How to append entries in `/etc/fstab` of disks using Ansible-playbook?

Question

I am using below playbook to write entries to /etc/fstab . And to create swap file:

---

- name: Configure SWAP
  hosts: localhost
  become: yes
  become_user: root

  tasks:
    - name: Configuring a SWAP
      command: "{{ item }}"
      loop:
        - mkswap -f "{{ ebs_swap }}"
        - echo "UUID=$(blkid -s UUID -o value {{ ebs_swap }})   swap    swap   defaults  0   0" | sudo tee -a /etc/fstab
        - swapon -a
      register: output

    - name: Display the variable
      debug:
       msg: "{{ output}}"

We are running it with command: ansible-playbook mount.yml -e "ebs_swap=/dev/xvdj"

O/P:

                "item": "echo \"UUID=$(blkid -s UUID -o value /dev/xvdj)   swap    swap   defaults  0   0\" | sudo tee -a /etc/fstab",
                "rc": 0,
                "start": "2020-04-09 14:51:23.890047",
                "stderr": "",
                "stderr_lines": [],
                "stdout": "UUID=$(blkid -s UUID -o value /dev/xvdj)   swap    swap   defaults  0   0 | sudo tee -a /etc/fstab",
                "stdout_lines": [
                    "UUID=$(blkid -s UUID -o value /dev/xvdj)   swap    swap   defaults  0   0 | sudo tee -a /etc/fstab"

Can any one tell me why am I unable to get the entry in /etc/fstab & when I am trying to run above commands its getting success.

Answer 1

I have resolved it by using below:

- name: Dispaly uuid & store in variable
  command: blkid -s UUID -o value {{ ebs_swap }}
  register: uuid_swap

- name: Add the below lines
  blockinfile:
    path: /etc/fstab
    state: present
    block: |
      UUID={{ uuid_swap.stdout }}   swap      swap defaults                         0   0

Answer 2

According to the module doc https://docs.ansible.com/ansible/latest/modules/command_module.html :

If you want to run a command through the shell (say you are using <, >, |, etc), you actually want the shell module instead. Parsing shell metacharacters can lead to unexpected commands being executed if quoting is not done correctly so it is more secure to use the command module when possible.

Anyway, I think you don't want this line to be added to your file on every run of this playbook, use lineinfile instead to ensure that this line exists:

- shell: blkid -s UUID -o value {{ ebs_swap }})
  register: blkid_out

- lineinfile:
    path: /etc/fstab
    regexp: "^UUID={{ blkid_out.stdout }}"
    line: "UUID={{ blkid_out.stdout }}   swap    swap   defaults  0   0"

Now the line will be added only when it doesn't exist