GNU bug report logs - #29390
chmod man page - clear setuid/setgid with numerical value

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Oliver Isaac <oisaac <at> gmail.com>
Subject: bug#29390: closed (Re: bug#29390: chmod man page - clear
 setuid/setgid with numerical value)
Date: Sun, 10 Dec 2017 02:34:02 +0000

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Your bug report

#29390: chmod man page - clear setuid/setgid with numerical value 

which was filed against the coreutils package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 29390 <at> debbugs.gnu.org.

-- 
29390: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=29390
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Pádraig Brady <P <at> draigBrady.com>
To: Oliver Isaac <oisaac <at> gmail.com>, 29390-done <at> debbugs.gnu.org
Subject: Re: bug#29390: chmod man page - clear setuid/setgid with numerical
 value
Date: Sat, 9 Dec 2017 18:32:53 -0800

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On 21/11/17 18:46, Oliver Isaac wrote:
> Hello,
> 
> There is an incorrect assertion made in the chmod man page:
> 
> Under the setuid/setgid header it says, "you can set (but not clear) the bits with a numeric mode"
> 
> This is not entirely true. If you prefix your numeric mode with a 0 then it will work:
> 
> e.g.:
> 
> touch myfile
> chmod 644 myfile
> ls -l myfile
> chmod g+s myfile
> Is -l myfile
> chmod 00644 myfile
> is -l myfile
> 
> 
> This simple test shows that you can clear the uid/gid bits with numeric mode which is especially useful in scripts.
> 
> An update to the man page to clarify this would be helpful. 

Yes we should update the man page to be consistent.

The current text was added in COREUTILS-6_9-89-gf4a5097
It was correct at the time, but slightly ambiguous as it
might be missed that the paragraph pertains only to directories,
and not files.

Then http://debbugs.gnu.org/8391 (v8.15-64-g8931cdb) changed things
to allow leading 00 to clear the setuid and setgid bits
of _directories_ with numeric modes.  BTW I notice solaris
accepts 00755 as a mode but does _not_ clear these bits
for directories.

I.E. the most portable and simplest way to access this functionality
is to use `chmod -s dir`

Proposed patch attached.

cheers,
Pádraig

[chmod-setgid-man.patch (text/x-patch, attachment)]

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From: Oliver Isaac <oisaac <at> gmail.com>
To: bug-coreutils <at> gnu.org
Subject: chmod man page - clear setuid/setgid with numerical value 
Date: Tue, 21 Nov 2017 20:46:33 -0600

Hello,

There is an incorrect assertion made in the chmod man page:

Under the setuid/setgid header it says, "you can set (but not clear) the bits with a numeric mode"

This is not entirely true. If you prefix your numeric mode with a 0 then it will work:

e.g.:

touch myfile
chmod 644 myfile
ls -l myfile
chmod g+s myfile
Is -l myfile
chmod 00644 myfile
is -l myfile


This simple test shows that you can clear the uid/gid bits with numeric mode which is especially useful in scripts.

An update to the man page to clarify this would be helpful. 

Thanks,
Oliver

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