Eu estava tentando instalar trilhos no Ubuntu Natty Narwhal 11.04, usando o ruby1.9.1.
Eu instalei o ruby usando o apt-get install ruby1.9.1-full
que contém o pacote dev. Eu pesquisei no erro e todos sugeriram que eu instale o 1.9.1-dev que eu já tenho.
Building native extensions. This could take a while...
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.
/usr/bin/ruby1.8 extconf.rb
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