There are several books available for preparing the certification exams:
- Michael Jang‘s RHCSA/RHCE Red Hat Linux Certification Study Guide Sixth Edition is certainly one of the best available books and perhaps the best one. It describes the exam objectives and explains all the topics one by one. Furthermore, it provides lots of exercises and two sample exams for each RHCSA & RHCE exam allowing you to test your new skills. Some chapters like virtualization (see this site) or encrypted file system (LUKS) are not very clear for a beginner and should be rewritten.
- Damian Tommasino‘s RHCSA and RHCE Cert Guide and Lab Manual is an interesting book. Its purpose is to help you to pass RHCSA & RHCE exams and to give you advanced level in some configuration domains (RAID, quotas, NIC bonding, etc). As the scope of the two exams is already very broad, it’s perhaps too ambitious and doesn’t help you to focus on the really needed skills.
- Asghar Ghori‘s Red Hat Certified System Administrator & Engineer is a book written by a system administrator for system administrators. It goes straight to the point but doesn’t go into the details. With this book, you will learn basic skills to pass the exams but don’t expect too many explanations. Some parts like Kerberos are hardly covered and it can be dry on some topics.
Books about CentOS 6 or RHEL 6 that are also interesting:
- Jonathan Hobson‘s CentOS 6 Linux Server Cookbook addresses many RHCE subjects (YUM, DNS, Samba, Apache, FTP, mail, etc) and provides advanced recipes on some subjects like NTP and network configurations.
- Sander van Vugt‘s Red Hat Enterprise Linux 6 Administration tackles several RHCE topics (KVM, YUM, DNS, Samba, Apache, FTP, mail, etc) but is mainly interesting because it explains in details how to set up an OpenLDAP server, which is indirectly a needed skill for the RHCSA exam (how to test a LDAP client configuration without building a LDAP server?).
- Sven Vermeulen‘s SELinux System Administration is the best current resource about SELinux.
For the beginners, Linup Front GmbH offers a basic introduction to Linux.
For the LPIC-1 exam, there is a LPIC Quick Reference Guide written by Daniele Raffo and regularly updated.
If you are preparing for the LPIC-2 exam, the free LPIC-2 Exam Prep is for you.
If you are interested in RHEL6/Windows integration, Integrating Red Hat Enterprise Linux 6 with Active Directory from Mark Heslin is a must-read. In this free whitepaper, you will find various scenarios explained.
If you want to learn the Bash shell, the Advanced Bash-Scripting Guide is for you.
Finally, you can look at this directory of free programming books.