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Initial Detection

This document will provide the information you should need to add basic detection for a new OS.


OS discovery is how LibreNMS detects which OS should be used for a device. Generally detection should use sysObjectID or sysDescr, but you can also snmpget an oid and check for a value. snmpget is discouraged because it slows down all os detections, not just the added os.

To begin, create the new OS file which should be called includes/definitions/pulse.yaml. Here is a working example:

os: pulse
text: 'Pulse Secure'
type: firewall
icon: pulse
    - { graph: device_bits, text: 'Device Traffic' }
    - { graph: device_processor, text: 'CPU Usage' }
    - { graph: device_mempool, text: 'Memory Usage' }
    - sysObjectID:
        - .

over: This is a list of the graphs which will be shown within the device header bar (mini graphs top right).

discovery: Here we are detecting this new OS using sysObjectID, this is the preferred method for detection. Other options are available:

  • sysObjectID The preferred operator. Checks if the sysObjectID starts with one of the strings under this item
  • sysDescr Use this in addition to sysObjectID if required. Check that the sysDescr contains one of the strings under this item
  • sysObjectID_regex Please avoid use of this. Checks if the sysObjectID matches one of the regex statements under this item
  • sysDescr_regex Please avoid use of this. Checks if the sysDescr matches one of the regex statements under this item
  • snmpget Do not use this unless none of the other methods work. Fetch an oid and compare it against a value.
            - oid: <someoid>
            - op: <["=","!=","==","!==","<=",">=","<",">","starts","ends","contains","regex","not_starts","not_ends","not_contains","not_regex","in_array","not_in_array","exists"]>
            - value: <'string' | boolean>
  • _except You can add this to any of the above to exclude that element. As an example:
          - .
          - 'Not some pulse'

group: You can group certain OS' together by using group, for instance ios, nx-os, iosxr are all within a group called cisco.

bad_ifXEntry: This is a list of models for which to tell LibreNMS that the device doesn't support ifXEntry and to ignore it:

     - cisco1941
     - cisco886Va
     - cisco2811

mib_dir: You can use this to specify an additional directory to look in for MIBs. An array is not accepted, only one directory may be specified.

mib_dir: juniper

poller_modules: This is a list of poller modules to either enable (1) or disable (0). Check misc/config_definitions.json to see which modules are enabled/disabled by default.

    cisco-ace-serverfarms: false
    cisco-ace-loadbalancer: false

discovery_modules: This is the list of discovery modules to either enable (1) or disable (0). Check misc/config_definitions.json to see which modules are enabled/disabled by default.

     cisco-cef: true
     slas: true
     cisco-mac-accounting: false
Discovery Logic

YAML is converted to an array in PHP. Consider the following YAML:

  - sysObjectID: foo
    sysDescr: [ snafu, exodar ]
    sysObjectID: bar

This is how the discovery array would look in PHP:

       "sysObjectID" => "foo",
       "sysDescr" => [
       "sysObjectID" => "bar",

The logic for the discovery is as follows:

  1. One of the first level items must match
  2. ALL of the second level items must match (sysObjectID, sysDescr)
  3. One of the third level items (foo, [snafu,exodar], bar) must match

So, considering the example:

  • sysObjectID: foo, sysDescr: ANYTHING matches
  • sysObjectID: bar, sysDescr: ANYTHING does not match
  • sysObjectID: bar, sysDescr: exodar matches
  • sysObjectID: bar, sysDescr: snafu matches

OS discovery

OS discovery collects additional standardized data about the OS. These are specified in the discovery yaml includes/definitions/discovery/<os>.yaml or LibreNMS/OS/<os>.php if more complex collection is required.

  • version The version of the OS running on the device.
  • hardware The hardware version for the device. For example: 'WS-C3560X-24T-S'
  • features Features for the device, for example a list of enabled software features.
  • serial The main serial number of the device.
Yaml based OS discovery
  • sysDescr_regex apply a regex or list of regexes to the sysDescr to extract named groups, this data has the lowest precedence
  • <field> specify an oid or list of oids to attempt to pull the data from, the first non-empty response will be used
  • <field>_regex parse the value out of the returned oid data, must use a named group
  • <field>_template combine multiple oid results together to create a final string value. The result is trimmed.
  • <field>_replace An array of replacements ['search regex', 'replace'] or regex to remove
  • hardware_mib MIB used to translate sysObjectID to get hardware. hardware_regex can process the result.
        sysDescr_regex: '/(?<hardware>MSM\S+) .* Serial number (?<serial>\S+) - Firmware version (?<version>\S+)/'
        features: UPS-MIB::upsIdentAttachedDevices.0
            - ENTITY-MIB::entPhysicalName.1
            - ENTITY-MIB::entPhysicalHardwareRev.1
        hardware_template: '{{ ENTITY-MIB::entPhysicalName.1 }} {{ ENTITY-MIB::entPhysicalHardwareRev.1 }}'
        serial: ENTITY-MIB::entPhysicalSerialNum.1
        version: ENTITY-MIB::entPhysicalSoftwareRev.1
        version_regex: '/V(?<version>.*)/'
PHP based OS discovery
public function discoverOS(\App\Models\Device $device): void
    $info = snmp_getnext_multi($this->getDeviceArray(), ['enclosureModel', 'enclosureSerialNum', 'entPhysicalFirmwareRev'], '-OQUs', 'NAS-MIB:ENTITY-MIB');
    $device->version = $info['entPhysicalFirmwareRev'];
    $device->hardware = $info['enclosureModel'];
    $device->serial = $info['enclosureSerialNum'];


If the device has MIBs available and you use it in the detection then you can add these in. It is highly recommended that you add mibs to a vendor specific directory. For instance HP mibs are in mibs/hp. Please ensure that these directories are specified in the yaml detection file, see mib_dir above.

It is highly recommended to use SVG images where possible, these scale and provide a nice visual image for users with HiDPI screens. If you can't find SVG images then please use png.

Create an SVG image of the icon and logo. Legacy PNG bitmaps are also supported but look bad on HiDPI.

  • A vector image should not contain padding.
  • The file should not be larger than 20 Kb. Simplify paths to reduce large files.
  • Use plain SVG without gzip compression.
  • The SVG root element must not contain length and width attributes, only viewBox.
  • Save the icon SVG to html/images/os/$os.svg.
  • Icons should look good when viewed at 32x32 px.
  • Square icons are preferred to full logos with text.
  • Remove small ornaments that are almost not visible when displayed with 32px width (e.g. ® or ™).
  • Save the logo SVG to html/images/logos/$os.svg.
  • Logos can be any dimension, but often are wide and contain the company name.
  • If a logo is not present, the icon will be used.

Hints for Inkscape:

  • You can open a PDF or EPS to extract the logo.
  • Ungroup elements to isolate the logo.
  • Use Path -> Simplify to simplify paths of large files.
  • Use File -> Document Properties… -> Resize page to content… to remove padding.
  • Use File -> Clean up document to remove unused gradients, patterns, or markers.
  • Use File -> Save As -> Plain SVG to save the final image.

By optimizing the SVG you can shrink the file size in some cases to less than 20 %. SVG Optimizer does a great job. There is also an online version.

The final check


./discovery.php -d -h HOSTNAME


lnms device:poll HOSTNAME

At this step we should see all the values retrieved in LibreNMS.

Note: If you have made a number of changes to either the OS's Discovery files, it's possible earlier edits have been cached. As such, if you do not get expected behaviour when completing the final check above, try removing the cache file first:

rm -f cache/os_defs.cache