Ansible User Notes

Updated Thu 2018-02-01 | 659 words

Ansible has two types of users: become_user and remote_user (and the deprecated ssh_user and sudo_user that I won't cover). Here's how to use them:

remote_user is the account that logs into the machine (ssh vagrant@tmp_ansible_test_vm would have vagrant as the remote user). If this user is going to do perform tasks as root or another user, it should have sudo permissions (i.e., be added to the wheel group on CentOS).

If the remote_user is going to perform tasks as root or another user, set the become: option to true (at either the playbook or the task level) and the become_user: option to the name of the other user or root. If you don't specify become_user, the default is to switch to root.

Setting remote_user and become_user

remote_user options can be set in the hosts file or with the following command line options (gleaned from ansible-playbook --help):

    -k, --ask-pass      ask for connection password
    --private-key=PRIVATE_KEY_FILE, --key-file=PRIVATE_KEY_FILE
                        use this file to authenticate the connection
    -u REMOTE_USER, --user=REMOTE_USER
                        connect as this user (default=None)

become_user options can be set per playbook, task, or via the following connection options (gleaned from ansible-playbook --help):

    -b, --become        run operations with become (does not imply password
                        prompting)
    --become-method=BECOME_METHOD
                        privilege escalation method to use (default=sudo),
                        valid choices: [ sudo | su | pbrun | pfexec | doas |
                        dzdo | ksu | runas | pmrun ]
    --become-user=BECOME_USER
                        run operations as this user (default=root)
    ... skipping some irrelevant ones
    -K, --ask-become-pass
                        ask for privilege escalation password

Using become_user and remote_user effectively

I prefer setting remote_user in the hosts file and become_user in the command line options because it's easier to change hosts files then playbooks. Unfortunately, as of Ansible 2.4, the documented remote_user and private_key_file options don't seem to work, so I resort to the older and undocumented ansible_ssh_user and ansible_ssh_private_key_file(they appear to be the same):

Setting remote_user in the host file for vagrant instances:

all:
  hosts:
    tmp-ansible-test_vm:
      ansible_host: 10.0.0.11
      ansible_ssh_user: vagrant  # remote_user / private_key_file doesn't seem to work
      ansible_ssh_private_key_file: ./.vagrant/machines/tmp_ansible_test_vm/virtualbox/private_key

Setting become_user in descending order of precedence:

Command line argument (least powerful)

This also specifies some other options for good measure

ansible-playbook \
    --user=vagrant \
    --ask-pass \
    --become-user=network-automation \
    --ask-become-pass \
    --inventory 10.0.0.11, \
    install_all.yaml

Playbook level

- hosts: all
  become: true
  become_user: network-automation  # Not recommended, see below
  ... # other stuff

Task level (most powerful)

  - name: Push the service file
    become: true
    become_user: root
    copy:
      src: "../systemd/my_service@.service"
      dest: /etc/systemd/system/my_service@.service

My strategy for using become_user:

  • become_user at the task level overrides become_user at the playbook level overrides become_user at the command switch level
  • After initial development, don't specify become_user at the playbook level- this will let you set it at the command option level (different servers need different ones for the same playbook) or at the task level (which, for most purposes, should only need root)
  • If you need to use root for a task, always use become: true and become_user: root. This will override whatever default become_user is set.

Getting the name of become_user as a variable

For some reason, this isn't normally exposed. Here's a way to get it:

{% raw %}  - name: Get become_user in stdout (hack for Ansible not providing it as a variable)
    command: whoami
    register: whoami_output
  - set_fact:
      become_user_var: "{{ whoami_output.stdout }}"{% endraw %}

Other Notes:

  • --ask-become-pass will break running the playbook if remote_user has passwordless sudo
  • become_user will fail if Ansible detects it has to do it insecurely (see the docs). Set the following option in ansbible.cfg to tell Ansible this is okay.
# This presents a window for a logged-in attacker,
# but it's a small window and I need what it enables
# See http://docs.ansible.com/ansible/latest/become.html#becoming-an-unprivileged-user
allow_world_readable_tmpfiles = True