On Tuesday 06 November 2007 11:48, James D. Parra wrote:
> Hello,
>
> Out of curiosity, what is the S for in, -rwxr-Sr-t? Is that a sticky
> bit and id so, how is it set with chmod?
>
> -rwxr-Sr-t   1 root root 25016 Nov  6 11:38 temp.txt
> -rw-r--r--   1 root root  9622 Mar 19  2005 generic
>
> Thank you,

Patrick's generic and universal answer notwithstanding, the 
particular 'S' flag you showed is the "set group ID" bit. That means 
that if executed, the resulting process would execute with an effective 
group ID equal to that of the file's group ID (in this case, "root," or 
it's numeric counterpart). There's a corresponding "set user ID" bit 
which would put the 'S' signifier in the corresponding user position:

% chmod g-s temp.txt
% chmod u+s temp.txt
% ls -l temp.txt
-rwSr--r-t   1 root root 25016 Nov  6 11:38 temp.txt

The capital 'S' is used when the corresponding execute bit is _not_ set. 
When the corresponding execute bit _is_ set, you get a lower-case 's'. 
In general, set-UID or set-GID have no real significance if the file to 
which they're applied is not executable.


There is a "sticky" bit, but its meaning is quite different. I'll leave 
it as an exercise for you to discover that one (extra credit for the 
now-obsolescent original meaning).


> James


Randall Schulz
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