Vagrantで立ち上げたUbuntu20.04が「SSH auth method: private key」で止まる問題の対処

Ubuntu Box「ubuntu/focal64」をvagrant upで起動しようとしても、SSH auth method: private keyでタイムアウトしてしまう。

❯ vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Importing base box 'ubuntu/focal64'...
==> default: Matching MAC address for NAT networking...
==> default: Checking if box 'ubuntu/focal64' version '20211026.0.0' is up to date...
==> default: Setting the name of the VM: **********************************
==> default: Fixed port collision for 22 => 2222. Now on port 2200.
==> default: Clearing any previously set network interfaces...
==> default: Preparing network interfaces based on configuration...
    default: Adapter 1: nat
    default: Adapter 2: hostonly
==> default: Forwarding ports...
    default: 22 (guest) => 2200 (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: 127.0.0.1:2200
    default: SSH username: vagrant
    default: SSH auth method: private key      # ここでタイムアウトしている
Timed out while waiting for the machine to boot. This means that
Vagrant was unable to communicate with the guest machine within
the configured ("config.vm.boot_timeout" value) time period.

If you look above, you should be able to see the error(s) that
Vagrant had when attempting to connect to the machine. These errors
are usually good hints as to what may be wrong.

If you're using a custom box, make sure that networking is properly
working and you're able to connect to the machine. It is a common
problem that networking isn't setup properly in these boxes.
Verify that authentication configurations are also setup properly,
as well.

If the box appears to be booting properly, you may want to increase
the timeout ("config.vm.boot_timeout") value.

該当箇所でネットの情報を見ると、vb.customize ["modifyvm", :id, "--cableconnected1", "on"] を設定すると治ったみたいな情報が出てくるが、実際にやっても変わらず。

Vagrant のissueを覗くと同じような事象のissueがあった。
Vagrantfileに以下の設定を行う事ですんなりvagrant upすることができた。

  config.vm.provider "virtualbox" do |vb|
    vb.customize ["modifyvm", :id, "--uart1", "0x3F8", "4"]
    vb.customize ["modifyvm", :id, "--uartmode1", "file", File::NULL]
  end