What is System Data on Mac and how to reduce it
System Data on Mac is the grey part of the bar in Storage settings, and sometimes it takes 50, 100 or more gigabytes. It isn’t one thing: macOS puts there everything it doesn’t sort into its other categories, from caches and logs to Time Machine local snapshots. Here is what’s inside, why it grows and what you can safely shrink.
- Open MacWashing and choose System Junk in the sidebar.
- Click Start Scan.
- Look through what it found and click Clean. Anything debatable stays unchecked.
Free trial · macOS 14 or later
What counts as System Data
- Caches of apps and of macOS itself.
- Logs and diagnostic reports.
- Time Machine local snapshots — copies of changed files kept on the startup disk until the next backup reaches your Time Machine disk.
- Virtual memory — swap files macOS writes when memory runs low, and the sleep image.
- App data that has no category of its own, such as virtual machines, simulator images and some support files.
- Temporary files, including what installations and updates leave behind.
Your documents, apps, photos and mail have their own categories and don’t count as System Data.
Why it grows
Caches and logs grow with use. Local snapshots pile up while your Time Machine disk is disconnected. Developer tools and virtual machines add many gigabytes at once. When space runs low, macOS deletes snapshots and some caches itself, which is why the number can change on its own.
Right after a macOS update, System Data is often larger: the installer leaves files that macOS removes a little later.
See what’s inside
Storage settings don’t break System Data down. To see where the space goes, open your home folder in Finder and choose View › as List, then View › Show View Options, turn on Calculate all sizes and sort by size. Press Shift-Command-. (period) to show hidden folders such as Library.
How to reduce System Data safely
- Clear caches. It’s usually the biggest part you can remove: see how to clear cache on Mac.
- Remove leftovers of deleted apps from your Library folder: see how to uninstall apps on Mac completely.
- Thin out Time Machine local snapshots. Connect your Time Machine disk and let a backup finish: macOS then deletes the snapshots it no longer needs. To list them, run
tmutil listlocalsnapshots /in Terminal. To delete one, runsudo tmutil deletelocalsnapshotsfollowed by its date from that list, like2026-10-08-093015.
- Delete old iPhone and iPad backups. In Finder, select your device in the sidebar, click Manage Backups, select the backups you don’t need and delete them.
- Clean up developer data. If you use Xcode, delete
~/Library/Developer/Xcode/DerivedData, remove unavailable simulators withxcrun simctl delete unavailable, and delete the folders of iOS versions you no longer test on in~/Library/Developer/Xcode/iOS DeviceSupport.
- Remove virtual machines you don’t use. Parallels, VMware, UTM and Docker keep disk images of tens of gigabytes. Delete them from inside the app.
- Restart your Mac. It clears temporary files and swap.
What not to touch
/System,/private/var/vmand other system folders: macOS manages them itself.- Snapshots while a Time Machine backup is running.
- Commands from the internet you don’t understand, especially ones with
sudo rm -rf.
A working Mac always needs some caches, logs and swap, so System Data never goes down to zero.
With MacWashing, it’s one click
MacWashing clears the parts of System Data that are safe to remove: app and system caches, logs, Xcode junk and leftovers of deleted apps. Time Machine snapshots and macOS’s own files are left alone, so the number goes down, but not to zero.
Free trial · macOS 14 or later
Questions and answers
Will MacWashing delete my own files when it cleans?
No. It removes only what it can match to a known app or a known kind of junk, in places apps leave files; macOS and Apple’s files are never touched. Anything debatable is marked and stays unchecked until you decide.
What about apps that are open?
If an open app holds files being cleaned, MacWashing waits for it to quit or quits it at your request, and opens it again afterwards.
Is it free?
Yes, within the free trial: System Junk and the Uninstaller free up to 25 GB in total, with no account or card needed.
Why is System Data so big on my Mac?
Usually because of caches, Time Machine local snapshots, developer tools or virtual machines. Snapshots are common on laptops whose backup disk is rarely connected.
Can I delete System Data?
Not as a whole, and not from Storage settings. You can shrink its parts: clear caches, remove leftovers of deleted apps, let Time Machine thin out snapshots and delete old device backups.
Does System Data shrink on its own?
Partly. macOS deletes snapshots and some caches when space runs low and removes update files after an update. Caches of apps you use keep growing back.