mohammad-oghli / Docker-Container-Basics

Docker Basic Commands

Sets of commands for using Docker on CentOS linux distribution:

Note: it's recommended to run this commands as root user or you should insert sudo before each command.

You can check how to install Docker on CentOS linux from Docker Documentation.

Start Docker platform on your local machine:

systemctl start docker

Check if Docker running properly on your local machine:

systemctl status docker

Create a container from hello world image and start the container on your local machine:

docker run hello-world

If you get the message Hello from Docker! then the container runs successfully.

Check the currently running containers on your local machine:

docker ps

You can add the option -a to view the previously running containers on your machine:

docker ps -a

It will show detailed info about each container previously running:

CONTAINER ID   IMAGE         COMMAND    CREATED          STATUS                      PORTS     NAMES
91582e45d7cc   ubuntu        "bash"     4 minutes ago    Exited (0) 11 seconds ago             agitated_pascal
949dcd991d2b   hello-world   "/hello"   49 minutes ago   Exited (0) 49 minutes ago             objective_dubinsky

As you see it gives you info about CONTAINER ID, Image Name and Instance Name of the container.

Check container images on your machine:

docker images

It will show detailed info about each container image:

REPOSITORY    TAG       IMAGE ID       CREATED        SIZE
ubuntu        latest    d2e4e1f51132   9 days ago     77.8MB
hello-world   latest    feb5d9fea6a5   7 months ago   13.3kB

Get ubuntu container image locally or pull it from Docker hub then create a new container from the image and start the container on your machine then enter the interactive bash remotely on the container:

docker run -it ubuntu bash

if you get root@2dff4fba5d4f:/# then you are now on the running container bash.

you can run ls to check the directories of the current ubuntu container:

bin boot dev etc home lib lib32 lib64 libx32 media mnt opt proc root run sbin srv sys tmp usr var

To check home directory contents:

ls -asl home

We will create new folder on home directory called lab:

cd home

mkdir lab

We can check that lab directory created on home:

ls

Then we will create file on the lab directory called container.txt and we will write on it "ubuntu container instance":

cd lab

echo "ubuntu container instance" -> container.txt

Check if the file created by running command:

cat container.txt

It will output :

ubunto container instance

Now after we create the new directory and file on ubuntu container we will exit from this container it will stop running directly:

exit

After exiting the container we can confirm that it stop running by:

docker ps

Then we will start ubuntu container another time:

docker run -it ubuntu bash

If we check the home directory now:

ls -asl home

We will not find lab directory and the file we created previously because each time we run ubuntu image we create new instance of the container.

we can check that by running:

docker ps -a

It will show these instances of ubuntu container:

CONTAINER ID   IMAGE         COMMAND    CREATED          STATUS                      PORTS     NAMES
91582e45d7cc   ubuntu        "bash"     4 minutes ago    Exited (0) 11 seconds ago             agitated_pascal
bc56e9119461   ubuntu        "bash"     20 minutes ago   Exited (0) 7 minutes ago              gracious_agnesi

To check the previous ubuntu container instance which we created lab directory on it:

First we start ubuntu container instance we can find the name of the instance from the table gracious_agnesi:

docker start gracious_agnesi

Then we enter the container instance bash using command:

docker attach gracious_agnesi

Now we can check the current container instance directory:

ls home -asl

It will show that the lab directory there then we check if the file container.txt is there:

ls home/lab -asl

It will show file is still there, so as you see that each instance of ubuntu container has its own state also it's separated from each other and that's one of the important features of containers technology.

Made with ❤ by Mohamad Oghli

I will update on this tutorial so check the GitHub repository.

Email: [e-mail]