AMENT_PREFIX_PATH Path Error

This document outlines a common environment-related issue in ROS 2, where an incorrect or outdated AMENT_PREFIX_PATH can cause build or runtime errors. It also explains the root cause and provides multiple solutions.

1. Error Case

During workspace build or launch, you may encounter warnings or errors such as:

Failed to find package: ...
ament_cmake not found
Resource not found for <package_name>

This typically happens when AMENT_PREFIX_PATH includes invalid or non-existent paths.

2. Root Cause Analysis

AMENT_PREFIX_PATH is an environment variable used by ROS 2 to locate installed packages. If this variable includes directories that no longer exist (e.g., deleted install folders), tools like colcon build, ros2 launch, or ament_index_cpp will fail to resolve dependencies correctly.

This issue often arises when:

  • Switching between multiple workspaces

  • Moving or deleting a workspace without updating environment variables

  • Hardcoding outdated paths in ~/.bashrc or ~/.zshrc

3. Solution

To resolve the issue, you can either clean specific entries from the variable or reset the workspace environment completely.

Option 1: Filter out broken paths

export AMENT_PREFIX_PATH=$(echo $AMENT_PREFIX_PATH | tr ':' '\n' | grep -v '/path/to/remove' | tr '\n' ':')

Option 2: Reset the workspace environment

unset AMENT_PREFIX_PATH

cd ~/ros2_ws  # or your workspace name
rm -rf build/ install/ log/
colcon build --symlink-install

# Ensure dependencies are installed
sudo apt update
sudo apt install python3-ament-package

rosdep install -r --from-paths . --ignore-src --rosdistro $ROS_DISTRO -y
source install/setup.bash

Tip: Avoid manually appending to AMENT_PREFIX_PATH in your shell configuration unless necessary. Use source install/setup.bash after each build to automatically configure paths.