Ansible: The conditional check 'result.rc == 0' failed

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.

# See what the variable actually holds on the failing host
ansible-playbook site.yml -l web01 -vvv
- debug: var=result

# A registered variable from a skipped task is still defined, but has no rc
- name: Check the service
  command: systemctl is-active nginx
  register: result
  when: ansible_facts['os_family'] == 'RedHat'
  changed_when: false
  failed_when: false

- name: Act on it
  debug: msg="running"
  when: result.rc is defined and result.rc == 0

# Defaults keep the expression evaluable everywhere
when: (result.rc | default(1)) == 0

# Do not wrap the whole condition in braces: when is already an expression
# when: "{{ result.rc == 0 }}"   wrong
# when: result.rc == 0          right

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: 'variable' is undefinedA variable used in a playbook or template was not defined in inventory, group_vars…
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• 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.
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• Ansible: SSH connection timeoutAnsible timed out trying to establish an SSH connection to the target host. The host may be…
• Ansible: Vault password not providedA playbook uses encrypted vault variables but no vault password was supplied at runtime.

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Something missing or wrong?

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.