If the script:
- command: "whoami"
become: true
become_user: "{{ deploy_user }}"
register: u
tags:
- f
- debug: msg="{{ u.stdout }}"
tags:
- fProduces the error:
Failed to set permissions on the temporary files Ansible needs to create when becoming an unprivileged user

Install the acl package that provides setfacl so that proper permissions can be applied to the /tmp folders. [Source]
- name: Install acl
apt:
state: latest
update_cache: true
pkg:
- acl
Ansible documentation is broken
Many links from Google and Ansible's own error messages from versions past are now broken. It's unfortunate that RedHat did not care enough to redirect pages to their new "improved" module doc hierarchy.
