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# <a name="filesystemBundle" />Filesystem Bundle
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## <a name="containerFormat" />Container Format
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This section defines a format for encoding a container as a *filesystem bundle* - a set of files organized in a certain way, and containing all the necessary data and metadata for any compliant runtime to perform all standard operations against it.
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See also [MacOS application bundles][macos_bundle] for a similar use of the term *bundle* .
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The definition of a bundle is only concerned with how a container, and its configuration data, are stored on a local filesystem so that it can be consumed by a compliant runtime.
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A Standard Container bundle contains all the information needed to load and run a container.
This MUST include the following artifacts:
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1. < a name = "containerFormat01" /> `config.json`: contains configuration data.
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This REQUIRED file MUST reside in the root of the bundle directory and MUST be named `config.json` .
See [`config.json` ](config.md ) for more details.
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2. < a name = "containerFormat02" /> A directory representing the root filesystem of the container.
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While the name of this REQUIRED directory may be arbitrary, users should consider using a conventional name, such as `rootfs` .
This directory MUST be referenced from within the `config.json` file.
While these artifacts MUST all be present in a single directory on the local filesystem, that directory itself is not part of the bundle.
In other words, a tar archive of a *bundle* will have these artifacts at the root of the archive, not nested within a top-level directory.
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[macos_bundle]: https://en.wikipedia.org/wiki/Bundle_%28macOS%29
