Hello, and welcome to today's video presentation on pulling an image using Podman on Oracle
Linux 8.
This video provides a series of demos covering inspecting a remote OCI (Open Container Initiative)
image and then pulling that image to your host to run a container at a later time.
So let us get started.
Before jumping onto the system, we need to clarify a few terms.
The first of these is an image.
An image is a non-changeable file containing a minimal operating system, libraries, source
code, tools, and other files needed to run applications.
Sometimes images are referred to as snapshots due to their read-only characteristics.
These images represent the application and the virtual environment at a given point in
time.
The other term is a container.
A container is the run time instance of images.
The container generates a virtualized environment during run-time allowing users to isolate
applications from the system underpinning it.
These containers are compact, portable units in which you can start up an application quickly
and easily.
With these terms covered, open a terminal and connect to your host system.
In this exercise, the host system is a fully patched Oracle Linux 8 instance on Oracle
Cloud Infrastructure.
This instance also has the podman and skopeo packages pre-installed.
To verify these packages are available, type "podman --version; skopeo --version" to display
each program's version.
The semicolon between the commands runs both commands one after the other, regardless of
the first command results.
If these packages are not available, see our other videos on Podman at oracle.com/goto/oraclelinuxlearning
under Virtualization and Container Videos.
Next, search for the Oracle Linux image.
Type the command "podman search oracle | head -n 10".
The search command takes any keyword and looks for images that match the requested criteria.
The "head -n 10" will restrict the command's output to only the first ten lines.
The output shows several images available from the Docker Hub repository.
The image we are interested in is the oraclelinux image associated with the Official Docker
builds of Oracle Linux.
This image also exists in the Oracle Container Registry, but Oracle Linux 8 does not configure
that specific registry location by default.
Details for the configuration and use of the Oracle Container Registry is outside the scope
of this video.
Next, use skopeo to check the information available for the oraclelinux image.
Type the command "skopeo inspect docker://docker.io/library/oraclelinux:8".
When inspecting an image from a registry, identify the container format, the registry
location, and the repository image.
The number 8 after the colon designates one of the images repository or repo tags.
Details on supported tags are available from the URL displayed on the screen.
[ silence ... https://hub.docker.com/_/oraclelinux ]
Hit Enter to execute the command.
Under the RepoTags section of the output displayed, we will discuss the 8 and 8-slim tags in this
demo.
The 8 tag provides an image with the latest version of Oracle Linux 8, while the 8-slim
tag offers the same operating system, but in the smallest possible image.
With the quick inspection complete, time to pull the latest Oracle Linux 8 image.
Type the command "podman pull docker.io/library/oraclelinux:8".
As with the skopeo command, the "podman pull" command takes the registry location, the repository
image, and a repository tag.
To avoid confusion, Oracle removed the latest tag from the Oracle Linux official images
in June 2020.
The latest tag is just a particular tag with a name indicating the last image build.
With Oracle's removal of the latest tag, a user must specify a valid tag when downloading
it.
The output displays podman pulling the image from the repository and completing the various
steps involved.
Verify the image downloaded successfully by typing "podman images."
This command displays a listing of all locally downloaded images.
The information contains the repository from where we pulled the image, the tag for the
specific image, the locally assigned image id, when its maintainer created the image,
and its size.
That completes this demonstration of pulling an image from a repository using Podman.
Thank you for watching this video and enjoy using Oracle Linux 8.
Please check our additional information on Oracle Linux 8 in the Oracle Linux 8 Documentation
or Oracle Linux Learning Library.