Mac System Data Too Large: How to Find and Clear It

Open Apple menu → System Settings → General → Storage on a Mac that has been in use for a few years and the System Data segment is frequently the largest thing on the bar — 80GB, 150GB, sometimes more on a machine with a big disk.

Hover over it and macOS tells you nothing useful. There is no breakdown and no button. But unlike iOS, a Mac gives you a real filesystem, which means every one of these categories can be found and dealt with directly.

What is actually in it

The first three account for the vast majority of a large figure on a normal Mac. If you develop software, the last row often beats all of them.

This is the same bucket older macOS versions and older guides call “Other” — see what is Other storage on Mac for the naming history and the broader cleanup picture.

Time Machine local snapshots: the usual culprit

This surprises people who do not use Time Machine, or who think they do not.

macOS takes hourly APFS snapshots of your boot volume whenever Time Machine is enabled, regardless of whether a backup drive is connected. They let you roll back recent changes and they serve as a staging area for the next real backup. They also consume space, sometimes tens of gigabytes.

macOS thins them automatically when free space drops — it keeps them until you need the room, then removes the oldest. That is why System Data often shrinks on its own after a low-disk warning, and why a cleaner app showing a dramatic recovery has usually just done that early.

See them

Open Terminal (Applications → Utilities → Terminal) and run:

tmutil listlocalsnapshots /

You get a list of snapshot dates. Each one is a point you could roll back to.

Remove them

The safe approach is to let macOS handle it by freeing space elsewhere first. If you want them gone now and you have a real Time Machine backup on an external drive:

tmutil deletelocalsnapshots /

This deletes every local snapshot on the boot volume. Before running it, confirm you have an actual backup on an external drive or network destination. If local snapshots are your only recovery mechanism, deleting them means an accidental file deletion from this morning is unrecoverable.

To stop them accumulating, turn Time Machine off entirely in System Settings → General → Time Machine — but only if you have another backup strategy. A Mac with no backup at all is a worse problem than a full disk.

iPhone and iPad backups

If you have ever backed up an iOS device to this Mac, those backups are sitting on the disk at full size, and old ones for devices you no longer own are common.

System Settings → General → Storage, then click the i beside iOS Files or iPhone Backups in the list. You get each backup with its device name, date and size. Select anything belonging to a device you no longer use and delete it.

Alternatively, in Finder: Go → Go to Folder, paste ~/Library/Application Support/MobileSync/Backup, and you will see one folder per backup. Deleting through System Settings is safer because it shows you which device each one belongs to.

Deleting a backup never affects the phone itself. You are only removing the restore point.

Caches

Caches are files apps write to avoid redoing work. They regenerate. They are also one of the places where bad advice does real damage.

Safe: clear the contents of ~/Library/Caches — the contents, not the folder itself. Quit your apps first, then in Finder use Go → Go to Folder, enter ~/Library/Caches, and look for the largest subfolders. Delete the contents of ones belonging to apps you recognise, particularly browsers, Spotify, Slack and Adobe apps.

Not safe: anything in /System, /Library/Caches at the root level without knowing exactly what it is, or the user ~/Library folder as a whole. The user Library holds your mail, keychains, app preferences and app data. Deleting it is one of the most damaging things you can do to a Mac that still boots.

Browser caches are better cleared from within the browser — Safari Settings → Privacy → Manage Website Data, Chrome Settings → Privacy → Clear browsing data. That way the browser updates its own index rather than finding its files missing.

The built-in tools

System Settings → General → Storage offers recommendations that are worth using before anything manual:

• Store in iCloud — moves Desktop, Documents and Photos originals to iCloud, keeping local copies only as needed. Effective, but it requires iCloud storage to match.
• Optimize Storage — removes watched Apple TV content and old Mail attachments.
• Empty Bin Automatically — deletes Bin items after 30 days.
• Review Files — a size-sorted browser of large files, documents and downloads. The Downloads folder alone is often tens of gigabytes of installers nobody needs.

What not to do

• Do not delete anything inside /System or /Library at the root level. macOS protects most of it with System Integrity Protection, but what you can reach, you can break. There is nothing worth recovering there.
• Do not delete the ~/Library folder to clear caches. Only ~/Library/Caches contents are safe, and only with apps closed.
• Do not delete /private/var/vm. That is swap and the sleep image. macOS manages it and will recreate it, usually at a worse moment.
• Do not run sudo rm -rf on anything you found in a forum post. A mistyped path with those flags is unrecoverable.
• Do not pay for a cleaner app to delete local snapshots. That is the bulk of what they recover and tmutil does it free in one line.
• Do not judge the result immediately. macOS recalculates storage lazily, and snapshot deletion in particular can take several minutes to show up.

A realistic sequence

1. Empty the Bin, and check the Downloads folder.
2. Delete old iOS device backups.
3. Check for local snapshots with tmutil listlocalsnapshots /, and clear them if you have a real backup.
4. Clear ~/Library/Caches contents with apps closed.
5. If you use Xcode, clear ~/Library/Developer/Xcode/DerivedData and remove unused simulators.
6. Restart, wait an hour, then check Storage again.

On a Mac that has never been cleaned, that sequence routinely recovers 40-120GB without touching a single system file. If the figure stays high afterwards, the remaining space is usually one or two large items — a virtual machine image, a video project, a Docker disk image — and what is Other storage on Mac covers how to track those down.