chmod changes ctime even if no changes were made

[Hans Ecke]

Hi,

I noticed that chmod changes the ctime of files, even if no permissions 
are actually changed.

I ran into this because some maintenance scripts here run
   "chmod -Rc ugoa+rX $directory"
every night for some directories that ought to be generally accessible.

Unfortunately this also triggers some OS-provided maintenance scripts 
that see "Oh, ctime has changed, let me rebuild this subsystem.". This 
is very annoying, and the users are not happy since their computers do 
pointless rebuilds, consuming CPU.

Is there any way that chmod could first see if the requested status 
change has already been fulfilled, and skip files where it would not 
change anything?

I can see that this would slow chmod down (one more stat (2) call per 
file), so making this an option would be fine...

Thanks

Hans

--
Hans Ecke                   address@hidden / address@hidden
Department of Geophysics    http://hans.ecke.ws
Colorado School of Mines    Tel: (USA) 303-273-3733
Golden, Colorado            Fax: (USA) 303-273-3478

We must all hang together, or assuredly we shall all hang separately.
                    -- Benjamin Franklin