If I copy a file with a base ACL of:


into a directory with a default ACL of:


I obtain a file with mask of m::r--. I would have expected the union of the permissions of the two group entries (i.e. m::rwx).

Why it is so? Does it depend on the mode parameter used by cp in the creation of the file?

1 Answer 1


(I assume you're working on Linux, the workings of ACLs differ between unix variants.)

cp doesn't do anything special when you copy the file; it creates the file with the mode of the original file, masked by the mask of the directory. Since cp doesn't do anything to the file's mask, the mask ends up being the intersection of the directory mask (rwx) and the file's group permissions (r).

open("dir/file", O_WRONLY|O_CREAT|O_EXCL, 0644)
  • When one has set the default ACL (which is passed on to newly created subfolders), how does the mask + default acl + folder perms get fused together, when a new subfolder is created???
    – nass
    Aug 6, 2013 at 12:03
  • @nass The default ACL is used if no ACL has been set explicitly. If there's an explicit ACL then its mask is used, otherwise the default mask is used. Aug 6, 2013 at 12:08
  • I am abit fuzzy about the mask acl. if I set an explicit acl to a folder, I expect this to be followed. you tell me that regardless of my explicit acl, the actual perms will be the intersection of the mask with the acl? and when I set a default acl then that is taken as is (ie without intersection with the mask acl?) may I also refer you to a question I have here unix.stackexchange.com/questions/85633/…
    – nass
    Aug 6, 2013 at 12:21

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