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RHCSA - Manage Containers: Find & Retrieve Container Images From a Remote Registry

Remote Registries Configuration

There are two configuration files that remote registries can be listed in:

/etc/containers/registries.conf: Global configuration file
~/.config/containers/registries.conf: User specific configuration file. Settings in here override the global configuration if different.

By default, the global configuration file contains the following entry:

unqualified-search-registries = ["registry.access.redhat.com", "registry.redhat.io", "docker.io"]

These are the registries that get searched and the order they are listed in matters, for example if you wanted docker.io to be searched first you would amend the configuration to:

unqualified-search-registries = ["docker.io", "registry.access.redhat.com", "registry.redhat.io"]

The configured registries can also be view with the podman info command:

Display configured container registries:

podman info | grep -A4 '^registries:'

This output should look similar to:

registries:
  search:
  - registry.access.redhat.com
  - registry.redhat.io
  - docker.io

Finding Container Images

To find container images you use the podman search command followed by the name of the image you are searching for. If you do not specify a registry in the image name, the command will search all configured registries. You can also specify a registry that has not been configured, for example if docker.io did not exist in /etc/containers/registries.conf you could still search docker.io for images.

There may be a scenario where you need to download a specific tagged version of an image. When performing a search you can add the --list-tags options to see what tags are available.

Search for nginx images for all configured repositories:

podman search nginx

The list is long so I have truncated the output you should receive, which shows the different images available from the 3 configured registries:

NAME                                         DESCRIPTION
registry.access.redhat.com/ubi8/nginx-120    Platform for running nginx 1.20 or building...
registry.access.redhat.com/ubi8/nginx-118    Platform for running nginx 1.18 or building...
registry.access.redhat.com/ubi9/nginx-120    rhcc_registry.access.redhat.com_ubi9/nginx-1...
registry.access.redhat.com/ubi8/nginx-122    rhcc_registry.access.redhat.com_ubi8/nginx-1...
registry.access.redhat.com/ubi9/nginx-122    rhcc_registry.access.redhat.com_ubi9/nginx-1...
...
...
registry.redhat.io/rhel8/nginx-114           Nginx is a web server and a reverse proxy se...
registry.redhat.io/rhel8/nginx-118           Platform for running nginx 1.18 or building...
registry.redhat.io/ubi8/nginx-120            Platform for running nginx 1.20 or building...
registry.redhat.io/rhel9/nginx-120           rhcc_registry.access.redhat.com_rhel9/nginx-...
registry.redhat.io/rhel8/nginx-122           rhcc_registry.access.redhat.com_rhel8/nginx-...
registry.redhat.io/rhel8/nginx-116           Platform for running nginx 1.16 or building...
registry.redhat.io/ubi8/nginx-118            Platform for running nginx 1.18 or building...
registry.redhat.io/rhel8/nginx-120           Platform for running nginx 1.20 or building...
registry.redhat.io/ubi9/nginx-120            rhcc_registry.access.redhat.com_ubi9/nginx-1...
registry.redhat.io/ubi8/nginx-122            rhcc_registry.access.redhat.com_ubi8/nginx-1...
registry.redhat.io/rhel9/nginx-122           rhcc_registry.access.redhat.com_rhel9/nginx-...
registry.redhat.io/ubi9/nginx-122            rhcc_registry.access.redhat.com_ubi9/nginx-1...
...
...
docker.io/library/nginx                      Official build of Nginx.
docker.io/library/unit                       Official build of NGINX Unit: Universal Web...
docker.io/nginxinc/nginx-unprivileged        Unprivileged NGINX Dockerfiles
docker.io/nginx/nginx-ingress                NGINX and  NGINX Plus Ingress Controllers fo...
docker.io/nginx/nginx-prometheus-exporter    NGINX Prometheus Exporter for NGINX and NGIN...
docker.io/nginx/unit                         NGINX Unit is a dynamic web and application...

Search for all ubuntu images from docker.io container repositories:

podman search docker.io/ubuntu/

The output shows just the ubuntu images for the docker.io registry:

NAME                              DESCRIPTION
docker.io/ubuntu/nginx            Nginx, a high-performance reverse proxy & we...
docker.io/ubuntu/squid            Squid is a caching proxy for the Web. Long-t...
docker.io/ubuntu/cortex           Cortex provides storage for Prometheus. Long...
docker.io/ubuntu/apache2          Apache, a secure & extensible open-source HT...
docker.io/ubuntu/kafka            Apache Kafka, a distributed event streaming...
docker.io/ubuntu/mysql            MySQL open source fast, stable, multi-thread...
docker.io/ubuntu/bind9            BIND 9 is a very flexible, full-featured DNS...
docker.io/ubuntu/prometheus       Prometheus is a systems and service monitori...
docker.io/ubuntu/zookeeper        ZooKeeper maintains configuration informatio...
docker.io/ubuntu/postgres         PostgreSQL is an open source object-relation...
docker.io/ubuntu/redis            Redis, an open source key-value store. Long-...
docker.io/ubuntu/grafana          Grafana, a feature rich metrics dashboard &...
docker.io/ubuntu/memcached        Memcached, in-memory keyvalue store for smal...
docker.io/ubuntu/dotnet-deps      Chiselled Ubuntu for self-contained .NET & A...
docker.io/ubuntu/dotnet-aspnet    Chiselled Ubuntu runtime image for ASP.NET a...
docker.io/ubuntu/cassandra        Cassandra, an open source NoSQL distributed...
docker.io/ubuntu/dotnet-runtime   Chiselled Ubuntu runtime image for .NET apps...
docker.io/ubuntu/telegraf         Telegraf collects, processes, aggregates & w...
docker.io/ubuntu/chiselled-jre    [MOVED TO ubuntu/jre] Chiselled JRE: distrol...
docker.io/ubuntu/jre              Distroless Java runtime based on Ubuntu. Lon...
docker.io/ubuntu/loki             Grafana Loki, a log aggregation system like...
docker.io/ubuntu/mlflow           MLFlow: for managing the machine learning li...
docker.io/ubuntu/grafana-agent    Ubuntu ROCK for Grafana Agent, an open-sourc...

Search for all available tagged versions for image docker.io/ubuntu/nginx:

podman search --list-tags docker.io/ubuntu/nginx

The output shows all available tags that can be used for downloaded the desired container image:

NAME                    TAG
docker.io/ubuntu/nginx  1.18-20.04_beta
docker.io/ubuntu/nginx  1.18-20.04_edge
docker.io/ubuntu/nginx  1.18-21.04_beta
docker.io/ubuntu/nginx  1.18-21.04_edge
docker.io/ubuntu/nginx  1.18-21.10_beta
docker.io/ubuntu/nginx  1.18-21.10_edge
docker.io/ubuntu/nginx  1.18-22.04_beta
docker.io/ubuntu/nginx  1.18-22.04_edge
docker.io/ubuntu/nginx  1.22-22.10_beta
docker.io/ubuntu/nginx  1.22-22.10_edge
docker.io/ubuntu/nginx  1.22-23.04_beta
docker.io/ubuntu/nginx  1.22-23.04_edge
docker.io/ubuntu/nginx  edge
docker.io/ubuntu/nginx  latest

Retrieving Container Images

To retrieve container images you use the podman pull command followed by the name of the image you are searching for.

It is worth noting that some remote registries may require a login, such as registry.redhat.io. If you intend to download from this registry then use the podman login <registry> command first

To confirm image downloads were successful you can use the podman images command, which will list the images stored locally along with the tag information.

Download the latest nginx image from docker.io/ubuntu/:

To download the latest image, run:

podman pull docker.io/ubuntu/nginx

The command will output the download process to screen. Notice how the latest tag was used by default as we did not specify any tags:

Trying to pull docker.io/ubuntu/nginx:latest...
Getting image source signatures
Copying blob 7d5ae4c6689d done  
Copying blob 53253dcacce9 done  
Copying blob 92209e819633 done  
Copying blob aae2f0d5fcf6 done  
Copying config 047208ad86 done  
Writing manifest to image destination
Storing signatures
047208ad86d4796fa6211cc72dfe3a676a69f2e9fef666c85042a966a68585ec

Download an nginx image by specifying a tag:

To specify the tag you include :tag after the container image name:

The tag specified may be out of date by the time you follow along so make sure to swap the tag for a tag that was outputted in the Finding Container Images exercises.

podman pull docker.io/ubuntu/nginx:1.22-22.10_beta

The command will output the download process and shows the tag we specified:

Trying to pull docker.io/ubuntu/nginx:1.22-22.10_beta...
Getting image source signatures
Copying blob 065dda2104ac done  
Copying blob f2284a6d1734 done  
Copying blob d7fafa60359f done  
Copying blob 89be66ebf161 done  
Copying config 8ee610fc81 done  
Writing manifest to image destination
Storing signatures
8ee610fc817d95605218759b8dd16c5840984ad16d650e019ad20a0bdd8dddf4

Display all local images:

podman images

The output shows the tags and image ID. If you download the same image but using a different tag you would see a row for each tag of the image.

REPOSITORY              TAG              IMAGE ID      CREATED       SIZE
docker.io/ubuntu/nginx  latest           047208ad86d4  2 weeks ago   146 MB
docker.io/ubuntu/nginx  1.22-22.10_beta  8ee610fc817d  2 months ago  141 MB

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