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:

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

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

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.