2018 Macbook Pro running Catalina.

I have an external 1TB USB drive (Samsung) partitioned into two equal partitions, where I keep mostly media files for work (videos I edit, some graphics, etc.). I recently (week or two ago) had some oddities with permissions in my home directory, so I went into Recovery and did the full permissions repair routine, along with reinstalling the OS (keeping all user data). Everything then looked fine and life went on, until today.

I noticed that for some reason, Preview would not allow me to edit a .png from my external drive, and save the change. It required that I make a copy of the file, and then it would save. I looked at permissions (Get Info) on the external drive, and it just says "You Have Custom Access". Both partitions in fact, state this. Clearly this isn't going to work! This is my personal laptop, I'm the only user account on it, ever, and I'm the admin. But I'm not allowed to change the permissions as I seem to not have permission to do so!

I've found numerous posts online about this issue, but not that don't include some very different elements. How can I get full permissions access again on my external partitions? I really would prefer not to brute-force this via chown etc. I would just like the OS to once again recognize that this drive and its partitions are mine, and everything on them should be under my user account control.

EDIT: results of diskutil list:

$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     314.6 MB   disk0s1
   2:                 Apple_APFS Container disk1         250.7 GB   disk0s2

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +250.7 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD - Data     128.5 GB   disk1s1
   2:                APFS Volume Preboot                 99.9 MB    disk1s2
   3:                APFS Volume Recovery                1.0 GB     disk1s3
   4:                APFS Volume VM                      3.2 GB     disk1s4
   5:                APFS Volume Macintosh HD            11.2 GB    disk1s5

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *1.0 TB     disk2
   1:               Windows_NTFS ExPart1                 499.6 GB   disk2s1
   2:               Windows_NTFS ExPart2                 500.6 GB   disk2s2
  • Before doing the perms dance - there's a small possibility your new user isn't the same internal number as you old one - try just checking the "Ignore ownership on this volume" box at the bottom of Get Info.
    – Tetsujin
    Mar 3 at 7:53
  • Problem is, there is no such option. All options regarding permissions are missing because "custom access".
    – JVC
    Mar 3 at 15:17
  • Please post the results of typing diskutil list into Terminal. You should only get 'custom access' on Time Machine & NTFS disks, but both should have actual, visible perms areas below, which any admin can unlock & change. The only time you ought to get custom access with no visible perms is on a FAT disk.
    – Tetsujin
    Mar 3 at 16:23
  • OK, added to OP.
    – JVC
    Mar 3 at 16:53
  • Ah… just occurred to me - What were you using before the reinstall to enable write to NTFS? Whatever it was appears to have not reactivated afterwards. [Mac cannot write to NTFS natively]
    – Tetsujin
    Mar 3 at 17:26


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