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As we know, that Docker Images command will list

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out all of the Docker Images stored in our machine

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with some basic information, such as image id,

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repository name, and image tag to identify

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different images. But what if we want to know more

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about any particular image?

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Well, for that, we have docker inspect command.

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'docker inspect' command returns information about every single

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Docker object who has contributed in the creation

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of a particular Docker Image, which can be very

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useful at the time of debugging. Let's list out

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all of the Ubuntu images available on our local

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machine by writing command docker images ubuntu.

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Here we are, we have four ubuntu images with

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different image tags under ubuntu repository.

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Let's inspect ubuntu:latest Docker image,

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type docker image inspect command followed by the

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image name that you want to inspect. We will type

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ubuntu:latest here. Press enter and as

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you can see, it has displayed the detailed

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information about the latest ubuntu image in JSON array.

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Here we can see the extended image Id of

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ubuntu:latest followed by Repo name and RepoDigests

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which is the 64 digit hex number.

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Next, we have Container identifier. Don't confuse it with

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the container running Ubuntu image, it is the

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intermediate container which Docker has created

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while building the Ubuntu image from Dockerfile.

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ContainerConfig is the configuration details

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about the same intermediate container which is

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stored as images metadata for reference.

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Next is the information related to scratch image and it's

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architecture which is used as the base image here.

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It also mentions the actual and VirtualSize of

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the final image. And at last, we have RouteFS

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identifier which shows digest of all intermediate

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layers of this image. If you want to access a

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specific detail about an image, you can format the

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output of docker inspect command, type docker inspect

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followed by the format tag.

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Provide arguments to format flag between inverted commas,

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RepoTags and RepoDigest separated by colon.

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At last, type docker image name, press enter and as

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a result, we got the RepoTag and RepoDigest of ubuntu:latest.

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We can also save the inspect

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results of an image to a file in JSON format for

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future references. Here we want to store the

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configuration details about this image in a text file.

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To do so, type 'docker image inspect --format',

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followed by json .Config in double inverted

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commas and curly braces, 'ubuntu' and store the

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result in 'inspect_report_ubuntu.txt' file.

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It is just a name that we have given to the file.

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You can give any name which you want.

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List out all of the available files.

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inspect report Ubuntu has been successfully

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created. Let's check out the contents of this file.

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Config details about latest Ubuntu image

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is available in the text file.

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If you remember, RootFS identifier in the

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inspection of ubuntu:latest image showed only the

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digest of all intermediate layers in the image.

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Based on only digests it is difficult to determine

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how the image was built, for that we have docker

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history command. 'docker history' will show us all

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the intermediate layers of an image. Let's find

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out the intermediate layers of this image.

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Type 'docker image history ubuntu' in terminal, we got

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all the intermediate layers for our latest Ubuntu image.

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These layers are stacked sequentially,

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starting from the base image at the bottom to the

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CMD layer at the top of the results.

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All the layers have their associated image ids, sizes and

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their creation time. To dig deeper into this, let

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us find history of one of the image which we have

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built on our local Docker host. We will find

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history of img_apache. Now type docker image history

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followed by the image name, which is

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img_apache and press enter. You might

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be wondering why some of the rows have image

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column in both the results contained missing

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and some of them have their image ids. As you may

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remember, the intermediate image ids are given to

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the layers created by Dockerfile instructions.

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And they can be used for caching purpose by our own

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Docker host. But if an image is pulled from Docker

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Hub, such caching would not happen and since it

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may cause environmental clashes. So we are not

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provided any image ids for intermediate layers

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of pulled images, all we can know is they exist.

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We have two types of intermediate images,

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which are easy to distinguish, one, which are built

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by some other Docker host and we have just used it

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as base image and the ones which are committed by

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our instructions. You can also identify them by

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the time they were committed. The base image

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intermediate layers are 17 months old,

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whereas the other ones are committed just a few hours ago.