I've encountered an issue that has me completely stumped. I have several identical Debian installations in KVM and on the Dom0 which don't cause this problem.
When ssh'ed into the Xen DomU, I try and switch to root using su and receive the following error (using the correct root password):
su: Authentication failure
However this command works:
me@server$ sudo su
I can also su from user -> root when logged in at the Virt-Manager VNC session.
ls -l /bin/su
-rwsr-xr-x 1 root root 34024 Feb 15 2011 /bin/su
su: pam_unix(su:auth): authentication failure; logname=me uid=1000 euid=0 tty=/dev/tty1$
su: pam_authenticate: Authentication failure
su: FAILED su for root by me
Any ideas would be greatly appreciated