• In many cases, it is helpful to be able to open a shell into a running container, so you can use bash commands to understand more about its behavior.
• This most obvious case for this approach is a scenario in which the container is not exiting early but the WAMV is still not moving.
• In this tutorial we will walk through opening a bash session into a competitor image while it is in the middle of a trial.

As in the previous tutorial, open two terminals before you begin:

• In one terminal, we will run the trial you want to debug, using the testing instructions.
• In the the other terminal we will open a bash session into your competitor container.

• Begin running your trial as described in the testing tutorial, using the command:

  ./run_trial.bash $TEAM $TASK $TRIAL
  

• Wait for the competitor container to launch (you can use docker container ls to check).
• Once the competitor container is running, run the following in your other terminal to open an interactive shell:

  docker exec -it vrx-competitor-system bash
  

• This command will open a shell into the competitor container that will remain open until the container exits at the end of the trial.

• Source the setup.bash file, if necessary:

  source /opt/ros/humble/setup.bash
  

  • Note that in many cases, competitor images may choose not to source setup.bash by default in their login shell, by adding a source command to bashrc.
  • This is not an error since you will not be using a login shell during the competition.
  • But, it means we have to do it manually when debugging.
• List rostopics:

  ros2 topic list 
  

  Make sure you can see the /vrx/task/info topic and any topics related to the particular task you are running.
• Check that you can read /vrx/task/info

  ros2 topic echo /vrx/task/info 
  

• If your WAMV is not moving, try sending a thrust command to verify the setup:

  RATE=1
  CMD=2.0
  ros2 topic pub /wamv/thrusters/right/thrust -r $RATE std_msgs/msg/Float64 data:\ $CMD  
  

  • Check that the command is publishing data as expected:

  ros2 topic echo /wamv/thrusters/right/thrust
  

  • You should receive /wamv/thrusters/right/thrust data (which is set to 2.0 in the script).
  • You should be able to see the effect of this command when playing back the trial.
• Check environment variables. For example:

  env | grep ROS
  

• If the commands in the previous section produce their expected outcomes, this indicates that the competitor container is able to communicate with the server.
• In this case, it is likely that the container's software is not running or misconfigured.
• You can use ps -ef or the top command to get a quick sense of what is running on your system.
• If a process that you expect to be running is not running, you can try to bring it up manually to see whether it executes correctly or produces a useful error message.

• A disadvantage of the above approach is that VRX trials have a time limit, and the bash session will close at the end of the trial.
• In addition, if the container is crashing or exiting early, there may not be time to log in and interact with it.
• The next tutorial provides one way of working around these limitations, by launching the competitor image manually.

Back: Basic Debugging	Up: VRX Docker Image Overview	Next: Run a Container Manually