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Duplicate DHCP leases when cloning a Ubuntu 20.04 LTS virtual machine

When cloning a Ubuntu 20.04 LTS VM inside Parallels Desktop, I saw some strange behavior: The cloned VM would get the same IP address from Parallels Desktop’s DHCP server as the original VM.

First, I thought that the DHCP lease file might be persisted somewhere, but this turned out to be wrong. Next I stumbled upon a bug report in the Parallels forum, which suggested that Parallels Desktop might hand out duplicate DHCP leases for cloned VMs under certain circumstances, but this turned out to be a wrong lead as well.

In the end, the problem is that in Ubuntu 20.04 LTS (in contrast to older versions), the network interface’s MAC address is not used as the DHCP client identifier any longer. Instead, the system’s machine ID is used.

When cloning a VM, Parallels Desktop assigns new MAC addresses to all interfaces of the VM, but it doesn’t change the VM’s UUID. In order to ensure that the cloned VM has it’s own system UUID, one has to edit the config.pvs file inside the cloned VMs directory and change the content of the <SourceVmUuid> tag to match the content of the <VmUuid> tag (instead of the content of the <VmUuid> tag of the original VM).

Unfortunately, the machine ID is also stored in a file inside the VMs file system, so after changing it in the VM’s configuration, one has to boot into the VM and do the following steps:

sudo rm /etc/machine-id
sudo systemd-machine-id-setup

After rebooting, the system should use the new machine ID.

Update (December 11, 2020): I had written to the Parallels support when I experienced this issue and even though I basically figured it out on my own, they now provided me with a link to a knowledge base article that describes a slightly nicer way of changing a virtual machine’s UUID. I still think that they could simply provide a button for this somewhere in the VM settings, but hey, what do I know…