Using and Administering Linux: Volume 2
David Both
Using and Administering Linux: Volume 3
Using and Administering Linux: Volume 1
Pro Linux System Administration
Dennis Matotek & James Turnbull & Peter Lieverdink
The Linux Philosophy for SysAdmins
Essential System Administration
Æleen Frisch
Principles of Network and System Administration 2nd Edition
Mark Burgess
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
Practical Linux System Administration
Kenneth Hess