Book Image

Linux Administration Cookbook

By : Adam K. Dean
Book Image

Linux Administration Cookbook

By: Adam K. Dean

Overview of this book

Linux is one of the most widely used operating systems among system administrators,and even modern application and server development is heavily reliant on the Linux platform. The Linux Administration Cookbook is your go-to guide to get started on your Linux journey. It will help you understand what that strange little server is doing in the corner of your office, what the mysterious virtual machine languishing in Azure is crunching through, what that circuit-board-like thing is doing under your office TV, and why the LEDs on it are blinking rapidly. This book will get you started with administering Linux, giving you the knowledge and tools you need to troubleshoot day-to-day problems, ranging from a Raspberry Pi to a server in Azure, while giving you a good understanding of the fundamentals of how GNU/Linux works. Through the course of the book, you’ll install and configure a system, while the author regales you with errors and anecdotes from his vast experience as a data center hardware engineer, systems administrator, and DevOps consultant. By the end of the book, you will have gained practical knowledge of Linux, which will serve as a bedrock for learning Linux administration and aid you in your Linux journey.
Table of Contents (15 chapters)

Rotating host keys and updating known_hosts

One thing we've not mentioned yet are host keys, and the known_hosts file.

This is something that is often overlooked, so I'd like to take a few minutes to go over these otherwise-ignored treasures.

In this section, we will inspect what happens when you first SSH to a new machine, and then we will change the keys of that machine to see what problems this causes us.

Getting ready

Connect to centos1 and centos2 in different sessions:

$ vagrant ssh centos1
$ vagrant ssh centos2

If you're working on a fresh setup, SSH to centos2 from centos1 and accept the host key when you're presented with it.

Log back out of centos2:

[vagrant@centos1 ~]$ ssh 192.168.33.11
The authenticity...