Unit 03 · lesson

Interrogate a Node With `ros2 node info`

Listing a node tells you it exists.

ros2 node info tells you how it connects.

With Turtlesim running:

ros2 node info /turtlesim

The Jazzy beginner documentation shows categories such as:

Subscribers
Publishers
Service Servers
Service Clients
Action Servers
Action Clients

Do not memorize the list

Read it as a responsibility map.

For example, if /turtlesim subscribes to /turtle1/cmd_vel, that is evidence that some other node can send velocity commands to it through that topic.

If /turtlesim provides /spawn, that is evidence it can respond to a service request to create another turtle.

Compare two nodes

Run:

ros2 node info /turtlesim
ros2 node info /teleop_turtle

Ask:

Which node publishes movement commands?
Which node receives them?
Which node provides simulation services?
Which node has an action client?
Which node has an action server?

You will learn each communication mechanism later. Right now, use the categories to see that nodes expose different interfaces.

Build a node card

Create:

Node:
Started by command:
Publishes:
Subscribes:
Provides services:
Uses services:
Action role:

Fill only what you can support from ros2 node info.

Checkpoint

Why is ros2 node info more useful than restarting a node when your question is simply "what is this node connected to?"