sudo apt-get -y install gtk-sharp2
sudo apt-get -y install mono-runtime
sudo apt-get -y install mono-complete
sudo apt-get -y install monodevelop

如果monodevelop无法安装，则可以根据官网教程进行安装。

Ubuntu18安装monodevelop

sudo apt install apt-transport-https dirmngr
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb https://download.mono-project.com/repo/ubuntu vs-bionic main" | sudo tee /etc/apt/sources.list.d/mono-official-vs.list
sudo apt update