The Debian Administrator’s Handbook
“Written by two Debian developers — Raphaël Hertzog and Roland Mas — the Debian Administrator’s Handbook started as a translation of their French best-seller known as Cahier de l’admin Debian (published by Eyrolles). It’s a fantastic resource for all users of a Debian-based distribution. Accessible to all, this book teaches the essentials to anyone who wants to become an effective and independant Debian GNU/Linux administrator.” (source)
Read about it here (in Hungarian).