Raphaël Hertzog and Roland Mas are authors of Debian Administrator’s Handbook. The Handbook is now available in many formats (free to download or read on-line). This is translation of their French best-seller known as Cahier de l’admin Debian
The book is great resource for all users of a Debian-based distribution. It is great help and teaches the essentials to anyone who wants to become an effective and independant Debian GNU/Linux administrator.
The book is freely available and only the paperback version will require payment. Donations are welcome from all users.