I ran into a tiny pickle while installing the ibm_db gem on Ubuntu:
Select which gem to install for your platform (i486-linux) 1. ibm_db 0.9.5 (ruby) 2. ibm_db 0.9.5 (mswin32) 3. ibm_db 0.9.4 (ruby) 4. ibm_db 0.9.4 (mswin32) 5. Skip this gem 6. Cancel installation > 1 Building native extensions. This could take a while... ERROR: While executing gem ... (Gem::Installer::ExtensionBuildError) ERROR: Failed to build gem native extension. ruby extconf.rb install ibm_db extconf.rb:9:in `require': no such file to load -- mkmf (LoadError) from extconf.rb:9
The problem is that mkmf isn’t included in the base Ruby package on Ubuntu. You need need the full development package to install gems from source. Installing it solves the problem.
sudo apt-get install ruby1.8-dev