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
About the Author
About the Reviewers

Identifying a bigger issue

Earlier while using mdadm to look at the current status of md127, we could see that the RAID device md127 had a disk removed from service. While looking through /proc/mdstat we discovered that there is another RAID device /dev/md126, and that too has a disk removed from service.

Another interesting item that we can see is that the RAID device /dev/md126 is a surviving disk: /dev/sda1. This is interesting because the surviving disk for /dev/md127 is /dev/sda2. If we remember from the earlier chapter /dev/sda1 and /dev/sda2 are simply 2 partitions from the same physical disk. Given the fact that both RAID devices have a missing drive and that our logs state that /dev/md127 had /dev/sdb1 removed and re-added. It is likely that both /dev/md127 and /dev/md126 are using partitions from /dev/sdb.

Since /proc/mdstat only has two statuses for RAID devices, up or down, we can confirm whether the second disk has actually been removed from /dev/md126 using the --detail flag...