Written 24 Aug 2026. This is a how-to, not a product card. Buy links are not tagged yet.
What a VM is, and when you do not need one
A pretend computer inside the leftover box. Useful later, when you want to try something without breaking Pi-hole. You do not need one this weekend.
The leftover box is already a computer. You can SSH in. Maybe ads are blocked. Maybe photos live in a share. A VM is not the next install. It is an idea for later.
What this is
A virtual machine, a VM, is a pretend computer running inside the leftover box. It has its own OS, its own name, its own files. If you break the pretend one, the real leftover box (and Pi-hole, and the share) keep running.
You already did the real work. SSH from the couch works. Maybe Pi-hole is answering names. Maybe a share holds photos. None of that needs a pretend computer.
Why people want one
A second OS to try. A messy app in a box you can delete. Experiments kept off the house services. Those are real jobs. They are later jobs.
Why you wait
A leftover OptiPlex with 8 GB of memory is already busy if Pi-hole and a share are on it. Each VM wants its own slice of memory. Day-one VMs are how the house internet dies at dinner.
When it is time
You have a reason to try something that could break the leftover box, and the box has spare memory. 16 GB is a much calmer starting point for VMs. Until then, skip it.
Two later paths
| Path | What that means |
|---|---|
| Stay on Debian or Ubuntu | The leftover box OS. Later you can add one VM with virt-manager, or just keep using the real box. Default: keep using the real box. |
| Reinstall as Proxmox | Only if the whole job is many pretend computers. That is a fresh install, not a package on top of Pi-hole. See what OS to put on the leftover box. |
Do not dual-purpose a Pi-hole box as a hypervisor this month.
You do not buy a second computer for this. You do not buy an N100 to have a hypervisor.
What next
Leave the leftover box alone. If you actually want to spend, used office gear is later. A tiny computer you can leave on is later too.
Skip
Skip installing Proxmox tonight. Skip Kubernetes. Skip Docker Swarm. Skip nested virtualization. Skip GPU passthrough. Skip buying RAM before you have a reason. Skip wiping the Pi-hole box to "do it right."
Sources
A plain explainer. Later reading, official pages only: Debian wiki: system virtualization. Proxmox VE Administration Guide. For the OS choice, see what OS to put on the leftover box. For the backup you already have, see a backup of the leftover-box folder. For the house ad block, see the first useful thing on the leftover box.