One of the most beloved features of macOS is “Quick Look.” When you select any file (a photo, a PDF, a video) in the Finder and press the Spacebar, a large, instant preview of the file pops up on your screen without requiring you to open the heavy parent application (like Photoshop or Preview). To make this lightning fast, macOS constantly generates and caches these preview thumbnails in a hidden system folder.
Over time, especially if you work with massive folders containing thousands of images, this Quick Look cache can become bloated or corrupted. When this happens, pressing the Spacebar might result in a blank window, an endlessly spinning loading wheel, or it might display the preview of a completely different file. To fix this, you must aggressively flush the Quick Look cache via the Terminal.
How to Clear the Mac Quick Look Cache via Terminal
You must use a specific command-line utility to dump the corrupted thumbnail database and force the background server to restart.
- Open the Finder, go to Applications, open the Utilities folder, and double-click Terminal (or press Command + Space and search for Terminal).
- In the Terminal window, carefully copy and paste the following exact command:
qlmanage -r cache - Press Enter. The Terminal will quickly output a message stating
qlmanage: call reset on cache, confirming the cache has been dumped. - However, the background server that generates the previews might still be hung up. To forcefully restart the Quick Look server, copy and paste this second command:
killall qlmanage - Press Enter. (If it says “No matching processes were found,” that simply means the server had already gracefully shut itself down, which is perfectly fine).
You can now close the Terminal window. Navigate back to your files in the Finder and press the Spacebar on an image or PDF. The Quick Look server will generate a fresh, uncorrupted preview instantly, resolving the blank screen issue.