Building native extensions. This could take a while...
ERROR: While executing gem ... (Gem::Installer::ExtensionBuildError)
ERROR: Failed to build gem native extension.
ruby extconf.rb install mysql
extconf.rb:1:in `require': no such file to load -- mkmf (LoadError)
from extconf.rb:1
解决方法： sudo apt-get install ruby1.8-dev
