What “System Data” on your Mac is, and how to shrink it safelyDraft

That’s why it’s hard to clear by hand: there’s no single folder to open. But most of it falls into a few places you can check.

What’s usually in it

• Caches in ~/Library/Caches, which apps rebuild when they need them.
• Logs in ~/Library/Logs and crash reports.
• Local Time Machine snapshots, kept on your disk while your backup drive isn’t connected.
• Developer files such as Xcode’s DerivedData and simulators.
• App data in ~/Library/Application Support: some of it important, some of it old.

Shrink it by hand

1. Restart your Mac. Temporary files and swap space are cleared on restart, and System Data often drops right away.
2. Check for local snapshots. In Terminal, tmutil listlocalsnapshots / lists them. macOS deletes them on its own when space runs low, but you can remove one with tmutil deletelocalsnapshots followed by its date.
3. Clear caches you don’t need. See Is it safe to delete ~/Library/Caches? for what’s safe.
4. Clear developer files if you use Xcode: How to delete Xcode DerivedData, old simulators and device support.

What not to touch

Don’t delete folders in /System or /Library you don’t recognise, and don’t empty ~/Library/Application Support wholesale: that’s where apps keep your settings and, sometimes, your data.