Describe linux/no such file to load -- mkmf (LoadError) here.

/usr/bin/ruby1.8 extconf.rb extconf.rb:1:in `require': no such file to load -- mkmf (LoadError) from extconf.rb:1

sudo apt-get install build-essential libopenssl-ruby ruby1.8-dev

debian 7: sudo apt-get install build-essential libopenssl-ruby ruby-dev