ROS2 Nodes

Each node in ROS should be responsible for a single, modular purpose, e.g. controlling the wheel motors or publishing the sensor data from a laser range-finder. Each node can send and receive data from other nodes via topics, services, actions, or parameters.

Commands

ros2 node list

ros2 node list will show you the names of all running nodes. This is especially useful when you want to interact with a node, or when you have a system running many nodes and need to keep track of them.

ros2 node info

One can access more information about nodes with:

ros2 node info <node_name>

ros2 node info returns a list of subscribers, publishers, services, and actions. i.e. the ROS graph connections that interact with that node. For example, the output for ros2 node info /my_turtle should look like:

/my_turtle
  Subscribers:
    /parameter_events: rcl_interfaces/msg/ParameterEvent
    /turtle1/cmd_vel: geometry_msgs/msg/Twist
  Publishers:
    /parameter_events: rcl_interfaces/msg/ParameterEvent
    /rosout: rcl_interfaces/msg/Log
    /turtle1/color_sensor: turtlesim/msg/Color
    /turtle1/pose: turtlesim/msg/Pose
  Service Servers:
    /clear: std_srvs/srv/Empty
    /kill: turtlesim/srv/Kill
    /my_turtle/describe_parameters: rcl_interfaces/srv/DescribeParameters
    /my_turtle/get_parameter_types: rcl_interfaces/srv/GetParameterTypes
    /my_turtle/get_parameters: rcl_interfaces/srv/GetParameters
    /my_turtle/list_parameters: rcl_interfaces/srv/ListParameters
    /my_turtle/set_parameters: rcl_interfaces/srv/SetParameters
    /my_turtle/set_parameters_atomically: rcl_interfaces/srv/SetParametersAtomically
    /reset: std_srvs/srv/Empty
    /spawn: turtlesim/srv/Spawn
    /turtle1/set_pen: turtlesim/srv/SetPen
    /turtle1/teleport_absolute: turtlesim/srv/TeleportAbsolute
    /turtle1/teleport_relative: turtlesim/srv/TeleportRelative
  Service Clients:
 
  Action Servers:
    /turtle1/rotate_absolute: turtlesim/action/RotateAbsolute
  Action Clients: