Cannot change APFS encryption password

I have a clean install of macOS High Sierra with APFS Encrypted file partition. During install I checked the "decrypt at login" option, but each have a different password. I now want to change my APFS password but I haven't been abled to:

• "change password" is greyed out in the Disk Utility for my APFS volume.
• diskutil apfs changePassphrase ... returned an error saying it can't do it.

Any idea how I can do that?

P.S. I also have FileVault turned on, with the same password as my login (so different from the APFS Encryption).

Solution 1:

You need to list your disks to find the APFS volume disk where you want to change the password:

sudo diskutil apfs list

Now find the UUID of the cryptographic Disk User:

sudo diskutil apfs listUsers <your APFS volume, like: disk1s1>

Finally you can change the APFS volume password:

sudo diskutil apfs changePassphrase <your APFS volume, like: disk1s1> -user <the Disk User cryptographic UUID, like: 12345678-1234-1234-1234567890AB>