Ruby: Installing rmagick on Ubuntu
Install the packages imagemagick and libmagickwand-dev (or libmagick9-dev). You should then be able to install the Rmagick Gem.
sudo apt-get install imagemagick libmagickwand-devIf not, you are missing ruby related development packages like build-essential and ruby1.8-dev. If that's the case, a generic "ubuntu install ruby 1.8" query in google should sort you out.
You don't need a lot of the other junk in these answers, just:
sudo apt-get install libmagickwand-dev
On Ubuntu 12.04 libmagick9-dev is gone. graphicsmagick-libmagick-dev-compat should be used instead.
apt-get install graphicsmagick-libmagick-dev-compat