An operator numeric mode is a numeric mode that is prefixed by a
+’, or ‘
=’ operator, which has the same
interpretation as in symbolic modes. For example, ‘
read permission for the file’s owner and group, ‘
execute permission for other users, and ‘
=600’ clears all
permissions except for enabling read-write permissions for the file’s
owner. Operator numeric modes can be combined with symbolic modes by
separating them with a comma; for example, ‘
=0,u+r’ clears all
permissions except for enabling read permission for the file’s owner.
The commands ‘
chmod =755 dir’ and ‘
chmod 755 dir’ differ in that the former clears the directory
setuid and setgid bits, whereas the latter preserves them.
See Directory Setuid and Setgid.
Operator numeric modes are a GNU extension.