This little project builds an RPM suitable for installing JRuby on your RPM-compatible system. It allows you to specify the version of JRuby you want, downloads the binaries for you, and builds a noarch RPM package out of it. This project assumes you are running it on a RedHat or CentOS system.
It might be obvious, but you need rpm. Also, you will need the rpm-build package, which is not obvious:
sudo yum install rpm-build
# download binaries and build jruby-1.7.9 RPM
./create_rpm.sh 1.7.9
# download binaries and build jruby-1.7.0 RPM
./create_rpm.sh 1.7.0