How to Shrink a VirtualBox Virtual Machine and Free Up Disk Space in nixos guest system? : <p>I was following this <a href="https://www.howtogeek.com/312883/how-to-shrink-a-virtualbox-virtual-machine-and-free-up-disk-space/" rel="nofollow noreferrer">instruction</a> to try to shrink my virtual nixos.
It says,</p>

<blockquote>
  <p>You can’t actually use zerofree on your / partition while you’re booted into the standard Linux environment. Instead, you’ll want to boot into a special recovery mode where your normal root partition isn’t mounted.</p>
</blockquote>

<p>But I can't find a place to boot into recovery mode in nixos.
Question: How to boot into some mode where my root partiion isn't mounted in nixos? Or how do I do zerofree in nixos?</p>
