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Installing and Configuring cloud-init in Linux

Installing and Configuring cloud-init in Linux
Hostman Team
Technical writer
Linux
26.09.2024
Reading time: 10 min

cloud-init is a free and open-source package designed for configuring Linux-based virtual machines during their startup.

In a traditional (home) environment, we would install systems from a CD or USB drive and manually configure them via a standard installer. However, in a cloud environment, we may need to configure systems regularly and frequently create, delete, and restart instances. In such cases, manual configuration becomes impractical and unfeasible.

cloud-init automates the configuration process and standardizes the setup of virtual machines.

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What Is cloud-init

The main task of cloud-init is to process input metadata (such as user data) and configure the virtual machine before it starts. This allows us to pre-configure servers, install software, prepare working directories, and create users with specific permissions.

Cloud-init and Hostman Cloud Servers

Hostman cloud servers support working with cloud-init scripts through the control panel. Hostman’s documentation includes a brief guide on using cloud-init scripts directly on their cloud dedicated servers. Essentially, Hostman offers a text editor for cloud-init scripts accessible via a web browser, allowing users to pass configuration data directly to the utility before the system starts.

Installing Cloud-init

There are several ways to get a Linux OS with cloud-init:

  • Use a specialized Linux OS image with pre-installed cloud-init (we’ll mention some key examples below).

  • Use pre-built distributions from cloud providers (most cloud platforms support cloud-init, though the setup processes may vary).

  • Build a custom OS image using HashiCorp Packer.

  • Manually install the cloud-init package.

Cloud-init Images

  • Ubuntu: The most common cloud-init image is Ubuntu 22.04 Cloud Images, officially created by Canonical for public cloud use. These images are optimized and tailored for cloud tasks.

  • Debian: Similarly, Debian Cloud offers specialized cloud images for Debian users.

  • Alma Linux: Another distribution designed for cloud deployment is Alma Linux Cloud.

  • VMware: VMware’s Photon image, built for cloud environments, also comes with pre-installed cloud-init.

Alternatively, you can install cloud-init manually.

And if you’re looking for a reliable, high-performance, and budget-friendly solution for your workflows, Hostman has you covered with Linux VPS Hosting options, including Debian VPS, Ubuntu VPS, and VPS CentOS.

Installation via APT

In most Linux distributions, cloud-init is installed like any other package and includes three systemd services located in the /lib/systemd/system/ directory:

  • cloud-init.service

  • cloud-config.service

  • cloud-final.service

Additionally, there are two more auxiliary systemd services:

  • cloud-init-local.service

  • cloud-init-hotplugd.service

Before installing, it's best to update the list of available repositories:

sudo apt update

Then, download the cloud-init package via APT:

sudo apt install cloud-init

In some Linux images, cloud-init may already be installed by default. If so, the system will notify you after running the install command.

cloud-init also supports additional modules that expand configuration capabilities. The full list of modules is available in the official documentation.

Running cloud-init

Since cloud-init operates as a service, it starts immediately after the systemd utility starts, i.e., when the physical machine starts and before the system connects to the network. This allows for pre-configuring network settings, gateways, DNS addresses, etc.

Cloud-init Workflow

There are three main stages in cloud-init’s workflow, during which the system is configured. Each stage triggers specific cloud-init services:

  1. Before networking (init): Initial setup before the network starts, including system settings, network configurations, and disk preparation.

    • cloud-init-local.service

    • cloud-init.service

  2. After networking (config): Network is available, so updates and required packages are installed.

    • cloud-config.service

  3. Final stage (final): Final configurations, such as user creation and permission assignments, are applied.

    • cloud-final.service

    • cloud-init-hotplugd.service

Cloud-init Modules

cloud-init offers additional modules that enhance system configuration. These modules run in sequence at various stages. Depending on the specific use case, they can be triggered during any of the three stages. Module execution is managed through three lists in the configuration file:

  • cloud_init_modules: Modules run during the initialization (init) stage before the network starts.

  • cloud_config_modules: Modules run during the configuration (cloud) stage after the network is up.

  • cloud_final_modules: Modules run during the final stage.

In more detail, cloud-init’s stages can be broken down into five steps:

  1. systemd checks if cloud-init needs to run during system boot.

  2. cloud-init starts, locates local data sources, and applies the configurations. At this stage, the network is configured.

  3. During the initial setup, cloud-init processes user data and runs the modules listed under cloud_init_modules in the configuration file.

  4. During the configuration phase, cloud-init runs the modules listed under cloud_config_modules.

  5. In the final stage, cloud-init runs the modules from cloud_final_modules, installing the specified packages.

You can find more details on the cloud-init workflow in the official documentation.

Each module also has an additional parameter that specifies how often the module runs during system configuration:

  • per instance: The module runs each time a new system instance (clone or snapshot) boots.

  • per once: The module runs only once during the initial system boot.

  • per always: The module runs at every system startup.

Cloud-init Configuration

In public (AWS, GCP, Azure, Hostman) or private clouds (OpenStack, CloudStack), a service usually provides the virtual machine with environment data. cloud-init uses these data in a specific order:

  • User data (user-data): Configurations and directives defined in the cloud.cfg file. These may include files to run, packages to install, and shell scripts. Typically, user-data configure specific virtual machine instances.

  • Metadata (meta-data): Environment information, such as the server name or instance ID, used after user-data.

  • Vendor data (vendor-data): Information from cloud service providers, used for default settings, applied after metadata.

Metadata is often available at a URL like http://localhost/latest/meta-data/, and user data at http://localhost/latest/user-data/.

Cloud-init Scripts

When the system boots, cloud-init first checks the YAML configuration files with the scripts and then executes the instructions. YAML is a format for data serialization that looks like markup but is not.

The primary YAML configuration file for cloud-init is located at /etc/cloud/cloud.cfg. This file serves as the main configuration script, with directives and parameters for specific cloud-init modules.

You can write scripts as YAML files (using #cloud-config) or as shell scripts (using #!/bin/sh).

Here’s a simple example of a cloud-init script setting a hostname:

#cloud-config
hostname: my-host
fqdn: my-address.com
manage_etc_hosts: true

In this example:

  • #cloud-config: indicates that the instructions are for cloud-init in YAML format.

  • hostname: sets the short hostname.

  • fqdn: sets the fully qualified domain name.

  • manage_etc_hosts: allows cloud-init to manage the /etc/hosts file.

If this option is set to false, cloud-init won’t overwrite manual changes to /etc/hosts on reboot.

Cloud-init Script Examples

Cloud-init configuration using YAML should start with #cloud-config.

Users and Groups

When a virtual machine starts, you can predefine users with the users directive:

#cloud-config
users:
  - name: userOne
    gecos: This is the first user
    groups: sudo
    shell: sh
    system: true

  - name: userTwo
    gecos: This is the second user
    groups: sudo
    shell: /bin/bash
    system: false
    expiredate: '2030-01-02'

As shown, each new user entry begins with a dash, and parameters are specified in a "key: value" format.

These parameters mean:

  • name: User account name

  • gecos: Brief info about the user

  • groups: Groups the user belongs to

  • shell: Default shell for the user, here set to the simplest sh.

  • system: If true, the account will be a system account without a home directory.

  • expiredate: The user's expiration date in the "YYYY-MM-DD" format.

Changing User Passwords

Another simple directive is chpasswd, used to reset an existing user's password. Example configuration:

#cloud-config
chpasswd:
  list: |
    userOne:passOne
    userTwo:passTwo
    userThree:passThree
  expire: false

This sets a list of users and their new passwords. The | symbol indicates a multi-line entry. The expire parameter defines whether the password will need to be changed after expiration.

Updating the Repository List

cloud-config has a directive for updating the available package list: package_update. It's the declarative equivalent of running

 sudo apt update 

By default, it's set to true, meaning cloud-init will always update the package list unless explicitly disabled:

#cloud-config
package_update: false

Installing Specific Packages

For updating or installing specific packages, use the packages directive:

#cloud-config
packages:
  - nginx
  - nodejs

Running Commands

The runcmd directive allows you to execute console commands through cloud-config. Simply pass a list of commands that cloud-init will run in sequence:

#cloud-config
runcmd:
  - echo 'This is a string command!' >> /somefile.txt
  - [ sh, -c, "echo 'This is a list command!' >> /somefile.txt" ]

Here, two types of commands are used:

  1. As a simple string.

  2. As a YAML list specifying the executable and its arguments.

Another similar directive is bootcmd. While runcmd runs commands only on the system's first boot, bootcmd runs commands on every boot:

#cloud-config
bootcmd:
  - echo 'Command that runs at every system boot!'

Creating and Running a Script

You can combine runcmd with the write_files directive to create and run a script:

#cloud-config
write_files:
  - path: /run/scripts/somescript.sh
    content: |
      #!/bin/bash
      echo 'This script just executed!'
    permissions: '0755'
runcmd:
  - [ sh, "/run/scripts/somescript.sh" ]

The permissions parameter (set to 0755) means the script is readable and executable by all, but only writable by the owner.

Overriding Module Execution

You can override the list of modules to be executed at specific configuration stages. For example, the default cloud_config_modules list might look like this:

#cloud-config
cloud_config_modules:
  - emit_upstart
  - snap
  - ssh-import-id
  - locale
  - set-passwords
  - grub-dpkg
  - apt-pipelining
  - apt-configure
  - ubuntu-advantage
  - ntp
  - timezone
  - disable-ec2-metadata
  - runcmd
  - byobu

Remember, there are three stages:

  • cloud_init_modules

  • cloud_config_modules

  • cloud_final_modules

If you remove runcmd, for example, the commands within it won’t execute.

Updating Repositories and Installing Packages via Shell Script

cloud-init configurations can also consist purely of shell scripts. In this case, the script starts with #!/bin/sh instead of #cloud-config:

#!/bin/sh
apt update
apt -y install nodejs
apt -y install nginx

The -y flag automatically answers "yes" to any prompts during installation.

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Conclusion

In this guide, we covered the theoretical and practical aspects of using cloud-init:

  • How cloud-init works.

  • How to interact with cloud-init for system configuration.

  • Writing scripts in YAML or shell format.

  • Example configurations.

cloud-init runs before the system boots, ensuring that the instance follows the desired configuration (network, directories, packages, updates). cloud-init uses modules for specific configuration tasks, and the system configuration is done in phases:

  • init (before networking)

  • config (after networking)

  • final (last stage)

More detailed information is available in the official documentation maintained by Canonical, the primary developer of Ubuntu.

Linux
26.09.2024
Reading time: 10 min

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I< 2024 0:00 [kworker/0:0H-events_highpri] Similarly, you can sort by memory usage to detect potential leaks: ps aux --sort=-%mem | head -n 10 Example output: USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND mysql 1734280 0.4 36.4 1325172 357284 ? Ssl Jan30 87:39 /usr/sbin/mysqld root 330 0.0 4.4 269016 43900 ? S<s 2024 22:43 /lib/systemd/systemd-journald root 368 0.0 2.7 289316 27100 ? SLsl 2024 8:19 /sbin/multipathd -d -s root 1548462 0.0 2.5 1914688 25488 ? Ssl Jan23 2:08 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock root 1317247 0.0 1.8 1801036 17760 ? Ssl Jan14 22:24 /usr/bin/containerd root 556 0.0 1.2 30104 11956 ? Ss 2024 0:00 /usr/bin/python3 /usr/bin/networkd-dispatcher --run-startup-triggers root 635 0.0 1.1 107224 11092 ? Ssl 2024 0:00 /usr/bin/python3 /usr/share/unattended-upgrades/unattended-upgrade-shutdown --wait-for-signal root 2090997 0.0 0.8 17456 8788 ? Ss 11:26 0:00 sshd: root@pts/0 root 2091033 0.0 0.8 9936 8480 pts/0 Ss 11:26 0:00 bash --rcfile /dev/fd/63 Real-Time Monitoring Combine ps aux with the watch command to refresh output every 2 seconds: watch -n 2 "ps aux --sort=-%cpu" This provides a dynamic view of CPU usage trends. Zombie Process Detection Zombie processes, though largely harmless, clutter the process list. Locate them with: ps aux | grep 'Z' Persistent zombies often indicate issues with parent processes failing to clean up child tasks. Practical Use Cases Now, let’s explore some common use cases of the ps aux command in Linux: Diagnosing High CPU Usage Follow the below steps: Execute this command to list processes by CPU consumption. ps aux --sort=-%cpu Identify the culprit—for example, a malfunctioning script using 95% CPU. If unresponsive, terminate the process gracefully with: kill [PID] Or forcibly with: kill -9 [PID] Detecting Memory Leaks Simply do the following: Sort processes by memory usage: ps aux --sort=-%mem Investigate tasks with abnormally high %MEM values. Restart the offending service or escalate to developers for code optimization. Auditing User Activity List all processes owned by a specific user (e.g., Jenkins): ps aux | grep ^jenkins This helps enforce resource quotas or investigate suspicious activity. Best Practices for Process Management Let’s now take a quick look at some best practices to keep in mind when managing Linux processes: Graceful Termination: Prefer kill [PID] over kill -9 to allow processes to clean up resources. Log Snapshots: Periodically save process lists for audits: ps aux > /var/log/process_audit_$(date +%F).log Contextual Analysis: A high %CPU value might be normal for a video encoder but alarming for a text editor. Hence, it’s essential to consider the context when making an analysis. Common Pitfalls to Avoid Here are some pitfalls to look out for when using ps aux in Linux: Misinterpreting VSZ: High virtual memory usage doesn’t always indicate a problem—it includes swapped-out data. Overlooking Zombies: While mostly benign, recurring zombies warrant investigating parent processes. Terminating Critical Services: Always verify the COMMAND field before using kill to avoid disrupting essential services. Conclusion The ps aux command is a cornerstone of Linux system administration, offering deep insights into process behavior and resource utilization. You can diagnose performance issues, optimize resource allocation, and maintain system stability by mastering its output interpretation, filtering techniques, and real-world applications.  Did you know? Hostman prepared an Object Storage for your project to save all necessary info for your server. Start using now! For further exploration, consult the ps manual (man ps) or integrate process monitoring into automated scripts for proactive system management. Frequently Asked Questions (FAQ) What is the ps aux command in Linux?  It is the most common command to view a snapshot of all running processes on the system. The flags break down as follows: a: Shows processes for all users, not just the current user. u: Displays the process's user/owner and provides detailed resource usage (CPU, RAM). x: Shows processes not attached to a terminal (background daemons). Why do we use the ps command in Linux? We use it to monitor system health and troubleshoot performance. It helps you identify which applications are consuming the most CPU or Memory, find the Process ID (PID) needed to stop a frozen program, and verify if background services are running correctly. How do you use the ps aux command to find zombie processes? Zombie processes (defunct) appear with a Z in the STAT column. You can filter for them specifically by running: ps aux | grep 'Z' Alternatively, to get a cleaner list excluding the grep command itself: ps aux | awk '$8=="Z" {print $0}' How do I sort the output by Memory or CPU usage?  By default, ps aux does not sort by usage. You can use the --sort option: Sort by Memory: ps aux --sort=-%mem Sort by CPU: ps aux --sort=-%cpu (The minus sign sorts in descending order). What do the VSZ and RSS columns mean? VSZ (Virtual Memory Size): The total virtual memory available to the process (including swap and shared libraries). RSS (Resident Set Size): The actual physical RAM the process is currently using. RSS is usually the more important number for checking memory usage. How do I kill a process I found using ps aux?  First, locate the PID (Process ID) in the second column of the output. Then run: sudo kill [PID] If the process refuses to close, you can force kill it with sudo kill -9 [PID].
22 January 2026 · 10 min to read
Linux

How to Create a Text File in Linux Terminal

In Linux, you can access and edit text files using a text editor that is designed to work with plain text. These files are not specifically coded or formatted. Choose your server now! There are several different ways to create a file in Linux. The Linux Command Line or Terminal is most likely the fastest. This is a crucial skill for any user, but especially for server administrators, who need to create text files, scripts, or configuration files quickly for their jobs. Let's proceed to the guide on four standard techniques for creating a text file on the terminal. And if you’re looking for a reliable, high-performance, and budget-friendly solution for your workflows, Hostman has you covered with Linux VPS Hosting options, including Debian VPS, Ubuntu VPS, and VPS CentOS. File Creation in Linux Can be Frustrating Sometimes Prerequisites for File Creation in Linux Ensure these prerequisites are met before generating files in a Linux environment using the command-line interface: Access to a Functional Linux System: You must either have a Linux-based operating system installed on your computer or secure access to a Linux server via SSH (Secure Shell) protocol. Operational Terminal Interface: Confirm that your terminal application is accessible and fully operational. The terminal serves as your primary gateway to executing commands. Adequate User Permissions: Verify you can create files within the chosen directory. You may need to use sudo (for directories with access restrictions) to escalate privileges. Fundamental Commands Proficiency: You must get familiar with essential commands, such as touch for file creation, echo for printing text, cat for viewing file contents, and text editors like nano, vim, or vi for editing files directly. Text Editing Utilities: Ensure your system includes text editing tools: nano for command line simplicity, vim for advanced configurations, or graphical options like gedit for user-friendly navigation. Directory Management Expertise: Develop familiarity with directory navigation commands like cd for changing the working directory and ls for listing directory contents. This knowledge streamlines your workflow and avoids potential errors. Using the touch Command Generally, we use the touch command to create empty files and change timestamps. It will create an empty file if it doesn't exist already.  To create a text file in the current directory with the touch command: Open your terminal emulator. Type the command: touch filename.txt Start with "touch" command Replace "filename" with the name you picked for the file. If the file with the same name already exists, the access and modification timestamps will be updated without affecting the content of the file. If not, a blank file with the specified name will be generated. Press Enter—if it is successful, there will be no output. Use the ls command to list the directory content and verify file creation. "LS" command is also important of you want to generate text file in Linux Using the echo Command Redirection The echo command is widely used to display text on the terminal. But its capabilities go beyond that; it may also be used to write content to a file or create an empty file. For this, combine the echo command with double redirect symbols (you can also use a single >) and the desired filename. A text file can be created by redirecting the output of the echo command to a file. See how it works: Open your terminal emulator. Type the command: echo “Your text content here” > filename.txt "Echo" command is also important in the process Replace the text in double quotations (do not delete them) with yours to add it to the file.  After you press Enter, your text will be added to the file filename.txt. It will overwrite an existing file, if there is one. Otherwise, it will just create a new one. Press Enter. To verify that the file has been created and contains the desired content, use cat command to display the content.  "Cat" command can help you to display your file you just created Using the cat Command Redirection In Linux, the cat command is mostly used to concatenate and show file contents. It can, however, also be used to generate a text document by redirecting the standard output of cat to a file. Open your terminal emulator. Type the following command: cat > filename.txt This is what you'll see after "cat" command Replace filename.txt with the name for your text file. This command instructs cat to receive input rom the terminal and to redirect it into the filename.txt. Press Enter. The terminal will be waiting for input.  Enter the text you want in the file. Press Enter after each line. Press Ctrl + D when you are done. This signals the end of input to the cat and saves the content.  Run the cat command to check that the file has been created and contains the desired content. This is how you can check how your file in Linux is created Using printf for Advanced File Creation The printf utility is a powerful alternative to echo, offering enhanced formatting options for structuring text. It allows users to create files with precisely formatted content. Open the terminal. Use printf to define the text layout, incorporating formatting elements like newlines (\n) or tabs (\t). Redirect the output to a file using the > operator. Example: printf "First Line\nSecond Line\nIndented\tThird Line\n" >  formatted_file.txt Run the cat command to inspect the file's content and ensure the formatting matches expectations. Append Without Overwriting: To add content to an existing file without overwriting its current data, replace > with the append operator >>: printf "Additional content here.\n" >> formatted_file.txt Using a Text Editor You can also create new files in linux text editors. There is always at least one integrated command-line text editor in your Linux distribution. But you can choose and install a different one according to your preferences, for example, Vim, Nano, or Emacs. Each of them has its own features and advantages. Vim vim, which stands for "Vi IMproved," is a very flexible and adaptable text editor. It is well-known for its modal editing, which allows for distinct modes for various functions like text entry, navigation, and editing. It allows split windows, multiple buffers, syntax highlighting, and a large selection of plugins for extra features. To create a text file using vim, follow the steps below: Open vim, with the desired filename as an argument. "Vim" command is one of the key steps in file creation Press i to switch to Insert mode. Start typing and editing the filename.txt.  To save and exit, press Esc to ensure that command mode is running. Type: wq (write and quit) and press Enter. Simple command to finish your work Nano nano is ideal for short adjustments and straightforward text files because it is lightweight and requires little setup. It provides support for basic text manipulation functions, search and replace, and syntax highlighting. To create a text file using nano, follow the steps below:  Run nano with the desired filename as an argument. It will open a new buffer for editing the file filename.txt. Nano is useful in you want to fix something in your text file Start typing and editing the filename.txt.  To save and exit, press Ctrl + O to write the file, confirm the filename, and then press Ctrl + X to exit Nano. Click "yes" to exit Emacs emacs is a powerful and flexible text editor that supports syntax highlighting, multiple buffers, split windows, and integration with external tools and programming languages. To create a text file using emacs, follow the steps below:  Open emacs, with the desired filename as an argument. Start typing and editing the filename.txt.  "Emacs" is more flexible text editor To save and exit, press Ctrl + X, followed by Ctrl + S to save the file, and then Ctrl + X, followed by Ctrl + C to exit Emacs. Note: If a message states that "VIM command not found", "nano command not found" or "emacs command not found" in Linux, it typically means that the vim, nano or emacs text editor is not installed on the system, or it's not included in the PATH environment variable, which is a list of directories where the operating system looks for executable files. Don't forget to install necessary command in Linux To resolve this, install the text editor first using the command:  apt-get install vim apt-get install nano  apt-get install emacs Gedit An intuitive text editor that supports working with plain text and has syntax highlighting for programming languages. A straightforward graphical interface makes it usable for various tasks, from quick edits to complex document preparation. Open the Gedit Application: Launch Gedit either through the applications menu or by executing the following command in the terminal: gedit example.txt Gedit will create a new file if the specified one does not exist. Input Your Text: Type or paste your desired content into the editor. Save the File: Save your work with Ctrl + S or select File > Save. If creating a new file, specify a filename and a location. Verify: Return to the terminal and confirm the file exists with the ls command or review its content with cat. Linux File Creation Recommendations Ensure you have sufficient permissions to create files in the target directory. If they are insufficient, consider working in a directory where you have full rights (or elevate privileges with sudo). Check if a file with the identical name is already present before using the > operator, as the command will overwrite existing content. To prevent data loss, opt for the append operator >>. Familiarize yourself with the printf, echo, and text editors like vim or nano. These tools will help you reduce errors when working with files in Linux, as well as boost productivity. Use printf for creating files requiring structured content, such as configuration files or scripts with precise formatting needs. Choose your server now! Conclusion Now you have acquainted yourself with the fundamental skill of creating a file in Linux using the terminal! Using the Linux command line, several fast and efficient methods exist to create and manage text files. Apply several techniques to meet a different requirement using the touch, echo, cat, printf commands, or text editors like vim, nano, gedit, or emacs. Users can select the method that sufficiently meets their requirements, such as creating empty files, appending text, or significantly modifying material. In summary, any of these methods enable Linux users to easily and quickly handle text files straight from the command line. Frequently Asked Questions (FAQ) How do I create an empty text file in Linux?  The standard command is touch. Simply run: touch filename.txt This creates a blank file immediately. How do I create a file and add content at the same time?  You can use the echo command with the redirection operator (>). echo "Hello World" > filename.txt This creates the file and puts "Hello World" inside it. How do I create and open a file for editing?  Use a terminal text editor like nano or vi. When you run: nano filename.txt Linux will open a blank editor screen. Once you type your text and save (Ctrl+O in nano), the file is created on your disk. What is the fastest way to create a file?  The redirection symbol alone is the quickest method for creating an empty file:> filename.txt This tells the shell to redirect "nothing" into a new file, creating it instantly. How do I create a large file for testing?  Use the fallocate command. For example, to create a 1GB file instantly:fallocate -l 1G bigfile.img How do I view the content of a text file?  Use the cat command to print the text to your terminal: cat filename.txtFor longer files, use less filename.txt to scroll through pages.
21 January 2026 · 10 min to read

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