/usr/ is in ruby-mkrf 0.2.3+dfsg-5.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/mkrf/
/usr/lib/ruby/vendor_ruby/mkrf/generator.rb
/usr/lib/ruby/vendor_ruby/mkrf/rakehelper.rb
/usr/lib/ruby/vendor_ruby/mkrf/availability.rb
/usr/lib/ruby/vendor_ruby/mkrf.rb
/usr/share/
/usr/share/doc/
/usr/share/doc/ruby-mkrf/
/usr/share/doc/ruby-mkrf/README
/usr/share/doc/ruby-mkrf/copyright
/usr/share/doc/ruby-mkrf/changelog.Debian.gz
/usr/share/rubygems-integration/
/usr/share/rubygems-integration/1.9.1/
/usr/share/rubygems-integration/1.9.1/specifications/
/usr/share/rubygems-integration/1.9.1/specifications/mkrf-0.2.3.gemspec
/usr/share/rubygems-integration/2.0/
/usr/share/rubygems-integration/2.0/specifications/
/usr/share/rubygems-integration/2.0/specifications/mkrf-0.2.3.gemspec