth0 missing in VirtualBox

Suppose you setup a linux virtual machine in VirtualBox and once you clone that hard disk and attach to a new virtual machine you notice that eth0 is not available. The problem is related to fact that since the MAC address of network adapter has changed (you created a new virtual machine) kernel has reconfigured it to be used by next available name, e.g. eth1. So what you need is simply open file /etc/udev/rules.d/70-persistent-net.rules in your favorite editor and remove a line that uses currently eth0 and change the line with NAME="eth1" to NAME="eth0". Here is an example:

# PCI device 0x1022:0x2000 (pcnet32)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", \
ATTR{address}=="08:00:27:43:0b:0f", ATTR{dev_id}=="0x0", \
ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

Probably simplest way to do this:

echo > /etc/udev/rules.d/70-persistent-net.rules
reboot