ROOT password OK su password not!

-I have been frequently going in and out of 'su' mode with my password to do some admin on my Mandrake 10.0 box.  

-I have also been able to login as "ROOT"  using the same password(with the nasty red screen and the "be careful" warning).

-I have not changed my password.

recently when I try to go to 'su' mode, I type in the password and it says the password is invalid.  I'm certain that I have typed it correctly (many times over, and I'm certain caps locks were off)

-I still am able to logout, and relog in as "root" with the same password!  So the password works if I totally log out and back in, but not if I try to go to 'su' from the command prompt. hmmm..

Why will this password not work with 'su', and how can I fix it?
The only thing I can think of is that I have just recently downloaded the security fixes (RPMs) from the Mandrake website.

Darrell ThomasEngineerAsked:
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jlevieConnect With a Mentor Commented:
Actually it is possible to fix anything that happens to a Linux system short of a failed disk drive without re-installing. Even in a case where the OS won't boot it can be repaired from a rescue boot. The difficulty lies in figuring out what's broken/missing. Sometimes that means setting up an identical system and comparing what packages are installed on each, adding/removing packages on the damaged system to bring then into sync. Other times it may be just a matter of running an 'rpm -q --verify -a' and see what is shown as corrupt.

Having said that I will also say that one has to weigh the amount of time it will take for a fix against the "cost" of a re-install. I always examine the failing system enough to figure out which is the "cheapest" solution.
I don't use Mandrake and I don't know what changes the latest security fixed may have introduced, but I'd guess they've placed restrictions on the use of su. It could be that, like FreeBSD, the user must be listed as a member of a specific group, or that the user must be mentioned in some specific file. The man page for su (see 'man su') should tell you.

Of course it is also possible that the latest fixes broke something.
Darrell ThomasEngineerAuthor Commented:
I think the latest fix broke something.  I ended up re-installing the entire operating system (not too bad, I hadn't started putting much on there yet) and when I patched with the updates, I persistantly checked to see if I could use "su".  All of the updates were installed, and "su" has returned its functionality.  

Maybe a bad install of some of the updates.  There should be a way to easily "uninstall" them.

I shouldn't have to go back to a clean hard drive just to fix this, but in my case it worked because I didn't really lose any work.

Darrell ThomasEngineerAuthor Commented:
true... very true...
i know this answer was accepted, but heres my $0.02.....does mandrake possible use a "wheel" group like i know freebsd does?
if user is not in group wheel, user cannot su.
I dont think i have ever seen a linux system do this, but i am a unix/bsd guy.
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