Introspection with command line tools
ROS 2 includes a suite of command-line tools for introspecting a ROS 2 system.
Usage
The main entry point for the tools is the command ros2
, which itself has various sub-commands for introspecting and working with nodes, topics, services, and more.
To see all available sub-commands run:
ros2 --help
Examples of sub-commands that are available include:
action
: Introspect/interact with ROS actionsbag
: Record/play a rosbagcomponent
: Manage component containersdaemon
: Introspect/configure the ROS 2 daemondoctor
: Check ROS setup for potential issuesinterface
: Show information about ROS interfaceslaunch
: Run/introspect a launch filelifecycle
: Introspect/manage nodes with managed lifecyclesmulticast
: Multicast debugging commandsnode
: Introspect ROS nodesparam
: Introspect/configure parameters on a nodepkg
: Introspect ROS packagesrun
: Run ROS nodessecurity
: Configure security settingsservice
: Introspect/call ROS servicestest
: Run a ROS launch testtopic
: Introspect/publish ROS topicstrace
: Tracing tools to get information on ROS nodes execution (only available on Linux)wtf
: An alias fordoctor
Example
To produce the typical talker-listener example using command-line tools, the topic
sub-command can be used to publish and echo messages on a topic.
Publish messages in one terminal with:
$ ros2 topic pub /chatter std_msgs/msg/String "data: Hello world"
publisher: beginning loop
publishing #1: std_msgs.msg.String(data='Hello world')
publishing #2: std_msgs.msg.String(data='Hello world')
Echo messages received in another terminal with:
$ ros2 topic echo /chatter
data: Hello world
data: Hello world
Behind the scenes
ROS 2 uses a distributed discovery process for nodes to connect to each other. As this process purposefully does not use a centralized discovery mechanism, it can take time for ROS nodes to discover all other participants in the ROS graph. Because of this, there is a long-running daemon in the background that stores information about the ROS graph to provide faster responses to queries, e.g. the list of node names.
The daemon is automatically started when the relevant command-line tools are used for the first time.
You can run ros2 daemon --help
for more options for interacting with the daemon.
Implementation
The source code for the ros2
command is available at https://github.com/ros2/ros2cli.
The ros2
tool has been implemented as a framework that can be extended via plugins.
For example, the sros2 package provides a security
sub-command that is automatically detected by the ros2
tool if the sros2
package is installed.