Unable to mount read-write in OS Catalina 10.15.4 in Single User Mode

Question

The command /sbin/mount -uw / no longer works after I upgraded to Catalina. I've read that this is due to Apple. Is there a new solution to mount to read and write through Single User Mode?

Answer 1

Catalina uses a new split-volume system for its file system, where system files are stored on a read-only volume, and user-modifiable parts of the filesystem are stored in a separate "Data" volume that's normally mounted read-write (see this article for more info). But in single-user mode they're both mounted read-only.

If you just need write access to the normally-writable parts of the filesystem, you just have to update the mount point for that volume:

mount -uw /System/Volumes/Data

If you need write access to the normally-read-only volume, things are more complicated. You'll need to:

1. Restart in Recovery mode and then either make your modifications there and call it a day, or...
2. Open Terminal (under the Utilities menu in Recovery), run csrutil enable --without fs (see my answer here)
3. Restart in single-user mode
4. Run mount -uw / and maybe also mount -uw /System/Volumes/Data
5. Do your modifications
6. Finally, restart back to Recovery and run csrutil enable to get the normal system protections back.

Answer 2

Yes, this is by design. Boot to recovery and choose terminal from the Utility menu.

• https://support.apple.com/en-us/HT201314

Here is an example of when you use terminal app from recovery for things we used to use single user mode to accomplish.

• https://support.apple.com/en-us/HT207584

Of course don’t follow all the steps above unless you want to erase a fusion drive equipped Mac, but it shows the steps to get to a command line environment on all OS that don’t work in single user mode.