Last week I reported that the Finder’s Locked file setting doesn’t work properly with iCloud Drive. As that’s one of a group of eight BSD flags supported in APFS, this article examines how iCloud Drive in macOS 26.5 handles those flags, and whether any of them are compatible. Its TL; DR is don’t let files with BSD flags near iCloud Drive, as they don’t work and will only upset it.

According to man chflags, that command tool currently supports a total of eight BSD flags:

• arch to set the archived flag (super-user)
• hidden to set the hidden flag, so hiding the file
• nodump to set the nodump flag
• opaque to set the opaque flag, making a directory opaque when viewed through a union mount
• sappnd to set the system append-only flag (super-user)
• schg to set the system immutable flag (super-user)
• uappnd to set the user append-only flag
• uchg to set the user immutable flag.

In APFS file systems, those are stored in the bsd_flags value in a file’s inode, so should be well-preserved in file operations.

To assess all these in macOS 26.5, I created a folder of eight small RTF files, and set each of the flags on one of those files using chflags in Terminal. To confirm the flags had been successfully set, the directory contents were listed using ls -lO:
ls -lO /Users/hoakley/Documents/0bsdflags
total 64
-rw-r--r--@ 1 hoakley staff arch 1675 13 Jul 2025 arch.rtf
-rw-r--r--@ 1 hoakley staff hidden 1675 13 Jul 2025 hidden.rtf
-rw-r--r--@ 1 hoakley staff nodump 1675 13 Jul 2025 nodump.rtf
-rw-r--r--@ 1 hoakley staff opaque 1675 13 Jul 2025 opaque.rtf
-rw-r--r--@ 1 hoakley staff sappnd 1675 13 Jul 2025 sappnd.rtf
-rw-r--r--@ 1 hoakley staff schg 1675 13 Jul 2025 schg.rtf
-rw-r--r--@ 1 hoakley staff uappnd 1675 13 Jul 2025 uappnd.rtf
-rw-r--r--@ 1 hoakley staff uchg 1675 13 Jul 2025 uchg.rtf

The whole folder was moved (not copied) into iCloud Drive, and allowed to sync. Of the eight files, three were shown with an iCloud Drive error: sappnd, schg and uappnd. In addition, the uchg flag was stripped as a result of that move, but the seven other flags remained when viewed from the same Mac:
ls -lO /Users/hoakley/Library/Mobile\ Documents/com\~apple\~CloudDocs/backup1/0bsdflags
total 64
-rw-r--r--@ 1 hoakley staff arch 1675 13 Jul 2025 arch.rtf
-rw-r--r--@ 1 hoakley staff hidden 1675 13 Jul 2025 hidden.rtf
-rw-r--r--@ 1 hoakley staff nodump 1675 13 Jul 2025 nodump.rtf
-rw-r--r--@ 1 hoakley staff opaque 1675 13 Jul 2025 opaque.rtf
-rw-r--r--@ 1 hoakley staff sappnd 1675 13 Jul 2025 sappnd.rtf
-rw-r--r--@ 1 hoakley staff schg 1675 13 Jul 2025 schg.rtf
-rw-r--r--@ 1 hoakley staff uappnd 1675 13 Jul 2025 uappnd.rtf
-rw-r--r--@ 1 hoakley staff - 1675 13 Jul 2025 uchg.rtf

When that iCloud Drive folder had synced with a separate Mac also running macOS 26.5, the three files that had been showing an iCloud error on the first Mac, bearing the sappnd, schg and uappnd flags, had failed to sync to iCloud Drive and weren’t visible on the second Mac. None of the flags could be detected on that second Mac using ls -lO, and the file flagged as being hidden was fully visible in the synced folder.

Thus the eight BSD flags behaved as follows:

• arch file synced, not flag
• hidden file synced, not flag
• nodump file synced, not flag
• opaque file synced, not flag
• sappnd file not synced, iCloud error
• schg file not synced, iCloud error
• uappnd file not synced, iCloud error
• uchg flag stripped completely, file synced without flag.

On the first, originating Mac, the iCloud error with sappnd, schg and uappnd flags started a prolonged sync. I therefore removed the folder containing these test files from iCloud Drive, returning it to its original location. That left the eight files in the state they had been in, with the uchg flag removed, but the other flags unchanged. However, the sync persisted, and was only terminated by restarting that Mac.

As none of these flags synced in iCloud Drive, one was stripped by moving the file to iCloud Drive, and three resulted in sync errors, it’s safe to conclude that in its current state, iCloud Drive is incompatible with these BSD flags, and their use on files in iCloud Drive should be avoided. As iCloud Drive has now adopted the FileProvider framework common to other cloud sharing services, and it appears likely that these problems result from shortcomings in that framework, this incompatibility may thus affect other cloud services using FileProvider, such as Dropbox and Microsoft OneDrive.