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

Using mdadm to examine the superblock

To view the event count, we will use the mdadm command with the --examine flag to examine the disk devices:

[nfs]# mdadm --examine /dev/sda1
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x1
     Array UUID : 7adf0323:b0962394:387e6cd0:b2914469
           Name : localhost:boot
  Creation Time : Wed Apr 15 09:39:22 2015
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 1023968 (500.07 MiB 524.27 MB)
     Array Size : 511936 (500.02 MiB 524.22 MB)
  Used Dev Size : 1023872 (500.02 MiB 524.22 MB)
   Super Offset : 1023984 sectors
   Unused Space : before=0 sectors, after=96 sectors
          State : clean
    Device UUID : 92d97c32:1f53f59a:14a7deea:34ec8c7c

Internal Bitmap : -16 sectors from superblock
    Update Time : Mon May 11 04:08:10 2015
  Bad Block Log : 512 entries available at offset -8 sectors
       Checksum : bd8c1d5b - correct
         Events : 60

   Device Role : Active device 0
   Array State...