Book Image

Practical Linux Security Cookbook - Second Edition

By : Tajinder Kalsi
Book Image

Practical Linux Security Cookbook - Second Edition

By: Tajinder Kalsi

Overview of this book

Over the last few years, system security has gained a lot of momentum and software professionals are focusing heavily on it. Linux is often treated as a highly secure operating system. However, the reality is that Linux has its share of security ?aws, and these security ?aws allow attackers to get into your system and modify or even destroy your important data. But there’s no need to panic, since there are various mechanisms by which these ?aws can be removed, and this book will help you learn about different types of Linux security to create a more secure Linux system. With a step-by-step recipe approach, the book starts by introducing you to various threats to Linux systems. Then, this book will walk you through customizing the Linux kernel and securing local files. Next, you will move on to managing user authentication both locally and remotely and mitigating network attacks. Later, you will learn about application security and kernel vulnerabilities. You will also learn about patching Bash vulnerability, packet filtering, handling incidents, and monitoring system logs. Finally, you will learn about auditing using system services and performing vulnerability scanning on Linux. By the end of this book, you will be able to secure your Linux systems and create a robust environment.
Table of Contents (20 chapters)
Title Page
Copyright and Credits
Contributors
Packt Upsell
Preface
Index

Using ACLs to access files


Implementing the basic file permissions using chmod is not enough, so we can use ACLs, or Access Control Lists. In addition to providing permissions for the owner and group for a particular file, we can set permissions for any user, any user group, or a group of all users who are not in the group of the particular user using ACLs.

Getting ready

Before using ACLs, we check whether it is enabled or not:

  1. To do this, we try to view the ACLs for any file, as shown here:

This command will show an output like this if ACLs are enabled. In our case, they are not enabled for /dev/sda1, as it is not listed in the mount options.

  1. To enable an ACL, we will add it to the filesystem, using the following command:
  1. Now, run the tune2fs command again to confirm the ACL is enabled:

Now, we can see the ACLs option in the /dev/sda1 partition.

How to do it...

To understand the workings of ACLs, let's follow these steps:

  1. We will first check the default ACL values for any file or directory. To do...