Create a Time Machine backup before major updates, disk operations, or security changes on macOS.
What you will achieve
Confirm your Mac has enough free space for a macOS install or upgrade, understand what System Data actually contains, and remove safe cruft without deleting something you will regret.
Apple publishes minimum requirements, but real-world installs need headroom for download, extraction, and snapshot creation. Running out mid-install can leave macOS in a half-updated state that is painful to recover from.
1) Check storage in System Settings
- Open System Settings → General → Storage.
- Note total capacity and the coloured bar — focus on free space at the right edge, not just the headline number.
- Click each category (Applications, Documents, System Data) to see what dominates.
On Apple Silicon Macs, local snapshots and sealed system volume copies consume space during updates. Intel Macs behave similarly but may show slightly different System Data growth patterns after major upgrades.
2) How much space you really need
- Point update (e.g. 14.6 → 14.7): aim for at least 15–20 GB free.
- Major upgrade (e.g. Sonoma → Sequoia): aim for 35–50 GB free — more if you run Xcode or large creative apps.
- Clean install from USB: 40 GB minimum on the target volume, plus space for your data restore.
3) Verify free space in Terminal
df -h /The Avail column on the root filesystem is the number that matters. Compare it with System Settings — they should align within a few gigabytes.
4) Safe cleanup before install
- Empty the Bin — stale deletions still reserve space until emptied.
- Remove old iOS device backups: System Settings → General → Storage → iOS Files (or Device Backups on older macOS).
- Delete stale downloads and old
.dmginstallers from Downloads. - Move large video archives or VM images to external storage rather than deleting.
- Developers: clear Xcode Derived Data and old simulators — they can consume tens of gigabytes.
Avoid deleting items inside /System or /Library unless you know exactly what they are. Third-party “cleaner” apps that promise to shrink System Data often remove caches macOS will rebuild anyway, or worse, break login items.
5) Understand System Data
System Data includes caches, logs, local Time Machine snapshots, iCloud local copies, and VM swap files. It often shrinks after a reboot and successful update. If System Data exceeds 100 GB on a 256 GB Mac with no obvious cause, investigate with Storage recommendations before forcing deletion.
6) When space still will not free up
Boot into Safe Mode (Intel: hold Shift at startup; Apple Silicon: hold power button → Options → select startup disk while holding Shift) and recheck storage. Local snapshots may purge after Safe Mode boot. If an install already failed once, remove partial installers from System Settings → General → Storage under macOS category before retrying.
Verify
df -h / shows adequate free space for your planned install type, and Storage settings no longer flag critical low-disk warnings.