Ergänzung:
und das Upgrade scheint noch nicht mal sicher zu funktionieren, wie ich gerade erst las:
Zitat Zitat von https://www.raspberrypi.org/blog/raspbian-stretch/
Upgrading an existing Jessie image is possible, but is not guaranteed to work in every circumstance. If you wish to try upgrading a Jessie image to Stretch, we strongly recommend taking a backup first – we can accept no responsibility for loss of data from a failed update.