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The Monitoring Plugins Interface
draft-kaestle-monitoring-plugins-interface-00

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Author Lorenz Kästle
Last updated 2023-06-21
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draft-kaestle-monitoring-plugins-interface-00
Network Working Group                                          L. Kästle
Internet-Draft                            The Monitoring Plugins Project
Intended status: Informational                              21 June 2023
Expires: 23 December 2023

                    The Monitoring Plugins Interface
             draft-kaestle-monitoring-plugins-interface-00

Abstract

   This document aims to document the Monitoring Plugin Interface, a
   standard more or less strictly implemented by different network
   monitoring solutions.  Implementers and Users of network monitoring
   solutions, monitoring plugins and libraries can use this as a
   reference point as to how these programs interface with each other.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-kaestle-monitoring-plugins-
   interface/.

   Source for this draft and an issue tracker can be found at
   https://github.com/RincewindsHat/rfc-monitoring-plugins-interface.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 23 December 2023.

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Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
     2.1.  Range expressions . . . . . . . . . . . . . . . . . . . .   3
       2.1.1.  Examples  . . . . . . . . . . . . . . . . . . . . . .   4
   3.  The basic Monitoring Plugin usage . . . . . . . . . . . . . .   4
   4.  Input Parameters for a Monitoring Plugin  . . . . . . . . . .   4
     4.1.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   9
   5.  Output of a Monitoring Plugin . . . . . . . . . . . . . . . .  10
     5.1.  Exit Code . . . . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  Textual Output  . . . . . . . . . . . . . . . . . . . . .  12
       5.2.1.  Human readable output . . . . . . . . . . . . . . . .  12
       5.2.2.  Performance data  . . . . . . . . . . . . . . . . . .  13
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  15
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  15
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   With the emergence of NetSaint/Nagios at the latest, these system and
   their successors/forks have relied on a loose group of programs
   called "Monitoring Plugins" to do the lower level task of actually
   determining the state of a particular entity or conduct measurements
   of certain values.

   This document shall help users and especially developers of those
   programs as a basis on how they should be implemented, how they
   should work and how they should behave.  It encourages the
   standardization of libraries, Monitoring Plugins and Monitoring
   Systems, to reduce the cognitive load on users, administrators and
   developers, if they work with different implementations.

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   This document aims to be as general as possible and not to assume a
   special implementation detail, e.g. the programming language, the
   install mechanism or the monitoring system which executes the
   Monitoring Plugin.

2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.1.  Range expressions

   In many cases thresholds for metrics mark a certain range of values
   where the values is considered to be good or bad if it is inside or
   outside.  While for significant number of metrics a upper (e.g. load
   on unixoid systems) or lower (e.g. effective throughput, free space
   in memory or storage) border might suffice, for some it does not, for
   example a temperature value from a temperature sensor should be
   within certain range (e.g. between 10℃ and 45℃).

   Regarding input parameters this might be handled with options like --
   critical-upper-temperature and --critical-lower-temperature, but this
   creates a problem in the performance data output, if only scalar
   values could be used.  To resolve this situation the _Range
   expression_ format was introduced, with the following definition:

   [@][start:][end]

   where:

   1.  At least start or end MUST be provided.

   2.  start <= end

   3.  If start == 0, then start can be omitted.

   4.  If end is omitted, it has the "value" of positive infinity.

   5.  Negative infinity can be specified with the tilde character ~.

   6.  If the prefix @ IS given, the value exceeds the threshold if it
       is INSIDE the range between start and end (including the
       endpoints).

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   7.  If the prefix @ is NOT given, the value exceeds the threshold if
       it is OUTSIDE of the range between start and end (including the
       endpoints).

2.1.1.  Examples

   +==================+===============================================+
   | Range definition | Exceeds threshold if x...                     |
   +==================+===============================================+
   | 10               | < 0 or > 10, (outside the range of {0 .. 10}) |
   +------------------+-----------------------------------------------+
   | 10:              | < 10, (outside {10 .. &#8734;})               |
   +------------------+-----------------------------------------------+
   | ~:10             | > 10, (outside the range of {-&#8734; .. 10}) |
   +------------------+-----------------------------------------------+
   | 10:20            | < 10 or > 20, (outside the range of {10 ..    |
   |                  | 20})                                          |
   +------------------+-----------------------------------------------+
   | @10:20           | >= 10 and <= 20, (inside the range of {10 ..  |
   |                  | 20})                                          |
   +------------------+-----------------------------------------------+

                                 Table 1

3.  The basic Monitoring Plugin usage

   A Monitoring System executes a Monitoring Plugin.  The Monitoring
   Plugin MAY accept parameters in the form of command line arguments,
   environment variables or a configuration file (the location of which
   MAY in turn be given on the command line or via environment
   variable).  The Monitoring Plugin then proceeds to execute its duty
   and returns the result to the Monitoring System.  Part of the process
   of returning the result is the termination of the execution of the
   Monitoring Plugin itself.

4.  Input Parameters for a Monitoring Plugin

   A Monitoring Plugin MUST expect input parameters as arguments during
   execution, if any are needed/expected at all.  It MAY accept these
   parameters given as _environment variables_ and it MAY accept them in
   a configuration file (with a default path or a path given via
   arguments or _environment variables_).

   In general positional arguments are strongly discouraged.

   Some arguments MUST have this predetermined meaning, if they are
   used:

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   +==========+=========+===============+=============+========+===========+
   |Argument  |Argument |Argument       |Meaning      |optional|can be     |
   |(long)    |(short   |               |             |        |given      |
   |          |version, |               |             |        |multiple   |
   |          |optional)|               |             |        |times      |
   +==========+=========+===============+=============+========+===========+
   |--help    |-h       |None           |Triggers the |no      |-- (makes  |
   |          |         |               |help         |        |no         |
   |          |         |               |functionality|        |difference)|
   |          |         |               |of the       |        |           |
   |          |         |               |Monitoring   |        |           |
   |          |         |               |Plugin,      |        |           |
   |          |         |               |showing the  |        |           |
   |          |         |               |individual   |        |           |
   |          |         |               |parameters   |        |           |
   |          |         |               |and their    |        |           |
   |          |         |               |meaning,     |        |           |
   |          |         |               |examples for |        |           |
   |          |         |               |usage of the |        |           |
   |          |         |               |Monitoring   |        |           |
   |          |         |               |Plugin and   |        |           |
   |          |         |               |general      |        |           |
   |          |         |               |remarks about|        |           |
   |          |         |               |the how and  |        |           |
   |          |         |               |why of the   |        |           |
   |          |         |               |Monitoring   |        |           |
   |          |         |               |Plugin.      |        |           |
   |          |         |               |SHOULD       |        |           |
   |          |         |               |overwrite all|        |           |
   |          |         |               |other        |        |           |
   |          |         |               |options,     |        |           |
   |          |         |               |meaning, they|        |           |
   |          |         |               |are ignored  |        |           |
   |          |         |               |if --help is |        |           |
   |          |         |               |given.  The  |        |           |
   |          |         |               |Monitoring   |        |           |
   |          |         |               |Plugin SHOULD|        |           |
   |          |         |               |exit with    |        |           |
   |          |         |               |state UNKNOWN|        |           |
   |          |         |               |(3).         |        |           |
   +----------+---------+---------------+-------------+--------+-----------+
   |--version |-V       |None           |Shows the    |no      |-- (makes  |
   |          |         |               |version of   |        |no         |
   |          |         |               |the          |        |difference)|
   |          |         |               |Monitoring   |        |           |
   |          |         |               |Plugin to    |        |           |
   |          |         |               |allow users  |        |           |
   |          |         |               |to report    |        |           |

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   |          |         |               |errors better|        |           |
   |          |         |               |and therefore|        |           |
   |          |         |               |help them and|        |           |
   |          |         |               |the          |        |           |
   |          |         |               |developers.  |        |           |
   |          |         |               |The          |        |           |
   |          |         |               |Monitoring   |        |           |
   |          |         |               |Plugin SHOULD|        |           |
   |          |         |               |exit with    |        |           |
   |          |         |               |state UNKNOWN|        |           |
   |          |         |               |(3).         |        |           |
   +----------+---------+---------------+-------------+--------+-----------+
   |--timeout |-t       |Integer        |Sets a limit |no      |no         |
   |          |         |(meaning       |for the time |        |           |
   |          |         |seconds) or a  |which a      |        |           |
   |          |         |time duration  |Monitoring   |        |           |
   |          |         |string         |Plugin is    |        |           |
   |          |         |               |given to     |        |           |
   |          |         |               |execute.     |        |           |
   |          |         |               |This is there|        |           |
   |          |         |               |to enforce   |        |           |
   |          |         |               |the abortion |        |           |
   |          |         |               |of the test  |        |           |
   |          |         |               |and improve  |        |           |
   |          |         |               |the reaction |        |           |
   |          |         |               |time of the  |        |           |
   |          |         |               |Monitoring   |        |           |
   |          |         |               |System (e.g. |        |           |
   |          |         |               |in bad       |        |           |
   |          |         |               |network      |        |           |
   |          |         |               |conditions it|        |           |
   |          |         |               |might be     |        |           |
   |          |         |               |helpful to   |        |           |
   |          |         |               |abort the    |        |           |
   |          |         |               |test         |        |           |
   |          |         |               |prematurely  |        |           |
   |          |         |               |and inform   |        |           |
   |          |         |               |the user     |        |           |
   |          |         |               |about that,  |        |           |
   |          |         |               |than trying  |        |           |
   |          |         |               |forever to do|        |           |
   |          |         |               |something    |        |           |
   |          |         |               |which won't  |        |           |
   |          |         |               |succeed.  Or |        |           |
   |          |         |               |if soft real |        |           |
   |          |         |               |time         |        |           |
   |          |         |               |constraints  |        |           |
   |          |         |               |are present, |        |           |

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   |          |         |               |a result     |        |           |
   |          |         |               |might be     |        |           |
   |          |         |               |worthless    |        |           |
   |          |         |               |altogether   |        |           |
   |          |         |               |after some   |        |           |
   |          |         |               |time).  A    |        |           |
   |          |         |               |sane default |        |           |
   |          |         |               |is probably  |        |           |
   |          |         |               |30 seconds,  |        |           |
   |          |         |               |although this|        |           |
   |          |         |               |depends      |        |           |
   |          |         |               |heavily on   |        |           |
   |          |         |               |the scenario |        |           |
   |          |         |               |and should be|        |           |
   |          |         |               |given a      |        |           |
   |          |         |               |thought      |        |           |
   |          |         |               |during       |        |           |
   |          |         |               |development. |        |           |
   |          |         |               |If the       |        |           |
   |          |         |               |execution is |        |           |
   |          |         |               |terminated by|        |           |
   |          |         |               |this timeout,|        |           |
   |          |         |               |it should    |        |           |
   |          |         |               |exit with    |        |           |
   |          |         |               |state UNKNOWN|        |           |
   |          |         |               |(3) and (if  |        |           |
   |          |         |               |possible)    |        |           |
   |          |         |               |give some    |        |           |
   |          |         |               |helpful      |        |           |
   |          |         |               |output in    |        |           |
   |          |         |               |which stage  |        |           |
   |          |         |               |of the       |        |           |
   |          |         |               |execution the|        |           |
   |          |         |               |timeout      |        |           |
   |          |         |               |occurred.    |        |           |
   +----------+---------+---------------+-------------+--------+-----------+
   |--hostname|-H       |String, meaning|If the       |yes     |no         |
   |          |         |either a DNS   |Monitoring   |        |           |
   |          |         |nameor an IP   |Plugin       |        |           |
   |          |         |address of the |targets      |        |           |
   |          |         |targeted system|exactly one  |        |           |
   |          |         |               |other system |        |           |
   |          |         |               |on the       |        |           |
   |          |         |               |network, this|        |           |
   |          |         |               |option should|        |           |
   |          |         |               |be used to   |        |           |
   |          |         |               |tell it which|        |           |
   |          |         |               |one.  If the |        |           |

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   |          |         |               |Monitoring   |        |           |
   |          |         |               |Plugin does  |        |           |
   |          |         |               |its test just|        |           |
   |          |         |               |locally or   |        |           |
   |          |         |               |the logic    |        |           |
   |          |         |               |does not     |        |           |
   |          |         |               |apply to it, |        |           |
   |          |         |               |this option  |        |           |
   |          |         |               |is, of       |        |           |
   |          |         |               |course,      |        |           |
   |          |         |               |optional.    |        |           |
   +----------+---------+---------------+-------------+--------+-----------+
   |--verbose |-v       |None           |Increases the|yes     |yes        |
   |          |         |               |verbosity of |        |           |
   |          |         |               |the output,  |        |           |
   |          |         |               |thereby      |        |           |
   |          |         |               |breaking the |        |           |
   |          |         |               |suggested    |        |           |
   |          |         |               |rules about a|        |           |
   |          |         |               |short and    |        |           |
   |          |         |               |concise      |        |           |
   |          |         |               |output.  The |        |           |
   |          |         |               |intention is |        |           |
   |          |         |               |to provide   |        |           |
   |          |         |               |more         |        |           |
   |          |         |               |information  |        |           |
   |          |         |               |to a user.   |        |           |
   +----------+---------+---------------+-------------+--------+-----------+
   |--exit-ok |         |The Monitoring |yes          |no      |           |
   |          |         |Plugin exits   |             |        |           |
   |          |         |unconditionally|             |        |           |
   |          |         |with OK (0).   |             |        |           |
   |          |         |Mostly useful  |             |        |           |
   |          |         |for the purpose|             |        |           |
   |          |         |of packaging   |             |        |           |
   |          |         |and testing    |             |        |           |
   |          |         |plugins, but   |             |        |           |
   |          |         |might be used  |             |        |           |
   |          |         |to always      |             |        |           |
   |          |         |ignore errors  |             |        |           |
   |          |         |(e.g. to just  |             |        |           |
   |          |         |collect data). |             |        |           |
   +----------+---------+---------------+-------------+--------+-----------+

                                  Table 2

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4.1.  Examples

   For the execution with --help:

   $ my_check_plugin --help

   the output might look like this:

   my_check_plugin version 3.1.4
   Licensed under the AGPLv1.
   Repository: git.example.com/jdoe/my_check_plugin

   This plugin just says hello. It fails if you don't give it a name.

   Usage:
    my_check_plugin --name NAME [--greeting GREETING]

   Options:
    --help
      this help
    --version
      Shows the version of the plugin
    --name NAME
      if given, uses NAME as a name to greet.
    --greeting GREETING
      if given, uses GREETING instead of Hello.

   Examples:
   $ my_check_plugin --name Jane
   Hello Jane

   $ my_check_plugin --greeting Ciao --name Alice
   Ciao Alice

   This imaginary Monitoring Plugin tries to be really helpful here,
   displays the version, the license and the upstream repository with
   the help (although not necessary), has a short description about the
   purpose, lists the options in an easily readable way and even gives
   some examples.

   For the execution with --version

   $ my_check_plugin --version

   the output might be a bit shorter:

   my_check_plugin version 3.1.4

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   or even:

   3.1.4

   where both show the necessary information.

5.  Output of a Monitoring Plugin

   The output of a Monitoring Plugin consists of two parts on the first
   level, the _Exit Code_ and output in textual form on _stdout_.

5.1.  Exit Code

   The Monitoring Plugin MUST make use of the _Exit Code_ as a method to
   communicate a result to the Monitoring System.  Since the _Exit Code_
   is more or less standardized over different systems as an integer
   number with a width of or greater than 8bit, the following mapping is
   used:

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   +=============+==========+=========================================+
   | Exit Code   | Meaning  | Meaning (extended)                      |
   | (numerical) | (short)  |                                         |
   +=============+==========+=========================================+
   | 0           | OK       | The execution of the Monitoring Plugin  |
   |             |          | proceeded as planned and the tests      |
   |             |          | appeared to function properly and the   |
   |             |          | measured values are within their        |
   |             |          | respective thresholds                   |
   +-------------+----------+-----------------------------------------+
   | 1           | WARNING  | The execution of the Monitoring Plugin  |
   |             |          | proceeded as planned and the tests      |
   |             |          | appeared to _not_ function properly or  |
   |             |          | the measured values are _not_ with      |
   |             |          | their respective thresholds.  The       |
   |             |          | problem(s) do(es) _not_ seem            |
   |             |          | exceptionally grave though and do(es)   |
   |             |          | _not_ require immediate attention       |
   +-------------+----------+-----------------------------------------+
   | 2           | CRITICAL | The execution of the Monitoring Plugin  |
   |             |          | proceeded as planned and the tests      |
   |             |          | appeared to _not_ function properly or  |
   |             |          | the measured values are _not_ with      |
   |             |          | their respective thresholds.  The       |
   |             |          | problem(s) _do(es)_ seem exceptionally  |
   |             |          | grave though and _do(es)_ require       |
   |             |          | immediate attention                     |
   +-------------+----------+-----------------------------------------+
   | 3           | UNKNOWN  | The execution of the Monitoring Plugin  |
   |             |          | _did not_ proceed as planned.  The      |
   |             |          | reasons might be manifold, e.g. missing |
   |             |          | permissions, missing libraries, no      |
   |             |          | available network connection to the     |
   |             |          | destination, etc.. In summary: The      |
   |             |          | Monitoring Plugin could _not_ determine |
   |             |          | the state of whatever it should have    |
   |             |          | been checking and can therefore make no |
   |             |          | reliable statement about it.            |
   +-------------+----------+-----------------------------------------+
   | 4-125       | reserved |                                         |
   |             | for      |                                         |
   |             | future   |                                         |
   |             | use      |                                         |
   +-------------+----------+-----------------------------------------+

                                 Table 3

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5.2.  Textual Output

   The original purpose of the output on _stdout_ was to provide human
   readable information for the user of the Monitoring System, a way for
   the Monitoring Plugin to communicate further details on what
   happened.  This purpose still exists, but was expanded with the, so
   called, performance data to allow the machine readable communication
   of measured values for further processing in the Monitoring System,
   e.g. for the creation of diagrams.

   Therefore the further explanation is split into _human readable
   output_ and _performance data_.

5.2.1.  Human readable output

   This part of the output should give an user information about the
   state of the test and, in the case of problems, ideally hint what the
   origin of the problem might be or what the symptoms are.  If the test
   relies on numeric values, this might be displayed to give an user
   more information about the specific problem.  It might consist of one
   or more lines of printable symbols.

   Although no strict guidelines for creating this part of the output
   can really be given, a developer should keep a potential user in
   mind.  It might, for example, be OK to put the output in a single
   line if there are only one or two items of a similar type (think:
   multiple file systems, multiple sensors, etc.) are present, but not
   if there 10 or 100, although this might present a valid use case.  If
   there are several different items exists in the output of the
   Monitoring Plugin they probably SHOULD be given their own line in the
   output.

5.2.1.1.  Examples

   Remaining space on filesystem "/" is OK

   Sensor temperature is within thresholds

   Available Memory is too low

   Sensore temperature exceeds thresholds

   are OK, but

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   Remaining space on filesystem "/" is OK ( 62GiB / 128GiB )

   Sensor temperature is within thresholds ( 42°C )

   Available Memory is too low ( 126MiB / 32GiB )

   Sensor temperature exceeds thresholds ( 78°C > 70°C )

   are better.

5.2.2.  Performance data

   In addition to the human readable part the output can contain machine
   readable measurement values.  These data points are separated from
   the human readable part by the "|" symbol which is in effect until
   the end of the output.  The performance data then MUST consist of
   space (ASCII 0x20) separated single values, these MUST have the
   following format:

   [']label[']=value[UOM][;warn[;crit[;min[;max]]]]

   with the following definitions:

   1.  label MUST consist of at least on non-space character, but can
       otherwise contain any printable characters except for the equals
       sign (=) or single quotes (').  If it contains spaces, it must be
       surrounded by single quotes

   2.  value is a numerical value, might be either an integer or a
       floating point number.  Using floating point numbers if the value
       is really discreet SHOULD be avoided.  The representation of a
       floating point number SHOULD NOT use the "scientific notation"
       (e.g. 6.02e23 or -3e-45), since some systems might not be able to
       parse them correctly.  Values with a base other then 10 SHOULD be
       avoided (see below for more information on Byte values).

   3.  UOM is the _Unit of measurement_ (e.g.  "B" for _Bytes_, "s" for
       seconds) which gives more context to the Monitoring System.

       *  The following constraints MUST be applied:

          1.  An UOM of % MUST be used for percentage values

          2.  An UOM of c MUST be used for continuous counters (commonly
              used for the sum of bytes transmitted on an interface)

       *  The following recommendations SHOULD be applied:

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          1.  The UOM for Byte values is B and although many systems do
              understand units like KB,KiB, MB, GB, TB they SHOULD be
              avoided, at the least to avoid the ugly hassle about
              people misinterpreting the _base10_ values as _base2_
              values and the other way round.  This is also a prime
              example where floating point number SHOULD NOT be used,
              since there are obviously only integer numbers included.

          2.  The UOM for time is s, meaning seconds, SI-Prefixes (e.g.
              ms for milli seconds) are allowed if necessary or useful.

          3.  In general, SI units and SI prefixes MAY be used as UOM if
              applicable, but the Monitoring System may not understand
              them correctly (mostly in uncommon cases), in that cases
              appropriate workarounds MAY be applied on the side of the
              Monitoring Plugin.  Since the values are not intented to
              be human readable normalized units are recommended (e.g.
              overall_power=14000000000W instead of overall_power=14GW)

          4.  warn and crit are the threshold values for this
              measurement, which may have been given by the user as
              input, may be hardcoded in the Monitoring Plugin or may be
              retrieved from a file or a device or somewhere else during
              the execution of the Monitoring Plugin.  The unit used
              MUST be the same as for _value_. These values are not
              simple numbers, but range expressions (Section 2.1).

          5.  min and max are the minimal respectively the maximal value
              the value could possibly be.  The unit MUST be the same as
              for value.  These values can be omitted, if the value is a
              percentage value, since min and max are always 0 and 100
              in this case.

6.  Implementation Status

   The interface metioned here is implemented by several network
   monitoring systems.  A non-exhaustive list of these systems includes:

   *  Icinga 2

   *  Naemon

   *  Nagios

   The other side of the interface is implemented by several different
   projects, again in an non-exhaustive list:

   *  The Monitoring Plugins Project

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   *  The Nagios Plugins Project

   *  The Linuxfabrik Monitoring Plugins

   *  Madrisan Nagios Plugins

7.  Security Considerations

   Special security considerations are hard to define regarding this
   topic.  Regarding the implementation of this interface, the usual
   programming security considerations should apply (e.g. sanitize
   inputs), but the risks and problems regarding security are dependent
   on the specific implementation and usage.

8.  IANA Considerations

   This document has no IANA actions.

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

Acknowledgments

   TODO acknowledge.

Author's Address

   Lorenz Kästle
   The Monitoring Plugins Project
   Email: lorenz@vulgrim.de

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