/usr/lib/ is in ruby-prometheus-client-mmap 0.9.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/fast_mmaped_file.bundle
/usr/lib/ruby/vendor_ruby/prometheus/
/usr/lib/ruby/vendor_ruby/prometheus/client/
/usr/lib/ruby/vendor_ruby/prometheus/client/configuration.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/counter.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/formats/
/usr/lib/ruby/vendor_ruby/prometheus/client/formats/text.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/gauge.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/helper/
/usr/lib/ruby/vendor_ruby/prometheus/client/helper/entry_parser.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/helper/file_locker.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/helper/json_parser.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/helper/metrics_processing.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/helper/metrics_representation.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/helper/mmaped_file.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/helper/plain_file.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/histogram.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/label_set_validator.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/metric.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/mmaped_dict.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/mmaped_value.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/push.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/rack/
/usr/lib/ruby/vendor_ruby/prometheus/client/rack/collector.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/rack/exporter.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/registry.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/simple_value.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/summary.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/support/
/usr/lib/ruby/vendor_ruby/prometheus/client/support/unicorn.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/uses_value_type.rb
/usr/lib/ruby/vendor_ruby/prometheus/client/version.rb
/usr/lib/ruby/vendor_ruby/prometheus/client.rb
/usr/lib/ruby/vendor_ruby/prometheus.rb
/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/2.5.0/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.5.0/fast_mmaped_file.so