coreutils: Umask and Protection
27.2.6 The Umask and Protection
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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.
Info Catalog
coreutils: Multiple Changes
coreutils: Symbolic Modes