wan_da's profile - activity

I am trying to build 2 new nodes, based on the minimal_publisher and minimal_subscriber examples provided by the ros2_ws overlay workspace. I have copied and pasted my code from the examples, with the intention to change them in the near future.

I then changed the names of the source files, and the name of the package, among other names. To ensure a successful build, I made several corresponding changes to the CMakeLists.txt and package.xml of each package as well.

Both packages built successfully. However, the only way I can run them is if I locate the binary files in the install directory of the ros2_ws workspace and run them from there.

If I run ros2 pkg list or ros2 pkg executables, none of my packages show up there. Predictably, when I run ros2 run publisht tester_publisht (publisht is the name of my pkg and tester_publisht is the name of the executable) , it just shows Package 'publisht' not found.

Why is it that ros2 pkg cannot find my package?

My publisht package in the install directory of ros2_ws:

publisht
├── lib
│   └── publisht
│       └── tester_publisht
└── share
    ├── ament_index
    │   └── resource_index
    │       ├── package_run_dependencies
    │       │   └── publisht
    │       ├── packages
    │       │   └── publisht
    │       └── parent_prefix_path
    │           └── publisht
    ├── colcon-core
    │   └── packages
    │       └── publisht
    └── publisht
        ├── cmake
        │   ├── publishtConfig.cmake
        │   └── publishtConfig-version.cmake
        ├── environment
        │   ├── ament_prefix_path.sh -> /home/user/ros2_ws/src/ament/ament_cmake/ament_cmake_core/cmake/environment_hooks/environment/ament_prefix_path.sh
        │   └── path.sh -> /home/user/ros2_ws/src/ament/ament_cmake/ament_cmake_core/cmake/environment_hooks/environment/path.sh
        ├── hook
        │   ├── cmake_prefix_path.ps1
        │   └── cmake_prefix_path.sh
        ├── local_setup.bash
        ├── local_setup.sh
        ├── local_setup.zsh
        ├── package.bash
        ├── package.ps1
        ├── package.sh
        ├── package.xml
        └── package.zsh

My tester directory in ros2_ws/src, which contains the source code for the 2 nodes I intend to make, publisht and subscribet:

tester 
├── publisht
│   ├── CMakeLists.txt
│   ├── package.xml
│   ├── publisht.cpp
│   └── README.md
├── README.md
└── subscribet
    ├── CMakeLists.txt
    ├── package.xml
    ├── README.md
    └── subscribet.cpp

My CMakeLists.txt for publisht:

cmake_minimum_required(VERSION 3.5) 
project(publisht)

# Default to C++14
if(NOT CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 14)
endif()

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)

add_executable(tester_publisht publisht.cpp)
ament_target_dependencies(tester_publisht rclcpp std_msgs)

install(TARGETS
  tester_publisht
  DESTINATION lib/${PROJECT_NAME}
)

ament_package()

And my package.xml for publisht:

<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="2">
  <name>publisht</name>
  <version>0.6.3</version>
  <description>Ready to publish to topics from selected nodes</description>
  <maintainer email="MAINTAINER@u.uni.edu">MAINTAINER</maintainer>
  <license>Apache License 2.0</license>
  <author>AUTHOR</author>

  <buildtool_depend>ament_cmake</buildtool_depend>

  <build_depend>rclcpp</build_depend>
  <build_depend>std_msgs</build_depend>

  <exec_depend>rclcpp</exec_depend>
  <exec_depend>std_msgs</exec_depend>

  <export>
    <build_type>ament_cmake</build_type>
  </export>
</package>

[ROS2] Unable to view topic across 2 machines I have 2 devices, a Raspberry Pi 3+ on a TurtleBot3 burger, and a Remote P

I am using ROS2 Crystal Clemmys in Ubuntu 18.04, and am successfully running rqt_graph gui on screen by using the command rqt_graph --force-discover (I had to use --force-discover as qt_gui_main() found no plugin matching "rqt_graph.ros_graph.RosGraph")

I would like to enable statistics on my graph, so that I can observe the publish frequency (in Hz) and the average age of message (in ms). In ROS1 the command is rosparam set enable_statistics true, as shown in the tutorial for rqt_graph here.

However, I am not sure what the command is for ROS2. I tried this:

user@ubuntu:~$ ros2 param set enable_statistics true
usage: ros2 param set [-h] [--spin-time SPIN_TIME] [--include-hidden-nodes]
                  node_name name value
ros2 param set: error: the following arguments are required: value

It couldn't find the parameter enable_statistics. So I went to find out the actual name of the parameter by:

user@ubuntu:~$ ros2 param list
./rqt_gui_py_node_11381:

There were no parameters for enabling statistics at all.

May I know the proper way of enabling statistics for rqt_graph in ROS2?

Edit: I think I keyed in another correct command:

user@ubuntu:~$ ros2 param set /rqt_gui_py_node_11381 /enable_statistics true
Set parameter successful

While the parameter has been found, still no statistics show up on the rqt_graph, even after I clicked on the refresh button.

How can I make the statistics appear, like in the picture in the tutorial?

Thank you to both.

Thank you for pointing out the problem of relevance with regard to 'inner-workings-type' questions. I understand that RO

Thank you. I understand that the user multicast port is not necessarily 7401, but my domain ID is definitely 0 at the

According to this, RTI Connext in ROS2 uses four ports for UDP transport. Each port has its own purpose: discovery multicast, user multicast, discovery unicast, and user unicast. As far as I could tell, the other DDS implementations use roughly the same ports for the same purposes.

What I want to know is what these mean in the context of ROS2? Like:

1. What does the discovery multicast port do? My impression from its name is that it serves as a socket for all the ros2_daemon to listen for all the nodes and take in any new nodes.
2. I have no idea what the user multicast port does, because it doesn't show up when I use lsof -iUDP or ss -uap. Apparently 7401 is the port number reserved for this function but no process is using this port on my machine.
3. I also do not know what the user unicast and discovery unicast ports do. I used WireShark to examine the UDP/RTPS traffic in my ROS2 communication graph. Apparently sometimes these ports receive packets from ephemeral ports from other nodes, at other times they do not send or receive any packets at all. So I do not understand what purpose these ports serve.
4. On the use of WireShark, I also do not understand my findings when investigating the traffic going to the discovery multicast port.

The large numbers are ephemeral ports from the rest of the nodes in the computational graph, like rqt_gui_py_node, _ros2cli_daemon_0 among other nodes that I created myself. However, they are all sending DATA and INFO_TS to port 7400. I feel that if the discovery multicast node is for discovering new nodes and keeping track of existing ones, they should be sending messages like ACKNACK or HEARTBEAT, according to the legend here.

May I have a simple explanation of what each ports do. or perhaps a link to more documentation? Thank you.

Thank you. I understand that the user multicast port is not necessarily 7401, but my domain ID is definitely 0 at the t

[ROS2] What does the "discovery multicast port" do? According to this, RTI Connext in ROS2 uses four ports for UDP trans

When I run ros2 launch turtlebot3_gazebo turtlebot3_world.launch.py, gazebo is launched.

Then, I run:

user@ubuntu:~/ros2_ws$ lsof -iUDP | grep gazebo
gazebo    27889 user    9u  IPv4 496548      0t0  UDP *:7400 
gazebo    27889 user   10u  IPv4 496554      0t0  UDP *:7418 
gazebo    27889 user   11u  IPv4 496560      0t0  UDP *:7419 
gazebo    27889 user   12u  IPv4 496563      0t0  UDP *:52459 
user@ubuntu:~/ros2_ws$ lsof -iUDP | grep gzserver
gzserver  27902 user    9u  IPv4 496548      0t0  UDP *:7400 
gzserver  27902 user   10u  IPv4 496554      0t0  UDP *:7418 
gzserver  27902 user   11u  IPv4 496560      0t0  UDP *:7419 
gzserver  27902 user   12u  IPv4 496563      0t0  UDP *:52459 
gzserver  27902 user   15u  IPv4 496615      0t0  UDP *:7400 
gzserver  27902 user   16u  IPv4 496623      0t0  UDP *:7422 
gzserver  27902 user   17u  IPv4 496631      0t0  UDP *:7423 
gzserver  27902 user   18u  IPv4 496634      0t0  UDP *:48586 
gzserver  27902 user   41u  IPv4 497324      0t0  UDP *:11317 
gzserver  27902 user   42u  IPv4 497329      0t0  UDP *:11318 
gzserver  27902 user   52u  IPv4 495547      0t0  UDP *:7400 
gzserver  27902 user   53u  IPv4 495555      0t0  UDP *:7424 
gzserver  27902 user   54u  IPv4 495563      0t0  UDP *:7425 
gzserver  27902 user   55u  IPv4 495566      0t0  UDP *:38077 
gzserver  27902 user   62u  IPv4 498712      0t0  UDP *:7400 
gzserver  27902 user   63u  IPv4 498720      0t0  UDP *:7426 
gzserver  27902 user   64u  IPv4 498728      0t0  UDP *:7427 
gzserver  27902 user   65u  IPv4 498731      0t0  UDP *:48999 
gzserver  27902 user   72u  IPv4 498740      0t0  UDP *:7400 
gzserver  27902 user   73u  IPv4 498748      0t0  UDP *:7428 
gzserver  27902 user   74u  IPv4 498756      0t0  UDP *:7429 
gzserver  27902 user   75u  IPv4 498759      0t0  UDP *:45287 
gzserver  27902 user   82u  IPv4 495579      0t0  UDP *:7400 
gzserver  27902 user   83u  IPv4 495587      0t0  UDP *:7430 
gzserver  27902 user   84u  IPv4 495595      0t0  UDP *:7431 
gzserver  27902 user   85u  IPv4 495598      0t0  UDP *:49441 
user@ubuntu:~/ros2_ws$ lsof -iUDP | grep gzclient
gzclient  27903 user    9u  IPv4 496548      0t0  UDP *:7400 
gzclient  27903 user   10u  IPv4 496554      0t0  UDP *:7418 
gzclient  27903 user   11u  IPv4 496560      0t0  UDP *:7419 
gzclient  27903 user   12u  IPv4 496563      0t0  UDP *:52459 
gzclient  27903 user   24u  IPv4 497351      0t0  UDP *:11317 
gzclient  27903 user   25u  IPv4 497356      0t0  UDP *:11318

What is the difference between gzclient, gzserver, gazebo? I understand that gzclient is the gazebo GUI, but I don't understand why gazebo pops up as another process. Why does gzclient and gazebo share some same ports as well?

Also, why does gzserver use so many ports? Is it because it is responsible for spinning up several nodes in the turtlebot3_world.launch.py file?

Sure. I will link my question here if it is answered on Gazebo Answers. Thank you.

Difference between gzclient, gzserver and gazebo When I run ros2 launch turtlebot3_gazebo turtlebot3_world.launch.py, ga

Oh wait, never mind. According to https://community.rti.com/forum-topic/how-understand-number-ports-used-dds-context-app

Okay, I now understand what is 7400, 7412 and 7413. However, I still don't understand what is 41004, or any of the large

I have created my own little node called tester_publisht, and am trying to find the originating socket of the node. However, the node is using 4 separate ports, and I have no idea what the output means.

user@ubuntu:~$ lsof -iUDP
COMMAND     PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
spotify    2067 user   92u  IPv4 276438      0t0  UDP *:57621 
spotify    2067 user  108u  IPv4 276451      0t0  UDP *:1900 
spotify    2067 user  128u  IPv4 276452      0t0  UDP *:55193 
tester_pu  9642 user    6u  IPv4 241204      0t0  UDP *:7400 
tester_pu  9642 user    7u  IPv4 241207      0t0  UDP *:7412 
tester_pu  9642 user    8u  IPv4 241210      0t0  UDP *:7413 
tester_pu  9642 user    9u  IPv4 241213      0t0  UDP *:41004 
rqt_graph 14766 user   24u  IPv4 243242      0t0  UDP *:7400 
rqt_graph 14766 user   25u  IPv4 243246      0t0  UDP *:7414 
rqt_graph 14766 user   26u  IPv4 243250      0t0  UDP *:7415 
rqt_graph 14766 user   27u  IPv4 243253      0t0  UDP *:39130 
_ros2_dae 19978 user    6u  IPv4 250922      0t0  UDP *:7400 
_ros2_dae 19978 user    7u  IPv4 250927      0t0  UDP *:7416 
_ros2_dae 19978 user    8u  IPv4 250932      0t0  UDP *:7417 
_ros2_dae 19978 user    9u  IPv4 250935      0t0  UDP *:36155

tester_publisht, rqt_graph and _ros2_daemon are the nodes that are running (sorry about Spotify :) ).

Running ros2 node list -a reveals the three nodes above, and running ros2 topic list returns /clock (the topic that tester_publisht is publishing to), /parameter_events and /rosout.

I tried to listen in on the ports for tester_publisht, but was only able to listen onto port 7400. The rest (7412, 7413, and 41004) could not be listened to:

user@ubuntu:~$ nc -lvu 7400
Listening on [0.0.0.0] (family 0, port 7400)
Connection from ubuntu 39130 received!
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     brqt_gui_py_node_14766,,(name=rqt_gui_py_node_14766;namespace=/;
^C
user@ubuntu:~$ nc -lvu 7412
nc: Address already in use
user@ubuntu:~$ nc -lvu 7413
nc: Address already in use
user@ubuntu:~$ nc -lvu 41004
nc: Address already in use

However, port 7400 is also shared with the other two nodes rqt_graph and _ros2_daemon, as shown in the first code block.

So I don't really understand what is the significance of port 7400. And also, which is the originating socket for tester_publisht, or for each of the nodes for that matter?