debian-handbook

The Debian Administrator's Handbook is 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 independent Debian GNU/Linux administrator.

The book is freely available (that is under the terms of a license compatible with the Debian Free Software Guidelines of course).

The money is used to keep the book up-to-date with new Debian releases.