Useful macOS defaults: Time Machine

com.apple.TimeMachine controls how Time Machine backups work.

Stop the "Do you want to use this disk for Time Machine?" prompt

When you plug in a new external drive, macOS asks if you want to use it for Time Machine. To stop this:

defaults write com.apple.TimeMachine DoNotOfferNewDisksForBackup -bool true

To bring the prompt back:

defaults write com.apple.TimeMachine DoNotOfferNewDisksForBackup -bool false

Speed up backups

Time Machine runs at low priority to avoid slowing down your Mac. If you want a faster backup and do not mind some slowdown while it runs:

sudo sysctl debug.lowpri_throttle_enabled=0

This turns off the low-priority throttle. Your backup will run much faster, but your Mac may feel sluggish while it is backing up.

To turn throttling back on (recommended for everyday use):

sudo sysctl debug.lowpri_throttle_enabled=1

This change does not survive a restart. The throttle goes back to normal when you reboot.

Check Time Machine status

defaults read com.apple.TimeMachine

See when the last backup ran

tmutil latestbackup

List all backups

tmutil listbackups

Start a backup from the command line

tmutil startbackup

Or start a backup and wait for it to finish:

tmutil startbackup --block

Notes

Most Time Machine settings are best managed through System Settings, then General, then Time Machine. The defaults commands are useful for the specific tweaks above, especially stopping the new disk prompt on machines where you plug in drives often.

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