Zabbix 5.0.47 API can't return vfs.fs.size[/,free] unless item exists

[Steve_cc]

Hi all,

I encountered a behavior difference between Zabbix 5.0.47 and Zabbix 7.4 regarding filesystem monitoring items retrieved via API.

Environment

• Zabbix Server: 5.0.47
• Template: Template OS Linux by Zabbix agent
• Agent type: Zabbix agent (passive)
• API used to retrieve item history / last values

Observed behavior (Zabbix 5.0.47)

When querying data for the item key:
vfs.fs.size[/,free]
the API response does not contain any value.

However, the agent itself clearly returns data:
zabbix_get -s 192.168.xxx.xxx -k vfs.fs.size[/,free]

This confirms:

• Agent side works correctly
• Item key is valid
• OS-level metric is available

After manually creating an item with key vfs.fs.size[/,free] under:

Template OS Linux by Zabbix agent → Items

the API immediately starts returning values as expected.

Behavior in Zabbix 7.4

In Zabbix 7.4, using:
vfs.fs.dependent.size[/,free]
data can be retrieved via API without manually creating a traditional item. It works directly through the default template structure.

Question

Why does Zabbix 5.0.47 require the vfs.fs.size[/,free] item to be explicitly created before the API can return data, even though:

• the agent can return the metric via zabbix_get
• the key is valid
• filesystem discovery is already in place

Is this related to architectural differences between:

• legacy filesystem items (vfs.fs.size)
• newer dependent item model (vfs.fs.dependent.size)
• or template design changes introduced in later versions?

Specifically, I’d like to understand whether this is:

• expected behavior in 5.x
• a template design limitation
• or a historical design constraint of how Zabbix stores item data vs agent capabilities