rbenv

rbenv install 2.3.1 -k
rbenv global 2.3.1

(-k keep source, helps compiling gems.)

gem install rails
sudo apt-get install -y nodejs &&
sudo ln -sf /usr/bin/nodejs /usr/local/bin/node
sudo apt-get install sqlite3 libsqlite3-dev

Starting point for addressing many security alerts:

# consider updating to the newest ruby
cd /home/slack/.rbenv/plugins/ruby-build && git pull && cd -
rbenv install x.x.x # latest https://www.ruby-lang.org/en/downloads/
rbenv local x.x.x

# update bundler and gems
gem install bundler
bundle update --bundler
bundle update rails

https://www.phusionpassenger.com/library/walkthroughs/deploy/ruby/ with minor modifications for rbenv – Apache site config should contain:

  PassengerRuby /home/slack/.rbenv/shims/ruby