Recommended Setup For PiCrate


Download the latest JRuby release here. You could use wget (substituting latest version for for



cd /opt
sudo tar xzvf ~/jruby-dist- # or ~/Downloads/...
sudo update-alternatives --install /usr/bin/jruby jruby /opt/jruby- 100
sudo update-alternatives --install /usr/bin/jgem jgem /opt/jruby- 100
sudo update-alternatives --install /usr/bin/jirb jirb /opt/jruby- 100


sudo update-alternatives --config jruby
sudo update-alternatives --config jgem
sudo update-alternatives --config jirb

Set a local gem environment

It is preferable to store gems in your local environment, if you have not installed ruby before we recommend you do the following:-

  1. Create local folders
  mkdir -p ~/.gem/ruby/2.5.0
  1. Set gem home/path in ~/.profile
  echo "export GEM_HOME=\"\$HOME/.gem/ruby/2.5.0\"" >> ~/.profile
  echo "export GEM_PATH=\"\$HOME/.gem/ruby/2.5.0\"" >> ~/.profile

This will set were gems get installed (unless you use rvm, which would be stupid to use on raspberrypi).

Add the ${GEM_PATH}/bin to PATH

echo "export PATH=\"\${PATH}:\${GEM_PATH}/bin\"" >> ~/.profile

You need to do this to use gem executables.

Installing/Updating jruby-launcher gem

First set the JAVA_HOME environmental variable, you can do this by editing the ~/.profile file:-

echo "export JAVA_HOME=/usr/lib/jvm/java-8-openjdk >> ~/.profile"
source ~/.profile # to use the edited ~/.profile in current shell
sudo jgem install jruby-launcher # NB: you do need sudo access here

Above assumes you are using java-8-openjdk on Buster, adjust for your setup. We do not currently recommend using java-11-openjdk, but if you are there is even more reason to install the jruby-launcher gem as it suppresses illegal-reflective access warning from JRuby (but not from the jogl jars)