"su" from VNC session doesn't work but works ok when at the terminal
 

When I connect to my workstation via Real VNC Viewer 4 to Xvnc running on the workstation, and running "su -" I get authentication failure as follows:

Nov 18 16:24:00 localhost su: pam_unix(su-l:auth): authentication failure; logname=xyz uid=500 euid=0 tty=pts/6 ruser=xyz rhost= user=root

So, effectively I cannot su when connected via VNC.

But if I'm at my workstation, I can su just fine:

Nov 18 16:24:30 localhost su: pam_unix(su-l:session): session opened for user root by xyz(uid=500)


Interestingly enough, I cannot su to my own userid over vnc, i.e.

su xyz

In /var/log/secure I get:

Nov 18 17:23:58 localhost su: pam_unix(su:auth): authentication failure; logname=xyz uid=500 euid=0 tty=pts/6 ruser=xyz rhost= user=xyz

I suspect it has something to do with PAM, but cannot figure it out.

Any help?

I'd also like to add that when I'm connected via VNC to my workstation and then ssh to my workstation (ssh xyz@localhost), then I can "su" successfully. So it appears that "su" works fine via ssh, even though the initial connection is via VNC.

This might be the same problem people have when trying to su in a X windows session and it does not work. Try adding your userid to the wheel group. For some reason that still escapes me it causes su issues.