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Building Proxmox Linux Containers with Nix

You can use 'make-system-tarball' to create a Linux Container that can run on Proxmox, for example like https://codeberg.org/raboof/nix-mastodon-bot/src/branch/main/default.nix#L31

NixOS

With a small amount of work, it is possible to use NixOS as a LXC container under Proxmox.

Finding a container tarball

Go to https://hydra.nixos.org/project/nixos, choose a release (small ones don't have the tarball we need), and open its Jobs tab. On that page, search for nixos.containerTarball, open the link corresponding to your architecture (probably x86_64). Choose the latest success and click on the number. That is the ID of the result. Under Build products, download the system-tarball, which will be named nixos-system-x86_64-linux.tar.xz.

Note the Build ID, it will be used when renaming the tarball... right when it's downloaded:

mv nixos-system-x86_64-linux.tar.xz nixos-${RELEASE}-default_${BUILDID}_amd64.tar.xz

This is a proxmox convention, and is useful to follow.

Preparing the container

But first, you will need to upload the container tarball to the storage.

Then, once this is done, you will need to access the CLI for the proxmox host. SSH or the web CLI will be fine.

CLI operations

In the CLI, create a container using the following command. If created as a template, I recommend setting a memorable ID.

pct create 99999 \
  --description nixos-template \
  local:vztmpl/nixos-${RELEASE}-default_${BUILDID}_amd64.tar.xz \
  -ostype unmanaged \
  -net0 name=eth0 \
  -storage local-lvm

Tip

use tab-completion in the CLI for the local:... path!

Note that in the previous command, the -ostype option is necessary; this way Proxmox will not try to do fancy stuff to the system.

The last step using the CLI, edit /etc/pve/lxc/99999.conf to add this line:

lxc.init.cmd: /sbin/init

Before NixOS version 21.11 it was

lxc.init.cmd: /init

.

Creating a template

It is not be possible to use the facilities to create a NixOS container under Proxmox. It is possible, though, to create a template that may be cloned as a base. In the GUI, with the container selected, click the More menu at the top, then Convert to template. Accept.

To create a new NixOS container, you can then clone the template instead of doing the preceding steps.

Expected issues

nixos-rebuild switch

nixos-rebuild switch may fail with errors for special mount points. This does not look like it affects the container.

[root@nixos:/]# nixos-rebuild switch
building Nix...
building the system configuration...
activating the configuration...
setting up /etc...
mount: /dev: cannot remount devtmpfs read-write, is write-protected.
mount: /dev/pts: cannot remount devpts read-write, is write-protected.
mount: /dev/shm: cannot remount tmpfs read-write, is write-protected.
mount: /proc: cannot remount proc read-write, is write-protected.
mount: /run: cannot remount tmpfs read-write, is write-protected.
mount: /run/keys: cannot mount ramfs read-only.
mount: /run/wrappers: cannot remount tmpfs read-write, is write-protected.
setting up tmpfiles
warning: error(s) occurred while switching to the new configuration

Black Console in Proxmox

The Proxmox console may appear black when launched. It is at the login prompt but no existing text is rendered. Just type "root" and hit enter and new text will get rendered just fine.