Parameters in ROS 2 are configuration values of a node, stored as integers, floats, booleans, strings, and lists. Use ros2 param list to see a node's parameters, ros2 param get to display a parameter's type and value, ros2 param set to change a parameter's value, and ros2 param dump to view and save all parameters. Use ros2 param load to load parameters from a file, and ros2 run with --params-file to start a node with saved parameters.

1. What are Parameters?

A parameter is a configuration value of a node. You can think of parameters as node settings. A node can store parameters as integers, floats, Booleans, strings, and lists. In ROS 2, each node maintains its own parameters.

2. ros2 param list

<aside> 💡 Check if /turtlesim & /teleop_turtle nodes are active, if not run ros2 run turtlesim turtlesim_node & ros2 run turtlesim turtle_teleop_key in separate terminal respectively. If no node is active, you will not get any output!

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<aside> 📒 Click on Orange text to learn more about the command

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ros2 param list

To see the parameters belonging to your nodes, open a terminal and enter the command:

ros2 param list

You will see the node namespaces, /teleop_turtle and /turtlesim, followed by each node’s parameters:

/teleop_turtle:
  qos_overrides./parameter_events.publisher.depth
  qos_overrides./parameter_events.publisher.durability
  qos_overrides./parameter_events.publisher.history
  qos_overrides./parameter_events.publisher.reliability
  scale_angular
  scale_linear
  use_sim_time
/turtlesim:
  background_b
  background_g
  background_r
  qos_overrides./parameter_events.publisher.depth
  qos_overrides./parameter_events.publisher.durability
  qos_overrides./parameter_events.publisher.history
  qos_overrides./parameter_events.publisher.reliability
  use_sim_time

<aside> 💡 Every node has the parameter use_sim_time, it’s not unique to turtlesim.

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3. ros2 param get

<aside> 💡 Make sure you have /turtlesim node active, if not run ros2 run turtlesim turtlesim_node If no node is active, you will not get any output!

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To display the type and current value of a parameter, use the command:

ros2 param get <node_name> <parameter_name>

In the example of getting the parameter value for the /turtlesim node’s parameter background_g:

ros2 param get /turtlesim background_g

Which will return the value: