Docker documentation mentions image reference in many places. However, running docker images command gives the list of images with the following properties: REPOSITORY, TAG, IMAGE ID, CREATED, SIZE - no reference. Is 'reference' a synonym for ID or digest, or something else?
The docker image reference is the combination of the REPOSITORY and TAG in this format REPOSITORY:TAG where they are both separated by :. So if you have an image with a REPOSITORY of IMAGE1 and a tag of latest the image reference would be IMAGE1:latest. The knowledge of an image reference would help you to filter by docker image list by reference by running:
docker images --filter=reference='myDocker*:*dev'
The above command will return all docker images that the repository name starts with myDocker and the tag name ends with dev.
To add on to Kelvin's answer, Reference is the Repository which you will use with the tag. Have a look the below example.
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
busybox latest e02e811dd08f 5 weeks ago 1.09 MB
busybox uclibc e02e811dd08f 5 weeks ago 1.09 MB
busybox musl 733eb3059dce 5 weeks ago 1.21 MB
busybox glibc 21c16b6787c6 5 weeks ago 4.19 MB
As you can see above, my reference would be respectively
busybox:latest
busybox:uclibc
busybox:musl
busybox:glibc
If you only use the reference as busybox, by default it will use the latest tag.
You can filter the images on the reference filter as well.
docker images --filter=reference='busy*:*libc'
REPOSITORY TAG IMAGE ID CREATED SIZE
busybox uclibc e02e811dd08f 5 weeks ago 1.09 MB
busybox glibc 21c16b6787c6 5 weeks ago 4.19 MB
You use the image reference in Dockerfile as well when you build the image by using the FROM directive.
FROM busybox #Reference is used as you can see and automatically, `latest` tag will be pulled
...
Ref:- https://docs.docker.com/engine/reference/commandline/images/
Ref:- https://docs.docker.com/engine/reference/builder/#from
Related
I have a bunch of docker images I want to get rid of and it would be convenient if I could remove them by specifying the repository name as it appears when I run docker images. For example if docker images returns:
REPOSITORY TAG IMAGE ID CREATED SIZE
ui_test 191127_manual 41a7ca9824d6 24 hours ago 1.42GB
ui git-24fa8d1a cdd254eff918 24 hours ago 1.44GB
ui git-31a4b052 9b4740060a62 25 hours ago 1.45GB
ui_test 191122_manual ba9cb04ce2d8 6 days ago 1.39GB
ui git-68110e426 f26ef80abc25 6 days ago 1.38GB
what command would I use to remove all of the ui_test images?
You can pass image IDs you want to delete to docker rmi:
docker rmi $(docker images -q 'ui_test')
From the docs:
The docker images command takes an optional [REPOSITORY[:TAG]] argument that restricts the list to images that match the argument. If you specify REPOSITORYbut no TAG, the docker images command lists all images in the given repository.
I have installed docker on my Windows 10, then I've created some images.
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-world latest 2cb0d9787c4d 3 weeks ago 1.85kB
Then I created my first machine using docker-machine create connected to hyperv driver.
so when I do docker images I get:
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
My question is how can I reconnect to the default docker engine so if I run docker images I get:
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-world latest 2cb0d9787c4d 3 weeks ago 1.85kB
try image instead of images
docker image list
There seems to be some inconsistency w.r.t the two i.e. image/images. Though one would expect the output to be same but there are few differences.
I need to change the name of the Docker repository. For example...
ORIGINAL:
[root#docker ~]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
registry.access.redhat.com/rhel7/rhel latest e64297b706b7 2 weeks ago 201MB
RENAMED:
[root#docker ~]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
rhel 7.5 e64297b706b7 2 weeks ago 201MB
You do not 'rename' images. What you see in docker images are tags. You can add a new tag or delete one, but not 'rename'. Try tagging your image with the new tag that you want and then (optionally), delete the old tag, e.g.:
docker tag registry.access.redhat.com/rhel7/rhel:latest rhel:7.5
docker rmi registry.access.redhat.com/rhel7/rhel:latest # remove old tag
I have been following the Docker tutorial here, and built a test image on my local OSX machine by committing changes to an existing image and tagging it with three different labels:
# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
adamatan/sinatra devel fccb6b4d21b4 8 minutes ago 469.5 MB
adamatan/sinatra junk fccb6b4d21b4 8 minutes ago 469.5 MB
adamatan/sinatra latest fccb6b4d21b4 8 minutes ago 469.5 MB
However, none of these images has a digest:
# docker images --digests adamatan/sinatra
REPOSITORY TAG DIGEST IMAGE ID CREATED SIZE
adamatan/sinatra devel <none> fccb6b4d21b4 9 minutes ago 469.5 MB
adamatan/sinatra junk <none> fccb6b4d21b4 9 minutes ago 469.5 MB
adamatan/sinatra latest <none> fccb6b4d21b4 9 minutes ago 469.5 MB
Other test images I have created with a Dockerfile do have a digest.
Why do some images have a digest and some don't? Is it related to the way the images were created (Dockerfile or not)?
Firstly, Please keep in mind that a digest could represent a manifest, a layer or a combination of them (we normally called that combination an image).
Manifest is a new term that introduced with Docker registry V2. Here is a short description fetched from Docker Registry V2 slides page21 ~ page23:
[Manifest] describes the components of an image in a single object
Layers can be fetched immediately, in parallel.
When you get the digests with command docker images --digests, here the digest is the SHA256 hash of image manifest, but image ID is the hash code of the local image JSON configuration (this configuration is different from manifest). In this case, if an image doesn't have an associated manifest, the digest of that image will be "none".
Normally, two scenarios could make an image doesn't have associated manifest:
This image has not been pushed to or pulled from a V2 registry.
This image has been pulled from a V1 registry.
To generate a manifest, the easiest way is to push the image to a V2 registry (V1 registry will not works). Docker client will generate a manifest locally, then push it with image layers to registry. When you pull the image back, the image will has a manifest.
Once the manifest existing, your image digest should not be "none".
Yes it is related to how the images were created. Docker can be a real stinker at times.
This may be helpful for you in this case.
I was also facing this issue (digest was none).
Reason was when I can the docker image and image was listed in docker images.
At this point, I was checking for the digest value using
docker images --digest
and the digest value comes as <none>.
Resolution:
Push the image in your docker repository, then image will show the digest value.
https://registry.hub.docker.com/_/ubuntu/
There is a _ in the url before the product name.
What is it for?
If you have a account on dockerhub called foobar:
# pull from your account (foobar)
docker pull foobar/ubuntu:latest
Otherwise, if you omit the username:
# pull from the official account (library)
docker pull ubuntu:latest
# almost the same as
docker pull library/ubuntu:latest
The underscore(_) is a special namespace used to publish the official repositories.
https://registry.hub.docker.com/_/ubuntu/ is almost the same as https://registry.hub.docker.com/u/library/ubuntu/
The only difference is that you will get different image-names with identical image-id:
$ docker pull ubuntu:latest
$ docker pull library/ubuntu:latest
$ docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
library/ubuntu latest 86ce37374f40 7 days ago 192.7 MB
ubuntu latest 86ce37374f40 7 days ago 192.7 MB