Fixing ProtonVPN Local Agent Build On Aarch64-linux In NixOS

Nov 26, 2025 by Alex Johnson 61 views

Fixing ProtonVPN Local Agent Build Failure on aarch64-linux in NixOS

Introduction

This article addresses a build failure encountered in NixOS when building the python313Packages.proton-vpn-local-agent package on aarch64-linux systems. The issue stems from how the proton-vpn-local-agent project handles architecture-specific builds, particularly the hard-coding of the x86_64 architecture in its build script. This article will delve into the root cause of the problem, provide a step-by-step explanation of the failure, and discuss potential solutions to resolve this issue. We aim to equip NixOS users and developers with the knowledge to troubleshoot and fix similar build failures, ensuring a smoother experience when working with packages that have architecture-specific build processes.

Understanding the Bug: Why the Build Fails

When working with NixOS, you might encounter build failures that can be puzzling. Let's dive into the specifics of the python313Packages.proton-vpn-local-agent build failure on aarch64-linux. The core of the issue lies in how the proton-vpn-local-agent project manages its builds. The project's build script, as seen in their GitHub repository, hard-codes the x86_64 architecture. This means that the build process is explicitly set up to produce binaries compatible with x86_64 systems.

But why is this a problem? Well, NixOS is designed to be architecture-agnostic, supporting a variety of systems including aarch64-linux. When you try to build the proton-vpn-local-agent on an aarch64 system, the build script's assumption that it's building for x86_64 leads to a mismatch. The build process looks for libraries and components in locations that are specific to x86_64, which don't exist on an aarch64 system. This discrepancy causes the build to fail.

The critical piece of code causing this issue is found in the build_wheel.py script within the python-proton-vpn-local-agent directory. Specifically, the script explicitly targets the x86_64 architecture, which is problematic when building on other architectures. This is because Nixpkgs builds the package from source, and this hardcoded architecture check prevents successful builds on non-x86_64 systems.

In essence, the build script's rigidity clashes with NixOS's flexibility, resulting in a build failure. To resolve this, we need to find a way to either patch the build script or instruct Nixpkgs to build the package in a way that respects the target architecture.

Steps to Reproduce the Build Failure

To truly understand a bug, reproducing it is key. Here’s how you can reproduce the build failure for python313Packages.proton-vpn-local-agent on aarch64-linux.

Set up an aarch64-linux environment: You'll need a system running aarch64-linux. This could be a physical machine, a virtual machine, or a container. Ensure NixOS is installed on this system.
Attempt to build the package: Use the Nix package manager to try building python313Packages.proton-vpn-local-agent. You can do this using the command nix-build -A python313Packages.proton-vpn-local-agent. This command tells Nix to build the specified package and its dependencies.
Observe the error: As Nix attempts to build the package, it will download the source code and run the build script. The build will fail, and you’ll see an error message similar to the one provided in the original bug report. The key part of the error message is FileNotFoundError: [Errno 2] No such file or directory: '/build/source/python-proton-vpn-local-agent/target/x86_64-unknown-linux-gnu/release/libpython_proton_vpn_local_agent.so'. This error indicates that the build process is looking for a library in a directory specific to x86_64, which does not exist on an aarch64 system.

By following these steps, you can reliably reproduce the build failure, confirming that the issue is indeed architecture-specific.

Analyzing the Error Logs

Error logs are a developer's best friend when debugging. Let's break down the relevant parts of the error log from the python313Packages.proton-vpn-local-agent build failure to understand what's going wrong.

The log snippet provided in the bug report gives us several clues:

The build process starts normally, with Nix setting up the build environment and unpacking the source archive.
Cargo, the Rust package manager, is used to build parts of the package, indicating that proton-vpn-local-agent includes Rust components.
Many Rust crates are compiled successfully, showing that the Rust toolchain is working correctly.
The critical error occurs in the final stages of the build process. The traceback shows a FileNotFoundError, specifically that the file /build/source/python-proton-vpn-local-agent/target/x86_64-unknown-linux-gnu/release/libpython_proton_vpn_local_agent.so cannot be found.

This FileNotFoundError is the key to the puzzle. It tells us that the build process is trying to locate a library (libpython_proton_vpn_local_agent.so) in a directory (target/x86_64-unknown-linux-gnu/release) that is specific to the x86_64 architecture. Since we are building on an aarch64 system, this directory does not exist, leading to the build failure.

The error log confirms that the issue is related to the hard-coded x86_64 architecture in the build script, as discussed earlier. The build process is not adapting to the target architecture (aarch64), causing it to look for files in the wrong place.

Potential Solutions: Patching the Build Script

Now that we understand the root cause of the build failure, let's explore potential solutions. One effective approach is to patch the build script to make it architecture-aware. This involves modifying the script so that it correctly identifies the target architecture and builds the package accordingly.

The problematic script, build_wheel.py, needs to be adjusted. Here’s a strategy for patching it:

Identify the architecture: Modify the script to detect the target architecture at runtime. This can be done using Python’s platform module, specifically the platform.machine() function, which returns the machine type (e.g., aarch64, x86_64).
Conditional build logic: Implement conditional logic based on the detected architecture. If the architecture is x86_64, the script should proceed as before. For other architectures, it should adjust the build process accordingly. This might involve changing the output directory or build flags.
Remove hard-coded paths: Replace any hard-coded paths that assume x86_64 with variables that are set based on the detected architecture. This ensures that the build process looks for libraries and components in the correct locations.

Here’s a conceptual example of how the patch might look:

import platform
import os

arch = platform.machine()

if arch == 'x86_64':
    lib_dir = 'target/x86_64-unknown-linux-gnu/release'
else:
    lib_dir = f'target/{arch}-unknown-linux-gnu/release'

LIB_PATH = os.path.join(BASE_DIR, lib_dir, 'libpython_proton_vpn_local_agent.so')

This code snippet demonstrates how to detect the architecture and set the library path dynamically. By applying similar changes throughout the script, we can make the build process architecture-aware.

Implementing a Nix Patch

While understanding the theory behind patching is crucial, implementing it within the Nix ecosystem requires specific steps. Nix uses a patching mechanism to apply modifications to source code before building. This ensures that the original source remains untouched and the build process is reproducible.

Here’s how you can create and apply a Nix patch to fix the python313Packages.proton-vpn-local-agent build:

Create a patch file: First, you need to create a patch file that contains the changes to the build_wheel.py script. You can do this by:
- Making the necessary changes to a local copy of the build_wheel.py file.
- Using the diff command to generate a patch file. For example, if you have the original file as build_wheel.py.orig and the modified file as build_wheel.py, you can run diff -u build_wheel.py.orig build_wheel.py > fix-aarch64-build.patch.
Integrate the patch into the Nix expression: Next, you need to modify the Nix expression for python313Packages.proton-vpn-local-agent to apply the patch. This involves adding a patches attribute to the package definition.

Here’s an example of how the Nix expression might look:

{ pkgs ? import <nixpkgs> {} }:

pkgs.python313Packages.buildPythonPackage {
  pname = "proton-vpn-local-agent";
  version = "1.6.0";
  src = ./source;

  patches = [
    ./fix-aarch64-build.patch
  ];

  # ... other attributes ...
}

This snippet shows how to add a patches attribute that points to the patch file you created. Nix will automatically apply this patch during the build process.

Test the build: Finally, test the build using nix-build to ensure that the patch fixes the issue and the package builds successfully on aarch64-linux.

By following these steps, you can effectively patch the build script and resolve the architecture-specific build failure.

Alternative Solutions and Workarounds

While patching the build script is a direct way to address the issue, there are alternative solutions and workarounds that might be applicable depending on the situation.

Conditional Build Logic in Nix: Instead of patching the Python script, you could add conditional build logic directly in the Nix expression. This involves using Nix’s built-in functions to check the target architecture and set build flags or environment variables accordingly.
```
{ pkgs ? import <nixpkgs> {} }:

pkgs.python313Packages.buildPythonPackage {
  pname = "proton-vpn-local-agent";
  version = "1.6.0";
  src = ./source;

  buildPhase = ''
    ${pkgs.stdenv.targetPlatform.system} == "aarch64-linux" && \
      echo "Building for aarch64-linux" || \
      echo "Building for other architectures"
    runHook preBuild
    # Your build commands here
    runHook postBuild
  '';

  # ... other attributes ...
}
```
This example shows how to use Nix’s targetPlatform.system attribute to check the architecture and execute different build commands. This approach keeps the build logic within Nix, making it more declarative and reproducible.
Overriding the build inputs: Another approach is to override the build inputs to provide architecture-specific dependencies. If the build failure is due to missing dependencies for aarch64, you can use Nix’s override mechanism to supply the correct dependencies.
Contributing upstream: If the issue is indeed due to a bug in the proton-vpn-local-agent project, consider contributing a fix upstream. This benefits the entire community and ensures that future releases will not have the same issue. You can submit a pull request to the project’s GitHub repository with your patch.
Using a Compatibility Layer: In some cases, it might be possible to use a compatibility layer like QEMU to emulate an x86_64 environment on aarch64. However, this is generally less efficient and should be considered a last resort.

Conclusion

In conclusion, the build failure of python313Packages.proton-vpn-local-agent on aarch64-linux in NixOS highlights the importance of architecture-aware build processes. The root cause of the issue is the hard-coding of the x86_64 architecture in the project’s build script, which clashes with NixOS’s architecture-agnostic design.

We’ve explored several solutions to address this issue:

Patching the build script: This involves modifying the build_wheel.py script to detect the target architecture and adjust the build process accordingly.
Implementing a Nix patch: This is the recommended approach for NixOS, as it keeps the changes declarative and reproducible.
Alternative solutions and workarounds: We discussed using conditional build logic in Nix, overriding build inputs, contributing upstream, and using a compatibility layer.

By understanding the cause of the build failure and the available solutions, you can effectively troubleshoot and fix similar issues in your NixOS projects. Remember, contributing fixes upstream benefits the entire community and ensures that future releases are more robust.

For further reading on NixOS and package building, consider exploring the official NixOS documentation and community resources. You can find valuable information and examples that will help you deepen your understanding of Nix and its capabilities. Check out the official NixOS website https://nixos.org/ for documentation and community resources.