Troubleshooting CentOS

Jonathan Hobson

• Publisher: Packt Publishing
• Year: 2015
• eBook ISBN: 9781785289828
• Edition: 1
• Topic: Computer Science
• Subtopic: Cyber Security
• Index: Computer Science

Troubleshooting CentOS

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Table of Contents

Troubleshooting CentOS

Credits

About the Author

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers, and more

Why subscribe?

Free access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Errata

Piracy

Questions

1. Basics of Troubleshooting CentOS

Installing some basic tools

Gathering hardware information

Understanding dmesg

Understanding log files

Reading log files and affecting the output

Using tail to monitor log files

Using cat, less, and more

Using grep

Using diff

Using truncation

Summary

References

2. Troubleshooting Active Processes

Tuning server performance with memory management and swap

Managing memory with vmstat

Checking the system load with the top command

Monitoring disk I/O with iotop

Checking processes with the ps command

Checking performance with iostat and lsof

Calculating the system load

Discovering process IDs with pgrep and systemctl

More about systemd

Issuing the kill signal

Dealing with an orphaned process

Summary

References

3. Troubleshooting the Network Environment

Using ping, dig, host, traceroute, and mtr

The ping command

The dig and host commands

The traceroute command

The mtr command

Monitoring network connections with the ss command

Packet analysis with tcpdump

Summary

References

4. Troubleshooting Package Management and System Upgrades

Gathering software information

Using Yum plugins

Fixing Yum operations

Installing additional Yum repositories

EPEL

Remi

The IUS repository

Downloading an RPM package with Yum

Diagnosing a corrupt RPM database

Minor release upgrades

Summary

References

5. Troubleshooting Users, Directories, and Files

Users

Adding users and forcing a password change

Deleting users

Modifying a user

Meet login.defs

Monitoring user activity with utmpdump

Resetting the root password and enhancing logging

Recovering lost or deleted files with Scalpel

Restoring file and directory permissions

Working with and extending the XFS filesystem

Running repairs on XFS

Investigating fragmentation on XFS

Auditing directories and files

Visualizing directories and files

Summary

References

6. Troubleshooting Shared Resources

Providing NFS shares on a CentOS 7 server

About NFS exports

Mounting NFS shares on a CentOS client

Mounting an external drive with CIFS

Using autofs to mount an external drive

Summary

References

7. Troubleshooting Security Issues

Auditing SELinux with aureport and setroubleshoot

SSH banners

Tuning SSH

Intrusion detection with Tripwire

Firewalld – zone, service, and port management

Removing Firewalld and returning to iptables

Summary

References

8. Troubleshooting Database Services

Getting up-and-running with MariaDB

Resetting and recovering a root password with MariaDB

Tuning MariaDB and MySQL

Obtaining metrics from MariaDB and MySQL

Returning to MySQL

Installing and configuring PostgreSQL 9

Summary

References

9. Troubleshooting Web Services

Auditing the server with cURL

Debugging Akamai headers with cURL

Adding Varnish to Apache

Testing Varnish with cURL

Using cURL to access an FTP directory

Enabling mod_status in Apache

Summary

References

10. Troubleshooting DNS Services

Changing the hostname and managing the FQDN

Performing system sanity checks with BIND

Monitoring bandwidth with iftop

Flushing the cache

Summary

References

Index

Troubleshooting CentOS

Copyright © 2015 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: June 2015

Production reference: 1220615

Published by Packt Publishing Ltd.

Livery Place

35 Livery Street

Birmingham B3 2PB, UK.

ISBN 978-1-78528-982-8

www.packtpub.com

Credits

Author

Jonathan Hobson

Reviewers

Mohamed Alibi

Toni de la Fuente

Commissioning Editor

Neil Alexander

Acquisition Editor

Usha Iyer

Content Development Editor

Anand Singh

Technical Editors

Dhiraj Chandanshive

Pramod Kumavat

Copy Editors

Janbal Dharmaraj

Rashmi Sawant

Project Coordinator

Vijay Kushlani

Proofreader

Safis Editing

Indexer

Hemangini Bari

Production Coordinator

Shantanu N. Zagade

Cover Work

Shantanu N. Zagade

About the Author

Jonathan Hobson is a professional Dev/Ops engineer who provides round-the-clock application and server support to one of the world's largest online newspapers. He has been using CentOS since its inception, and as the author of the best-selling CentOS 6 Linux Server Cookbook, Packt Publishing (ISBN-13: 978-1849519021), Jonathan maintains a strong reputation for the generation of ideas, problem solving, building business confidence, and finding innovative solutions in challenging environments.

Jonathan has worked in a variety of environments, and with more than 20 years of experience as a professional developer, database administrator, and server engineer, he continues to support the open source community at large.

Following a wide range of interests beyond the computer screen, Jonathan also enjoys walking his dogs and gett...

Table of contents

• Troubleshooting CentOS