6.4. Runlevels............................................................................................................ 103

6.5. Fonts................................................................................................................... 105

6.6. Additional Resources ......................................................................................... 106

II. Security Reference ..................................................................................................................... 109

7. Pluggable Authentication Modules (PAM)....................................................................... 111

7.1. Advantages of PAM ........................................................................................... 111

7.2. PAM Configuration Files ................................................................................... 111

7.3. PAM Modules .................................................................................................... 112

7.4. PAM Module Control Flags............................................................................... 113

7.5. PAM Module Paths ............................................................................................ 114

7.6. PAM Module Arguments ................................................................................... 114

7.7. Sample PAM Configuration Files ...................................................................... 114

7.8. PAM and Device Ownership.............................................................................. 116

7.9. Additional Resources ......................................................................................... 117

8. TCP Wrappers and

xinetd

.............................................................................................. 119

8.1. What Are TCP Wrappers? ................................................................................. 119

8.2. Host Based Access Control Lists....................................................................... 119

8.3. Access Control Using

xinetd

.......................................................................... 122

8.4. Additional Resources ......................................................................................... 126

9. SSH Protocol..................................................................................................................... 129

9.1. Features of SSH ................................................................................................. 129

9.2. Event Sequence of an SSH Connection ............................................................. 130

9.3. Layers of SSH Security...................................................................................... 130

9.4. OpenSSH Configuration Files ........................................................................... 132

9.5. More Than a Secure Shell.................................................................................. 133

9.6. Require SSH for Remote Connections .............................................................. 134

10. Kerberos .......................................................................................................................... 137

10.1. Advantages of Kerberos................................................................................... 137

10.2. Kerberos Disadvantages................................................................................... 137

10.3. Kerberos Terminology ..................................................................................... 137

10.4. How Kerberos Works ....................................................................................... 139

10.5. Kerberos and PAM........................................................................................... 140

10.6. Configuring a Kerberos 5 Server ..................................................................... 140

10.7. Configuring a Kerberos 5 Client ...................................................................... 142

10.8. Additional Resources ....................................................................................... 142

11. Tripwire........................................................................................................................... 145

11.1. How to Use Tripwire........................................................................................ 145

11.2. Installing the Tripwire RPM ............................................................................ 146

11.3. Customizing Tripwire ...................................................................................... 147

11.4. Initialize the Tripwire Database....................................................................... 149

11.5. Running an Integrity Check ............................................................................. 150

11.6. Examining Tripwire Reports............................................................................ 150

11.7. Updating the Tripwire Database ...................................................................... 152

11.8. Updating the Tripwire Policy File ................................................................... 153

11.9. Updating the Tripwire Configuration File ....................................................... 154

11.10. Tripwire File Location Reference .................................................................. 155

11.11. Additional Resources ..................................................................................... 156