How to Install Flatpak on Ubuntu 22.04

cloud-init is the de facto industry standard for automated initialization of virtual machines in cloud environments. This powerful configuration tool is activated at the first boot of an instance and allows execution of a predefined set of tasks without manual intervention. Its key functions include: Automating basic system setup, including assigning a hostname. User account management: creating users, assigning permissions, and configuring authentication mechanisms. Automatic deployment of SSH keys for secure access. Configuration of network interfaces according to specified parameters. Operations with disk storage, such as mounting and formatting volumes. Execution of custom scripts for post-installation configuration, which may include installing software, deploying application code, and applying fine-tuned settings. Although cloud-init is primarily designed for public clouds (AWS, Google Cloud, Azure, Hostman), it can also be used on local virtual machines and even on physical servers to standardize their initial setup. In this article, we will look at how to install, configure, and use cloud-init on Ubuntu. Installation In most Ubuntu images, cloud-init is already preinstalled. Canonical (the developer of Ubuntu) also releases images called Ubuntu Cloud Images, specially prepared and optimized for running in cloud environments. In Hostman, all Ubuntu images already include cloud-init. You can additionally check for cloud-init with the command: cloud-init --version If the command outputs a version (as shown in the screenshot above), then cloud-init is already installed in the system. If the response is Command cloud-init not found, install the utility with: apt update && apt -y install cloud-init After installation, cloud-init will automatically run at every system boot. Note that cloud-init runs before the server connects to the network. Configuration File Structure All cloud-init configuration files are located in /etc/cloud/: /etc/cloud/clean.d/ — directory for cleanup scripts. These scripts are executed when the command cloud-init clean is run. /etc/cloud/cloud.cfg — the main configuration file. This sets the default settings for all initialization stages. /etc/cloud/cloud.cfg.d/ — directory for user configuration files with the .cfg extension. Files are processed in alphabetical order and override settings from the main file. This is the preferred location for custom configurations. /etc/cloud/templates/ — contains templates used by cloud-init to generate system files. /var/lib/cloud/ — stores cache, data, and scripts generated during cloud-init execution. Modules Modules in cloud-init are separate executable components that perform specific configuration tasks when a VM first boots. Each module is responsible for its own area: network configuration, user creation, package installation, etc. An important feature of modules is their execution order: they do not run randomly, but in a strict sequence consisting of stages: Init Stage (Initialization stage): Runs immediately after mounting the root filesystem. Modules needed to prepare the system for main configuration are executed here (e.g., mounting additional disks). Config Stage (Configuration stage): The main stage where most modules run: network setup, package installation, SSH key setup, user creation. Final Stage: Executes modules for tasks that should occur at the very end, such as sending system readiness notifications or running user scripts. Local Usage of cloud-init Let’s test cloud-init locally, i.e., run it after the server has already booted. We will create two scenarios: The first scenario will create a new user named new-admin, assign a password, and grant administrator rights. The second scenario will install the packages atop, tree, net-tools. Since we will use a password for the new user, we need to generate its hash, as all passwords (and other secrets) are specified in plain text by default. . To get a hash, install the whois package, which contains the mkpasswd utility: apt -y install whois Run the utility with the SHA-512 hashing algorithm: mkpasswd -m sha-512 --stdin Enter the password for the user and press Enter. The utility will generate a password hash. Copy this hash for later use. As noted earlier, user configuration files are stored in /etc/cloud/cloud.cfg.d. Create a new file 99-new-admin-config.cfg:nano /etc/cloud/cloud.cfg.d/99-new-admin-config.cfg Use the following content: #cloud-config users: - name: new-admin passwd: $6$BSAzGG4SFvsn//vD$ds8oM53OIs6qXiCIhMTl10bwQfe9u5WxGKADzwyPsODniGhYAXCUOAoyUkJLs.H9z0PxqLr7BxEJ18hT2VEyR/ sudo: ALL=(ALL) ALL shell: /bin/bash groups: sudo Check syntax for errors: cloud-init schema --config-file /etc/cloud/cloud.cfg.d/99-new-admin-config.cfg If there are no errors, the command will return Valid schema. Before running the script, clear the previous configuration: cloud-init clean Run the configuration:cloud-init single --name users-groups --file /etc/cloud/cloud.cfg.d/99-new-admin-config.cfg After the new configuration is applied, check for the new-admin user: id new-admin Next, install the packages. Create a new file: nano /etc/cloud/cloud.cfg.d/99-install-packages.cfg Use the following content: #cloud-config package_update: true package_upgrade: true packages: - atop - tree - net-tools Check syntax: cloud-init schema --config-file /etc/cloud/cloud.cfg.d/99-install-packages.cfg Clear configuration:  cloud-init clean Run the script to install the packages: cloud-init single --name package_update_upgrade_install --file /etc/cloud/cloud.cfg.d/99-install-packages.cfg Verify the installed packages: dpkg -l | grep -E "atop|tree|net-tools" Using cloud-init in Hostman Hostman cloud servers running Linux support cloud-init via the control panel. Scenarios can be configured both during server ordering and later during usage. Let’s look at the practical use of cloud-init. We will create a scenario that will: Create a new user named new-usr; Configure SSH key authentication for new-usr; Install two packages: mc, ncdu; Change the hostname to hostman-server; Create a file test-file.txt in the /tmp directory. If cloud-init scripts have already been run on the server, run cloud-init clean before applying the configuration below. Our script will run when creating a virtual server; we can add it at step 7: Since SSH key authentication will be used for the new user, generate keys in advance. On another device (Windows, macOS, Linux), run the command: ssh-keygen Save the keys in the default directory (.ssh in the home directory). Then obtain the public key value (.pub file): cat ~/.ssh/id_ed25519.pub Replace id_ed25519.pub with your own filename if different. In the control panel, in the cloud-init block, enter the following syntax: #cloud-config packages: - mc - ncdu users: - name: "new-usr" groups: sudo shell: /bin/bash sudo: ['ALL=(ALL) NOPASSWD:ALL'] ssh_authorized_keys: - ssh-rsa AAAAC3NzaC1lZDI1NTE5AAAAIFoUTI5BKDBDgKLIMpM71m/YI7dTtFKQiSIivRk9pUbs alex@DESKTOP-VTUJHJ9 lock_passwd: true hostname: hostman-server preserve_hostname: false runcmd: - [touch, /tmp/test-file.txt] In the ssh_authorized_keys field, enter your own public key. Complete the server order by clicking “Order.” Once the server is created, connect via SSH with the new user and verify that all specified actions were completed. Verify the user: id new-usr Verify installed packages: dpkg -l | grep -E "mc|ncdu" Verify hostname: hostname Verify file existence: ls -lah /tmp/test-file.txt Conclusion cloud-init is a powerful tool for automating the initial setup of servers in Ubuntu. With its capabilities, you can deploy fully configured servers in seconds, minimize human error, and easily scale infrastructure. The main strength of cloud-init lies in its ability to transform a virtual machine template into a fully configured, production-ready server instance without manual intervention. Automating network configuration, security updates, user creation, and software deployment are the advantages that make it indispensable for DevOps engineers and system administrators.

Managing multiple Java versions on Ubuntu is essential for developers working on diverse projects. Different applications often require different versions of the Java Development Kit (JDK) or Java Runtime Environment (JRE), making it crucial to switch between these versions efficiently. Ubuntu provides powerful tools to handle this, and one of the most effective methods is using the update-java-alternatives command. Switching Between Java Versions In this article, the process of switching between Java versions using updata-java-alternatives will be shown. This specialized tool simplifies the management of Java environments by updating all associated commands (such as java, javac, javaws, etc.) in one go.  Overview of Java version management A crucial component of development is Java version control, especially when working on many projects with different Java Runtime Environment (JRE) or Java Development Kit (JDK) needs. In order to prevent compatibility problems and ensure efficient development workflows, proper management ensures that the right Java version is utilized for every project. Importance of using specific Java versions You must check that the Java version to be used is compatible with the application, program, or software running on the system. Using the appropriate Java version ensures that the product runs smoothly and without any compatibility issues. Newer versions of Java usually come with updates and security fixes, which helps protect the system from vulnerabilities. Using an out-of-date Java version may expose the system to security vulnerabilities. Performance enhancements and optimizations are introduced with every Java version. For maximum performance, use a Java version that is specific to the application. Checking the current Java version It is important to know which versions are installed on the system before switching to other Java versions.  To check the current Java version, the java-common package has to be installed. This package contains common tools for the Java runtimes including the update-java-alternatives method. This method allows you to list the installed Java versions and facilitates switching between them. Use the following command to install the java-common package: sudo apt-get install java-common Upon completing the installation, verify all installed Java versions on the system using the command provided below: sudo update-java-alternatives --list The report above shows that Java versions 8 and 11 are installed on the system. Use the command below to determine which version is being used at the moment. java -version The displayed output indicates that the currently active version is Java version 11. Installing multiple Java versions Technically speaking, as long as there is sufficient disk space and the package repositories support it, the administrator of Ubuntu is free to install as many Java versions as they choose. Follow the instructions below for installing multiple Java versions. Begin by updating the system using the following command:   sudo apt-get update -y && sudo apt-get upgrade -y To add another version of Java, run the command below. sudo apt-get install <java version package name> In this example, installing Java version 17 can be done by running:  sudo apt-get install openjdk-17-jdk openjdk-17-jre Upon completing the installation, use the following command to confirm the correct and successful installation of the Java version: sudo update-java-alternatives --list Switching and setting the default Java version To switch between Java versions and set a default version on Ubuntu Linux, you can use the update-java-alternatives command.  sudo update-java-alternatives --set <java_version> In this case, the Java version 17 will be set as default: sudo update-java-alternatives --set java-1.17.0-openjdk-amd64 To check if Java version 17 is the default version, run the command:  java -version The output shows that the default version of Java is version 17. Managing and Switching Java Versions in Ubuntu Conclusion In conclusion, managing multiple Java versions on Ubuntu Linux using update-java-alternatives is a simple yet effective process. By following the steps outlined in this article, users can seamlessly switch between different Java environments, ensuring compatibility with various projects and taking advantage of the latest features and optimizations offered by different Java versions. Because Java version management is flexible, developers may design reliable and effective Java apps without sacrificing system performance or stability.

A secure connection between a client and a server is made possible via the SSH network protocol. Since all communications are encrypted, distant network attacks and data theft across the network are avoided. Let’s say you have ordered a cloud server from Hostman. You will need SSH installed and configured to connect to and administer the server. The guide below will describe how to install SSH on Ubuntu 22.04 and configure it. SSH Key configuration is pretty simple on Ubuntu Prerequisites Before proceeding with the installation and configuration of the Secure Shell service, ensure the following requirements are met: Linux Command Line Skills for Configuration Having a solid grasp of basic Linux commands like sudo, apt, nano, and systemctl is essential when setting up the service. These commands will be frequently used during the installation and configuration process. It's crucial to be comfortable working within the command line environment to manage the service effectively. Root or Sudo Access for Setup To install and configure the server, administrative (root) privileges are required. Users must either have sudo access or be logged in as root. Without these privileges, the setup process cannot proceed. Internet Connection for Package Download A stable internet connection is necessary to install the OpenSSH server and any additional related packages. Without a functional connection, the system cannot retrieve the required software components. Configuring Firewall for Access If a firewall, like ufw, is enabled on the system, it may block remote access by default. It is essential to configure your firewall to allow incoming connections. Use ufw or another firewall tool to ensure port 22 is open and accessible. Access to the System (Local or Remote) To configure the service locally, you must have physical access to your computer; otherwise, it must be remotely accessible through its IP address. To connect, make sure the system is correctly linked to the network. Don't forget, that you can deploy your cloud server fast and cheap by choosing our VPS Server Hosting Step 1: Prepare Ubuntu The first thing you need to do before you start installing SSH on Ubuntu is to update all apt packages to the latest versions. To do this, use the following command: sudo apt update && sudo apt upgrade Step 2: Install SSH on Ubuntu OpenSSH is not pre-installed on the system, so let's install it manually. To do this, type in the terminal: sudo apt install openssh-server The installation of all the necessary components will begin. Answer "Yes" to all the system prompts.  After the installation is complete, go to the next step to start the service. Step 3: Start SSH Now you need to enable the service you just installed using the command below: sudo systemctl enable --now ssh On successful startup, you will see the following system message. The --now key helps you launch the service and simultaneously set it to start when the system boots. To verify that the service is enabled and running successfully, type: sudo systemctl status ssh The output should contain the Active: active (running) line, which indicates that the service is successfully running. If you want to disable the service, execute:  sudo systemctl disable ssh It disables the service and prevents it from starting at boot. Step 4: Configure the firewall Before connecting to the server via SSH, check the firewall to ensure it is configured correctly. In our case, we have the UFW installed, so we will use the following command: sudo ufw status In the output, you should see that SSH traffic is allowed. If you don't have it listed, you need to allow incoming SSH connections. This command will help with this: sudo ufw allow ssh Step 5: Connect to the server Once you complete all the previous steps, you can log into the server using the SSH protocol. You will need the IP address or domain name of the server as well as the name of a user that was created on the server in order to complete this step. In the terminal line, enter the command: ssh username@IP_address Or:  ssh username@domain Important: To successfully connect to a remote server, SSH must be installed and configured on the remote server and the user's computer from which you make the connection.  - Step 6 (optional): Create Key Pair for Secure Authentication For enhanced security, consider configuring a key pair instead of relying on password authentication. To generate one, use the following command: ssh-keygen Step 7: Configure SSH Having completed the previous five steps, you can already connect to the server remotely. However, you can further increase the connection's security by changing the default connection port to another or changing the password authentication to key authentication. These and other changes require editing the SSH configuration file. The main OpenSSH server settings are stored in the main configuration file sshd_config (location: /etc/ssh). Before you start editing, you should create a backup of this file:  sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.initial If you get any errors after editing the configuration file, you can restore the original file without problems. After creating the backup, you can proceed to edit the configuration file. To do this, open it using the nano editor: sudo nano /etc/ssh/sshd_config In the file, change the port to a more secure one. It is best to set values from the dynamic range of ports (49152 - 65535) and use different numbers for additional security. For example, let's change the port value to 49532. To do this, we uncomment the corresponding line in the file and change the port as shown in the screenshot below. SSH Key Configuration Description in Linux Terminal In addition to this setting, we recommend changing the password authentication mode to a more secure key authentication mode. To do this, uncomment the corresponding line and make sure the value is "Yes", as shown in the screenshot. Authentication Key should be Enabled Now, let's prohibit logging on to the server as a superuser by changing the corresponding line as shown in the picture below. Don't Forget to Close Access to Root Login There are other settings you can configure to increase the server security:  UseDNS checks if the hostname matches its IP address. The value "Yes" enables this parameter. PermitEmptyPasswords prohibits using empty passwords for authentication if the value is "No." MaxAuthTries limits the number of unsuccessful attempts to connect to the server within one communication session.  AllowUsers and AllowGroups are responsible for the list of users and groups allowed to access the server: # AllowUsers User1, User2, User3# AllowGroups Group1, Group2, Group3 Login GraceTime sets the time provided for successful authorization. We recommend reducing the value of this parameter by four times. ClientAliveInterval limits the time of user inactivity. After exceeding the specified limit, the user is disconnected. After making all the changes in the main configuration file, save them and close the editor.  Restart the service to make the changes take effect: sudo systemctl restart ssh If you have changed the port in the configuration file, you should connect using the new port:  ssh -p port_number username@IP_address Or: ssh -p port_number_port_username@domain Troubleshooting Connection Issues Ensure the service is running with: sudo systemctl status ssh Restart it if necessary: sudo systemctl restart ssh Check firewall settings to allow traffic on port 22: sudo ufw allow 22 Confirm the system is reachable by running: ping <server-ip-address> Disabling the Service If you need to disable remote access for any reason, follow these steps: Stop the Service To temporarily stop accepting connections: sudo systemctl stop ssh Prevent Automatic Startup To disable it from starting on reboot: sudo systemctl disable ssh Confirm Inactive Status Verify that the service is no longer running: sudo systemctl status ssh Uninstall the Server If the service is no longer needed, remove it and its associated configuration files: sudo apt remove openssh-server Conclusion This article presents a step-by-step guide on installing and configuring SSH in Ubuntu 22.04 and describes how to edit the main configuration file to improve security. We hope this guide helps you to set up a secure remote connection to your Ubuntu server.To see more about SSH keys click here.