Use serial to run a play against 20% of hosts at a time

Short answer

Use the serial keyword to limit how many hosts Ansible processes in each batch.

Request

check uptime and date on 20% of hosts at a time using the serial keyword; changed_when: false

Example

A quick heads-up: Every environment is different. Review and test this example before you run it on systems you care about.

---
- name: Check uptime and date on 20% of hosts at a time
  hosts: all
  gather_facts: true
  serial: "20%"
  tasks:
    - name: Check uptime
      ansible.builtin.command:
        cmd: uptime
      register: uptime_result
      changed_when: false

    - name: Check date
      ansible.builtin.command:
        cmd: date
      register: date_result
      changed_when: false

    - name: Display uptime
      ansible.builtin.debug:
        msg: "{{ uptime_result.stdout }}"

    - name: Display date
      ansible.builtin.debug:
        msg: "{{ date_result.stdout }}"

How it works

serial accepts a number or a percentage. Ansible finishes one batch before it starts the next batch. Set changed_when to false on read-only command tasks so they do not report changed.

When to use it

• Use serial when you must update hosts in controlled batches.
• Do not use serial when every host must change in one wave.
• Rolling updates across a large inventory

Requirements

• Ansible: >=2.14
• An inventory with multiple hosts

Validation

• Syntax validated
• Execution passed
• Last verified 2026-09-03