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How to Install Nextcloud with Docker

How to Install Nextcloud with Docker
Hostman Team
Technical writer
Docker
27.09.2024
Reading time: 10 min

Nextcloud is an open-source software for creating and using your own cloud storage. It allows users to store data, synchronize it between devices, and share files through a user-friendly interface. This solution is ideal for those prioritizing privacy and security over public cloud services. Nextcloud offers a range of features, including file management, calendars, contacts, and integration with other services and applications.

When deploying Nextcloud, Docker provides a convenient and efficient way to install and manage the application. Docker uses containerization technology, simplifying deployment and configuration and ensuring scalability and portability. Combining Docker with Docker Compose allows you to automate and standardize the deployment process, making it accessible even to users with minimal technical expertise.

In this guide, we'll walk you through installing Nextcloud using Docker Compose, configuring Nginx as a reverse proxy, and obtaining an SSL certificate with Certbot to secure your connection.

Installing Docker and Docker Compose

Docker is a powerful tool for developers that makes deploying and running applications in containers easy. Docker Compose simplifies orchestration of multi-container applications using YAML configuration files, which streamline the setup and management of complex applications.

  1. Download the installation script by running the command:

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

This script automates the Docker installation process for various Linux distributions.

  1. Run the installation script:

sudo sh ./get-docker.sh

This command installs both Docker and Docker Compose. You can add the --dry-run option to preview the actions without executing them.

  1. After the script completes, verify that Docker and Docker Compose are installed correctly by using the following commands:

docker -v
docker compose version

These commands should display the installed versions, confirming successful installation.

Preparing to Install Nextcloud

Creating a Working Directory

In Linux, third-party applications are often installed in the /opt directory. Navigate to this directory with the command:

cd /opt

Create a folder named mynextcloud in the /opt directory, which will serve as the working directory for your Nextcloud instance:

mkdir mynextcloud

Configuring the docker-compose.yml File

After creating the directory, navigate into it:

cd mynextcloud

We will define the Docker Compose configuration in the docker-compose.yml file. To edit this file, use a text editor such as nano or vim:

nano docker-compose.yml

In the docker-compose.yml file, you should include the following content:

version: '2'

volumes:
  mynextcloud:
  db:

services:
  db:
    image: mariadb:10.6
    restart: unless-stopped
    command: --transaction-isolation=READ-COMMITTED --log-bin=binlog --binlog-format=ROW
    volumes:
      - db:/var/lib/mysql
    environment:
      - MYSQL_ROOT_PASSWORD=RootPass
      - MYSQL_PASSWORD=NextPass
      - MYSQL_DATABASE=nextclouddb
      - MYSQL_USER=nextclouduser

  app:
    image: nextcloud
    restart: unless-stopped
    ports:
      - 8081:80
    links:
      - db
    volumes:
      - mynextcloud:/var/www/html
    environment:
      - MYSQL_PASSWORD=NextPass
      - MYSQL_DATABASE=nextclouddb
      - MYSQL_USER=nextclouduser
      - MYSQL_HOST=db

Parameters in this file:

  • version: '2': Specifies the version of Docker Compose being used. Version 2 is known for its simplicity and stability.

  • volumes: Defines two named volumes: mynextcloud for app data and db for database storage.

  • services:

    • db:

      • image: Uses the MariaDB 10.6 image.

      • restart: Automatically restarts the service unless manually stopped.

      • volumes: Binds the db volume to /var/lib/mysql in the container for persistent database storage.

      • environment: Sets environment variables like passwords, database name, and user credentials.

    • app:

      • image: Uses the Nextcloud image.

      • ports: Maps port 8081 on the host to port 80 inside the container, allowing access to Nextcloud through port 8081.

      • links: Links the app container to the db container for database interaction.

      • volumes: Binds the mynextcloud volume to /var/www/html for storing Nextcloud files.

      • environment: Configures database-related environment variables, linking the Nextcloud app to the database.

This configuration sets up your application and database environment. Now, we can move on to launching and configuring Nextcloud.

Running and Configuring Nextcloud

Once the docker-compose.yml configuration is ready, you can start the project.

Run the following commands in the mynextcloud directory to download the necessary images and start the containers:

docker compose pull
docker compose up

The docker compose pull command will download the required Nextcloud and MariaDB images. The docker compose up command will launch the containers based on your configuration.

The initial setup may take a while. When it’s complete, you will see messages like:

nextcloud-app-1  | New nextcloud instance
nextcloud-app-1  | Initializing finished

After the initial configuration, you can access Nextcloud through your browser. Enter http://server-ip:8081 into the browser’s address bar.

You will be prompted to create an administrator account by providing your desired username and password.

During the initial configuration, you can also choose additional apps to install.

Stopping and Restarting Containers in Detached Mode

After verifying that Nextcloud is running correctly through the web interface, you can restart the containers in detached mode to keep them running in the background.

If the containers are still running in interactive mode (after executing docker compose up without the -d flag), stop them by pressing Ctrl+C in the terminal.

To restart the containers in detached mode, use the command:

docker compose up -d

The -d flag stands for "detached mode," which allows the containers to run in the background independently of your terminal session.

Now the containers are running in the background. If you have a domain ready, you can proceed with configuring the server as a reverse proxy.

Setting up Nginx as a Reverse Proxy

Installation

Nginx is often chosen as a reverse proxy due to its performance and flexibility. You can install it by running the command:

sudo apt install nginx

Configuring Nginx

Create a configuration file for your domain (e.g., nextcloud-test.com). Use a text editor to create the file in the /etc/nginx/sites-available directory:

sudo nano /etc/nginx/sites-available/nextcloud-test.com

Add the following directives to the file:

server {
    listen 80;
    server_name nextcloud-test.com;

    location / {
        proxy_pass http://localhost:8081;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        add_header Strict-Transport-Security "max-age=15552000; includeSubDomains" always;
    }

    location ^~ /.well-known {
        location = /.well-known/carddav { return 301 /remote.php/dav/; }
        location = /.well-known/caldav  { return 301 /remote.php/dav/; }
        location /.well-known/acme-challenge { try_files $uri $uri/ =404; }
        location /.well-known/pki-validation { try_files $uri $uri/ =404; }
        return 301 /index.php$request_uri;
    }
}

This configuration sets up the web server to proxy requests to Nextcloud running on port 8081, with headers for security and proxying.

Key Configuration Details
  • Basic Configuration:

server {
    listen 80;
    server_name nextcloud-test.com;

    location / {
        proxy_pass http://localhost:8081;
        ...
    }
}

This block configures the server to listen on port 80 (standard HTTP) and handle requests directed to nextcloud-test.com. Requests are proxied to the Docker container running Nextcloud on port 8081.

  • Proxy Settings:

proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;

These headers ensure that the original request information (like the client’s IP address and request protocol) is passed on to the application, which is important for proper functionality and security.

  • HSTS (HTTP Strict Transport Security):

add_header Strict-Transport-Security "max-age=15552000; includeSubDomains" always;

This header enforces security by instructing browsers only to use HTTPS when accessing your site for the next 180 days.

  • Well-Known URI Settings:

location ^~ /.well-known {
    ...
}

This block handles special requests to .well-known URIs, used for service discovery (e.g., CalDAV, CardDAV) and domain ownership verification (e.g., for SSL certificates).

Enabling the Nginx Configuration

Create a symbolic link to the configuration file from the /etc/nginx/sites-enabled/ directory:

sudo ln -s /etc/nginx/sites-available/nextcloud-test.com /etc/nginx/sites-enabled/

Now restart Nginx to apply the new configuration:

sudo systemctl restart nginx

At this point, your web server is configured as a reverse proxy for the Nextcloud application, and you can access it via your domain (note that you might initially see an "Access through untrusted domain" error, which we’ll fix later).

Configuring SSL Certificates with Certbot

Installing Certbot

Certbot is a tool from the Electronic Frontier Foundation (EFF) used for obtaining and managing SSL certificates from Let's Encrypt. It automates the process, enhancing your website's security by encrypting the data exchanged between the server and its users. To install Certbot and the Nginx plugin, use the following command:

sudo apt install certbot python3-certbot-nginx

Obtaining and Installing the SSL Certificate

To obtain an SSL certificate for your domain and configure the web server to use it, run the command:

sudo certbot --non-interactive -m [email protected] --agree-tos --no-eff-email --nginx -d nextcloud-test.com

In this command:

  • --non-interactive: Runs Certbot without interactive prompts.

  • -m [email protected]: Specifies the admin email for notifications.

  • --agree-tos: Automatically agrees to Let's Encrypt’s terms of service.

  • --no-eff-email: Opts out of EFF-related emails.

  • --nginx: Uses the Nginx plugin to automatically configure SSL.

  • -d nextcloud-test.com: Specifies the domain for which the certificate is issued.

Certbot will automatically update the Nginx configuration to use the SSL certificate, including setting up HTTP-to-HTTPS redirection. After Certbot completes the process, restart Nginx to apply the changes:

sudo systemctl restart nginx

Now, your Nextcloud instance is secured with an SSL certificate, and all communication between the server and clients will be encrypted.

Fixing the "Access through Untrusted Domain" Error

When accessing Nextcloud through your domain, you may encounter an "Access through untrusted domain" error. This occurs because the initial configuration was done using the server’s IP address.

Since our application is running inside a container, you can either use docker exec or modify the Docker volume directly. We’ll use the latter method since we created Docker volumes earlier in the docker-compose.yml file.

  1. First, list your Docker volumes:

docker volume ls

Find the volume named mynextcloud_mynextcloud.

  1. To access the volume, run:

docker volume inspect mynextcloud_mynextcloud

Look for the Mountpoint value to find the path to the volume.

  1. Change to that directory:

cd /var/lib/docker/volumes/mynextcloud_mynextcloud/_data
  1. Navigate to the config directory and open the config.php file for editing:

cd config
nano config.php
  1. In the file, update the following lines:

    • Change overwrite.cli.url from http://server_ip:8081 to https://your_domain.

    • In the trusted_domains section, replace server_ip:8081 with your domain.

    • Add the line 'overwriteprotocol' => 'https' after overwrite.cli.url to ensure all resources load via HTTPS.

  2. Save the changes (in Nano, use Ctrl+O, then Ctrl+X to exit).

After saving the changes in config.php, you should be able to access the application through your domain without encountering the "untrusted domain" error.

Conclusion

Following these steps, you’ll have a fully functional, secure Nextcloud instance running in a containerized environment.

Docker
27.09.2024
Reading time: 10 min

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Script Examples Script for Deploying Jenkins in Docker: #!/bin/bash # Jenkins Parameters JENKINS_IMAGE="jenkins/jenkins:lts" CONTAINER_NAME="jenkins-server" JENKINS_PORT="8080" JENKINS_AGENT_PORT="50000" VOLUME_NAME="jenkins_home" CONFIG_DIR="$(pwd)/jenkins_configuration" # Create a volume to store Jenkins data docker volume create $VOLUME_NAME # Run Jenkins container with JCasC docker run -d \ --name $CONTAINER_NAME \ -p $JENKINS_PORT:8080 \ -p $JENKINS_AGENT_PORT:50000 \ -v $VOLUME_NAME:/var/jenkins_home \ -v $CONFIG_DIR:/var/jenkins_home/casc_configs \ -e CASC_JENKINS_CONFIG=/var/jenkins_home/casc_configs \ $JENKINS_IMAGE The JCasC configuration file jenkins.yaml was discussed earlier. Setting Up a CI/CD Pipeline for Jenkins Updates To set up a CI/CD pipeline, follow these steps: Open Jenkins and go to the home page. Click on Create Item. Enter a name for the new item, select Pipeline, and click OK. If this section is missing, you need to install the plugin in Jenkins. Go to Manage Jenkins → Manage Plugins. In the Available Plugins tab, search for Pipeline and install the Pipeline plugin. Similarly, install the Git Push plugin. After installation, go back to Create Item. Select Pipeline, and under Definition, choose Pipeline script from SCM. Select Git as the SCM. Add the URL of your repository; if it's private, add the credentials. In the Branch Specifier field, specify the branch that contains the Jenkinsfile (e.g., */main). Note that the Jenkinsfile should be created without an extension. If it's located in a subdirectory, specify it in the Script Path field. Click Save. Example of a Jenkinsfile pipeline { agent any environment { JENKINS_CONTAINER_NAME = 'new-jenkins-server' JENKINS_IMAGE = 'jenkins/jenkins:lts' JENKINS_PORT = '8080' JENKINS_VOLUME = 'jenkins_home' } stages { stage('Setup Docker') { steps { script { // Install Docker on the server if it's not installed sh ''' if ! [ -x "$(command -v docker)" ]; then curl -fsSL https://get.docker.com -o get-docker.sh sh get-docker.sh fi ''' } } } stage('Pull Jenkins Docker Image') { steps { script { // Pull the latest Jenkins image sh "docker pull ${JENKINS_IMAGE}" } } } stage('Cleanup Old Jenkins Container') { steps { script { // Stop and remove the old container if it exists def existingContainer = sh(script: "docker ps -a -q -f name=${JENKINS_CONTAINER_NAME}", returnStdout: true).trim() if (existingContainer) { echo "Stopping and removing existing container ${JENKINS_CONTAINER_NAME}..." sh "docker stop ${existingContainer} || true" sh "docker rm -f ${existingContainer} || true" } else { echo "No existing container with name ${JENKINS_CONTAINER_NAME} found." } } } } stage('Run Jenkins Container') { steps { script { // Run Jenkins container with port binding and volume mounting sh ''' docker run -d --name ${JENKINS_CONTAINER_NAME} \ -p ${JENKINS_PORT}:8080 \ -p 50000:50000 \ -v ${JENKINS_VOLUME}:/var/jenkins_home \ ${JENKINS_IMAGE} ''' } } } stage('Configure Jenkins (Optional)') { steps { script { // Additional Jenkins configuration through Groovy scripts or REST API sh ''' # Example script for performing initial Jenkins setup curl -X POST http://localhost:${JENKINS_PORT}/scriptText --data-urlencode 'script=println("Jenkins is running!")' ''' } } } } post { always { echo "Jenkins setup and deployment process completed." } } } On the page of your new pipeline, click Build Now. Go to Console Output. In case of a successful completion, you should see the following output. For this pipeline, we used the following files.  Dockerfile: FROM jenkins/jenkins:lts USER root RUN apt-get update && apt-get install -y docker.io docker-compose.yml: version: '3.7' services: jenkins: build: . ports: - "8081:8080" - "50001:50000" volumes: - jenkins_home:/var/jenkins_home - /var/run/docker.sock:/var/run/docker.sock environment: - JAVA_OPTS=-Djenkins.install.runSetupWizard=false networks: - jenkins-network volumes: jenkins_home: networks: jenkins-network: Ports 8081 and 50001 are used here so that the newly deployed Jenkins can occupy ports 8080 and 50000, respectively. This means that the main Jenkins, from which the pipeline is running, is currently located at http://localhost:8081/. One way to check if Jenkins has been deployed is to go to http://localhost:8080/, as we specified this in the pipeline. Since this is a new image, a welcome message with authentication will appear on the homepage. Conclusion Automating the deployment, updates, and backups of Jenkins is crucial for ensuring the reliability and security of CI/CD processes. Using modern tools enhances this process with a variety of useful features and resources. If you're further interested in exploring Jenkins capabilities, we recommend the following useful resources that can assist with automating deployments: Official Jenkins website Jenkins Configuration as Code documentation Pipeline Syntax
30 January 2025 · 19 min to read
Docker

Docker Exec: How to Use It to Run Commands in a Container

Docker is an effective and versatile environment built to assist you in the matter of running, creating, as well as deploying apps within containers. One of the significant utilities in it is docker exec. It permits you to run code within a particular container. Furthermore, you can maintain as well as build a reliable, compact container through it. During creation or installation, it is significant to analyze different operations/configurations and examine the current condition or resolve bugs. Therefore, it offers an environment where commands can be run in dockerized apps. This tutorial will cover docker exec, complete with possible use cases and explanations. Prerequisites You must meet certain prerequisites before beginning the article: Installation: Verify that Docker is already installed. If not, check our tutorial to install it. Permissions: The user account should have permissions/privileges to run the script. Running Container: A container needs to be accessible as well as running at the moment. Through the docker ps, you can determine the ID or name of the container. General Concepts: You should be familiar with core concepts of Docker. Familiarity with Linux systems and Docker basics will help in troubleshooting any issues during configuration. These requirements are necessary before beginning the setup. Basic Introduction  docker exec permits greater control, enhanced privacy, as well as better security for your apps. It helps users with regarding, management, monitoring, and debugging running apps within the particular container. Explore its features to boost your productivity and automate workflows. In this way, you can run direct commands by performing several operations like opening sessions, shell commands, and even running scripts. This significantly enhances workflow by enabling interaction with the active/operational app. You can address issues as well as make configurations without the need for a full container restart, which improves efficiency. General Syntax  The general syntax is: docker exec [OPTIONS] CONTAINER CODE [ARG...] OPTIONS: These are flags for customizing the behaviour of the particular command. Several options are as below: -i: It indicates STDIN is launched even if not connected. -t: It addresses the allocation of a pseudo-TTY. -u USER: It indicates the particular user for running the command. -w WORKDIR: It indicates the directory which is working for the particular command. CONTAINER: It indicates the container ID or name, where instructions are executed. CODE:  This is the script or command that you require to run inside the container ARG: It represents the additional parameters that are required to be passed to the particular CODE. How to Use Docker Exec to Run Commands in a Container Through this utility, you can run programs, check logs, and perform other admin operations inside the particular running container by accessing its CLI. It is beneficial for effective management since it increases adaptability and gives more hold of dockerized apps. Testing with a Sample Container Before running the specific command, you should have the minimum of one container that is currently operational. If you do not have it yet, execute the below command by with the particular container name. In our case, we use mynginx:  docker run -d --name mynginx nginx Finding the Active Container ID Before beginning, you are required to know the ID or name of the running container. Let’s run the below command to obtain the info on all dockerized apps that are currently operational: docker ps In the figure, the operational instance ID is b51dc8e05c77 and the name is mynginx.  Working With a Particular Directory In this first example, you can run the command in the particular directory of the operational container. To achieve this, the --workdir or -w option is used by mentioning the folder name. Look at a use case where the pwd is run within the operational container mynginx: docker exec --workdir /tmp mynginx pwd Here: docker exec: It is the core command to run the command within the operational container. --workdir /tmp: This OPTION indicates our working directory. mynginx: It indicates the CONTAINER name.  pwd: It indicates the executed CODE within the container. In the figure, the pwd executes within the particular mynginx instance and allocates the working directory to /tmp.  Single Command Execution  In this example, execute a single command. For this, first mention the container name or ID, and afterwards, the particular command that you are required to execute. Here, mynginx is the name of the operational container, and the echo "Hello, Hostman Users!" is the command: docker exec mynginx echo "Hello, Hostman Users!" In the figure, there is an execution of the echo "Hello, Hostman Users!" command within mynginx. Several Commands Execution  You can execute several commands in a single line statement by splitting them with semicolon. Let’s look at the below statement: docker exec mynginx /bin/bash ls; free -m; df -h; In the result, ls shows the content inside of the mentioned folder, free -m shows the system memory and df -h disk space usage. It permits you to analyze the memory state, filesystem, and other info in one statement. Enabling the Shell Through Name You can enable the shell within the dockerized app. It permits an interface for the file system as well as script execution. Here, the -it option activates interactive mode and assigns the interface: docker exec -it mynginx /bin/bash The figure enables the bash shell interface within mynginx. But, /bin/bash is not guaranteed to be present in every image of Docker. Therefore, other shells like sh can also be enabled. Now, input exit and press ENTER to close the interface: exit To launch other shells like sh (which is a symbolic link to bash or another shell), use /bin/sh in the below statement line: docker exec -it mynginx /bin/sh In the figure, the code line launches the shell interface, which is operational.  Enabling the Shell Through ID In this particular use case, enable the session through the b51dc8e05c77 container ID inside the Docker app. Furthermore, you have the ability to interact with the interface as though you directly logged in via the -it flag. The -t indicates the assignment of pseudo-TTY, and the -i opens the STDIN. Both are beneficial for analysis, debugging, as well as managerial operations: docker exec -it b51dc8e05c77 bash Furthermore, you can analyse the information of the current folder inside the particular shell (in a detailed format), e.g., file size, owner, group, number of links, modification date, and file permissions: ls -l It gives detailed information on each file as well as the folder that assists you in knowing their attributes and managing them effectively. Working As a Particular User You can execute a command as the specific user through the -u option. It is beneficial when you are permitted to work with specific privileges. It runs the command in the operational container through the particular user and group: docker exec -u <user>:<group> <container_id> <command>  For instance, the whoami runs as the www-data in the mynginx container: docker exec -u www-data mynginx whoami In the figure, www-data verifies that the particular command is executed successfully with the correct user permissions and within the expected interface.  Enabling a Non-Interactive Shell Sometimes, users prefer not to have any interaction. For such circumstances, they can execute the command without any argument: docker exec mynginx tail /etc/passwd  The last 10 lines of the passwd file have been shown. This passwd file is stored in the /etc/passwd folder containing the user information. It helps you monitor the user account information, permitting you to quickly check for troubleshooting or update issues.  Working With a Single Environment Variable You may need to pass environment variables to the command that is run in the operational container. To achieve this, use the -e option as below: docker exec -e MY_VAR=value mynginx printenv MY_VAR In the figure, the printenv MY_VAR is successfully executed in mynginx when the MY_VAR is set to value correctly. Working With Multiple Environment Variables You can set more than one variable through the -e flag.  docker exec -e TEST=john -e ENVIRONMENT=prod mynginx env The figure confirms that the two variables TEST and ENVIRONMENT have been set to john and prod in the mynginx. Working With the Detached Mode You can run commands in the detached mode through the -d flag. Therefore, it runs in the background: docker exec -d mynginx sleep 500 The figure confirms that the mynginx is executing the sleep 500 command. Working With the Privileged Mode Here, the --privileged flag permits you to execute the command, such as mount, with elevated privileges in the running container: docker exec --privileged mynginx mount In the figure, mount permits the system to create a mount point with the particular permissions in the mynginx. More Information on docker exec The --help option shows the manual with a list of available options with concise explanations.  docker exec --help Final Words docker exec is an effective utility for controlling and interacting with active containers. It is helpful for operations like monitoring, managing, and debugging apps without interfering with their functionality. It permits you to run code, launch shells, customize several configuration aspects, and also set environment variables. Once you become familiar with the usage of this utility, you can manage containers easily. It makes your operations much smoother for creating and deploying apps.
29 January 2025 · 8 min to read
Docker

Converting a Container to a Virtual Machine

A tricky question often asked during technical interviews for a DevOps engineer position is: "What is the difference between a container and a virtual machine?" Most candidates get confused when answering this question, and some interviewers themselves don’t fully understand what kind of answer they want to hear. To clearly understand the differences and never have to revisit this question, we will show you how to convert a container into a virtual machine and run it in the Hostman cloud. The process described in this article will help better understand the key differences between containers and virtual machines and demonstrate each approach's practical application. This article will be especially useful for working with systems requiring a specific environment. We will perform all further actions in a Linux OS environment and use a virtual machine based on the KVM hypervisor created with VirtualBox to prepare the necessary image. You can also use other providers such as VMware, QEMU, or virt-manager. Configuration of Our Future Virtual Machine Let’s start this exciting journey by creating a container. For this, we will use Docker. If it is not installed yet, install it using the command below (before that, you may need to update the list of available packages with sudo apt update): sudo apt install docker.io -y Create a container based on the minimal Alpine image and attach to its shell: sudo docker run --name test -it alpine sh Install the necessary programs using the apk package manager that you plan to use in the future virtual machine. You don’t necessarily have to limit yourself to packages from the standard Alpine repository — you can also add other repositories or, if needed, download or compile packages directly in the container. apk add tmux busybox-extras openssh-client openssh-server iptables dhclient ppp socat tcpdump vim openrc mkinitfs grub grub-bios Here’s a list of minimally required packages: tmux — a console multiplexer. It will be useful for saving user sessions and the context of running processes in case of a network disconnect. busybox-extras — an extended version of BusyBox that includes additional utilities but remains a compact distribution of standard tools. openssh-client and openssh-server — OpenSSH client and server, necessary for setting up remote connections. iptables — a utility for configuring IP packet filtering rules. dhclient — a DHCP client for automating network configuration. ppp — a package for implementing the Point-to-Point Protocol. socat — a program for creating tunnels, similar to netcat, with encryption support and an interactive shell. tcpdump — a utility for capturing traffic. Useful for debugging network issues. vim — a console text editor with rich customization options. It is popular among experienced Linux users. openrc — an initialization system based on dependency management that works with SysVinit. It’s a key component needed to convert a container into a virtual machine, as containers do not have it by default. mkinitfs — a package for generating initramfs, allowing you to build necessary drivers and modules that are loaded during the initial system initialization. grub and grub-bios — OS bootloader. In this case, we are specifically interested in creating a bootloader for BIOS-based systems using an MBR partition table. Set the root password: export PASSWORD=<your secret password>  echo "root:$PASSWORD" | chpasswd   Create a user. You will need it for remote SSH access later: export USERNAME=<username>  adduser -s /bin/sh $USERNAME   Set the SUID bit on the executable file busybox. This is necessary so that the user can execute commands with superuser privileges: chmod u+s /bin/busybox   Create a script to be executed during system initialization: cat <<EOF > /etc/local.d/init.start #!/bin/sh dmesg -n 1 mount -o remount,rw / ifconfig lo 127.0.0.1 netmask 255.0.0.0 dhclient eth0 # ifconfig eth0 172.16.0.200 netmask 255.255.255.0 # route add -net default gw 172.16.0.1 busybox-extras telnetd EOF Let’s go through the script line by line: dmesg -n 1 — Displays critical messages from the Linux kernel's message buffer so that potential issues can be detected during startup. mount -o remount,rw / — Remounts the root file system (/) with the rw (read-write) flag. This allows modifications to the file system after boot. ifconfig lo 127.0.0.1 netmask 255.0.0.0 — Configures the loopback interface (lo) with IP address 127.0.0.1 and subnet mask 255.0.0.0. This ensures internal network communication on the machine. dhclient eth0 — Runs the DHCP client for the eth0 interface to automatically obtain IP address settings and other network parameters from a DHCP server. # ifconfig eth0 172.16.0.200 netmask 255.255.255.0 — This line is commented out, but if uncommented, it will assign a static IP address 172.16.0.200 and subnet mask 255.255.255.0 to the eth0 interface. We included this line in the script in case a static network configuration is needed. # route add -net default gw 172.16.0.1 — This line is also commented out, but if uncommented, it will add a default route with gateway 172.16.0.1. This determines how packets will be routed outside the local network. busybox-extras telnetd — Starts the Telnet server. Please note that using the Telnet protocol in production environments is not recommended due to the lack of encryption for data transmission. Make the script executable: chmod +x /etc/local.d/init.start Add the script to the autostart: rc-update add local Add the OpenSSH server daemon to the autostart. This will allow you to connect to the cloud server via SSH later: rc-update add sshd default Set the default DNS server: echo nameserver 8.8.8.8 > /etc/resolv.conf Exit the terminal using the exit command or the keyboard shortcut CTRL+D. The next step is to save the container's file system to the host as an archive, which can also be done using Docker. In my case, the final artifact is only 75 megabytes in size. sudo docker export test > test.tar Transforming a Docker Image into a Virtual Machine Image Containers are a Linux-specific technology since they don't have their own kernel and instead rely on abstractions of the host's Linux kernel to provide isolation and resource management. The key abstractions include: namespaces: isolation for USER, TIME, PID, NET, MOUNT, UTS, IPC, CGROUP namespaces. cgroups: limitations on resources like CPU, RAM, and I/O. capabilities: a set of capabilities for executing specific privileged operations without superuser rights. These kernel components make Docker and other container technologies closely tied to Linux, meaning they can't natively run on other operating systems like Windows, macOS, or BSD. For running Docker on Windows, macOS, or BSD, there is Docker Desktop, which provides a virtual machine with a minimal Linux-based operating system kernel. Docker Engine is installed and running inside this virtual machine, enabling users to manage containers and images in their usual environment. Since we need a full operating system and not just a container, we will require our own kernel. Create the image file we will work with: truncate -s 200M test.img Use fdisk to create a partition on the test.img image: echo -e "n\np\n1\n\n\nw" | fdisk test.img n — create a new partition p — specify that this will be a primary partition 1 — the partition number \n\n — use default values for the start and end sectors w — write changes Associate the test.img file with the /dev/loop3 device, starting from an offset of 2048 blocks (1 MB): sudo losetup -o $[2048*512] /dev/loop3 test.img Note that /dev/loop3 may already be in use. You can check used devices with: losetup -l Format the partition linked to /dev/loop3 as EXT4: sudo mkfs.ext4 /dev/loop3 Mount the partition at /mnt: sudo mount /dev/loop3 /mnt Extract the Docker image (test.tar) into the /mnt directory: sudo tar xvf test.tar -C /mnt Create the /mnt/boot directory to store the bootloader and kernel files: sudo mkdir -pv /mnt/boot Download the Linux kernel source code: wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.8.9.tar.xz Extract the Linux kernel source code in the current directory: tar xf linux-6.8.9.tar.xz Install the necessary packages for building the Linux kernel: sudo apt install git fakeroot build-essential ncurses-dev xz-utils libssl-dev bc flex libelf-dev bison -y Navigate to the kernel source directory and create the default configuration file: cd linux-6.8.9make defconfig Add necessary configuration options to the .config file: echo -e "CONFIG_BRIDGE=y\nCONFIG_TUN=y\nCONFIG_PPP=y\nCONFIG_PPP_ASYNC=y\nCONFIG_PPP_DEFLATE=y" >> .config CONFIG_BRIDGE=y — Enables network bridge support, allowing multiple network interfaces to be combined into one. CONFIG_TUN=y — Enables support for virtual network interfaces like TUN/TAP, useful for VPN setups. CONFIG_PPP=y — Enables support for the Point-to-Point Protocol (PPP). CONFIG_PPP_ASYNC=y — Enables asynchronous PPP for serial ports. CONFIG_PPP_DEFLATE=y — Enables PPP data compression using the DEFLATE algorithm. Prepare the source code for building: make prepare -j4 Create the necessary scripts, build the compressed kernel image (bzImage) and the kernel modules: make scripts -j4make bzImage -j4make modules -j4 Install the built kernel and modules into the /mnt/boot directory (which contains the virtual machine image filesystem): sudo make INSTALL_PATH=/mnt/boot installsudo make INSTALL_MOD_PATH=/mnt modules_install Install the GRUB bootloader into the /mnt/boot directory. Make sure you're in the directory containing the test.img file: sudo grub-install --target=i386-pc --boot-directory=/mnt/boot/test.img --modules='part_msdos' Bind-mount the host system’s /proc, /sys, and /dev directories to the /mnt directory. This is necessary for creating the initramfs: sudo mount --bind /proc /mnt/proc/sudo mount --bind /sys /mnt/sys/sudo mount --bind /dev /mnt/dev/ Change root (chroot) into the /mnt filesystem using a shell: sudo chroot /mnt /bin/sh Generate the initial RAM filesystem (initramfs) for the kernel version you are working with: mkinitfs -k -o /boot/initrd.img-6.8.9 6.8.9 Generate the GRUB bootloader configuration file: grub-mkconfig -o /boot/grub/grub.cfg By completing these steps, you will have created a small virtual machine image with a fully working Linux kernel, a bootloader (GRUB), and an initramfs. Local Verification of the Built Image For local verification, it’s most convenient to use QEMU. This package is available for Windows, macOS, and Linux. Install it by following the instructions for your OS on the official website. Convert the test.img to the qcow2 format. This will reduce the size of the final image from 200 MB to 134 MB. qemu-img convert test.img -O qcow2 test.qcow2 Run the image using QEMU. qemu-system-x86_64 -hda test.qcow2 If all steps were completed correctly, the initialization process will be successful, and an interactive menu for entering the login and password will appear. To check the version of the installed kernel, use the uname -a command, which will output the necessary information. Creating a Virtual Machine in Hostman Go to the Cloud Servers section and start creating a new server. Select the prepared and tested image as the server’s base. To do this, first add it to the list of available images. Supported formats include: iso, qcow2, vmdk, vhd, vhdx, vdi, raw, img. Upload the image in one of the available ways: from your computer or by link. Note that after uploading, the image will also be available via URL. Continue with the creation of the cloud server and specify the other parameters of its configuration. Since the image is minimal, it can be run even on the smallest configuration. Once the cloud server is created, go to the Console tab and verify whether the virtual machine was successfully created from the image. The virtual machine has been created and works correctly. Since we added the OpenSSH daemon to the autostart in advance, it is now possible to establish a full remote connection to the server using the username, IP address, and password. Conclusion To turn a container into a full-fledged lightweight virtual machine, we sequentially added key components: the OpenRC initialization system, GRUB bootloader, Linux kernel, and initramfs. This process highlighted the importance of each component in the overall virtual machine architecture and demonstrated the practical differences from container environments. As a result of this experiment, we realized the importance of understanding the architecture and functions of each component to successfully create images for specific needs and to manage virtual machines more effectively from a resource perspective. The image built in this article is quite minimal since it is a Proof-of-Concept, but one can go even further. For example, you could use a special guide to minimize the kernel and explore minimal Linux distributions such as Tiny Core Linux or SliTaz. On the other hand, if your choice is to add functionality by increasing the image size, we strongly recommend checking out the Gentoo Wiki. This resource offers extensive information on fine-tuning the system.
22 January 2025 · 11 min to read

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