Docker images are the backbone of containerization. They are essentially snapshots of a specific environment, including the operating system, application, and dependencies. They can be used to deploy containers on any machine that has Docker installed, making them a convenient and efficient way to manage and distribute applications. In this article, we’ll explore how to list and manage Docker images on your system.
Understanding the Docker Image Format
Before diving into listing and managing images, it’s essential to understand the format of a Docker image. Images are identified by a unique name and tag, which is in the format of “name:tag”. For example, the official nginx image would be identified as “nginx:latest”. The “name” portion of the image is the name of the image, and the “tag” is used to specify a specific version of the image.
The “latest” tag is used to specify the most recent version of the image. However, you can also specify other tags, such as “1.16” or “1.17”, to indicate a specific version of the image. When listing images, you can use the name or tag to filter and display the images you want to see.
Listing All Docker Images
To list all the images on your system, you can use the “docker images” command. This command will display a list of all the images on your system, including the name, tag, and size of each image.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
nginx latest 34b1b75e1f12 3 weeks ago 109MB
node 14-alpine b9f5f5a5a8a5 4 weeks ago 112MB
redis 5.0.9 7a8c8e2a04d2 3 months ago 97MB
In the example above, we can see that we have three images on our system: nginx, node, and redis. We can also see the tag, image ID, and size of each image.
Filtering Images by Name or Tag
The “docker images” command also allows you to filter images by name or tag. For example, if you only want to see the nginx image, you can use the following command:
$ docker images nginx
REPOSITORY TAG IMAGE ID CREATED SIZE
nginx latest 34b1b75e1f12 3 weeks ago 109MB
You can also filter images by tag, which is useful if you have multiple versions of an image. For example, if you want to see all versions of the node image, you can use the following command:
$ docker images node --all
REPOSITORY TAG IMAGE ID CREATED SIZE
node 14-alpine b9f5f5a5a8a5 4 weeks ago 112MB
node 13-alpine a7b5c5a4a3a2 2 months ago 105MB
Removing Images
As you use Docker, you’ll likely end up with a lot of images on your system. To free up space, you can remove images that you no longer need. To remove an image, you can use the “docker rmi” command followed by the image ID or name:tag.
For example, to remove the nginx image, you can use the following command:
$ docker rmi nginx:latest
Untagged: nginx:latest
Deleted: sha256:34b1b75e1f12...
You can also remove multiple images at once by specifying multiple image IDs or names:tags. For example, to remove both the nginx and node images, you can use the following command:
$ docker rmi nginx:latest node:14-alpine
Untagged: nginx:latest
Deleted: sha256:34b1b75e1f12...
Untagged: node:14-alpine
Deleted: sha256:b9f5f5a5a8a5...
Removing an image will also remove all the associated tags, so be careful when using this command.
Cleaning Up Dangling Images
As you remove images, you may end up with “dangling” images, which are images that are no longer in use but are still taking up space on your system. To remove these images, you can use the “docker image prune” command. This command will remove all the images that are not currently in use.
$ docker image prune
WARNING! This will remove all dangling images.
Are you sure you want to continue? [y/N] y
Deleted Images:
sha256:a7b5c5a4a3a2...
sha256:c6d6e6f6g6h6...
This command is also useful if you want to remove all the images on your system and start fresh.
Conclusion
Docker images are an essential part of containerization and are used to deploy and distribute applications. Understanding how to list and manage images is crucial to keeping your system organized and efficient. By using the “docker images” command, you can list and filter images by name or tag. You can also remove images that you no longer need and clean up dangling images using the “docker rmi” and “docker image prune” commands. With these tools, you can keep your Docker images organized and take control of your system’s resources.
