Using and Administering Linux: Volume 2
David Both
Using and Administering Linux: Volume 3
Using and Administering Linux: Volume 1
The Linux Philosophy for SysAdmins
Principles of Network and System Administration 2nd Edition
Mark Burgess
Essential System Administration
Æleen Frisch
Practical Linux System Administration
Kenneth Hess
Pro Linux System Administration
Dennis Matotek & James Turnbull & Peter Lieverdink
SELinux User's and Administrator's Guide
Mirek Jahoda & Barbora Ančincová & Ioanna Gkioka & Tomáš Čapek
UNIX and Linux System Administration Handbook
Evi Nemeth & Garth Snyder & Trent R. Hein & Ben Whaley