## TL;DR
Fix this in Chronicle by acting on the exact message first: add a parser mapping in Chronicle for the vendor field that carries the hostname, map it to the UDM principal hostname field, validate the mapping on one raw log, and reprocess the affected alerts so the normalized record shows the hostname. Do not rerun the whole job unchanged, because the same inputs produce the same failure. Prove the fix on one item, then rerun the full scope and reconcile the counts.

```text
Chronicle error UDM field unmapped hostname missing from normalized alert
```

## Use this when
- The operation in Chronicle fails with this exact message: Chronicle error UDM field unmapped hostname missing from normalized alert.
- The same failure repeats on retry with unchanged inputs.
- An alert, incident or enrichment step is blocked until this item completes.

## Not for this skill when
- The message is a permission or outage notice from the platform. Resolve that first, then return here if this error remains.
- The operation completes and you only disagree with its output. That is a quality review, not this failure.

## Steps
1. Reproduce the failure with the smallest scope that still shows it in Chronicle, and copy the full message plus the alert, incident or enrichment record involved into the run notes. Verify: the error is reproduced on demand with a named item, not only seen in a log.
2. Apply the specific fix for this error: add a parser mapping in Chronicle for the vendor field that carries the hostname, map it to the UDM principal hostname field, validate the mapping on one raw log, and reprocess the affected alerts so the normalized record shows the hostname. Verify: the single failing item now behaves as the fix predicts, or the corrected value is visible on the record.
3. Check the neighbouring items that share the same config, template, feed or credential, because this class of failure rarely affects only one item. Verify: the neighbouring items are listed and each is marked affected or clear.
4. Compare the result counts, decisions or alerts against the source in Chronicle so a silent partial success is caught before sign off. Verify: counts match the source or every difference is named and explained.
5. Rerun the original operation in Chronicle on the previously failing scope, watching for the same message rather than assuming success from a quiet log. Verify: the operation completes and the original message does not appear.
6. Record the fix, the triggering input and the verification result on the item so the next occurrence is recognised immediately. Verify: the record names the error, the fix applied and the evidence of success.

## Why it happens
Chronicle normalization only fills UDM fields the parser explicitly maps, so a hostname sent under a vendor specific field name is dropped during parsing and never reaches the normalized alert.

## Variant phrasings

### Chronicle error UDM field unmapped hostname missing from normalized alert
The verbatim form searchers paste from the terminal or console. Treat it identically: same fix, same single item proof, then the full rerun.

### How to fix - Chronicle error UDM field unmapped hostname missing from normalized alert
The how-to phrasing for the same failure in Chronicle. The steps above apply unchanged; start at the reproduction step rather than skipping to the rerun.

### Chronicle troubleshooting for this failure
The symptom-first phrasing used when the console hides the full message. Surface the full message first, confirm it matches the code block above, then follow the steps.

Compatibility: Chronicle at current versions, plus the platform API or console the query names; no extra tooling beyond a text editor and the source system access needed to verify counts.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_3LOOW9lNckI0pLsOnVXPfg