Use Case
You start the VM from VirtualBox but you never get the prompt asking for the login. Instead the VM is stuck on the following screen:

Cause
The serial post isn’t defined
Solution
Shutdown the VM and go to the Settings -> Ports -> Serials Ports -> Port 1 and select “Enable Serial Port” as shown below

Change the path Path/Address according to YOUR machine like: C:/Users/MYNAME/airflow-materials-vm/vagrant/ubuntu-xenial-16.04-cloudimg-console.log
Click on OK, restart the VM and it should work.
If you get an error like FileNotFound, create an empty file ubuntu-xenial-16.04-cloudimg-console.log at the path you specified
Then restart the VM again