You are previewing Nagios, 2nd Edition.

Nagios, 2nd Edition

Cover of Nagios, 2nd Edition by Wolfgang Barth Published by No Starch Press
  1. Nagios: System and Network Monitoring, 2nd Edition
    1. Foreword to the second edition
      1. What's New in the Second Edition?
      2. Information Sources on the Internet
    2. Introduction
      1. The tests
      2. The suppliers of information
      3. Keeping admins up-to-date
      4. Taking in information from outside
      5. Other tools for network monitoring
      6. About This Book
      7. Further notes on the book
      8. Note of Thanks
    3. I. From Source Code to a Running Installation
      1. 1. Installation
      2. 2. Nagios Configuration
      3. 3. Startup
    4. II. In More Detail...
      1. 4. Nagios Basics
      2. 5. Service Checks and How They Are Performed
      3. 6. Plugins for Network Services
      4. 7. Testing Local Resources
      5. 8. Plugins for Special Tasks
      6. 9. Executing Plugins via SSH
      7. 10. The Nagios Remote Plugin Executor (NRPE)
      8. 11. Collecting Information Relevant for Monitoring with SNMP
      9. 12. The Nagios Notification System
      10. 13. Passive Tests with the External Command File
      11. 14. The Nagios Service Check Acceptor (NSCA)
      12. 15. Distributed Monitoring
    5. III. The Web Interface and Other Ways to Visualize Nagios Data
      1. 16. The Classical Web Interface
      2. 17. Flexible Web Interface with the NDOUtils
      3. 18. NagVis
      4. 19. Graphic Display of Performance Data
    6. IV. Part IV Special Applications
      1. 20. Monitoring Windows Servers
      2. 21. Monitoring Room Temperature and Humidity
      3. 22. Monitoring SAP Systems
      4. 23. Processing Events with the EventDB
    7. V. Part V Development
      1. 24. Writing Your Own Plugins
      2. 25. Determining File and Directory Sizes
      3. 26. Monitoring Oracle with the Instant Client
    8. VI. Part VI Appendixes
      1. A. An Overview of the Nagios Configuration Parameters
      2. B. Rapidly Alternating States: Flapping
      3. C. Event Handlers
      4. D. Macros
      5. E. Single Sign-On for the Nagios Web Interface
      6. F. Tips on Optimizing Performance
      7. G. The Embedded Perl Interpreter
      8. H. What's New in Nagios 3.0?

4.3 States of Hosts and Services

Nagios uses plugins for the host and service checks. They provide four different return values (see Table 6-1 in page 105): 0 (OK), 1 (WARNING), 2 (CRITICAL), and 3 (UNKNOWN).

The return value UNKNOWN means that the running of the plugin generally went wrong, perhaps because of wrong parameters. You can normally specify the situations in which the plugin issues a warning or a critical state when it is started.

Nagios determines the states of services and hosts from the return values of the plugin. The states for services are the same as the return values OK, WARNING, CRITICAL, and UNKNOWN. For the hosts the picture is slightly different: the UP state describes a reachable host, DOWN means that the computer is down, ...

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