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I have noticed that thumbnails on Mac OS X don't seem to be generated every time I open a folder, but to be somehow "cached" instead.

I wasn't able, however, to find a folder where they clearly look to be stored.

I thought then they could be saved as some kind of metadata; i found, however, that when deleting a file (e.g. from the Desktop) and saving immediately after a file by the same name, the preview for the previous file is showed for ~ a second.

Are they stored separately from data? How and when are they invalidated (e.g. only when a file by the same name appears in the same directory)?

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Probably in the infamous .DS_Store file in the same directory. –  Daniel Beck Oct 19 '12 at 15:51
I also took this as a possibility, however it doesn't seem to contain anything about the thumbnails. –  Alberto Moriconi Oct 19 '12 at 16:03

1 Answer 1

up vote 4 down vote accepted

The quicklookd background process is responsible for creating and managing file thumbnails. Those thumbnails are stored in a folder named com.apple.QuickLook.thumbnailcache in a folder like /var/folders/39/ggldtdps6034ct7d_y6x4_v80000gn/C that is specific to your user account. The file index.sqlite contains a SQLite database with information about stored thumbnails; access it using the sqlite3 command line tool.

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Great! I was able to dump the index.sqlite db, take a look and get an insight of how this works! Thanks :) –  Alberto Moriconi Oct 19 '12 at 17:17

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