I found a web site, http://www.linuxtopia.org/online_books/ You should check it out if you are ever needing any Linux or other Open Source Software references.

General book topics include:

• Linux Beginner
  
• Linux System Administration
• Linux Security
• Linux Virtualization
• Linux Kernel
• Linux Development
• Linux Installation
• Linux database (mysql, postgresql, etc)
• Linux GUI Toolkit
• Linux Tools & Utilities
• Linux Howto Guides
• Linux Problem Solutions

There is also a user forum area