chmod on Mac: -R 644 Exits 0 and Skips Every File Inside
I ran chmod -R 644 on a test folder on my Mac mini. It printed nothing and exited 0. The folder itself changed to drw-r--r--. Not one file or subfolder inside it changed. GNU chmod on the same folder printed two Permission denied lines and exited 1. Apple's chmod reported success.
That was one of 33 cases I ran through chmod on macOS 26.4.1, plus a smaller set on four scratch disk images (APFS, HFS+, exFAT, FAT32) and a read-only one. Most of chmod on a Mac works the way any Unix guide says. This post covers the places where it doesn't: where it reports success without doing the work, and where it says Operation not permitted and why.
The short answer
# files 644, folders 755, recursively (capital X = execute only on folders
# and on files that already have it)
chmod -R u=rwX,go=rX folder
# make one script executable
chmod +x script.sh
# see what changed, old and new mode
chmod -vv 640 file
# read a file's mode as a number
stat -f '%Lp %N' fileIf you came here for chmod -R 755: it works, but it also makes every file executable. In my run, files that started at 644 ended at -rwxr-xr-x. The u=rwX,go=rX form gave folders 755 and files 644 from a starting point of 700 and 600.
chmod -R exits 0 and changes nothing inside
I tried nine recursive modes on a folder holding a 755 file and a 755 subfolder. Six of them left both untouched, exited 0 and wrote nothing to stderr: 644, 600, 444, -x, a-x and u-x. The two that worked, 700 and go-rwx, keep the owner's execute bit on folders. That is the whole pattern. If the new mode takes away your own x on a directory, chmod changes the directory first and then can't get inside it.
The reason is in Apple's chmod.c. chmod walks the tree with fts and changes each directory when it first visits it. I wrote a ten-line C program that does the same walk. After the mode change, fts did not return the folder's children at all. It returned the folder a second time as "post-order" (FTS_DP) with errno 13. chmod's handler for that case is continue;, with the comment "Already changed at FTS_D". The error is never looked at.
Two variations do report it. With chmod -R -L, fts hands back the children as unreadable entries and chmod prints d/f: Permission denied. With mode 000, the folder can't even be listed, and chmod prints chmod: d: Permission denied and exits 1. Both are easy to recover from: chmod -R 755 folder on the 000 folder fixed every file in it, because chmod opens the folder up before it walks inside.
If you want 644 files and 755 folders and your tree is not something X can sort out, split it with find:
find folder -type d -exec chmod 755 {} +
find folder -type f -exec chmod 644 {} +Use +, not \;. On 2,000 empty files, -exec chmod 600 {} \; took 2.28 seconds and {} + took 0.02. chmod -R on the same folder took 0.01.
chmod exits 0 on files it isn't allowed to touch
This one surprised me more. As a normal user I ran chmod 644 /etc/hosts, a file owned by root. It exited 0. So did chmod u+w /etc/hosts and chmod g-w /etc/hosts. Only chmod o+w /etc/hosts failed, with Unable to change file mode on /etc/hosts: Operation not permitted.
The first three asked for the mode the file already had. chmod compares the new mode with the current one and skips the system call when they match, so the permission check never runs. Even -v prints nothing for those files, because nothing changed. That explains an Ask Different question titled "Recursive chmod fails": sudo chmod -v -R u+w on a root-owned folder "returns nothing". Those files already had u+w. The asker needed g+w.
The -f flag goes further. The man page says it suppresses the message and the exit status, and it does: chmod -f 600 /etc/hosts exited 0 while leaving the file at 644. In a script, -f means you can't tell whether anything happened.
What "Operation not permitted" meant in my tests
| Case | Message | Exit |
|---|---|---|
File owned by someone else (/etc/hosts), different mode | Unable to change file mode on /etc/hosts: Operation not permitted | 1 |
System binary (/usr/bin/true, flags restricted) | Unable to change file mode on /usr/bin/true: Operation not permitted | 1 |
Your own file, locked (uchg flag) | Unable to change file mode on f: Operation not permitted | 1 |
| Three files, middle one locked | Error for the locked one only; the other two changed | 1 |
| File on a read-only volume | Unable to change file mode on f: Read-only file system | 1 |
ACL on exFAT or FAT32 (chmod +a) | Failed to set ACL on file 'f': Operation not supported | 1 |
| Mode change on exFAT or FAT32 | none, mode stays -rwx------ | 0 |
The locked case is the one you can fix yourself. Finder's Locked checkbox is the uchg flag: I set the Locked attribute with SetFile -a L and ls -lO showed uchg. Even the owner can't chmod a locked file. Check with ls -lO file and clear it with chflags nouchg file (see the chflags man page). The /usr/bin/true row has the restricted flag that System Integrity Protection uses, but I can't separate that from plain ownership without sudo, which this machine doesn't give me. If you see Operation not permitted on a file you own in Desktop or Documents, that is privacy protection (TCC), not file modes, and I didn't test it here.
The last row matters most if you work with USB drives. On exFAT and FAT32 every new file showed -rwx------, and chmod 600, 755, 000, 444, 4755 and 644 all exited 0 and left it there. Those formats have no Unix modes to store. If permissions matter, use APFS or HFS+; my external SSD format tests compare what else each format drops.
Three more traps
umask. chmod +w on a 444 file gave 644, not 666. When you don't say who (u, g, o or a), chmod applies your umask, which was 022. chmod a+w gives everyone write. chmod +x on a 644 file gave 755, since the umask doesn't mask execute.
ACLs survive chmod. I added deny write for my own user on a file, then ran chmod 666. ls -l showed -rw-rw-rw- and echo y > f still failed with permission denied. A numeric mode does not clear the ACL; chmod -N f does. Two details: echo z >> f worked, because append is a separate right, and ls showed @ rather than + because the file also had extended attributes. Use ls -le to see ACL entries.
.* in bash. The man page warns that .* can match ... In bash 3.2, which macOS still ships as /bin/bash, I ran chmod -R go+r .* in a subfolder meant to fix its hidden files. It also changed the parent folder (700 to 744) and a file next to the subfolder (600 to 644). zsh, the default shell, does not match .., and its * skips hidden files. That's the same family of glob surprise as files that start with a dash.
If you set +x and still get zsh: permission denied, the mode was not the problem. I mapped the other causes in zsh permission denied.
FAQ
How do I chmod a folder recursively on Mac?
Run chmod -R u=rwX,go=rX folder in Terminal. That gives folders 755 and files 644, and keeps execute only on files that already had it. Avoid chmod -R 644 or chmod -R 600 on a folder: on macOS 26.4.1 they changed only the top folder, skipped everything inside and still exited 0. To set files and folders separately, use find folder -type d -exec chmod 755 {} + and find folder -type f -exec chmod 644 {} +.
Why does chmod say Operation not permitted on Mac?
In my tests it meant one of four things: you don't own the file (use sudo), the file is locked with the uchg flag (Finder's Locked checkbox; clear it with chflags nouchg), it's a system file protected by SIP, or, with the Read-only file system message, the volume is mounted read-only. In Desktop, Documents and Downloads the same message can come from privacy protection instead of file modes.
Why doesn't chmod work on my USB drive?
If the drive is exFAT or FAT32, the format has no Unix permissions. On macOS 26.4.1 every file on those volumes showed -rwx------ and chmod exited 0 without changing it. Reformat the drive as APFS or Mac OS Extended if you need modes to stick; chmod worked normally on both.
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How this was tested: Mac mini, macOS 26.4.1 (25E253), Apple chmod from file_cmds-479, GNU chmod from Homebrew coreutils, as a normal user without sudo, umask 022. 33 cases ran in a home-directory folder; eight more ran on 64 MB sparse images formatted APFS, HFS+, exFAT and FAT32, and one on a read-only APFS image. The fts behavior was checked with a small C program calling fts_open with FTS_PHYSICAL and FTS_LOGICAL. I also pulled all 27 Ask Different questions with chmod in the title through the Stack Exchange API to see which problems people actually hit; root-owned files, SIP-protected files and the silent -v case above came from there. References: Apple's chmod man page and the GNU chmod manual. For copying files without losing their dates, see changing a file's creation date.