How to List and Inspect Docker Images?

Docker images are important parts of the Docker platform. They act like blueprints for making Docker containers. Each image holds all the files, tools, and settings we need to run a certain app or service. Knowing how to list and check Docker images is very important for developers and system admins. This helps us manage our containers well, save space, and make sure we use the right app versions.

In this article, we will look at different ways to list and check Docker images. We will talk about what Docker images are and why they matter. We will show how to use the Docker command line for listing images. We will also explain how to get detailed info about images. We will cover how to filter images with command options and give tips on how to remove unused Docker images safely. Lastly, we will answer some common questions about Docker images.

  • How to List and Check Docker Images?
  • What Are Docker Images and Why They Matter?
  • How to Use Docker Command Line for Listing Images?
  • How to Get Detailed Info About Docker Images?
  • How to Filter Docker Images with Command Options?
  • How to Safely Remove Unused Docker Images?
  • Common Questions

For more info about Docker, you can check these articles: What is Docker and Why Should You Use It?, What Are Docker Images and How Do They Work?, and What Is a Docker Image and How Is It Different from a Container?.

What Are Docker Images and Their Importance?

Docker images are small, stand-alone packages. They include everything we need to run software. This means they have the code, runtime, libraries, and system tools. Docker images are the base of Docker containers. They help us package and share applications easily.

Importance of Docker Images:

  1. Portability: We can run Docker images in many places. They work the same in development, testing, and production. This means our applications act the same no matter where we put them.

  2. Version Control: We can give each Docker image a version. This helps us manage changes and go back to older versions if needed. It is important for keeping our applications stable and reliable.

  3. Layered Architecture: Docker images are made in layers. This helps us save space and share images easily. We can reuse layers in different images. This cuts down on the space we need and makes building faster.

  4. Isolation: Docker images keep applications and their needs together. This gives us isolation from the host system and other apps. It helps avoid conflicts and makes things safer.

  5. Speed and Efficiency: We can create Docker images fast and easy. This allows us to deploy and scale applications quickly. This is very important in modern DevOps work.

  6. Ecosystem and Community: We can share Docker images through Docker Hub or private places. This helps create a big community. Developers can work together and use ready-made images for common apps.

For more details about Docker images and how they work, check this article on What Are Docker Images and How Do They Work?.

How to Use Docker Command Line for Image Listing?

To list Docker images, we can use the Docker command line interface (CLI). The main command we need is docker images. This command shows all the images that are on our local machine.

Basic Command

docker images

Output Fields

The output usually has these columns:

  • REPOSITORY: This is the name of the image repository.
  • TAG: This is the image tag. It helps to identify different versions of the same image.
  • IMAGE ID: This is a unique ID for the image.
  • CREATED: This shows when the image was created.
  • SIZE: This is the size of the image.

Example

When we run the command:

docker images

We might see an output like this:

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
nginx               latest              4bb46517c4c2        2 weeks ago        132MB
ubuntu              20.04               f643c72bc251        3 weeks ago        72.9MB

Additional Options

To get more details or change how we list images, we can use these options:

  • Filter Images: We can use the --filter option to filter images based on some criteria.
docker images --filter "dangling=true"

This command lists all images that are not tagged and not used by any containers.

  • Format Output: We can format the output using the --format option.
docker images --format "{{.Repository}}:{{.Tag}}"

This command shows only the repository and tag of each image.

With these commands, we can easily manage and check Docker images on our system. For more information about Docker images, we can check out What Are Docker Images and How Do They Work?.

How to Get Detailed Information About Docker Images?

We can get detailed information about Docker images using the docker inspect command. This command gives us lots of info in JSON format about a specific image. It shows us things like its settings, layers, environment variables, and more.

Basic Usage

To inspect a Docker image, we need to use this command:

docker inspect <image_name_or_id>

Example

For example, if we want to inspect an image called nginx, we should run:

docker inspect nginx

Output Information

The output shows many details such as:

  • Id: This is the unique identifier of the image.
  • RepoTags: This is a list of tags related to the image.
  • Created: This shows when the image was created.
  • Size: This tells us the size of the image in bytes.
  • Config: This includes settings like environment variables, entry point, and command.
  • Layers: This gives details of the image layers.

Filtering Output

We can filter the output to get only specific fields using the --format option. For example, if we want just the image ID and size, we can run:

docker inspect --format='{{.Id}}: {{.Size}}' nginx

JSON Output

If we want to see the information in a more readable JSON format, we can use jq like this:

docker inspect nginx | jq

For more details about Docker images, we can read about what Docker images are and how they work.

How to Filter Docker Images Using Command Options?

We can filter Docker images easily using the docker images command with different options. This helps us to reduce the list of images based on certain criteria. We can filter images by their repository name, tag, or image ID.

Basic Filtering with --filter

We can use the --filter option to filter images. Here are some common filter options:

  • reference: This filters images by repository name or tag.

    docker images --filter=reference='ubuntu:*'

  • before: This shows images created before a specific image or time.

    docker images --filter=before='ubuntu:20.04'

  • since: This displays images created after a certain image or time.

    docker images --filter=since='ubuntu:18.04'

  • dangling: This lists images that are not tagged or not used by any container. Set it to true to see only dangling images.

    docker images --filter=dangling=true

Combining Filters

We can also combine several filters to make our search better. For example:

docker images --filter=reference='node:*' --filter=dangling=false

This command will show all non-dangling images that match the node repository.

Using Format for Custom Output

We can use the --format option to change the output of the image list. For example:

docker images --filter=reference='nginx:*' --format '{{.Repository}}:{{.Tag}}'

This command will show only the repository names and tags of the filtered images.

By using these command options well, we can manage and check our Docker images easily. For more information about Docker images and what they do, you can check What Are Docker Images and How Do They Work?.

How to Remove Unused Docker Images Safely?

To remove unused Docker images safely, we can use the docker image prune command. This command helps us clean up images that are not being used and saves disk space. Here are the simple steps and options we can use:

  1. Remove Dangling Images: This command removes images that do not have tags and are not linked to any containers. We can run:

    docker image prune

  2. Remove All Unused Images: If we want to remove all unused images, not just the dangling ones, we add the -a or --all flag. We can run:

    docker image prune -a

  3. Interactive Mode: If we want to confirm before removing images, we can use the --interactive (or -i) option. We can run:

    docker image prune -a -i

  4. Specify Filter Options: We can filter images based on conditions. For example, we can remove images older than a certain time. We can run:

    docker image prune --filter "until=24h"

  5. Remove Specific Images: If we know the IDs or names of the images we want to remove, we can use the docker rmi command. We can run:

    docker rmi <image_id_or_name>

  6. Check for Unused Images: Before we remove images, we can list them to see what we might remove. We can run:

    docker images

  7. Force Removal: If an image is used by a stopped container, we can force its removal by adding the -f flag. We can run:

    docker rmi -f <image_id_or_name>

Using these commands will help us manage and remove unused Docker images safely. This way, our environment stays clean and free from unnecessary data. For more details on Docker images and how to manage them, we can check what are Docker images and how do they work.

Frequently Asked Questions

1. What is a Docker image and how does it work?

A Docker image is a small and standalone package. It has everything we need to run a software. This includes the code, runtime, libraries, and other dependencies. Knowing how Docker images work is very important for us to manage our container apps well. For more details on Docker images, check out what are Docker images and how do they work.

2. How can I list all Docker images on my system?

To see all Docker images on our system, we can use the command line. Just type this command:

docker images

This command shows us a list of all images. It includes the repository, tag, image ID, and size. For more info on using the Docker command line, look at the section on how to use Docker command line for image listing.

3. What is the difference between a Docker image and a Docker container?

A Docker image is a file that has the instructions to create a Docker container. On the other hand, a Docker container is a running version of that image. It is important for us to know this difference if we work with Docker. For a deeper look at this topic, read what is a Docker image and how is it different from a container.

4. How do Docker image layers work?

Docker images are made in layers. Each layer shows a set of file changes. This layered system helps us save space and build images faster since we can reuse layers for different images. For more details, see what is a Docker image layer and why does it matter.

5. How can I safely remove unused Docker images?

To safely remove unused Docker images, we can use this command:

docker image prune

This command will delete dangling images and free space. It is important to manage our Docker images to keep our development area clean. For more tips, visit how to remove unused Docker images safely.

By answering these common questions, we can improve our knowledge on how to list and check Docker images. This helps us manage our containerized apps better.