| :title: Images |
| :description: Definition of an image |
| :keywords: containers, lxc, concepts, explanation, image, container |
| |
| .. _image_def: |
| |
| Image |
| ===== |
| |
| .. image:: images/docker-filesystems-debian.png |
| |
| In Docker terminology, a read-only :ref:`layer_def` is called an |
| **image**. An image never changes. |
| |
| Since Docker uses a :ref:`ufs_def`, the processes think the whole file |
| system is mounted read-write. But all the changes go to the top-most |
| writeable layer, and underneath, the original file in the read-only |
| image is unchanged. Since images don't change, images do not have state. |
| |
| .. image:: images/docker-filesystems-debianrw.png |
| |
| .. _parent_image_def: |
| |
| Parent Image |
| ............ |
| |
| .. image:: images/docker-filesystems-multilayer.png |
| |
| Each image may depend on one more image which forms the layer beneath |
| it. We sometimes say that the lower image is the **parent** of the |
| upper image. |
| |
| .. _base_image_def: |
| |
| Base Image |
| .......... |
| |
| An image that has no parent is a **base image**. |
