What is the correct way to leave gunicorn running?

use --daemon to the binding command of gunicorn. ex:

gunicorn --bind 0.0.0.0:8001 your_project.wsgi --daemon

Use --daemon option while running gunicorn. Example:

gunicorn grand56.wsgi:application --name grand56 --workers 3 --user=root --group=root --bind=127.0.0.1:1001 --daemon

Try this:

nohup gunicorn app:app &

I'd look into something like Supervisor.

Very useful tutorial can be found here https://www.codingforentrepreneurs.com/blog/hello-linux-setup-gunicorn-and-supervisor/