A (more) complete cheatsheet for Arel, including NamedFunction functions, raw SQL and window functions.
posts = Arel::Table.new(:posts)
posts = Post.arel_table # ActiveRecord
wget http://download.gna.org/wkhtmltopdf/0.12/0.12.3/wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
tar -xvf wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
cd wkhtmltox/bin/
sudo mv wkhtmltopdf /usr/bin/wkhtmltopdf
sudo mv wkhtmltoimage /usr/bin/wkhtmltoimage