/usr/lib/ruby/ is in libfssm-ruby1.9.1 0.1.4-2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/1.9.1/
/usr/lib/ruby/1.9.1/fssm.rb
/usr/lib/ruby/1.9.1/fssm/
/usr/lib/ruby/1.9.1/fssm/monitor.rb
/usr/lib/ruby/1.9.1/fssm/path.rb
/usr/lib/ruby/1.9.1/fssm/pathname.rb
/usr/lib/ruby/1.9.1/fssm/support.rb
/usr/lib/ruby/1.9.1/fssm/tree.rb
/usr/lib/ruby/1.9.1/fssm/backends/
/usr/lib/ruby/1.9.1/fssm/backends/fsevents.rb
/usr/lib/ruby/1.9.1/fssm/backends/inotify.rb
/usr/lib/ruby/1.9.1/fssm/backends/polling.rb
/usr/lib/ruby/1.9.1/fssm/backends/rubycocoa/
/usr/lib/ruby/1.9.1/fssm/backends/rubycocoa/fsevents.rb
/usr/lib/ruby/1.9.1/fssm/state/
/usr/lib/ruby/1.9.1/fssm/state/directory.rb
/usr/lib/ruby/1.9.1/fssm/state/file.rb