I was trying to install rails on Ubuntu Natty Narwhal 11.04, using ruby1.9.1.
I installed ruby using
apt-get install ruby1.9.1-full which contains the dev package. I googled the error and all have suggested I install the 1.9.1-dev which I already have.
Building native extensions. This could take a while... ERROR: Error installing rails: ERROR: Failed to build gem native extension.
extconf.rb:36:in `require’: no such file to load – mkmf (LoadError) from extconf.rb:36
Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/bcrypt-ruby-3.0.1 for inspection. Results logged to /usr/lib/ruby/gems/1.8/gems/bcrypt-ruby-3.0.1/ext/mri/gem_make.out