CODEWITHSUNDEEP
linuxdocker
Poperton
Poperton

Reputation: 2166

Does docker images list the size of the entire image or just a layer of it?

user@localhost:~/docker-pyzmq$ sudo docker images
REPOSITORY                                               TAG                 IMAGE ID            CREATED             SIZE
alpinepyzmq_raw                                          latest              fd24a753f505        2 minutes ago       23.9MB
<none>                                                   <none>              3f763de0fb0b        7 minutes ago       23.9MB
alpinepyzmq_small                                        latest              c7a1f42d0bfd        14 minutes ago      94.8MB
alpinepyzmq                                              latest              5be9ed0fcbcb        17 minutes ago      317MB
<none>                                                   <none>              97aa31fe216a        19 minutes ago      317MB
<none>                                                   <none>              b167c481edc2        22 minutes ago      338MB
<none>                                                   <none>              fe8504847607        29 minutes ago      304MB
<none>                                                   <none>              5b845a00f4d9        32 minutes ago      79.5MB
<none>                                                   <none>              2d6926b0c665        32 minutes ago      79.5MB

Does the output above mean alpinepyzmq_raw can be run inside a computer and it'll just weight 23.9mb? Or is this size dependent on other layers? If so, how can I figure out the entire image size?

Upvotes: 7

Views: 9226

Answers (3)

abestrad
abestrad

Reputation: 906

The docs can help to answer this question,

The SIZE is cumulative space taken up by the image and all its parent images. This is also the disk space used by the contents of the Tar file created when you docker save an image.

Notice here that: An image will be listed more than once if it has multiple repository names or tags. This single image (identifiable by its matching IMAGE ID) uses up the SIZE listed only once.

Source

Upvotes: 1

vishal sharma
vishal sharma

Reputation: 54

In docker images are created using dockerfile. Each image consists of multiple layers. Each layer corresponds to a certain instruction from dockerfile. Docker uses Union File System to mount these layers on top of each other. Therefore you can think of an image as the final layer built on top of multiple read-only layers (UFS). You can see the layers a docker image is based up on by docker image inspect -f '{{.RootFS.Layers}}' <image>. In general you want to keep your image size as low as possible, therefore use && in your dockerfile extensively. For example:- You will want to prefer

From Ubuntu
RUN aptg-get update && apt-get install vim

rather than

From Ubuntu
RUN apt-get update
RUN apt-get install vim

as, since docker 1.10, the RUN, ADD and COPY statements add a new layer to your image.

Also you should use multi-stage builds where you can use multiple base in same dockerfile, with each of them beginning new stage of build. With this, you can leave everything behind that you don't want in the final image.

The image size shown in the output above is the final image size, and yes you can run this image inside a container but that is not the final size of the container that is running this image. When you run a container from an image, you essentially create a read-write copy of that image inside the container. This is the container layer which allows modification of the entire copy of the image. Therefore your container can grow in size. You can see a container size using docker system df -v

Upvotes: 1

davidxxx
davidxxx

Reputation: 131396

Does the output above mean alpinepyzmq_raw can be run inside a computer and it'll just weight 23.9mb?

Image size and container size are two distinct things.

Image size :

When you execute docker image ls, the column size is not necessarily the size of the image because that is the size of the current image + all these parent images :

The SIZE is the cumulative space taken up by the image and all its parent images. T 23.9

While for a base image without parent such as Alpine, you can consider that the image size.
In docker, parent images are not merged in each child images but stored in distinct layers to be shared.
To know the real size of an image (without the parent sizes), use docker history IMAGE.

Container size :

The container size is not strictly equal to the image size.
Besides, containers use both memory (ram) and disk.
To know disk occupation size :

docker system df

That does echo to the famous df linux command that shows used/free space on disks.

Upvotes: 6

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