FreeSoftwareBooks.com
the name says it all

Home Page  |   Languages   | Java/J2EE    |  Microsoft    |   Unix/Linux    |   Computer Science    |   Databases    |  Web   |   Networking  
Unix and Linux 
Core Unix Core Linux Shell Programming
Unix and Linux System & Application Programming Text Editing System Administration
GUI and X Windows Unix and Linux Networking FreeBSD
Oracle Magazine Unix and Linux Security