Diagnose Launch Failures

Launch adds configuration power and therefore new failure boundaries.

Package/executable not found

Use Unit 7 evidence:

ros2 pkg executables robotnix_pubsub

If the executable is not installed/discoverable, the launch file cannot start it.

Launch file not found in package

If direct file launch works but:

ros2 launch robotnix_pubsub student_system.launch.py

cannot find it, inspect the Python package data_files, rebuild, and source a clean overlay.

Node starts with unexpected name

Inspect:

ros2 node list

Then compare launch name/namespace configuration.

Both nodes start but no messages arrive

Inspect the resolved topic endpoints:

ros2 topic list -t
ros2 topic info <resolved_topic> --verbose

A remapping mismatch can separate a publisher and subscriber while both processes remain healthy.

Launch syntax/import error

Read the Python traceback or launch error. Do not diagnose a graph connection until the launch description itself loads.

Checkpoint

For one controlled launch failure, write:

Launch symptom:
Process evidence:
Graph evidence:
Configuration inspected:
Root cause:
Repair: