Disk Utility may show “Could not unmount disk” when an app, background process, or macOS is still using the drive. The safest fix is to close files and apps that may be accessing the disk, then try again. If that fails, restart your Mac, use macOS Recovery, or identify the process holding the disk with Terminal.
Do not erase or partition the disk until you have confirmed that any important data is backed up. Erasing a disk permanently deletes its contents.
Quick Answer
Try these fixes in order:
- Close files and apps that may be using the disk.
- In Disk Utility, select the volume and choose Unmount again.
- Restart your Mac, reconnect the drive, and retry.
- In Disk Utility, select View > Show All Devices and work with the correct volume or physical disk.
- If the disk is an external drive, disconnect other accessories and reconnect it directly.
- Use macOS Recovery if you are trying to unmount or repair the startup disk.
- Use Terminal only if you understand which disk identifier you are targeting.
Why macOS Cannot Unmount a Disk
Unmounting removes a disk’s file system from macOS so the system can safely disconnect, erase, partition, or repair it. macOS refuses to unmount a disk when something still has an open file or active connection to it.
Common causes include:
- A document or media file is open from the disk.
- Finder is copying, indexing, or previewing files.
- An app is using the disk as a library or backup location.
- A Terminal window is currently located on the disk.
- Time Machine or another backup tool is accessing the drive.
- Antivirus, synchronization, or cloud-storage software is scanning it.
- The disk is being used as a startup disk.
- A file system error has caused an operation to hang.
- The disk is disconnected, damaged, or not responding correctly.
A disk can have several volumes. A volume is the usable storage area that appears in Finder, while the physical disk is the hardware containing one or more volumes. This distinction matters when using Disk Utility.
Before You Begin
Back up important files
If the disk contains files you need, copy them to another location before attempting repairs, erasing, or forced unmounting. If the disk is making clicking noises, repeatedly disconnecting, or showing read errors, avoid repeated repair attempts and prioritize data recovery.
Stop active disk operations
Wait for file transfers, backups, exports, downloads, and sync operations to finish. If an operation appears frozen, save your work and quit the related app before continuing.
Close applications
Quit apps that may be reading from or writing to the disk, including:
- Photos and video-editing apps
- Music and audio-production apps
- Virtual machine software
- Backup utilities
- File synchronization tools
- Disk-cloning software
- Torrent or download apps
- Security software
Unsaved work may be lost when you force an app to quit or restart your Mac.
Method 1: Close the Process Using the Disk
Start with the least disruptive solution: close anything that may be using the disk.
- Save your work in every open app.
- Quit open apps by pressing Command-Q or choosing [App Name] > Quit [App Name] from the menu bar.
- Close Finder windows displaying the disk.
- Close Terminal windows whose current folder is on the disk.
- Wait a few seconds for copying, indexing, or backup activity to stop.
- Open Disk Utility from Applications > Utilities.
- Select the volume in the sidebar.
- Click Unmount in the toolbar.
- If you need to remove the drive, wait until the volume disappears from Finder before disconnecting it.
If Disk Utility does not show enough detail, choose View > Show All Devices. This displays the physical disk, containers, and volumes, making it easier to select the right item. For more help identifying these entries, see how to use Show All Devices in Disk Utility on Mac.
Method 2: Restart Your Mac
A restart closes most processes that may be holding the disk open.
- Save your work and quit all apps.
- Choose Apple menu > Restart.
- If the disk is external, leave it connected while the Mac restarts.
- After signing in, open Disk Utility.
- Select the disk or volume and try Unmount again.
If the external disk does not reappear, disconnect and reconnect it after macOS finishes starting. Connect it directly to the Mac rather than through a hub or dock when possible.
A restart may not solve the problem if the disk is the current startup disk or if a background service immediately reopens it.
Method 3: Unmount the Correct Volume in Disk Utility
The error can occur when you select the wrong level in the disk hierarchy. Disk Utility may show:
- The physical device
- A partition container
- Individual volumes
- Specialized system or data volumes
To identify the correct item:
- Open Disk Utility.
- Choose View > Show All Devices.
- Expand the external disk or internal storage device in the sidebar.
- Select the volume you want to unmount.
- Click Unmount.
If you are trying to erase or repartition the entire device, select the physical disk only after confirming that you have backed up all volumes on it. Do not erase the physical disk merely to resolve an unmount error.
Some volumes cannot be unmounted while macOS is running from them. The startup disk must generally be handled from macOS Recovery instead.
Method 4: Disconnect Other Accessories
Another device may be causing a USB, Thunderbolt, or power-related problem that prevents the disk from responding normally.
- Save your work and quit open apps.
- Disconnect other nonessential USB, Thunderbolt, and external storage devices.
- If the drive uses a hub or dock, connect it directly to the Mac.
- If it has a separate power adapter, confirm that the adapter is connected.
- Try a different cable or port if available.
- Open Disk Utility and try to unmount the disk again.
Do not unplug a disk while data is being written to it. If macOS is unresponsive and you have no safe software option, shut down the Mac before disconnecting the hardware.
Method 5: Use macOS Recovery for the Startup Disk
You cannot normally unmount the disk from which macOS is actively running. If the error involves the internal startup disk, use macOS Recovery.
Before starting, save your work. Recovery tools can repair or erase storage, and erasing deletes data.
- Choose Apple menu > Shut Down.
- Start the Mac in macOS Recovery:
– On a Mac with Apple silicon, press and hold the power button until startup options appear, select Options, and click Continue.
– On an Intel-based Mac, turn it on and immediately hold Command-R until the Apple logo or another startup screen appears. - Select a user account if prompted, then enter its password.
- Open Disk Utility.
- Choose View > Show All Devices.
- Select the appropriate volume or device.
- Click Unmount, First Aid, or Erase, depending on your goal.
Run First Aid before erasing a disk when you are trying to correct file system problems. If you are repairing a startup disk, work from the lowest-level volume upward as Disk Utility presents the hierarchy, then retry the operation.
If the internal disk does not appear in Recovery, or repair fails repeatedly, the issue may involve the storage hardware or its connection. Additional symptoms such as an unusually slow Mac, repeated crashes, or a missing startup disk warrant further diagnosis.
Method 6: Find the Process with Terminal
Terminal can show which processes are using a disk. This method is useful when closing normal apps and restarting have not helped, but it requires care.
Identify the disk
- Open Terminal from Applications > Utilities.
- Run:
diskutil list
This displays connected disks, partitions, containers, and volumes. Find the identifier for the volume you want to unmount, such as disk2s1. Match the identifier carefully; targeting the wrong disk can affect another drive.
Check which processes are using the volume
Replace /Volumes/YourDiskName with the actual mounted path:
sudo lsof +D "/Volumes/YourDiskName"
Enter your administrator password when prompted. The command lists open files and the processes using them. A large disk may take some time to scan.
If the command reports a process associated with an app, close that app normally. Do not terminate a process unless you understand what it does.
Attempt a normal unmount
You can ask macOS to unmount the volume by identifier:
diskutil unmount /dev/disk2s1
Replace disk2s1 with the identifier shown by diskutil list. This changes the volume’s mounted state but does not erase its data.
Attempt a forced unmount only as a last resort
diskutil unmount force /dev/disk2s1
A forced unmount closes the volume even when a process may still be using it. Unsaved data can be lost, and files being written may become corrupted. Do not use this command during a backup, file transfer, or other active write operation.
There is no general “undo” command for a forced unmount. To make the volume available again, reconnect the disk or mount it with:
diskutil mount /dev/disk2s1
Mounting makes the volume available to macOS again; it does not repair damage caused by interrupted writes.
Troubleshooting
Disk Utility says the disk is still in use
Quit all apps, close Finder windows showing the disk, and check for backup or synchronization activity. Restart the Mac if the message continues. If the disk is an external drive, connect it directly and try another cable.
The disk disappears after unmounting
That is usually expected for an unmounted volume. In Disk Utility, select the physical device and check whether the volume is listed but inactive. Select it and click Mount to make it available again.
If the entire device disappears, check the cable, port, power supply, hub, and enclosure. A failing drive may disconnect under load.
You are trying to eject an external disk
Unmounting a volume and ejecting a physical device are related but not identical. First unmount the volume in Disk Utility. Then eject the device from Finder by clicking its eject icon in the sidebar, or by Control-clicking it and choosing Eject.
Never remove a disk while macOS is copying files to it.
First Aid cannot repair the disk
First Aid may report that it cannot repair the volume, especially when the file system or hardware is seriously damaged. Confirm that you have a backup, then consider using Recovery to run First Aid on the device and its volumes.
If the disk contains important files and remains accessible, copy the data before more repair attempts. Repeated errors, read failures, or disconnections may indicate hardware failure rather than a simple mounting problem.
The startup disk is missing
If the internal startup disk does not appear in Disk Utility, shut down the Mac and start macOS Recovery again. Confirm that View > Show All Devices is enabled. If the physical device remains absent, do not erase another disk by mistake. The problem may require professional service.
Frequently Asked Questions
Does “Could not unmount disk” mean the disk is damaged?
Not necessarily. The most common cause is an app or system process using the disk. However, repeated errors, slow access, file system warnings, and unexpected disconnections can indicate damage or failing hardware.
Will unmounting delete my files?
No. Normal unmounting only makes the volume unavailable to macOS. Erasing, repartitioning, or formatting the disk is different and deletes data.
Can I unplug the disk when macOS cannot unmount it?
Do not unplug it while files are being copied or written. Close apps and try to unmount it normally. If necessary, shut down the Mac before disconnecting an unresponsive external disk.
Why can’t I unmount my Mac’s internal disk?
macOS is running from the startup disk, so it cannot normally remove that disk from active use. Start macOS Recovery and use Disk Utility there.
Should I use diskutil unmount force?
Only as a last resort, after saving work and stopping active transfers. Forced unmounting can discard unsaved changes or interrupt writes.
What should I do if the error keeps returning?
Back up the disk, test another cable or port, run First Aid from macOS Recovery when appropriate, and watch for signs of hardware failure. A disk that repeatedly disconnects or reports read errors may need replacement.
Final Thoughts
Start with the safe fixes: close apps, stop active transfers, restart your Mac, and select the correct volume in Disk Utility. Use macOS Recovery for the startup disk, and reserve forced unmounting or Terminal commands for situations where you understand the risks. If the disk shows repeated errors or disappears unexpectedly, protect your data first and investigate possible hardware failure.