Docker Guide#

Caution

This guide has been fully based on LLVM’s A guide to Dockerfiles for building LLVM.

Introduction#

You can find a number of sources to build docker images in docker folder. They can be used by anyone who wants to build the docker images for their own use, or as a starting point for someone who wants to write their own Dockerfiles.

Each project currently provide Dockerfiles with a variety of different images, including Alpine 3, CentOS 7, CentOS 8 and Ubuntu 20.04.

Why?#

Docker images provide a way to produce binary distributions of software inside a controlled environment. Having Dockerfiles to builds docker images inside a specific repo makes them much more discoverable than putting them into any other place.

Docker basics#

If you’ve never heard about Docker before, you might find this section helpful to get a very basic explanation of it. Docker is a popular solution for running programs in an isolated and reproducible environment, especially to maintain releases for software deployed to large distributed fleets. It uses linux kernel namespaces and cgroups to provide a lightweight isolation inside currently running linux kernel. A single active instance of dockerized environment is called a docker container. A snapshot of a docker container filesystem is called a docker image. One can start a container from a prebuilt docker image.

Docker images are built from a so-called Dockerfile, a source file written in a specialized language that defines instructions to be used when build the docker image (see official documentation for more details). A minimal Dockerfile typically contains a base image and a number of RUN commands that have to be executed to build the image. When building a new image, docker will first download your base image, mount its filesystem as read-only and then add a writable overlay on top of it to keep track of all filesystem modifications, performed while building your image. When the build process is finished, a diff between your image’s final filesystem state and the base image’s filesystem is stored in the resulting image.

Quick start#

Installation#

We use here the Debian-like system and command-line interface.

  1. Install docker.

    sudo apt-get install -y docker.io

  2. Grant your user correct permissions.

    sudo usermod -aG docker $USER

    This is a required step to avoid below message when executing any docker command:

    docker: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.24/containers/create: dial unix /var/run/docker.sock: connect: permission denied.

    Note

    You can find more in this SO thread.

Usage#

Build image#

  • If Dockerfile is located at the root of the repo, you should run

    docker build -t <your_name_for_this_image> .

    For example:

    docker build -t "my_centos_8" .

  • If Dockerfile is located in docker folder, you must run this command at the root of the repo

    docker build -t <your_name_for_this_image> -f "docker/<YOUR_OS>.Dockerfile"

    For example:

    docker build -t "my_centos_8" -f "docker/CentOS8.Dockerfile"

Enter image#

If you need to enter into a specific docker image, you should run this

docker run -it <your_name_for_this_image>

For example:

docker run -it "my_centos_8"

Note

Please remember that all your changes will be discarded once you exist a docker image.

If you need to download and test a specific pre-build docker image from the Docker Hub, you should run this

docker run -it python:3-alpine /bin/sh

Mount host directories#

If you need to share a specific folder from your host system to a docker image, you should run this

docker run -it -v <host_folder>:/<docker_image_folder> <your_name_for_this_image>

For example:

docker run -it -v $(pwd):/work "my_centos_8"
cd work
cmake -S. -Bbuild

Remove image(s)#

  • To delete all docker images, you should run

    docker rmi -f $(docker images -aq)

  • To delete all docker containers including its volumes, you should run

    docker rm -vf $(docker ps -aq)

  • To make a full clean-up, you should run

    docker rmi -f $(docker images -aq)
docker rm -vf $(docker ps -aq)

    Or you can try this

    docker system prune -a --volumes

Note

You can find more in this SO thread.

Clean-up cheatsheet#

Stop all containers.

docker stop $(docker ps -qa)

Remove all containers.

docker rm $(docker ps -qa)

Remove all images.

docker rmi -f $(docker images -qa)

Remove all volumes.

docker volume rm $(docker volume ls -q)

Remove all networks.

docker network rm $(docker network ls -q)

Your installation should now be all fresh and clean.

The following commands should not output any items:

docker ps -a
docker images -a
docker volume ls

The following command show only show the default networks:

docker network ls