passwords not recognized when su'ing from a terminal

[Alain Cochard]

Andreas Bernauer writes:

 > Alain Cochard wrote on Fri, Jul 20 2007 at 11:59 (+0200):

 > > Just a few days ago, I stopped being able to 'su' or 'su
 > > some_user' from a terminal: the passwords are no longer accepted.
 > > Same problem to unlock a session (need to enter the password).

 > You may not have noticed, but the problem seems to be that PAM is
 > denying access.  Check the file /etc/pam.d/su to see why it may be
 > doing this.  My su-file looks like the one attached and is from
 > FC6.

Thanks Andreas.  Unfortunately, my /etc/pam.d/su file is exactly
identical to yours...

 > You may also want to turn on some 'debug' option flag in the pam
 > modules.  However, there is no general debug interface to PAM
 > (unfortunately).

Well, I read the pam and pam_authenticate manuals, but have no idea of
how to start on that.  It appears to be way beyond my abilities.

Any more clues, anyone?

Alain