How to clear System Data on a Mac, safely

By Mohit Nippanikar, who makes SiftMac

Open System Settings › General › Storage and there’s often a grey bar called System Data taking 30, 80, sometimes 200 GB. macOS doesn’t say what’s in it, and there’s no button to clear it.

That’s because System Data isn’t one thing. It’s everything the storage bar can’t put under Applications, Documents, Photos or its other groups: caches, logs, Time Machine snapshots, iPhone backups, old macOS installers, Docker and virtual machine disks, AI models, and parts of macOS itself. Some of it you can clear, some of it clears itself, and some of it has to stay.

1. Restart first

A restart clears swap files and many temporary files, and makes macOS count again. That alone often takes a few gigabytes off System Data. The number in Storage settings is worked out in the background, so give it a few minutes after the restart before you read it.

2. See what’s really there

macOS won’t break System Data down, but Terminal can. First let Terminal see everything: System Settings › Privacy & Security › Full Disk Access, and turn on Terminal (you can turn it off again when you’re done). Then paste this. It lists the 15 biggest folders in your Library, biggest last:

du -sh ~/Library/* 2>/dev/null | sort -h | tail -15

To look one level deeper, put the folder’s name in, for example your caches:

du -sh ~/Library/Caches/* 2>/dev/null | sort -h | tail -15

For the whole disk, which takes a minute or two and asks for your password:

sudo du -xhd 1 /System/Volumes/Data 2>/dev/null | sort -h | tail -15

Terminal’s numbers won’t match the storage bar exactly. On APFS, copies made with Finder (clones) and snapshots share space, so adding up folders counts some of it twice.

3. Time Machine snapshots and purgeable space

If you use Time Machine, macOS keeps local snapshots on your Mac’s own disk, so you can restore files while the backup drive isn’t connected. Apple keeps each one for about 24 hours, or until the space is needed. They count toward System Data, and so does other purgeable space, such as iCloud Drive files macOS can download again.

macOS deletes purgeable space by itself as soon as something needs room, so it rarely causes a real problem. To list the snapshots:

tmutil listlocalsnapshots /

To see how much is purgeable, select Macintosh HD in Finder and choose File › Get Info: the Available line includes it.

Some installers check free space without counting purgeable space and refuse to start. Only then is it worth deleting the snapshots yourself:

sudo tmutil deletelocalsnapshots /

That removes every local snapshot of the startup disk. The backups on your Time Machine drive aren’t affected.

4. Caches and logs

Apps keep caches so they open and load faster. Removing them is safe: an app rebuilds what it needs, and the first launch afterwards may be a little slower. Quit the app first, and delete what’s inside its folder rather than the folder itself. Open a folder with Finder › Go › Go to Folder (⇧⌘G) and paste its path.

5. iPhone and iPad backups and updates

Backups your Mac makes of an iPhone or iPad live in ~/Library/Application Support/MobileSync/Backup, often tens of gigabytes each, and old ones are never removed for you. Delete them the safe way: System Settings › General › Storage, click ⓘ next to iOS Files, select a backup and click Delete. Or connect the device, select it in Finder’s sidebar and click Manage Backups.

Keep the newest backup of each device you still use. Older backups, and backups of devices you’ve sold or replaced, are the ones to remove. Once deleted, a backup is gone for good, so check the date first.

When Finder updates or restores an iPhone or iPad, it also downloads the whole system, several gigabytes, into ~/Library/iTunes/iPhone Software Updates (or iPad Software Updates). Those .ipsw files are safe to delete; Finder downloads them again when it needs one.

6. Old macOS installers

“Install macOS Sequoia” and its siblings in Applications take over 12 GB each. An installer usually deletes itself after a successful upgrade, so the ones left behind were downloaded but never run, or kept to make a USB installer. If you already have that version of macOS, drag the installer to the Trash. If it’s for a newer macOS you haven’t installed yet, keep it until you upgrade.

7. Docker, virtual machines, AI and developer files

Docker Desktop keeps every image, container and volume in one disk image, Docker.raw, inside ~/Library/Containers/com.docker.docker. It’s a sparse file: Finder shows the most it can grow to, while du -h shows what it really uses. Don’t delete the file; ask Docker what it can give back, then let it free the space:

docker system df
docker system prune

docker system prune lists what it will remove (stopped containers, unused networks, dangling images and build cache) and asks before doing it. Volumes are kept unless you add --volumes; they hold databases and other data, so leave them unless you’re sure. To stop the file growing as large again, lower the disk limit in Docker Desktop’s Settings › Resources.

Virtual machines from Parallels, UTM or VMware Fusion are one large file or bundle each. Delete the ones you don’t use from inside the app, so it cleans up properly.

AI models from Ollama, LM Studio and Hugging Face are 4–40 GB each and live in hidden folders in your home folder. Remove them with each tool’s own command: What Claude Code, Cursor, Ollama and Hugging Face leave on your Mac.

Xcode build data, simulators and device support files can reach tens of gigabytes on a developer’s Mac: what’s safe to delete in DerivedData, node_modules and Docker.

8. What not to delete

• /System, /usr, /bin and /private/var/db: macOS itself. System Integrity Protection blocks most of it anyway.
• /private/var/vm: swap files and the sleep image. macOS manages them, and a restart clears swap.
• ~/Library/Preferences, ~/Library/Keychains and ~/Library/Mail: your settings, passwords and mail. Delete mail from Mail, not from Finder.
• ~/Library/Mobile Documents: your iCloud Drive. Deleting here deletes from iCloud too.
• Apple Intelligence models and other system downloads: macOS manages them, and removing them by hand doesn’t stick.
• Anything you don’t recognise. If you can’t tell what a folder is for, leave it. Is it safe to delete? covers 40 common ones.

9. Why System Data comes back

Some of it is meant to. Caches refill as you use your apps, Time Machine takes a new snapshot every hour, and Docker and AI tools grow with use. Clearing once is fine; what helps more is knowing which parts grow on your Mac, and checking those every month or two.

If System Data grows by gigabytes a day for no clear reason, look for one runaway folder with the commands in step 2: a log that never stops, a crash-reporting loop, or an oversized Spotlight index. You can rebuild the index with sudo mdutil -E /; search won’t find everything until it has finished indexing again.