Hi @clusher ,
Thanks for reporting this issue, I understand your issue. The reason why I believe this happens is due to the fact that this course, when it was designed, was made on Ignition Gazebo Fortress. Fortress is the last version of the new Gazebo Simulator before it got re-branded to the old name, Gazebo (from Ignition).
So when the course got published, it was configured to use ROS2 Humble and Gazebo Garden instead of Gazebo Fortress at the last minute.
I believe an update is pending for the course with Gazebo Garden + ROS2 Humble.
Gazebo Garden is backwards compatible with ign commands along with its new gz commands.
Whereas, Ignition is not compatible with the “future” version gz commands.
That is why ign commands work, but gz commands do not work in the current version of the course.
I think this error is due to a recent event/update from GazeboSim that has marked the old ign based messages as deprecated, in favor of using gz messages to retain similarity with the old Gazebo classic version commands.
So, in conclusion.
In your computer, you might be having Ignition Fortress or an earlier build of Garden on which ign messages will be processed. It works and still working on my laptop also (Ubuntu 22.04 + RO2 Humble + Ignition Fortress).
In the online course, there could have been a new patch update on the VM to get the latest Gazebo Garden that has deprecated the ign messages, so that might be the issue. Because, right after the course was published, everything worked well. It is only recently, things got messy.
I hope this information helps.
Regards,
Girish