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

Introduction


The cron daemon, which is usually started automatically by the OS, looks at all of the crontab files once every minute. If the criterion has been met, the command is run. In this chapter we show how to create and maintain your crontab files using the crontab program.

Depending on how your system is set up, cron jobs are permitted (allowed or not allowed) based on the user. The files that control this are in /etc and are named cron.allow and cron.deny. These are explained in the following section:

  • cron.allow: If this file exists, then the user must be listed in it, in order to use crontab

  • cron.deny: If cron.allow does not exist but cron.deny does exist then the user must not be listed in the cron.deny file

If neither of the file exists, then only the root user can use the command. In most Linux systems only cron.deny exists and it is empty. Check this on your system before running the following commands.

We will use a user account to experiment with crontab. The crontab command is...