Installing Owncloud server in Debian 9

wget -nv https://download.owncloud.org/download/repositories/10.0/Debian_9.0/Release.key -O Release.key
sudo apt-key add - < Release.key
sudo nano /etc/apt/sources.list.d/owncloud.list

add this line

deb http://download.owncloud.org/download/repositories/stable/Debian_9.0/ / 

and then:

sudo apt-get update
sudo apt-get install owncloud-files