Turning GUI on and off again at runtime

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Hey,

I'm using gazebo with gazebo_ros_pkg for reinforcement learning. To make things go faster, I turned off Gazebo's GUI. I'd like to be able to turn it on in the middle of the training to see how its going for a few iterations, then turn it off again.

Is there a way to do that ? Is it possible from inside a ROS node or a Gazebo plugin ?

I thought about recording rosbags to replay on another instance of Gazebo with GUI on, but unfortunately rosbags cannot record service calls.

I'm using ROS melodic with Gazebo9 on Ubuntu 18.04.

Thanks for your help.