What services are using the camera and how can I turn them off temporarily?

What is the problem?

I can't seem to use raspistill and I think it is because there are other services using the camera and only one service can be used at a time. What other services are using the camera and how can I temporarily disable them?

What did you already try to solve it?

The full problem is here but I thought this might be a good independent question for others that might want to know.

On OctoPi that would be sudo service webcamd stop - the problem you may be experiencing is it restarting mjpg streamer when it is stopped.