$sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
$echo "deb http://download.mono-project.com/repo/debian alpha main" | sudo tee /etc/apt/sources.list.d/mono-xamarin.list
$sudo apt-get update
$sudo apt-get install mono-devel mono-complete ca-certificates-mono mono-xsp4 #take time
$sudo apt-get install monodevelop=5.10.0.871-0xamarin2
#[1]
May be you will get this message at create project:
Access to the path “/etc/mono/registry” is denied, then
$sudo mkdir /etc/mono/registry
$sudo chmod uog+rw /etc/mono/registry
References:
[1] https://askubuntu.com/questions/770299/monodevelop-on-xubuntu-missing-asp-net