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During many years, using different versions of MacOS ( Yosemite, El Capitan, Sierra, High Sierra, Mojave, Big Sur ) I got this error message upon trying to launch Preview ( and sometimes Safari ): The application Preview is not open anymore. I am not yet able to reproduce this bug ( otherwise I would have submitted a useful bug report ). In the case I am working on now, the error is true: Preview is not open anymore. Neither ps nor Activity Monitor find it. If I try to start the application with: open /Applications/Preview.app I get a slightly more intelligent error message: LSOpenURLsWithRole() failed with error -600 for the file /Applications/Preview.app. But it appears that in fact this function is deprecated ( from the developer official documentation ). I am actually working with opensnoop and dtruss to get which process is seeing this application not present and why this could block it starting again. How may I further debug this blocking error of MacOS?

I am using InternetSharing and running a web proxy to redirect all traffic through. How may I automatically add the correct redirect rules to the anchor InternetSharing is : com.apple.internet-sharing/base_v4 Where is the documentation to manage anchors in a constructive way not interfering with the GUI "System Preferences..."?