Mac OS X 10.6 (Snow Leopard): Beware of QuickLook plug-ins

Posted by Pierre Igot in: Macintosh
November 10th, 2009 • 12:11 am

Earlier today, I wrote a post about a new performance problem that I was having in Snow Leopard with the preview column in Finder windows.

After reading the post, a reader wrote to me to say that he couldn’t reproduce the problem and that I should take a look at my “QuickLook previewers.”

QuickLook is a feature that was introduced in Leopard and enables you to take a quick look (hence the name) at files without opening them.

It’s an extensible architecture, meaning that third parties can produce QuickLook plug-in files that end with the “.qlgenerator” file extension and go inside either your home library’s “QuickLook” folder (you can create one if there is none) or inside the main library’s “QuickLook” folder (if you have admin access and want the plug-in to be available to all users).

This way, third parties can add to the functionality by adding QuickLook support for various other file types beyond the ones supported by the shipping Mac OS X.

What I didn’t know is that the same QuickLook plug-ins or “generators” are also involved in the display of the preview column in Finder windows. And I didn’t realize that some could interfere with the display of the previews of some common files such as disk images.

I had three QuickLook plug-ins in my home library’s “QuickLook” folder:

Suspicious Package.qlgenerator

and four QuickLook plug-ins in my main library’s “QuickLook” folder:


The ones in the main library were automatically installed by various software installers (Apple’s Logic Studio and Parallels, among others). The three in my home library’s folder were installed manually by me, a while ago.

Through a quick elimination process, I was able to determine that the culprit is, apparently, the EPSQLPlugIn plug-in. I have removed it, and the disk image preview icon is now display more or less instantly, regardless of the size of the file.

What EPS files have to do with disk images, I have no idea. But I am not really interested in investigating. EPS support in QuickLook is a convenience, not exactly a necessity.

I also checked the latest version of the plug-in and it still says that it’s version 1, which is the version I had installed, although it does not have the exact same creation date. (The web site also says that the download is 600 KB when the actual file is three times as big.) Again, I am not really interested in investigating the issue any further.

But the lesson here seems to be that, as soon as a new feature is added to Mac OS X with some level of extensibility through plug-ins and the like, the user is required to be very careful about what he adds or does not add. Because obviously this is not a problem that Apple itself is concerned with. And some of these third-party developers might be too small or unreliable to be counted on to do proper testing and so on.

Incidentally, I also found some weird behaviour in Snow Leopard itself. I did the elimination process in a separate user environment that I use for testing purposes only, and logged out and back in after each change. But the first time I logged back in after removing or adding a QuickLook plug-in, the Finder would open, and then it would immediately disappear altogether, along with the menu bar at the top. I could still use the Dock, but the force-quit dialog box showed zero application open. I was able to open another application through the Dock and then the menu bar with the Apple menu reappeared and I was able to log back out and then back in, and after that things were fine, but it was still a bit strange, and it occurred several times, each time after I altered the contents of the home library’s QuickLook folder and logged out and back in. Weird.

Anyway, thanks to Dan H. for pointing me in the right direction. And to all Betalogue readers: beware of QuickLook plug-ings.

One Response to “Mac OS X 10.6 (Snow Leopard): Beware of QuickLook plug-ins”

  1. Problem with preview column in finder windows? « Chicago Mac/PC Support says:

    [...] with preview column in finder windows? It could be because of quicklook plug-ins!  Click here to learn more about [...]