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Bash Cookbook

Bash Cookbook

By : Brash, Ganesh Sanjiv Naik
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Bash Cookbook

Bash Cookbook

1 (1)
By: Brash, Ganesh Sanjiv Naik

Overview of this book

In Linux, one of the most commonly used and most powerful tools is the Bash shell. With its collection of engaging recipes, Bash Cookbook takes you through a series of exercises designed to teach you how to effectively use the Bash shell in order to create and execute your own scripts. The book starts by introducing you to the basics of using the Bash shell, also teaching you the fundamentals of generating any input from a command. With the help of a number of exercises, you will get to grips with the automation of daily tasks for sysadmins and power users. Once you have a hands-on understanding of the subject, you will move on to exploring more advanced projects that can solve real-world problems comprehensively on a Linux system. In addition to this, you will discover projects such as creating an application with a menu, beginning scripts on startup, parsing and displaying human-readable information, and executing remote commands with authentication using self-generated Secure Shell (SSH) keys. By the end of this book, you will have gained significant experience of solving real-world problems, from automating routine tasks to managing your systems and creating your own scripts.
Table of Contents (10 chapters)
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Blocking IP addresses from failed SSH attempts


In this recipe, we will learn about finding the failed SSH attempts and blocking those IP addresses. To find failed attempts, we will use grep as well as cat commands. The login attempts to the SSH Server are tracked and recorded into the rsyslog daemon.

Getting ready

Besides having a Terminal open, we need to remember a few concepts:

  • Basic knowledge of the grep and cat commands
  • Ensure that grep is installed

How to do it…

We will find the failed SSH login attempts using the grep and cat commands. First, be a root user. Type the sudo su command. Next, run the following command to fetch the failed attempts using the grep command:

# grep "Failed password" /var/log/auth.log

You can do this using the cat command also. Run the following command:

# cat /var/log/auth.log | grep "Failed password"

You can block the particular IP address that has failed SSH login attempt using tcp-wrapper. Navigate to the /etc directory. Look for the hosts.deny file, add the following...

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