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-dev

If 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