This was an issue I encountered while fixing a deployment in AWS EB. Whenever I ran:
supervisorctl -c supervisord.conf restart celery
I got this error:
celery: ERROR (no such process)
To solve this, I had to run:
supervisorctl reread
supervisorctl update
But another important thing to remember is that this issue also occurs if you started supervisor with a relative url for -c and then try supervisorctl from a different directory.
Recommended - Always use an absolute path:
supervisord -c /etc/supervisor/supervisord.conf