How to install and use Docker on Linux

This article mainly introduces you to the method of installing and using Docker on Linux. The editor thinks it is quite good. Now I share it with you, hoping to help everyone.

Docker makes it extremely easy to create, deploy, and manage containers. Even better, installing and using Docker is particularly convenient on the Linux platform.

I will show you how easy it is to install Docker on Linux and get you started with Docker. My demonstration platform is Ubuntu 16.04 Server, but the process is similar on most other Linux platforms.

I assume here that you have started Ubuntu Server 16.04.

Installation

Since Ubuntu Server 16.04 lacks a graphical interface, I will install and use Docker entirely through the command line. Before you install, you need to update apt and then perform the necessary upgrades. It is important to note that if the system kernel is upgraded, you will need to restart the system. Therefore, it is best to choose a time when the server can be restarted.

Run the following command to update apt:

sudo apt update

After completion, use the command to upgrade the system:

sudo apt upgrade

If the kernel has been upgraded, you need to restart the server with the following command:

sudo reboot

If the kernel has not been upgraded, you can install Docker (no restart required). The command to install Docker is:

sudo apt install docker.io

If you are using other Linux distributions, you will find that there is no docker.io package when you try to install it using the corresponding package manager. , then you should install the docker package. For example, the command to install on Fedora should be:

sudo dnf install docker

If you are using CentOS 7, it is best to use the installation script to install docker. First use the command sudo yum check-update to update the system. After the upgrade, enter the following command to download and run the required scripts:

curl -fsSL https://get.docker.com/ | sh

By default, only administrator privileges can run docker commands. For security reasons, you don't want to run Docker as root or use sudo. To solve this problem, you need to add your own user to the docker group. The command is as follows:

sudo usermod -a -G docker $USER

After completing the operation, log out of the system and then log in again, and it should be done. However, if your platform is Fedora, when you add a user to the docker group, you will find that this group does not exist. So what to do? You need to create this group first. The command is as follows:

sudo groupadd docker && sudo gpasswd -a ${USER} docker && sudo systemctl restart docker
newgrp docker

Log out and then log in again. You can start using Docker.

Start, pause and enable Docker

After installing Docker, you can have the system automatically start the Docker daemon at startup. Use the following two commands to achieve this:

sudo systemctl start docker
sudo systemctl enable docker

If you need to pause or restart the Docker daemon, the command is:

sudo systemctl stop docker
sudo systemctl restart docker

Now you can use Docker to deploy containers.

Pull the image

For Docker, the image is the cornerstone of building containers. You can pull down an image (such as NGINX) and deploy as many containers as you like based on this image. Before using the image, you first need to pull the image into the system. The image is pulled from the registration warehouse. By default, the installed Docker contains a default registration warehouse Docker Hub - this registration warehouse contains a large number of images contributed by others (including official images and those contributed by users themselves). mirror).

Suppose you want to pull an Nginx web server-related image. Before starting to pull, first check what images are already in the system. Enter the docker images command and you will find that no image exists yet (Figure 1).

Figure 1: No mirror yet.

Let’s pull an image. Use the following command to download the Nginx image from Docker Hub:

docker pull nginx

The above command will download the latest (official) Nginx image from Docker Hub. Now run the docker images command and you will see the images listed (Figure 2).

Figure 2: The NGINX image has been pulled down.

Did you notice that what I said here is the "official" Nginx image? There are many unofficial Nginx images on Docker Hub. These unofficial mirrors are created for various purposes. You can use the following command to search all Nginx images in Docker Hub:

docker search nginx

你会发现（图 3 中），有很多基于不同目的所创建的 Nginx 镜像（反向代理、PHP-FPM（LCTT 译注：FastCGI 进程管理器FastCGI Process Manager是一个 PHPFastCGI 管理器，旨在将 FastCGI 进程管理整合进 PHP 包中）功能、LetsEncrypt（LCTT 译注：由 ISRG 提供的免费 SSL 项目），Bitnami，在树莓派上使用的 Nginx 和 Drupal，等等很多很多)。

图 3：Docker Hub 上找到的各种 NGINX 镜像。

假设，你想要下载内建有反向代理功能的 Nginx 镜像，有个非官方的镜像 jwilder/nginx-proxy。因此输入下面命令来拉取这个镜像：

docker pull jwilder/nginx-proxy

再输入 docker images 命令来查看新拉下来的这个镜像（图 4）。

图 4：已经有了两种不同的 NGINX 镜像了。

处于谨慎考虑，我建议只使用官方镜像，毕竟你无法确定非官方镜像是否包含了恶意代码。

有了镜像后就可以用它来部署容器了。下次我们再聊聊如何通过这些 Nginx 镜像来发布容器。

Docker 是一个超级强力的系统可以让你的工作更简单，让你的公司更具有伸缩性，也更灵活。想知道 Docker 还能做什么，运行 man docker 然后阅读它的帮助文档吧。

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