# <a name="filesystemBundle" />Filesystem Bundle

## <a name="containerFormat" />Container Format

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.
See also [OS X application bundles](http://en.wikipedia.org/wiki/Bundle_%28OS_X%29) for a similar use of the term *bundle*.

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.

A Standard Container bundle contains all the information needed to load and run a container.
This MUST include the following artifacts:

1. <a name="containerFormat01" />`config.json`: contains configuration data.
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.

2. <a name="containerFormat02" />A directory representing the root filesystem of the container.
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.