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Merge pull request #408 from yangyuqian/explain_downloaded_image_and_container_size 

Explain downloaded image and container sizes
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John Mulhausen 2016-11-28 14:55:08 -08:00 committed by GitHub
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@ -559,6 +559,35 @@ Delete the `training/sinatra` image as you don't need it anymore.
> **Note:** To remove an image from the host, please make sure
> that there are no containers actively based on it.
## Check sizes of images and containers
An image is
[stored in layers](../userguide/storagedriver/imagesandcontainers.md),
shared with other images on the host, so the real disk usage depends on
how much layer overlap is happening between images on a host.
A container runs on
[a writable layer](../userguide/storagedriver/imagesandcontainers.md#/container-and-layers)
on top of a readonly rootfs.
Use `docker history` to see the size of image layers on your host:
$ docker history centos:centos7
IMAGE CREATED CREATED BY SIZE
970633036444 6 weeks ago /bin/sh -c #(nop) CMD ["/bin/bash"] 0 B
<missing> 6 weeks ago /bin/sh -c #(nop) LABEL name=CentOS Base Imag 0 B
<missing> 6 weeks ago /bin/sh -c #(nop) ADD file:44ef4e10b27d8c464a 196.7 MB
<missing> 10 weeks ago /bin/sh -c #(nop) MAINTAINER https://github.c 0 B
Check the size of containers with `docker ps -s`:
$ docker ps -s
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES SIZE
cb7827c19ef7 docker-docs:is-11160-explain-image-container-size-prediction "hugo server --port=8" About a minute ago Up About a minute 0.0.0.0:8000->8000/tcp evil_hodgkin 0 B (virtual 949.2 MB)
# Next steps
Until now you've seen how to build individual applications inside Docker