For jdk versions greater than jdk8 running JRuby runs into a lot of reflective access warnings, but there is a solution that seems to work well on linux at least. But you need to do the following:-

  1. Make sure you set JAVA_HOME environmental version (jruby uses this to determine whether fix is required if java –version greater than version 8)
  2. Install jruby-launcher gem sudo jgem install jruby-launcher
  3. Now many previous reflective access warnings disappear
  4. Use --add-opens to fix remaining warnings in .jruby.java_opts file.