The short answer
Purgeable space holds things macOS can delete without asking: Time Machine local snapshots, snapshots made before a macOS update, iCloud files that are also stored online, and caches. Finder and Disk Utility include it in “Available”, while df in Terminal doesn't, so the numbers differ. You normally don't need to clear it: macOS removes it when an app needs the room. If you need the space right now, restart, then in System Settings → General → Time Machine → Options set Backup Frequency to Manually for a few minutes so the local snapshots are deleted, and turn automatic backups back on.
On this page
What counts as purgeable
| What | Why it's safe to remove |
|---|---|
| Time Machine local snapshots | Apple says Time Machine saves a snapshot about every hour and keeps it for 24 hours, and deletes snapshots as they age or as space is needed. |
| macOS update snapshots | Apple says another snapshot is saved before any macOS update is installed. Your Mac counts the space snapshots use as available storage. |
| iCloud files stored online | With Optimize Mac Storage on, files and full-size photos that are in iCloud can be removed from the Mac and downloaded again when you open them. |
| Caches and watched video | System caches are created again as needed. Apple TV movies you've watched can be downloaded again. |
Time Machine local snapshots
- Why it's safe to remove
- Apple says Time Machine saves a snapshot about every hour and keeps it for 24 hours, and deletes snapshots as they age or as space is needed.
macOS update snapshots
- Why it's safe to remove
- Apple says another snapshot is saved before any macOS update is installed. Your Mac counts the space snapshots use as available storage.
iCloud files stored online
- Why it's safe to remove
- With Optimize Mac Storage on, files and full-size photos that are in iCloud can be removed from the Mac and downloaded again when you open them.
Caches and watched video
- Why it's safe to remove
- System caches are created again as needed. Apple TV movies you've watched can be downloaded again.
Apple's own description of snapshots is the simplest way to think about all of it: your Mac counts that space as available storage, and it doesn't use the space needed for downloading files, copying files or installing software.
Why the free space numbers don't match
| Where you look | What it shows |
|---|---|
| Finder (Get Info on the disk) and Disk Utility | “Available”, which includes purgeable space, with the purgeable amount in brackets. |
| System Settings → General → Storage | Used space by category, and what's available. |
df -h in Terminal | Only the space that's free right now. Purgeable space counts as used. |
Finder (Get Info on the disk) and Disk Utility
- What it shows
- “Available”, which includes purgeable space, with the purgeable amount in brackets.
System Settings → General → Storage
- What it shows
- Used space by category, and what's available.
df -hin Terminal- What it shows
- Only the space that's free right now. Purgeable space counts as used.
df -h /System/Volumes/Datatmutil listlocalsnapshots /Names starting with com.apple.TimeMachine are Time Machine snapshots, and names starting with com.apple.os.update were saved for a macOS update. If Finder says 60 GB available and df says 20 GB, the other 40 GB is purgeable.
Do you need to clear it?
Usually not. When you download, copy or install something, macOS removes purgeable items first to make room. It becomes a problem only when something checks the free space before macOS has cleared anything, for example an installer or a virtual machine that refuses to start, or a very large copy that fails part of the way through.
How to clear purgeable space
- Empty the Trash and restart. Space from the Trash isn't available until it's emptied, and a restart clears temporary files.
- Let Time Machine delete its local snapshots. This is Apple's method: open System Settings → General → Time Machine, click Options, choose Manually from Backup Frequency and click Done. Wait a few minutes, then set it back to automatic. Your backups on the Time Machine disk aren't touched.
- Or ask in Terminal. The first command below asks macOS to reclaim about 20 GB from local snapshots, at the highest urgency. The second deletes every local Time Machine snapshot on the startup disk.
- Start up in safe mode once. Apple notes that safe mode clears certain system caches, which can give you enough room for a task such as a macOS update.
tmutil thinlocalsnapshots / 20000000000 4tmutil deletelocalsnapshots /If the disk is still full after that, purgeable space wasn't the cause. See what's taking up space on your Mac to find the folders and files that are.
The faster way: the Storage map in iKnowMyMac
iKnowMyMac's Storage map shows purgeable space as its own section, next to your largest folders, large files, old downloads and developer caches. You can see at a glance how much of a full disk macOS will take back by itself and how much is yours to deal with.