/usr/include/ is in ruby1.9.1-dev 1.9.3.484-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ruby-1.9.1/
/usr/include/ruby-1.9.1/ruby/
/usr/include/ruby-1.9.1/ruby/defines.h
/usr/include/ruby-1.9.1/ruby/encoding.h
/usr/include/ruby-1.9.1/ruby/digest.h
/usr/include/ruby-1.9.1/ruby/subst.h
/usr/include/ruby-1.9.1/ruby/st.h
/usr/include/ruby-1.9.1/ruby/dl.h
/usr/include/ruby-1.9.1/ruby/io.h
/usr/include/ruby-1.9.1/ruby/re.h
/usr/include/ruby-1.9.1/ruby/util.h
/usr/include/ruby-1.9.1/ruby/regex.h
/usr/include/ruby-1.9.1/ruby/backward/
/usr/include/ruby-1.9.1/ruby/backward/st.h
/usr/include/ruby-1.9.1/ruby/backward/rubysig.h
/usr/include/ruby-1.9.1/ruby/backward/util.h
/usr/include/ruby-1.9.1/ruby/backward/classext.h
/usr/include/ruby-1.9.1/ruby/backward/rubyio.h
/usr/include/ruby-1.9.1/ruby/version.h
/usr/include/ruby-1.9.1/ruby/missing.h
/usr/include/ruby-1.9.1/ruby/intern.h
/usr/include/ruby-1.9.1/ruby/ruby.h
/usr/include/ruby-1.9.1/ruby/vm.h
/usr/include/ruby-1.9.1/ruby/oniguruma.h
/usr/include/ruby-1.9.1/x86_64-linux/
/usr/include/ruby-1.9.1/x86_64-linux/ruby/
/usr/include/ruby-1.9.1/x86_64-linux/ruby/config.h
/usr/include/ruby-1.9.1/ruby.h