How to fix: The volume can't be ejected because it's currently in use
After working with an external hard drive (further simply - disk) I want to cleanly unmount it. But to my surprise when pressing the ‘eject’ button Finder warns me with the following error messages:
The volume can't be ejected because it's currently in use.
The disk "Elements" wasn't ejected because one or more programs may be using it.
For regular users, I recommend reading another article about this issue. It describes how to do almost the same thing using the Activity Monitor application, instead of using commands in the Terminal. This article is intended for advanced users (when the “QuickLookUI” process is not the cause) and/or for coder’s fun 
After several attempts, I tried to use the umount command in the Terminal app, and get the same error:
$ umount /Volumes/Elements umount(/Volumes/Diskname): Resource busy -- try 'diskutil unmount'
And the same with the diskutil unmount command recommended in previous error message:
$ diskutil unmount /Volumes/Elements Volume Elements on disk4s1 failed to unmount: dissented by PID 16314 (/System/Library/Frameworks/Quartz.framework/Versions/A/Frameworks/QuickLookUI.framework/Versions/A/XPCServices/QuickLookUIService.xpc/Contents/MacOS/QuickLookUIService)
What causes this error
This error message is self explanatory. It means that we are trying to eject the disk that is currently in use. If we have any file stored on the disk open in any app, macOS may prevent us from ejecting the disk so we don’t lose any of our data. If this happens, we just need to close the file in question and try again eject the disk. But I’m sure I have not launched any app neither opened any file from the disk.
In some cases, macOS will allow us to “force-eject” the disk, but we may still lose data, so force eject is not reasonable.
What I have:
- Drive: WD Elements Portable 1Tb
- OS: macOS High Sierra 10.13.1
- Computer: MacBook Air 11-inch (2014)
How to solve it
First I found this article on the Apple Support website, but unfortunately it did not help. In short, it says to logout, then login again and try to eject the disk. And if you still can’t eject the disk, it suggest to shut down the computer and then unplug the disk… 
As I’m in the middle of doing multiple tasks, logging out and logging in is not preferred as is the installation of third party software like the What’s Keeping Me? or the Why not unmount?. I prefer a clean unmount of the drive. So I need to find the solution myself.
As far as I’m aware, I’m not using the disk but Finder says I do, so I must be wrong. Now I need to know what app is using my disk so I can properly quit that app and eject my disk. To solve this, we will use the Terminal app and few console tools. All the tools are built-in in macOS, so we do not need to download or install anything. Let’s begin!
Launch the Terminal app from the Utilities folder of your Applications folder, or use Spotlight to find it.
Firstly we need to find the proper name of our disk:
ls /Volumes/
Elements Macintosh HD
“Macintosh HD” is an internal MacBook drive, and “Elements” is my external hard drive. So, in my case, the name of the disk is “Elements”. In your case, the disc name will be different.
The below commands assume this is Elements, but replace Elements with the correct disk name if it’s something different.
Now let’s find out which system process uses our disk. For this we use the lsof tool.
sudo lsof | grep /Volumes/Elements
We must run the above command with
sudo(as an Admin). For this we need to enter our password when prompted.
Note! Do not forget to replace “Elements” with the name of your disk before pressing Enter.
Enter your password after prompted and then watch the magic happen…
mds 83 root 21r DIR 1,15 288 2 /Volumes/Elements mds 83 root 22r DIR 1,15 288 2 /Volumes/Elements mds 83 root 24r DIR 1,15 2208 21 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35 mds 83 root 25r DIR 1,15 288 2 /Volumes/Elements mds 83 root 27u REG 1,15 0 72 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/journalExclusion mds_store 252 root txt REG 1,15 24 620 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexDates mds_store 252 root txt REG 1,15 10 621 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexGroups mds_store 252 root txt REG 1,15 8 627 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexCompactDirectory mds_store 252 root txt REG 1,15 2056 626 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexDirectory mds_store 252 root txt REG 1,15 8192 588 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexCompactDirectory mds_store 252 root txt REG 1,15 13108 582 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexGroups mds_store 252 root txt REG 1,15 16448 587 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexDirectory mds_store 252 root txt REG 1,15 96 619 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexIds mds_store 252 root txt REG 1,15 32768 581 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexDates mds_store 252 root txt REG 1,15 65536 630 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.directoryStoreFile mds_store 252 root txt REG 1,15 72256 628 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexArrays mds_store 252 root txt REG 1,15 131072 57 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/reverseDirectoryStore mds_store 252 root txt REG 1,15 131072 580 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexIds mds_store 252 root txt REG 1,15 131072 591 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.directoryStoreFile mds_store 252 root txt REG 1,15 2097152 584 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexTermIds mds_store 252 root txt REG 1,15 2097152 586 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexPositionTable mds_store 252 root txt REG 1,15 4194304 589 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexArrays mds_store 252 root 27r DIR 1,15 2208 21 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35 mds_store 252 root 42r REG 1,15 72256 628 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexArrays mds_store 252 root 44r DIR 1,15 2208 21 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35 mds_store 252 root 65u REG 1,15 28 28 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/indexState mds_store 252 root 66u REG 1,15 593920 55 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/store.db mds_store 252 root 67u REG 1,15 593920 56 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/.store.db mds_store 252 root 68r REG 1,15 8 627 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexCompactDirectory mds_store 252 root 69u REG 1,15 4096 618 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexHead mds_store 252 root 70u REG 1,15 96 619 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexIds mds_store 252 root 71u REG 1,15 24 620 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexDates mds_store 252 root 72r REG 1,15 1694 622 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexPostings mds_store 252 root 79r REG 1,15 2056 626 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.indexDirectory mds_store 252 root 99u REG 1,15 65536 630 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/0.directoryStoreFile mds_store 252 root 103u REG 1,15 4096 579 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexHead mds_store 252 root 106u REG 1,15 131072 580 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexIds mds_store 252 root 108u REG 1,15 13108 582 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexGroups mds_store 252 root 109u REG 1,15 2097152 583 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexPostings mds_store 252 root 110u REG 1,15 2097152 584 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexTermIds mds_store 252 root 111u REG 1,15 8388608 585 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexPositions mds_store 252 root 112u REG 1,15 2097152 586 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexPositionTable mds_store 252 root 113u REG 1,15 16448 587 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexDirectory mds_store 252 root 114u REG 1,15 8192 588 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexCompactDirectory mds_store 252 root 115u REG 1,15 4194304 589 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.indexArrays mds_store 252 root 116u REG 1,15 131072 591 /Volumes/Elements/.Spotlight-V100/Store-V2/C59C29F8-4296-456C-B45B-CBD4AF706C35/live.0.directoryStoreFile QuickLook 16314 arthur 3r REG 1,15 2283237221 3207 /Volumes/Elements/PATH/TO/FILE/filename.mov
The output of the command may seem complicated in understanding, but it is not. The first column indicates the running process, and the last column indicates the file on our disk that is currently in use. In my case, three processes are running: mds, mds_store and QuickLook. Also, the hidden folder .Spotlight-V100 and the file filename.mov are used. So now I know what is preventing me from ejecting my disk.
The mds and mds_store processes are related to Spotlight. You can learn more about it here. Running these processes mean that the Spotlight is currently indexing our disk. We can leave the disk turned on for a while, so that the Spotlight could finish its work, or we can force the process to stop.
The QuickLook process is a feature that was introduced in the Mac OS X 10.5 Leopard. You can learn more about it here. I noticed that when I use the Quicklook feature to preview a video in any format, the process keeps active even when the Quicklook window was already closed. If I preview any other file like PDF or JPG the disk can be ejected normally. Why does Quicklook preventing me from ejecting my disk? I suspect that this is just a bug.
Once we know what process is preventing us from ejecting our disk, we can force it to stop. For this we use the killall tool.
sudo killall mds
We must run the above command with
sudo(as an Admin). For this we need to enter our password when prompted.
Note! Do not forget to replace “mds” with the name of process that you want to stop before pressing Enter.
Also we can do this by using the Activity Monitor.
Finally, issue the following command to unmount the disk, replacing “Elements” with your actual disk name.
diskutil unmount /Volumes/Elements
Volume Elements on disk4s1 unmounted
Conclusion
That’s it, you’re done. Now our disk should be safely ejected. So simple isn’t it?
If you are having trouble fixing this problem with the instructions above, but are being able to solve this problem with any another method please describe it in the comment section below. Thanks!
If this article has helped you solve the problem then please leave a comment
Thanks for reading!
Arthur is a designer and full stack software engineer. He is the founder of Space X-Chimp and the blog My Cyber Universe. His personal website can be found at arthurgareginyan.com.
