Update an existing tunable by its ID. Use tunable_list to find the ID. All fields are optional — only provide the ones to change.
AI agents use tunable_update to create or update resources in Truenas — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Truenas environment.
This tool modifies system tunables (kernel/runtime parameters) on a TrueNAS SCALE instance. While it is a reversible write operation (values can be changed back), modifying system tunables can have significant system-wide impact, potentially destabilizing the system or causing service outages if incorrect values are applied. The severity is high due to the blast radius of misconfigured kernel or system parameters.
From the tool's definition Update an existing tunable by its ID. All fields are optional — only provide the ones to change.
Documented attack patterns abuse exactly the kind of access tunable_update gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Truenas, and nothing reaches the server without passing your rules. This is the rule we recommend for tunable_update:
{
"version": "1",
"default": "deny",
"tools": {
"tunable_update": {
"limits": [
{
"counter": "tunable_update_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}tunable_update stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Update an existing tunable by its ID. Use tunable_list to find the ID. All fields are optional — only provide the ones to change. It is categorised as a Write tool in the Truenas MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Truenas MCP server in PolicyLayer and add a rule for tunable_update: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Truenas. Nothing to install.
tunable_update is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the tunable_update rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for tunable_update. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
tunable_update is provided by the Truenas MCP server (spranab/truenas-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Truenas, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
279 Truenas tools catalogued and risk-classified — across an index of 43,000+ MCP servers.