QuickLook Is Holding Your Drive Hostage (Here's Why)

You copied some files to your external drive. You closed the Finder window. You click eject, and macOS says no. You haven’t touched the drive in five minutes. What’s using it?

Check Activity Monitor for QuickLookUIService. There’s a good chance that’s your culprit.

What QuickLook is doing

QuickLook is the system that powers file previews in macOS. Press Space on a file in Finder and you get a preview window. Browse files in column view and you see thumbnails. Open a save dialog and there are those previews again. QuickLook is everywhere.

When you browse a folder, QuickLook starts generating previews for files it thinks you might want to see. It reads files, extracts thumbnails, and caches them for faster access later. For images, PDFs, videos, and documents, this means opening the file and processing its contents.

The problem is that QuickLook can be slow to release files after it’s done with them. You’ve moved on to a different folder. You’ve closed the Finder window entirely. But QuickLookUIService still has file handles open on your external drive.

Why this blocks ejection

macOS won’t let you eject a drive while any process has open files on it. This is a safety feature. If something is actively reading or writing, ejecting could corrupt data or crash the application.

QuickLook isn’t reading or writing anything important at this point. It’s just holding onto file handles it doesn’t need anymore. But macOS doesn’t distinguish between “actively using a file” and “forgot to close a file.” A handle is a handle.

The result is that you can’t eject your drive because of previews you glanced at five minutes ago.

How to fix it

The quick fix is to kill QuickLookUIService. Open Terminal and run:

killall QuickLookUIService

This terminates the process immediately. macOS will restart it automatically the next time you need a preview. Your drive should now eject normally.

If you want to be more surgical, you can first confirm QuickLook is the problem:

sudo lsof /Volumes/YourDriveName | grep -i quicklook

If you see QuickLookUIService in the output, that’s your blocker.

You can also reset QuickLook’s cache, which sometimes helps with persistent issues:

qlmanage -r cache

This clears the thumbnail cache and restarts the QuickLook system.

Why videos are the worst offender

QuickLook is particularly aggressive about holding onto video files. When you preview a video, QuickLook opens the file and keeps it open in case you want to scrub through or watch more. Even after you close the preview window, the file handle often persists.

If you have video files on your external drive and you previewed any of them (intentionally or accidentally while browsing in column view), there’s a high probability QuickLook is blocking ejection.

The same issue affects large images and PDFs to a lesser extent. Basically, any file type where QuickLook does real work to generate a preview.

Preventing the problem

You can’t really disable QuickLook without losing a lot of macOS functionality. But you can minimize how much it interferes with external drives.

Switch to list or icon view when browsing external drives. Column view automatically triggers QuickLook for the selected file. List and icon view don’t generate previews unless you explicitly request them.

Avoid pressing Space to preview files on external drives. If you need to check a file, open it directly rather than using QuickLook.

Give it a moment after browsing. QuickLook will eventually release file handles on its own. If you just finished browsing files on an external drive, wait 30 seconds before trying to eject.

Close all Finder windows before ejecting. Even if the Finder window isn’t showing your external drive anymore, it might have QuickLook references lingering from earlier browsing.

None of these are great solutions. They’re workarounds for a system process that doesn’t clean up after itself properly.

The real fix

The frustrating thing about QuickLook blocking ejection is that you have no way of knowing it’s happening. macOS tells you “something” is using the drive. You close everything you can think of. The drive still won’t eject.

You’re expected to either guess which invisible background process is the culprit, or start running Terminal commands to investigate. For something as routine as unplugging a drive, that’s absurd.

Ejecta shows you exactly what’s blocking ejection. When QuickLookUIService is the problem, you see it immediately. One click quits the process and releases your drive. No guessing, no Terminal, no wondering if you’re about to break something.

QuickLook is a useful feature that occasionally causes unnecessary problems. You shouldn’t have to become a Unix detective to deal with its failure to release file handles.