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Re: chmod octal form of sgid/suid removal fails

From: John Cowan
Subject: Re: chmod octal form of sgid/suid removal fails
Date: Mon, 14 May 2007 22:46:56 -0400
User-agent: Mutt/1.5.13 (2006-08-11)

(Apologies to those, if any, who got an earlier version of this message.)

Paul Eggert scripsit:

> The counterargument is that it's strange if a leading
> zero changes the semantics of a number, as this is not what many
> people expect.

Fair enough.  However, if the directory has mode 6755 and you
do "chmod 2755 dir", the mode remains 6755.  This violates the
Law of Least Astonishment, I think.

I had earlier thought that it doesn't matter, because setuid
doesn't mean anything on directories in most *ix variants, but
on FreeBSD it causes files created in the directory to be
owned by the directory owner, analogously to setgid.  See
http://www.greenend.org.uk/rjk/2004/perms.html for details.

> Please see the thread rooted here:

Thanks for the pointer.

> If you read that root, by the way, you'll see that existing practice
> is wildly different in this area.  For example, on Solaris,
> "chmod 2755 DIR" silently ignores the "2".

Quite so.  File modes are a mess, anyway.  I suppose that on the whole
stability trumps "correctness".

As you read this, I don't want you to feel      John Cowan
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will die someday.                               http://www.ccil.org/~cowan
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