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

Starting with a log entry


In Chapter 7, FileSystem Errors and Recovery while looking through the /var/log/messages log file to identify issues with the NFS servers filesystems, we noticed the following messages:

Apr 26 10:25:44 nfs kernel: md/raid1:md127: Disk failure on sdb1, disabling device.
md/raid1:md127: Operation continuing on 1 devices.
Apr 26 10:25:55 nfs kernel: md: unbind<sdb1>
Apr 26 10:25:55 nfs kernel: md: export_rdev(sdb1)
Apr 26 10:27:20 nfs kernel: md: bind<sdb1>
Apr 26 10:27:20 nfs kernel: md: recovery of RAID array md127
Apr 26 10:27:20 nfs kernel: md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
Apr 26 10:27:20 nfs kernel: md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for recovery.
Apr 26 10:27:20 nfs kernel: md: using 128k window, over a total of 511936k.
Apr 26 10:27:20 nfs kernel: md: md127: recovery done.

The preceding messages indicate that the RAID device /dev/md127 had a failure. Since the previous chapter was solely...