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* Added User Guide section outlines. * Added User Guide to menu. * Moved HTTPS example to articles. * Replaced Hello World example with User Guide. * Moved use cases out of examples. * Updated Introduction to add User Guide. * Redirected migrated /use and /articles links. * Added Docker.io section * Added Dockerized section * Added Using Docker section * Added Docker Images section * Added Docker Links section * Added Docker Volumes section Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
44 lines
1.7 KiB
Markdown
44 lines
1.7 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 [*Image*](/terms/image), Docker
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fetches the image and its [*Parent Image*](/terms/image), and repeats the
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process until it reaches the [*Base Image*](/terms/image/#base-image-def). Then
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the [*Union File System*](/terms/layer) adds a read-write layer on top. That
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read-write layer, plus the information about its [*Parent
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Image*](/terms/image)
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and some additional information like its unique id, networking
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configuration, and resource limits is called a **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*](/terms/image) with `docker commit`.
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Once a container is an image, you 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 command line. 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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