# Managing cache

Earthly cache works similarly to Dockerfile layer-based caching. In fact, the same [technology](https://github.com/moby/buildkit) is used underneath.

## Cache layers

Many Earthfile commands create cache layers. A cache layer may be reused in a future build, if the conditions under which it is created are the same.

Examples of commands which create layers are `COPY` and `RUN`.

One of the main things influencing the conditions are "sources". Sources are created through commands like `COPY` and `GIT CLONE`. `RUN`, however, is not a source, even if the command itself involves downloading content from an external location. This means that a `RUN` command, on its own, would always be cached if it has been run under the same circumstances previously (except for the `RUN --push` variant).

For a primer into Dockerfile caching see [this article](https://pythonspeed.com/articles/docker-caching-model/). The same principles apply to Earthfiles.

## Cache location

Earthly cache is persisted in a docker volume called `earthly-cache` on your system. When Earthly starts for the first time, it brings up a BuildKit daemon in a Docker container, which initializes the `earthly-cache` volume. The volume is managed by Earthly's BuildKit daemon and there is a regular garbage-collection for old cache.

{% hint style="info" %}

#### Checking current cache size

You can check the current size of the cache by running:

```bash
sudo du -h /var/lib/docker/volumes/earthly-cache | tail -n 1
```

{% endhint %}

## Specifying cache size limit

The default cache size is adaptable depending on available space on your system. If you would like to limit the cache size more aggressively, you can specify a different limit by modifying the `cache_size_mb` and/or `cache_size_pct` settings in the [configuration](https://docs.earthly.dev/earthly-0.6/docs/earthly-config). For example:

```yaml
global:
  cache_size_mb: 10000
  cache_size_pct: 70
```

## Resetting cache

The cache can be safely deleted manually, if the daemon is not running

```bash
docker stop earthly-buildkitd
docker rm earthly-buildkitd
docker volume rm earthly-cache
```

However, it is easier to simply use the command

```bash
earthly prune --reset
```

which restarts the daemon and resets the contents of the cache volume.

## See also

* [Advanced local caching techniques](https://docs.earthly.dev/earthly-0.6/docs/guides/advanced-local-caching)
* [Remote caching](https://docs.earthly.dev/earthly-0.6/docs/remote-caching)