Book Image

Linux Utilities Cookbook

By : James Kent Lewis
Book Image

Linux Utilities Cookbook

By: James Kent Lewis

Overview of this book

<p>Linux is a stable, reliable and extremely powerful operating system. It has been around for many years, however, most people still don't know what it can do and the ways it is superior to other operating systems. Many people want to get started with Linux for greater control and security, but getting started can be time consuming and complicated. <br /><br />A practical, hands-on guide that provides you with a number of clear step-by-step examples to help you solve many of the questions that crop up when using an operating system you may not be familiar with.</p> <p>Presenting solutions to the most common Linux problems in a clear and concise way, this helpful guide starts with spicing up the terminal sessions by command retrieval and line editing, and shell prompt variables. We will then get to know the different desktops (GUIs) available for Linux systems and which is the best fit for you. We will then explore the world of managing files and directories, connectivity, and what to do when it goes wrong. We will also learn a range of skills, from creating and managing user accounts to securing your system, managing and limiting processes, and letting information flow from one process to another using pipes. Later, we will master disk management, working with scripts and automating tasks quickly, and finally, understand the need for a custom kernel and tips on how to build one.</p> <p><br />Based on the author's extensive experience, there is a section on best practices that every Linux user should be familiar with.</p>
Table of Contents (19 chapters)
Linux Utilities Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

Working with the firewalls and router settings


A firewall is used to prevent unauthorized network access to a machine(s) while still allowing normal (or legal) traffic to pass through. The iptables command is used to set up, configure, and view the tables of the IPv4 rules in the kernel. It is somewhat complicated and so this will serve as just a simple overview.

iptables uses one or more tables. Each table has a number of pre-made chains and can also contain user-created chains. A chain is a list of rules, and a rule specifies what to do with a packet that matches. This “match” is called a target.

When a packet does not match, the next rule in the chain is looked at. If it does match, one of the following can be specified for the packet:

  • ACCEPT: It allows the packet to pass on

  • DROP: It rejects the packet

  • QUEUE: It passes the packet on to the user space

  • RETURN: It stops the running of this chain and continues at the next rule in the calling chain

How to do it...

Here are a few iptable commands...