Installing Mono on CentOS 7
Obtain necessary gpg keys
mkdir Mono
cd Mono
wget http://download.mono-project.com/repo/xamarin.gpg
Import gpg key
sudo rpm --import xamarin.gpg
Add Mono package repository
sudo yum-config-manager --add-repo http://download.mono-project.com/repo/centos/
Add EPEL
sudo rpm -Uvh http://download.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-2.noarch.rpm
Update everything
sudo yum update
Start installing Mono
sudo yum install mono-devel
sudo yum install mono-complete
Optional: Test your Mono installation
http://www.mono-project.com/docs/getting-started/mono-basics/
Running Mono
cd ~/foo/bar/
mono foo.exe
Reference
http://www.mono-project.com/docs/getting-started/install/linux/
http://www.mono-project.com/docs/getting-started/mono-basics/
https://fedoraproject.org/wiki/EPEL/FAQ