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What is inside System Data on Mac: a Terminal audit

Updated 2026-10-21

Quick answer: System Data is not one folder. Run a handful of read-only du commands and add up the results. The big ones are almost always ~/Library/Caches, ~/Library/Application Support, ~/Library/Developer and ~/.cache.

Before you start

  • Everything below only reads sizes. Nothing is deleted.
  • System locations ask for your administrator password because of sudo.
  • Operation not permitted on some folders is normal: macOS protects them.
  • Sizes here use du, which counts the space really used on disk.

Step 1: your user Library

du -sh ~/Library/Caches ~/Library/Application\ Support ~/Library/Developer ~/Library/Containers ~/Library/Logs 2>/dev/null

Step 2: tool folders in your home directory

du -sh ~/.cache ~/.npm ~/.gradle ~/.cargo ~/.docker 2>/dev/null

Step 3: system-wide locations

sudo du -sh /Library/Caches /private/var/log /private/var/vm 2>/dev/null

Step 4: the whole data volume, folder by folder

sudo du -xhd 1 /System/Volumes/Data 2>/dev/null | sort -h | tail -15

The -x flag stays on one volume so nothing is counted twice.

Step 5: snapshots

tmutil listlocalsnapshots /
diskutil apfs listSnapshots /

A real example

These are the results from one developer's Mac:

LocationSize
~/Library/Caches31 GB
~/Library/Developer9.8 GB
~/Library/Application Support7.8 GB at the time
~/.cache4.5 GB
~/Library/Containers2.0 GB
/private/var/vm (swap)2.0 GB
~/.npm1.4 GB
/Library/Caches120 MB
/private/var/log85 MB
~/Library/Logs15 MB

And the data volume by top-level folder: Users 135 GB, Applications 46 GB, System 28 GB, Library 13 GB, private 7 GB, opt 4.5 GB, usr 1 GB and a 210 MB hidden .fseventsd, about 234 GB in total. Storage settings on the same Mac said roughly 340 GB used. The gap is the part files alone do not explain: other volumes in the same APFS container (the sealed system volume alone was 13.7 GB), snapshots and metadata.

Turn the numbers into actions

If this is bigRead
~/Library/CachesIs it safe to delete ~/Library/Caches
~/Library/DeveloperClearing Xcode DerivedData
~/Library/Application SupportApplication Support too big
Docker data in ContainersDocker.raw looks huge
SnapshotsDeleting local snapshots
Swap and system logsLeave them alone. macOS manages them

If you would rather see all of this at a glance, See Your Disk runs the same measurement and draws it as a map, with whatever no folder explains shown as its own System Data block. The full cleanup order is in how to clear System Data safely.

See Your Disk
A map of your Mac's disk, and a safe way to clean it.
Download on the Mac App StoreGitHub

Frequently asked questions

Why do the numbers not add up to what Storage settings says?

Files you can measure are only part of used space. The rest is other volumes in the same APFS container, snapshots, purgeable space and metadata. On the Mac below, the files on the data volume added up to about 234 GB while Storage settings reported roughly 340 GB used.

Do I need sudo for these commands?

Only for system locations such as /Library and /private. Commands on folders in your own home folder do not need it.

Are these commands safe?

Yes. du, ls, tmutil list and diskutil list only read sizes and names. Nothing in this guide deletes anything.

What is /private/var/folders?

A set of per-user temporary and cache folders that macOS manages. Do not delete things there by hand.

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