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Linux Level 1, Task 14: Changing the Default Boot Target

Today's task was a fundamental system administration skill: changing the default boot target (or "runlevel") of a server. My goal was to reconfigure all app servers to boot into a graphical user interface (GUI) by default, instead of the standard command-line interface.

This exercise was a perfect opportunity to contrast the repetitive manual approach with a powerful, automated solution using Ansible. This document is my first-person guide, detailing both methods and explaining the concepts behind systemd targets.

The Task

My objective was to change the default boot behavior on all three Nautilus app servers. The specific requirements were: - Set the default boot target to the graphical user interface. - Do not reboot the servers after making the change.

Solution 1: The Manual Approach (Server by Server)

This method involves logging into each server individually and running the same commands. It's direct but not scalable.

The Workflow (Repeated 3 Times)

  1. Connect to the Server: I started by connecting to the first app server. 

    ssh tony@stapp01

  2. Check the Current Default: I used systemctl to see the current default boot target. 

    systemctl get-default
# Output: multi-user.target
    This confirmed the server was set to boot into the command line.

  3. Set the New Default: This was the core of the task. I set the new default to graphical.target. 

    sudo systemctl set-default graphical.target
    This command creates a symbolic link that systemd reads on the next boot.

  4. Verification: I ran the get-default command again to confirm the change was made successfully. 

    systemctl get-default
# Output: graphical.target
    Seeing this output was the definitive proof of success for that server.

I then had to exit and repeat this entire process for stapp02 and stapp03.

Solution 2: The Automated Approach (with Ansible)

This is the professional, scalable solution. I performed all my work from the jump host, using Ansible to orchestrate the change on all three app servers at once.

1. The Inventory (inventory.ini)

First, I created an "address book" for Ansible on the jump host. 

[app_servers]
stapp01 ansible_host=172.16.238.10 ansible_user=tony ansible_ssh_pass=Ir0nM@n ansible_become_pass=Ir0nM@n
stapp02 ansible_host=172.16.238.11 ansible_user=steve ansible_ssh_pass=Am3ric@ ansible_become_pass=Am3ric@
stapp03 ansible_host=172.16.238.12 ansible_user=banner ansible_ssh_pass=BigGr33n ansible_become_pass=BigGr33n

2. The Playbook (playbook.yml)

Next, I wrote a simple "to-do list" in YAML. 

---
- name: Set Default Boot Target to Graphical
  hosts: app_servers
  become: yes
  tasks:
    - name: Set default target to graphical.target
      ansible.builtin.command:
        cmd: systemctl set-default graphical.target

3. The Execution

Finally, from the jump host, I ran a single command to execute the playbook. 

ansible-playbook -i inventory.ini playbook.yml
Ansible then connected to all three servers and ran the command, completing the task for the entire fleet in seconds.

Key Concepts (The "What & Why")

  • Runlevels and systemd Targets: These define the state a Linux system boots into.
    • In older systems, these were numeric "runlevels" (e.g., runlevel 3 for text, 5 for GUI).
    • In modern systems using systemd, these are descriptive "targets." A target is a collection of systemd units that should be started to reach a certain state.
  • multi-user.target: This is the standard target for a server. It starts all the necessary networking and system services to allow multiple users to log in via the command line, but it does not start a graphical display manager. This is efficient and uses minimal resources.
  • graphical.target: This target includes everything in multi-user.target and adds the services needed to run a full graphical desktop environment (like GNOME or KDE). This is the standard for desktop Linux distributions but is less common on servers unless specific GUI-based tools are required.
  • systemctl set-default: This is the command used to change the default target for the next boot. It works by creating a symbolic link at /etc/systemd/system/default.target that points to the desired target file (e.g., /usr/lib/systemd/system/graphical.target). It does not change the current running state, which is why a reboot was not required for this task.

Commands I Used

Manual Commands

  • systemctl get-default: A command to check the currently configured default boot target. I used this for both initial investigation and final verification.
  • sudo systemctl set-default graphical.target: The main command for this task. It sets the default boot target for systemd to the graphical environment.

Ansible Modules

  • ansible-playbook -i [inventory] [playbook]: The main command to run an Ansible playbook.
  • ansible.builtin.command: An Ansible module that allows you to run a simple shell command on the remote host(s). While there are more specific modules for managing systemd, this is a direct and effective way to run the set-default command. become: yes was used in the playbook to ensure the command was run with sudo.