Ansible: 'variable' is undefined

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

# Define in playbook vars
vars:
  my_var: value
# Or in group_vars/all.yml
# Or provide at runtime
ansible-playbook playbook.yml -e "my_var=value"
# Use default filter
{{ my_var | default('fallback') }}

How to diagnose Ansible errors

Ansible errors split cleanly between transport problems (it cannot reach or authenticate to the host) and execution problems (it reached the host but the play failed). The message header tells you which: UNREACHABLE! is transport, FAILED! is execution. Transport issues are SSH issues wearing an Ansible hat and should be debugged with plain ssh first.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

1. Run ansible -m ping all before running any playbook. It isolates connectivity and privilege escalation from your task logic.
2. Raise verbosity progressively: -v shows results, -vvv shows the SSH command line, -vvvv shows connection debugging. Most unreachable errors are solved at -vvv.
3. Use --check --diff to see what a play would change without changing it. This turns a destructive debugging loop into a safe one.
4. For undefined-variable errors, dump the actual scope with a debug task (var: hostvars[inventory_hostname]) rather than reasoning about precedence from the docs.
5. Remember variable precedence order: extra vars (-e) beat everything, role defaults lose to everything. Surprising values are nearly always a precedence surprise.

Tools worth reaching for

• ansible -m ping
• ansible-playbook --check --diff
• ansible-lint
• ssh -vvv

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

📖 docs.ansible.com

Related Ansible errors

• Ansible: Host unreachableCannot connect to target host via SSH. Network issues, wrong IP, SSH not running, or key…
• Ansible: Jinja2 template errorA Jinja2 template in a playbook or template file has a syntax error such as unclosed braces…
• Ansible: Module not foundSpecified module doesn't exist or isn't installed. Wrong module name or collection not…
• Ansible: Playbook syntax errorYAML syntax error in playbook. Indentation issues, invalid YAML, or missing required fields.
• Ansible: Privilege escalation password requiredTask requires sudo but password not provided. Target user needs sudo password for privilege…
• Ansible: SSH connection timeoutAnsible timed out trying to establish an SSH connection to the target host. The host may be…
• Ansible: The conditional check 'result.rc == 0' failedThe when expression could not be evaluated, usually because the variable it names does not…
• Ansible: Vault password not providedA playbook uses encrypted vault variables but no vault password was supplied at runtime.

See all 10 Ansible errors →

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This entry is maintained by hand. If the fix is out of date, incomplete, or you have a better one, email a correction and it will be reviewed.