Hey there and welcome back. This is a continuation of my previous article, , where we will look at some of the basic docker commands that should get you started and use docker with ease.But first, lets define a few terminologies that we will mention from time to time:
- Docker registries: A Docker registry stores Docker images. Docker Hub is a public registry that anyone can use, and Docker is configured to look for images on Docker Hub by default.
- Images: An image is a read-only template with instructions for creating a Docker container. Often, an image is based on another image, with some additional customization. For example, you may build an image which is based on the ubuntu image, but installs the Apache web server and your application, as well as the configuration details needed to make your application run.
- Containers: A container is a runnable instance of an image. You can create, start, stop, move, or delete a container using the Docker API or CLI. You can connect a container to one or more networks, attach storage to it, or even create a new image based on its current state.
- Docker daemon: The Docker daemon (dockerd) listens for Docker API requests and manages Docker objects such as images, containers, networks, and volumes.
Lets get started, shall we 💁🏾♂️
Before anything else, to display the docker help options either run docker with no parameters or execute docker help
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docker
To check the status, start or stop the docker daemon:
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sudo systemctl status docker
sudo systemctl start docker
sudo systemctl stop docker
To automatically start Docker and Containerd on boot, use the commands below:
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sudo systemctl enable docker.service
sudo systemctl enable containerd.service
To list all your images
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docker images
List currently running containers
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docker ps
List all containers and commands run previously
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docker ps -a
To view system-wide information about Docker
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docker info
To List networks available.
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docker network ls
By default, all containers run on bridged network (172.17.0.0/16)
To inspect a specific network
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docker network inspect bridge
If you want to pull an image from the docker registry, simply run docker pull <image_name>
Lets pull our first image from docker registry since we don’t have it locally
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docker pull ubuntu
We can then run it using the command below:
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docker run -it ubuntu:latest /bin/bash
exit
Lets first explain what the command above does.
When you run this command, it runs an ubuntu container, attaches interactively to your local command-line session, and runs /bin/bash. Instead of concatenating -it , you can also write it as -i -t.
- Docker creates a new container, as though you had run a
docker container createcommand manually. - Docker allocates a read-write filesystem to the container, as its final layer. This allows a running container to create or modify files and directories in its local filesystem.
- Docker creates a network interface to connect the container to the default network, since we did not specify any networking options. This includes assigning an IP address to the container. By default, containers can connect to external networks using the host machine’s network connection.
- Docker starts the container and executes
/bin/bash. Because the container is running interactively and attached to your terminal (due to theiandtflags), you can provide input using your keyboard while the output is logged to your terminal. - When you type exit to terminate the /bin/bash command, the container stops but is not removed. You can start it again or remove it.
Say you want to search for a specific image on the docker registry, you can do so directly on docker hub, or the command line as shown below:
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docker search <image_name>
For example:
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docker@docker:~$ docker search centos
NAME DESCRIPTION STARS OFFICIAL AUTOMATED
centos The official build of CentOS. 6906 [OK]
ansible/centos7-ansible Ansible on Centos7 135 [OK]
consol/centos-xfce-vnc Centos container with "headless" VNC session… 131 [OK]
jdeathe/centos-ssh OpenSSH / Supervisor / EPEL/IUS/SCL Repos - … 121 [OK]
centos/systemd systemd enabled base container. 105 [OK]
centos/mysql-57-centos7 MySQL 5.7 SQL database server 92
imagine10255/centos6-lnmp-php56 centos6-lnmp-php56 58 [OK]
tutum/centos Simple CentOS docker image with SSH access 48
centos/postgresql-96-centos7 PostgreSQL is an advanced Object-Relational … 45
jdeathe/centos-ssh-apache-php Apache PHP - CentOS. 31 [OK]
kinogmt/centos-ssh CentOS with SSH 29 [OK]
guyton/centos6 From official centos6 container with full up… 10 [OK]
nathonfowlie/centos-jre Latest CentOS image with the JRE pre-install… 8 [OK]
centos/tools Docker image that has systems administration… 7 [OK]
drecom/centos-ruby centos ruby 6 [OK]
darksheer/centos Base Centos Image -- Updated hourly 3 [OK]
mamohr/centos-java Oracle Java 8 Docker image based on Centos 7 3 [OK]
amd64/centos The official build of CentOS. 2
miko2u/centos6 CentOS6 日本語環境 2 [OK]
dokken/centos-7 CentOS 7 image for kitchen-dokken 2
blacklabelops/centos CentOS Base Image! Built and Updates Daily! 1 [OK]
mcnaughton/centos-base centos base image 1 [OK]
myheritage/centos7-git-java CentOs based docker image for Jenkins slave 1 [OK]
starlabio/centos-native-build Our CentOS image for native builds 0 [OK]
smartentry/centos centos with smartentry 0 [OK]
Congrats for the far you have come. At this point, you know how to pull images,inspect networks and run containers. Lets go a step further.
By default, if you create a container without specifying what name you want to call it, docker assigns it random names. For instance in the snippet below, the names assigned were epic_jackson & tender_pike:
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docker@docker:~$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a8ff9e854a5d ubuntu:latest "/bin/bash" 7 seconds ago Exited (0) 2 seconds ago epic_jackson
24bcb9c20f67 ubuntu:latest "/bin/bash" 37 seconds ago Exited (0) 33 seconds ago tender_pike
If you would like to give your containers meaningful names, you can do so by running your container as follows:
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docker run -it --name <container_name> ubuntu:latest /bin/bash
If we check the name this time round, you will notice the difference.
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docker@docker:~$ docker run -it --name my-application ubuntu:latest /bin/bash
root@a4d490a7347a:/# exit
exit
docker@docker:~$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a4d490a7347a ubuntu:latest "/bin/bash" 12 seconds ago Exited (0) 7 seconds ago my-application
You can also rename a container as follows:
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docker rename <old_name> <new_name>
For instance:
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docker@docker:~$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a8ff9e854a5d ubuntu:latest "/bin/bash" 42 minutes ago Exited (0) 42 minutes ago epic_jackson
docker@docker:~$ docker rename epic_jackson test-application
docker@docker:~$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a8ff9e854a5d ubuntu:latest "/bin/bash" 43 minutes ago Exited (0) 43 minutes ago test-application
Say you wanna jump back into the previously run container
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docker start <container id>
# or
docker start <wierd_name>
The command above starts the container but to get a shell, simple used attach
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docker attach <container id>
# or
docker attach <wierd_name>
If you have a shell on a container and would like to exit without terminating it, you can simply background it as follows:
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Ctrl+p , Ctrl+q
To remove the history of a container
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docker rm <container_name>
To know more info about a container
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docker inspect <container_name>
# or
docker container inspect <container_name>
To remove an image
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docker rmi <image_id>
# or
docker rmi <repository_name>:<tag>
Say you want to delete an image and you have a running container… you’ll get an error
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docker rmi image
- To fix the error, you need to first stop the container,
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docker stop <image_id>
- Remove the container
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docker container rm <image_id>
- Finally remove the image
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docker rmi image
This would look something like this:
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Say you want to save your docker image into a tarball
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docker save -o xxxxx.tar ubuntu:latest
You can load the saved tar file in docker as follows:
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docker load -i xxxxxx.tar
If you want to rename your images, you can do so by running
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docker tag Ubuntu:latest ubuntu:v1