How to list the tag of a container image

SystemMen - How to list the tag of a container image? In the previous article, you already know what the tag of an image container is.

On the Docker Hub website, you can see all the tags easily.

But if you use the search command, how can you list all tags of an image?

Docker registry API

If you remember, the search command in docker does not display the image tag. So what will we do?

Docker supports something called Docker registry API, you can use these APIs to get the information you need.

The idea is that you will use the API to get information about the tag of a certain image.

What is MJSON?

A little more you will understand why we use MJson. So what is it?

Mjson is a tool that helps us print json results in “better” form. In general, its purpose is to make it easier to see results.

The command list all tags of an image

The following command will help you list all tags of an image.

curl https://registry.hub.docker.com//v1/repositories/<image-name>/tags

The syntax of the command is very simple, you just need to change the name of the image before the tag section.

For example, I use the search command to list all image centos.

root@linux:~# docker search centos
NAME                               DESCRIPTION                                     STARS               OFFICIAL            AUTOMATED
centos                             The official build of CentOS.                   5325                [OK]
ansible/centos7-ansible            Ansible on Centos7                              121                                     [OK]
jdeathe/centos-ssh                 CentOS-6 6.10 x86_64 / CentOS-7 7.5.1804 x86…   107                                     [OK]
consol/centos-xfce-vnc             Centos container with "headless" VNC session…   86                                      [OK]
imagine10255/centos6-lnmp-php56    centos6-lnmp-php56                              54                                      [OK]
centos/mysql-57-centos7            MySQL 5.7 SQL database server                   51
tutum/centos                       Simple CentOS docker image with SSH access      44
openshift/base-centos7             A Centos7 derived base image for Source-To-I…   43
gluster/gluster-centos             Official GlusterFS Image [ CentOS-7 +  Glust…   41                                      [OK]
centos/postgresql-96-centos7       PostgreSQL is an advanced Object-Relational …   37
centos/python-35-centos7           Platform for building and running Python 3.5…   35
kinogmt/centos-ssh                 CentOS with SSH                                 26                                      [OK]
openshift/jenkins-2-centos7        A Centos7 based Jenkins v2.x image for use w…   20
centos/php-56-centos7              Platform for building and running PHP 5.6 ap…   20
pivotaldata/centos-gpdb-dev        CentOS image for GPDB development. Tag names…   10
openshift/wildfly-101-centos7      A Centos7 based WildFly v10.1 image for use …   6
openshift/jenkins-1-centos7        DEPRECATED: A Centos7 based Jenkins v1.x ima…   4
pivotaldata/centos                 Base centos, freshened up a little with a Do…   3
darksheer/centos                   Base Centos Image -- Updated hourly             3                                       [OK]
pivotaldata/centos-mingw           Using the mingw toolchain to cross-compile t…   2
blacklabelops/centos               CentOS Base Image! Built and Updates Daily!     1                                       [OK]
pivotaldata/centos-gcc-toolchain   CentOS with a toolchain, but unaffiliated wi…   1
openshift/wildfly-81-centos7       A Centos7 based WildFly v8.1 image for use w…   1
smartentry/centos                  centos with smartentry                          0                                       [OK]
pivotaldata/gpdb6-centos6-build    CentosOS 6 image for GPDB 6 compilation         0

And now I want to know the tags of the image named ansible/centos7-ansible.

We will make 2 examples with mjson and no mjson.

Without mjson.

root@linux:~# curl https://registry.hub.docker.com//v1/repositories/ansible/centos7-ansible/tags
[{"layer": "", "name": "latest"}, {"layer": "", "name": "1.7"}, {"layer": "", "name": "1.8"}, {"layer": "", "name": "devel"}, {"layer": "", "name": "master"}, {"layer": "", "name": "stable"}]

And with mjson.

root@linux:~# curl https://registry.hub.docker.com//v1/repositories/ansible/centos7-ansible/tags | python -mjson.tool
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   191    0   191    0     0    185      0 --:--:--  0:00:01 --:--:--   185
[
    {
        "layer": "",
        "name": "latest"
    },
    {
        "layer": "",
        "name": "1.7"
    },
    {
        "layer": "",
        "name": "1.8"
    },
    {
        "layer": "",
        "name": "devel"
    },
    {
        "layer": "",
        "name": "master"
    },
    {
        "layer": "",
        "name": "stable"
    }
]

You see the results are different. With mjson, we have a better looking result.

Conclusion

This is just a simple trick, it does not require you to have a deep understanding of docker. But it is a very useful thing because you don’t always have a browser to use. You work with the command line server and you must use the command. Right?