siehe Buch S.261 bzw
good method with ssl certificate creation
http://www.avoiderrors.net/owncloud-raspberry-pi/
nextcloud artikel:
https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-nextcloud-on-ubuntu-16-04
do: sudo apt-get install snap snapd for xubuntu 14.04
https://github.com/nextcloud/nextcloud-snap/wiki/Finding-files
https://docs.nextcloud.com/server/9/admin_manual/configuration_files/external_storage_configuration_gui.html