Tag Archives: nix

Keeping your system-wide configuration files intact after updating SteamOS

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Introduction

If you use SteamOS and you like to install third-party tools or modify the system-wide configuration some of your changes might be lost after an OS update. Read on for details on why this happens and what to do about it.

As you all know SteamOS uses an immutable root filesystem and users are not expected to modify it because all changes are lost after an OS update.

However this does not include configuration files: the /etc directory is not part of the root filesystem itself. Instead, it’s a writable overlay and all modifications are actually stored under /var (together with all the usual contents that go in that filesystem such as logs, cached data, etc).

/etc contains important data that is specific to that particular machine like the configuration of known network connections, the password of the main user and the SSH keys. This configuration needs to be kept after an OS update so the system can keep working as expected. However the update process also needs to make sure that other changes to /etc don’t conflict with whatever is available in the new version of the OS, and there have been issues due to some modifications unexpectedly persisting after a system update.

SteamOS 3.6 introduced a new mechanism to decide what to to keep after an OS update, and the system now keeps a list of configuration files that are allowed to be kept in the new version. The idea is that only the modifications that are known to be important for the correct operation of the system are applied, and everything else is discarded1.

However, many users want to be able to keep additional configuration files after an OS update, either because the changes are important for them or because those files are needed for some third-party tool that they have installed. Fortunately the system provides a way to do that, and users (or developers of third-party tools) can add a configuration file to /etc/atomic-update.conf.d, listing the additional files that need to be kept.

There is an example in /etc/atomic-update.conf.d/example-additional-keep-list.conf that shows what this configuration looks like.

Sample configuration file for the SteamOS updater

Developers who are targeting SteamOS can also use this same method to make sure that their configuration files survive OS updates. As an example of an actual third-party project that makes use of this mechanism you can have a look at the DeterminateSystems Nix installer:

https://github.com/DeterminateSystems/nix-installer/blob/v0.34.0/src/planner/steam_deck.rs#L273

As usual, if you encounter issues with this or any other part of the system you can check the SteamOS issue tracker. Enjoy!

  1. A copy is actually kept under /etc/previous to give the user the chance to recover files if necessary, and up to five previous snapshots are kept under /var/lib/steamos-atomupd/etc_backup ↩︎

More ways to install software in SteamOS: Distrobox and Nix

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Introduction

In my previous post I talked about how to use systemd-sysext to add software to the Steam Deck without modifying the root filesystem. In this post I will give a brief overview of two additional methods.

Distrobox

distrobox is a tool that uses containers to create a mutable environment on top of your OS.

Distrobox running in SteamOS

With distrobox you can open a terminal with your favorite Linux distro inside, with full access to the package manager and the ability to install additional software. Containers created by distrobox are integrated with the system so apps running inside have normal access to the user’s home directory and the Wayland/X11 session.

Since these containers are not stored in the root filesystem they can survive an OS update and continue to work fine. For this reason they are particularly suited to systems with an immutable root filesystem such as Silverblue, Endless OS or SteamOS.

Starting from SteamOS 3.5 the system comes with distrobox (and podman) preinstalled and it can be used right out of the box without having to do any previous setup.

For example, in order to create a Debian bookworm container simply open a terminal and run this:

$ distrobox create -i debian:bookworm debbox

Here debian:bookworm is the image that this container is created from (debian is the name and bookworm is the tag, see the list of supported tags here) and debbox is the name that is given to this new container.

Once the container is created you can enter it:

$ distrobox enter debbox

Or from the ‘Debian’ entry in the desktop menu -> Lost & Found.

Once inside the container you can run your Debian commands normally:

$ sudo apt update
$ sudo apt install vim-gtk3

Nix

Nix is a package manager for Linux and other Unix-like systems. It has the property that it can be installed alongside the official package manager of any distribution, allowing the user to add software without affecting the rest of the system.

Nix running in SteamOS

Nix installs everything under the /nix directory, and packages are made available to the user through a new entry in the PATH and a ~/.nix-profile symlink stored in the home directory.

Nix is more things, including the basis of the NixOS operating system. Explaning Nix in more detail is beyond the scope of this blog post, but for SteamOS users these are perhaps its most interesting properties:

  • Nix is self-contained: all packages and their dependencies are installed under /nix.
  • Unlike software installed with pacman, Nix survives OS updates.
  • Unlike podman / distrobox, Nix does not create any containers. All packages have normal access to the rest of the system, just like native SteamOS packages.
  • Nix has a very large collection of packages, here is a search engine: https://search.nixos.org/packages

The only thing that Nix needs from SteamOS is help to set up the /nix directory so its contents are not stored in the root filesystem. This is already happening starting from SteamOS 3.5 so you can install Nix right away in single-user mode:

$ sudo chown deck:deck /nix
$ wget https://nixos.org/nix/install
$ sh ./install --no-daemon

This installs Nix and adds a line to ~/.bash_profile to set up the necessary environment variables. After that you can log in again and start using it. Here’s a very simple example (refer to the official documentation for more details):

# Install and run Midnight Commander
$ nix-env -iA nixpkgs.mc
$ mc

# List installed packages
$ nix-env -q
mc-4.8.31
nix-2.21.1

# Uninstall Midnight Commander
$ nix-env -e mc-4.8.31

What we have seen so far is how to install Nix in single-user mode, which is the simplest one and probably good enough for a single-user machine like the Steam Deck. The Nix project however recommends a multi-user installation, see here for the reasons.

Unfortunately the official multi-user installer does not work out of the box on the Steam Deck yet, but if you want to go the multi-user way you can use the Determinate Systems installer: https://github.com/DeterminateSystems/nix-installer

Conclusion

Distrobox and Nix are useful tools and they give SteamOS users the ability to add additional software to the system without having to modify the base operating system.

While for graphical applications the recommended way to install third-party software is still Flatpak, Distrobox and Nix give the user additional flexibility and are particularly useful for installing command-line utilities and other system tools.