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Red Hat Enterprise Linux Troubleshooting Guide
Benjamin Cane
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- English
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eBook - ePub
Red Hat Enterprise Linux Troubleshooting Guide
Benjamin Cane
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About This Book
Identify, capture and resolve common issues faced by Red Hat Enterprise Linux administrators using best practices and advanced troubleshooting techniques
About This Book
- Develop a strong understanding of the base tools available within Red Hat Enterprise Linux (RHEL) and how to utilize these tools to troubleshoot and resolve real-world issues
- Gain hidden tips and techniques to help you quickly detect the reason for poor network/storage performance
- Troubleshoot your RHEL to isolate problems using this example-oriented guide full of real-world solutions
Who This Book Is For
If you have a basic knowledge of Linux from administration or consultant experience and wish to add to your Red Hat Enterprise Linux troubleshooting skills, then this book is ideal for you. The ability to navigate and use basic Linux commands is expected.
What You Will Learn
- Identify issues that need rapid resolution against long term root cause analysis
- Discover commands for testing network connectivity such as telnet, netstat, ping, ip and curl
- Spot performance issues with commands such as top, ps, free, iostat, and vmstat
- Use tcpdump for traffic analysis
- Repair a degraded file system and rebuild a software raid
- Identify and troubleshoot hardware issues using dmesg
- Troubleshoot custom applications with strace and knowledge of Linux resource limitations
In Detail
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.
Style and approach
This is an easy-to-follow guide packed with examples of real-world core Linux concepts. All the topics are presented in detail while you're performing the actual troubleshooting steps.
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Information
Red Hat Enterprise Linux Troubleshooting Guide
Table of Contents
Red Hat Enterprise Linux Troubleshooting Guide
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
Downloading the example code
Errata
Piracy
Questions
1. Troubleshooting Best Practices
Styles of troubleshooting
The Data Collector
The Educated Guesser
The Adaptor
Choosing the appropriate style
Troubleshooting steps
Understanding the problem statement
Asking questions
Tickets
Humans
Attempting to duplicate the issue
Running investigatory commands
Establishing a hypothesis
Putting together patterns
Is this something that I've encountered before?
Trial and error
Start by creating a backup
Getting help
Books
Team Wikis or Runbooks
Google
Man pages
Reading a man page
Name
Synopsis
Description
Examples
Additional sections
Info documentation
Referencing more than commands
Installing man pages
Red Hat kernel docs
People
Following up
Documentation
Root cause analysis
The anatomy of a good RCA
The problem as it was reported
The actual root cause of the problem
A timeline of events and actions taken
Any key data points to validate the root cause
A plan of action to prevent the incident from reoccurring
Establishing a root cause
Sometimes you must sacrifice a root cause analysis
Understanding your environment
Summary
2. Troubleshooting Commands and Sources of Useful Information
Finding useful information
Log files
The default location
Common log files
Finding logs that are not in the default location
Checking syslog configuration
Checking the application's configuration
Other examples
Using the find command
Configuration files
Default system configuration directory
Finding configuration files
Using the rpm command
Using the find command
The proc filesystem
Troubleshooting commands
Command-line basics
Command flags
The piping command output
Gathering general information
w – show who is logged on and what they are doing
rpm – RPM package manager
Listing all packages installed
Listing all files deployed by a package
Using package verification
df – report file system space usage
Showing available inodes
free – display memory utilization
What is free, is not always free
The /proc/meminfo file
ps – report a snapshot of current running processes
Printing every process in long format
Printing a specific user's processes
Printing a process by process ID
Printing processes with performance information
Networking
ip – show and manipulate network settings
Show IP address configuration for a specific device
Show routing configuration
Show network statistics for a specified device
netstat – network statistics
Printing network connections
Printing all ports listening for tcp connections
Delay
Performance
iotop – a simple top-like I/O monitor
iostat – report I/O and CPU statistics
Manipulating the output
vmstat – report virtual memory statistics
sar – collect, report, or save system activity information
Using the sar command
Summary
3. Troubleshooting a Web Application
A small back story
The reported issue
Data gathering
Asking questions
Duplicating the issue
Understanding the environment
Where is this blog hosted?
Lookup IPs with nslookup
What about ping, dig, or other tools?
Ok, it's within our environment; now what?
What services are installed and running?
Validate the web server
Validating the database service
Validating PHP
A summary of installed and running services
Looking for error messages
Apache logs
Finding the location of Apache's logs
Reviewing the logs
Using curl to call our web application
Requesting a non-PHP page
Reviewing generated log entries
What we learned from httpd logs
Verifying the database
Verifying the WordPress database
Finding the installation path for WordPress
Checking the default configuration
Finding the database credentials
Connecting as the WordPress user
Validating the database structure
What we learned from the database validation
Establishing a hypothesis
Resolving the issue
Understanding database data files
Finding the MariaDB data folder
Resolving data file issues
Validating
Final validation
Summary
4. Troubleshooting Performance Issues
Performance issues
It's slow
Performance
Application
CPU
Top – a single command to look at everything
What does this output tell us about our issue?
Individual processes from top
Determining the number of CPUs available
Threads and Cores
lscpu – Another way to look at CPU info
ps – Drill down deeper on individual processes with ps
Using ps to determine process CPU utilization
Putting it all together
A quick look with top
Digging deeper with ps
Memory
free – Looking at free and used memory
Linux memory buffers and caches
Swapped memory
What free tells us about our system
Checking for oomkill
ps - Checking individual processes memory utilization
vmstat – Monitoring memory allocation and swapping
Putting it all together
Taking a look at the system's memory utilization with free
Watch what is happening with vmstat
Finding the processes that utilize the most memory with ps
Disk
iostat – CPU and device input/output statistics
CPU details
Reviewing I/O statistics
Identifying devices
Who is writing to these devices?
ps – Using ps to identify processes utilizing I/O
iotop – A top top-like command for disk i/o
Putting it all together
Using iostat to determine whether there is a I/O bandwidth problem
Using iotop to determine which processes are consuming disk bandwidth
Using ps to understand more about processes
Networ...