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- :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**.
- Image IDs
- .........
- All images are identified by a 64 hexadecimal digit string (internally a 256bit
- value). To simplify their use, a short ID of the first 12 characters can be used
- on the command line. There is a small possibility of short id collisions, so the
- docker server will always return the long ID.
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