# System Failure Injection

System failure injection allows you to induce different types of sensor and system failures, either programmatically using the [MAVSDK failure plugin](https://mavsdk.mavlink.io/main/en/cpp/api_reference/classmavsdk_1_1_failure.html), or "manually" via a PX4 console like the [MAVLink shell](../debug/mavlink_shell.md#mavlink-shell).
This enables easier testing of [safety failsafe](../config/safety.md) behaviour, and more generally, of how PX4 behaves when systems and sensors stop working correctly.

Failure injection is disabled by default, and can be enabled using the [SYS_FAILURE_EN](../advanced_config/parameter_reference.md#SYS_FAILURE_EN) parameter.

:::warning
Failure injection still in development.
At time of writing (PX4 v1.14):

- It can only be used in simulation (support for both failure injection in real flight is planned).
- It requires support in the simulator.
  It is supported in Gazebo Classic
- Many failure types are not broadly implemented.
  In those cases the command will return with an "unsupported" message.

:::

## Failure System Command

Failures can be injected using the [failure system command](../modules/modules_command.md#failure) from any PX4 console/shell, specifying both the target and type of the failure.

### Syntax

The full syntax of the [failure](../modules/modules_command.md#failure) command is:

```sh
failure <component> <failure_type> [-i <instance_number>]
```

where:

- _component_:
  - 传感器：
    - `gyro`: Gyro.
    - `accel`: Accelerometer.
    - `mag`: Magnetometer
    - `baro`: Barometer
    - `gps`: GPS
    - `optical_flow`: Optical flow.
    - `vio`: Visual inertial odometry.
    - `distance_sensor`: Distance sensor (rangefinder).
    - `airspeed`: Airspeed sensor.
  - Systems:
    - `battery`: Battery.
    - `motor`: Motor.
    - `servo`: Servo.
    - `avoidance`: Avoidance.
    - `rc_signal`: RC Signal.
    - `mavlink_signal`: MAVLink signal (data telemetry).
- _failure_type_:
  - `ok`: Publish as normal (Disable failure injection).
  - `off`: Stop publishing.
  - `stuck`: Report same value every time (_could_ indicate a malfunctioning sensor).
  - `garbage`: Publish random noise. This looks like reading uninitialized memory.
  - `wrong`: Publish invalid values (that still look reasonable/aren't "garbage").
  - `slow`: Publish at a reduced rate.
  - `delayed`: Publish valid data with a significant delay.
  - `intermittent`: Publish intermittently.
- _instance number_ (optional): Instance number of affected sensor.
  0 (default) indicates all sensors of specified type.

### Example

To simulate losing RC signal without having to turn off your RC controller:

1. Enable the parameter [SYS_FAILURE_EN](../advanced_config/parameter_reference.md#SYS_FAILURE_EN).
2. Enter the following commands on the MAVLink console or SITL _pxh shell_:

  ```sh
  # Fail RC (turn publishing off)
  failure rc_signal off

  # Restart RC publishing
  failure rc_signal ok
  ```

## MAVSDK Failure Plugin

The [MAVSDK failure plugin](https://mavsdk.mavlink.io/main/en/cpp/api_reference/classmavsdk_1_1_failure.html) can be used to programmatically inject failures.
It is used in [PX4 Integration Testing](../test_and_ci/integration_testing_mavsdk.md) to simulate failure cases (for example, see [PX4-Autopilot/test/mavsdk_tests/autopilot_tester.cpp](https://github.com/PX4/PX4-Autopilot/blob/main/test/mavsdk_tests/autopilot_tester.cpp)).

The plugin API is a direct mapping of the failure command shown above, with a few additional error signals related to the connection.
