Linux Operations
Linux DNS Resolution Debugging Guide
Debug Linux name-resolution failures across application resolvers, NSS, systemd-resolved, search domains, containers and authoritative DNS evidence. This reference is written for developers who need practical validation behavior, reviewable rules and safe examples rather than copied snippets with no explanation.
Recommended workflow
| Step | Why it matters |
|---|---|
| Reproduce through the application path | Use getent or the runtime resolver before comparing direct DNS tools. |
| Inspect resolver configuration | Review NSS order, resolv.conf ownership, search domains and per-link DNS state. |
| Test specific servers | Query configured recursive servers to separate local stub and upstream behavior. |
| Check container boundaries | Compare host, container and orchestration DNS configuration and suffix expansion. |
Starter snippet
getent hosts example.com; resolvectl query example.comReview checks
- Record A and AAAA behavior.
- Check negative caching after fixes.
- Use fully qualified names during diagnosis.
- Preserve split-DNS and VPN context.
Common mistakes
- Replacing resolv.conf without knowing its manager.
- Using ping as the only DNS test.
- Assuming dig matches application NSS behavior.
Validation should help users correct input while protecting systems from bad data. Keep syntax checks, product policy, security review and deliverability checks separate.
Related Formalint references
Continue with Dns Debugging Guide, Docker Compose Debugging Guide, Kubernetes Pod Debugging Guide.