Class 'DOMDocument' not found

I've found an error on a page in my Magento application; it always show this message error when I visit it:

Fatal error: Class 'DOMDocument' not found in /home/.../lib/Zend/Feed/Abstract.php on line 95

Solution

You need to install the DOM extension. You can do so on Debian / Ubuntu using:

sudo apt-get install php-dom