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How do I set Time Machine to eject my external Time Machine backup drive automatically after each backup?

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    An interesting observation: when doing a TimeMachine backup to a network drive TimeMachine will automatically mount, backup and then unmount the remote TimeMachine share on the network drive. I wonder if you could exploit that to achieve what you want?
    – Ian C.
    May 25 '11 at 14:39
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+50

~/bin/timemachine:

#!/bin/bash

d="Time Machine"  # (change this to match the name of your backup drive)
diskutil mount "$d" && tmutil startbackup -b && diskutil eject "$d"

~/Library/LaunchAgents/timemachine_eject.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC -//Apple Computer//DTD PLIST 1.0//EN http://www.apple.com/DTDs/PropertyList-1.0.dtd>
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>timemachine_eject</string>
    <key>Program</key>
    <string>/Users/username/bin/timemachine</string> <!-- Replace "username" with your username. "~/bin/timemachine" doesn't work -->
    <key>StartInterval</key>
    <integer>120</integer> <!-- run every two minutes for testing. -->
        <!-- Change this to a higher number like 43200 (run every 12 hours) once you've confirmed it works. -->
</dict>
</plist>

Make the script executable, unload the default plist, and load the new one:

chmod +x ~/bin/timemachine
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.backupd-auto.plist
launchctl load ~/Library/LaunchAgents/timemachine_eject.plist

Any time you want to make changes to the plist file, you have to unload and load it:

launchctl unload ~/Library/LaunchAgents/timemachine_eject.plist
launchctl load ~/Library/LaunchAgents/timemachine_eject.plist
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    I love this solution, I further automated this process to mount and unmount work when I plug my drive and on a schedule. Visit my post here: somethinginteractive.com/blog/2013/07/24/… Jul 31 '13 at 6:07
  • On Maveriks this did not work for me, strangely the script looped and the backup was done continuously. The following change works though: <key>ProgramArguments</key> <array> <string>/Users/martin/bin/timemachine</string> </array>
    – Martin
    Jan 5 '15 at 14:21
  • somethinginteractive.com is down, archived version: web.archive.org/web/20160409130936/http://…
    – Pro Backup
    Nov 27 '17 at 18:03
  • Could you explain why this works? Nov 30 '21 at 13:59
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There might be a better way, but one solution might be to Applescript it. I haven't yet found any way to run an applescript after a backup, but you could:

  1. Turn off automatic TM backup
  2. Set up an applescript to run TM
    • Some googling turned up this line to force an immediate TM build: do shell script "/System/Library/CoreServices/backupd.bundle/Contents/Resources/backupd-helper >/dev/null 2>&1 &"
  3. Add a line to eject the disk afterwards.
    • eject disk somedrivename

If you want this to happen on a regular basis, you could attach it to a cron job.

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    Looks promising, but there needs to be some way to start #3 only after #2 ends.
    – Adam A
    Aug 30 '10 at 14:27
  • If I remember, I'll try to rig this up and test it when I get home tonight (and try to enforce waiting for the backup to finish before ejecting). Aug 30 '10 at 14:49
  • Here is a similar idea at Mac OS X Hints, using a python script. Jun 24 '11 at 21:31
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Haven't tried this, but it looks like it might work:

Jettison (Mac App Store link)

Ejects external drives when going to sleep and remounts them waking from sleep.

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No longer available on app store, available here instad: https://www.stclairsoft.com/Jettison/ or via brew cask install jettison. Well worth the $5 after the trial expires.

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