Inspect the System Before Touching It

When a running system behaves strangely, collect a baseline before changing it.

Discovery baseline

ros2 node list
ros2 topic list -t
ros2 service list -t
ros2 action list -t
ros2 param list

You do not need to dump every output into a report. Capture the subset relevant to the symptom.

Node-level inspection

ros2 node info <node_name>

Communication-level inspection

ros2 topic info <topic_name> --verbose
ros2 interface show <interface_type>

Why baseline evidence matters

If you restart the system first, you may erase the original state that could have told you what was wrong.

The same principle applies outside ROS 2: observe before modifying.

Checkpoint

Invent this symptom:

The listener terminal is open but no messages appear.

List the first three inspection commands you would run and what each one would prove.