In this lesson we will briefly talk about the ROS 2 Logging System.
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Open the Home directory on your Ubuntu system → Check Show Hidden Files.
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Open .ros/log folder.
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Inside /home/pritam/.ros/log folder , we can see the log files that gets generated whenever we run our nodes (publisher & subscriber) in the terminal.
For now, delete all the log files, so that we can create new fresh log files for each publisher node and subscriber node.
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Open a new terminal inside the ros2_cpp_udemy_tutorial workspace and from there, run the subscriber node using the following commands:
source install/setup.bash ros2 run udemy_ros2_pkg subscriber -
Open a new terminal inside the ros2_cpp_udemy_tutorial workspace and from there, run the publisher node using the following commands:
source install/setup.bash ros2 run udemy_ros2_pkg publisher -
After both the nodes get successfully started - Use Ctrl+C on both the terminals to stop both the node operations.
Notice the ^C[INFO] [1674548072.891387889] [rclcpp]: signal_handler(signum=2) & ^C[INFO] [1674548069.829954488] [rclcpp]: signal_handler(signum=2) lines that gets logged on the terminal after we hit Ctrl+C on both the terminals.
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Now if we check the log files inside /home/pritam/.ros/log folder, we will find a log file for each of the publisher and subscriber nodes - which we ran just now on a terminal.
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If we open the both the log files, we can see the last log message that we saw on the terminal of both publisher and subscriber nodes after hitting Ctrl+C to stop the terminal operations.
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Now, the main purpose of a log file that gets generated while running a node on the terminal is to record every statement that gets logged on the terminal while running the node till the node operation is stopped using Ctrl+C on the terminal.
But here, if you observe the log file for the subscriber node, we cannot see any hello world messages - sent by the publisher - that got logged on the subscriber terminal.
That is because, till now we have been using the
std::coutfunction to log our messages to the terminal. -
To use the ROS 2 Logging System for recording the hello world messages that are getting logged on the subscriber terminal, comment out the line of code
std::cout << msg.data << std::endl;in the subcriber.cpp and the add the following code in the same place.// std::cout << msg.data << std::endl; RCLCPP_INFO(this->get_logger(), msg.data.c_str());
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Now save the file and build the workspace once again.
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Run the publisher and subscriber nodes.
source install/setup.bash ros2 run udemy_ros2_pkg publishersource install/setup.bash ros2 run udemy_ros2_pkg subscriberpublisher Terminal:
subscriber Terminal:
publisher log file:
subscriber log file:
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Apart from the [INFO] type of messages, ROS 2 Logging System also provides [WARN], [ERROR] & [DEBUG] types of messages.
To see a demo of all different types of logging messages ROS2 provides, run the command
ros2 run logging_demo logging_demo_mainon a terminal.
Related log file in the home/.ros folder:
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To also see the [WARN], [DEBUG] & [ERROR] types of messages along with the [INFO] type messages in the subscriber node terminal, add the following lines of code below
RCLCPP_INFO(this->get_logger(), msg.data.c_str());in the subscriber.cpp file.// std::cout << msg.data << std::endl; RCLCPP_INFO(this->get_logger(), msg.data.c_str()); RCLCPP_WARN(this->get_logger(), msg.data.c_str()); RCLCPP_DEBUG(this->get_logger(), msg.data.c_str()); RCLCPP_ERROR(this->get_logger(), msg.data.c_str());
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Now save the file and build the workspace once again.
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Run the commands:
source install/setup.bash ros2 run udemy_ros2_pkg publishersource install/setup.bash ros2 run udemy_ros2_pkg subscribersubcriber terminal:
Operation log file of subscriber node:
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In order to see the [DEBUG] messages, we have to initialize a debug state in the terminal. To do that, run the subscriber node using the following command:
source install/setup.bash ros2 run udemy_ros2_pkg subscriber --ros-args --log-level hello_world_sub_node:=debug # In the ros2 run command above, hello_world_sub_node is the name of the node.
And start the publisher node once again:
source install/setup.bash ros2 run udemy_ros2_pkg publishersubcriber terminal:
Operation log file of subscriber node:
std::cout << msg.data << std::endl; //RCLCPP_INFO(this->get_logger(), msg.data.c_str()); //RCLCPP_WARN(this->get_logger(), msg.data.c_str()); //RCLCPP_DEBUG(this->get_logger(), msg.data.c_str()); //RCLCPP_ERROR(this->get_logger(), msg.data.c_str());
Since we do not want to generate huge log files every time we run our nodes in a terminal - we will keep the logger lines of code commented in the subscriber.cpp file as above.
Finally, build the workspace to make the changes permanent.
#include <rclcpp/rclcpp.hpp>
#include <std_msgs/msg/string.hpp>
#include <iostream>
class HelloWorldSubNode : public rclcpp::Node
{
private:
rclcpp::Subscription<std_msgs::msg::String>::SharedPtr subscriber_;
void sub_callback(const std_msgs::msg::String &msg) const
{
std::cout << msg.data << std::endl;
// RCLCPP_INFO(this->get_logger(), msg.data.c_str());
// RCLCPP_WARN(this->get_logger(), msg.data.c_str());
// RCLCPP_DEBUG(this->get_logger(), msg.data.c_str());
// RCLCPP_ERROR(this->get_logger(), msg.data.c_str());
}
public:
HelloWorldSubNode() : Node("hello_world_sub_node")
{
subscriber_ = this->create_subscription<std_msgs::msg::String>(
"hello_world",
10,
std::bind(&HelloWorldSubNode::sub_callback, this, std::placeholders::_1));
}
};
int main(int argc, char * argv[])
{
rclcpp::init(argc, argv);
rclcpp::spin(std::make_shared<HelloWorldSubNode>());
rclcpp::shutdown();
return 0;
}