System Data on Mac: What It Is and How to Reduce It Safely

You opened Storage settings and found a gray bar called System Data eating tens or even hundreds of gigabytes, with no obvious way to open it. This guide explains what System Data on Mac actually is, how to see what’s behind it, and how to reduce it without breaking macOS.

Short version: most of it is temporary or rebuildable, a lot of it shrinks on its own, and the safe fixes take a few minutes.

What System Data on Mac is

System Data is a catch-all category. Apple describes it as a general category for Apple and third-party files that don’t fit a more specific storage category. If a file isn’t counted as an app, a document, a photo, mail, an iCloud file or part of macOS, it lands here.

On macOS Big Sur and earlier the same bar was called Other. Apple renamed it System Data in macOS Monterey.

It’s also worth knowing that System Data is partly an estimate. Storage settings measures the named categories and attributes much of what’s left to System Data, so its size can look inflated, especially right after you’ve deleted a lot of files.

What’s inside System Data

These are the usual contents, roughly from most to least likely to be large:

What	Where it lives	Safe to remove?
Local Time Machine snapshots	APFS snapshots on your startup disk	Yes, with tmutil (see below)
User caches	~/Library/Caches	Yes, folder by folder, with apps quit
Virtual memory (swap) and sleep image	/private/var/vm	No, but a restart resets swap
System caches and temporary files	/Library/Caches, /private/var/folders	Leave to macOS; a restart cleans up
Logs and diagnostic reports	/private/var/log, /Library/Logs, ~/Library/Logs	macOS rotates and removes these itself
App support files	~/Library/Application Support, ~/Library/Containers	Only for apps you’ve already deleted
Virtual machine and container disk images	Often inside ~/Library (for example Docker Desktop’s disk image)	Yes, from within the app
Fonts, plug-ins, staged updates	Various system locations	Leave to macOS

Local Time Machine snapshots

If you back up with Time Machine, macOS keeps local snapshots on your internal disk so you can restore files even when the backup drive isn’t connected. Snapshots preserve deleted files too, which is why deleting a big folder sometimes frees no space at all: the snapshot still holds it.

macOS removes local snapshots automatically when space runs low and after about 24 hours, but they’re the most common reason System Data looks suddenly huge.

Swap and the sleep image

When your apps need more memory than your Mac has, macOS moves some of it to swap files on disk. With heavy use, swap can reach several gigabytes. Macs that sleep also keep a sleep image. Both are managed by macOS, and swap is reset when you restart.

Caches, logs and app support files

Browsers, music and video apps, messaging apps and developer tools all build caches. Apps you’ve deleted often leave support files behind in ~/Library/Application Support and ~/Library/Containers. Logs and crash reports are usually small, but a misbehaving app can make them balloon.

Backups and developer data

On recent versions of macOS, iPhone and iPad backups are listed separately under iOS Files, and Xcode data under Developer. On some setups, and on older versions of macOS, they can end up counted in System Data instead. Either way, they’re worth checking.

How to check how big System Data is

1. Choose Apple menu › System Settings.
2. Click General › Storage.
3. Wait for the bar to finish calculating, then hover over the gray segment or scroll down to System Data.

There’s no ⓘ button to browse System Data, because it isn’t one folder. To see the folders behind it, use one of these:

• A disk analyzer. Apps like DaisyDisk, GrandPerspective and OmniDiskSweeper show folders by size, including hidden ones in ~/Library. See our roundup of the best disk space analyzers for Mac.
• Finder. Press ⌘ Command + ⇧ Shift + G, go to ~/Library, switch to list view, and turn on Calculate all sizes in View › Show View Options.
• Terminal (read-only). This lists the size of each folder in your Library, largest last, without changing anything:

du -sh ~/Library/* 2>/dev/null | sort -h

You may see “Operation not permitted” for some folders. That’s privacy protection and harmless. You can give Terminal Full Disk Access in System Settings › Privacy & Security › Full Disk Access if you want complete numbers, but it isn’t required.

How to reduce System Data safely

Do these in order. Check Storage settings after each step, giving it a few minutes to recalculate.

1. Restart your Mac

A restart clears swap files and many temporary files and caches. It’s the safest step and often the most effective. Use Apple menu › Restart, not just closing the lid.

2. Delete local Time Machine snapshots

1. Open Terminal from Applications › Utilities.
2. List your snapshots:

tmutil listlocalsnapshots /

You’ll see lines like com.apple.TimeMachine.2026-10-27-101530.local. If nothing is listed, snapshots aren’t the problem.

3. Delete a snapshot by its date:

sudo tmutil deletelocalsnapshots 2026-10-27-101530

4. Enter your login password when asked (it won’t appear as you type) and press Return.

Repeat for each date. This only removes snapshots stored on your Mac. Backups on your Time Machine drive or network backup aren’t touched. As long as Time Machine is on, new local snapshots will be created over time; that’s expected.

Tip: Run your next Time Machine backup soon after, so you still have a recent restore point.

3. Clear caches in your user Library

Quit your apps, open ~/Library/Caches, and delete the contents of the largest app folders, not the Caches folder itself. Our step-by-step guide on how to clear cache on Mac walks through it, including browser caches and the DNS cache.

4. Remove old backups, simulators and virtual machines

• In Storage settings, click ⓘ next to iOS Files and delete backups of devices you no longer use.
• Click ⓘ next to Developer to remove Xcode caches and build files.
• If you use Docker Desktop, reduce its disk usage from inside the app (removing unused images, or lowering the disk image limit in its settings) rather than deleting its files in Finder.
• Delete virtual machines you no longer need from within Parallels, VMware Fusion or UTM.

5. Clean up leftovers from deleted apps

Look in ~/Library/Application Support and ~/Library/Containers for large folders named after apps you’ve already removed. Move them to the Trash, restart, and empty the Trash once you’re sure nothing is broken. Our guide to deleting apps on Mac explains how to remove apps completely in the first place.

Warning: Only remove folders for apps that are no longer installed. Application Support and Containers also hold real data for apps you use, like notes, databases and game saves.

6. Install pending macOS updates

Downloaded but uninstalled updates can sit on your disk. Install them from System Settings › General › Software Update, or, if you don’t want them, they’ll be cleaned up by macOS over time.

What you should never do

• Don’t delete anything in /System. It’s protected for a reason.
• Don’t delete files in /private/var, including /private/var/vm. Swap and the sleep image are in use while your Mac runs. Restart instead.
• Don’t turn off System Integrity Protection to “clean” system folders. Any guide that asks you to is putting your Mac at risk.
• Don’t run rm -rf commands copied from forums on Library or system paths.

When System Data is normal

A System Data figure of a few dozen gigabytes is common, and on Macs with lots of free space macOS is happy to keep larger caches because it can. If you have plenty of room, there’s no need to chase the number. Purgeable data, which Finder’s Get Info window and Disk Utility can show, is space macOS will free on its own when it needs it.

If space is actually tight, work through our full guide on how to free up space on Mac, which covers iCloud optimization, large files and unused apps. Apple’s own Free up storage space on Mac article is also worth a read.