Question about nethack and setgid

[Robert Bonomi]

> Date: Wed, 02 Mar 2011 23:51:45 +0100
> From: David Demelier <demelier.david at gmail.com>
> To: freebsd-questions at freebsd.org
> Subject: Question about nethack and setgid
>
> Hello,
>
> I don't understand how nethack can store the score in
> /usr/local/lib/nethack/logfile.
>
> the real binary is here /usr/local/lib/nethack/nethack
>
> And the mode is
>
> -rwxr-sr-x  1 games  games  1793635 25 Jan 2011
> /usr/local/lib/nethack/nethack
>
> So that means people in games group will run nethack as games user (owner 
> of file)

Actually, it means that the program will run with the _group_ id of the
file -- i.e. the 'games' group.  _That_ 's' is the 'sgid' or 'set groupID'
bit.

>         but I'm not in games group ! and I can save the file located in
>
> /usr/local/lib/nethack/logfile which mode is -rw-rw-r--  games  games

Lo and behold!  The file _is_ writable by the games group.

> I'm writing a game that will store file too, because I can't make it 
> works like nethack I was planning using the setuid mode but I don't like 
> much this ..
>
> What am I misunderstanding?

the function of the 'setgid' bit.  <grin.
>
> Cheers,
>
> --
> David Demelier
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