How to Clear System Data on Mac (and What That Gray Bar Is)
How to Clear System Data on Mac
There is no Delete button for System Data. macOS uses that label for everything it cannot file under Apps, Photos, or Documents. You clear it by removing three things, in this order:
- Local Time Machine snapshots — copies of the disk stored on the disk itself. These are usually the tens or hundreds of gigabytes.
- Old iPhone and iPad backups in Finder. One forgotten phone is 4–8 GB.
- App caches in
~/Library/Caches. Browsers and creative apps rebuild these.
See the size first: Apple menu → System Settings → General → Storage. That is also how to check Mac storage. Wait for the colored bar. The gray segment is System Data. On a 256 GB MacBook, 100 GB there is a problem. On a 2 TB Studio it can be normal snapshot overhead.
This page is the disk inside the Mac. If the warning says "iCloud Storage Full," that is a different quota.
Time Machine snapshots
In Terminal:
tmutil listlocalsnapshots /
Thin them (this asks Time Machine to free about 10 GB of local snapshots):
sudo tmutil thinlocalsnapshots / 10000000000 4
Or plug in the backup drive and let a normal backup finish. macOS often drops stale local snapshots on its own after that.
iPhone and iPad backups
Finder → your iPhone in the sidebar → Manage Backups → delete the ones you do not need. iCloud backups of the phone do not live here; those count against iCloud storage, not this bar.
App caches
Finder → Go → Go to Folder → ~/Library/Caches. Sort by size. Quit the app first, then delete the contents of the obvious offenders (Chrome, Adobe, Slack). Do not delete the Caches folder itself.
Do not delete anything you do not recognize under /System or /Library. That is not System Data you can safely touch.
How to Check Storage on Mac
Apple menu → System Settings → General → Storage. That is how to check storage on Mac. Wait for the colored bar to finish calculating. Click the info button next to a category to see what is actually inside it.
The check takes two minutes. Clearing System Data, above, is what you do when the gray bar is the thing that filled the disk.
The Exact Clicks (Ventura, Sonoma, Sequoia, Tahoe)
- Click the Apple menu in the top-left corner.
- Choose System Settings.
- In the sidebar, click General.
- Click Storage.
- Wait. The first open is slow because macOS is classifying files, not because the window is broken.
- Click the (i) button next to a category to drill in.
There is no Storage tab in About This Mac anymore. That path died with Monterey. About This Mac still opens; it just does not show the bar.
Monterey and earlier
- Apple menu → About This Mac.
- Click the Storage tab.
- Click Manage… for the per-category list and recommendations.
From Terminal
Total, used, and free on the startup disk:
df -h /
Largest items in your home folder:
du -sh ~/* 2>/dev/null | sort -hr | head -20
df is the number Disk Utility trusts. The Storage bar in System Settings can lag behind by minutes after a big delete.
What the Colored Bars Mean
| Category | What is in it | What usually bloats it |
|---|---|---|
| Applications | Installed apps | Adobe, Final Cut, games, leftover .app files |
| Documents | Files in your home folder that do not fit elsewhere | Downloads, DMGs, exports, unzipped archives |
| Photos | The Photos app library | Originals, 4K clips, duplicates |
| iCloud Drive | Files synced with iCloud Drive | Desktop & Documents turned on |
| System Data | Caches, snapshots, device backups, logs | Local Time Machine snapshots, old iPhone backups |
| macOS | The operating system | Leave it. You cannot shrink this in any useful way. |
| Other Users | Other accounts on this Mac | Someone else's Photos library |
Keep 10–15% of the disk free. Below that, macOS has nowhere to put virtual memory and temp files, and the machine feels slow even if the CPU is fine.
Apps and Documents are the easy wins. The gray bar is where the confusing gigabytes hide.
What System Data Actually Is
System Data is not a folder. There is no "Clean Up System Data" button. macOS uses that label for everything it cannot file under Apps, Photos, or Documents.
Typical contents:
- Local Time Machine snapshots — copies of your disk stored on the disk itself, even when the backup drive is unplugged. These routinely run tens or hundreds of gigabytes.
- iPhone and iPad backups — Finder backups of old devices. One backup can be 4–8 GB. Three forgotten phones add up.
- App caches —
~/Library/Caches. Browsers and creative apps rebuild these. Safe to empty the contents of a bloated cache folder, not the folder itself. - Logs and support files — usually small unless one app has been crashing for months.
The steps that actually shrink it are above: snapshots, device backups, then caches. Measure the bar before you delete, and leave unknown files in system Library folders alone.
After You Have Checked: Free Space Without Deleting Keepers
The Storage screen also lists recommendations. Use the ones that match how you work; skip the rest.
- Empty Trash automatically — files in Trash still occupy the disk. This one is safe.
- Reduce Clutter — large files and old downloads. Review before deleting. A 4 GB
.dmgin Downloads is almost always trash; a 4 GB project folder is not. - Store in iCloud / Optimize Storage — moves local files to iCloud and leaves stubs. Fine for movies you already watched. Dangerous if your iCloud quota is already full. Stubs are not a backup.
For files you still need — exports, camera video, PDFs, photo libraries — compress them instead of offloading them. That is the gap Apple's recommendations skip. A 4K clip that is 400 MB in camera is often 30–50 MB after a sensible re-encode, and it stays on the Mac. Reducing file size on Mac covers the file-by-file version; image size on Mac covers photos.
Finder search is useful once you know the bar is Documents or Downloads: press Command-F in a new Finder window, change Kind to File Size, and show files larger than 1 GB. Old screen recordings and installers show up first.
A longer cleanup checklist lives in how to free up space on Mac. This page stops at: check, read the bar, shrink System Data, compress what you keep.
Frequently Asked Questions
How do I clear System Data on a Mac?
You cannot delete the category. Thin local Time Machine snapshots with tmutil, delete old iPhone backups in Finder → Manage Backups, and empty bloated folders in ~/Library/Caches. Leave unknown files under /System and /Library alone.
How do I check storage on a Mac?
System Settings → General → Storage on Ventura and later. About This Mac → Storage → Manage on Monterey and earlier. Wait for the bar to calculate, then open a category with the info button.
Why is System Data so large?
Local Time Machine snapshots and old device backups are the usual answer. Caches are next. The operating system itself sits in the macOS bar, not System Data.
Is it safe to delete System Data?
You cannot delete the category. You can delete snapshots, old iPhone backups, cache contents, and leftover installers. Leave unknown files in system Library folders alone.
Why is free space unchanged after I deleted 10 GB?
Local snapshots and a full Trash. Empty the Trash, restart, reopen Storage. df -h / in Terminal updates faster than the Settings bar.
How often should I check Mac storage?
Monthly for a 512 GB machine used for documents. Weekly if you edit video or fill the disk past 85%. The check takes two minutes; the "startup disk almost full" dialog takes an afternoon.
Do not wait for the warning. Clear the snapshots and backups behind System Data, then compress the files you actually want to keep. Download Compresto to shrink video, images, and PDFs on the Mac without sending them through a browser.