About
This page is about the container image in Docker.
OCI is the standardized container format used by Docker
Management
Location
Docker stores downloaded images on the Docker host at the Docker Root Dir location
sudo ls /var/lib/docker/image/aufs
distribution imagedb layerdb repositories.json
Identification
imageId
# or
[user/]image:tag
# or where tag default to latest (ie same repository:latest)
[user/]repository
where:
- user identify user images. The user that created the image. For example the image training/sinatra has been created by the user training.
List
- One
docker images --filter reference=image-name
- All
docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
docker-whale latest 1351cae1fdfb About a minute ago 275.1 MB
ubuntu latest f753707788c5 7 weeks ago 127.2 MB
hello-world latest c54a2cc56cbb 5 months ago 1.848 kB
docker/whalesay latest 6b362a9f73eb 18 months ago 247 MB
training/webapp latest 6fae60ef3446 19 months ago 348.8 MB
where
- repository is what repository they came from, for example ubuntu.
- tag are the tags for each image, for example 14.04.
- Image id: The image ID of each image.
Id
name[:tag]
where:
Name
[user/]name
Tag
A repository potentially holds multiple variants of an image
In the case of the ubuntu image, there is multiple variants covering Ubuntu 10.04, 12.04, 12.10, 13.04, 13.10 and 14.04. Each variant is identified by a tag and you can refer to a tagged image like so:
ubuntu:14.04
Base
A base image is a minimal linux image where you start to build more complicated image. See Docker - dockerfile
Example:
Remove
docker rmi -f (name or id)
where:
- name: name of the image
- id: id of the image
Visualization
Visualization of the image and their different layer:
(Pre) load
Docker will automatically download any image you use that isn’t already present on the Docker host when you try to run it. If you want to pre-load an image you can download it using the docker pull
Layer
When doing a pull, you can see that each layer of the image has been pulled down
docker pull centos
Using default tag: latest
latest: Pulling from library/centos
f1b10cd84249: Pull complete
c852f6d61e65: Pull complete
7322fbe74aa5: Pull complete
Digest: sha256:90305c9112250c7e3746425477f1c4ef112b03b4abe78c612e092037bfecc3b7
Status: Downloaded newer image for centos:latest
Create
To create an image, you can
- use a Dockerfile to specify instructions to (create|build) an image.
- create a commit from an existing container
docker commit containerName imageName
Update
You can update a container created from an image and commit the results to an image.
You can commit the changes made to an image
docker commit -m "Added json gem" -a "Kate Smith" 0b2616b0e5a8 ouruser/sinatra:v2
where:
- -m: commit message
- -a: commit author
- 0b2616b0e5a8: the container ID
- ouruser/sinatra:v2: the target image
Searching
# docker search searchTerm
docker search oracle
NAME DESCRIPTION STARS OFFICIAL AUTOMATED
wnameless/oracle-xe-11g Oracle Express 11g R2 on Ubuntu 16.04 LTS 352 [OK]
oraclelinux Oracle Linux is an open-source operating s... 260 [OK]
alexeiled/docker-oracle-xe-11g This is a working (hopefully) Oracle XE 11... 185 [OK]
sath89/oracle-12c Oracle Standard Edition 12c Release 1 with... 78 [OK]
sath89/oracle-xe-11g Oracle xe 11g with database files mount su... 76 [OK]
where:
- OFFICIAL means that it comes from an official repository
- AUTOMATED means that the build is automated.
Run
A container is a running instance of an image that you create with a run command.
Save / Export
docker save [OPTIONS] IMAGE [IMAGE...]
Inspect
To see the property of the image such as the entrypoint, you can use the inspect command