/usr/ is in ruby-mysql 2.9.1-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/
/usr/lib/x86_64-linux-gnu/
/usr/lib/x86_64-linux-gnu/ruby/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.3.0/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.3.0/mysql/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.3.0/mysql/mysql_api.so
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/mysql/
/usr/lib/ruby/vendor_ruby/mysql/version.rb
/usr/lib/ruby/vendor_ruby/mysql.rb
/usr/share/
/usr/share/rubygems-integration/
/usr/share/rubygems-integration/2.3.0/
/usr/share/rubygems-integration/2.3.0/specifications/
/usr/share/rubygems-integration/2.3.0/specifications/mysql-2.9.1.gemspec
/usr/share/doc/
/usr/share/doc/ruby-mysql/
/usr/share/doc/ruby-mysql/README.html
/usr/share/doc/ruby-mysql/copyright
/usr/share/doc/ruby-mysql/changelog.Debian.gz
/usr/share/doc/ruby-mysql/README_ja.html
/usr/share/doc/ruby-mysql/tommy.css