Perform container management using commands such as podman and skopeo

In this guide, you'll learn how to efficiently handle container images using Skopeo—a powerful command-line utility that complements Podman. With Skopeo, you can manage container images and repositories directly without needing to download them onto your local disk.

Installing Skopeo

Before you begin, ensure that Skopeo is installed on your system. If it's not already installed, you can set it up using YUM. This command installs Skopeo along with all its necessary dependencies:

$ sudo yum install skopeo

Inspecting Container Repositories

Skopeo allows you to examine remote container repositories without using local disk space. The skopeo inspect command retrieves a JSON output containing various details such as repository tags, creation date, Docker version, and system architecture.

For example, to inspect a Fedora image hosted on the Fedora registry, run:

$ skopeo inspect docker://registry.fedoraproject.org/fedora:latest

The output will include information similar to:

{
  "Name": "registry.fedoraproject.org/fedora",
  "Digest": "sha256:655721ff6163ee7664126b5e05ae81598e1b0c3bcf7017c36c4472cb092fef9",
  "RepoTags": [
    "24",
    "25",
    "26-modular"
  ],
  "Created": "2020-04-29T06:48:16Z",
  "DockerVersion": "1.10.1",
  "Labels": {
    "license": "MIT",
    "name": "fedora",
    "vendor": "Fedora Project",
    "version": "32"
  },
  "Architecture": "amd64",
  "OS": "linux",
  "Layers": [
    "sha256:30887217d7b674cfobe64cd3fc00c25aab921cacf35fa0e7b1578500a3e1653"
  ],
  "Env": [
    "DISTTAG=f32container",
    "FGC=f32",
    "container=oci"
  ]
}

Inspecting Container Configurations

Beyond repository details, Skopeo can also inspect the configuration of a container image. By using the --config flag with skopeo inspect, and piping the result through jq, you can view neatly formatted configuration details. For instance:

$ skopeo inspect --config docker://registry.fedoraproject.org/fedora:latest | jq

This command outputs a detailed JSON summary of the container's configuration, including environmental variables, command information, and more:

{
  "created": "2020-04-29T06:48:16Z",
  "architecture": "amd64",
  "os": "linux",
  "config": {
    "Env": [
      "DISTTAG=f32container",
      "FGC=f32"
    ],
    "cmd": [
      "/bin/bash"
    ]
  },
  "Labels": {
    "license": "MIT",
    "name": "fedora",
    "vendor": "Fedora Project",
    "version": "32"
  },
  "rootfs": {
    "type": "layers",
    "diff_ids": [
      "sha256:4ac0fa2b217d3fd63d51e5a6fd59432e543d499cdf2b1ac48fbe424f2ddd1"
    ]
  },
  "history": [
    {
      "created": "2020-04-29T06:48:16Z",
      "comment": "Created by Image Factory"
    }
  ]
}

Copying Container Images

Skopeo is not just for inspection—it also enables you to transfer container images across different storage mechanisms. Whether you're dealing with remote registries, local container storage backends, or OCI directories, Skopeo simplifies the process.

Copying Between Registries

To transfer an image from a public repository to an internal enterprise registry, use the following command:

$ skopeo copy docker://quay.io/buildah/stable docker://registry.kodekloud.com/buildah

Copying from an OCI Layout Directory

If you need to copy an image from a local OCI layout directory to another local directory, this command will do the trick:

$ skopeo copy oci:busybox_ocilayout:latest dir:myemptydirectory

Deleting Container Images

Removing an image from a repository is straightforward with Skopeo’s delete command. Simply specify the image address to delete it:

$ skopeo delete docker://localhost:5000/imagename:latest

Synchronizing Registries

For maintaining consistency between registries, Skopeo offers a synchronization feature. This is especially beneficial when managing a local container registry that mirrors a remote repository. For example, to sync a remote registry with a local directory, run:

$ skopeo sync --src docker --dest dir registry.kodekloud.com/busybox /media/usb

Accessing Skopeo Man Pages

For comprehensive details about Skopeo and its various commands, the manual pages are an excellent resource. Use the man command to explore them.

To access the general Skopeo manual, run:

$ man skopeo

This displays the manual which covers the tool’s overview, usage, and options. Here is an excerpt:

SKOPEO(1) August 2016 SKOPEO(1)

NAME
skopeo -- Command line utility used to interact with local and remote container images and container image registries

SYNOPSIS
skopeo [global options] command [command options]

DESCRIPTION
skopeo is a command line utility providing various operations with container images and container image registries.

Similarly, for information on specific commands such as copying images, inspect the dedicated man page:

$ man skopeo-copy

This command details how to execute the skopeo copy operation, including its options and usage.

Summary

Skopeo is a versatile tool that enhances container management by providing streamlined ways to inspect, copy, delete, and synchronize container images across various platforms. With seamless integration alongside Podman, managing container workflows becomes more efficient and flexible.

For further reading and advanced usage, consider exploring more resources:

• Skopeo GitHub Repository
• Podman Documentation

By following the steps outlined in this guide, you can improve your container management strategies and streamline operations in your containerized environments.