Docker 101

Last modified 10 months ago / Edit on Github

πŸ‘‰ Note: All Docker notes

What and Why?

Intuitive images

What's docker

Container  vs Virtual Machine
Container vs Virtual Machine, souce

RAM usage: Docker  vs Virtual Machine
RAM usage: Docker vs Virtual Machine, souce


  • ps = process status : check running containers (with -a for all)
  • -i = interactive : used in docker exec or docker run
  • -t = terminal : used in docker exec or docker run
  • -m = memory
  • -v or --volume : corresponding folders in/out containers.
  • --rm : create temprarily a container (removed after exit)


Success icon

πŸ‘‰ For all platforms, check official guide. It's up to date!

  • You mind find this article is useful for Ubuntu/Pop!_OS.
  • After installing, if you meet Got permission denied while trying to connect to the Docker daemon socket, check this.
  • For Linux, check this!

    Show codes

    Unninstall old versions

    sudo apt-get remove docker docker-engine containerd runc
    sudo apt-get update
    sudo apt-get install \
    apt-transport-https \
    ca-certificates \
    curl \
    gnupg-agent \
    curl -fsSL | sudo apt-key add -

    Make sure: 9DC8 5822 9FC7 DD38 854A E2D8 8D81 803C 0EBF CD88

    sudo apt-key fingerprint 0EBFCD88
    sudo add-apt-repository \
    "deb [arch=amd64] \
    $(lsb_release -cs) \

    Install docker engine

    sudo apt-get update
    sudo apt-get install docker-ce docker-ce-cli

    Check if everything is ok

    sudo docker run hello-world

    Incase docker-compose isn't installed

    sudo apt install docker-compose

    If you use Ubuntu 20.04+, replace $(lsb_release -cs) with eoan because docker currently (17 May 20) doesn't support 20.04 yet!

  • If wanna run docker without root, check this.

    sudo groupadd docker # create a docker group
    sudo usermod -aG docker <user> # add <user> to group
    newgrp docker # activate the changes
  • Configure docker start on boot (Ubuntu 15.04 or later)

    sudo systemctl enable docker

πŸ‘‰ Check this.


πŸ‘‰ Note: Docker + WSL2

Check the requirements

You must have Windows 10: Pro, Enterprise, or Education (Build 15063 or later). Check other requirements.

# check window version
Get-WmiObject -Class Win32_OperatingSystem | % Caption
# check window build number
Get-WmiObject -Class Win32_OperatingSystem | % Buildnumber

Active Hyper-V and Containers (you can do it manually in Turn Windows features on or off)

# Open PowerShell with Administrator and run following
Enable-WindowsOptionalFeature -Online -FeatureName containers –All
Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V –All
# restart
  1. Download and install.
  2. Check docker version.
  3. Try docker run hello-world.
With GPUs support?

Check this note.



# from docker official
sudo apt-get remove docker docker-engine containerd runc
# identify what installed package you have
dpkg -l | grep -i docker

# uninstall
sudo apt-get purge -y docker-engine docker docker-ce docker-ce-cli
sudo apt-get autoremove -y --purge docker-engine docker docker-ce
# remove images containers
sudo rm -rf /var/lib/docker /etc/docker
sudo rm /etc/apparmor.d/docker
sudo groupdel docker
sudo rm -rf /var/run/docker.sock

Login & Download images

docker login
# using username (not email) and password

  • Download at Docker Hub.
  • Download images are store at C:\ProgramData\DockerDesktop\vm-data (Windows) by default.

Check info

# docker's version
docker --version


# list images on the host
docker images
# check image's info
docker inspec <image_id>
# Where are images stored?
docker info
# normally, /var/lib/docker/


# list running containers
docker ps
docker ps -a # all (including stopped)
# only the ids
docker ps -q
docker ps -a -q
# container's size
docker ps -s
docker ps -a -s
# container's names only
docker ps --format '{{.Names}}'
docker ps -a --format '{{.Names}}'
# Check the last command in container
docker ps --format '{{.Command}}' --no-trunc
# check log
# useful if we wanna see the last running tasks's
docker container logs <container_name>
# get ip address
docker inspect <container_name> | grep IPAddress
# Attach to the running container
docker attach <container_name>


# RAM & CPU usages
docker stats
docker stats <container_name>

Attach / Start / Stop

We can use sometimes interchangeable between <container_id> and <container_name>.

# get info (container's id, image's id first)
docker ps -a
# start a stopped container
docker start <container_id>

# start and enter the container
docker start -i <container>
# stop a container
docker stop <container_id>
# Entering the running container (not attach)
docker exec -it <container_name> bash
# stop all running containers
docker stop $(docker ps -a -q)
# Attach to the running container
docker attach <container_name>


Read more here.


# any resources
docker system prune
# with all unused images
docker system prune -a


# list all images
docker images -a
# remove a specific image
docker image rm <IMAGE_ID>

Dangling images are layers that have no relationship to any tagged images.

# list dangling images
docker images -f dangling=true
# remove dangling images
docker images purge
Info icon

If you use docker images -a and see a lot of <none>:<none> images. Don't be worry to fast, if they're dangling images, they take spaces, otherwise, they're harmless to your drive! Check this SO.


# remove a specific containers
docker rm -f <container-id>
# remove all containers
docker rm -f $(docker ps -a -q)

Zsh in a container

If you have already a container, enter that container and then,

# Enter
docker exec -it container_name bash

# Install zsh
apt-get update
apt-get install zsh

# Install curl
apt-get install curl

# Install oh-my-zsh
sh -c "$(curl -fsSL"

If you want to integrate the zsh installation in the Dockerfile,

RUN apt-get install zsh && apt-get install curl
RUN PATH="$PATH:/usr/bin/zsh"
RUN sh -c "$(curl -fsSL"
Idea icon

Now, enter the container by docker exec -it zsh (instead of bash)!

Build an image


# build image with Dockerfile
docker build -t <img_name> .

# custom
docker build -t <img_name> . -f
# with docker-compose
docker-compose up
# with custom file
docker-compose -f docker-compose.amin.yml up -d
# if success
# service name "docker_thi"
docker run -it <service_name> bash
# from current container
docker ps -a # check all containers
docker commit <container_id> <new_image_name>


docker image tag old:latest myname/new:latest


πŸ‘‰ Official doc: Best practices for writing Dockerfiles

An example
FROM nvidia/cuda:10.2-base

# encoding

# fix (tzdatachoose)
ARG DEBIAN_FRONTEND=noninteractive

RUN apt-get -y update && \
apt-get -y upgrade && \
apt-get install -y openssh-server && \
apt-get install -y python3-pip python3-dev locales git r-base

# ssh server
RUN mkdir /var/run/sshd
RUN echo 'root:qwerty' | chpasswd
RUN sed -i 's/#PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config
# SSH login fix. Otherwise user is kicked off after login
RUN sed 's@session\s*required\s* optional' -i /etc/pam.d/sshd
# need?
ENV NOTVISIBLE "in users profile"
RUN echo "export VISIBLE=now" >> /etc/profile

# create alias
RUN echo 'alias python="python3"' >> ~/.bashrc
RUN echo 'alias pip="pip3"' >> ~/.bashrc

# create shortcuts
RUN ln -s /abc/xyz /xyz/xyz

# install python's requirements
COPY requirements_dc.txt requirements.txt
RUN python3 -m pip install --upgrade pip && \
python3 -m pip install -r requirements.txt
COPY . .

# export port ssh

# run
CMD ["sh","-c","cd /data_controller/utils/ && sh && cd /srv/ && sh"]
Connect to container via ssh
FROM ubuntu:20.04

RUN apt-get update && apt-get install -y openssh-server
RUN mkdir /var/run/sshd
RUN echo 'root:THEPASSWORDYOUCREATED' | chpasswd
RUN sed -i 's/#*PermitRootLogin prohibit-password/PermitRootLogin yes/g' /etc/ssh/sshd_config

# SSH login fix. Otherwise user is kicked off after login
RUN sed -i 's@session\s*required\s* optional' /etc/pam.d/sshd

ENV NOTVISIBLE "in users profile"
RUN echo "export VISIBLE=now" >> /etc/profile

CMD ["/usr/sbin/sshd", "-D"]

For more about ssh connection, check official doc.

If .env doesn't work? => This is expected. SSH wipes out the environment as part of the login process. [ref]

# For example, all environement variables are stored in a
# /home/thi/.env

# add them to container's env
cat /home/thi/.env >> /etc/environment

# exit current ssh session
# connect again

# check

More references: here and here.

Meaning of terms
  • FROM: the base image you use, can be obtained from Docker Hub. For example, FROM ubuntu:18.04 (18.04 is a tag, latest is default)

  • WORKDIR app/: Use app/ as the working directory.

  • RUN: install your application and packages requited, e.g. RUN apt-get -y update.

    • RUN <command> (shell form)
    • RUN ["executable", "param1", "param2"] (exec form)
  • CMD: sets default command and/or parameters, which can be overwritten if docker container runs with command lines. If there are many CMDs, the last will be used.

    # in Dockerfile
    CMD echo "Hello world"
    # run only
    docker run -it <image>
    # output: "Hello world"

    # run with a command line
    docker run -it <image> /bin/bash
    # output (CMD ignored, bash run instead): root@7de4bed89922:/#
    • CMD ["executable","param1","param2"] (exec form, preferred)
    • CMD ["param1","param2"] (sets additional default parameters for ENTRYPOINT in exec form)
    • CMD command param1 param2 (shell form)
    • Multiple commands: CMD ["sh","-c","mkdir abc && cd abc && touch new.file"]
  • ENTRYPOINT: configures a container that will run as an executable. Look like CMD but ENTRYPOINT commands and parameters are not ignored when Docker container runs with command line parameters.

    More detail
    # Dockerfile
    ENTRYPOINT ["/bin/echo", "Hello"]
    CMD ["world"]
    # run
    docker run -it <image>
    # produces 'Hello world'

    # but run
    docker run -it <image> John
    # produces 'Hello John' (only CMD command is override)
    • ENTRYPOINT ["executable", "param1", "param2"] (exec form, preferred)
    • ENTRYPOINT command param1 param2 (shell form)
  • Check this SO for CMD vs ENTRYPOINT.

  • EXPOSE 5000: Listen on the specified port

  • COPY . app/: Copy the files from the current directory to app/

Warning icon

You cannot use something like COPY .. . (parent of the folder containing the Dockerfile) in the Dockerfile because it uses the "build context" and it can access to files within that context. Ref.

Solution for above problem

In the Dockerfile, change COPY .. . to COPY . ..

Next, cd .. (go to the parent of the folder containing the Dockerfile, let's say docker/) and then use option -f docker/Dockerfile when you build an image.

Or you can use something below (no need to cd ..)

docker build -f ../Dockerfile
Example of run mutiple commands

If we run multiple interative commands (wait for action), for example, a jupyter notebook with a ssh server, we cannot put them directly in CMD command.

Solution: using a file .sh and put & at the end of the 1st command like:

$(which sshd) -Ddp 22 &

jupyter lab --no-browser --allow-root --ip= --NotebookApp.token='' --NotebookApp.password=''

Create a container


# container test from an image
docker create --name container_test -t -i <image_id> bash
docker start container_test
docker exec -it container_test bash
docker run --name <container_name> -dp 3000:3000 -v todo-db:/etc/todos <docker_img>
# run a command in a running docker without entering to that container
# e.g. running "/usr/sbin/sshd -Ddp 22"
docker exec -it -d docker_thi_dc /usr/sbin/sshd -Ddp 22
# "-d" = Detached mode
# want docker auto removes a container after exit
docker run --rm ...


Use to create various services with the same image.

docker-compose up -d # up and detach
docker-compose -f file_name.yml up -d # custom docker-compose.yml file name

# if you run 2 container in the same folder name
docker-compose -p "project_1" up -d
docker-compose -p "project_2" up -d
An example
# docker-compose.yml

# run by `docker-compose up`
version: '3'
container_name: docker_thi
image: docker_thi_img:latest
- "8888:8888"
- "/local-folder/:/docker-folder/"
working_dir: /srv
Info icon

To upgrade docker-compose file format from version 2.x to version 3.x, check this guide. Also check this: Compose file versions and upgrading.

Meaning of terms
  • depends_on:[ref] Express dependency between services (with orders).

    In docker-compose.yml: db and redis start before web.

    version: "3.8"
    build: .
    - db
    - redis
    image: redis
    image: postgres
  • command:[ref] Override the default command.

  • stdin_open: true and tty: true: keep container alive!

  • volumes (outside containers): volumes controlled by docker. They're located on different places,

    # check info of a volume
    docker volume inspect <volume_name>
  • restart: always (auto start container after logging in), no (default), on-failure.

  • build: <dir_to_Dockerfile_file>: build an image before using docker-compose.

  • runtime: nvidia: if docker-compose --version higher than 2.3 and there is NVIDIA GPU on your computer (check more detail in this note).

πŸ”… If there is no already built image, you can use a Dockerfile in the same place as docker-compose.yml. In docker-compose.yml, use

build: .

Then run docker-compose up --build.

πŸ”… Update to the newer version of docker-compose? Included in Docker Desktop (on Windows and MacOS), read this SO (Linux).


Docker can't connect to docker daemon`.

# check if daemon is running?
ps aux | grep docker

# run
sudo /etc/init.d/docker start

sudo systemctl restart docker meets Job for docker.service failed because the control process exited with error code.

  1. Try to remove failed daemon.json file in /etc/docker/ (if the problem comes from here)
  2. Try running either sudo /etc/init.d/docker start or sudo service docker restart (twice if needed).

perl: warning: Please check that your locale settings: when using below in the Dockerfile,


# Replace them by
RUN echo "LC_ALL=en_US.UTF-8" >> /etc/environment
RUN echo "en_US.UTF-8 UTF-8" >> /etc/locale.gen
RUN echo "LANG=en_US.UTF-8" > /etc/locale.conf
RUN locale-gen en_US.UTF-8

# On Windows + WSL2
The process cannot access the file 'ext4.vhdx' because it is being used by another process.
  1. Quit docker.
  2. Open Task Manager, try to end the processes wsappx (all of them).
  3. Reopen docker.


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