How to determine which process is creating a file?

fs_usage is your tool for this.

The file system usage tool is ideal since it taps in to the real time file system events and dumps activity to a file or the screen. Since you know the exact path of the file, you can filter out all the thousands of irrelevant (to this case) filesystem changes and see what reads / writes to that file pretty quickly.

If your home directory is /Users/me then you can filter for /Users/me/aa

mac:~ me$ sudo fs_usage | grep /Users/me/aa
09:35:21  stat64            /Users/me/aa      0.000033   touch       
09:35:21  utimes            /Users/me/aa      0.000104   touch       
09:35:21  fsgetpath         /Users/me/aa      0.000119   Finder      
09:35:22  lstat64           /Users/me/aa      0.000039   fseventsd   
09:35:22  fsgetpath         /Users/me/aa      0.000027   mds         
09:35:22  getattrlist       /Users/me/aa      0.000064   mds         
09:35:22  listxattr         /Users/me/aa      0.000012   mds         
09:35:22  getattrlist       /Users/me/aa      0.000130   mds         
09:35:22  getattrlist       /Users/me/aa      0.000033   mds         
09:35:22  open              /Users/me/aa      0.000071   mdworker_sha
09:35:22    RdData[AT2]     /Users/me/aa      0.000331 W mdworker_sha
09:35:22  getattrlist       /Users/me/aa      0.000042   mds         
09:35:24  lstat64           /Users/me/aa      0.000114   rm          
09:35:24  access            /Users/me/aa      0.000209   rm          
09:35:24  unlink            /Users/me/aa      0.000909   rm          
09:35:25  lstat64           /Users/me/aa      0.000042   fseventsd   
09:35:25  lstat64           /Users/me/aa      0.000006   rm          

(note: I deleted a lot of white space above - the fs_usage command outputs a wide amount of empty space so you can't easily see the touch command on the far right if I copy/paste the exact output.)

Here I use the touch command to create the file, append a string to it and then rm it from the command line.

mac:~ me$ touch ~/aa
mac:~ me$ echo foo >> ~/aa
mac:~ me$ rm ~/aa

There will be tons of other apps that read, so you can filter on the stat64 and lstat74 operations if there are too many attribute reads and spotlight activity around the file once it's created.

• http://toddsnotes.blogspot.com/2014/02/use-fsusage-to-monitor-file-system.html
• https://developer.apple.com/library/archive/documentation/Performance/Conceptual/FileSystem/Articles/FileSystemCalls.html

The manual page for this command is quite dense (and not a "how-to") which is typical but better than no documentation from Apple on how to use it.