What is “System Data” on a Mac?
In your Mac’s storage settings, System Data is the grey category that can grow to dozens of gigabytes with no obvious explanation.
What’s inside it
System Data is everything macOS doesn’t file under another category. Typically that includes:
- Caches and temporary files
- Logs
- Local Time Machine snapshots
- Virtual memory and sleep image files
- Data from apps that store things outside the usual places
Why it grows
Caches and logs build up over time, and Time Machine keeps local snapshots on your disk between backups. macOS removes snapshots on its own when it needs the space, so the number can look larger than the space you can really reclaim.
What you can safely do
- Restart your Mac. This clears some temporary files and swap.
- Clear app caches for apps you aren’t using.
- If you use Time Machine, let a backup finish. You can list local snapshots in Terminal with the command below.
tmutil listlocalsnapshots /What to avoid
Don’t delete anything inside /System or /Library unless you know exactly what it is. Most of the reclaimable space in System Data comes from caches in your own Library folder.