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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?

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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.
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  • will disabling and then reenabling using csrutil cause any problems/side effects? – Albert Apr 16 '20 at 14:31
  • @Albert Temporarily disabling SIP protection shoudn't have any lasting effect after you re-enable it, but the changes you made with it disabled might. – Gordon Davisson Apr 16 '20 at 19:14
  • Thank you for your help! – Albert Apr 16 '20 at 19:19
  • @GordonDavisson csrutil enable --without fs says Requesting an unsupported configuration.. – xiaoyu2006 Mar 13 at 12:10
  • @xiaoyu2006 That's just a warning message; you should be able to proceed. (Although if you are using Big Sur, the process has gotten more complicated; see this question). – Gordon Davisson Mar 13 at 17:59
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Yes, this is by design. Boot to recovery and choose terminal from the Utility menu.

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

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.

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