Docker command cheat sheet

By Rex Resurreccion Aug 08, 2020
Docker commands cheat sheet

This Docker command cheat sheet is for those who manage their Docker image and container. I intend not to mix this up with Swarm, docker-compose and docker-machine so I will create a separate cheat sheet for my next topic.

If you have not had experience on Docker containers before, please read my topic first about Why you should learn Docker.

Manage Docker Image

docker image --help
docker image ls -f dangling=true

The value 6f4b0659e2ea is the Image ID, dockerhubacct/publish is a repository name, and sometag is the name of the tag.

The -f dangling=true flag will filter the list of images by showing only those that has no relationship or use with other images.

docker tag \
6f4b0659e2ea dockerhubacct/publish:sometag

Push and Pull Docker Image

docker login -u dockerhubacct
docker push dockerhubacct/publish:sometag
docker pull dockerhubacct/publish:sometag

Before you can start pushing and pulling image in Docker hub you will need to login first using your account, and you can do that in the command line using docker login command.

docker image prune
docker image prune -a

The prune command will remove the unused dangling images. And adding the -a flag will remove all unused images, not just dangling ones.

Build an image with arguments

docker build \
--build-arg project_port=8001 \
--build-arg project_root_dir=myproject \
-t dockerhubacct/publish:sometag .

With the --build-arg you can pass build-time variables. The -t flag is the name and optionally a tag in the name:tag format.

Another important part of this command is the dot ( . ) at the very end. That means the path of the Dockerfile is in the same folder location from where you are executing the command.

Archive Docker image

docker image save dockerhubacct/publish:sometag > myproject-docker-image.tar

Load image from .tar File

docker load < myproject-docker-image.tar

Manage Docker Container

docker container --help
docker container ls -a
docker container rm $(docker container ls -aq)
docker container top mycontainer
docker container rename mycontainer myoldcontainer

In these commands, the -a flag means show all containers and the -q will only display the numeric identification of the container.

To remove all containers with rm command it is possible to use this in conjunction with the result of listing the container ID $(docker container ls -aq).

Inspecting a Docker Container

docker container inspect -f "{{ .Config.Env }}" mycontainer
docker container inspect \
-f '{{.Name}}: {{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' mycontainer

Copy and list files inside the container

docker container cp foo.text mycontainer:/var/www
docker container exec mycontainer ls /var/www

The foo.text file is in the host server, copying this inside the container /var/www folder.

Setting environment variables and run a container

docker run -e SETTINGS=development --name mycontainer dockerhubacct/publish:sometag
docker run \
--network=host --name mycontainer \

Run container using the Host network. The port mappings will be disregarded when the container is running using Host network.

sudo docker container create --name mycontainer -p 8001:8001 dockerhubacct/publish:sometag

Prepare the container for running. Similar to docker run -d except the container is never started

docker run --rm --name mycontainer --entrypoint "/bin/bash" dockerhubacct/publish:sometag

Override entry point specified in the Dockerfile. Run the container and execute /bin/bash command instead. Moreover, the --rm will remove the container when it exit.

docker exec $(docker container ls --format {{.Names}} | grep 'webapp') \
bash -c "./" >> /var/log/webapp.log

Firstly, we are passing the result of the $(docker container ls --format {{.Names}} | grep 'webapp') to the exec command. And the result are the names of the containers by using the --format {{.Names}} flag.

Secondly, inside the container run a bash script That means all the returned containers with “webapp” in its name will run the script respectively.

Lastly, the output of the exec command will be logged in the host server /var/log/webapp.log.

This is useful if you have a maintenance script that you need to run within the container. For instance, you may setup a periodical task in the host server and use the docker exec command to run the script.

sudo docker exec -it mycontainer /bin/bash

Run a command in a running container. The -i flag will keep STDIN open even if not attached, and -t flag will allocate a pseudo-TTY. /bin/bash is the command that will be executed inside the container.

docker commit --change="ENV DEBUG=True PROJECT_PORT=8002" --change="EXPOSE 8002" mycontainer dockerhubacct/publish:sometagv2

Create a new image from a container’s change.

To summarize this Docker command cheat sheet, I have shown you the commands for managing Docker Image, Containers and how to execute commands inside the container.

© 2020