mirror of
https://github.com/MobAI-App/simslim.git
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jpancotti
d566c616dc
* Expand simulator management and disk tooling * Add the SimSlim macOS app * Document and verify the macOS workflow
125 lines
6.8 KiB
Markdown
125 lines
6.8 KiB
Markdown
# Disk cleanup safety model
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Service slimming and disk cleanup have different guarantees. Service slimming
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is reversible with `simslim off`. Disk cleanup permanently removes files.
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## Boundary
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simslim only considers data below one exact simulator's device-data directory:
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```text
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~/Library/Developer/CoreSimulator/Devices/<UDID>/data
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```
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It never changes an iOS runtime. Apple describes a Simulator runtime as an OS
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package used by multiple simulator devices, and modern runtime disk images are
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kept in system-managed protected storage. Built-in apps and core OS language
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resources therefore are not per-device savings and are outside simslim's
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cleanup boundary.
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- [Apple: Adding additional simulators](https://developer.apple.com/documentation/safari-developer-tools/adding-additional-simulators)
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- [Xcode 14 release notes: system-managed Simulator runtime disk images](https://developer.apple.com/documentation/Xcode-Release-Notes/xcode-14-release-notes)
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## Current categories
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| Category | Action | Main downside | Recovery |
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|---|---|---|---|
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| 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 |
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| 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 |
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| 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 |
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| 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 |
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| Required Siri Assets | Measured only | Manual deletion is unsupported and iOS downloads required assets again | Required assets return automatically after boot |
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Apple Developer Forum reports document CoreSimulator's
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`Library/Caches/com.apple.containermanagerd/Dead` cache growing unexpectedly;
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it is covered by the cache category.
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- [Apple Developer Forums: Core Simulator cache consuming disk space](https://developer.apple.com/forums/thread/758703)
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## Recovery
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There are two distinct recovery models:
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1. Cleanup data such as caches, logs, diagnostics, and temporary files is
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disposable but its old contents are permanent history. `xcrun simctl erase
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<UDID>` does not bring those contents back. iOS and apps can generate new
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caches, logs, and temporary files on future boots.
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2. Downloaded system-managed assets such as Siri models and language data are
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split by observed behavior. The exact LinguisticData catalog is opt-in and
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on-demand. Required Siri, speech, and voice catalogs remain informational
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because iOS automatically restores them after boot.
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## Read-only storage breakdown
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`disk-plan` and the app report durable storage separately from cleanup choices:
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- **Installed Apps** measures app and test-runner bundles installed into that
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simulator. Built-in apps are not counted because they live in the shared
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runtime.
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- **Documents** measures app and app-group `Documents` directories.
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- **App Data** measures preferences, databases, and support files while
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excluding Documents and the cleanable cache, log, and temporary directories.
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- **User Media** measures the simulator media library.
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These rows can explain where disk space is going, but they are never selectable
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for bulk deletion. Apple likewise distinguishes an app's bundle, documents, and
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other data when discussing app disk usage.
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- [Apple: Reducing your app's disk usage](https://developer.apple.com/documentation/xcode/reducing-your-app-s-disk-usage)
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- [Apple: Files and directories](https://developer.apple.com/documentation/technologyoverviews/files-and-directories)
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## Xcode 26.6 validation
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The three cleanable rows were exercised on disposable simulator clones. A
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combined pass reclaimed about 1.38 GB on one clone and 1.68 GB on another. In
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an individual-category pass, caches reclaimed about 408 MB and logs about
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177 MB. A seeded 8 MB temporary file was discovered and removed while its
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`tmp` directory remained intact. Cleanup also restored the prior boot state
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when requested.
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The MobileAsset path was tested destructively on disposable iOS 26.5 clones,
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never on source simulators. Clearing the original broad Siri and language
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allowlist reclaimed about 1.43 GB. In a boot-only control with no apps opened,
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the required footprint started growing about 20 seconds after boot and reached
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about 1.17 GB within a minute.
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The roughly 235 MiB difference was then identified at the asset-bundle level:
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about 141 MiB was an English `LinguisticData` package and about 88 MiB was an
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additional neural voice bundle. Removing only those two bundles survived
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repeated boots, idle time, keyboard input, a normal developer-app launch,
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opening Siri settings, opening the voice list, and a Siri request. Only the
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LinguisticData catalog is exposed for cleanup: it has an exact stable directory
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boundary and iOS can fetch it on demand. The extra voice bundle remains
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protected because selecting individual voice assets would depend on private
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MobileAsset catalog metadata and could leave a stale catalog.
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An erased test clone also completed data migration, booted successfully, and
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opened Settings normally. Erase is therefore a recovery path to a usable fresh
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device, not a way to preserve or permanently remove system-managed assets.
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Erase can return a damaged per-device data tree to a usable fresh state sourced
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from the unchanged runtime, but it is not an undo operation. The simulator's
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prior apps, settings, credentials, user data, logs, and cache contents are not
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restored.
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If a shared runtime were modified, erasing a device would not repair it; the
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runtime would need to be reinstalled. simslim prevents that situation by never
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allowing runtime paths into a cleanup plan.
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## Implementation safeguards
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- Exact UDIDs are resolved through `simctl`; aliases such as `all` are rejected.
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- Every cleanup path is generated from a fixed category, checked to remain
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below the device's `data` directory, and rejected if the target or an
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intermediate path component resolves outside it.
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- Name-based discovery skips Documents, media, and MobileAsset trees so a
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user-created folder named `Caches`, `Logs`, or `tmp` is never enough to make
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durable content eligible for cleanup.
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- Downloaded language cleanup uses one exact MobileAsset catalog path; required
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Siri, speech, and voice catalogs are rejected by selection validation.
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- Only directory contents are removed; required container directories remain.
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- Child symlinks are unlinked without following them.
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- Booted devices are shut down before cleanup.
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- The CLI requires `--confirm`; the app requires the user to type `CLEAN`.
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- Analysis and estimated sizes are always read-only.
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