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slug: /1234/dagger-types-reference
displayed_sidebar: "0.2"
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# Dagger Types Reference

Dagger Types are primitives that hold internal references to values stored in the Dagger Engine. They extend the CUE type system and can be used in [Dagger Actions](../core-concepts/1221-action.md). Their definitions can be imported from the `dagger.io/dagger` package.

The following types are available:

| Definition     | File                                                                                        | Description                                           |
| :------------- | :------------------------------------------------------------------------------------------ | :---------------------------------------------------- |
| `#FS`          | [types.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/types.cue)    | Reference to a filesystem tree                        |
| `#Secret`      | [types.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/types.cue)    | Secure reference to an external secret                |
| `#Socket`      | [types.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/types.cue)    | Reference to a network socket: unix or npipe          |

And there's a special instance of a Dagger Type:

| Definition     | File                                                                                        | Type  | Description                                   |
| :------------- | :------------------------------------------------------------------------------------------ | : --- | :-------------------------------------------- |
| `#Scratch`     | [values.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/values.cue)  | `#FS` | An empty filesystem tree                      |

## Data structures

There's also some data structures that are tightly coupled to [core actions](./1222-core-actions-reference.md). Their definitions are in the `dagger.io/dagger/core` package.

### Related to mounts

| Definition     | File                                                                                             | Description                                           |
| :------------- | :----------------------------------------------------------------------------------------------- | :---------------------------------------------------- |
| `#Mount`       | [core/exec.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/core/exec.cue) | Transient filesystem mount                            |
| `#CacheDir`    | [core/exec.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/core/exec.cue) | A (best effort) persistent cache dir                  |
| `#TempDir`     | [core/exec.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/core/exec.cue) | A temporary directory for command execution           |

### Related to container images

| Definition     | File                                                                                             | Description                                           |
| :------------- | :----------------------------------------------------------------------------------------------- | :---------------------------------------------------- |
| `#ImageConfig` | [core/image.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/image.cue)    | Container image config                                |
| `#HealthCheck` | [core/image.cue](https://github.com/dagger/dagger/blob/v0.2.4/pkg/dagger.io/dagger/image.cue)    | Container health check                                |