Name  | Meaning  | 
replace  | permissions shall replace the file's permission bits with perm  | 
add  | permissions shall replace the file's permission bits with
  the bitwise OR of perm and the file's current permission bits.  | 
remove  | permissions shall replace the file's permission bits with
  the bitwise AND of the complement of perm and the file's current permission bits.  | 
nofollow  | permissions shall change the permissions of a symbolic link itself
  rather than the permissions of the file the link resolves to.  |