How to Fix Ansible Error when Using Nested Sudo

In this article we will fix Ansible error involving tasks involving nested sudo commands. The problem manifested as a successful run on Ubuntu 20.04 but a failure on Ubuntu 24.04, specifically regarding the handling of password prompts within nested sudo calls. The core issue lies in the differing behaviors of sudo between these Ubuntu versions when dealing with non-interactive sessions.

The Scenario:

The Ansible playbook aimed to execute a Python script (child.py) that, in turn, utilizes sudo to run an apt-get update. The Ansible task leverages become: yes for privilege escalation, executing the Python script with the user's privileges, and then subsequently the script uses sudo internally.

Here's the relevant code:

child.py:

# This program must NOT be executed with sudo
import subprocess

subprocess.run(['sudo', 'apt-get', 'update'], check=True)
    

playbooks/roles/debug_role/tasks/main.yml :

- name: Debug sudo in child process
  command: >-
    sudo -E -H -u {{ ansible_user }} \
    /bin/bash -lc "python3 child.py"
  become: yes
    

playbooks/playbook.yml :

- hosts: all
  roles: [debug_role]
    

This setup worked flawlessly on Ubuntu 20.04, successfully updating the package list. However, on Ubuntu 24.04, the execution failed with the error: sudo: a terminal is required to read the password; either use the -S option to read from standard input or configure an askpass helper.

Root Cause Analysis:

The error message clearly indicates that sudo requires a terminal to prompt for the password in the nested execution context. The difference in behavior between Ubuntu 20.04 and Ubuntu 24.04 stems from changes in how sudo interacts with non-interactive processes. Ubuntu 24.04, by default, enforces a stricter security policy for sudo in scenarios where a terminal isn't available. This is a security enhancement designed to prevent unauthorized password entry.

The -S option suggested in the error message provides a solution—it tells sudo to read the password from standard input. However, simply adding -S isn’t sufficient within the current Ansible setup because the password prompt isn’t handled correctly in this nested execution scenario. The Ansible become mechanism handles the initial privilege escalation, but the subsequent sudo call within child.py operates in a different context, lacking the necessary interactive capabilities.

Resolution and Improved Code:

To address this, a more robust approach is needed. We can avoid the nested sudo entirely by modifying the Ansible task to directly execute apt-get update with appropriate privileges, eliminating the need for the intermediate Python script and the nested sudo call altogether.

Revised Ansible task:

- name: Update apt packages
  become: yes
  command: apt-get update
    

This revised task directly utilizes the become functionality to run apt-get update with elevated privileges, eliminating the source of the problem entirely.

Further Considerations and Best Practices:

• Avoid Nested sudo: Nested sudo calls should generally be avoided in Ansible playbooks due to their inherent complexity and potential for unexpected behavior across different systems and versions. Directly using Ansible’s become feature is often a cleaner and more reliable solution.

• Ansible's become_method: Experiment with different become_method options in your Ansible configuration (e.g., sudo, pkexec, su). While sudo is commonly used, other methods might offer better compatibility or security in specific environments. Consult your Ansible documentation for detailed information about become_method configurations.

• Idempotency: Ensure that your Ansible tasks are idempotent. Idempotency means that running a task multiple times has the same effect as running it once. This is a crucial aspect of Ansible's design for reliable and predictable automation. The apt-get update command itself is generally considered idempotent, as subsequent executions won't cause any harm if the package list is already up-to-date.

• Error Handling: Always incorporate robust error handling into your Ansible playbooks. This involves checking the return codes of commands and gracefully handling potential failures. While the improved solution is simpler, it still would benefit from adding error handling to ensure that failures are reported appropriately.

This refined approach simplifies the process, eliminates the problematic nested sudo, and provides a more reliable and maintainable solution. By directly using Ansible’s built-in privilege escalation capabilities and adhering to best practices, you can effectively manage system administration tasks without encountering the complications of nested sudo calls.

Keywords: Ansible, sudo, nested sudo, Ubuntu, apt-get, privilege escalation, automation, security, error handling, idempotency, Ansible best practices, command execution, become, become_method