I am running into this problem when trying to use gfortran (which should be a subset of gcc ... but in fact is not in /usr/bin eskimo: I assume you are refering to this paragraph: New in macOS Big Sur 11.0.1, the system ships with a built-in dynamic linker cache of all system-provided libraries. As part of this change, copies of dynamic libraries are no longer present on the filesystem. Code that attempts to check for dynamic library presence by looking for a file at a path or enumerating a directory will fail. Instead, check for library presence by attempting to dlopen() the path, which will correctly check for the library in the cache. (62986286) But not sure how to interpret it... where is this 'cache'??? Doing, for example a locate libSystem.dylib /Applications/Xcode.app/Contents/Developer/Platforms/AppleTVOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/tvOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libSystem.dylib /Applications/Xcode.app/Contents/Developer/Platforms/WatchOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/watchOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libSystem.dylib /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libSystem.dylib /System/DriverKit/usr/lib/libSystem.dylib /System/Volumes/Update/mnt1/Applications/Xcode.app/Contents/Developer/Platforms/AppleTVOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/tvOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libSystem.dylib /System/Volumes/Update/mnt1/Applications/Xcode.app/Contents/Developer/Platforms/WatchOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/watchOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libSystem.dylib /System/Volumes/Update/mnt1/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libSystem.dylib /System/Volumes/Update/mnt1/System/DriverKit/usr/lib/libSystem.dylib But the directory /System/Volumes/Update/mnt1/ is empty.... And I assume the others don't apply to a Big Sur on an older (2.2 GHz Quad-Core Intel Core i7) mac Bottom line, which directory should I include to find