I've started learning Ruby on Rails, and I needed the mysql driver. Should be simple, right? Just gem install mysql or something?
root@asuka:~# gem install mysql Building native extensions. This could take a while... ERROR: Error installing mysql: ERROR: Failed to build gem native extension. /usr/bin/ruby1.8 extconf.rb extconf.rb:1:in `require': no such file to load -- mkmf (LoadError) from extconf.rb:1 Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/mysql-2.7 for inspection. Results logged to /usr/lib/ruby/gems/1.8/gems/mysql-2.7/gem_make.out root@asuka:~#
Once tangled mess of Google, Debian, and Ruby later, I found a bug report and a solution (for me at least).
Debian Bug 373843 - Long story short, you need ruby1.8-dev or, it appears, libmysql-ruby.