ROS2-014-Communication Mechanisms, Wrapping Up: Communication-mechanism Tools (1) — Overview and the Command-Line Tools

Jeacson She4/12/25...About 4 min

Introduction

In the previous chapter we learned about the various communication mechanisms in ROS2, and got to know the implementation flow, the relevant APIs and the characteristics of each communication model. In real development we may run into a few problems:

Once a complete robot system is up, its composition is fairly complex — it may contain a dozen, several dozen or even a hundred nodes, and different nodes may contain one or more communication objects (topic publisher, topic subscriber, server, client, action server, action client, parameter server, parameter client), and communication also needs all sorts of msg, srv or action interface messages. So during development, how do you conveniently get at the information about those nodes, topics, services, actions, parameters and interfaces?
Writing a communication implementation involves at least two sides. Once one side is written, how do you verify the program runs properly?
In topic communication, the publisher program sets a publishing frequency for its messages. How do you tell whether the actual publishing frequency at runtime matches the one you set?
......

ROS2 provides some tools that solve the above problems quickly and easily, and in fact we used them for debugging back when we were learning. Here we'll go through them more systematically.

Concepts

In ROS2 there are two types of tool related to communication mechanisms:

Command-line tools
GUI tools (rqt)

Command-line tools are a collection of terminal commands, while GUI tools are a collection of visualisation tools that ROS2 built on the QT framework for robot development. Using these tools makes program debugging more convenient, raises development efficiency and improves the user experience.

1. Command-line tools

The commands commonly used in ROS2 are:

ros2 node: node-related command-line tool
ros2 interface: interface (msg, srv, action) message-related command-line tool
ros2 topic: topic communication-related command-line tool
ros2 service: service communication-related command-line tool
ros2 action: action communication-related command-line tool
ros2 param: parameter service-related command-line tool

Built-in help is generally available for how to use a command; here's how to get it:

You can see the help for a given command by adding the argument -h or the argument --help after it, for example:

ros2 node -h

ros2 node --help

And the arguments under a command can likewise be looked up by adding the argument -h or the argument --help, for example:

ros2 node list -h

ros2 node list --help

Make good use of the argument docs!

The command-line tools described here won't cover everything; if you're not sure about some more detailed command, you can look up the matching help either inside the command-line tool or in the official documentation.

1.ros2 node

The basic usage syntax of ros2 node is:

info Output information about a node | outputs node information
list Output a list of avaliable nodes | outputs the list of running nodes

2.ros2 interface

The basic usage syntax of ros2 interface is:

list List all interface types avaliable | outputs all available interface messages
package Output a list of avaliable interface types within one package | outputs the list of interface types a given package provides
packages Output a list of packages that provide interfaces | outputs the list of packages containing interface messages
proto Output an interface prototype | outputs the interface message prototype
show Output the interface definition | outputs the interface message definition format

3.ros2 topic

The basic usage syntax of ros2 topic is:

bw Display bandwidth used by topic | outputs the bandwidth a topic takes up in message transmission
delay Display delay of topic from timestamp in header | outputs the topic delay time obtained from the timestamp in the header
echo Output messages from a topic | outputs the messages under a given topic
hz Print the average publishing rate to screen | outputs the average publishing rate of the messages
info Print information about a topic | outputs the relevant information of a given topic
list Output a list of avaliable topics | outputs the list of all available (running) topics
pub Publish a message to a topic | publishes a given message to a given topic
type Print a topic's type | outputs the interface type the topic uses

4.ros2 service

The basic usage syntax of ros2 service is:

call Call a service | sends a request to / calls a particular service
echo Echo a service | shows in real time the response data the server returns when the service is called
find Output a list of avaliable service of a given type | outputs the list of available services under a given type
info Print information about a service | outputs the relevant information of a given service
list Output a list of avaliable services | outputs the list of all available (running) services and their types
type Print a service's type | outputs the interface type the service uses

5.ros2 action

The basic usage syntax of ros2 action is:

info Print information about an action | outputs the relevant information of a given action
list Output a list of action names | outputs the list of all available (running) actions
send_goal Send an action goal | sends a request to / calls a particular action
type Print an action's type | outputs the interface type the action uses

6.ros2 param

The basic usage syntax of ros2 param is:

delete Delete parameter | deletes a parameter
describe Show descriptive information about declared parameters | outputs the description of a parameter
dump Show all of the parameters of a node in a YAML file format | writes the node parameters to a file on disk in YAML format
get Get parameter | gets a given parameter
list Output a list of avaliable parameters | outputs the list of all available (running) parameters
load Load parameter file for a node | loads parameters from a file on disk into a node
set Set parameter | sets a parameter

The second half is in ROS2-014-Communication Mechanisms, Wrapping Up: Communication-mechanism Tools (2) — the GUI Tool (rqt) and a Summary

Important

This article was translated by Hermes Agent; the original text can be found at here. The translation is for reference only. Translation time: 2026-11-05