Why I cannot write in /System/Library/QuickLook/ not even by sudo command? I try to add the Mail.qlgenerator plugin in that directory, but macOS replies I haven't permission to write in it.

1 Answer 1


The OS is on a separate, secure, read-only volume. "Your Data" -- everything you add -- is on another volume. The Finder presents the two as one combined file structure.

If you want to add a QuickLook plug-in, then put it in /Library/QuickLook, or the QuickLook sub-folder of your User account's Library folder.

The /Library folder (as opposed to/System/Library) is designed to be the place where additions to the system are placed. The same is true in the user Library folder, but it only affects that user.

MacOS keeps things separate so that you know what you've added, and what comes with the OS. (On top of the security.)

  • So, my iMac isn't actually my
    – Marcello
    Jan 31 at 9:10
  • @Marcello Yes it is. If you want to make changes to the OS, then there are ways of doing that, but they involve supplementing, rather than replacing, the original content. Some Linuxes also mount the OS as read-only. You are of course total free to write your own OS, as well!
    – benwiggy
    Jan 31 at 12:46

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