Failed to build gem native extension — Rails install
mkmf is part of the ruby1.9.1-dev package. This package contains the header files needed for extension libraries for Ruby 1.9.1. You need to install the ruby1.9.1-dev package by doing:
sudo apt-get install ruby1.9.1-dev
Then you can install Rails as per normal.
Generally it's easier to just do:
sudo apt-get install ruby-dev
The suggested answer only works for certain versions of ruby. Some commenters suggest using ruby-dev; that didn't work for me either.
sudo apt-get install ruby-all-dev
worked for me.
sudo apt-get install ruby-dev
worked for me