/usr/ is in ruby-buff-ignore 1.1.1-2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/
/usr/share/rubygems-integration/
/usr/share/rubygems-integration/all/
/usr/lib/
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/buff/
/usr/lib/ruby/vendor_ruby/buff/ignore/
/usr/lib/ruby/vendor_ruby/buff/ignore/ignore_file.rb
/usr/lib/ruby/vendor_ruby/buff/ignore/errors.rb
/usr/lib/ruby/vendor_ruby/buff/ignore/version.rb
/usr/lib/ruby/vendor_ruby/buff/ignore.rb
/usr/share/rubygems-integration/all/specifications/
/usr/share/rubygems-integration/all/specifications/buff-ignore-1.1.1.gemspec
/usr/share/doc/
/usr/share/doc/ruby-buff-ignore/
/usr/share/doc/ruby-buff-ignore/copyright
/usr/share/doc/ruby-buff-ignore/changelog.Debian.gz
/usr/share/doc/ruby-buff-ignore/README.md