Prove the Environment Before Running Anything

Many ROS errors are actually shell-environment errors.

Before debugging code, inspect:

printenv | grep -i ROS

Look for the intended distribution.

Then inspect package search behavior:

ros2 pkg list | grep robotnix_pubsub
ros2 pkg executables robotnix_pubsub

Ask three questions

1. Is Jazzy installed on disk?
2. Is Jazzy sourced in this shell?
3. Is the local workspace overlay sourced in this shell?

Those are different questions.

Compare terminals

Create two clean terminals:

A: source only /opt/ros/jazzy/setup.bash.

B: source Jazzy plus ~/ros2_ws/install/local_setup.bash.

Compare package/executable discovery.

Checkpoint

Write one sentence for each failure:

• "ROS 2 is not installed";
• "ROS 2 is installed but not sourced";
• "Jazzy is sourced but my overlay is not sourced."

Name the command evidence that distinguishes them.