Guide
What is System Data on a Mac?
System Data is macOS's catch-all for anything that does not fit another storage category. It can grow to tens of gigabytes. Some of it is yours to clear, and some macOS manages on its own.
Updated
What it contains
- App caches and logs in your Library folder.
- Time Machine local snapshots, which macOS keeps when your backup disk is not connected.
- Virtual memory swap files and the sleep image.
- App data that macOS cannot attribute to a category, such as virtual machine and container images or developer tools.
On macOS 11 and earlier the same category was called Other.
Parts macOS manages for you
Local snapshots are removed automatically when space runs low, and swap files shrink after a restart. A restart is a reasonable first step if System Data looks unusually large.
tmutil listlocalsnapshots /Parts you can clear safely
- Caches and logs in ~/Library/Caches and ~/Library/Logs. Disk Cleaner does this with a review step.
- Leftovers from apps you have removed. See uninstalling apps completely.
- Developer data such as Xcode's DerivedData, old simulators and container images, if you use those tools.
- Large forgotten files in your Library. Point Large & Old Files at ~/Library to find them.
What not to do
Do not delete files from /System, /private/var or /Library by hand. macOS protects most of them, and removing the rest can stop apps or the system from working.
Questions
Why does the number change without me doing anything?
Snapshots, swap and caches come and go as you use your Mac, and macOS recalculates the storage figures in the background.
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