Create a Label in Checkmk

There are three ways to get a label onto a host in Checkmk via the Syncer. All three end with the same step: whitelisting the attribute in the Filter rule so it gets exported.

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Step 1: Whitelist the attribute in the Filter Rule

No matter how you create or transform an attribute, it only reaches Checkmk as a label if you explicitly allow it in the filter rule.

Navigate to Modules → Checkmk → Filter Attributes for Checkmk Export and add the attribute name as an outcome:

Field	Value
Outcome	os

Any existing Syncer attribute can be used here directly — just enter its name as the outcome. The Syncer will then send it as a label to Checkmk on the next export.

Note

This applies to all attributes already on the host — whether they come from an import, inventory, custom attributes, or a rewrite rule. If the name is in the filter, it goes to Checkmk.

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Way 1: Use an existing attribute

If the host already has the attribute you need (e.g. os, location, serial), you only need to whitelist it as described in Step 1. Nothing else is required.

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Way 2: Create a global Custom Attribute

Use this when you want to assign a fixed value (or a Jinja-based value) to all hosts that match a condition — without depending on an existing import attribute.

Navigate to Syncer Rules → Custom Attributes.

Create a new rule:

Field	Example
Condition	os equals windows
Outcome name	monitoring_team
Outcome value	windows_ops

This creates the attribute monitoring_team = windows_ops on every host where os is windows.

Since version 3.12.1, the outcome value supports Jinja:

Outcome value	Result for hostname srv01
team_{{ location }}	team_dc1
{{ os }}-server	windows-server

Then whitelist monitoring_team in the filter rule as described in Step 1.

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Way 3: Create or transform an attribute in the Rewrite section

The Checkmk-specific rewrite rules let you create new attributes or modify existing ones just before the export — without affecting other modules.

Navigate to Modules → Checkmk → Rewrite and Create Custom Syncer Attributes.

Rename an existing attribute

Field	Value
Old Attribute Name	csv_ipaddress
Operation (Name)	Overwrite with fixed String
New Attribute Name	ipaddress
Operation (Value)	Don't change

This renames csv_ipaddress to ipaddress for the Checkmk export only.

Create a new attribute from other attributes

Set an attribute name that does not exist yet as Old Attribute Name — the Syncer will create it:

Field	Value
Old Attribute Name	cmk_alias
Operation (Name)	Don't Use
Operation (Value)	With Jinja Template
New Value	{{ os }}-{{ location }}

This creates cmk_alias = linux-dc1 on a host with os = linux and location = dc1.

Then whitelist cmk_alias in the filter rule as described in Step 1.

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Summary

Approach	Where	When to use
Existing attribute	Filter rule only	Attribute already exists on the host
Custom Attribute	Syncer Rules → Custom Attributes	Assign fixed or computed values based on conditions, across all modules
Rewrite	Modules → Checkmk → Rewrite	Rename, transform, or create attributes specifically for the Checkmk export

All three require the attribute to be whitelisted in Modules → Checkmk → Filter Attributes for Checkmk Export.