Inspecting a Docker Image

Understanding how Docker images are built from multiple layers can help you optimize, debug, and secure your container workflows. In this guide, we’ll explore essential Docker CLI commands to:

List local images
Examine image history
Inspect detailed metadata
Filter output with JSONPath

Prerequisites
Listing Local Images
Viewing Image History
Inspecting Image Metadata
Filtering with JSONPath
References

Prerequisites

Ensure you have Docker installed and running. Check your version with docker version.
For full installation steps, visit the Docker Docs.

Listing Local Images

To see all images stored on your host machine, use:

docker image list

Example output:

REPOSITORY    TAG       IMAGE ID       CREATED       SIZE
httpd         latest    c2aa7e16edd8   2 weeks ago   165MB
ubuntu        latest    549b9b86cb8d   4 weeks ago   64.2MB

Command	Description
`docker image list`	List all images locally

Viewing Image History

Examining an image’s history reveals each layer and the command that created it. This is especially valuable if the Dockerfile isn’t available.

docker image history ubuntu

Sample output:

IMAGE          CREATED        CREATED BY                                      SIZE
549b9b86cb8d   4 weeks ago    /bin/sh -c #(nop) CMD ["/bin/bash"]             0B
<missing>      4 weeks ago    /bin/sh -c mkdir -p /run/systemd && echo 'do…   7B
<missing>      4 weeks ago    /bin/sh -c set -xe && echo '#!/bin/sh' > ./…    745B
<missing>      4 weeks ago    /bin/sh -c [ -z "$(apt-get indextargets)" ]      987kB
<missing>      4 weeks ago    /bin/sh -c #(nop) ADD file:53f100793e6c0adfc…   63.2MB

Command	Description
`docker image history <IMAGE>`	Show layer-by-layer build commands

Inspecting Image Metadata

The inspect command returns comprehensive image metadata in JSON format, including environment variables, exposed ports, volumes, and more.

docker image inspect ubuntu

Abbreviated example:

[
  {
    "Id": "549b9b86cb8d...",
    "RepoTags": ["ubuntu:latest"],
    "Created": "2020-09-15T23:05:57.348340124Z",
    "ContainerConfig": {
      "ExposedPorts": {
        "80/tcp": {}
      }
    },
    "DockerVersion": "18.09.7",
    "Architecture": "amd64",
    "Os": "linux",
    "Size": 137532780
  }
]

Inspecting very large images may output extensive JSON. Use filtering (see next section) or redirect output to a file:

docker image inspect ubuntu > ubuntu-inspect.json

Command	Description
`docker image inspect <IMAGE>`	Display full image metadata (JSON)

Filtering with JSONPath

Docker’s inspect supports the -f flag with JSONPath templates to extract specific fields.

Common Filters

Filter Template	Description
`-f '{{.Os}}'`	Display the OS
`-f '{{.Architecture}}'`	Show the architecture
`-f '{{.Architecture}} {{.Os}}'`	Combine architecture and OS

docker image inspect httpd -f '{{.Os}}'
docker image inspect httpd -f '{{.Architecture}}'
docker image inspect httpd -f '{{.Architecture}} {{.Os}}'
# Output: amd64 linux

Retrieving Exposed Ports

To list all ports exposed by an image:

docker image inspect httpd \
  -f '{{range $p := .ContainerConfig.ExposedPorts}}{{printf "%s " $p}}{{end}}'

Example output:

80/tcp

Introduction

Docker Engine

Docker Image Management

Docker Engine - Security

Docker Engine - Networking

Docker Engine - Storage

Docker Compose

Docker Swarm

Kubernetes

Docker Engine Enterprise

Docker Trusted Registry

Disaster Recovery

Inspecting a Docker Image

Table of Contents

Prerequisites

Listing Local Images

Viewing Image History

Inspecting Image Metadata

Filtering with JSONPath

Common Filters

Retrieving Exposed Ports

References

Watch Video

​Table of Contents

​Prerequisites

​Listing Local Images

​Viewing Image History

​Inspecting Image Metadata

​Filtering with JSONPath

​Common Filters

​Retrieving Exposed Ports

​References

Watch Video

Table of Contents

Prerequisites

Listing Local Images

Viewing Image History

Inspecting Image Metadata

Filtering with JSONPath

Common Filters

Retrieving Exposed Ports

References