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 file permissions


Since Linux was designed to be a multiuser operating system, every file has file permissions and ownership associated with it. This is to prevent one user from overwriting the files of another (either intentionally or unintentionally). The root user can (usually) access every file in the system.

Getting ready

Here is a quick review of basic file system permissions. For this example, it is assumed umask is set to 0022. Run umask to make sure.

Observe the following ls -la listing of my backup script b:

-rwxr-xr-x. 1 guest1 root 559 Mar 28 12:43 b

Starting from the left, the first position indicates what kind of file this is. A -, as shown, means this is a regular file. A d there would mean a directory, and an l would indicate it’s a link. The next three sets of three letters are the file permissions and can be referred to in either symbolic or numeric mode. We are going to use numeric (octal) mode.

The first three sets, rwx, are the settings for the owner (guest1...