Docker - Basics

The following notes assume you are using an M1 Mac system.

Install the Docker image.

First, we must see if there’s an Ubuntu image in the Docker container:

$ docker search ubuntu

Then we download the Ubuntu image:

$ docker pull ubuntu:22.04 --platform=linux/amd64

:22.04 is the version of the Ubuntu image, and I specified the platform so that it won’t automatically install the arm64 platform (the default platform is arm64).

Create a shared folder.

In a Mac OS environment, we need docker volume that functions as the shared folder in order to share files. We create a folder in the local machine, and copy the folder name by using:

$ pwd

Create a Docker container and a shared folder.

We make a container using the following command:

$ docker run -it --name=<docker name> \
-v <local directory>:<container directory> \
-v ~/.Xauthority:/root/.Xauthority \
-e DISPLAY=host.docker.internal:0 \
ubuntu:22.04 /bin/bash

Paste the folder name printed from pwd to <local directory>. <container directory> must be given an easy-to-remember name. It is because a folder is automatically made when the Docker container is created. To check if it was created correctly, enter the following command to verify if it is registered in the list:

$ docker container ls

Remove Docker image.

If you happen to install a Docker image incorrectly or have unnecessary images, you need to clean them up. To delete an image, enter the following command:

$ docker image rm <image name>

Remove the Docker container.

To delete a Docker container, you enter the following command:

$ docker rm <container name or id>

Set root password.

The initial root password in a Docker container is set by:

$ passwd

Create a new user.

When you run Docker, it basically connects you to the root account. To work stably, it is recommended to create a personal user account. Create a new user by entering the following command:

$ adduser <username>

Execute the container.

To work with this user, enter the following command:

$ docker exec -it -u ‘<username>’ <docker name> /bin/bash

If you want to directly get into the home directory:

$ docker exec -it -u ‘<username>’ <docker name> bash -c "cd ~ && exec bash"

where exec is a command for connecting to the container that is already running. If the container is stopped and we want to restart this container, enter the command below:

$ docker start (unpaused) <docker name>

If there is an access error, modify the authorization of the corresponding group to 666.

$ chmod 666 /var/run/docker.sock

Save the Docker container as .tar or an image.

We can save our own container, not pushing to the registry like Docker Hub. A Docker container can be saved as a tar file or an image with the command below:

$ docker export <container ID or name> > <file name>.tar

In order to transform this file into a Docker image:

$ docker import <file name> <image name:tag name>

Docker has commands such as export, import, save, and load. export saves the whole root file system, while save saves the layer structure on top of that.

To save a Docker container as an image:

$ docker stop <container name>
$ docker commit -a <author name> <container ID> <image name:tag name>