Please note that Xamarin.Android on Linux is officially unsupported. However, it is possible to manually install Xamarin.Android and configure Rider so that it can build and run Xamarin.Android apps on Linux. This guide has been tested on Ubuntu 16.04.
See http://www.mono-project.com/download/
sudo apt-key adv –keyserver hkp://keyserver.ubuntu.com:80 –recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb http://download.mono-project.com/repo/ubuntu xenial main" | sudo tee /etc/apt/sources.list.d/mono-official.list
sudo apt-get update