SIP is disabled, but /usr/bin is write protected anyway (macOS Catalina beta 10.5)

Question

I disabled SIP, but directory /usr/bin is write protected anyway. How to get write access for /usr/bin? Please don\'t suggest to switch to /usr/local/bin.

Answer 1

Catalina has a new file system arrangement where most of the system files are write-protected. Apple uses two partitions, a read-only one for the main system files and a writeable one for other files, and melds them together and presents them as one to the user.

For details see the WWDC video What's New in Apple Filesystems