From the console:
adelevie@ubuntu:~$ gem install passenger
Building native extensions. This could take a while...
ERROR: Error installing passenger:
ERROR: Failed to build gem native extension.
/usr/bin/ruby1.8 extconf.rb
/usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require': no such file to load -- mkmf (LoadError)
from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `require'
from extconf.rb:8
Gem files will remain installed in /home/adelevie/ruby/gems/gems/fastthread-1.0.7 for inspection.
Results logged to /home/adelevie/ruby/gems/gems/fastthread-1.0.7/ext/fastthread/gem_make.out
What does this mean and what are my options?