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 chmod to set permissions on files and directories


chmod, or Change Mode, is a Linux command used to modify the access permissions of files and directories. Everybody wants to keep their data secure and properly organized. For this reason, Linux has the concept of associating an owner and group with every file and directory. These owners and groups have different permissions to access a particular file.

Getting ready

Before we see the use of the chmod command, we need to know that, for different types of users, the symbolic representations that are used are as follows:

  • u is used for user/owner
  • g is used for group
  • o is used for others

Now, let's create a file named file1.txt to check out the different commands of chmod.

How to do it...

Now, we will see how to use chmod in different ways to set different permissions:

  1. We first check the current permission of the file and when it was created:

As we can see, currently only the user/owner has read and write permission, whereas groups and other users...