Book Image

Linux Shell Scripting Cookbook, Second Edition - Second Edition

Book Image

Linux Shell Scripting Cookbook, Second Edition - Second Edition

Overview of this book

The shell remains one of the most powerful tools on a computer system — yet a large number of users are unaware of how much one can accomplish with it. Using a combination of simple commands, we will see how to solve complex problems in day to day computer usage.Linux Shell Scripting Cookbook, Second Edition will take you through useful real-world recipes designed to make your daily life easy when working with the shell. The book shows the reader how to effectively use the shell to accomplish complex tasks with ease.The book discusses basics of using the shell, general commands and proceeds to show the reader how to use them to perform complex tasks with ease.Starting with the basics of the shell, we will learn simple commands with their usages allowing us to perform operations on files of different kind. The book then proceeds to explain text processing, web interaction and concludes with backups, monitoring and other sysadmin tasks.Linux Shell Scripting Cookbook, Second Edition serves as an excellent guide to solving day to day problems using the shell and few powerful commands together to create solutions.
Table of Contents (16 chapters)
Linux Shell Scripting Cookbook
About the Authors
About the Reviewers

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...