(fileutils.info) Numeric Modes

 
 Numeric Modes
 =============
 
    File permissions are stored internally as 16 bit integers.  As an
 alternative to giving a symbolic mode, you can give an octal (base 8)
 number that corresponds to the internal representation of the new mode.
 This number is always interpreted in octal; you do not have to add a
 leading 0, as you do in C.  Mode 0055 is the same as mode 55.
 
    A numeric mode is usually shorter than the corresponding symbolic
 mode, but it is limited in that it can not take into account a file's
 previous permissions; it can only set them absolutely.
 
    The permissions granted to the user, to other users in the file's
 group, and to other users not in the file's group are each stored as
 three bits, which are represented as one octal digit.  The three special
 permissions are also each stored as one bit, and they are as a group
 represented as another octal digit.  Here is how the bits are arranged
 in the 16 bit integer, starting with the lowest valued bit:
 
      Value in  Corresponding
      Mode      Permission
      
                Other users not in the file's group:
         1      Execute
         2      Write
         4      Read
      
                Other users in the file's group:
        10      Execute
        20      Write
        40      Read
      
                The file's owner:
       100      Execute
       200      Write
       400      Read
      
                Special permissions:
      1000      Save text image on swap device
      2000      Set group ID on execution
      4000      Set user ID on execution
 
    For example, numeric mode 4755 corresponds to symbolic mode
 `u=rwxs,go=rx', and numeric mode 664 corresponds to symbolic mode
 `ug=rw,o=r'.  Numeric mode 0 corresponds to symbolic mode `ugo='.
Info Catalog
(fileutils.info) Symbolic Modes
(fileutils.info) File permissions
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