I faced an issue today, I was trying to install a package using gem command but ended up in the following error
Building native extensions. This could take a while...
ERROR: Error installing cassandra:
ERROR: Failed to build gem native extension.
/usr/bin/ruby extconf.rb
mkmf.rb can't find header files for ruby at /usr/lib/ruby/ruby.h
So in order to fix this you need to install the ruby-devel package.
you can use yum or rpm or which ever you are comfortable with.
