# tunable_update

Update an existing tunable by its ID. Use tunable_list to find the ID. All fields are optional — only provide the ones to change.

Agent View of the PolicyLayer registry record for `tunable_update`. HTML page: https://policylayer.com/tools/spranab-truenas-mcp/tunable-update

## Facts

- Tool: `tunable_update`
- Server: Truenas (`spranab/truenas-mcp`) — https://policylayer.com/tools/spranab-truenas-mcp.md
- Homepage: https://github.com/spranab/truenas-mcp
- Risk category: Write (Medium risk)
- Registry record: grade F, identity unverified
- Server rate-limited: no
- Parameters: 0
- Recommended policy verdict: Rate-limited

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "tunable_update",
    "arguments": {}
  }
}
```

## Why tunable_update is rated Medium

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 own definition: "Update an existing tunable by its ID. All fields are optional — only provide the ones to change."

## Use case

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.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Truenas:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "tunable_update": {
      "limits": [
        {
          "counter": "tunable_update_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on Truenas (278)

- `acme_dns_authenticator_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/acme-dns-authenticator-delete.md
- `alertservice_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/alertservice-delete.md
- `api_key_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/api-key-delete.md
- `app_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/app-delete.md
- `app_rollback` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/app-rollback.md
- `boot_attach_disk` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/boot-attach-disk.md
- `boot_detach_disk` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/boot-detach-disk.md
- `bootenv_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/bootenv-delete.md
- `certificate_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/certificate-delete.md
- `cloud_backup_abort` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/cloud-backup-abort.md
- `cloud_backup_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/cloud-backup-delete.md
- `cloudsync_credentials_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/cloudsync-credentials-delete.md
- `cloudsync_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/cloudsync-delete.md
- `cronjob_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/cronjob-delete.md
- `dataset_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/dataset-delete.md
- `directory_services_leave` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/directory-services-leave.md
- `disk_wipe` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/disk-wipe.md
- `group_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/group-delete.md
- `initshutdown_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/initshutdown-delete.md
- `iscsi_extent_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/iscsi-extent-delete.md
- `iscsi_initiator_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/iscsi-initiator-delete.md
- `iscsi_portal_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/iscsi-portal-delete.md
- `iscsi_target_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/iscsi-target-delete.md
- `iscsi_targetextent_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/iscsi-targetextent-delete.md
- `keychaincredential_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/keychaincredential-delete.md
- `network_interface_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/network-interface-delete.md
- `network_rollback_changes` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/network-rollback-changes.md
- `network_static_route_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/network-static-route-delete.md
- `nfs_share_delete` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/nfs-share-delete.md
- `pool_export` — Destructive — https://policylayer.com/tools/spranab-truenas-mcp/pool-export.md
- …and 248 more: https://policylayer.com/tools/spranab-truenas-mcp.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=spranab-truenas-mcp · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/spranab-truenas-mcp