> For the complete documentation index, see [llms.txt](https://documentation.ocsinventory-ng.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://documentation.ocsinventory-ng.org/user-docs/asset-management/inventory-and-templates.md).
# Inventory and Templates
Assets' inventories in OCS are composed of two main elements: the **base inventory** and the **template inventory**.
## Base inventory
The **base inventory** provides a default set of core information about an asset. This inventory is always available and includes the following fields:
* Name
* Description
* Serial Number
* OS Name
* OS Version
* UUID
* IP Address
* Mac Address
* Domain
* Agent Version
## Template inventory
To extend the **base inventory**, OCS uses a **template system**. These templates add extra fields and define what method should be used to retrieve the corresponding data.
### **Preloaded Templates**
By default, OCS includes six preloaded templates, visible at **Configurations** **→** **Inventory** **→** **Templates**:
* **Legacy** (for compatibility with legacy agents, version 2.X)
* **Linux (Debian based)**
* **Linux (RHEL based)**
* **MacOS**
* **Windows**
* **Generic SNMP**
Template fields and their retrieval methods for Linux
{% tabs %}
{% tab title="Example: Retrieving the Serial Number field" %}
Let's check how the SSN value is retrieved within the Linux (Debian based) template.
Here’s where to find this in the console:
{% stepper %}
{% step %}
Navigate to **Configurations → Templates**.
{% endstep %}
{% step %}
Click the **pen icon** in the **Action** column for the Linux (Debian based) template.
{% endstep %}
{% step %}
On the template details page, click the **Bios** section to expand it.
The top table identifies the inventory section and what command should be used to retrieve data, among other options.
For this template, the command (**Target** field) is `dmidecode`.
The **Retrieval method** field tells us how this command needs to be executed : as a **Bash command** in this instance.
The **Retrieval output** tells the agent how the output of this command should be processed to get the relevant data: **Regex processing**.
{% endstep %}
{% step %}
Locate the **SERIAL** **NUMBER** field.
The table below lists all the fields for this section.
The **Retrieval value** field contains the key or regex that will be used to retrieve the serial number value from the output of `dmidecode`.
{% endstep %}
{% endstepper %}
{% endtab %}
{% endtabs %}
## Template assignment
### Using Rules (automatic)
Templates are assigned to assets based on their operating systems. OCS uses the **Rule Engine** to determine and apply the correct template when an asset inventories itself for the first time.
Out of the box, OCS provides six predefined rules, evaluated against the **OS Name** or **Agent** field of the base inventory and used to assign Templates automatically:
{% columns %}
{% column width="33.33333333333333%" %}
{% endcolumn %}
{% endcolumns %}
{% hint style="info" %}
#### **Notes on automatic assignment:**
* Rules are evaluated with each incoming inventory.
* If no rule matches, the asset will only report using the base inventory.
* Template assignment can also be switched to manual selection per device. More details are available on the [Managing Rules](/administrator-docs/server-setup/configuration/advanced/managing-rules.md) page.
{% endhint %}
### **Manual Template assignment**
In addition to automatic assignment, templates can also be manually assigned to assets from the asset’s detail page.
#### **Steps to manually assign a Template:**
{% stepper %}
{% step %}
Navigate to the asset's detail page.
{% endstep %}
{% step %}
On the right side, click the **Options** icon.
{% endstep %}
{% step %}
Select **Assign inventory template** from the drop-down.
{% endstep %}
{% step %}
Choose the desired template for the asset from the list.
{% endstep %}
{% endstepper %}
{% hint style="info" %}
### A manually assigned template will never be overridden by Rules.
To switch back to automatic assignment:
1. Open the asset’s detail page.
2. Click the **Options** icon at the top right.
3. In the drop-down menu, select **Reset inventory template**.
The template will be reset, and a new one will be automatically assigned during the next inventory if a Rule matches.
{% endhint %}
---
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