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