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Docker.md

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Docker

To install Docker on Ubuntu 20.04, refer to the install script.

docker info

Example: docker info

This will:

  • print very useful information about the docker environment

docker search <some-image>

Example: docker search ubuntu

This will:

  • search the image on docker hub

docker pull <image-name>

Example: docker pull ubuntu

This will:

  • download an image from docker hub

docker images

Example: docker images

This will:

  • show what images are available on the local machine

docker container [command] [options]

Example: docker container ls -a

This will:

  • print out all the containers including the stopped ones
  • print out only the running containers if -a is not specified

docker rmi <image_id or repository:tag>

Example: docker rmi ubuntu:latest or docker image rmi 4e2eef94cd6b

This will:

  • remove the image from the local machine

docker rm <container_id>

Example: docker rm 977eb67441ff

This will:

  • remove the container from the local machine

docker run [options] <image-name> [command] [args]

Example: docker run hello-world

This will:

  • run the command in a new container based on the image specified.
  • the same with docker container run
  • will start an interactive (-i) psuedo-tty bash (-t) session if -it is specified, e.g., docker run -it ubuntu /bin/bash
  • will give the container a name if --name is specified, e.g., docker run --name testubuntu ubuntu:latest
  • keep the container running in the background (detached mode) even it's not running any command, using -d, e.g., docker run -dit ubuntu /bin/bash
  • redirect a port from the host to the container using -p, e.g., docker run -it -p 8080:80 ubuntu /bin/bash, which will redirect the 8080 port of the host to the 80 port of the container

docker start <container-id or container-name>

Example: docker start testubuntu

This will:

  • start a container specified by container id or container name, which has already been created based on an image

docker exec <container-id or container-name> <command> [args]

Example: docker exec testubuntu echo "abcd"

This will:

  • run the command in the specified running container

docker stop <container-id or container-name>

Example: docker stop testubuntu

This will:

  • stop the specified container

docker ps

Example: docker ps

This will:

  • list all the running containers
  • list all the containers including the stopped ones if -a is specified

docker attach <container-id or container-name>

Example: docker attach testubuntu

This will:

  • attach the standard input, output and error streams to the specified running container (as a root user)

Ctrl [p -> q]

Meaning: press control and p, then don't let go the control key, press the q key

This will:

  • exit a container but don't stop the container
  • be very useful if we use docker attach to enter a container and want to exit it but don't want to stop it

docker commit [options] <container-id or name> [repository:[tag]]

Example: docker commit apacheubuntu ubuntu/apache-server:1.0

This will:

  • create an image based on the container specified

Dockerfile

Dockerfile is a script to create a docker image automatically.

Example:

FROM ubuntu
# update the container's packages
RUN apt update; apt dist-upgrade -y
# install apache2 and vim
RUN apt install -y apache2 vim
# make apache automatically start-up
RUN echo "/etc/init.d/apache2 start" >> /etc/bash.bashrc
# the entrypoint (default command to run)
CMD ["/bin/bash"]

This will:

  • use a base image specified by FROM
  • run the command in the image being created specified by RUN
  • specify a default command for the container to run specified by CMD

docker build -t <image-name:tag> .

Example: docker build -t ubuntu/apache-server:1.0 .

This will:

  • use the Dockerfile in the current directory to create an image, so the . at the end of the command is important

Reference

Book: Mastering Ubuntu Server, 2nd Edition, by Jay LaCroix.