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Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
46 lines
1.8 KiB
Markdown
46 lines
1.8 KiB
Markdown
page_title: Container
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page_description: Definitions of a container
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page_keywords: containers, lxc, concepts, explanation, image, container
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# Container
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## Introduction
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Once you start a process in Docker from an
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[*Image*](../image/#image-def), Docker fetches the image and its
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[*Parent Image*](../image/#parent-image-def), and repeats the process
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until it reaches the [*Base Image*](../image/#base-image-def). Then the
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[*Union File System*](../layer/#ufs-def) adds a read-write layer on top.
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That read-write layer, plus the information about its [*Parent
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Image*](../image/#parent-image-def) and some additional information like
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its unique id, networking configuration, and resource limits is called a
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**container**.
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## Container State
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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 processes
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running on the host.
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When the container is exited, the state of the file system and its exit
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value is preserved. You can start, stop, and restart a container. The
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processes restart from scratch (their memory state is **not** preserved
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in a container), but the file system is just as it was when the
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container was stopped.
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You can promote a container to an [*Image*](../image/#image-def) with
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`docker commit`. Once a container is an image, you
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can use it as a parent for new containers.
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## Container IDs
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All containers are identified by a 64 hexadecimal digit string
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(internally a 256bit value). To simplify their use, a short ID of the
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first 12 characters can be used on the commandline. There is a small
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possibility of short id collisions, so the docker server will always
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return the long ID.
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