DOCKER

Docker

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  • Overview

    Docker is container software. It is commonly used as a lightweight alternative to a virtual machine.

    Running Docker Without sudo

    By default, Docker has to be run with sudo commands otherwise you will experience errors such as:

    $ dial unix /var/run/docker.sock: connect: permission denied

    (this particular error was trying to run docker pull …)

    1. Create a new docker group:

      $ sudo groupadd docker 
    2. Add the current user (you) to the docker group:

      $ sudo gpasswd -a ${USER} docker
    3. Restart the docker service:

      $ sudo service docker restart
    4. Apply the changed settings to the current terminal process (logging out and back in would have the same effect):

      newgrp docker
    5. All done! You should now be able to use docker commands without sudo.

    What Are Images? What Are Containers?

    An image is a file which contains all the information/data about a particular system setup. When you run an image, you create a container of this image. You can create many containers based of the same image.

    Images

    Getting Images (docker pull)

    Images can be downloaded from Docker Hub using the docker pull command.

    $ docker pull image_name

    Images can be removed with:

    $ docker rmi image_name

    Inspecting Local Images

    You can view all of the docker images present on the local machine with:

    $ docker images

    Delete All Images

    The following command will remove all Docker images from your system:

    $ docker rmi $(docker images -q)

    Containers

    Inspecting

    To show only running containers:

    $ docker ps

    To show all containers (included those that are not running):

    $ docker ps -a

    To Start A New Bash Session Within A Container

    Enter this on the a shell session running in the host computer to enter a shell session inside the docker container.

    docker exec -it <container_id> bash

    To Exit A Container Without Stopping It

    If the container is being run inside a bash shell, you can press Ctrl-P then Ctrl-Q.

    How To Stop/Remove All Containers At Once

    docker stop $(docker ps -a -q)
    docker rm $(docker ps -a -q)

    If there are many docker containers, these commands can take some time (seconds).

    Dockerfiles

    Dockerfiles are configuration files which tell Docker how to build an image.

    Below is an example Dockerfile:

    # Extend base image ubuntu 16.04
    FROM ubuntu:16.04
    
    ## Update Ubuntu Software repository
    RUN apt-get update
    
    ## Install git
    RUN apt-get install -y git
    

    If you are currently in the directory which has a Dockerfile, you can compile it with the following command:

    docker build -t my-docker-image .

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