Mac
Mac purgeable space and local snapshots: what to check
What Time Machine local snapshots do, how macOS counts their space, and when to leave them alone or reclaim them after a real storage failure.
Start here: Confirm a real shortage
Read Storage's available space and retry the failing copy, save, or update.
Problem summary
Time Machine local snapshots are on the Mac's own APFS disk. They can retain older versions of deleted files, but Apple counts their space as available and normally removes snapshots when space is needed. A large System Data or purgeable figure alone is not proof that they block work. First check available space and whether an operation actually fails. If it does, verify that local snapshots exist and that you have a separate off-device backup before considering removal.
Read available space in Storage settings and record the operation that fails.
df -h /
A reproducible low-space failure makes reclamation relevant.
Only delete snapshots once a real off-device backup exists.
Layer path
Step-by-step runbook
Start here. Do each check in order, compare it to the expected result, and stop when the evidence explains the failure or the safe stop point applies.
Confirm a real shortage
Check: Read Storage's available space and retry the failing copy, save, or update.
Expected result: You know whether space is actually blocking work.
If not: If work succeeds, leave snapshots alone regardless of the category bar.
See the snapshots
Check: Run `the "List the local Time Machine snapshots" command below` (and optionally `diskutil apfs listSnapshots /`).
Expected result: You can see how many local snapshots exist and how old they are.
If not: If the list is empty, switch to the System Data breakdown.
Thin gently first
Check: Only after checking other data and an off-device backup, ask macOS to thin eligible snapshots.
Expected result: Available space may rise or the task may now succeed.
If not: If nothing changes, stop targeting snapshots and inspect other files.
Stop the refill
Check: Set Time Machine to Manually (or remove the destination) so no new hourly snapshots form.
Expected result: Apple documents this temporary path for removing local snapshots, while new automatic backups pause.
If not: Re-enable automatic backups once reclaimed — don't leave backups off.
Verify and attribute the rest
Check: Re-run `the "Measure filesystem space alongside Storage settings" command below` and re-open Storage settings.
Expected result: The task now succeeds or available space increased enough.
If not: If still full, use the System Data page to identify a specific large file or app.
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Decision tree
If: An operation fails for lack of space and local snapshots are listed.
Then: Snapshots are a possible contributor, but their presence is not proof; macOS normally purges them when needed.
Action: First inspect large files; with an off-device backup, consider Apple's temporary Manual Time Machine option and re-measure.
Safe stop: Only delete snapshots once a real off-device backup exists.
If: Thinning frees little and only recent snapshots exist.
Then: The shortage may be elsewhere or the snapshot blocks may be shared.
Action: Stop targeting snapshots and inspect other large files.
If: Snapshots older than ~24 hours persist and won't age out.
Then: Age alone does not establish why the snapshot remains.
Action: Check `tmutil status` and destination health without assuming the backup failed.
If: Purgeable space refills within hours of clearing.
Then: A large file churn (VM image, Docker.raw, sync folder) is being snapshotted hourly.
Action: Find the churn with `du -x`, then exclude or relocate it rather than repeatedly deleting snapshots.
If: Snapshots are gone but the disk is still full.
Then: The low-space cause may be another identifiable file or app data.
Action: Switch to the System Data breakdown; stop deleting snapshots, which won't help.
Evidence table
| Symptom | Evidence to collect | Likely layer | Next action |
|---|---|---|---|
| Deleted big files / emptied Trash, free space barely moved. | Storage settings reports available space; retrying the operation reproduces the failure. | Cause still needs attribution; a snapshot list alone is insufficient. | Inspect large files and backup status before removing recovery points. |
| 'System Data' or 'purgeable' shows tens of GB. | `tmutil listlocalsnapshots /` lists several dated snapshots. | Local snapshots exist, but their space is normally available. | Leave them alone unless a real operation fails and other storage checks support intervention. |
| Snapshots older than a day won't clear. | `tmutil status` shows recent backups failing. | Backup status needs inspection; age alone does not prove a stalled cleanup cycle. | Check destination health and the actual backup error before changing settings. |
| Purgeable space refills within hours. | `du -x` flags a large VM image / Docker.raw / sync folder rewriting often. | File churn being captured into hourly snapshots. | Exclude or relocate the churn; stop fighting it with repeated deletes. |
| Snapshots removed but disk still full. | The original operation still fails or Storage shows little available space. | Another file or app may own the missing space. | Move to the System Data reclamation page. |
Commands and settings paths
Measure filesystem space alongside Storage settings
df -h /Where: Terminal on the Mac.
Expected: Reports filesystem usage; compare it with Storage's available space and the failed task.
Failure means: APFS accounting can differ between views; a mismatch does not identify the cause.
Safe next step: If a task truly fails, inspect user-owned files and snapshot status.
List the local Time Machine snapshots
tmutil listlocalsnapshots /Where: Terminal on the Mac.
Expected: Prints dated local snapshots; their presence alone does not prove a shortage.
Failure means: An empty list means snapshots aren't the cause.
Safe next step: If listed, leave them unless a real low-space failure justifies further action.
Thin local snapshots the supported way
tmutil thinlocalsnapshots / 21474836480 4Where: Terminal on the Mac (the number is bytes to reclaim; 4 = high urgency).
Expected: macOS may reclaim eligible snapshot space; the result is not an exact byte guarantee.
Failure means: If little is freed, do not assume snapshots remain the cause.
Safe next step: Retry the original task and inspect other files if it still fails.
Delete one stuck snapshot by timestamp
tmutil deletelocalsnapshots 2026-06-02-101500Where: Terminal on the Mac, using a timestamp from the list.
Expected: Removes that local recovery point; shared blocks mean available space may barely change.
Failure means: A refusal needs the exact error; do not infer why it failed.
Safe next step: Wait for the operation to finish, then retry; never delete mid-restore.
Hardware and platform boundary
Change only when
- Add a real off-device backup (external Time Machine drive or NAS) before you ever delete snapshots — local snapshots are not a backup.
- Consider a larger internal disk on your next Mac if you routinely run VMs, Docker, or large media that keep purgeable space high; Apple Silicon storage isn't user-upgradeable.
Evidence that matters
- A real, independent backup target so snapshots are a convenience, not your only recovery.
- Enough internal headroom for the actual work you perform, measured by available space.
- An external/NAS Time Machine destination so most history lives off the internal disk.
Evidence that does not matter
- A large purgeable number without a failed task — it does not by itself justify deleting snapshots.
- A cleaner app's 'purgeable space removed' figure — tmutil does the same thing natively and safely.
- RAID level of any backup volume as 'snapshot insurance' — RAID is uptime, not backup or snapshots.
Avoid
- Treating local snapshots as a backup — they share the disk that would fail.
- Blanket-deleting all snapshots as routine maintenance — you lose your only on-disk recovery between full backups.
- Cleaner apps that 'free purgeable space' — they wrap the same tmutil calls while adding risk.
Related tool/checklist
Use the linked tool when you need a guided plan from your exact symptoms instead of a static checklist.
Backup plan builderRelated problems
Last reviewed
2026-09-18 · Reviewed by HomeTechOps. Rechecked 2026-09-18 against Apple's local snapshot and storage guidance. Apple counts snapshot space as available and removes snapshots when needed; a large category bar or df/Finder difference alone is not proof of a storage fault. Removal is considered only after a real failure and an off-device backup.
Sources/assumptions
- Assumes an APFS-formatted Mac (every modern macOS) where Time Machine keeps local snapshots on the internal disk; the behaviour is the same across recent macOS versions including Tahoe (macOS 26).
- Apple says Time Machine local snapshots count as available space and are normally removed when space is needed (rechecked 2026-09-18).
- tmutil flags and byte arguments follow Apple's documented behaviour; thinlocalsnapshots reclaims approximately, not exactly, the requested amount.
Source-backed checks
HomeTechOps turns official docs and conservative safety rules into a shorter runbook. These links are the source trail for the page direction.
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