Learning Nagios 4

Table of Contents

Learning Nagios 4

Credits

About the Author

About the Reviewers

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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. Introducing Nagios

Understanding the basics of Nagios

The benefits of monitoring resources

Main features

Soft and hard states

What's new in Nagios 4.0

Summary

2. Installing Nagios 4

Installation

Upgrading from previous versions

Installing prerequisites

Obtaining Nagios

Setting up users and groups

Compiling and installing Nagios

Compiling and installing Nagios plugins

Setting up Nagios as a system service

Resolving errors with script for Nagios system service

Configuring Nagios

Creating the main configuration file

Understanding macro definitions

Configuring hosts

Configuring host groups

Configuring services

Configuring service groups

Configuring commands

Configuring time periods

Configuring contacts

Configuring contact groups

Verifying the configuration

Understanding notifications

Templates and object inheritance

Summary

3. Using the Nagios Web Interface

Setting up the web interface

Configuring the web server

Creating an administrative user for Nagios

Accessing the web interface

Troubleshooting

Using the web interface

Checking the tactical overview

Viewing the status map

Managing hosts

Checking statuses

Viewing host information

Managing services

Checking statuses

Viewing service information

Managing downtime

Checking downtime statuses

Scheduling downtime

Managing comments

Nagios information

Viewing process information

Checking performance information

Generating reports

Changing the look of the Nagios web interface

Third-party Nagios web interfaces

Summary

4. Using the Nagios Plugins

Understanding how checks work

Monitoring using the standard network plugins

Testing the connection to a remote host

Testing the connectivity using TCP and UDP

Monitoring the e-mail servers

Checking the POP3 and IMAP servers

Testing the SMTP protocol

Monitoring network services

Checking the FTP server

Verifying the DHCP protocol

Monitoring the Nagios process

Testing the websites

Monitoring the database systems

Checking MySQL

Checking PostgreSQL

Checking Oracle

Checking other databases

Monitoring the storage space

Checking the swap space

Monitoring the disk status using SMART

Checking the disk space

Testing the free space for remote shares

Monitoring the resources

Checking the system load

Checking the processes

Monitoring the logged-in users

Monitoring other operations

Checking for updates with APT

Monitoring the UPS status

Gathering information from the lm-sensors

Using the dummy check plugin

Manipulating other plugins' output

Additional and third-party plugins

Monitoring the network software

Using third-party plugins

Summary

5. Advanced Configuration

Creating maintainable configurations

Configuring the file structure

Defining the dependencies

Creating the host dependencies

Creating the service dependencies

Using the templates

Creating the templates

Inheriting from multiple templates

Using the custom variables

Understanding flapping

Summary

6. Notifications and Events

Creating effective notifications

Using multiple notifications

Sending instant messages via Jabber

Notifying users with text messages

Integrating with HipChat

Understanding escalations

Setting up escalations

Understanding how escalations work

Sending commands to Nagios

Adding comments to hosts and services

Scheduling host and service checks

Modifying custom variables

Creating event handlers

Restarting services automatically

Modifying notifications

Using adaptive monitoring

Summary

7. Passive Checks and NSCA

Understanding passive checks

Configuring passive checks

Sending passive check results for hosts

Sending passive check results for services

Troubleshooting errors

Using NSCA

Downloading NSCA

Compiling NSCA

Configuring the NSCA server

Sending results over NSCA

Configuring NSCA for secure communication

Summary

8. Monitoring Remote Hosts

Monitoring over SSH

Configuring the SSH connection

Using the check_by_ssh plugin

Performing multiple checks

Troubleshooting the SSH-based checks

Monitoring using NRPE

Obtaining NRPE

Compiling NRPE

Configuring the NRPE daemon

Setting up NRPE as a system service

Configuring Nagios for NRPE

Using command arguments with NRPE

Troubleshooting NRPE

Comparing NRPE and SSH

Alternatives to SSH and NRPE

Summary

9. Monitoring using SNMP

Introducing SNMP

Understanding data objects

Working with SNMP and MIB

Using graphical tools

Setting up an SNMP agent

Using SNMP from Nagios

Receiving traps

Using additional plugins

Summary

10. Advanced Monitoring

Monitoring Windows hosts

Setting up NSClient++

Performing tests using check_nt

Performing checks with NRPE protocol

Performing passive checks using NSCA Protocol

Understanding distributed monitoring

Introducing obsessive notifications

Configuring Nagios instances

Performing freshness checking

Using templates for distributed monitoring

Creating the host and service objects

Customizing checks with custom variables

Summary

11. Programming Nagios

Introducing Nagios customizations

Programming in C with libnagios

Creating custom active checks

Testing the correctness of the MySQL database

Monitoring local time with a time server

Writing plugins correctly

Checking websites

Virtualization and clouds

Monitoring VMware

Monitoring Amazon Web Services

Writing commands to send notifications

Managing Nagios

Using passive checks

Summary

12. Using the Query Handler

Introducing the query handler

Communicating with the query handler

Using the query handler programmatically

Using the core service

Introducing Nagios Event Radio Dispatcher

Displaying real-time status updates

Displaying checks using Gource

Summary

Index

Learning Nagios 4

Learning Nagios 4

Copyright © 2014 Packt Publishing

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Second Edition: March 2014

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Credits

Author

Wojciech Kocjan

Reviewers

Péter Károly Stone Juhász

Emilien Kenler

Daniel Parraz

Pall Sigurdsson

Acquisition Editors

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Cover Work

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About the Author

Wojciech Kocjan is a system administrator and programmer with 10 years of experience. His work experience includes several years of using Nagios for enterprise IT infrastructure monitoring. He also has experience in large variety of devices and servers, routers, Linux, Solaris, AIX servers and i5/OS mainframes. His programming experience includes multiple languages (such as Java, Ruby, Python, and Perl) and focuses on web applications as well as client-server solutions.

I'd like to thank my wife Joanna and my son Kacper for all of the help and support during the writing of this book.

About the Reviewers

Péter Károly Stone Juhász was born in 1980 in Hungary, where he lives with his family and their cat. He holds an MSc degree in Programmer Mathematics. At the very beginning of his career, he turned toward operations. Since 2004, he has been working as a general—mainly GNU/Linux—system administrator.

His average working day includes patching in the server room, installing servers, managing PBX, maintaining VMware vSphere infrastructure and servers at Amazon AWS, managing storage and backups, monitoring with Nagios, trying out new technology, and writing scripts to ease everyday work.

His interests in IT are Linux, server administration, virtualization, artificial intelligence, network security, and distributed systems. His hobbies include learning Chinese, program developing, reading, hiking, playing the game Go, listening to music and unicycling. For his contact information or to find out more about him, you can visit his website at http://midway.hu.

Emilien Kenler, after working on small web projects, began to focus on Game Development in 2008, when he was in high school. Until 2011, he worked for different groups and has specialized in system administration. In 2011, he founded a company, HostYourCreeper (http://www.hostyourcreeper.com) to sell Minecraft servers, while he was studying Computer Science Engineering. He created a lightweight IaaS based on new technologies such as Node.js and RabbitMQ.

Thereafter, he worked at TaDaweb as a system administrator, building its infrastructure and creating tools to manage deployments and monitoring. In 2014, he began a new adventure at Wizcorp, Tokyo. He will graduate at the end of the year from the University of Technology of Compiègne.

Daniel Parraz was raised in New Mexico and began using computer-type devices at an early age. After graduating from school, he found a technical support job and started to learn Linux. He has been administrating Linux/Unix systems since 2001 and has worked on large storage engineering and installations with Fortune 500 companies and start-ups. He currently lives in Albuquerque, New Mexico, with his family, and enjoys hiking, reading, and growing fruits and vegetables as a volunteer with an agriculture group supported by a local community. 

Pall Sigurdsson is a lifelong open source geek with special interest in automation and monitoring. He is known for his work in developing Adagios, a modern web status, and a configuration interface to monitor systems that are compatible with Nagios.

Pall also maintains other projects such as Pynag (a high-level python API for Nagios configuration files) and okconfig (a set of preconfigured Nagios plugins and configuration templates).

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Preface

The book is a practical guide to setting up Nagios 4, an open source network monitoring tool. It is a system that checks whether hosts and services are working properly and notifies users when problems occur. The book covers the installation and configuring of Nagios 4 on various operating systems, and it focuses on the Ubuntu Linux operating system.

The book takes the reader through all the steps of compiling Nagios from sources, installing, and configuring advanced features such as setting up redundant monitoring. It also mentions how to monitor various services such as e-mail, WWW, databases, and file sharing. The book describes what SNMP is and how it can be used to monitor various devices. It also gives the details of monitoring the Microsoft Windows computers. The book contains troubleshooting sections that aid the reader in case any problems arise while setting up the Nagios functionalities.

No previous experience with network monitoring is required, although it is assumed that the reader has a basic understanding of the Unix systems. It also mentions examples to extend Nagios in several languages such as Perl, Python, Tcl, and Java so that readers who are familiar with at least one of these technologies can benefit from extending Nagios. When you finish this book, you'll be able to set up Nagios to monitor your network and will have a good understanding of what can be monitored.

What this book covers

Chapter 1, Introducing Nagios, talks about Nagios and system monitoring in general. It shows the benefits of using system monitoring software and the advantages of Nagios in particular. It also introduces the basic concepts of Nagios.

Chapter 2, Installing Nagios 4, covers the installation of Nagios both when compiling from source code or using the prebuilt packages. Details on how to configure users, hosts, and services as well as information on how Nagios sends notifications to users are given in this chapter.

Chapter 3, Using the Nagios Web Interface, talks about how to set up and use the Nagios web interface. It describes the basic views for hosts and services and gives detailed information on each individual item. It also introduces some features such as adding comments, scheduled downtimes, viewing detailed information, and generating reports.

Chapter 4, Using the Nagios Plugins, goes through the standard set of Nagios plugins that allows you to perform checks of various services. It shows how you can check for standard services such as e-mail, Web, file, and database servers. It also describes how to monitor resources such as CPU usage, storage, and memory usage.

Chapter 5, Advanced Configuration, focuses on the efficient management of large configurations and the use of templates. It shows how dependencies between hosts and services can be defined and discusses custom variables and adaptive monitoring. It also introduces the concept of flapping and how it detects services that start and stop frequently.

Chapter 6, Notifications and Events, describes the notification system in more details. It focuses on effective ways of communicating problems to the users and how to set up problem escalations. It also describes how events work in Nagios and how they can be used to perform automatic recovery of services.

Chapter 7, Passive Checks and NSCA, focuses on cases where external processes send results to Nagios. It introduces the concept of passive check, which is not scheduled and run by Nagios, and gives practical examples of when and how it can be used. It also shows how to use Nagios Service Check Acceptor (NSCA) to send notifications.

Chapter 8, Monitoring Remote Hosts, covers how Nagios checks can be run on remote machines. It walks through details of deploying checks remotely over SSH using public key authentication. It also shows how Nagios Remote Plugin Executor (NRPE) can be used for deploying plugins remotely.

Chapter 9, Monitoring using SNMP, describes how the Simple Network Management Protocol (SNMP) can be used from Nagios. It provides an overview of SNMP and its versions. It explains the reading of SNMP values from the SNMP-aware devices and covers how that can then be used to perform checks from Nagios.

Chapter 10, Advanced Monitoring, focuses on how Nagios can be set up on multiple hosts and how that information could be gathered on a central server. It also covers how to monitor computers that run the Microsoft Windows operating system.

Chapter 11, Programming Nagios, shows how to extend Nagios. It explains how to write custom check commands, how to create custom ways of notifying users, and how passive checks and NSCA can be used to integrate your solutions with Nagios. The chapter covers many programming languages to show how Nagios can be integrated with them.

Chapter 12, Using the Query Handler, focuses on the use of the Nagios query handler to send commands to Nagios as well as receive results and notifications from these commands. It shows how the query handler can be used from multiple programming languages and how it can be used to build an application to display Nagios updates in real time.

What you need for this book

This book requires a Linux server. As all of the examples are created using Ubuntu Linux, it is recommended that you use this distribution. The book goes through the process of setting up Nagios, so installing it is not a prerequisite of this book.

The Nagios web interface requires a web server. Chapter 3, Using the Nagios Web Interface, provides a step-by-step instruction on how to set up an Apache web server and configure it so that it be used with Nagios.

Who this book is for

The target readers of this book are System Administrators who are interested in using Nagios. This book will introduce Nagios along with the new features of Version 4.

Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text, object names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: This service group consists of the mysql and pgsql services on the linuxbox01 host.

A block of code is set as follows:

define service{

  host_name                      linuxbox01

  service_description            mysql

  check_command                  check_ssh

  servicegroups                  databaseservices

  }

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

define service{

  host_name                      linuxbox01

  service_description            mysql

  check_command                  check_ssh

  servicegroups                  databaseservices

  }

Any command-line input or output is written as follows:

# cp /usr/src/asterisk-addons/configs/cdr_mysql.conf.sample

/etc/asterisk/cdr_mysql.conf

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: You should start by downloading the source tarball of the latest Nagios 4.x branch. It is available under the Get Nagios Core section.

Note

Warnings or important notes appear in a box like this.

Tip

Tips and tricks appear like this.

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Downloading the example code

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Errata

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Questions

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Chapter 1. Introducing Nagios

Imagine you're working as an administrator of a large IT infrastructure. You just started receiving e-mails that a web application just stopped working. When you try to access the same page, it just doesn't load. What are the possibilities? Is it the router? Is it the firewall? Perhaps the machine hosting the page is down? Before you even start thinking rationally on what to do, your boss calls about the critical situation and demands explanations. In all this panic, you'll probably start plugging everything in and out of the network, rebooting the machine…and that doesn't help.

After hours of nervous digging into the issue, you've finally found the solution: the web server was working properly, but it would time out communication with the database server. This was because the machine with the DB did not receive the correct IP as yet another box ran out of memory and killed the DHCP server on it. Imagine how much time it would take to find all that manually? It would be a nightmare if the database server was in another branch of the company or in a different time zone and perhaps guys over there were still sleeping.

But what if you had Nagios up and running across your entire company? You would just go to the web interface and see that there are no problems with the web server and the machine on which it is running. There would also be a list of issues—the machine serving IP addresses to the entire company does not do its job and the database is down. If the setup also monitored the DHCP server itself, you'd get a warning e-mail that little swap memory is available on it or too many processes are running. Maybe it would even have an event handler for such cases to just kill or restart noncritical processes. Also, Nagios will try to restart the dhcpd process over the network in case it is down.

In the worst case, Nagios would speed up hours of investigation to 10 minutes. In the best case, you would just get an e-mail that there was such a problem and another e-mail that it's already fixed. You would just disable a few services and increase the swap size for the DHCP machine and solve the problem once and for all. Nobody would even notice that there was such a problem.

Understanding the basics of Nagios

Nagios is a tool for system monitoring. It means that Nagios watches computers or devices on your network and ensures that they are working as they should. Nagios constantly checks if other machines are working properly. It also verifies that various services on those machines are working fine. In addition, Nagios accepts other processes or machines reporting their status, for example, a web server can directly report if it is not overloaded to Nagios.

The main purpose of system monitoring is to detect as soon as possible any system that is not working properly so that users of that system will not report the issue to you first.

System monitoring in Nagios is split into two categories of objects: hosts and services. Hosts represent a physical or virtual device on your network (servers, routers, workstations, printers, and so on). Services are particular functionalities, for example, a Secure Shell (SSH) server (sshd process on the machine) can be defined as a service to be monitored. Each service is associated with a host on which it is running. In addition, machines can be grouped into host groups.

A major benefit of Nagios' performance checks is that it only uses four distinct states—Ok, Warning, Critical, and Unknown. It is also based on plugins—this means if you want to check something that's not yet possible to do, you just need to write a simple piece of code, and that's it!

The approach to only offer three states allows administrators to ignore monitoring values themselves and just decide on what the warning/critical limits are. This is a proven concept, and is far more efficient than monitoring graphs and analyzing trends. For example, system administrators tend to ignore things such as gradually declining storage space. People often simply ignore the process until a critical process runs out of disk space. Having a strict limit to watch is much better, because you always catch a problem regardless of whether it turns from warning to critical in 15 minutes or in a week. This is exactly what Nagios does. Each check performed by Nagios is turned from numeric values (such as the amount of disk space or CPU usage) to one of the three possible states.

Another benefit is a report stating that X services are up and running, Y are in warning state, and Z are currently critical, which is much more readable than a matrix of values. It saves you the time of analyzing what's working and what's failing. It can also help prioritize what needs to be handled first, and which problems can be handled later.

Nagios performs all of its checks using plugins. These are external components for which Nagios passes information on what should be checked and what the warning and critical limits are. Plugins are responsible for performing the checks and analyzing results. The output from such a check is the status (working, questionable, or failure) and additional text describing information on the service in details. This text is mainly intended for system administrators to be able to read the detailed status of a service.

Nagios comes with a set of standard plugins that allow performance checks for almost all services your company might offer. See Chapter 4, Using the Nagios Plugins, for detailed information on plugins that are developed along with Nagios. Moreover, if you need to perform a specific check (for example, connect to a Web service and invoke methods), it is very easy to write your own plugins. And that's not all—they can be written in any language and it takes less than 15 minutes to write a complete check command! Chapter 11, Programming Nagios, talks about that ability in more detail.

The benefits of monitoring resources

There are many reasons for you to ensure that all your resources are working as expected. If you're still not convinced after reading the introduction to this chapter, here are a few important points why it is important to monitor your infrastructure.

The main reason is quality improvement. If your IT staff can notice failures quicker by using a monitoring tool, they will also be able to respond to them much faster. Sometimes it takes hours or days to get the first report of a failure even if many users bump into errors. Nagios ensures that if something is not working, you'll know about it. In some cases, event handling can even be done so that Nagios can switch to the backup solution until the primary process is fixed. A typical case would be to start a dial-up connection and use it as a primary connection in cases when the company VPN is down.

Another reason is much better problem determination. Very often what the users report as a failure is far from the root cause of the problem, such as an email system is down due to the LDAP service not working correctly. If you define dependencies between hosts correctly, then Nagios will point out that the POP3 e-mail server is assumed to be not working because the LDAP service that it depends upon has a problem. Nagios will start checking the e-mail server as soon as the problem with LDAP has been resolved.

Nagios is also very flexible when it comes down to notifying people of what isn't functioning correctly. In most cases, your company has a large IT team or multiple teams. Usually, you want some people to handle servers, others to handle network switches/routers/modems. There might also be a team responsible for network printers or a division is made based on geographical locations. You can instruct Nagios on who is responsible for particular machines or groups of machines, so that when something is wrong, the right people will get to know of it. You can also use Nagios' web interface to manage who is working on what issue.

Monitoring resources not only is useful for finding problems, but also saves you from having them—Nagios handles warnings and critical situations differently. This means that it's possible to be aware of situations that may become problems really soon. For example, if your disk storage on an e-mail server is running out, it's better to be aware of this situation before it becomes a critical issue.

Monitoring can also be set up on multiple machines across various locations. These machines will then communicate all their results to a central Nagios server so that information on all hosts and services in your system can be accessed from a single machine. This gives you a more accurate picture of your IT infrastructure, as well as allows testing more complex systems such as firewalls. For example, it is vital that a testing environment is accessible from a production environment, but not the other way around.

It is also possible to set up a Nagios server outside the company's intranet (for example, over a dedicated DSL) to make sure that traffic from the Internet is properly blocked. It can be used to check if only certain services are available, for example, verify that only SSH and Hypertext Transfer Protocol (HTTP) are accessible from external IP addresses, and that services such as databases are inaccessible to users.

Main features

Nagios' main strength is flexibility—it can be configured to monitor your IT infrastructure in the way you want it. It also has a mechanism to react automatically to problems and has a powerful notification system. All of this is based on a clear object definition system, which in turn is based on a few types of objects, shown as follows:

Commands: These are definitions of how Nagios should perform particular types of checks. They are an abstraction layer on top of actual plugins that allow you to group similar types of operations.

Time periods: These are date and time spans at which an operation should or should not be performed. For example, Monday–Friday, 09:00–17:00.

Hosts and host groups: These are devices along with the possibility to group hosts. A single host might be a member of more than one group.

Services: These are various functionalities or resources to monitor on a specific host. For example, CPU usage, storage space, or Web server.

Contacts and contact groups: These are people that should be notified with information on how and when they should be contacted; contacts can be grouped, and a single contact might be a member of more than one group.

Notifications: These define who should be notified of what, for example, all errors for the linux-servers host group should go to the linux-admins contact group during working hours and to the critsit-team contact group outside of working hours. Notifications are not strictly an object, but a combination of all the preceding objects and are an essential part of Nagios.

Escalations: These are an extension to notifications; they define that after an object is in same state for specific period of time, other people should get notified of certain events—for example, a critical server being down for more than 4 hours should alert IT management so that they track the issue.

A beneficial feature of using Nagios is that it is a mature dependency system. For any administrator, it is obvious that if your router is down, then all machines accessed via it will fail. Some systems don't take that into account, and in such cases, you get a list of several failing machines and services. Nagios allows you to define dependencies between hosts to reflect actual network topology. For example, if a router that connects you to the rest of your network is down, Nagios will not perform checks for the subsequent parts and machines that are dependent on the router. This is illustrated in the following figure:

You can also define that a particular service depends on another service, either on the same host or a different host. In case one of the dependent services is down, a check for a service is not even performed.

For example, in order for your company's intranet application to function properly, both an underlying Web server and database server must be running properly. So, if a database service is not working properly, Nagios will not perform checks and/or not send notifications that your application is not working, because the root cause of the problem is that the database is not working properly. The database server might be on the same host or a different host. If the database is not working properly, if the dependent machine is down or not accessible, all services dependent on the database service will not be checked as well.

Nagios offers a consistent system of macro definitions. These are variables that can be put into all object definitions and depend on the context. They can be put inside commands, and depending on the host, service, and many other parameters, macro definitions are substituted accordingly. For example, a command definition might use an IP address of the host it is currently checking in all remote tests. It also makes it possible to put information such as the previous and current status of a service in a notification e-mail. Nagios 3 also offers various extensions to macro definitions, which make it an even more powerful