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Conditionals

Sometimes you want a task to run only under certain conditions – for example, only on a specific operating system, or only if a file exists. Ansible conditionals give you that control.

The when Clause

Add a when statement to a task. The task runs only if the condition evaluates to true.
- name: Shut down Debian systems
  command: /sbin/shutdown -t now
  when: ansible_os_family == "Debian"

Common Conditionals

Ansible provides many built‑in facts (gathered by setup module). Use ansible_facts or the short variable names:
  • ansible_os_family – e.g., Debian, RedHat
  • ansible_distribution – e.g., Ubuntu, CentOS
  • ansible_processor_cores
  • ansible_memtotal_mb
  • ansible_hostname
View all facts:
ansible localhost -m setup

Example: Install Apache on RHEL, Nginx on Debian

- name: Install web server
  hosts: all
  become: yes
  tasks:
    - name: Install nginx on Debian
      apt:
        name: nginx
        state: present
      when: ansible_os_family == "Debian"

    - name: Install httpd on RedHat
      yum:
        name: httpd
        state: present
      when: ansible_os_family == "RedHat"

Using when with Variables and Register

You can test variables or registered results:
- name: Check if file exists
  stat:
    path: /etc/myapp.conf
  register: myapp_config

- name: Only run if config exists
  command: /usr/bin/validate_config
  when: myapp_config.stat.exists

Multiple Conditions

Use logical operators:
when: ansible_distribution == "Ubuntu" and ansible_distribution_major_version == "20.04"
Or:
when: ansible_os_family == "Debian" or ansible_os_family == "RedHat"


Two Minute Drill
  • when conditionally runs a task.
  • Use facts like ansible_os_family for OS‑specific tasks.
  • Check registered results with when: result.stat.exists.
  • Combine conditions with and/or.

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