This video describes how to use Pluggable Authentication Modules, PAM for short, to limit access to specific users. The key to this security feature is the pam underscore listfile dot so module, available in the live slash security directory. Generally, to make sure the command respects what you do with the module, you'll want to insert the module atop the file, unless of course there's a rootok module in that file. Let's take a look at the configuration file associated with the Halt command. There is a rootok module in the file so we insert the listfile module after that, as we don't want to override root user privileges. The way this module limits user access depends on the options you add to the command. First, the onerr equals succeed is sort of a safety valve. In case I forget to configure the etc slash users file correctly, this command will still work. It'll just ignore the specific directive. Next, the item option limits the type of listfile access that is configured, which use item equals user because we're focused on user level restrictions. Next, there's the sense option based on the following question: if a user is seen in the file, in this case, access is allowed. Finally, the file option specifies the list, in this case, the list of users to be configured. Now, let's sum up. For the PAM module, as configured, I could forget to create the etc slash users configuration file, and the onerr equals succeed option would save me, leaving Halt as a usable command. The item equals user option specifies user level restrictions as configured in the file equals etc slash users file. And the sense equals allow means that users in etc slash users are allowed access to the Halt command. That's it for the videos in the RHCE course. Congratulations. Remember, to pass the RHCE Exam you need to practice, practice, practice. Practice installing Red Hat Enterprise Linux 5 per the latest RHCE Exam Prep Guide. Practice creating problems with Red Hat Enterprise Linux 5 systems so you can recognize them during your exam. Practice configuring Red Hat Enterprise Linux 5 network services, or basic shares and configure them for basic operation. Practice with key tools like the Security Level Configuration, the SELinux Management tool, as well as service specific tools. And, of course, I encourage you to review the videos in this course as you need them. Thank you for listening, and good luck on your exam.
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