>At the boot screen enter ' init=/bin/bash ' as extra boot option and let the system boot (assuming you are using the GRUB boot loader). This should bring you to a shell prompt with root mounted.

If under xen environment. this way was worked under my sles11sp2.

xen-dom0:/etc/xen/vm # cp my-domu my-domu-rescue <-- backup
xen-dom0:/etc/xen/vm # cat my-domu-rescue
:
extra=" init=/bin/bash" <---- change this line
:
xen-dom0:/etc/xen/vm # xm create -c my-domu-rescue

from yast2(GUI) > Virt-Manager > open MyVm screen

$ passwd
> new-root-passwd
> retype new-root-passwd
$

but noway to accept 'shutdown -h 0' command so I did 'xm destroy myvm' and

xen-dom0:/etc/xen/vm # xm create -c my-domu

root password was reset successfully.

--
#xm create -c myvm extra= single
require root password under sles11sp2.

I hope work fine for everybody.