How to Fix Failure with Thumbnail Cache in High Sierra?

The fourteenth release of macOS is associated with a large number of major improvements and new features that provided Apple aficionados with the speedier and smarter user experience. Specifically, the software upgrade allows better organization of media files and pro-level photo editing, which is appreciated by those who cannot live without tweaking and adjusting their snapshots.

Unfortunately, despite the introduction of slick software refinements, some users noticed a deterioration in the functioning of the Finder. Namely, preview thumbnails of video files are not properly displayed. Instead of seeing thumbnails, which are extremely useful for finding relevant files, users are presented with generic icons. Most importantly, the issue cannot be resolved by changing the Show Icon Preview preferences. After the problem appears, the file containing thumbnail cache stops expanding. Fortunately, there are several workarounds for this irritating problem.

Delete the Finder Preferences File

The solution to the issue of missing file previews is grounded in changing the Finder preferences. What needs to be done is to delete the Finder plist file and reboot a computer. It has to be borne in mind, however, that by deleting the file all Finder preferences will be gone, which means that a user will have to reintroduce all changes involving extension visibility, icon spacing, font size, and other preferences.

To this end:

  1. Click on the Finder icon, which is located in the Dock;
  2. Once in the Finder, go to the Preferences by using the Command + Shift + G key combination and entering the following: ~/Library/Preferences/;
  3. In the Preferences, find the file named as apple.finder.plist and delete it

Note that the file can be copied prior to the deletion as an extra precaution;

  1. Close the Preferences folder;
  2. Go the Apple Menu and reboot the computer by clicking on the Restart button;

It should be noted that the plist file has to be regenerated; therefore, it is not sufficient to just relaunch the Finder to introduce the changes.

Sometimes, the Finder can be completely inaccessible, which makes it impossible to remove the plist file. However, the advanced search feature can be accessed with the help of the macOS command line. To do so:

  1. Open the Applications and go to the Utilities folder;
  2. Start the Terminal app (alternatively, use the Spotlight search to find the application);
  3. Enter the following command: mv ~/Library/Preferences/ ~/Desktop/;
  4. Hit Enter to run the command

Note that the command moves the plist file to the desktop instead of deleting it altogether, which makes for the easier recovery;

  1. Close the Terminal app;
  2. Reboot the Mac by clicking on the Restart button in the Apple Menu (alternatively, use the following command: sudo shutdown –r now “Restarting Now”).

After the Mac is rebooted, the preview function will allow viewing thumbnails in the process of finding relevant video files. If the preview operates properly, the old plist file, which is located on the desktop, can be moved to the Trash.

Update macOS

The issue can be resolved by keeping macOS software up to date. By installing the latest supplemental update macOS High Sierra 10.13.2, it is possible to return the full preview of media files. To upgrade the software on a Mac:

  1. Open the App Store;
  2. Click on the Updates tab in the toolbar;
  3. Find the available update;
  4. Use the Update button to install the supplemental update.