Time Machine Error 112 on Mac: Causes and Fixes

What Time Machine Error 112 Means

Error 112 (code -112) in Time Machine is a macOS system failure code indicating a problem with writing data to the backup disk. In the Console logs, you can see the full error text, for example:

Backup failed: The operation couldn’t be completed. (OSStatus error 112.)

The error appears when Time Machine attempts to write a new system snapshot to an external disk or during an incremental backup creation. It completely halts the backup process, and your data stops being protected.

Causes

Error 112 is not an isolated failure but a symptom of one of the following issues:

1. File system corruption on the Time Machine disk. The most common case. The disk (especially HFS+ or APFS) has structural errors that prevent new files or folders from being created correctly.
2. Permissions conflict. Your macOS user account has lost write (Read & Write) permissions for the Backups.backupdb folder on the Time Machine disk. This can happen after a password change, migration to a new Mac, or changes to sharing settings.
3. Insufficient disk space. Although less characteristic for error 112 than for error 45, a full disk can cause cascading write failures, masquerading as error code 112.
4. Hardware disk failure. The appearance of bad blocks or a disk controller failure (for HDD/SSD) leads to an inability to complete the I/O operation.
5. Conflict with antivirus or encryption software. Some third-party security programs may block Time Machine's access to the disk for "protection" purposes.
6. Corruption of the Time Machine disk's metadata. The internal database Time Machine uses to track files is damaged.

Solutions

The recommended order of actions is from simple and quick to complex and radical. Before any actions, if the disk contains critically important old backups, make a full copy of it to another storage device.

Method 1: Basic Reboot and Connection Check

Often helps with temporary USB/Thunderbolt connection or disk driver glitches.

1. Disconnect the Time Machine disk from your Mac.
2. Restart your Mac (Apple → Restart).
3. After booting, reconnect the disk.
4. Wait for the disk to mount in Finder.
5. Start a backup manually via the Time Machine menu in the menu bar.

If the error recurs, move to the next step.

Method 2: Disk Verification and Repair (Disk Utility)

This is the primary method for fixing file system corruption.

1. Go to Applications → Utilities → Disk Utility.
2. In the left sidebar, select the physical disk (not the volume) used for Time Machine. It usually has the manufacturer's name and capacity.
3. Click the First Aid button in the top toolbar.
4. In the window that appears, click Run. The utility will check the disk structure and attempt to repair any found errors.
5. If First Aid is also offered for the volume (after repairing the disk), run it as well.
6. After completion, restart your Mac and try to create a backup.

⚠️ Important: If First Aid reports that the disk "cannot be repaired" or finds irreparable errors, this is a sign of hardware failure. Replace the disk immediately.

Method 3: Reset and Check Permissions

A permissions issue is the second most common cause.

1. Open Finder.
2. Navigate to the Volumes folder (or Go → Go to Folder... → enter /Volumes).
3. Find your Time Machine disk's folder (e.g., TimeMachineBackup).
4. Inside, locate the Backups.backupdb folder.
5. Right-click the Backups.backupdb folder → Get Info (or Cmd+I).
6. At the bottom of the window, in the Sharing & Permissions section, click the lock icon to unlock changes (enter an administrator password).
7. Ensure your user (or the staff group) has Read & Write privileges. If not, change them.
8. Also check permissions for the disk's root folder itself (not just Backups.backupdb). It should have similar privileges.
9. Close the window and try to create a backup.

If the problem isn't permissions, you can try resetting ACLs (Access Control Lists) via Terminal:

# Replace 'TimeMachineBackup' with your disk's name
sudo chmod -R -N /Volumes/TimeMachineBackup/Backups.backupdb

This command removes all extended attributes (ACLs) from the backups folder, reverting them to macOS defaults.

Method 4: Resolve Software Conflicts

1. Temporarily disable antivirus/firewall. Try creating a backup with protective software turned off. If the error disappears, configure an exclusion for the Time Machine disk in that software's settings.
2. Check encryption. If the Time Machine disk is encrypted, ensure you enter the correct password when mounting it. Try disabling encryption (via Disk Utility) and check the backup. Warning: Disabling encryption requires fully copying the data and can take a long time.
3. Check Spotlight. Sometimes indexing the Time Machine disk conflicts with its operation. You can temporarily exclude the disk from indexing:
   • System Settings → Spotlight → Privacy.
   • Add the Time Machine disk to the list.
   • Try the backup. Then, remove the disk from the list to re-include it.

Method 5: Create a New Backup Disk (Radical)

If all previous steps failed, the problem likely lies in the Time Machine disk's structure or its controller. The most reliable solution is to start a new backup chain on a different drive.

1. Prepare a new disk. Format it as APFS (or Mac OS Extended (Journaled) for older Macs) using Disk Utility. Give it a clear name, e.g., TimeMachineNew.
2. Configure Time Machine to use the new disk.
   • System Settings → General → Time Machine.
   • Click Select Disk....
   • Choose the newly formatted disk.
   • Check the box for Back up automatically.
3. Start the initial backup. Time Machine will begin creating a full copy of your Mac. This will take a long time (hours, depending on data volume).
4. The old disk. Once the new backup is complete, you can format the old disk and use it as a secondary backup or for other purposes. Do not delete old backups until you are certain the new ones work perfectly.

💡 Tip: Use a separate physical disk for Time Machine, not a partition on your system disk. This improves reliability and simplifies diagnostics.

Prevention

To minimize the risk of error 112:

1. Regularly check disk health. Run First Aid on your Time Machine disk every 3-6 months.
2. Do not interrupt backups. Try not to disconnect the disk during an active backup (when the Time Machine icon in the menu bar is animated).
3. Use quality disks and cables. Cheap or damaged USB cables are a common cause of connection failures.
4. Ensure ventilation. Overheating an external HDD can lead to read/write errors.
5. Monitor free space. Keep at least 20-30% free space on the Time Machine disk beyond the volume of data on your Mac.
6. Update macOS. Apple regularly releases fixes for Time Machine components and file system drivers.