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Seeing a [container](./what-is-a-container) is an isolated process, where does it get its files and configuration? How do you share those environments?
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Seeing a [container](./what-is-a-container.md) is an isolated process, where does it get its files and configuration? How do you share those environments?
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That's where container images come in!
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A container image is a standardized package that includes all of the files, binaries, libraries, and configurations to run a container.
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That's where container images come in. A container image is a standardized package that includes all of the files, binaries, libraries, and configurations to run a container.
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For a [PostgreSQL](https://hub.docker.com/_/postgres) image, that image will package the database binaries, config files, and other dependencies. For a Python web app, it'll include the Python runtime, your app code, and all of its dependencies.
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There are two important principles of images:
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1. Images are immutable. Once an image is created, it can't be modified. You can only make a new image or add changes on top of it.
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2. Container images are composed of layers. Each layer represented a set of file system changes that add, remove, or modify files.
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2. Container images are composed of layers. Each layer represents a set of file system changes that add, remove, or modify files.
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These two principles let you to extend or add to existing images. For example, if you are building a Python app, you can start from the [Python image](https://hub.docker.com/_/python) and add additional layers to install your app's dependencies and add your code. This lets you focus on your app, rather than Python itself.
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@@ -50,19 +48,18 @@ In this hands-on, you will learn how to search and pull a container image using
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1. Open the Docker Desktop Dashboard and select the **Images** view in the left-hand navigation menu.
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2. Select the **Search images to run** button. If you don't see it, select the _global search bar_ at the top of the screen.
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3. In the **Search** field, enter "welcome-to-docker". Once the search has completed, select the `docker/welcome-to-docker` image.
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4. Select **Pull** to download the image.
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### Learn about the image
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Once you have an image downloaded, you can learn quite a few details about the image either through the GUI or the CLI.
@@ -71,13 +68,11 @@ Once you have an image downloaded, you can learn quite a few details about the i
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2. Select the **docker/welcome-to-docker** image to open details about the image.
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3. The image details page presents you with information regarding the layers of the image, the packages and libraries installed in the image, and any discovered vulnerabilities.
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{{< /tab >}}
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@@ -87,103 +82,101 @@ Follow the instructions to search and pull a Docker image using CLI to view its
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### Search for and download an image
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1. Open a terminal and search for images using the [`docker search`](/reference/cli/docker/search/) command:
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```console
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docker search docker/welcome-to-docker
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```
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1. Open a terminal and search for images using the [`docker search`](/reference/cli/docker/search.md) command:
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You will see output like the following:
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```console
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docker search docker/welcome-to-docker
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```
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```console
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NAME DESCRIPTION STARS OFFICIAL
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docker/welcome-to-docker Docker image for new users getting started w… 20
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```
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You will see output like the following:
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This output shows you information about relevant images available on Docker Hub.
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```console
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NAME DESCRIPTION STARS OFFICIAL
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docker/welcome-to-docker Docker image for new users getting started w… 20
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```
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2. Pull the image using the [`docker pull`](/reference/cli/docker/image/pull/) command.
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This output shows you information about relevant images available on Docker Hub.
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```console
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docker pull docker/welcome-to-docker
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```
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2. Pull the image using the [`docker pull`](/reference/cli/docker/image/pull.md) command.
Status: Downloaded newer image for docker/welcome-to-docker:latest
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docker.io/docker/welcome-to-docker:latest
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```
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You will see output like the following:
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Each of line represents a different downloaded layer of the image. Remember that each layer is a set of filesystem changes and provides functionality of the image.
Status: Downloaded newer image for docker/welcome-to-docker:latest
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docker.io/docker/welcome-to-docker:latest
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```
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Each of line represents a different downloaded layer of the image. Remember that each layer is a set of filesystem changes and provides functionality of the image.
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### Learn about the image
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1. List your downloaded images using the [`docker image ls`](/reference/cli/docker/image/ls/) command:
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```console
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docker image ls
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```
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1. List your downloaded images using the [`docker image ls`](/reference/cli/docker/image/ls.md) command:
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You will see output like the following:
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```console
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docker image ls
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```
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```console
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REPOSITORY TAG IMAGE ID CREATED SIZE
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docker/welcome-to-docker latest eedaff45e3c7 4 months ago 29.7MB
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```
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You will see output like the following:
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The command shows a list of Docker images currently available on your system. The `docker/welcome-to-docker` has a total size of approximately 29.7MB.
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```console
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REPOSITORY TAG IMAGE ID CREATED SIZE
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docker/welcome-to-docker latest eedaff45e3c7 4 months ago 29.7MB
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```
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> **Image size**
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>
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> The image size represented here reflects the uncompressed size of the image, not the download size of the layers.
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The command shows a list of Docker images currently available on your system. The `docker/welcome-to-docker` has a total size of approximately 29.7MB.
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2. List the image's layers using the [`docker image history`](/reference/cli/docker/image/history/) command:
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> **Image size**
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>
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> The image size represented here reflects the uncompressed size of the image, not the download size of the layers.
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```console
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docker image history docker/welcome-to-docker
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```
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2. List the image's layers using the [`docker image history`](/reference/cli/docker/image/history.md) command:
<missing> 5 months ago /bin/sh -c #(nop) CMD ["/bin/sh"] 0B
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<missing> 5 months ago /bin/sh -c #(nop) ADD file:ff3112828967e8004… 7.66MB
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```
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> **Viewing the full command**
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>
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> If you add the `--no-trunc` flag to the command, you will see the full command. Note that, since the output is in a table-like format, longer commands will cause the output to be very difficult to navigate.
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This output shows you all of the layers, their sizes, and the command used to create the layer.
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> **Viewing the full command**
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>
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> If you add the `--no-trunc` flag to the command, you will see the full command. Note that, since the output is in a table-like format, longer commands will cause the output to be very difficult to navigate.
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{{< /tab >}}
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{{< /tabs >}}
@@ -194,12 +187,12 @@ In this walkthrough, you searched and pulled a Docker image. In addition to pull
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The following resources will help you learn more about exploring, finding, and building images:
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- [Docker Trusted Content](/trusted-content/)
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- [Docker Official Images docs](/trusted-content/official-images/)
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