Hey I'm trying to write a behavior tree plugin following this tutorial


I'm on Ubuntu20.04 using Ros2 galactic and v3 for behavior_tree (going to v4 had not solved the problem)

So I'm launching a bt_navigator node for autonomous navigation with couple of plugins and a behavior_tree for managing the robot behavior. But I want to include a custom action inside that tree.

The custom xml tag I use is called CustomRecXNode, and it should call an action client

It is supposed to be triggered here in my tree in the middle of other bt_navigation's tasks.

    <Control ID="RoundRobin" name="RecoveryActions">
            <Sequence name="ClearingActions">
              <Action ID="ClearEntireCostmap" name="ClearLocalCostmap-Subtree" service_name="local_costmap/clear_entirely_local_costmap" />
            <Action ID="Wait" wait_duration="3"/>
            <CustomRecXNode order="10"/>
            <Action ID="BackUp" backup_dist="2.0" backup_speed="0.4" />

But when I launch my bt_navigator node it does not find my plugin.

[bt_navigator-3] [INFO] [1718168941.935772843] [bt_navigator]: Configuring
[bt_navigator-3] [ERROR] [1718168941.960941808] []: Caught exception in callback for transition 10
[bt_navigator-3] [ERROR] [1718168941.960966865] []: Original error: Could not load library: libcustom_recx_bt_node.so: cannot open shared object file: No such file or directory
[bt_navigator-3] [WARN] [1718168941.961002492] []: Error occurred while doing error handling.
[bt_navigator-3] [FATAL] [1718168941.961012991] [bt_navigator]: Lifecycle node bt_navigator does not have error state implemented
[lifecycle_manager-8] [ERROR] [1718168941.961570466] [lifecycle_manager_navigation]: Failed to change state for node: bt_navigator
[lifecycle_manager-8] [ERROR] [1718168941.961608117] [lifecycle_manager_navigation]: Failed to bring up all requested nodes. Aborting bringup.

Yet, I did what the tutorial said and I look at how they do it on nav2_behavior_tree https://github.com/ros-navigation/navigation2/blob/main/nav2_behavior_tree/plugins/action/follow_path_action.cpp (follow_path_action for exemple)

This is my custom_recx_node.cpp and I'm registering the tag

 * @file custom_recx_bt_node.cpp
 * @author Emonot--De Carolis Evrard
 * @brief Custom behavior tree node implementation for calling recx action and return success
 * @version 1.0
 * @date 2024-05-07
#include <memory>
#include <string>
#include "custom_recx_bt_node.hpp"

namespace nav2_behavior_tree

    const std::string& xml_tag_xml,
    const std::string& action_name,  
    const BT::NodeConfiguration& config)
    : BtActionNode<kisui_msgs::action::TestAction>(xml_tag_xml, action_name, config), client_(std::make_shared<RecXClient>())

  void CustomRecXNode::on_tick() 
        auto order = getInput<int>("order");
        if (!order) {
            throw BT::RuntimeError("missing required input [order]: ", order.error());

    BT::NodeBuilder builder =
    [](const std::string & name, const BT::NodeConfiguration & config)
      return std::make_unique<nav2_behavior_tree::CustomRecXNode>(name, "CustomRecXNode", config);
    factory.registerBuilder<nav2_behavior_tree::CustomRecXNode>("CustomRecXNode", builder);

and the hpp :

 * @file custom_recx_bt_node.hpp
 * @brief Custom behavior tree node header for calling recx action and return success
 * @version 1.0
 * @date 2024-05-07


#include <string>
#include <nav2_behavior_tree/bt_action_node.hpp>
#include <behaviortree_cpp_v3/action_node.h>
#include <behaviortree_cpp_v3/bt_factory.h>
#include "recx_client.hpp"

namespace nav2_behavior_tree

class CustomRecXNode : public BtActionNode<kisui_msgs::action::TestAction>{
        const std::string& xml_tag_xml,
        const std::string& action_name,  
        const BT::NodeConfiguration& config); 
    void on_tick() override;

    void on_wait_for_result() override;
    static BT::PortsList providedPorts()
        return providedBasicPorts(

    std::shared_ptr<RecXClient> client_;



I put it in the CMakeFile.txt

find_package(nav2_msgs REQUIRED)
find_package(nav2_bt_navigator REQUIRED)
find_package(nav2_behavior_tree REQUIRED)
  TARGETS stuff_i_cant_show
add_library(custom_recx_bt_node SHARED src/custom_recx_bt_node.cpp)
ament_target_dependencies(custom_recx_bt_node ${COMMON_DEPENDENCIES})
target_link_libraries(custom_recx_bt_node ${rclcpp_LIBRARIES} ${rclcpp_action_LIBRARIES})

and add to the plugin of my parameters

    use_sim_time: True
    global_frame: map
    robot_base_frame: base_footprint
    odom_topic: /local_odom
    transform_tolerance: 0.2
    goal_reached_tol: 2.0
    default_nav_to_pose_bt_xml: replace/with/path/to/bt.xml #don't be triggered by this it finds the behavior_tree, it's just handle somewhere else in the code
    goal_blackboard_id: goal
    goals_blackboard_id: goals
    path_blackboard_id: path
    navigators: ['navigate_to_pose', 'navigate_through_poses']
      plugin: "nav2_bt_navigator/NavigateToPoseNavigator"
      plugin: "nav2_bt_navigator/NavigateThroughPosesNavigator"    
    - nav2_compute_path_to_pose_action_bt_node
    -... many other nav2_plugin
    - custom_recx_bt_node

This is the piece of code that launch the node :


What name should you put in the plugins ? where this libcustom_recx_bt_node.so should be generated ? is bt_navigator looking at the wrong place ?

Thanks for your help.

  • $\begingroup$ Could you make sure the correct bt is loaded? It should be a parameter set for the bt_navigator-node. So you just launch it all and do ros2 param list bt_navigator and see what behavior tree is loaded. My experience says most of the time it's just not loaded correctly, but the default bt is loaded instead. $\endgroup$
    – Scoeerg
    Commented Jun 12 at 11:47

1 Answer 1


Try adding the same to export ament_export_libraries() at the end of CMake

  • $\begingroup$ Yes I add but did not really solve the problem, I managed to delete the error by writting by exporting the library path by typing this in the terminal export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:~/my_ws/install/my_package/lib But my xml tag is still a problem as my robot does not move and now I don't have any error message. when I remove the custom tag bt_navigator function normally $\endgroup$ Commented Jun 12 at 8:06
  • $\begingroup$ github.com/ros-navigation/navigation2/blob/main/… use this as a reference and try to write your CMake. This has worked for me in the past $\endgroup$
    – Sriram
    Commented Jun 12 at 9:41
  • $\begingroup$ Thanks I correct this error by adding this in the cmake install(TARGETS custom_recx_bt_node ARCHIVE DESTINATION lib LIBRARY DESTINATION lib RUNTIME DESTINATION bin ) install(DIRECTORY include/ DESTINATION include/ ) When I launch my bt_navigator node, it says activating but then nothing happens unless I remove my XML tag from the behavior tree. It still doesn't work but shows no error. [lifecycle_manager-8] [INFO] [1718766602.381426689] [lifecycle_manager_navigation]: Activating bt_navigator [bt_navigator-5] [INFO] [1718766602.381994634] [bt_navigator]: Activating $\endgroup$ Commented Jun 19 at 3:15
  • $\begingroup$ This might have something to do with the behaviour that you are running. Also I noticed you're calling the action at every tick. The behaviour tree constantly ticks the node if it returns running, the rate is defined in nav2 params file, as bt_loop_duration, if you want to call the action once and check status, call the action from the constructor. $\endgroup$
    – Sriram
    Commented Jun 19 at 4:23

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