simslim-mirror/docs/disk-cleanup.md

Disk cleanup safety model

Service slimming and disk cleanup have different guarantees. Service slimming is reversible with simslim off. Disk cleanup permanently removes files.

Boundary

simslim only considers data below one exact simulator's device-data directory:

~/Library/Developer/CoreSimulator/Devices/<UDID>/data

It never changes an iOS runtime. Apple describes a Simulator runtime as an OS package used by multiple simulator devices, and modern runtime disk images are kept in system-managed protected storage. Built-in apps and core OS language resources therefore are not per-device savings and are outside simslim's cleanup boundary.

• Apple: Adding additional simulators
• Xcode 14 release notes: system-managed Simulator runtime disk images

Current categories

Category	Action	Main downside	Recovery
System & App Caches	Clears contents of directories named Caches	Slower first launch; cached/offline content disappears	Old contents are not restored by erase; new caches usually regenerate
Logs & Diagnostics	Clears logs, unified-log traces, and UUID text	Existing debugging and crash history disappears	Old history is not restored by erase; new logs are generated
Temporary Files	Clears contents of tmp directories	Misbehaving apps may lose in-progress work	Old contents are not restored by erase; directories remain and are reused
Downloaded Language Data	Opt-in; clears the exact per-device LinguisticData catalog	Search, Siri, and text analysis may be limited until needed assets return	iOS downloads the package again when a feature requests it
Required Siri Assets	Measured only	Manual deletion is unsupported and iOS downloads required assets again	Required assets return automatically after boot

Apple Developer Forum reports document CoreSimulator's Library/Caches/com.apple.containermanagerd/Dead cache growing unexpectedly; it is covered by the cache category.

• Apple Developer Forums: Core Simulator cache consuming disk space

Recovery

There are two distinct recovery models:

1. Cleanup data such as caches, logs, diagnostics, and temporary files is disposable but its old contents are permanent history. xcrun simctl erase <UDID> does not bring those contents back. iOS and apps can generate new caches, logs, and temporary files on future boots.
2. Downloaded system-managed assets such as Siri models and language data are split by observed behavior. The exact LinguisticData catalog is opt-in and on-demand. Required Siri, speech, and voice catalogs remain informational because iOS automatically restores them after boot.

Read-only storage breakdown

disk-plan and the app report durable storage separately from cleanup choices:

• Installed Apps measures app and test-runner bundles installed into that simulator. Built-in apps are not counted because they live in the shared runtime.
• Documents measures app and app-group Documents directories.
• App Data measures preferences, databases, and support files while excluding Documents and the cleanable cache, log, and temporary directories.
• User Media measures the simulator media library.

These rows can explain where disk space is going, but they are never selectable for bulk deletion. Apple likewise distinguishes an app's bundle, documents, and other data when discussing app disk usage.

• Apple: Reducing your app's disk usage
• Apple: Files and directories

Xcode 26.6 validation

The three cleanable rows were exercised on disposable simulator clones. A combined pass reclaimed about 1.38 GB on one clone and 1.68 GB on another. In an individual-category pass, caches reclaimed about 408 MB and logs about 177 MB. A seeded 8 MB temporary file was discovered and removed while its tmp directory remained intact. Cleanup also restored the prior boot state when requested.

The MobileAsset path was tested destructively on disposable iOS 26.5 clones, never on source simulators. Clearing the original broad Siri and language allowlist reclaimed about 1.43 GB. In a boot-only control with no apps opened, the required footprint started growing about 20 seconds after boot and reached about 1.17 GB within a minute.

The roughly 235 MiB difference was then identified at the asset-bundle level: about 141 MiB was an English LinguisticData package and about 88 MiB was an additional neural voice bundle. Removing only those two bundles survived repeated boots, idle time, keyboard input, a normal developer-app launch, opening Siri settings, opening the voice list, and a Siri request. Only the LinguisticData catalog is exposed for cleanup: it has an exact stable directory boundary and iOS can fetch it on demand. The extra voice bundle remains protected because selecting individual voice assets would depend on private MobileAsset catalog metadata and could leave a stale catalog.

An erased test clone also completed data migration, booted successfully, and opened Settings normally. Erase is therefore a recovery path to a usable fresh device, not a way to preserve or permanently remove system-managed assets.

Erase can return a damaged per-device data tree to a usable fresh state sourced from the unchanged runtime, but it is not an undo operation. The simulator's prior apps, settings, credentials, user data, logs, and cache contents are not restored.

If a shared runtime were modified, erasing a device would not repair it; the runtime would need to be reinstalled. simslim prevents that situation by never allowing runtime paths into a cleanup plan.

Implementation safeguards

• Exact UDIDs are resolved through simctl; aliases such as all are rejected.
• Every cleanup path is generated from a fixed category, checked to remain below the device's data directory, and rejected if the target or an intermediate path component resolves outside it.
• Name-based discovery skips Documents, media, and MobileAsset trees so a user-created folder named Caches, Logs, or tmp is never enough to make durable content eligible for cleanup.
• Downloaded language cleanup uses one exact MobileAsset catalog path; required Siri, speech, and voice catalogs are rejected by selection validation.
• Only directory contents are removed; required container directories remain.
• Child symlinks are unlinked without following them.
• Booted devices are shut down before cleanup.
• The CLI requires --confirm; the app requires the user to type CLEAN.
• Analysis and estimated sizes are always read-only.