Book Image

Red Hat Enterprise Linux Troubleshooting Guide

By : Benjamin Cane
Book Image

Red Hat Enterprise Linux Troubleshooting Guide

By: Benjamin Cane

Overview of this book

Red Hat Enterprise Linux is an operating system that allows you to modernize your infrastructure, boost efficiency through virtualization, and finally prepare your data center for an open, hybrid cloud IT architecture. It provides the stability to take on today's challenges and the flexibility to adapt to tomorrow's demands. In this book, you begin with simple troubleshooting best practices and get an overview of the Linux commands used for troubleshooting. The book will cover the troubleshooting methods for web applications and services such as Apache and MySQL. Then, you will learn to identify system performance bottlenecks and troubleshoot network issues; all while learning about vital troubleshooting steps such as understanding the problem statement, establishing a hypothesis, and understanding trial, error, and documentation. Next, the book will show you how to capture and analyze network traffic, use advanced system troubleshooting tools such as strace, tcpdump & dmesg, and discover common issues with system defaults. Finally, the book will take you through a detailed root cause analysis of an unexpected reboot where you will learn to recover a downed system.
Table of Contents (19 chapters)
Red Hat Enterprise Linux Troubleshooting Guide
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

What we have learned so far


From the troubleshooting steps that we have taken so far, we have collected quite a few key pieces of data. Let's walk through what we have learned and what we can infer from these findings:

  • On our system, we have two RAID devices.

    Using the mdadm command and the contents of /proc/mdstat, we were able to determine that this system has two RAID devices—/dev/md126 and /dev/md127.

  • Both RAID devices are a RAID 1 and missing a mirrored device.

    With the mdadm command and output of dmesg, we were able to identify that both RAID devices are set up as a RAID 1 device. On top of that, we were also able to see that both RAID devices were missing a disk; both the missing devices were partitions from the /dev/sdb hard disk.

  • Both /dev/sdb1 and /dev/sdb2 have mismatched event counts.

    With the mdadm command, we were able to inspect the superblock details of the /dev/sdb1 and /dev/sdb2 devices. During this, we were able to see that the event counts for those devices are not matching...