Time Machine won’t back up

After updating to Sierra or High Sierra, some users find that Time Machine simply won’t back up. Fixing the problem requires an SMC reset and a PRAM reset.

SMC Reset

  1. Shut down your Mac.
  2. If you can remove the battery or disconnect the power cable, do that. Wait ten seconds before proceeding.
  3. If you cannot disconnect the power, use a keystroke instead. After your Mac shuts down, press Shift + Control + Option on the left side of the built-in keyboard, then press the Power button at the same time. Hold these keys and the power button for ten seconds.
  4. Plug the power cable back in or replace the battery if you removed it.

PRAM Reset

  1. Turn on the computer.
  2. Press and hold Command + Option + P + R. Continue holding the keys down until the computer restarts again and you hear the startup chime twice.
  3. Continue booting as normal.

Drive is read-only

If your drive’s permissions have been damaged, you will often be prevented from writing to the disk. To address this problem, you can try to repair the problems with the disk. The simplest method requires diskutil in Terminal. Keep in mind that this can be a result of early problems with the disk itself. It might indicate that there’s a problem with the drive. You may need to consider replacing the drive if this problem appears more than once.

  1. Open Terminal from “Applications/Utilities/Terminal.app” or type “Terminal” into Spotlight.

  2. List the attached disks by typing diskutil list.

  3. Locate the partition used for Time Machine. Find the device and disk number, formatted like disk1s5, as in our example.

  4. Verify the volume by typing diskutil verifyVolume [volume name]. In our example we would use diskutil verifyVolume /dev/disk1s5.

  5. If you find any errors, run disktuil repairVolume [volume name].

Time Machine hangs on “Preparing Backup”

One of the most common bugs in Time Machine involves hanging on the beginning of the backup process. If the Time Machine process is starting or appears to be lagging, open the Time Machine preference pane in System Preferences.

Look for the text underneath the Time Machine progress bar. If the backup is progressing properly, it should show the number of items remaining to be processed. That number should be steadily, if slowly, increasing. If you don’t see that number increase over 30 minutes, you’ll need to take action.

Troubleshooting the Problem

  1. Uncheck the box next to “Back Up Automatically” in the Time Machine preference window. This will disable Time Machine and stop any backup processes.

  2. Make sure Spotlight is not indexing your backup by adding your Time Machine volume to the Privacy pane of the Spotlight preferences window in System Preferences.

  3. Find and remove the “.inProgress” folder. You’ll find that folder in the “Backups.backupdb” folder on your Time Machine drive. It will have a name like 2018-05-04-175540.inProgress. When you find that folder, delete it.

  4. Turn Time Machine back on.

Conclusion

Time Machine is extremely convenient, but it can be a troublesome backup tool. While it has become more reliable since its introduction, problems still occur. Time Machine shouldn’t be your only backup tool, but it is useful as part of your backup process.