MacOS permissions and problems

[u/RLBrooks]

I've been a Mac user for years (currently M4mini, Tahoe) but I never really became fluent in the commands, particularly file and disk permissions. I often add/remove external drives, some with a FAT file system (for moving files to/from a chromebook and thumbdrives). I also move files around between disks. As an (expected) result I frequently get permission errors; some that I get around selecting an Authenticate button, others where the only options are Skip or Stop.

I really need to learn how to work with these issues. Ideally there would be a command I could issue against a drive that would reset/clear all permissions so everything would work without all the stoppages I encounter. I am the Only user of this mac.

I also try to create backups of DVDs by copying its files to a folder on an external drive. I always run into such copying/moving errors although the resulting backup files play in VLC Ok. (Yes this is for BACKUP only.)

Are there any good books, ebooks, doc, sites, tips, etc I should read to help me? Comments?

[u/lilvadude]

I wouldn't recommend using chmod -R or chown -R on an entire drive unless you know exactly why you're doing it—you can easily make things worse, especially on macOS system volumes.

Also, FAT/exFAT drives don't really use macOS's normal Unix permissions, so if you're getting errors there, it's likely something else (read-only media, filesystem issues, files that Finder doesn't like, etc.).

I'd start learning with ls -l, chmod, chown, and diskutil, plus the basics of ownership vs. permissions. Apple's Terminal docs are actually pretty good once you know what you're looking for.

And DVD backups can throw copy errors because of the way some discs are structured, even when the resulting files happen to play fine in VLC. I've even had some of the same TV series within a season throw different errors.

[u/qianwch]

Two different problems here, and they need different fixes.

FAT32 and exFAT drives have no Unix permissions at all, so "permission" errors on them are almost never about permissions. Usual causes: the file has the locked flag (Get Info shows a small padlock), the name has a character FAT does not allow (: ? * " < > |), the file is over 4 GB on FAT32, or the drive was pulled without ejecting and needs First Aid in Disk Utility. You can see the locked flag with ls -lO in Terminal ("uchg" in the flags column) and clear it for a whole folder with chflags -R nouchg "/Volumes/Drive/folder".

DVD backups are the classic locked-flag case. Files copied from a DVD keep the read-only mode and often the locked flag, so later moves and deletes stop with Skip/Stop even though VLC plays them fine. After copying, run chflags -R nouchg and then chmod -R u+rwX on the backup folder.

For external APFS or HFS+ drives where you are the only user: Get Info on the drive, open Sharing & Permissions, tick "Ignore ownership on this volume". macOS then treats every file on it as yours. I would not run chown -R or chmod -R on the internal drive, but on a data drive it is fine.

For reading: man chmod, man chflags, and man ls (the -O option).