Storage

“Purgeable” space eating your disk? It's local Time Machine snapshots — here's how to clear them

By the Noah team·Updated August 23, 2026·5 min read

Short answerIf your disk is full but your own files don't explain it — and a big slice shows as “purgeable” or “System Data” — the usual cause is local Time Machine snapshots:

Time Machine quietly keeps hourly backups on your internal disk, so it can restore even when your backup drive is unplugged. These are local snapshots.
macOS is supposed to delete them automatically when space runs low, but they can pile up — especially if you rarely connect the backup drive.
They're safe to remove: your real backups live on the external drive. Clearing the local copies frees the space and loses nothing.

See them with tmutil listlocalsnapshots /, then reclaim space with tmutil thinlocalsnapshots / 999999999999 4. The steps below explain each.

You go to save a file or install an update and the Mac says the disk is full — but when you add up your own files, they don't come close. Open About This Mac and a large chunk is labeled “System Data,” or Finder shows space as “purgeable.” Nine times out of ten on a Mac that's backed up, this is local Time Machine snapshots.

Here's what they are, how to see how much they're using, and how to clear them safely. You can do it by hand, or let Noah find them, show you exactly how much it'll reclaim, and purge them on your approval (more at the end).

What local snapshots are

Time Machine is the Mac's built-in backup. Between backups to your external drive, it also saves periodic copies on your own internal disk — local snapshots — so you can roll back a file even when the backup drive isn't plugged in. Handy, and normally invisible.

macOS marks that space “purgeable”: space it will free the moment you actually need it. That's why the snapshots aren't a bug. They only become a problem when macOS's automatic cleanup falls behind — usually because the backup drive is rarely connected — and they grow enough to block an install or an update.

See how much they're using

First, list them. Open Terminal (press ⌘ Space, type Terminal, Return) and run:

zsh — Terminal

% tmutil listlocalsnapshots /

Sample result

com.apple.TimeMachine.2026-08-23-084500.local
com.apple.TimeMachine.2026-08-23-094500.local
com.apple.TimeMachine.2026-08-23-104500.local

Each line is one dated snapshot held on your internal disk. A long list is your answer.

To see the space itself, check the Avail and Capacity columns for your startup disk:

zsh — Terminal

% df -h /

Or open > About This Mac > More Info > Storage, and look at “System Data.”

Clear them safely

A long list above, and a full or nearly-full startup disk you can't otherwise explain.

The clean way is to ask macOS to thin the snapshots — purge them to reclaim space — rather than deleting files by hand. This asks it to free as much as it can, urgently:

zsh — Terminal

% tmutil thinlocalsnapshots / 999999999999 4

The big number is how many bytes to try to reclaim (here, everything); 4 means highest urgency. No password needed for your own startup disk.

Fixrun the thinlocalsnapshots command above, then re-check with df -h /. The space comes back within a minute or two. This removes only the local copies — the backups on your external Time Machine drive are untouched, so you lose no real backup history.

NoahNoah finds the local snapshots, shows you exactly how many gigabytes it can reclaim before it does anything, and purges them on your approval — so you get the space back without typing tmutil commands or worrying whether you're deleting a real backup.

Stop them piling up

Local snapshots only balloon when they can't flush to your backup drive. Connect your Time Machine drive regularly (or leave a network backup reachable) and macOS moves the snapshots off and trims the local copies on its own. If you've stopped using Time Machine entirely, turning it off in > System Settings > General > Time Machine stops new snapshots from forming.

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Frequently asked questions

Is it safe to delete local Time Machine snapshots?

Yes. Local snapshots are convenience copies kept on your internal disk between real backups. Your actual backup history lives on your external Time Machine drive and isn't affected. Clearing the local copies frees space and loses nothing you can't restore from the backup drive.

Why does my Mac have local snapshots if my backup drive is unplugged?

That's exactly why they exist — so Time Machine can still roll back a file when the drive isn't connected. macOS takes them roughly hourly and is meant to purge them under space pressure, but they can accumulate when the drive is rarely plugged in.

What's the difference between “purgeable” and “System Data”?

“Purgeable” is space macOS will free automatically when you need it — local snapshots are the biggest part of it. “System Data” (once “Other”) is the catch-all storage category in About This Mac, and swollen local snapshots are a common reason it looks huge.

How do I clear local snapshots without Terminal?

Freeing disk space normally (emptying Trash, deleting large files) triggers macOS to purge them, since they're purgeable. Or let Noah do it: it finds the snapshots, shows how much it'll reclaim, and purges them on your approval — no commands.

Will this delete my Time Machine backups?

No. tmutil thinlocalsnapshots only removes the local copies on your internal disk. The backups on your external or network Time Machine destination stay intact.

Commands in this guide are standard, read-only macOS diagnostics unless noted; anything that changes your system is called out. When in doubt, back up first with Time Machine.