1. ansible.posix.at：写一个playbook，让所有的受控主机在20分钟之后，执行命令ls -d / >/dev/null，确保这个任务是独一无二的；
2. ansible.posix.at：写一个playbook，确保任务ls -d / >/dev/null不存在；
3. ansible.posix.cron：写一个playbook，对于用户centos，每天的2点和5点都会运行任务ls -alh > /dev/null；
4. ansible.posix.cron：写一个playbook，对于用户centos，每周五16点每隔两分钟，都会运行任务ls -alh > /dev/null；
5. ansible.builtin.service：启动并开机自启httpd服务；
6. ansible.builtin.systemd：启动并开机自启httpd服务；
7. ansible.builtin.systemd：重新加载所有对于httpd配置的改动，然后重启httpd服务；
8. ansible.builtin.command：写一个playbook，将默认target设置为multi-user.target；
9. ansible.builtin.reboot：重启受控主机；

1. /* A20240605.yaml */
---
- name: Play1
  hosts: all
  tasks:
    - name: Task1
      ansible.posix.at:
        command: ls -d / >/dev/null
        count: 20
        units: minutes
        unique: yes
...
2. /* B20240605.yaml */
---
- name: Play1
  hosts: all
  tasks:
    - name: Task1
      ansible.posix.at:
        command: ls -d / >/dev/null
        state: absent
...
3. /* C20240605.yaml */
---
- name: Play1
  hosts: all
  tasks:
    - name: Task1
      ansible.builtin.cron:
        user: centos
        name: job1
        job: "ls -alh > /dev/null"
        hour: "2,5"
...
4. /* D20240605.yaml */
---
- name: Play1
  hosts: all
  tasks:
    - name: Task1
      ansible.builtin.cron:
        user: centos
        name: job2
        job: "ls -alh > /dev/null"
        weekday: "5"
        hour: "16"
        minute: "*/2"
...
5. /* E20240605.yaml */
---
- name: Play1
  hosts: all
  tasks:
    - name: Task1
      ansible.builtin.service:
        name: httpd
        state: started
        enabled: true
...
6. /* F20240605.yaml */
---
- name: Play1
  hosts: all
  tasks:
    - name: Task1
      ansible.builtin.systemd:
        name: httpd
        state: started
        enabled: true
...
7. /* G20240605.yaml */
---
- name: Play1
  hosts: all
  tasks:
    - name: Task1
      ansible.builtin.systemd:
        name: httpd
        state: reloaded
        daemon_reload: yes
...
8. /* H20240605.yaml */
---
- name: Play1
  hosts: all
  vars:
    - target: multi-user.target
  tasks:
    - name: Task1
      ansible.builtin.command:
        cmd: systemctl get-default
      changed_when: false
      register: Task1result
    - name: Task2
      ansible.builtin.command:
        cmd: systemctl set-default {{ target }}
      when: target not in Task1result.stdout
...
9. /* I20240605.yaml */
---
- name: Play1
  hosts: centos7.example.com,centos8.example.com
  tasks:
    - name: Task1
      ansible.builtin.reboot:
        reboot_timeout: 180
...