## TL;DR
Fix name resolution for the W&B host before retrying the sync: wandb cannot resolve its host in online mode, so check DNS from the run machine, correct any stale hosts entry or proxy setting, and sync again once the host resolves. A resolve failure is below HTTP entirely: the client never reached W&B. Offline runs keep queuing locally while the network fault persists, which is why the data is usually safe.

```text
wandb sync failed error "wandb: ERROR Network error: failed to resolve host" in online mode
```

## Use this when
- The check or run fails with this symptom: a wandb sync fails with network error failed to resolve host in online mode.
- You are working on a Weights and Biases client in online mode on a training machine or cluster node and the failure repeats on the same data or configuration.
- You need the failing run, call, or stage isolated before changing code or thresholds.

## Not for this skill when
- A self-hosted W&B instance whose internal name only resolves inside one network, which needs the run moved or the name published.
- The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

## Steps
1. Resolve the W&B host name from the failing machine. Verify: resolution fails there while it may succeed elsewhere
2. Check the machine DNS configuration, any local hosts overrides, and proxy environment settings. Verify: the stale or missing resolver entry is identified
3. Correct the resolver or proxy setting, or switch the run to the reachable host address for a self-hosted instance. Verify: the host name resolves
4. Run the wandb sync for the queued run. Verify: the run uploads and appears in the project
5. Confirm the run data is complete in the UI. Verify: metrics and config match the local run directory

## Variant phrasings
### wandb sync failed resolve host network error online
The shorter phrasing focused on the named failure.
### wandb ERROR network error failed to resolve host
The symptom phrasing a searcher tries next.
### wandb dns resolve host fix
The variant naming the failing stage or tool directly.

Compatibility: Weights and Biases online and offline modes, DNS and proxy configuration on training hosts

## Why it happens
Cluster nodes, containers, and VPN-less remote machines often have partial network setups where package mirrors resolve but external service names do not. W&B reports the raw resolver failure, and because training itself succeeded, the sync failure is discovered late.

## Edge cases / pitfalls
- Offline mode plus a scheduled sync job is the resilient pattern for unreliable training networks; the failure then never blocks a run.
- A proxy that resolves names on the client behalf needs the W&B host allowed through it; a direct DNS fix will not help that setup.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_prQYnSn4cXBTX1o5k7sq9w