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41 lines
1.4 KiB
ReStructuredText
41 lines
1.4 KiB
ReStructuredText
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:title: Container
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:description: Definitions of a container
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:keywords: containers, lxc, concepts, explanation, image, container
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.. _container_def:
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Container
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=========
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.. image:: images/docker-filesystems-busyboxrw.png
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Once you start a process in Docker from an :ref:`image_def`, Docker
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fetches the image and its :ref:`parent_image_def`, and repeats the
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process until it reaches the :ref:`base_image_def`. Then the
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:ref:`ufs_def` adds a read-write layer on top. That read-write layer,
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plus the information about its :ref:`parent_image_def` and some
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additional information like its unique id, networking configuration,
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and resource limits is called a **container**.
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.. _container_state_def:
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Container State
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...............
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Containers can change, and so they have state. A container may be
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**running** or **exited**.
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When a container is running, the idea of a "container" also includes a
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tree of processes running on the CPU, isolated from the other
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processes running on the host.
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When the container is exited, the state of the file system and
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its exit value is preserved. You can start, stop, and restart a
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container. The processes restart from scratch (their memory state is
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**not** preserved in a container), but the file system is just as it
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was when the container was stopped.
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You can promote a container to an :ref:`image_def` with ``docker
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commit``. Once a container is an image, you can use it as a parent for
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new containers.
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