ROS Launch file Issue

Question

I am implementing a simple roslaunch file but I am getting an exit code 2 status I have pasted the exact log below any idea what would cause this and how I can rectify it. It works perfectly when used as a node via rosrun.

kshitij@Kshitij:~/catkin_ws$ roslaunch apriltag_ros apriltag.launch 
... logging to /home/kshitij/.ros/log/c7672d6c-479d-11ec-bd02-c56b9aa24743/roslaunch-Kshitij-20782.log
Checking log directory for disk usage. This may take a while.
Press Ctrl-C to interrupt 
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://Kshitij:38583/

SUMMARY
========

PARAMETERS
* /rosdistro: noetic
* /rosversion: 1.15.13

NODES
/
apriltag_ros (apriltag_ros/tagdetector.py)

auto-starting new master
process[master]: started with pid [20790]
ROS_MASTER_URI=http://localhost:11311

setting /run_id to c7672d6c-479d-11ec-bd02-c56b9aa24743
process[rosout-1]: started with pid [20800]
started core service [/rosout] 
process[apriltag_ros-2]: started with pid [20803]
usage: tagdetector.py [-h] [-f FAMILIES] [-B N] [-t N] [-x SCALE] [-b SIGMA] [-0] [-1] [-2] [-c]
tagdetector.py: error: unrecognized arguments: __name:=apriltag_ros __log:=/home/kshitij/.ros/log/c7672d6c-479d-11ec-bd02-c56b9aa24743/apriltag_ros-2.log
[apriltag_ros-2] process has died [pid 20803, exit code 2, cmd /home/kshitij/catkin_ws/src/apriltag_ros/scripts/tagdetector.py __name:=apriltag_ros __log:=/home/kshitij/.ros/log/c7672d6c-479d-11ec-bd02-c56b9aa24743/apriltag_ros-2.log].
log file: /home/kshitij/.ros/log/c7672d6c-479d-11ec-bd02-c56b9aa24743/apriltag_ros-2*.log

The launch file code is as below

<?xml version = "1.0"?>

<launch>
    <node name = "apriltag_ros" pkg = "apriltag_ros" type = "tagdetector.py"  output="screen" />
</launch>

Link to the same question on the ROS Forum: https://answers.ros.org/question/391124/roslaunch-exit-code-2-error/

Answer 1

The output

usage: tagdetector.py [-h] [-f FAMILIES] [-BN] [-t N] [-x SCALE] [-b SIGMA] [-0] [-1] [-2] [-c]

shows, that tagdetector.py is a script which needs to be called with some specific parameters. First of all you should make sure, if the script is a rosnode to ensure launching it via roslaunch like this is correct. Secondly, have a look at the launch documentation which shows how to add arguments to the node.

So you need to add some of the mentioned parameters to your launchfile by adding

args="-h"

to the node launch entry.