The Linux Reading List HOWTO
http://www.linuxdoc.org/HOWTO/Reading-List-HOWTO
The Linux System Administrators' Guide
http://www.linuxdoc.org/LDP/sag/index.html
Linux Administration Made Easy
http://www.linuxdoc.org/LDP/lame/LAME/linux-admin-made-easy/index.html
Linux Administrators' Security Guide
http://www.linuxdoc.org/LDP/lasg
The Linux Network Administrators' Guide
http://www.linuxdoc.org/LDP/nag2/index.html
Securing and Optimizing Linux
http://www.linuxdoc.org/LDP/solrhe/
Securing-Optimizing-Linux-RH-Edition-v1.3/index.html