Member Avatar for redAPPLE

hi.

i have an external firewire drive. i would log in as "admin" and set the permission that i = admin is the owner with read and write rights, group has only read rights and others has only read rights (or no access).

once i log in as a different user, the owner suddenly becomes this! user (and not as admin as previously configured).

any good unix experts here?

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Dani AI

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Good checks from and — two different things usually cause the behavior you describe. First, volumes formatted as MS‑DOS/FAT (and exFAT) do not store POSIX ownership/permission metadata, so macOS will effectively present files as owned by whoever mounts or creates them. Second, on POSIX filesystems the owner of a file is the account that created it, so files a second user writes will naturally show that user as owner. (FAT/exFAT lack POSIX ownership.) (superuser.com)

Quick checklist to run now: 1) In Finder select the external disk → File → Get Info and note the Format (e.g. “MS‑DOS (FAT)”, “exFAT”, “Mac OS Extended (Journaled)”, “APFS”). 2) Or in Terminal run the diskutil query below to see filesystem type and whether owners are enabled. If the format is FAT/exFAT you cannot persist per‑file Unix ownership; if it’s HFS+/APFS you can. Examples: 

diskutil info "/Volumes/YourDrive" | egrep 'File System Personality|Owners'
ls -ld "/Volumes/YourDrive"

(How to check format/diskutil info.) (apple.stackexchange.com)

What to do next:

  • If the drive is FAT/exFAT and you need per‑user ownership, back up and reformat to a Mac filesystem (APFS or Mac OS Extended) or create an HFS+/APFS disk image on the drive and store data inside it. Reformatting erases data, so back up first. ([Apple: use Get Info / Disk Utility to check and format.]) (support.apple.com)
  • If the drive is HFS+/APFS and Owners are enabled, you can set ownership from Terminal (example below). Note: chown will silently do nothing on volumes that ignore ownership or on filesystems that don’t support owners.
sudo chown -R adminusername "/Volumes/YourDrive"
sudo chmod -R u=rwX,go=rX "/Volumes/YourDrive"

(If the volume is mounted with owners ignored, changing owner may silently fail.) (apple.stackexchange.com)

Summary: start by checking the Format/Owners fields (Finder or diskutil). If it’s FAT/exFAT, the observed owner changes are expected; choose reformat or use an HFS/APFS image. If it’s HFS+/APFS and Owners are enabled, use chown/chmod (and verify the “Ignore ownership on this volume” setting) to enforce the permissions you want.

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Member Avatar for gortonsfi

Did you make sure the other user doesn't have admin privileges?

Member Avatar for redAPPLE

Did you make sure the other user doesn't have admin privileges?

uh, you mean in system preferences:accounts?

Member Avatar for yellow

Did you follow the link I posted? It has the solution.

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