How do I unlock Catalina's protected file system?

[Hervé]

With Catalina 10.15, Apple went further into increasing the security of its OS and the system's/root partition is now locked upon system startup. One of the consequences is that, by default, /System/Library/Extensions folder (/S/L/E) is locked and can not be modified in any way. In the same respect, other reserved folders such as /usr/bin or /usr/sbin are locked too.

 

This can be a problem for such situations where a vanilla kext has to be replaced in /S/L/E or a file of /S/L/CoreServices has to be patched.

 

The trick is basically to mount Catalina's root partition in Read-Write (RW) mode instead of Read-Only (RO) mode. This can be accomplished through Terminal with the following command:

sudo mount -uw /

followed a restart of the Finder through Terminal command:

sudo killall Finder

or simply by relaunching the Finder from the Apple menu: