(coreutils.info.gz) Umask and Protection

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(coreutils.info.gz) Symbolic Modes

 
 27.2.6 The Umask and Protection
 -------------------------------
 
 If the USERS part of a symbolic mode is omitted, it defaults to `a'
 (affect all users), except that any permissions that are _set_ in the
 system variable `umask' are _not affected_.  The value of `umask' can
 be set using the `umask' command.  Its default value varies from system
 to system.
 
    Omitting the USERS part of a symbolic mode is generally not useful
 with operations other than `+'.  It is useful with `+' because it
 allows you to use `umask' as an easily customizable protection against
 giving away more permission to files than you intended to.
 
    As an example, if `umask' has the value 2, which removes write
 permission for users who are not in the file's group, then the mode:
 
      +w
 
 adds permission to write to the file to its owner and to other users who
 are in the file's group, but _not_ to other users.  In contrast, the
 mode:
 
      a+w
 
 ignores `umask', and _does_ give write permission for the file to all
 users.
 

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(coreutils.info.gz) Symbolic Modes