Mac storage is full — here's how to free up space (and what “System Data” actually is)

First, see where the space went

Don't start deleting blindly. Open > System Settings > General > Storage. The bar at the top splits your disk into categories — Applications, Documents, Photos, macOS, and the vague System Data. Click the little ⓘ next to Documents and Applications to see your largest files and apps, biggest first.

For a precise view from Terminal, one command lists the biggest folders in your home directory. Open Terminal (⌘ Space, type Terminal, Return) and run:

% du -sh ~/* ~/Library/* 2>/dev/null | sort -rh | head -20

Sorts your top-level folders biggest-first. The 2>/dev/null part just hides harmless permission warnings.

And to see how full you really are — and how much room is left:

% df -h /

Filesystem        Size    Used   Avail Capacity iused ifree %iused  Mounted on
/dev/disk3s1s1   460Gi    13Gi   144Gi     9%    459k  1.5G    0%   /

Read two columns. “Capacity” is how full the disk is — this example shows a healthy 9%. “Avail” is the free space you have left. macOS starts to drag and refuses updates once Capacity climbs past about 90%, so that's the number to beat.

One catch: some of that free space is purgeable — caches and snapshots macOS will delete for you the moment an app needs the room. It's why the free space you see can jump around on its own. The steps below reclaim space you can count on.

What “System Data” really is (and how to shrink it)

“System Data” (called “Other” on older macOS) is the category everyone panics about. It isn't one thing — it's everything macOS doesn't file elsewhere: caches, logs, local Time Machine snapshots, app support files, fonts, plugins, and temporary files. On a healthy Mac it's often 10–40GB. When it balloons past 100GB, one of the things below is the cause.

You can't delete “System Data” directly — there's no single folder to trash, and you shouldn't try. You shrink it by clearing the specific culprits: snapshots, caches, and old backups. Do those, and the number drops on its own.

Local Time Machine snapshots

“System Data” is huge, and you have Time Machine turned on.

Even when your backup drive is unplugged, macOS keeps local snapshots — spare copies of your files — on your internal disk. They're meant to be temporary, but they can quietly hold tens of gigabytes. Check for them:

% tmutil listlocalsnapshots /

Each line is one snapshot taking up space on your internal disk.

FixmacOS thins these on its own when space runs low, but you can force it now. This clears older local snapshots and keeps the 4 most recent:

% sudo tmutil thinlocalsnapshots / 999999999999 4

Frees the space held by older local snapshots right away. Asks for your password.

Trash, Downloads, and big forgotten files

You deleted things, but the disk is still full — and Downloads is a graveyard of installers.

The easy wins. The Trash still counts against your disk until you empty it — right-click the Trash icon > Empty. The Downloads folder is where installers (.dmg files), large attachments, and one-off files pile up; sort it by size and clear what you don't need.

Fixempty the Trash, clear out Downloads, then hunt down large files anywhere on your Mac:

% find ~ -type f -size +1G 2>/dev/null

Lists every file larger than 1GB in your home folder. Look before you delete.

Caches and logs

“System Data” creeps up steadily over months, for no obvious reason.

Apps and the system write caches (scratch files that make things load faster) and logs as they run, and don't always clean them up. Most live in ~/Library/Caches. See what's there:

% du -sh ~/Library/Caches/* 2>/dev/null | sort -rh | head -15

The biggest cache folders, largest first.

Fixclear individual app caches — apps rebuild them — but quit the app first. Never delete the Library folder itself, and never touch anything in /System. If you're not sure what a folder is, leave it; the space it holds is rarely worth breaking an app over.

App data: iOS backups, Xcode, GarageBand, Photos

A few apps you use quietly eat tens of gigabytes each.

Some apps are notorious hogs. iPhone and iPad backups stored on your Mac run to many gigabytes. Xcode (Apple's app for developers) hides huge caches and old test devices. GarageBand and Logic bundle gigabytes of sound libraries you may never open. And the Photos library — duplicates and videos especially — is often the single largest item on a personal Mac.

Fixmanage iPhone backups in the Finder sidebar (your device > Manage Backups), delete Xcode's cache at ~/Library/Developer/Xcode/DerivedData and its old simulators, remove unused sound libraries from GarageBand's settings, and thin out duplicate photos and old videos.

Offload to iCloud (without losing anything)

You've cleared the junk but still want more room — without deleting anything real.

The safest way to reclaim space is to move files off your disk instead of deleting them. Files you rarely open are kept in the cloud and downloaded again the moment you need them — nothing is lost.

Fixin > System Settings > General > Storage, turn on “Store in iCloud.” For Photos, Optimize Mac Storage does the same for your library. Everything stays available; only the local copy is freed.

The short version

1. Open Storage settings and note the breakdown; run df -h / to see how full you really are.
2. Empty the Trash and clear Downloads.
3. Thin local Time Machine snapshots.
4. Delete large unused files, old iOS backups, and dev caches.
5. Turn on Store in iCloud / Optimize Storage, then restart.

That sequence reclaims space on almost any Mac — and you'll watch “System Data” shrink as you go.