rbenv or RVM

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

Setting production server-wide:

Create /etc/profile.d/rails_env.sh:

export RAILS_ENV=production

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 -k   # 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

Gemfile.lock is there to ensure that the production server uses exactly the same gems as in development. If you are struggling with conflicts, you can just remove it and see what happens.

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

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

apt install docx2txt