Hi, I'm trying to lock a file from objective-c (or plain C) so that other processes cannot read or write to it. So far, unsuccessfully. I've tried to use all APIs I can think of, but none locked the file: open then flock open then lockf open with O_EXLOCK open then fcntl (F_SETLK) open then NSDistributedLock I'm running macOS 11.6.1 on an APFS drive. For every API used, I was able to open and edit the file from command line using vi or just using cat on the file. Isn't there any way of preventing another process from accessing a file, until I'm done with it (ie. I closed the file, or the file handle is relinquished)? Thanks, Chris