Add documentation for cleaning images

README.md

@@ -38,3 +38,31 @@ podman push <image name> docker://<host name>:5000/<image name>
 ```
 
 To use it in Kubernetes, see <https://kubernetes.io/docs/tasks/configure-pod-container/pull-image-private-registry/>
+
+## Maintenance
+
+### Remove images / tags
+
+In short:
+
+* login to the registry container
+* delete the directories keeping the metadata of the images and tags
+* run command *registry garbage_collect* to delete the unreferenced blobs
+
+In practice:
+
+```bash
+## Login to the machine with the dedicated user
+ssh registry@tiptop
+## Run a shell in a registry container
+# podman run -it --rm myregistry sh # if the registry is not started
+podman exec -it mycontainer sh
+# List all images and their tags
+ls -lsd /var/lib/registry/docker/registry/v2/repositories/*/_manifests/tags/*
+## To remove an image with all its tags:
+rm -rf /var/lib/registry/docker/registry/v2/repositories/image_to_be_deleted
+## To remove only a tag, eg "latest":
+rm -rf /var/lib/registry/docker/registry/v2/repositories/image_to_be_deleted/_manifests/tags/latest
+## Clean up the unreferenced  blobs
+registry garbage-collect -m /etc/docker/registry/config.yml
+```