Vagrant box ubuntu/focal64 and Ubuntu 20.04 freezing on vagrant up - fix by enabling serial console writing to /dev/null.

gistfile1.txt

Bringing machine 'default' up with 'virtualbox' provider...
==> default: Box 'ubuntu/focal64' could not be found. Attempting to find and install...
    default: Box Provider: virtualbox
    default: Box Version: >= 0
==> default: Loading metadata for box 'ubuntu/focal64'
    default: URL: https://vagrantcloud.com/ubuntu/focal64
==> default: Adding box 'ubuntu/focal64' (v20200714.0.0) for provider: virtualbox
    default: Downloading: https://vagrantcloud.com/ubuntu/boxes/focal64/versions/20200714.0.0/providers/virtualbox.box
Download redirected to host: cloud-images.ubuntu.com
Progress: 75% (Rate: 47.5M/s, Estimated time remaining: 0:00:03)
==> default: Successfully added box 'ubuntu/focal64' (v20200714.0.0) for 'virtualbox'!
==> default: Importing base box 'ubuntu/focal64'...
==> default: Matching MAC address for NAT networking...
==> default: Checking if box 'ubuntu/focal64' version '20200714.0.0' is up to date...
==> default: Setting the name of the VM: test_default_1594985727622_38381
==> default: Clearing any previously set network interfaces...
==> default: Preparing network interfaces based on configuration...
    default: Adapter 1: nat
==> default: Forwarding ports...
    default: 22 (guest) => 2222 (host) (adapter 1)
==> default: Running 'pre-boot' VM customizations...
==> default: Booting VM...
==> default: Waiting for machine to boot. This may take a few minutes...
    default: SSH address: 127.0.0.1:2222
    default: SSH username: vagrant
    default: SSH auth method: private key

Vagrantfile

Vagrant.configure("2") do |config|
  config.vm.box = "ubuntu/focal64"
  config.vm.provider "virtualbox" do |vb|
     vb.customize [ "modifyvm", :id, "--uartmode1", "file", "/dev/null" ]
  end
end