# Golden images (/docs/guides/golden-images)



A brand-new simulator's first boot takes 1–10 min, and about 80% of that is the one-time data migration. Measured:

| Scenario                         | Time           |
| -------------------------------- | -------------- |
| fresh create + first boot        | 146–239 s      |
| clone of a settled golden + boot | 3.7 s + 11.9 s |
| 3 clones booted in parallel      | \~20 s         |

So when `warden claim ios` needs a **new** pool device, it clones it (`simctl clone`) from a **golden image**: a sim warden booted once, waited on until its data migration finished (`DMLastMigrationResults`, since `bootstatus -b` can return early) and its CPU settled, then shut down.

* The golden is built on first use and keyed by Xcode build + runtime + runtime build + device type + recipe. An Xcode or runtime upgrade simply builds a new one.
* Clones are APFS copy-on-write (\~30 MB each).
* If cloning fails, warden falls back to `simctl create`. `WARDEN_GOLDEN=0` turns cloning off.
* A pool device that already exists is always reused first; a second boot takes \~6.5 s.
* Goldens are never allocated, adopted, booted by `gc` or counted in the pool; `warden devices` labels them `golden`.

## Commands [#commands]

```bash
warden golden ensure --profile iphone-17   # build ahead of time, so the first claim doesn't pay
warden golden ls
warden golden prune                        # delete stale goldens; --all deletes every one
```

## Cloning your own sim [#cloning-your-own-sim]

`warden clone <udid|name> [--name x]` duplicates any **shut-down** sim — e.g. one you've set up by hand — into warden's pool. warden refuses a booted source rather than shutting it down.