Inspecting what is going on

When our system is running, we might have several nodes and many more topics publishing messages among nodes. Also, we might have nodes providing actions or services as well. For large systems, it is important to have tools that let us see what is running at a given time. ROS provides basic but powerful tools with this aim, from the CLI to GUI applications.

Listing nodes, topics, services, and parameters

In our honest opinion, we will start with the most basic level of introspection. We are going to see how to obtain the list of nodes running and topics and services available at a given time:

Obtain the list of all	Command
Nodes running	rosnode list
Topics of all nodes running	rostopic list
Services of all nodes running	rosservice list
Parameters on the server	rosparam list

We recommend that you go back to Chapter 2, ROS Architecture and Concepts, to see how these commands also allow us to obtain the message type sent by a particular topic as well...