# ISystemStartStop

> Optional interface for start/stop notifications on systems.

## Definition

* **Type:** Interface
* **Namespace:** [Unity.Entities](/engine/7000.0/script-reference/unity/entities.md)
* **Assembly:** UnityEngine.EntitiesModule

```csharp
public interface ISystemStartStop
```

## Methods

| Method                                                                                              | Description                                                                                                                                                                                                                                                                                                        |
| --------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| [OnStartRunning](/engine/7000.0/script-reference/unity/entities/isystemstartstop/onstartrunning.md) | Called before the first call to OnUpdate and when a system resumes updating after being stopped or disabled.                                                                                                                                                                                                       |
| [OnStopRunning](/engine/7000.0/script-reference/unity/entities/isystemstartstop/onstoprunning.md)   | Called when this system stops running because no entities match the system's [EntityQuery](/engine/7000.0/script-reference/unity/entities/entityquery.md) objects or because you change the system [SystemState.Enabled](/engine/7000.0/script-reference/unity/entities/systemstate/enabled.md) property to false. |