Resolved Catalina - Prevent APFS Volume Mount at Boot w/ FSTB

[Buadhai]

I have CCC create bootable clones. CCC unmounts those volumes when the clone is complete.

However, if the machine reboots those volumes are mounted. I used to be able to prevent that with entries in FSTB like this:

UUID=4675A27D-E063-3131-9DA3-217C18107C09       none    apfs     rw,noauto

But that doesn't seem to work anymore.

Anyone got this working?

 

[Buadhai]

Turns out that you need to put the UUID of both the read-only System volume and the writeable DATA volume in the FSTB file. This works:

## Clorox
UUID=0D4EE102-A8C3-31A6-A0BD-C82A702697A2       none    apfs    rw,noauto
UUID=BEC5D911-9473-4C3A-97C7-E68999C9ACFD       none    apfs    rw,noauto

where "Clorox" is the name of the volume you see in the finder and the UUIDs are for both the System and Data volumes.

 

[CuteBaby]

## Clorox
UUID=0D4EE102-A8C3-31A6-A0BD-C82A702697A2 none apfs rw,noauto
UUID=BEC5D911-9473-4C3A-97C7-E68999C9ACFD none apfs rw,noauto

This method doesn’t work for me. Just tried it for the first time. macOS Catalina 10.15.5. The external boot drive (APFS, FileVault-enabled) still mounts. Can you confirm if this method is still working on your end with 10.15.5?

Edit: Also, is your external boot drive FileVault-enabled?

 

[Buadhai]

Still working here. That volume (Clorox) is not mounted:

drwxr-xr-x   9 root     wheel    288 May 30 11:15 .
drwxr-xr-x  24 root     admin    768 May 28 06:57 ..
lrwxr-xr-x   1 root     wheel      1 May 28 07:02 Amonia -> /
drwxrwxr-x   7 root     admin    306 Nov  4  2019 Empty
drwxr-xr-x  48 root     staff   1700 May 28 00:47 Media
drwxrwxr-x  14 root     admin    544 May 30 10:39 TM
drwxrwxr-x   7 root     admin    306 Oct 22  2019 Unused
drwx------   1 mnewman  staff  16384 May 30 07:17 chaampihome
drwxr-xr-x@  3 root     wheel     96 Jan 29 06:53 com.apple.TimeMachine.localsnapshots

 

[CuteBaby]

Thanks for the confirmation. Is the volume FileVault-enabled?

 

[Buadhai]

No, it is not

 

[CuteBaby]

Ah, that’s probably the issue on my end. I’ll need to find a solution that works with FileVault-enabled APFS volumes. Thanks anyway!

 

[canhaz]

Adding 2c here, it does seem filevault-enabled APFS volumes disregard the "noauto" option in /etc/fstab.

Currently spent hours searching the web and see absolutely no way to stop a filevault enabled APFS volumes from auto-mounting when using macOS 10.15.5. Madness.

On a side note, diskarbitrationd or whatever is mounting this, does indeed read the /etc/fstab. How do I know this? Because if one uses the "ro" (aka read only) option (in fstab) for the external filvevault enabled apfs volume, it listens and automounts it read only (irrespective if noauto is specified or not).