Sujay Kundu

Sujay Kundu

Sujay Kundu is a Certified Web developer and Digital Marketing Expert. He is currently working as Nodejs Developer at Katerra. Know more about him..

Docker Cheatsheet

Posted on August 2, 2020

To pull a docker image from the docker hub, we can use the command:

$ docker pull <image-name:tag>

To run that image, we can use the command :

$ docker run <image-name:tag> or $ docker run <image-id>

To list down all the images in our system, we can give the command :

$ docker images

To list down all the running containers, we can use the command :

$ docker ps

To list down all the containers ( even if they are not running ) :

$ docker ps -a

Creating a Dockerfile

Docker file - It contains instructions for building a docker image. Instructions contain various keywords.

FROM -> This keyword indicates the base image from which the container is built. RUN -> This keyword indicates the command that needs to be executed on the image.

Command to build an image:

$ docker build -t [image-name]:tag

eg. $ docker build -t gamershub:1.0

Command to Run the newly built image :

$ docker run --name "container-name" -p <host port>:<container port><image_name:tag>

eg.

$ docker run --name "ubuntutomcat7" -p 8080:8080 gamershub:1.0

Start / Stop Containers

  • We can start / stop containers by just running a command from the terminal
  • We need to specify the container id as parameter

To list down all the containers and their ID’s, use :

$ docker ps -a

To start the container, use the command :

$ docker start <container id>

To restart the container, use the command :

$ docker restart <container id/name>

To pause or unpause the container, use the command :

$ docker pause <container name/id>
$ docker unpause <container name/id>

To stop the container, use the command :

$ docker stop <container id>

To remove the container, use the below command after stopping the container

$ docker rm <container name>

To delete an image, we can use :

$ docker rmi <image id>
$ docker rmi <repo:tag>

To show all containers

$ docker ps -aq

To stop all containers

$ docker stop $(docker ps -aq)

To remove all containers

$ docker rm $(docker ps -aq)

To remove all images

$ docker rmi $(docker images -q)

To build image using dockerfile

$ docker build --no-cache -t ubuntu-py3 .

To run image

$ docker run -i -t ubuntu-py3 /bin/bash

Saving State

Normally we dont want to save the state : we do something like this, suppose we want to run a ubuntu container, we will install all the dependencies, we do something like this. For example i will install heroku in this ubuntu :

$ docker run -i -t ubuntu /bin/bash

After bash is open:

$ apt-get update
$ apt-get install curl

To install heroku cli

$ curl https://cli-assets.heroku.com/install.sh | sh
heroku -v

Heroku will be installed !

But once you close/exit the container. All your changes will be lost. What if we want to save state ? We dont want to reinstall this everytime. What if i want to reuse whatever i did earlier.. and make things easier !

How to save state ?

Cool to demonstrate, lets create a new container named “boringshawubuntu” from ubuntu image

$ docker container run -i -t --name boring_shaw_ubuntu ubuntu /bin/bash

Create a new docker container

Do all the changes in this container:

I installed heroku cli. like the previous steps in this container too.

Install Heroku in docker container

Lets now save the state , Open a new terminal and type :

$ docker container commit boring_shaw_ubuntu ubuntu-heroku

Save state of docker container

This will create a new image with the changes with name ubuntu-heroku: You can see in the image below,

Lets now test our new image that we created

Checking the state in docker container

If you run this image this will have heroku already installed.

Saving the container as Image

What if we want to make this image portable. We can save it as compressed file :

$ docker image save -o ubuntu-heroku.tar ubuntu-heroku

So this will create a ubuntu-heroku.tar , which is portable

$ docker image load -i ubuntu-heroku.tar

and then you can run the container using :

$ docker run -i -t ubuntu-heroku /bin/bash

Running saved state in docker container

Some Great Tutorials on Docker :

Intro to Docker Containers