> For the complete documentation index, see [llms.txt](https://developer.harness.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.harness.io/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-io-attribute-override.md).

# Pod IO attribute override

Pod IO attribute override is a Kubernetes pod-level chaos fault that rewrites the attributes returned by filesystem stat-family syscalls (`stat`, `lstat`, `fstat`) on a target container's mounted volume for a configurable duration. The application sees the wrong attributes (permissions, size, owner, mode, and so on) without the on-disk file actually changing. When the fault ends, the original attributes are reported again immediately.

Use this fault to test how a service behaves when filesystem metadata changes unexpectedly: a permissions drift, a misconfigured `subPath`, a CSI driver that returns inconsistent ownership, or a file that suddenly appears to be a different size.

{% hint style="warning" %}

* Due to the large blast radius of this fault, we recommend you do not execute it in the production environment.
* Through the fault execution, the application pod can potentially fail to perform successful IO writes if the `write` system call is being targeted. This can cause any data produced in this duration to be lost.
* Any data produced before the execution of the fault is not harmed as a result of its execution.
  {% endhint %}

{% hint style="info" %}
**RUN YOUR FIRST EXPERIMENT**

If you have not configured the chaos infrastructure yet, go to [Quickstart](/resilience-testing/chaos-engineering/new-to-chaos-engineering/quickstart.md) to install the chaos infrastructure and run an experiment end to end.
{% endhint %}

***

### Use cases <a href="#use-cases" id="use-cases"></a>

Run this fault when you want to answer concrete questions like:

* **Permission-drift detection:** When the application reads a file's mode and sees `0`, does it refuse to use it, fall back to a default, or crash?
* **Ownership-driven authorization:** If `stat()` reports a different UID for a credentials file, does the runtime continue to load it or treat it as untrusted?
* **Size-based pre-allocation:** Backups and uploaders that pre-allocate based on file size, do they handle a reported size that does not match real bytes?
* **Modification-time caches:** Does an mtime-keyed cache invalidate or thrash when timestamps flicker?
* **Symlink and special-file handling:** Override the file mode to a different type (regular vs symlink vs device) and confirm the application's type checks.

***

### Prerequisites <a href="#prerequisites" id="prerequisites"></a>

* **Kubernetes version:** 1.21 or later. Go to [What's supported](/resilience-testing/chaos-engineering/new-to-chaos-engineering/whats-supported.md) to confirm distribution support.
* **Target pod is Running:** The pod you intend to target is in the `Running` state with a mounted volume.
* **Privileged pods allowed:** The cluster lets you schedule privileged pods in the chaos namespace. GKE Autopilot supports this fault but requires the one-time setup in [Chaos on GKE Autopilot](/resilience-testing/chaos-engineering/use-chaos-engineering/gke-autopilot.md); other locked-down distributions may need similar exemptions.
* **Container runtime access:** The chaos pod can reach the container runtime socket on the target node (`/run/containerd/containerd.sock`, `/var/run/docker.sock`, or `/var/run/crio/crio.sock`).
* **Mounted volume:** The target container has at least one mounted volume reachable at `MOUNT_PATH`.
* **Workload selector defined:** The chaos experiment knows the target workload by kind, namespace, and either names or labels.

***

### Supported environments <a href="#supported-environments" id="supported-environments"></a>

| Platform                                 | Support status                                                                                                 |
| ---------------------------------------- | -------------------------------------------------------------------------------------------------------------- |
| Amazon EKS                               | Supported                                                                                                      |
| Azure AKS                                | Supported                                                                                                      |
| Google GKE                               | Supported                                                                                                      |
| Red Hat OpenShift                        | Supported                                                                                                      |
| Rancher                                  | Supported                                                                                                      |
| VMware Tanzu                             | Supported                                                                                                      |
| Self-managed Kubernetes (CNCF-certified) | Supported                                                                                                      |
| GKE Autopilot                            | Supported with [Autopilot setup](/resilience-testing/chaos-engineering/use-chaos-engineering/gke-autopilot.md) |
| EKS Fargate, ACI virtual nodes           | Not supported (no access to container runtime sockets)                                                         |

***

### Permissions required <a href="#permissions-required" id="permissions-required"></a>

The fault runs under the chaos infrastructure's service account.

| Resource (`apiGroup`)                                               | Verbs                                                                    | Why it is needed                                            |
| ------------------------------------------------------------------- | ------------------------------------------------------------------------ | ----------------------------------------------------------- |
| `pods` (`""`)                                                       | `get`, `list`, `create`, `delete`, `deletecollection`, `patch`, `update` | Discover target pods and run the chaos pod on the same node |
| `pods/log` (`""`)                                                   | `get`, `list`, `watch`                                                   | Stream chaos pod logs for status and debugging              |
| `deployments`, `statefulsets`, `replicasets`, `daemonsets` (`apps`) | `get`, `list`                                                            | Resolve the target workload to the pods it owns             |
| `events` (`""`)                                                     | `get`, `list`, `create`, `patch`, `update`                               | Record fault progress as Kubernetes events                  |
| `jobs` (`batch`)                                                    | `get`, `list`, `create`, `delete`, `deletecollection`                    | Run the chaos job that drives the fault                     |

The default Harness chaos infrastructure service account already includes these permissions.

***

### Fault tunables <a href="#fault-tunables" id="fault-tunables"></a>

Configure the following fault parameters when you add Pod IO attribute override to an experiment in Chaos Studio. Defaults are shown for reference.

**Chaos parameters**

| Tunable                | Description                                                                                                                                                                                              | Default         |
| ---------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------- |
| `ATTRIBUTES`           | JSON object of file attributes and their override values. Common keys: `perm` (mode bits), `size`, `uid`, `gid`, `atime`, `mtime`, `ctime`. Example: `'{"perm":72}'` sets the mode bits to octal `0110`. | `'{"perm":72}'` |
| `PERCENTAGE`           | Percentage of matching stat requests to override, between `0` and `100`. `100` overrides every request.                                                                                                  | `100`           |
| `TOTAL_CHAOS_DURATION` | Duration of the fault in seconds.                                                                                                                                                                        | `60`            |

**Filters**

| Tunable        | Description                                                                                               | Default |
| -------------- | --------------------------------------------------------------------------------------------------------- | ------- |
| `MOUNT_PATH`   | Volume mount path inside the container to scope the fault. Empty applies to all mounts.                   | `""`    |
| `FILE_PATH`    | File path or glob beneath `MOUNT_PATH` to scope the fault. Empty applies to all files under `MOUNT_PATH`. | `""`    |
| `METHOD_TYPES` | Comma-separated syscall types to override: `read`, `write`, `open`. Empty applies to all three.           | `""`    |

**Targeting**

| Tunable                   | Description                                                                                                          | Default    |
| ------------------------- | -------------------------------------------------------------------------------------------------------------------- | ---------- |
| `TARGET_PODS`             | Comma-separated list of pod names to target. Empty selects from the workload's pods using `POD_AFFECTED_PERCENTAGE`. | `""`       |
| `TARGET_CONTAINER`        | Container in the pod whose filesystem to affect. Empty targets the first container in the pod spec.                  | `""`       |
| `NODE_LABEL`              | Label selector to filter target pods by the node they run on. Empty disables node-based filtering.                   | `""`       |
| `POD_AFFECTED_PERCENTAGE` | Percentage of the workload's pods to target. `0` means one pod.                                                      | `0`        |
| `SEQUENCE`                | When multiple pods are targeted, inject `parallel` (all at once) or `serial` (one after another).                    | `parallel` |

**Runtime and helper**

| Tunable             | Description                                                                                                                                                                                                      | Default                           |
| ------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------- |
| `CONTAINER_RUNTIME` | Container runtime on the target nodes. One of `containerd`, `docker`, `crio`.                                                                                                                                    | `containerd`                      |
| `SOCKET_PATH`       | Path to the container runtime socket on the target node. Set to match `CONTAINER_RUNTIME`.                                                                                                                       | `/run/containerd/containerd.sock` |
| `RAMP_TIME`         | Wait period in seconds before and after the fault. Go to [ramp time](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/common-tunables-for-all-faults.md#ramp-time) to read how it is applied. | `0`                               |

Common pod selection tunables (`TARGET_WORKLOAD_KIND`, `TARGET_WORKLOAD_NAMESPACE`, `TARGET_WORKLOAD_NAMES`, `TARGET_WORKLOAD_LABELS`) are documented in [common pod fault tunables](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/common-tunables-for-pod-faults.md). Tunables that apply to every fault are documented in [common tunables for all faults](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/common-tunables-for-all-faults.md).

{% hint style="info" %}
**REFERENCE FOR COMMON ATTRIBUTE KEYS**

Mode bits in `perm` are decimal representations of the underlying octal mode. For example, `420` is octal `0644` (rw-r--r--), and `493` is octal `0755` (rwxr-xr-x).
{% endhint %}

#### Configure for your container runtime <a href="#configure-for-your-container-runtime" id="configure-for-your-container-runtime"></a>

Set `CONTAINER_RUNTIME` and `SOCKET_PATH` to match the runtime on the target node:

| `CONTAINER_RUNTIME`    | `SOCKET_PATH`                     |
| ---------------------- | --------------------------------- |
| `containerd` (default) | `/run/containerd/containerd.sock` |
| `docker`               | `/var/run/docker.sock`            |
| `crio`                 | `/var/run/crio/crio.sock`         |

***

### Fault execution in brief <a href="#fault-execution-in-brief" id="fault-execution-in-brief"></a>

Intercepts filesystem stat-family syscalls inside the target container's mount namespace and rewrites the attributes returned to the caller using the keys and values in `ATTRIBUTES`, optionally limited to a configurable percentage and scoped by path and method.

***

### Expected behavior during fault execution <a href="#expected-behavior-during-fault-execution" id="expected-behavior-during-fault-execution"></a>

* Matched stat syscalls return the overridden attribute values. The on-disk attributes are not modified.
* Applications that gate behavior on `stat()` (permission checks, size pre-allocation, owner-based trust) see the wrong values and react accordingly.
* File-system-walking tools (`ls -l`, `find`, build systems) display the overridden values for files under the filter.
* Operations like `open()`, `read()`, `write()` still go through the real on-disk file unless their behavior depends on the overridden attribute first.

{% hint style="info" %}
**WHEN THE FAULT ENDS**

Stat syscalls return the real on-disk attributes again immediately.
{% endhint %}

#### Signals to watch <a href="#signals-to-watch" id="signals-to-watch"></a>

Attach [resilience probes](/resilience-testing/chaos-engineering/use-chaos-engineering/probes.md) to assert each layer:

* **Permission errors:** Use a [command probe](/resilience-testing/chaos-testing/probes/command-probe.md) to grep container logs for `permission denied` or `EACCES` strings.
* **Pod readiness:** Use a [Kubernetes probe](/resilience-testing/chaos-testing/probes/k8s-probe.md) to fail when the target pod stops being `Ready`.
* **Application error rate:** Use an [HTTP probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/http-probe.md) to detect 5xx responses that correlate with the fault window.

***

### Verify the fault execution effect <a href="#verify-the-fault-execution-effect" id="verify-the-fault-execution-effect"></a>

While the experiment is running, confirm `stat()` returns the override:

1. **Stat a matched file from inside the container.**

   ```bash
   kubectl exec -n <namespace> <target-pod> -c <target-container> -- \
     stat <MOUNT_PATH>/<FILE_PATH>
   ```

   The reported mode (or other overridden attribute) should match the values in `ATTRIBUTES`.
2. **Confirm application-level impact.**

   ```bash
   kubectl logs -n <namespace> <target-pod> -c <target-container> --tail=200
   ```

   Look for permission errors, type-mismatch errors, or unexpected fallbacks tied to the overridden attribute.

***

### Recovery and cleanup <a href="#recovery-and-cleanup" id="recovery-and-cleanup"></a>

* **End of duration:** Stat syscalls return real attributes again automatically.
* **Abort the experiment:** Stopping the experiment from Chaos Studio triggers the same cleanup path.
* **Failed cleanup:** If the application cached the wrong attributes and cannot refresh, restart the target pod.

***

### Limitations <a href="#limitations" id="limitations"></a>

* **Serverless Kubernetes (EKS Fargate, ACI virtual nodes):** These platforms do not expose container runtime sockets and reject the privileged access the fault needs. GKE Autopilot is supported once the one-time setup in [Chaos on GKE Autopilot](/resilience-testing/chaos-engineering/use-chaos-engineering/gke-autopilot.md) is in place.
* **Windows containers:** This fault is supported on Linux pods only.
* **Attributes are reported, not stored:** The on-disk file is unchanged. Use Pod IO mistake or Pod IO error if you need actual writes to be corrupted or rejected.
* **Cached attributes:** Applications that cache stat results (Go's `os.FileInfo`, Java's `File` metadata) may continue to see the overridden values briefly after the fault ends until the cache refreshes.

***

### Troubleshooting <a href="#troubleshooting" id="troubleshooting"></a>

<details>

<summary>Pod IO attribute override experiment stays Pending or never starts in Harness Chaos Engineering</summary>

Inspect the chaos pods in the experiment namespace with kubectl describe pod -n . The most common causes are taints on the target node that the chaos pods do not tolerate, insufficient resources, or a PodSecurity admission policy blocking privileged pods. Add the required tolerations to the experiment or run in a namespace with privileged Pod Security level.

</details>

<details>

<summary>No attribute change observed during pod-io-attribute-override</summary>

The most common causes are: MOUNT\_PATH does not match a real mount inside the container (verify with kubectl exec -- mount); FILE\_PATH filter is too narrow; ATTRIBUTES is not valid JSON; or the application reads cached metadata rather than calling stat. Re-run with PERCENTAGE=100, empty FILE\_PATH, and a minimal ATTRIBUTES value to confirm the path is working.

</details>

<details>

<summary>Connection to container runtime fails for pod-io-attribute-override in Harness Chaos Engineering</summary>

The default SOCKET\_PATH is /run/containerd/containerd.sock. For Docker, set CONTAINER\_RUNTIME=docker and SOCKET\_PATH=/var/run/docker.sock. For CRI-O, set CONTAINER\_RUNTIME=crio and SOCKET\_PATH=/var/run/crio/crio.sock.

</details>

***

### Related faults <a href="#related-faults" id="related-faults"></a>

* [Pod IO error](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-io-error.md): Fail filesystem syscalls with a configurable error code.
* [Pod IO latency](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-io-latency.md): Add delay to filesystem syscalls.
* [Pod IO mistake](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-io-mistake.md): Corrupt filesystem read or write data with wrong values.
* [Pod IO stress](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-io-stress.md): Generate sustained read and write load.
* [Common pod fault tunables](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/common-tunables-for-pod-faults.md): Shared environment variables for selecting target pods and workloads.