Running NixOS on Proxmox

One of the stumbling blocks I ran into when trying out NixOS was that I couldn’t run it under Proxmox, my preferred virtual machine server.

Through some trial and error, I figured out how to install NixOS as a Proxmox container.

Download the NixOS container image 🔗︎

First, download the latest NixOS x86_x64 lxdContainerImage image. For other hardware architectures, see this GitHub comment.

At the time of this writing, the latest NixOS container build is 275970650, but you can just click whatever is the latest build as you read this.

From the build result page, click the link labeled nixos-system-x86_64-linux.tar.xz to download the image:

Upload the image to Proxmox 🔗︎

Now, it’s time to upload the image to Proxmox. Scroll down to one of your Proxmox storage nodes.

Click the storage node you’d like to use. The default is called local, but you may have others.

From the storage node, click “CT Templates,” and then click “Download from URL.”

The NixOS container image download doesn’t include any version or date information. For organization, I renamed my image file to:

• nixos-2024-10-21-lxdContainerImage.x86_64-linux.tar.xz

Renaming will help you identify which version of NixOS this is when you see it later in Proxmox, though this step is optional.

Click “Download” to download the template to Proxmox.

Create a NixOS container 🔗︎

For the next step, SSH to your Proxmox system and switch to the root user context:

ssh root@pve

From the Proxmox SSH session, select the settings for the new NixOS container:

# Where the template file is located
TEMPLATE_STORAGE='local'
# Name of the template file downloaded from Hydra.
TEMPLATE_FILE='nixos-2024-10-21-lxdContainerImage.x86_64-linux.tar.xz'
# Name to assign to new NixOS container.
CONTAINER_HOSTNAME='nixos'
# Which storage location to place the new NixOS container.
CONTAINER_STORAGE='local'
# How much RAM to assign the new container.
CONTAINER_RAM_IN_MB='8192'
# How much disk space to assign the new container.
CONTAINER_DISK_SIZE_IN_GB='80'

With those settings in place, create the new NixOS container with pct create:

pct create "$(pvesh get /cluster/nextid)" \
  --arch amd64 \
  "${TEMPLATE_STORAGE}:vztmpl/${TEMPLATE_FILE}" \
  --ostype unmanaged \
  --description nixos \
  --hostname "${CONTAINER_HOSTNAME}" \
  --net0 name=eth0,bridge=vmbr0,ip=dhcp,firewall=1 \
  --storage "${CONTAINER_STORAGE}" \
  --memory "${CONTAINER_RAM_IN_MB}" \
  --rootfs ${CONTAINER_STORAGE}:${CONTAINER_DISK_SIZE_IN_GB} \
  --unprivileged 1 \
  --features nesting=1 \
  --cmode console \
  --onboot 1 \
  --start 1

Log in to NixOS 🔗︎

Your NixOS container is now configured and should be running.

Confusingly, if you visit the Console tab for your new container, you’ll see only a black screen:

If you hit “Enter,” you should see the standard NixOS prompt. You can log in with username root and no password.

Get SSH access to NixOS 🔗︎

Strangely, the configuration.nix file that ships with the NixOS container image does not work. If you try to run nixos-rebuild, you’ll see errors about a missing lxd.nix file. Even if you fix those, there are other systemd errors.

Before you fix those, it’s easier if you have SSH access. The easiest way I’ve found to do that is to download your SSH keys to the system. If you have a GitHub account with SSH keys enabled, you can do that as follows:

GITHUB_USERNAME='your-github-username' # Replace this.

mkdir -p ~/.ssh && \
  curl "https://github.com/${GITHUB_USERNAME}.keys" > ~/.ssh/authorized_keys

After this, you should be able to SSH in to your NixOS system with ssh root@nixos.

Configuring NixOS 🔗︎

I’ve created a basic configuration for a NixOS server system as a Proxmox container. You can download this configuration by running the following command:

curl \
  --show-error \
  --fail \
  https://mtlynch.io/notes/nixos-proxmox/configuration.nix \
  > /etc/nixos/configuration.nix

Apply the new configuration by running the following commands:

nix-channel --update && \
  nixos-rebuild switch --upgrade && \
  echo "install complete, rebooting..." && \
  poweroff --reboot

From there, you have a basic NixOS server system, which you can configure however you like.

References 🔗︎

• https://nixos.wiki/wiki/Proxmox_Linux_Container
• https://blog.xirion.net/posts/nixos-proxmox-lxc/
• https://taoofmac.com/space/blog/2024/08/17/1530