The latest articles on DEV Community by mous-design (@mousdesign). https://dev.to/mousdesign https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.us-east-2.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F3600473%2F02a0a6d8-8f43-42d1-8802-fe32c710544a.png https://dev.to/mousdesign en mous-design Sun, 08 Nov 2026 07:34:20 +0000 https://dev.to/mousdesign/plug-in-back-up-auto-eject-time-machine-for-a-disk-you-dont-leave-connected-14gk https://dev.to/mousdesign/plug-in-back-up-auto-eject-time-machine-for-a-disk-you-dont-leave-connected-14gk <p>If your Time Machine disk lives on a dock, you know the danger: unplug your laptop and you get a “Disk Not Ejected Properly” warning. Furthermore, if you leave the disk connected with default settings, Time Machine backs up every hour, filling it with way too many snapshots.</p> <p>What I actually wanted was simple: when I plug the disk in, back up if it's been a while, then eject it so I can just yank the cable. So I wrote a small Folder Action that does exactly that.</p> <h2> How it works </h2> <p>macOS can run a script whenever something changes in a folder. Disks mount under <code>/Volumes</code>, so a Folder Action on <code>/Volumes</code> fires whenever a disk appears. The script then:</p> <ol> <li>Checks whether the disk that appeared is the correct disk.</li> <li>Checks with <code>tmutil latestbackup</code> when the last backup was.</li> <li>If it's older than <code>MIN_INTERVAL</code> (I use 12 hours), runs <code>tmutil startbackup --block</code>, which waits until the backup is done.</li> <li>Unmounts the disk with <code>diskutil unmount</code>, falling back to a forced unmount if needed.</li> </ol> <p>Plug in, have a coffee, unplug. No clicking.</p> <h2> Failing visibly </h2> <p>One design choice I care about: <strong>if anything goes wrong, the disk stays mounted.</strong> A disk that's still there when you expected it gone is a visible signal that something needs a look. The reason ends up in <code>~/Library/Logs/backup-action.log</code>. Silent failure is the worst kind of failure (for any code actually), specially for backups.</p> <h2> Setup </h2> <p>Nothing to install. It's one zsh script plus Automator (see README for details):</p> <ol> <li>Set the disk name and interval at the top of the script.</li> <li>Set Time Machine to back up manually (otherwise it'll keep doing its own hourly thing).</li> <li>Give <code>FolderActionsDispatcher</code> Full Disk Access in System Settings / Privacy &amp; Security. Without this, <code>tmutil</code> can't do its job from a Folder Action.</li> <li>Create a Folder Action in Automator on <code>/Volumes</code> that runs the script.</li> </ol> <p>You can test it from Terminal first by passing the disk path as an argument, which is much nicer than plugging and unplugging while debugging.</p> <p>Tested on macOS 26.</p> <h2> Get it </h2> <p><strong><a href="https://github.com/mous-design/backup-action" rel="noopener noreferrer">github.com/mous-design/backup-action</a></strong> (MIT)</p> <p>If you have a different setup (multiple backup disks, network targets) I'd be curious how you'd extend it. Issues and PRs welcome.</p> macos automation showdev shell