Time Machine has a nice way to keep copies of files as you change versions, even if it can’t connect to a Time Machine backup volume. It creates local snapshots on your startup disk and other attached HFS+ volumes, then transfers them to Time Machine targets when you reconnect to the network. Readers of Macworld have questions about how to manage these snapshots.
Apple changed this in High Sierra. Apple says that High Sierra doesn’t store snapshots on HFS+ volumes, but only uses APFS-formatted “all-flash” storage (i.e. no Fusion Drive), whether it’s an internal or external flash drive. This seems like a step backwards since not all portable Macs running High Sierra have a flash boot volume. (It’s also odd, since Apple hasn’t gotten Time Machine to work on APFS drives yet, but this suggests it can create local Time Machine snapshots on APFS volumes.)
Apple goes on to say that it only stores snapshots on drives with “a lot of free space,” which in the past has meant that it doesn’t store snapshots that result in less than 20 percent of the drive’s unused capacity remaining. It deletes old snapshots if it cannot keep all old snapshots before reconnecting to your Time Machine volume.
You can also delete specific local backups from the Terminal. Launch the Terminal (from Applications > Utilities), and then copy and paste this command and press Return:
tmutil listlocalsnapshots /
The terminal displays a list of local snapshots named
com.apple.TimeMachine.2018-03-01-002010. To delete snapshots:
- Copy and paste this command:
sudo tmutil deletelocalsnapshots
- Enter a space, then paste the date portion of the snapshot.
- Press Enter, and finally press Enter.
- Overall, based on the sample snapshot above, it looks like this:
sudo tmutil deletelocalsnapshots 2018-03-01-002010
If deleted correctly, you will see “2018-03-01-002010” as a response in Terminal Delete Local Snap.
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What are Time Machine local snapshots?
The usual explanation for how Time Machine works is that it takes a copy of every file or file that has changed since the last recorded backup and stores it on the backup drive. With continuous backups of changed files, it creates adjustable snapshots of files on your Mac at various points in the past, which can be retrieved and used when needed.
In addition to the primary backup on the external drive, Time Machine also creates a second version, called a local snapshot, which is stored on the Mac’s main drive instead of the external drive.
How to delete all Time Machine local snapshots
- Open Time Machine Preferences. You can do this from System Preferences and Time Machine, or click the Time Machine clock, then click Open Time Machine Preferences.
- In Time Machine preferences, turn off the autosave option.
- Wait a few minutes for macOS to delete local snapshots you no longer need, and then re-enable the Auto Backup option.
How to Manually Delete Time Machine Local Snapshots
- Open terminal
- Enter the tmutil listlocalsnapshots / command.
- Press Enter. This will display a list of all date and time stamped snapshots on disk.
- For each snapshot, enter the sudo tmutil deletelocalsnapshots command followed by the date and time stamp. Example: sudo tmutil deletelocalsnapshots 2021-06-26-123740
- When prompted, enter your user account password and press Enter.
- Once you see the “Delete Local Snapshot” instruction followed by a date and time stamp, the local snapshot has been deleted.
If you want to delete many or all snapshots, it is best to use the first method, then use the listlocalsnapshots terminal command to check if they are gone.