Add repository

add-apt-repository ppa:mrazavi/openvas

Install

apt-get install openvas9
apt-get install sqlite3
#the following is needed for pdf reports
apt-get install texlive-latex-extra --no-install-recommends
#openvas-nasl utility
apt-get install libopenvas9-dev

finalize

greenbone-nvt-sync
greenbone-scapdata-sync
greenbone-certdata-sync
service openvas-scanner restart
service openvas-manager restart
openvasmd --rebuild --progress

Download check setup

wget https://svn.wald.intevation.org/svn/openvas/trunk/tools/openvas-check-setup --no-check-certificate

execute

chmod +x openvas-check-setup
./openvas-check-setup --v9

Edit the websites default port in the following file

/etc/default/openvas-gsa

and restart the service

service openvas-gsa restart

To set a SSL cert with LetsEncrypt, check the following link: Blackhat.pm - Tutorial GSA LetsEncrypt

Host seems to be dead, no results:

execute the following

openvasmd --update
service openvas-manager restart
service openvas-scanner restart