tutorials vrx_docker_examine

Examine a Running Container

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