I’ve come across a number of posts giving instructions on how to get debugging to work with ruby 1.9.x and they all seem to involve downloading gems and installing them. Here is what I did on my Ubuntu 12.04 workstations that was very easy though not trivial to figure out.

sudo gem install linecache19 --pre
sudo gem install ruby-debug-base19 --pre -- --with-ruby-include=/usr/include/ruby-1.9.1/ruby-1.9.3-p0/
sudo gem install ruby-debug-base19x --pre
sudo gem install ruby-debug-ide --pre