Problem

You are trying to install rmagick in an Ubuntu 12.04 virtual box, but you get the following error:

Can't install RMagick 2.13.1. Can't find Magick-config

Solution

Make sure you install both the imagemagick and the libmagickwand-dev packages with either apt-get :

sudo apt-get install imagemagick libmagickwand-dev

or in a puppet script as:

package {
  "imagemagick":
    ensure => installed
}

package {
  "libmagickwand-dev":
    ensure  => installed
}