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Linux Shell Scripting Cookbook, Second Edition

You're reading from   Linux Shell Scripting Cookbook, Second Edition Don't neglect the shell – this book will empower you to use simple commands to perform complex tasks. Whether you're a casual or advanced Linux user, the cookbook approach makes it all so brilliantly accessible and, above all, useful.

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Product type Paperback
Published in May 2013
Publisher Packt
ISBN-13 9781782162742
Length 384 pages
Edition 2nd Edition
Tools
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Toc

Table of Contents (16) Chapters Close

Linux Shell Scripting Cookbook
Credits
About the Authors
About the Reviewers
www.PacktPub.com
Preface
1. Shell Something Out FREE CHAPTER 2. Have a Good Command 3. File In, File Out 4. Texting and Driving 5. Tangled Web? Not At All! 6. The Backup Plan 7. The Old-boy Network 8. Put on the Monitor's Cap 9. Administration Calls Index

Monitoring user logins to find intruders


Logfiles can be used to gather details about the state of the system. Here is an interesting scripting problem statement:

We have a system connected to the Internet with SSH enabled. Many attackers are trying to log in to the system, and we need to design an intrusion detection system by writing a shell script. Intruders are defined as users who are trying to log in with multiple attempts for more than two minutes and whose attempts are all failing. Such users are to be detected, and a report should be generated with the following details:

  • User account to which a login is attempted

  • Number of attempts

  • IP address of the attacker

  • Host mapping for the IP address

  • Time for which login attempts were performed

Getting ready

We can write a shell script that scans through the logfiles and gather the required information from them. For dealing with SSH login failures, it is useful to know that the user authentication session log is written to the logfile /var/log/auth...

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