To allow openvasmd to work, you need to do the following

# Generate a Server Certificate
openvas-mkcert

# Generate a Client Certificate
openvas-mkcert-client -n -i

# get nvt feed
openvas-nvt-sync (free) or greenbone-nvt-sync (commercial)

# get scap feed
openvas-scapdata-sync (free) or greenbone-scapdata-sync (commercial)

# get cert feed
openvas-certdata-sync (free) or greenbone-certdata-sync (commercial)

# Generate initial NVT cache (takes some minutes)
rc-service openvassd create_cache or openvassd --foreground --only-cache

# Start the OpenVAS Scanner
rc-service openvassd start or systemctl start openvassd.service

# Initialize the Database (This is going to take some time, perhaps time to get coffee?)
openvasmd --rebuild --progress -v

# Create an admin user and note down the initial password
openvasmd --create-user=admin --role=Admin

# Start the OpenVAS Manager
rc-service openvasmd start or systemctl start openvasmd

# Start the Greenbone Security Assistant
rc-service gsad start or systemctl start gsad