Managing update with apt-get and cron-apt on debian-based systems

In this Howto I'd like to show how you can download updates automatically and receive notifications when they're available on your debian-based system.

All the debian repositories, apt-get uses are normally listed in this file:
The current list of updates can be downloaded using:
apt-get update
The Update is installed simply by executing:
apt-get upgrade
Now it would be great if the server would download (just download, not install) the updates automatically and send a notifcation to the administrator, so he can take care of it as soon as possible.
This can be done with cron-apt. The installation is quite easy:
apt-get install cron-apt
As said, cron-apt will download the available updates (we'll configure it to download them, not to automatically install them) and send a notification.
Therefore you edit the file /etc/cron-apt/config and remove the comment signs (#) on the beginning of the following lines:
The e-mail address has to be replaced by the administrator's email address.
For cron-apt to really send an e-mail notification, we still have to copy a cron-apt script into the good place:
cp /usr/share/doc/cron-apt/examples/9-notify /etc/cron-apt/action.d/
The directory action.d contains actions that can be executed by cron-apt.
From now the administrator will receive an e-mail notification, and updates can be installed just by executing:
apt-get upgrade