Unable to prevent APFS partition from mounting automatically in Mojave (10.14.5)

I'm trying to prevent macOS from asking me the FileVault password for 2 APFS partitions on boot. I don't want them to be mounted at all.

APFS container:

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +121.1 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume macOS                   43.2 GB    disk1s1
   2:                APFS Volume Preboot                 121.3 MB   disk1s2
   3:                APFS Volume Recovery                1.0 GB     disk1s3
   4:                APFS Volume VM                      1.1 GB     disk1s4
   5:                APFS Volume Shared                  7.7 GB     disk1s5
   6:                APFS Volume macOS Beta - Data       21.7 GB    disk1s6
   7:                APFS Volume macOS Beta              10.0 GB    disk1s7

Partition 1:

   Device Identifier:         disk1s6
   Device Node:               /dev/disk1s6
   Whole:                     No
   Part of Whole:             disk1

   Volume Name:               macOS Beta - Data
   Mounted:                   No

   Partition Type:            41504653-0000-11AA-AA11-00306543ECAC
   File System Personality:   APFS
   Type (Bundle):             apfs
   Name (User Visible):       APFS
   Owners:                    Disabled

   OS Can Be Installed:       No
   Booter Disk:               disk1s2
   Recovery Disk:             disk1s3
   Media Type:                Generic
   Protocol:                  PCI
   SMART Status:              Verified
   Volume UUID:               C6C28412-1505-4F19-8056-369FAE57B0CF
   Disk / Partition UUID:     C6C28412-1505-4F19-8056-369FAE57B0CF

   Disk Size:                 121.1 GB (121123069952 Bytes) (exactly 236568496 512-Byte-Units)
   Device Block Size:         4096 Bytes

   Volume Total Space:        0 B (0 Bytes) (exactly 0 512-Byte-Units)
   Volume Free Space:         0 B (0 Bytes) (exactly 0 512-Byte-Units)

   Read-Only Media:           No
   Read-Only Volume:          Not applicable (not mounted)

   Device Location:           Internal
   Removable Media:           Fixed

   Solid State:               Yes
   Hardware AES Support:      No

Partition 2:

   Device Identifier:         disk1s7
   Device Node:               /dev/disk1s7
   Whole:                     No
   Part of Whole:             disk1

   Volume Name:               macOS Beta
   Mounted:                   No

   Partition Type:            41504653-0000-11AA-AA11-00306543ECAC
   File System Personality:   APFS
   Type (Bundle):             apfs
   Name (User Visible):       APFS
   Owners:                    Disabled

   OS Can Be Installed:       No
   Booter Disk:               disk1s2
   Recovery Disk:             disk1s3
   Media Type:                Generic
   Protocol:                  PCI
   SMART Status:              Verified
   Volume UUID:               55930D94-2CF3-481B-B845-FEAB3C492F23
   Disk / Partition UUID:     55930D94-2CF3-481B-B845-FEAB3C492F23

   Disk Size:                 121.1 GB (121123069952 Bytes) (exactly 236568496 512-Byte-Units)
   Device Block Size:         4096 Bytes

   Volume Total Space:        0 B (0 Bytes) (exactly 0 512-Byte-Units)
   Volume Free Space:         0 B (0 Bytes) (exactly 0 512-Byte-Units)

   Read-Only Media:           No
   Read-Only Volume:          Not applicable (not mounted)

   Device Location:           Internal
   Removable Media:           Fixed

   Solid State:               Yes
   Hardware AES Support:      No

Current /etc/fstab which doesn't work:

UUID=55930D94-2CF3-481B-B845-FEAB3C492F23 none apfs rw,noauto
UUID=C6C28412-1505-4F19-8056-369FAE57B0CF none apfs rw,noauto

What am I doing wrong? Is it because of a mistake I made or is /etc/fstab no longer supported? What's /etc/fstab.hd for?

Operating System: macOS Mojave 10.14.5
Hardware: MacBook Air (13-inch, Early 2015)

Solution 1:

"Educated" guess:

In your case FileVault unlocking is managed by the preboot APFS volume (disk1s2).

Your specific APFS container configuration implies that preboot manages booting to macOS 10.14.5 as well as macOS 10.15 beta.

At this boot stage disk1s1's /etc/fstab is probably not yet involved and thus entries won't work.

If you really want to disable disk1s6/disk1s7, you probably have to rename one of the two folders with UUID names (one for macOS 10.14.5 and the other for macOS 10.15 beta) in preboot. The folder names correspond with the APFS boot volume UUIDs you get with diskutil ap list.

You have to rename the one which is identical with the UUID of macOS 10.15 beta's boot volume.

Not tested - absolutely not recommended!

BTW: I tried to find some kernel flag to add to /Volumes/Preboot/[UUID]/Library/Preferences/SystemConfiguration/com.apple.Boot.plist to prevent FV unlocking but failed.