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playbooks/append_to_cmdline_txt.md

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+To create an Ansible playbook that appends the specified kernel parameters (`rootwait cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory`) to the `/boot/firmware/cmdline.txt` file only if they are not already present, you can use the `lineinfile` Ansible module.
+
+Here's how the playbook can be written:
+
+### Ansible Playbook (`append_cmdline.yml`):
+
+```yaml
+---
+- name: Ensure required parameters are in /boot/firmware/cmdline.txt
+  hosts: raspberry_pi
+  become: yes
+  tasks:
+    - name: Append kernel parameters to cmdline.txt if not present
+      lineinfile:
+        path: /boot/firmware/cmdline.txt
+        line: "rootwait cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory"
+        insertafter: EOF
+        state: present
+        create: yes
+        backup: yes  # This creates a backup of the file before making changes
+      notify:
+        - Reboot system
+
+  handlers:
+    - name: Reboot system
+      reboot:
+        msg: "Rebooting system to apply new kernel parameters"
+        reboot_timeout: 600
+        test_command: uptime
+```
+
+### Explanation of the Playbook:
+
+- **`hosts: raspberry_pi`**: Targets the Raspberry Pi group from your inventory.
+- **`become: yes`**: Ensures that the task runs with elevated privileges (sudo), which is necessary for modifying system files like `/boot/firmware/cmdline.txt`.
+  
+### Task:
+
+- **`lineinfile` module**: 
+  - `path: /boot/firmware/cmdline.txt`: This specifies the file to modify.
+  - `line`: This is the exact string to ensure is present in the file.
+  - `insertafter: EOF`: This ensures the line is appended at the end of the file if it is not already there.
+  - `state: present`: Ensures that the specified line exists in the file.
+  - `create: yes`: If the file doesn't exist, it will be created (though it's unlikely in this case because `/boot/firmware/cmdline.txt` should exist on a Raspberry Pi).
+  - `backup: yes`: This creates a backup of the file before modifying it (important for safety).
+
+### Handler:
+
+- **`Reboot system` handler**: 
+  - This handler is triggered if the task changes the file (i.e., if it appends the line). 
+  - It will reboot the Raspberry Pi to apply the changes, which often requires a reboot to take effect.
+  - `reboot_timeout: 600` specifies that the playbook will wait up to 600 seconds for the system to reboot successfully.
+  - `test_command: uptime` ensures that the system is back up and running after the reboot.
+
+### To run the playbook:
+
+1. Save the playbook to a file, e.g., `append_cmdline.yml`.
+2. Run the playbook with the following command:
+
+   ```bash
+   ansible-playbook -i inventory.ini append_cmdline.yml
+   ```
+
+This will ensure the specified parameters are added to `/boot/firmware/cmdline.txt` only if they are not already present and reboot the system if necessary. If you have any more questions or need further adjustments, feel free to ask!