A common task when using Docker is to list the docker containers and docker images available on the system. I recently wrote about installing Docker on Fedora. This post will look at creating a new Docker container using a Fedora image – whist along the way looking at how to list docker containers and how to list docker images.
Searching and Downloading Docker Images
We can search for Fedora Docker images on the docker hub by running ‘docker search fedora’:
[root@localhost ~]# docker search fedora NAME DESCRIPTION STARS OFFICIAL AUTOMATED fedora Official Fedora 21 base image and semi-off... 243 [OK] fedora/couchdb 31 [OK] dockingbay/fedora-rust Trusted build of Rust programming language... 2 [OK] vbatts/fedora-varnish https://github.com/vbatts/laughing-octo/tr... 2 [OK] darksheer/fedora22 Base Fedora 22 Image -- Updated hourly 1 [OK] startx/fedora 1 [OK]
The search will return a number of Docker images. The one we are interested in is the first in the list, which is the official Fedora 21 Docker image. To download the image, run:
[root@localhost ~]# docker pull fedora Pulling repository fedora c7d2f0130dae: Download complete b0082ba983ef: Download complete Status: Downloaded newer image for fedora:latest
List Docker Images
We can list the images on our system using the ‘docker images’ command. Running this now should display the newly downloaded Fedora image:
[root@localhost ~]# docker images REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE fedora 23 c7d2f0130dae 2 weeks ago 204.3 MB fedora latest c7d2f0130dae 2 weeks ago 204.3 MB
Running the docker image ls command will generate the same output. Now, this is fine if we have a small number of images on our docker host. But what if we have a lot of docker images on the system? Then we can look at filtering the docker image list.
Format the Docker Image List Output
We can apply a custom format to the docker image list output. For example, if we just wanted to list the image repository and tag we could use:
$ docker images --format "table {{.Repository}}\t{{.Tag}}"
Applying a filter to the Docker Image List
The docker image list output can be filtered using the –filter flag. The basic syntax for this is:
$ docker images --filter "<key>=<value>"The current available filters are:
- dangling – find dangling images
- label
- before – filter images created before given id
- since – filter images created since given id
- reference – filter images whose reference matches the specified pattern
Using a filter to find Dangling Images
We can list dangling images by running the following:
$ docker images --filter "dangling=true"Dangling images, are layers that have no relationship to any tagged images. We can use this filter to help automatically remove dangling images by running:
$ docker rmi -f $(docker images -f "dangling=true" -q)
Using a filter to find an Image based on name
We can also use a filter to find docker images with a particular name. For example, to list Centos images we could use a filter such as:
$ docker images --filter "reference=cen*"This will list all images on the docker host beginning with ‘cen’:
$ docker images --filter "reference=cen*"
REPOSITORY TAG IMAGE ID CREATED SIZE
centos latest 831691599b88 9 days ago 215MB
Creating a Docker Container from a chosen Image
Now we have the Fedora image, we can create a docker container from it:
[root@localhost ~]# docker run -i -t fedora /bin/bash
The above command creates a new container using the Fedora image, and drops us into a bash shell within the container:
[root@localhost ~]# docker run -i -t fedora /bin/bash
Typing ‘exit’ in the shell will exit us from the container.
List Docker Containers
We can list the docker containers on the system by running:
[root@localhost ~]# docker ps --all CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES ff0eb34d2d94 fedora:23 "/bin/bash" 16 seconds ago Exited (0) 15 seconds ago jovial_rosalind 3d3f8b8079bc fedora:23 "/bin/bash" 54 seconds ago Exited (0) 32 seconds ago suspicious_wright 58b4a78f5b63 fedora:23 "echo test" About a minute ago Exited (0) About a minute ago tender_curie 7b5e49ddee91 fedora:23 "/bin/bash" 31 minutes ago Exited (0) 30 minutes ago stoic_wilson
The above command shows all Docker containers on the system. The output of the command contains the following columns:
Container ID– A unique string that identifies each container.Image– The Docker image used to create the container.Command– The command that is executed when starting the container.Created– The create time of the container.Status– The current status of the container.Ports– The container’s published ports.Name– The friendly name of the container, by default this is automatically generated.
It’s possible to format the output of the command using the –format option. For example:
$ docker container ls --format 'table {{.containerid}}\t{{.image}}'
CONTAINER ID IMAGE
ff0eb34d2d94 fedora:23
Docker List Running Containers
To list only running Docker containers you can use:
# docker ps
To list the most recently created Docker container, you can run:
[root@localhost ~]# docker ps -l CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES ff0eb34d2d94 fedora:23 "/bin/bash" 6 minutes ago Exited (0) 6 minutes ago jovial_rosalind
Listing the Size of a Docker Container
Finally, to list the size of a Docker container, you can use the ‘-s‘ option:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES SIZE ff0eb34d2d94 fedora:23 "/bin/bash" 27 minutes ago Exited (0) 27 minutes ago jovial_rosalind 0 B 3d3f8b8079bc fedora:23 "/bin/bash" 27 minutes ago Exited (0) 27 minutes ago suspicious_wright 5 B 58b4a78f5b63 fedora:23 "echo test" 28 minutes ago Exited (0) 28 minutes ago tender_curie 0 B 7b5e49ddee91 fedora:23 "/bin/bash" 58 minutes ago Exited (0) 57 minutes ago stoic_wilson 8 B
This adds an additional column displaying the size of each container.
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