Create a new directory at the specified path. Optionally set the UNIX mode (permissions).
AI agents use filesystem_mkdir 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.
Creating directories is a reversible write operation - the directory can be deleted later. It does not execute arbitrary code, delete existing data, move money, or perform reads. While filesystem modifications have moderate blast radius (could fill disk, create organizational issues, or affect system layout), this is a standard write operation rather than destructive or execute-class severity.
From the tool's definition Tool description explicitly states 'Create a new directory' which is a write operation that modifies the filesystem by creating new data/structure. The ability to set UNIX mode (permissions) adds a configuration dimension to the write operation.
Documented attack patterns abuse exactly the kind of access filesystem_mkdir 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 filesystem_mkdir:
{
"version": "1",
"default": "deny",
"tools": {
"filesystem_mkdir": {
"limits": [
{
"counter": "filesystem_mkdir_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}filesystem_mkdir 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.
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Create a new directory at the specified path. Optionally set the UNIX mode (permissions). 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 filesystem_mkdir: 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.
filesystem_mkdir 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 filesystem_mkdir 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 filesystem_mkdir. 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.
filesystem_mkdir 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.
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279 Truenas tools catalogued and risk-classified — across an index of 43,000+ MCP servers.