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About Luca Berton

Luca Berton is an Ansible automation expert, author of 8 Ansible books published by Apress and Leanpub including "Ansible for VMware by Examples" and "Ansible for Kubernetes by Example", and creator of the Ansible Pilot YouTube channel. He shares practical automation knowledge through tutorials, books, and video courses to help IT professionals and DevOps engineers master infrastructure automation.

Ansible Fix 'VARIABLE IS NOT DEFINED' Error: Undefined Variables — Video Tutorial

Fix Ansible VARIABLE IS NOT DEFINED error. Troubleshoot undefined variables, missing facts, gather_facts issues, and use default filter for safe access.

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Tutorial summary

What you'll learn

  • Introduction
  • Playbook
  • error code
  • error execution
  • fix code
  • fix execution
  • Conclusion
  • Why Does This Error Happen?
  • Common Variables That Require gather_facts
  • Variables That DON'T Require gather_facts
Introduction Today we’re going to talk about Ansible troubleshooting, specifically about VARIABLE IS NOT DEFINED! Message. Most of the time the root cause is a misspelled variable or a variable really not defined. This use case is special about the `ansible_hostname` internal variable. I’m Luca Berton and welcome to today’s episode of Ansible Pilot. Playbook The best way of talking about Ansible troubleshooting is to jump in a live Playbook to show you practically the VARIABLE IS NOT DEFINED! and how to solve it! error code ```yaml --- - name: hostname Playbook hosts: all gather_facts: false tasks: - name: print hostname ansible.builtin.debug: var: ansible_hostname ``` error execution ```bash ansible-pilot $ ansible-playbook -i virtualmachines/demo/inventory troubleshooting/variablenotdefined_error.yml PLAY [hostname Playbook] ****************************************************************************** TASK [print hostname] ***************************************************************************** ok: [demo.example.com] => { "ansible_hostname": "VARIABLE IS NOT DEFINED!" } PLAY RECAP **************************************************************************************** demo.example.com : ok=1 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0 ansible-pilot $ ``` fix code ```yaml --- - name: hostname Playbook hosts: all gather_facts: true tasks: - name: print hostname ansible.builtin.debug: var: ansible_hostname ``` fix execution ```bash ansible-pilot $ ansible-playbook -i virtualmachines/demo/inventory troubleshooting/variablenotdefined_fix.yml PLAY [hostname Playbook] ****************************************************************************** TASK [Gathering Facts] **************************************************************************** ok: [demo.example.com] TASK [print hostname] ***************************************************************************** ok: [demo.example.com] => { "ansible_hostname": "Playbook" } PLAY RECAP **************************************************************************************** demo.example.com : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0 ansible-pilot $ ``` [code with ❤️ in GitHub](https://github.com/lucab85/ansible-pilot/tree/master/troubleshooting) Conclusion Now you know better how to troubleshoot the Ansible VARIABLE IS NOT DEFINED! message. Why Does This Error Happen? Ansible has two types of variables: 1. **User-defined variables** — you create them with `vars:`, `set_fact`, `register`, etc. 2. **Facts (built-in variables)** — Ansible collects them automatically from managed hosts Facts like `ansible_hostname`, `ansible_os_family`, `ansible_distribution`, and `ansible_default_ipv4` are **only available if `gather_facts: true`** (which is the default). If you set `gather_facts: false`, these variables don't exist. Common Vari

About this tutorial

  • Author: Luca Berton
  • Difficulty: Beginner
  • Read time: 9 min
  • Category: troubleshooting

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