Modbus

Pack assets

Templates

The Monitoring Connector Modbus brings a host template:

App-Protocol-Modbus-custom

The connector brings the following service templates (sorted by the host template they are attached to):

App-Protocol-Modbus-custom
Not attached to a host template

No services are created by default for this host template.

Service Alias	Service Template	Service Description
Numeric-Value-Generic	App-Protocol-Modbus-Numeric-Value-Generic-custom	Monitor metrics via Modbus

The services listed above are not created automatically when a host template is applied. To use them, create a service manually, then apply the service template you want.

Collected metrics & status

Here is the list of services for this connector, detailing all metrics linked to each service.

Numeric-Value-Generic

This mode is generic, so there are no default metrics.

Prerequisites

The monitored server must have a Modbus service running and available.

Installing the monitoring connector

Pack

The installation procedures for monitoring connectors are slightly different depending on whether your license is offline or online.

If the platform uses an online license, you can skip the package installation instruction below as it is not required to have the connector displayed within the Configuration > Connectors > Monitoring Connectors menu. If the platform uses an offline license, install the package on the central server with the command corresponding to the operating system's package manager:

Alma / RHEL / Oracle Linux 8
Alma / RHEL / Oracle Linux 9
Debian 11
CentOS 7

dnf install centreon-pack-applications-protocol-modbus

dnf install centreon-pack-applications-protocol-modbus

apt install centreon-pack-applications-protocol-modbus

yum install centreon-pack-applications-protocol-modbus

Whatever the license type (online or offline), install the Modbus connector through the Configuration > Connectors > Monitoring Connectors menu.

Plugin

Since Centreon 22.04, you can benefit from the 'Automatic plugin installation' feature. When this feature is enabled, you can skip the installation part below.

You still have to manually install the plugin on the poller(s) when:

Automatic plugin installation is turned off
You want to run a discovery job from a poller that doesn't monitor any resource of this kind yet

More information in the Installing the plugin section.

Use the commands below according to your operating system's package manager:

Alma / RHEL / Oracle Linux 8
Alma / RHEL / Oracle Linux 9
Debian 11
CentOS 7

dnf install centreon-plugin-Applications-Protocol-Modbus

dnf install centreon-plugin-Applications-Protocol-Modbus

apt install centreon-plugin-applications-protocol-modbus

yum install centreon-plugin-Applications-Protocol-Modbus

Using the monitoring connector

Using a host template provided by the connector

Log into Centreon and add a new host through Configuration > Hosts.
Fill in the Name, Alias & IP Address/DNS fields according to your resource's settings.
Apply the App-Protocol-Modbus-custom template to the host. A list of macros appears. Macros allow you to define how the connector will connect to the resource, and to customize the connector's behavior.
Deploy the configuration. The host appears in the list of hosts, and on the Resources Status page. The command that is sent by the connector is displayed in the details panel of the host: it shows the values of the macros.

Using a service template provided by the connector

If you have used a host template and checked Create Services linked to the Template too, the services linked to the template have been created automatically, using the corresponding service templates. Otherwise, create manually the services you want and apply a service template to them.
Fill in the macros you want (e.g. to change the thresholds for the alerts). Some macros are mandatory (see the table below).

Numeric-Value-Generic

Macro	Description	Default value	Mandatory
CONFIG	Define the configuration of the check (can be a file or a json string directly).		X
EXTRAOPTIONS	Any extra option you may want to add to the command (a --verbose flag for example). All options are listed here.

CONFIG : More information is available here.

Deploy the configuration. The service appears in the list of services, and on the Resources Status page. The command that is sent by the connector is displayed in the details panel of the service: it shows the values of the macros.

How to check in the CLI that the configuration is OK and what are the main options for?

Once the plugin is installed, log into your Centreon poller's CLI using the centreon-engine user account (su - centreon-engine). Test that the connector is able to monitor a resource using a command like this one (replace the sample values by yours):

/usr/lib/centreon/plugins/centreon_protocol_modbus.pl \
	--plugin=apps::protocols::modbus::plugin \
	--mode=numeric-value \
	--tcp-host=''  \
	--config='my-modbus.json' 

The expected command output is shown below:

OK: All metrics are OK | 'metric1'=10;;;; 'metric2'=40;;;; 'metric3'=72;;;; 

The JSON file content can also be passed directly:
--config='{ "selection": { "metric1": { ... } } }'

General structure of the JSON file

{
  "selection": { ... },
  "virtualcurve": { ... },
  "command": { ... }
}

Section	Required	Description
`selection`	Yes	Defines the Modbus registers to read
`virtualcurve`	No	Aggregates and transforms the read values
`command`	No	Customizes the global formatting of the output

Section `selection`

Each entry in selection corresponds to a Modbus register (or group of registers) to read. The key is the name of the resulting metric.

{
  "selection": {
    "<metric_name>": {
      "address": <integer>,
      "quantity": <integer>,
      "type": "<register_type>",
      "display": <true|false>,
      "formatting": { ... }
    }
  }
}

Available keys in `selection`

Key	Type	Required	Description
`address`	integer	Yes	Modbus register address (decimal)
`quantity`	integer	Yes	Number of consecutive registers to read
`type`	string	No	Register type (see values below). Default: `holding`
`display`	boolean	No	Display the raw value in the output. Default: `true`
`formatting`	object	No	Customize the output message (see Formatting section)

Possible values for `type`

Value	Description
`holding`	Holding register (read/write) — most common
`input`	Input register (read-only)
`coil`	Coil (binary value 0/1, read/write)
`discrete`	Discrete input (binary value 0/1, read-only)

Minimal example

{
  "selection": {
    "temperature": {
      "address": 100,
      "quantity": 1,
      "type": "holding",
      "display": true
    }
  }
}

Example with multiple metrics

{
  "selection": {
    "metric1": { "address": 1, "quantity": 1, "type": "holding", "display": true },
    "metric2": { "address": 2, "quantity": 1, "type": "holding", "display": true },
    "metric3": { "address": 3, "quantity": 1, "type": "holding", "display": true }
  }
}

Reading multiple registers at once (`quantity > 1`)

When quantity is greater than 1, the plugin reads multiple consecutive registers and names them automatically <name>.0, <name>.1, etc. This is useful to reduce network exchanges on low-bandwidth links.

{
  "selection": {
    "phases": {
      "address": 1045,
      "quantity": 3,
      "type": "holding",
      "display": false
    }
  }
}

The generated metrics will be named: phases.0, phases.1, phases.2

Section `virtualcurve`

The virtualcurve section allows you to create derived metrics from the values read in selection. It is essential for:

Applying a scaling factor (e.g. dividing by 10 if the device returns 153 for 15.3A)
Aggregating multiple registers (average, sum, min, max)
Defining warning and critical thresholds
Performing complex calculations (e.g. power = current × voltage)

{
  "virtualcurve": {
    "<metric_name>": {
      "aggregation": "<method>",
      "pattern": "<regex>",
      "custom": "<expression>",
      "unit": "<unit>",
      "warning": "<threshold>",
      "critical": "<threshold>",
      "formatting": { ... }
    }
  }
}

Available keys in `virtualcurve`

Key	Type	Required	Description
`aggregation`	string	Yes	Aggregation method for the selected values
`pattern`	string	No	Regular expression to filter source metrics from `selection`. If absent, all metrics are used
`custom`	string	No	Arithmetic expression applied to the aggregated value
`unit`	string	No	Unit of the resulting metric (e.g. `A`, `W`, `°C`)
`warning`	string	No	Warning threshold (Nagios format: simple value or range `min:max`)
`critical`	string	No	Critical threshold (Nagios format: simple value or range `min:max`)
`formatting`	object	No	Customize the output message (see Formatting section)

Possible values for `aggregation`

Value	Description
`avg`	Average of the selected values
`sum`	Sum of the selected values
`min`	Minimum value among the selected values
`max`	Maximum value among the selected values

Section `command` (global formatting)

The command section allows you to modify the display of all metrics globally, and to override this behavior for a specific metric via override.

{
  "selection": { ... },
  "command": {
    "formatting": {
      "printf_msg": "My Metric '%s' value is %.2f",
      "printf_var": "$self->{result_values}->{instance}, $self->{result_values}->{value}"
    },
    "override": {
      "metric3": {
        "formatting": {
          "printf_msg": "Override '%s' value is %.2f",
          "printf_var": "$self->{result_values}->{instance}, $self->{result_values}->{value}"
        }
      }
    }
  }
}

Formatting output messages

The formatting object (available in selection, virtualcurve or command) allows you to customize the text displayed for each metric.

Key	Description
`printf_msg`	Message format, Perl `printf` syntax (e.g. `"Metric '%s' value is %.2f"`)
`printf_var`	Perl variables to inject into the message

Available variables in printf_var:

Variable	Content
`$self->{result_values}->{instance}`	Name of the metric
`$self->{result_values}->{value}`	Numeric value of the metric

Examples of custom calculations (`custom`)

The custom attribute accepts a Perl arithmetic expression that will be applied to the aggregated value. The current value is implicit — the expression starts directly with the operator.

Simple scaling

The device returns 1530 to represent 15.3 A:

{
  "selection": {
    "rawCurrent": { "address": 1045, "quantity": 1, "display": false }
  },
  "virtualcurve": {
    "currentA": {
      "aggregation": "avg",
      "custom": "/10",
      "unit": "A",
      "warning": "45",
      "critical": "50"
    }
  }
}

Power calculation (current × voltage)

From the raw current value, calculate the power in kW (assuming 230V voltage):

{
  "selection": {
    "rawCurrent": { "address": 1045, "quantity": 1, "display": false }
  },
  "virtualcurve": {
    "currentA": {
      "aggregation": "avg",
      "custom": "/10",
      "unit": "A"
    },
    "powerKW": {
      "aggregation": "avg",
      "custom": "/10*230/1000",
      "unit": "kW",
      "formatting": {
        "printf_msg": "Power '%s' is %.3f kW",
        "printf_var": "$self->{result_values}->{instance}, $self->{result_values}->{value}"
      }
    }
  }
}

Aggregating multiple registers with `pattern`

Read 4 registers at once and calculate two averages over pairs:

{
  "selection": {
    "phases": {
      "address": 1,
      "quantity": 4,
      "type": "holding",
      "display": false
    }
  },
  "virtualcurve": {
    "avg_phases_12": {
      "pattern": "phases\\.[01]$",
      "aggregation": "avg",
      "unit": "V"
    },
    "avg_phases_34": {
      "pattern": "phases\\.[23]$",
      "aggregation": "avg",
      "unit": "V"
    }
  }
}

The metrics phases.0, phases.1, phases.2, phases.3 are created automatically by quantity: 4. The pattern then filters which ones are included in each virtualcurve.

Full example — Monitoring an electric generator based on a community use case

This file monitors the battery voltage, current and power of a generator. The device returns values ×10 (e.g. 230 = 23.0 V).

{
  "selection": {
    "batteryVoltageRaw": { "address": 1029, "quantity": 1, "type": "holding", "display": false },
    "currentPhase1Raw":  { "address": 1045, "quantity": 1, "type": "holding", "display": false },
    "currentPhase2Raw":  { "address": 1046, "quantity": 1, "type": "holding", "display": false },
    "currentPhase3Raw":  { "address": 1047, "quantity": 1, "type": "holding", "display": false }
  },
  "virtualcurve": {
    "batteryVoltage": {
      "aggregation": "avg",
      "custom": "/10",
      "unit": "V",
      "warning": "22",
      "critical": "20",
      "formatting": {
        "printf_msg": "Battery voltage '%s' is %.1f V",
        "printf_var": "$self->{result_values}->{instance}, $self->{result_values}->{value}"
      }
    },
    "currentPhase1": {
      "pattern": "currentPhase1Raw",
      "aggregation": "avg",
      "custom": "/10",
      "unit": "A",
      "warning": "45",
      "critical": "50"
    },
    "powerPhase1": {
      "pattern": "currentPhase1Raw",
      "aggregation": "avg",
      "custom": "/10*230/1000",
      "unit": "kW"
    },
    "currentPhase2": {
      "pattern": "currentPhase2Raw",
      "aggregation": "avg",
      "custom": "/10",
      "unit": "A",
      "warning": "45",
      "critical": "50"
    },
    "currentPhase3": {
      "pattern": "currentPhase3Raw",
      "aggregation": "avg",
      "custom": "/10",
      "unit": "A",
      "warning": "45",
      "critical": "50"
    }
  }
}

Threshold format (`warning` / `critical`)

Thresholds follow the standard Nagios/Centreon syntax:

Example	Meaning
`"50"`	Alert if value > 50
`"0:50"`	Alert if value is outside `[0, 50]`
`"@0:50"`	Alert if value is inside `[0, 50]` (inverted)
`"~:50"`	Alert if value > 50 (no lower bound)
`"50:"`	Alert if value < 50

Troubleshooting

Please find the troubleshooting documentation for Centreon Plugins typical issues.

Available modes

In most cases, a mode corresponds to a service template. The mode appears in the execution command for the connector. In the Centreon interface, you don't need to specify a mode explicitly: its use is implied when you apply a service template. However, you will need to specify the correct mode for the template if you want to test the execution command for the connector in your terminal.

All available modes can be displayed by adding the --list-mode parameter to the command:

/usr/lib/centreon/plugins/centreon_protocol_modbus.pl \
	--plugin=apps::protocols::modbus::plugin \
	--list-mode

The plugin brings the following modes:

Mode	Linked service template
numeric-value [code]	App-Protocol-Modbus-Numeric-Value-Generic-custom

Available options

Modes options

All available options for each service template are listed below:

Numeric-Value-Generic

Option	Description
--mode	Define the mode in which you want the plugin to be executed (see--list-mode).
--dyn-mode	Specify a mode with the module's path (advanced).
--list-mode	List all available modes.
--mode-version	Check minimal version of mode. If not, unknown error.
--version	Return the version of the plugin.
--custommode	When a plugin offers several ways (CLI, library, etc.) to get information the desired one must be defined with this option.
--list-custommode	List all available custom modes.
--multiple	Multiple custom mode objects. This may be required by some specific modes (advanced).
--pass-manager	Define the password manager you want to use. Supported managers are: environment, file, keepass, hashicorpvault and teampass.
--verbose	Display extended status information (long output).
--debug	Display debug messages.
--filter-perfdata	Filter perfdata that match the regexp. Example: adding --filter-perfdata='avg' will remove all metrics that do not contain 'avg' from performance data.
--filter-perfdata-adv	Filter perfdata based on a "if" condition using the following variables: label, value, unit, warning, critical, min, max. Variables must be written either %{variable} or %(variable). Example: adding --filter-perfdata-adv='not (%(value) == 0 and %(max) eq "")' will remove all metrics whose value equals 0 and that don't have a maximum value.
--explode-perfdata-max	Create a new metric for each metric that comes with a maximum limit. The new metric will be named identically with a '_max' suffix). Example: it will split 'used_prct'=26.93%;0:80;0:90;0;100 into 'used_prct'=26.93%;0:80;0:90;0;100 'used_prct_max'=100%;;;;
--change-perfdata --extend-perfdata	Change or extend perfdata. Syntax: --extend-perfdata=searchlabel,newlabel,target[,[newuom],[min],[m ax]] Common examples: Convert storage free perfdata into used: --change-perfdata='free,used,invert()' Convert storage free perfdata into used: --change-perfdata='used,free,invert()' Scale traffic values automatically: --change-perfdata='traffic,,scale(auto)' Scale traffic values in Mbps: --change-perfdata='traffic_in,,scale(Mbps),mbps' Change traffic values in percent: --change-perfdata='traffic_in,,percent()'
--extend-perfdata-group	Add new aggregated metrics (min, max, average or sum) for groups of metrics defined by a regex match on the metrics' names. Syntax: --extend-perfdata-group=regex,namesofnewmetrics,calculation[,[ne wuom],[min],[max]] regex: regular expression namesofnewmetrics: how the new metrics' names are composed (can use $1, $2... for groups defined by () in regex). calculation: how the values of the new metrics should be calculated newuom (optional): unit of measure for the new metrics min (optional): lowest value the metrics can reach max (optional): highest value the metrics can reach Common examples: Sum wrong packets from all interfaces (with interface need --units-errors=absolute): --extend-perfdata-group=',packets_wrong,sum(packets_(discard \|error)_(in\|out))' Sum traffic by interface: --extend-perfdata-group='traffic_in_(.*),traffic_$1,sum(traf fic_(in\|out)_$1)'
--change-short-output --change-long-output	Modify the short/long output that is returned by the plugin. Syntax: --change-short-output=pattern~~replacement~~modifier Most commonly used modifiers are i (case insensitive) and g (replace all occurrences). Example: adding --change-short-output='OKUpgi' will replace all occurrences of 'OK', 'ok', 'Ok' or 'oK' with 'Up'
--change-exit	Replace an exit code with one of your choice. Example: adding --change-exit=unknown=critical will result in a CRITICAL state instead of an UNKNOWN state.
--range-perfdata	Rewrite the ranges displayed in the perfdata. Accepted values: 0: nothing is changed. 1: if the lower value of the range is equal to 0, it is removed. 2: remove the thresholds from the perfdata.
--filter-uom	Mask the units when they don't match the given regular expression.
--opt-exit	Replace the exit code in case of an execution error (i.e. wrong option provided, SSH connection refused, timeout, etc). Default: unknown.
--output-ignore-perfdata	Remove all the metrics from the service. The service will still have a status and an output.
--output-ignore-label	Remove the status label ("OK:", "WARNING:", "UNKNOWN:", CRITICAL:") from the beginning of the output. Example: 'OK: Ram Total:...' will become 'Ram Total:...'
--output-xml	Return the output in XML format (to send to an XML API).
--output-json	Return the output in JSON format (to send to a JSON API).
--output-openmetrics	Return the output in OpenMetrics format (to send to a tool expecting this format).
--output-file	Write output in file (can be combined with json, xml and openmetrics options). E.g.: --output-file=/tmp/output.txt will write the output in /tmp/output.txt.
--disco-format	Applies only to modes beginning with 'list-'. Returns the list of available macros to configure a service discovery rule (formatted in XML).
--disco-show	Applies only to modes beginning with 'list-'. Returns the list of discovered objects (formatted in XML) for service discovery.
--float-precision	Define the float precision for thresholds (default: 8).
--source-encoding	Define the character encoding of the response sent by the monitored resource Default: 'UTF-8'.
--rtu-port	The serial port to open. Example: --rtu-port=/dev/ttyUSB0
--rtu-baudrate	A valid baud rate (default: 9600)
--rtu-databits	An integer from 5 to 8 (default: 8)
--rtu-parity	Either 'even', 'odd' or 'none' (default: none)
--rtu-stopbits	1 or 2 (default: 1)
--tcp-host	Host address
--tcp-port	Host port (default: 502)
--timeout	Timeout in seconds (default: 10)
--config	Specify the config (can be a file or a json string directly).
--filter-counters	Filter some counter (can be 'unique' or 'global') Useless, if you use selection/filter but not global/virtual curves
--warning-*	Warning threshold (can be 'unique' or 'global') (Override config if set)
--critical-*	Critical threshold (can be 'unique' or 'global') (Override config if set)

All available options for a given mode can be displayed by adding the --help parameter to the command:

/usr/lib/centreon/plugins/centreon_protocol_modbus.pl \
	--plugin=apps::protocols::modbus::plugin \
	--mode=numeric-value \
	--help

Pack assets​

Templates​

Collected metrics & status​

Prerequisites​

Installing the monitoring connector​

Pack​

Plugin​

Using the monitoring connector​

Using a host template provided by the connector​

Using a service template provided by the connector​

How to check in the CLI that the configuration is OK and what are the main options for?​

General structure of the JSON file​

Section selection​

Available keys in selection​

Possible values for type​

Minimal example​

Example with multiple metrics​

Reading multiple registers at once (quantity > 1)​

Section virtualcurve​

Available keys in virtualcurve​

Possible values for aggregation​

Section command (global formatting)​

Formatting output messages​

Examples of custom calculations (custom)​

Simple scaling​

Power calculation (current × voltage)​

Aggregating multiple registers with pattern​

Full example — Monitoring an electric generator based on a community use case​

Threshold format (warning / critical)​

Troubleshooting​

Available modes​

Available options​

Modes options​