Free up storage
How to Clear 'System Data' on Mac: A No-Nonsense Guide
System Data eating 100GB on your Mac? Here's exactly what's in it, what you can safely clear, and what you should never touch.
System Data on a fresh macOS install is roughly 10-15GB. On a Mac that’s been running for two years without cleanup, it’s routinely 100GB+. Same operating system, same apps. Where did the difference come from?
Mostly: caches that never expire, logs that never rotate, snapshots that never delete, and backups from devices nobody plugs in anymore. Apple decided to hide all of this under one label, which is why it feels mysterious. It isn’t, really. Once you know where to look, clearing System Data becomes a 20-minute project.
Why System Data exists in the first place
Apple uses “System Data” as the catch-all for anything that doesn’t fit Apps, Documents, Music, Photos, or Mail. That’s a lot of stuff. Caches, logs, plugin data, snapshot files, language files, leftover update installers, and — usefully — anything macOS itself genuinely depends on.
The frustrating part is that the storage screen in System Settings doesn’t break this down. It just shows you a teal bar labeled “System Data” with no breakdown and no “Manage” button. So you’re stuck either trusting a third-party tool or going hunting yourself.
The first place to look: caches
Roughly half of bloated System Data is application caches. Quit your apps first, then check these locations:
~/Library/Caches/— user-level app caches/Library/Caches/— system-wide caches (admin password required)~/Library/Containers/<app>/Data/Library/Caches/— sandboxed app caches
Open Finder, hit Cmd+Shift+G, paste ~/Library/Caches/, then sort by Size in the Finder column. The biggest folders are typically:
- Spotify (audio cache, often 4-8GB)
- Slack
- Adobe apps (Photoshop, Premiere, etc. — easily 5GB+ each)
- Microsoft Teams or OneDrive
- Browsers
- Any Electron-based app
Drag the contents to the Trash. Apps rebuild what they need on next launch. Worst case you lose your offline Spotify queue, which takes 30 seconds to rebuild.
Time Machine snapshots that never went away
Even if your Time Machine drive is unplugged, macOS keeps “local snapshots” of your data on the internal disk. They’re APFS snapshots, designed to give you a recovery point between cloud backups. Useful concept. Significant storage cost.
Check what you’ve got:
tmutil listlocalsnapshots /
Each entry there is a snapshot. They can be 5-15GB each, and you might have a dozen.
To clear them aggressively:
sudo tmutil thinlocalsnapshots / 9999999999 4
The big number is the bytes of free space you want to maintain — passing something huge tells the system to delete everything it can. The 4 is urgency. macOS does this automatically when storage gets critical, but you can absolutely force it earlier.
If you don’t use Time Machine at all, you can disable it entirely in System Settings → General → Time Machine. New snapshots stop being created. That said, having them is a real safety net — I usually recommend just thinning regularly rather than turning the feature off.
iOS backups eating 50GB+
Open Finder, do Cmd+Shift+G, paste ~/Library/Application Support/MobileSync/Backup/. Each subfolder there is an iOS device backup. They’re often 30-100GB each.
These don’t auto-delete. macOS will keep a backup from a 2020 iPhone forever unless you remove it manually. Easiest way:
- Plug in your current iOS device
- Open Finder, click the device in the sidebar
- Click Manage Backups
- Delete any backups that aren’t your current device
Or just delete folders directly from the MobileSync directory. Verify by date — keep the newest, delete the rest.
Mail attachment cache
Apple Mail caches every attachment you’ve previewed. Folder is ~/Library/Mail/V10/MailData/ (V10 number varies by macOS). On accounts you’ve had for years, this casually hits 20GB.
Cleanest fix: open Mail, click each mailbox, then Mailbox menu → Rebuild. macOS re-downloads everything from the server, dropping orphaned attachments along the way. It’s slow — give it an hour.
A faster fix is deleting the Envelope Index file (Mail rebuilds it next launch) — but that doesn’t shrink the attachment cache. If you’re on Gmail or any IMAP server, you can also drop your local cache size by going to Mail → Settings → Accounts → your account → “Download Attachments” set to “Recent” or “None.”
Xcode is its own disaster
If you’ve ever opened Xcode — even just once — it left behind 5-10GB of caches and frameworks. If you actually use Xcode, that number is more like 50-100GB.
Folders to check:
~/Library/Developer/Xcode/DerivedData/— temporary build artifacts. Safe to delete entirely.~/Library/Developer/Xcode/iOS DeviceSupport/— debug symbols for iOS versions. Safe to delete; Xcode re-downloads as needed.~/Library/Developer/Xcode/Archives/— old app archives. Safe unless you need them for App Store submissions.~/Library/Developer/CoreSimulator/Caches/— simulator caches.~/Library/Developer/CoreSimulator/Devices/— simulator devices themselves. Each is several GB. You can delete unused ones in Xcode → Settings → Platforms.~/Library/Caches/com.apple.dt.Xcode/— general Xcode cache.
If you don’t actively need Xcode, just uninstall it. The full Xcode app itself is around 12GB on disk, but with all its associated caches and runtimes, removing it can free 80GB+ on a developer’s machine.
System logs that grew too long
Log files don’t typically blow up — except when they do. A misbehaving app or daemon can write a multi-gigabyte log silently for weeks.
Check these:
/var/log/~/Library/Logs//Library/Logs//Library/Logs/DiagnosticReports/
Sort each by size. Anything over 100MB is suspect. If the file is named after a specific app, that app probably has a bug — check Activity Monitor for the process and quit it before deleting the log.
You can safely delete log files. The system creates new ones as needed.
Update installer remnants
Every time you update macOS (e.g. Sonoma 14.3 → 14.4), the installer downloads a multi-gigabyte package, applies it, and is supposed to clean up. Sometimes it doesn’t, especially if the update was interrupted or rolled back.
Check /Library/Updates/ and ~/Library/Updates/. Anything in there that’s gigabytes large and dated weeks ago can usually go.
There’s also occasionally a leftover macOS installer in /Applications named something like “Install macOS Sonoma.app.” It’s 12-15GB. If you’ve already updated, you don’t need it.
Language files for software you don’t use in 30 languages
Most apps ship with localizations for dozens of languages. Each is anywhere from 5-30MB. Across 200 apps, that’s 1-6GB you’ll never read.
You can manually delete unused languages from each app’s bundle, but it’s tedious — right-click an app → Show Package Contents → Contents/Resources → look for .lproj folders. Removing every .lproj except en.lproj (or your preferred language) saves the space.
Honestly, don’t do this manually. Either use a tool that handles it in bulk, or skip this one. Per-app savings are too small to be worth the click count, and you risk breaking apps that expect their localizations.
What to leave alone
Some of System Data really does belong there. Don’t touch:
/System/Library/— core macOS, mostly protected by SIP anyway~/Library/Keychains/— your saved passwords~/Library/Containers/(the parent folder)/private/var/db//private/var/folders/— temporary files macOS manages itself- The sleepimage and swap files
Also, ignore guides that tell you to “verify and repair disk permissions” or “rebuild your Spotlight index” to free space. Neither of those does anything for storage on modern macOS.
How to verify your work
After clearing, the System Data number in System Settings often doesn’t update immediately. macOS recalculates in the background. To check the real number, open Disk Utility, click Macintosh HD, and look at the Used vs. Free figures at the top. Those are accurate.
If you cleaned aggressively and System Data is still huge, you’ve got something specific eating space — usually a virtual machine disk image, an iOS backup you missed, or a database file from an app like Photos or Mail. Spotlight search with Cmd+F → File Size > 5GB → “This Mac” finds these in seconds.
The honest assessment: System Data isn’t a single problem with a single fix. It’s a dozen small problems, each one trivial. The reason cleaning tools exist is that doing this every quarter manually is the kind of chore most people skip — until the disk fills up and it becomes urgent. Whether you do it by hand or with a tool, the important thing is to do it before macOS starts refusing to save your work.