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I know similar questions have been asked before but I just can't believe this can't be solved, so I am going to ask again with specific details.

I have two partitions that are bootable on the internal drive of my Mac running macOS Catalina 10.15.7. Both are encrypted APFS volumes.

Whenever I log in to one of them, I am getting a promt, asking me for the password of the other. I do not want to store the password in the keychain to work around the prompt (for security reasons), in fact I do not want the other volume to be automatically mounted at all. All I want is to be able to choose the boot volume on startup (via the [Opt] key).


I tried

  1. adding this line to my /etc/fstab using vifs:
UUID=<UUID of the volume> none apfs rw,noauto

but this does not prevent the prompt from appearing.

  1. changing the volume role via
diskutil ap changeVolumeRole <diskId> D

but this returns the error: Error setting APFS Volume role: Unable to set the APFS Volume Role (-69599)


Is there seriously no way of preventing disks from being automounted? Can the Finder be at leat taught to not ask for the password?

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  • idk the exact syntax rules for fstab, but I keep drives unmounted at boot with UUID=[UUID] none auto noauto
    – Tetsujin
    Oct 24 '20 at 7:30
  • @Tetsujin and this works with Catalina? Oct 24 '20 at 12:57
  • I don't have any Mac with Catalina to test. Try it, it will take 5 minutes.
    – Tetsujin
    Oct 24 '20 at 15:26
  • 1
    The /etc/fstab UUID=[UUID] none auto noauto trick now works in Big Sur 11.2. Feb 2 '21 at 5:40
  • 1
    Thanks @PlinkPanther, you are right! I added an answer for people looking for an clear description. Feb 3 '21 at 10:33
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Starting with MacOS BigSur 11.1. the /etc/fstab/ solution works (again):

  1. find the volume label from the volume name:
    diskutil list | grep <volume name>
    the last entry (e.g. disk2s2) is the volume label.
  2. find out the volume UUID from the volume label
    diskutil info <volume label> | grep "Volume UUID"
  3. open /etc/fstab for editing:
    sudo vifs
  4. add a line preventing the auto-mount of the volume:
    UUID=<volume uuid> none auto noauto

Here's a complete example:

> diskutil list | grep "Macintosh HD2 - Data"
2:                APFS Volume Macintosh HD2 - Data⁩       341.8 GB   disk2s2

> diskutil info disk2s2 | grep "Volume UUID"
Volume UUID:               C58A1BDC-593C-4854-B954-702A73ABD67C

> sudo vifs
# add the following line:
UUID=C58A1BDC-593C-4854-B954-702A73ABD67C none auto noauto

On the next reboot the popup asking for the password will no longer appear.

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