Change the `uid` of the

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Summary

The issue at hand involves a permissions conflict when attempting to change the uid of a user while another user is still connected to the system. This is a common problem in Linux system administration and Ansible playbook management. The goal is to temporarily switch users in a playbook to modify the uid of the original user without encountering a “user is currently used by process” error.

Root Cause

The root cause of this issue is due to the following reasons:

  • The original user ‘a’ is still connected to the system when attempting to change their uid.
  • The Ansible connection is not properly reset before switching to the new user ‘c’.
  • The processes owned by user ‘a’ are still running, preventing the uid change.

Why This Happens in Real Systems

This issue occurs in real systems because:

  • Concurrency and parallelism in playbooks can lead to unexpected behavior.
  • User session management is not properly handled by default in Ansible.
  • Linux system calls can be unpredictable when dealing with user and process management.

Real-World Impact

The real-world impact of this issue includes:

  • Failed playbooks and inconsistent system states.
  • Security vulnerabilities due to inadequate user management.
  • System downtime and administrative overhead.

Example or Code

- name: Change uid of user 'a' as user 'c'
  become: yes
  become_user: c
  user:
    name: a
    uid: 1001
  when: ansible_user == 'c'

How Senior Engineers Fix It

Senior engineers fix this issue by:

  • Using Ansible’s built-in features such as become and become_user to manage user sessions.
  • Resetting connections using meta: reset_connection before switching users.
  • Ensuring proper user and process management using Linux system calls and Ansible modules.

Why Juniors Miss It

Juniors may miss this issue because:

  • Lack of experience with Ansible and Linux system administration.
  • Insufficient understanding of user and process management.
  • Overlooking the importance of proper connection management in playbooks.