Whether we could hide the presence of a file by modifiying the gid/uid?
closed as not a real question by Ignacio Vazquez-Abrams, Nifle, harrymc, random♦ Jan 8 '11 at 15:38
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The way to do that is to put the file in a directory and revoke the "r" and "x" permissions on the directory from whomever you don't want. There is no standard way to hide a file by just modifying the permissions of the file itself.