passwords not recognized when su'ing from a terminal [SOLVED]

[Alain Cochard]

Mikkel L. Ellertson writes:

 > Another check would be to run "rpm -V coreutils" to verify the su
 > binary. If it returns without printing anything, then su and
 > /etc/sudoers are the same as originally installed. If it shows
 > something has changed, you have a place to start.
 > 
 > $ type su
 > su is /bin/su
 > $ rpm -qf /bin/su
 > coreutils-5.97-12.5.fc6
 > $ rpm -V coreutils
 > $

Indeed, this showed a change in mode for /bin/su from 

  -rwsr-xr-x 

to

  -rwxr-xr-x

After the appropriate chmod, everything went back in order.  I even
understand how this happened:  by mistake I did

   chown -R cochard.cochard many_files

including the /bin directory.   I   did changed back

   chown root.root same_many_files

but I didn't know that the modes would stay at -rwxr-xr-x

Many thanks to everybody who answered, whether it be publicly or
privately!

Alain