Run these commands as root on Ubuntu 20.04 to get the REMnux installer:
curl -Lo remnux-cli-linux https://github.com/REMnux/remnux-cli/releases/download/v1.4.3/remnux-cli-linux
chmod +x remnux-cli-linux
sudo mv remnux-cli-linux /usr/local/bin/remnux
Before running REMnux installer, use apt to install "gnupg" and "git".