Parameters Still Exists After Shutting Down All Nodes In Docker?

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It does make sense to me that the built-in parameter server should not persist after shutting down the ROS Master.

However, I am only using the built-in ROS parameter server, and I can still see parameters and their values after I shut down all nodes launched by a single launch file (by Ctrl-C).

Then, to see if the ROS Master has really been shut down, I used $rostopic list and saw \rosout and several other topics. However I could not get anything from \rosout when I tried to echo it. Therefore, I am not sure if the ROS Master has really been shut down.