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 sqlite3-ruby
extconf.rb:1:in `require': no such file to load -- mkmf (LoadError)
from extconf.rb:1
Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/sqlite3-ruby-1.2.0 for inspection.
Results logged to /usr/lib/ruby/gems/1.8/gems/sqlite3-ruby-1.2.0/ext/sqlite3_api/gem_make.out